Email alert
RSS2015 Vol. 27, No. 05
Recommend Articles
Display Method:
2015,
27: 051001.
doi: 10.11884/HPLPB201527.051001
Abstract:
In high power laser facilities, the GRMS is a key specification to evaluate the low frequency wavefront distortion. While the deformable mirror is widely used to correct the distortion, the raw GRMS specification should include the effect of deformable mirror. The article presents the method to decompose the influence of deformable mirror and the partial coherent characteristic of corrected wavefront. The relation between the GRMS and the size of laser focus of corrected wavefront is verified. Based on the research, the procedure of setting up the GRMS specification of the optics is established.
In high power laser facilities, the GRMS is a key specification to evaluate the low frequency wavefront distortion. While the deformable mirror is widely used to correct the distortion, the raw GRMS specification should include the effect of deformable mirror. The article presents the method to decompose the influence of deformable mirror and the partial coherent characteristic of corrected wavefront. The relation between the GRMS and the size of laser focus of corrected wavefront is verified. Based on the research, the procedure of setting up the GRMS specification of the optics is established.
2015,
27: 051002.
doi: 10.11884/HPLPB201527.051002
Abstract:
It is difficult to find commercial laser products meeting the requirements of ERL photocathode gun. Therefore, a drive laser system is being developed at Institute of High Energy Physics(IHEP), which comprises two kinds of laser seeds, 1.3 GHz and 100 MHz at repetition rate. Fiber amplifiers were being constructed and a test system was set up. The output power of the main amplifier can reach up to 27 W. With a 5-mm-long LBO crystal, the green second harmonic laser of 6 W was achieved in the preliminary validation experiment.
It is difficult to find commercial laser products meeting the requirements of ERL photocathode gun. Therefore, a drive laser system is being developed at Institute of High Energy Physics(IHEP), which comprises two kinds of laser seeds, 1.3 GHz and 100 MHz at repetition rate. Fiber amplifiers were being constructed and a test system was set up. The output power of the main amplifier can reach up to 27 W. With a 5-mm-long LBO crystal, the green second harmonic laser of 6 W was achieved in the preliminary validation experiment.
2015,
27: 051003.
doi: 10.11884/HPLPB201527.051003
Abstract:
With the existence of atmospheric turbulence, laser propagation in atmosphere can lead to light spot tilt and energy convergence decline. Correcting tilt aberration can increase the quality of laser propagation in atmosphere, and fast steering mirror is the key component of tilt aberration correction. A two-dimension PZT driving fast steering mirror with flexible axis structure was designed, which used the high voltage operational amplifier PA96 to make the driving power, and selected the DSP chip of TMS320F2812 version as the core processor of the control system. Indicated by the test of experiments, the range of deflection of the fast steering mirror is 1.8 mrad, the resonant frequency is 432 Hz, and the angle resolution is about 0.5 rad. The mirror system was used in the experiment of correcting tilt aberration in laser propagation in atmosphere .The experiment shows that the system can effectively increase facula energy convergence and reduce facula shift, and it can be applied to correcting tilt aberration in laser propagation in atmosphere.
With the existence of atmospheric turbulence, laser propagation in atmosphere can lead to light spot tilt and energy convergence decline. Correcting tilt aberration can increase the quality of laser propagation in atmosphere, and fast steering mirror is the key component of tilt aberration correction. A two-dimension PZT driving fast steering mirror with flexible axis structure was designed, which used the high voltage operational amplifier PA96 to make the driving power, and selected the DSP chip of TMS320F2812 version as the core processor of the control system. Indicated by the test of experiments, the range of deflection of the fast steering mirror is 1.8 mrad, the resonant frequency is 432 Hz, and the angle resolution is about 0.5 rad. The mirror system was used in the experiment of correcting tilt aberration in laser propagation in atmosphere .The experiment shows that the system can effectively increase facula energy convergence and reduce facula shift, and it can be applied to correcting tilt aberration in laser propagation in atmosphere.
2015,
27: 051004.
doi: 10.11884/HPLPB201527.051004
Abstract:
In order to achieve a coherent light source with large modulation bandwidth and high repetition rate for synthetic aperture ladar (SAL), a Synthetic Frequency-Stepped linearly-Chirping Signal (SFSCS) is proposed and a SAL using SFSCS illumination (SFSCS-SAL) is investigated both theoretically and experimentally. The SFSCS is synthesized by multiple independent lasers with relatively narrow chirping bandwidth and high repetition rate. Data equations, as well as the image formation theory, on the SFSCS-SAL are given. The theoretical studies show that under proper conditions, the SFSCS-SAL follows the same image formation theory as a conventional SAL; whereas, the range resolution in an SFSCS-SAL will be raised at least N times compared to that of a SAL with only one piece of sub-pulse laser (N is the number of independent lasers in the SFSCS). In the experimental demonstration, an SFSCS of N=3 was produced by optically chopping a linearly wavelength-scanning laser output into 3 sub-pulses; an SFSCS-SAL was set up using the SFSCS and high resolution images were obtained with either retro-reflective or diffusive targets. The experimental results are in well agreement with the theoretical analysis.
In order to achieve a coherent light source with large modulation bandwidth and high repetition rate for synthetic aperture ladar (SAL), a Synthetic Frequency-Stepped linearly-Chirping Signal (SFSCS) is proposed and a SAL using SFSCS illumination (SFSCS-SAL) is investigated both theoretically and experimentally. The SFSCS is synthesized by multiple independent lasers with relatively narrow chirping bandwidth and high repetition rate. Data equations, as well as the image formation theory, on the SFSCS-SAL are given. The theoretical studies show that under proper conditions, the SFSCS-SAL follows the same image formation theory as a conventional SAL; whereas, the range resolution in an SFSCS-SAL will be raised at least N times compared to that of a SAL with only one piece of sub-pulse laser (N is the number of independent lasers in the SFSCS). In the experimental demonstration, an SFSCS of N=3 was produced by optically chopping a linearly wavelength-scanning laser output into 3 sub-pulses; an SFSCS-SAL was set up using the SFSCS and high resolution images were obtained with either retro-reflective or diffusive targets. The experimental results are in well agreement with the theoretical analysis.
2015,
27: 051005.
doi: 10.11884/HPLPB201527.051005
Abstract:
A temporal-spatial filtering algorithm based on kernel density estimation structure is presented for infrared image background suppression in infrared search and track system. The algorithm can be divided into spatial filtering and temporal filtering. Smoothing process is applied to the background of an infrared image sequence by using the kernel density estimation algorithm in spatial filtering. The probability density of the image gray values after spatial filtering is calculated with the kernel density estimation algorithm in temporal filtering. The background residual and blind pixels are picked out based on their gray values, and are further filtered. The algorithm is validated with a real infrared image sequence. The image sequence is processed by using Fuller kernel filter, Uniform kernel filter and high-pass filter. Quantitatively analysis shows that the temporal-spatial filtering algorithm based on the nonparametric method is a satisfactory way to suppress background clutter in infrared images. The SNR is significantly improved as well.
A temporal-spatial filtering algorithm based on kernel density estimation structure is presented for infrared image background suppression in infrared search and track system. The algorithm can be divided into spatial filtering and temporal filtering. Smoothing process is applied to the background of an infrared image sequence by using the kernel density estimation algorithm in spatial filtering. The probability density of the image gray values after spatial filtering is calculated with the kernel density estimation algorithm in temporal filtering. The background residual and blind pixels are picked out based on their gray values, and are further filtered. The algorithm is validated with a real infrared image sequence. The image sequence is processed by using Fuller kernel filter, Uniform kernel filter and high-pass filter. Quantitatively analysis shows that the temporal-spatial filtering algorithm based on the nonparametric method is a satisfactory way to suppress background clutter in infrared images. The SNR is significantly improved as well.
2015,
27: 051006.
doi: 10.11884/HPLPB201527.051006
Abstract:
High power pulsed fiber lasers are attractive for light detection and ranging (lidar) systems. However, the amplified spontaneous emission (ASE) noise of the high power pulsed fiber laser degrades the system performance. A method to measure the ASE noise inherited in the high power pulsed laser is proposed. Using this new method, the high power laser is attenuated firstly, and then the relative energies of the ASE noise and the laser pulse are measured and calculated separately in time domain. The attenuated ASE noise profiles as well as the ratios of the ASE noise energy to the laser pulse energy are presented at different pump conditions.
High power pulsed fiber lasers are attractive for light detection and ranging (lidar) systems. However, the amplified spontaneous emission (ASE) noise of the high power pulsed fiber laser degrades the system performance. A method to measure the ASE noise inherited in the high power pulsed laser is proposed. Using this new method, the high power laser is attenuated firstly, and then the relative energies of the ASE noise and the laser pulse are measured and calculated separately in time domain. The attenuated ASE noise profiles as well as the ratios of the ASE noise energy to the laser pulse energy are presented at different pump conditions.
2015,
27: 051007.
doi: 10.11884/HPLPB201527.051007
Abstract:
A PCNN infrared image segmentation algorithm based on genetic algorithm parameter optimization is proposed. The algorithm first carries out the ignition process for input images using PCNN global coupling and pulse synchronization. Entropy is calculated according to the PCNN output and used for the fitness function of genetic algorithm. The entropy change is used as the convergence criterion of genetic algorithm. Combination of optimization is made for parameters effecting image segmentation in PCNN model. To find the optimal values of key parameters biological visual characteristics of PCNN and solution space random search of the genetic algorithm are adopted. Combination of genetic algorithm and PCNN can make full use of the advantages. Compared with OTSU, maximum entropy histogram segmentation algorithm and PCNN segmentation method, quantitative analysis is conducted for the image after segmentation using cross entropy and region contrast objective index. Simulation results show that, judging either by subjective vision or by objective index, the proposed method is superior to other comparative method in segmentation effect.
A PCNN infrared image segmentation algorithm based on genetic algorithm parameter optimization is proposed. The algorithm first carries out the ignition process for input images using PCNN global coupling and pulse synchronization. Entropy is calculated according to the PCNN output and used for the fitness function of genetic algorithm. The entropy change is used as the convergence criterion of genetic algorithm. Combination of optimization is made for parameters effecting image segmentation in PCNN model. To find the optimal values of key parameters biological visual characteristics of PCNN and solution space random search of the genetic algorithm are adopted. Combination of genetic algorithm and PCNN can make full use of the advantages. Compared with OTSU, maximum entropy histogram segmentation algorithm and PCNN segmentation method, quantitative analysis is conducted for the image after segmentation using cross entropy and region contrast objective index. Simulation results show that, judging either by subjective vision or by objective index, the proposed method is superior to other comparative method in segmentation effect.
2015,
27: 051008.
doi: 10.11884/HPLPB201527.051008
Abstract:
A novel graded tapered fiber optic interface device is proposed. The interface device is a tapered graded photonic crystal fiber (PCF) about 150 mm in length. Using the finite element method, we studied the loss between different fibers with great difference in mode field diameters when they were splicing. The results showed that the coupling loss can effectively reduce after joining the tapered optical fiber between the fibers with the mode field diameter 9 m and 10.4m, and coupling losses are maintained at a low level at different wavelengths. Thus, the interface device can achieve the transition of the physical structure when the optical fibers splice and the conversion between the optical fibers with different mode field radius, thereby minimizing the splicing loss.
A novel graded tapered fiber optic interface device is proposed. The interface device is a tapered graded photonic crystal fiber (PCF) about 150 mm in length. Using the finite element method, we studied the loss between different fibers with great difference in mode field diameters when they were splicing. The results showed that the coupling loss can effectively reduce after joining the tapered optical fiber between the fibers with the mode field diameter 9 m and 10.4m, and coupling losses are maintained at a low level at different wavelengths. Thus, the interface device can achieve the transition of the physical structure when the optical fibers splice and the conversion between the optical fibers with different mode field radius, thereby minimizing the splicing loss.
2015,
27: 051009.
doi: 10.11884/HPLPB201527.051009
Abstract:
The theoretical experimental studies on thermal effect of LD side-pumped grazing-incidence slab chain were carried out. The thermodynamic model of amplifier grazing-incidence slab amplifier was built up. The temperature distribution, thermal distortion and thermal lensing effect were analyzed in detail. Also, the temperature distribution, thermal stress and thermal strain were simulated by finite element analysis. The influence of different incidence angle, pumping region and slab thickness on the thermal focal length and the optical path difference was discussed. The simulation results provided a basis for predicting the thermal effect, compensating thermal effect and designing amplifier chain.
The theoretical experimental studies on thermal effect of LD side-pumped grazing-incidence slab chain were carried out. The thermodynamic model of amplifier grazing-incidence slab amplifier was built up. The temperature distribution, thermal distortion and thermal lensing effect were analyzed in detail. Also, the temperature distribution, thermal stress and thermal strain were simulated by finite element analysis. The influence of different incidence angle, pumping region and slab thickness on the thermal focal length and the optical path difference was discussed. The simulation results provided a basis for predicting the thermal effect, compensating thermal effect and designing amplifier chain.
2015,
27: 051010.
doi: 10.11884/HPLPB201527.051010
Abstract:
In order to realize the beam shaping of high-power diode laser stack by microlens array, the technique of high-power diode laser stack slow axis direction beam collimation is researched, the high-power diode laser stack is accompanied with micro-cylindrical-lens of fast axis collimation. On the basis of the analysis of the slow axis direction beam collimation, the impact of fill factor in the slow axis on the beam collimation is studied chiefly, and the collimating programs of diode lasers with different fill factors are analyzed. Using the bar as the collimating unit for the high-power diode laser stack with the fill factor 0.5, we test the remaining divergence angle of slow axis direction beam after collimation by the testing equipment based on space scanning, and achieve the half of the remaining divergence angle 2.12. The experimental results show that the collimating way of diode laser slow axis direction beam is effective.
In order to realize the beam shaping of high-power diode laser stack by microlens array, the technique of high-power diode laser stack slow axis direction beam collimation is researched, the high-power diode laser stack is accompanied with micro-cylindrical-lens of fast axis collimation. On the basis of the analysis of the slow axis direction beam collimation, the impact of fill factor in the slow axis on the beam collimation is studied chiefly, and the collimating programs of diode lasers with different fill factors are analyzed. Using the bar as the collimating unit for the high-power diode laser stack with the fill factor 0.5, we test the remaining divergence angle of slow axis direction beam after collimation by the testing equipment based on space scanning, and achieve the half of the remaining divergence angle 2.12. The experimental results show that the collimating way of diode laser slow axis direction beam is effective.
2015,
27: 051011.
doi: 10.11884/HPLPB201527.051011
Abstract:
The adaptive polarization conversion system which converts the non-polarization maintaining laser to polarization maintaining one based on stochastic parallel gradient descent (SPGD) algorithm is reported in this paper. Using polarization controller to control polarized component in X and Y direction directly, adopting SPGD optimization technology to optimize the output extinction ratio, it finally realizes polarization conversion of non-polarization maintaining laser to polarization maintaining one. In theory, the model of adaptive polarization conversion is built based on the principle of the controller and the SPGD algorithm. In experiment, we first realized adaptive conversion of non-polarization maintaining laser to polarization maintaining one with an extinction ratio of 14.1 dB. Then we used the system to change the polarization direction of the linearly polarized laser from any direction (0-360) to the expected direction with high extinction ratio, and the average extinction ratio is about 12 dB.
The adaptive polarization conversion system which converts the non-polarization maintaining laser to polarization maintaining one based on stochastic parallel gradient descent (SPGD) algorithm is reported in this paper. Using polarization controller to control polarized component in X and Y direction directly, adopting SPGD optimization technology to optimize the output extinction ratio, it finally realizes polarization conversion of non-polarization maintaining laser to polarization maintaining one. In theory, the model of adaptive polarization conversion is built based on the principle of the controller and the SPGD algorithm. In experiment, we first realized adaptive conversion of non-polarization maintaining laser to polarization maintaining one with an extinction ratio of 14.1 dB. Then we used the system to change the polarization direction of the linearly polarized laser from any direction (0-360) to the expected direction with high extinction ratio, and the average extinction ratio is about 12 dB.
2015,
27: 051012.
doi: 10.11884/HPLPB201527.051012
Abstract:
Aerosol optical depths calculated from surface visibility and water vapor pressure are compared with those observed by sun photometers. The precision of calculated aerosol optical depths is evaluated by root-mean-square deviation and relative deviation. Analysis of calculated aerosol optical depths shows the existence of systemic errors. A factor is introduced to revise the calculated aerosol optical depths, and comparison of revised and observed aerosol optical depths reveals distinct improvement of calculating precision.
Aerosol optical depths calculated from surface visibility and water vapor pressure are compared with those observed by sun photometers. The precision of calculated aerosol optical depths is evaluated by root-mean-square deviation and relative deviation. Analysis of calculated aerosol optical depths shows the existence of systemic errors. A factor is introduced to revise the calculated aerosol optical depths, and comparison of revised and observed aerosol optical depths reveals distinct improvement of calculating precision.
2015,
27: 051013.
doi: 10.11884/HPLPB201527.051013
Abstract:
Based on space-based data of RXTE satellite, we established the method of a space-time coordinate system conversion, time correction and epoch folding, constructed the Crab pulsar contour for extracting navigation information, analyzed the structure and characteristics of space-based loads, and simulated the background radiation with RXTE satellite. In the setting condition of navigation, the accuracies of a single satellite orbit and multi-satellite orbit positionings were quantitatively analyzed, and the urgent attention to the technical problems to improve the navigation and positioning accuracy was described in the later pulsar navigation detection.
Based on space-based data of RXTE satellite, we established the method of a space-time coordinate system conversion, time correction and epoch folding, constructed the Crab pulsar contour for extracting navigation information, analyzed the structure and characteristics of space-based loads, and simulated the background radiation with RXTE satellite. In the setting condition of navigation, the accuracies of a single satellite orbit and multi-satellite orbit positionings were quantitatively analyzed, and the urgent attention to the technical problems to improve the navigation and positioning accuracy was described in the later pulsar navigation detection.
2015,
27: 051014.
doi: 10.11884/HPLPB201527.051014
Abstract:
Several plans for orbital debris elimination with lasers have been carried out in the international world in recent years. Orbital debris is non-cooperative target when effected with lasers. Laser beam would irradiate the orbital debris at a random incidence angle. The surface of debris would vaporize rapidly when irradiated by high power laser. Steam plasma of high temperature and pressure would spray at high speed. An experimental facility was set up to observe and record the plasma plume expansion of 6061 aluminum target at different laser incident angle. Images got in the experiment were disposed and the results were fitted with numerical method. The region of plasma expansion plume is 5 mm5 mm outside of the target surface. The velocity of the plasma plume expansion is roughly axisymmetrically distributed with different laser incidence angle. Laser ablation impulse is along the normal direction relative to the target surface when the laser irradiates within the small angle to the normal direction. The plasma plume expansion velocity is 20-40 kms-1 along the normal direction. The plasma plume expansion velocity is greater when the laser irradiate at oblique incidence. Gaussian function is a good way to describe plasma plume expansion velocity distribution.
Several plans for orbital debris elimination with lasers have been carried out in the international world in recent years. Orbital debris is non-cooperative target when effected with lasers. Laser beam would irradiate the orbital debris at a random incidence angle. The surface of debris would vaporize rapidly when irradiated by high power laser. Steam plasma of high temperature and pressure would spray at high speed. An experimental facility was set up to observe and record the plasma plume expansion of 6061 aluminum target at different laser incident angle. Images got in the experiment were disposed and the results were fitted with numerical method. The region of plasma expansion plume is 5 mm5 mm outside of the target surface. The velocity of the plasma plume expansion is roughly axisymmetrically distributed with different laser incidence angle. Laser ablation impulse is along the normal direction relative to the target surface when the laser irradiates within the small angle to the normal direction. The plasma plume expansion velocity is 20-40 kms-1 along the normal direction. The plasma plume expansion velocity is greater when the laser irradiate at oblique incidence. Gaussian function is a good way to describe plasma plume expansion velocity distribution.
2015,
27: 051015.
doi: 10.11884/HPLPB201527.051015
Abstract:
An approach to focused coherent beam combining (CBC) is proposed. Based on the beam steering technology by liquid crystal optical phased array (LCOPA), a combined beam can be obtained in an arbitrary position within the target region. A theory model of CBC is built based on practical parameters. When 5 coherent beams are combined in position with 100 m distance and 2 m coordinate, the value of peak intensity increases to 16.9 times. Trends of peak intensity in the target region are researched. Analysis indicates that the direct reason for beam jitter is the distortion of the phase front, and the deeper reason is the error of the phase delay caused by voltage quantization. When the quantization bit is less than 16, the position error decreases and the peak intensity increases as the quantization bit increases. However, when the quantization bit is greater than 16, the quantization bit is not the main reason any more. As the transmission distance is larger than 5000 m, the focused CBC is equivalent to the parallel CBC. The peak intensity increases to N2 times when the number of coherent beams is N. Research results can lay a foundation of the application of LCOPA in CBC.
An approach to focused coherent beam combining (CBC) is proposed. Based on the beam steering technology by liquid crystal optical phased array (LCOPA), a combined beam can be obtained in an arbitrary position within the target region. A theory model of CBC is built based on practical parameters. When 5 coherent beams are combined in position with 100 m distance and 2 m coordinate, the value of peak intensity increases to 16.9 times. Trends of peak intensity in the target region are researched. Analysis indicates that the direct reason for beam jitter is the distortion of the phase front, and the deeper reason is the error of the phase delay caused by voltage quantization. When the quantization bit is less than 16, the position error decreases and the peak intensity increases as the quantization bit increases. However, when the quantization bit is greater than 16, the quantization bit is not the main reason any more. As the transmission distance is larger than 5000 m, the focused CBC is equivalent to the parallel CBC. The peak intensity increases to N2 times when the number of coherent beams is N. Research results can lay a foundation of the application of LCOPA in CBC.
2015,
27: 052001.
doi: 10.11884/HPLPB201527.052001
Abstract:
Laser-plasma interactions (LPI) is very important to the success of indirect-drive inertial confinement fusion on NIF. LPI is related not only to laser intensity or laser quality, but also to the plasma state on laser path. Simulations show that the He plasma near gold wall in inner cone laser path is prone to produce SRS in ignition hohlraums. The plasma state can be optimized by changing hohlraum parameters to depress LPI. Accordingly, two methods (using large hohlraums and high laser energy, changing the filling gases) are proposed to reduce SRS gain at this position. Simulations show the peak SRS gain is reduced by 70% and 63% respectively by these two methods.
Laser-plasma interactions (LPI) is very important to the success of indirect-drive inertial confinement fusion on NIF. LPI is related not only to laser intensity or laser quality, but also to the plasma state on laser path. Simulations show that the He plasma near gold wall in inner cone laser path is prone to produce SRS in ignition hohlraums. The plasma state can be optimized by changing hohlraum parameters to depress LPI. Accordingly, two methods (using large hohlraums and high laser energy, changing the filling gases) are proposed to reduce SRS gain at this position. Simulations show the peak SRS gain is reduced by 70% and 63% respectively by these two methods.
2015,
27: 052003.
doi: 10.11884/HPLPB201527.052003
Abstract:
Foam shells with millimeter size were fabricated by microfluidic technology. By design and discussion, Y model channel has the best fluid velocity distribution uniformity in different channels. Y model microfluidic chip was obtained by soft template technology, with which the control conditions of TMPTA are discussed. Results show that the diameter and shell thickness can be controlled by adjusting the fluid velocity in different channels. Furthermore, the density of foam shell is dominated by concentration of reaction monomer. The foam shells with density of 20-100 mg/cm3 and diameter of more than 3 mm were obtained by optimizing the control conditions.
Foam shells with millimeter size were fabricated by microfluidic technology. By design and discussion, Y model channel has the best fluid velocity distribution uniformity in different channels. Y model microfluidic chip was obtained by soft template technology, with which the control conditions of TMPTA are discussed. Results show that the diameter and shell thickness can be controlled by adjusting the fluid velocity in different channels. Furthermore, the density of foam shell is dominated by concentration of reaction monomer. The foam shells with density of 20-100 mg/cm3 and diameter of more than 3 mm were obtained by optimizing the control conditions.
2015,
27: 052004.
doi: 10.11884/HPLPB201527.052004
Abstract:
In this paper, ALD was used to deposit HfO2 single layer films with organic and inorganic precursors at 100, 200 and 300 ℃, respectively. Optical properties such as film absorption, refractive index and microstructure were investigated. Especially, laser damage properties as a key property for thin films used as laser system components were analyzed using 1-on-1 measurement method. Laser damage morphologies were analyzed by scan electron microscope (SEM). For the HfO2 thin films deposited with different process parameters, the damage was mainly caused by film absorption and crystallization. When the HfCl4 precursor was used at 100 ℃, HfO2 films had the least absorption and the best LIDT (about 31.8 J/cm2, 1064 nm, 3 ns), which was the best result as reported.
In this paper, ALD was used to deposit HfO2 single layer films with organic and inorganic precursors at 100, 200 and 300 ℃, respectively. Optical properties such as film absorption, refractive index and microstructure were investigated. Especially, laser damage properties as a key property for thin films used as laser system components were analyzed using 1-on-1 measurement method. Laser damage morphologies were analyzed by scan electron microscope (SEM). For the HfO2 thin films deposited with different process parameters, the damage was mainly caused by film absorption and crystallization. When the HfCl4 precursor was used at 100 ℃, HfO2 films had the least absorption and the best LIDT (about 31.8 J/cm2, 1064 nm, 3 ns), which was the best result as reported.
2015,
27: 052005.
doi: 10.11884/HPLPB201527.052005
Abstract:
Aiming at the problem of plasma stealth for aircraft inlet, we create a three-dimensional model for cylindrical inlet. A finite element model is used to solve the wave equation to gain the RCS (radar cross section) of inlet whose inner wall is covered with uniform plasmas. The model operates at a collision frequency of 1-100 GHz, an electron number density of 1016-1018 m-3, a microwave frequency of 1-3 GHz, and an incident angle of 0-80. The results show that the attenuation is significant when the inlet is covered with plasmas and decreases with the microwave frequency; there are several attenuation peaks because of the cavity geometry structure; the attenuation increases with the electron density, but it can deteriorate while the electron density is too high; the optimum collision frequency is related with the microwave frequency and the electron density, but it is generally about 9 GHz; the attenuation increases with the thickness of plasma, but it can deteriorate because of the reflection on the interface between the plasma and the air while the electron density is too high; the attenuation can be significant in whole microwave band (1-3 GHz) at the appropriate incident angle and plasma density, which is important for designing plasma source to applied the plasma stealth.
Aiming at the problem of plasma stealth for aircraft inlet, we create a three-dimensional model for cylindrical inlet. A finite element model is used to solve the wave equation to gain the RCS (radar cross section) of inlet whose inner wall is covered with uniform plasmas. The model operates at a collision frequency of 1-100 GHz, an electron number density of 1016-1018 m-3, a microwave frequency of 1-3 GHz, and an incident angle of 0-80. The results show that the attenuation is significant when the inlet is covered with plasmas and decreases with the microwave frequency; there are several attenuation peaks because of the cavity geometry structure; the attenuation increases with the electron density, but it can deteriorate while the electron density is too high; the optimum collision frequency is related with the microwave frequency and the electron density, but it is generally about 9 GHz; the attenuation increases with the thickness of plasma, but it can deteriorate because of the reflection on the interface between the plasma and the air while the electron density is too high; the attenuation can be significant in whole microwave band (1-3 GHz) at the appropriate incident angle and plasma density, which is important for designing plasma source to applied the plasma stealth.
2015,
27: 052006.
doi: 10.11884/HPLPB201527.052006
Abstract:
A novel method for laser induced damage threshold (LIDT) test of dielectric coatings is discussed in order to solve the time-consuming problem in traditional LIDT test. Single shot with large beam is used to get the LIDTs based on image processing technique. Following the coordinate conversion, image girding and compression procedure, the damage information could be extracted by comparing the sub-damage-spots distribution with the laser intensity distribution in the irradiated region. And finally the LIDT could be obtained from this information. This new method could greatly increase the efficiency of LIDT test. Moreover, the single-shot large beam LIDT testing bench is introduced and the availability of this method is confirmed on HfO2/SiO2 high reflectors.
A novel method for laser induced damage threshold (LIDT) test of dielectric coatings is discussed in order to solve the time-consuming problem in traditional LIDT test. Single shot with large beam is used to get the LIDTs based on image processing technique. Following the coordinate conversion, image girding and compression procedure, the damage information could be extracted by comparing the sub-damage-spots distribution with the laser intensity distribution in the irradiated region. And finally the LIDT could be obtained from this information. This new method could greatly increase the efficiency of LIDT test. Moreover, the single-shot large beam LIDT testing bench is introduced and the availability of this method is confirmed on HfO2/SiO2 high reflectors.
2015,
27: 053001.
doi: 10.11884/HPLPB201527.053001
Abstract:
In order to modulate the phase of RF signal continuously, a new miniaturized Ka-band analog electrically controlled phase shifter is presented. The phase shifter based on 90 directional coupler and parallel variable capacitance diodes(VCD) achieves matching circuits and shift phase, and the circuit can gain wide range of phase shift by changing the bias voltage of variable capacitance diodes(VCD). At the same time, insertion loss fluctuations have a significant improvement by parallel compensation resistance. Simulation and experimental results show that the phase shifter obtains 180 phase shift, the insertion loss is less than 6.5 dB, the insertion loss fluctuations are within 1 dB, and the phase shift errors are less than 10 in 29-31 GHz range.
In order to modulate the phase of RF signal continuously, a new miniaturized Ka-band analog electrically controlled phase shifter is presented. The phase shifter based on 90 directional coupler and parallel variable capacitance diodes(VCD) achieves matching circuits and shift phase, and the circuit can gain wide range of phase shift by changing the bias voltage of variable capacitance diodes(VCD). At the same time, insertion loss fluctuations have a significant improvement by parallel compensation resistance. Simulation and experimental results show that the phase shifter obtains 180 phase shift, the insertion loss is less than 6.5 dB, the insertion loss fluctuations are within 1 dB, and the phase shift errors are less than 10 in 29-31 GHz range.
2015,
27: 053002.
doi: 10.11884/HPLPB201527.053002
Abstract:
In order to solve the problems of poor insulation, low resolution and sparking etc., a retarding field energy analyzer is upgraded, simulated and analyzed to test and analyze the electron beam parameters accurately, which derive from the guns of traveling wave tubes and beams after beam-wave interaction, providing a reference for the design, performance improvement and development of the traveling wave tubes. The retarding energy analyzer with a controllable focusing voltage insulates high-voltage cylinder electrically from retarding mesh and applies a controllable small voltage between them. The second electrostatic lens accelerates and focuses the diverging beam near the area of the mesh, to weaken too much expansion in the region of the weak part that the first lens functions, due to space-particle effects and beam emittance, etc. and optimize the slope of the particle trajectory and resolution. Meanwhile, the whole structure tends to miniaturizition and lightweight. A computer code called CST is used to simulate the particle distribution in particle interfaces and the whole electric field distribution, and Matlab code helps data processing and exports the key parameters. Besides, the paper focuses on analyzing the optimization and improvement of the performance reflected by the resolution and Full Width at Half Maximum, etc. The result shows that this energy analyzer is competent to apply to the experiments of electron beams.
In order to solve the problems of poor insulation, low resolution and sparking etc., a retarding field energy analyzer is upgraded, simulated and analyzed to test and analyze the electron beam parameters accurately, which derive from the guns of traveling wave tubes and beams after beam-wave interaction, providing a reference for the design, performance improvement and development of the traveling wave tubes. The retarding energy analyzer with a controllable focusing voltage insulates high-voltage cylinder electrically from retarding mesh and applies a controllable small voltage between them. The second electrostatic lens accelerates and focuses the diverging beam near the area of the mesh, to weaken too much expansion in the region of the weak part that the first lens functions, due to space-particle effects and beam emittance, etc. and optimize the slope of the particle trajectory and resolution. Meanwhile, the whole structure tends to miniaturizition and lightweight. A computer code called CST is used to simulate the particle distribution in particle interfaces and the whole electric field distribution, and Matlab code helps data processing and exports the key parameters. Besides, the paper focuses on analyzing the optimization and improvement of the performance reflected by the resolution and Full Width at Half Maximum, etc. The result shows that this energy analyzer is competent to apply to the experiments of electron beams.
2015,
27: 053003.
doi: 10.11884/HPLPB201527.053003
Abstract:
A megavoltage compact and repetitive Marx generator is designed. The charge-discharge circuit is simplified, and the energy loss is also decreased; The effect of isolating inductance change on the output pulse voltage waveform from generator is analysed. The volume of isolating inductors is reduced, and the validity of isolation is also improved; The chamber structure of switch is optimized. The continuous adjustment of space is realized, which is not affected by the change of peripheral structure and oscillation. Thirteen gaps lie in the same vertical line. The ultraviolet ray or radioactive ray excited by spark discharge are mutually irradiated, which accelerate switch conduction and decrease output voltage jitter of the Marx generator. Plastic case capacitors are used under decreased voltage, which improve the reliability of the generator. The miniaturization of generator is realized by Pspice simulation and three-dimensional static electric field analysis. The entire Marx generator is laid in a sealed metal cylindrical shell with pure SF6, whose volume is less than 0.25 m3. By means of optimal design and experimental research, the generator has the following parameters: The output peak voltage on high-impedance load is 1.02 MV, the rise time is about 30 ns, the energy storage is 290 J, the voltage magnitude jitter is about 10%, the rise time jitter is less than 10 ns, and the system can operate stably under 20 Hz repetition rate.
A megavoltage compact and repetitive Marx generator is designed. The charge-discharge circuit is simplified, and the energy loss is also decreased; The effect of isolating inductance change on the output pulse voltage waveform from generator is analysed. The volume of isolating inductors is reduced, and the validity of isolation is also improved; The chamber structure of switch is optimized. The continuous adjustment of space is realized, which is not affected by the change of peripheral structure and oscillation. Thirteen gaps lie in the same vertical line. The ultraviolet ray or radioactive ray excited by spark discharge are mutually irradiated, which accelerate switch conduction and decrease output voltage jitter of the Marx generator. Plastic case capacitors are used under decreased voltage, which improve the reliability of the generator. The miniaturization of generator is realized by Pspice simulation and three-dimensional static electric field analysis. The entire Marx generator is laid in a sealed metal cylindrical shell with pure SF6, whose volume is less than 0.25 m3. By means of optimal design and experimental research, the generator has the following parameters: The output peak voltage on high-impedance load is 1.02 MV, the rise time is about 30 ns, the energy storage is 290 J, the voltage magnitude jitter is about 10%, the rise time jitter is less than 10 ns, and the system can operate stably under 20 Hz repetition rate.
2015,
27: 053004.
doi: 10.11884/HPLPB201527.053004
Abstract:
The design principle of a TE□10-TE○01 broad band cruciform mode converter was addressed in this paper, and the scheme of a set of W-band low loss input coupling system was presented. According to this scheme, the 3-D model was optimized and simulated by HFSS. A TE□10-TE○01 broad bandmode converter with a loss of less than 0.14 dB, a maximum VSWR of 1.388, and a band width of 10 GHz was obtained through simulation. For the whole system, a calculated loss of less than 1 dB, which was far less than that of TE10 mode in the rectangle waveguide(about 15 dB), was given. It leaded to the increase of the transmission efficiency and reduction of the energy loss. A pair of manufactured mode converters was tested in the experiment, and the loss was about 1 dB. So the loss of the whole system was equal to 3 dB, which was greatly improved compared with the loss in the rectangle waveguide.
The design principle of a TE□10-TE○01 broad band cruciform mode converter was addressed in this paper, and the scheme of a set of W-band low loss input coupling system was presented. According to this scheme, the 3-D model was optimized and simulated by HFSS. A TE□10-TE○01 broad bandmode converter with a loss of less than 0.14 dB, a maximum VSWR of 1.388, and a band width of 10 GHz was obtained through simulation. For the whole system, a calculated loss of less than 1 dB, which was far less than that of TE10 mode in the rectangle waveguide(about 15 dB), was given. It leaded to the increase of the transmission efficiency and reduction of the energy loss. A pair of manufactured mode converters was tested in the experiment, and the loss was about 1 dB. So the loss of the whole system was equal to 3 dB, which was greatly improved compared with the loss in the rectangle waveguide.
2015,
27: 053005.
doi: 10.11884/HPLPB201527.053005
Abstract:
Based on the advantages of the relativistic backward wave oscillator (RBWO) with low magnetic field and vircator, a novel configuration of vircator with a high beam-wave conversion efficiency is presented and the 2.5-D particle-in-cell simulations are carried out using a PIC code. When the energy of the electron is 480 keV while the beam current is 23 kA, a simulated result of 2.6 GW output microwave power with a frequency of 3.7 GHz is obtained, for which the beam-wave conversion efficiency of the vircator is 23%.
Based on the advantages of the relativistic backward wave oscillator (RBWO) with low magnetic field and vircator, a novel configuration of vircator with a high beam-wave conversion efficiency is presented and the 2.5-D particle-in-cell simulations are carried out using a PIC code. When the energy of the electron is 480 keV while the beam current is 23 kA, a simulated result of 2.6 GW output microwave power with a frequency of 3.7 GHz is obtained, for which the beam-wave conversion efficiency of the vircator is 23%.
2015,
27: 053006.
doi: 10.11884/HPLPB201527.053006
Abstract:
To study the reaction of the complex metal cylinders irradiated by high power microwave, a three-dimensional induced field ratio (IFR) algorithm for analyzing the scattering field of the finite length parallel cylinders is presented. A three- dimensional induced field ratio model is established to calculate the scattering fields by method of moments (MoM), and equivalent radiation currents are derived. The impedance distribution of a thin wire antenna is taken for reference to deduce the distribution on the thin cylinders. The induced field ratio matrix related to the length and the radius of cylinders and observation angle is derived. Three parallel cylinders are arranged to obtain the scattering field of an array composed of cylinders with different length and distance as exemplified. The accuracy is proved by comparing the results with that from MoM. The induced field ratio matrix is only needed, which accelerates the computing with high accuracy, to obtain the scattering field of the array consisting of cylinders with different distance and length.
To study the reaction of the complex metal cylinders irradiated by high power microwave, a three-dimensional induced field ratio (IFR) algorithm for analyzing the scattering field of the finite length parallel cylinders is presented. A three- dimensional induced field ratio model is established to calculate the scattering fields by method of moments (MoM), and equivalent radiation currents are derived. The impedance distribution of a thin wire antenna is taken for reference to deduce the distribution on the thin cylinders. The induced field ratio matrix related to the length and the radius of cylinders and observation angle is derived. Three parallel cylinders are arranged to obtain the scattering field of an array composed of cylinders with different length and distance as exemplified. The accuracy is proved by comparing the results with that from MoM. The induced field ratio matrix is only needed, which accelerates the computing with high accuracy, to obtain the scattering field of the array consisting of cylinders with different distance and length.
2015,
27: 053007.
doi: 10.11884/HPLPB201527.053007
Abstract:
The structure of the cathode-heater assembly has been changed appropriately in order to reduce the heating power of some X-band space pulsed TWT. Thermal characters of cathode-heater assembly are analyzed using finite element software ANSYS, and its steady-state temperature distribution, cathode temperature transient solution and the relationship between heating power and cathode temperature are obtained. Simulation results are compared with test data, which shows that the calculation error of cathode temperature is within 1.3%, indicating the model and the methods have been correctly used. Then the structure of the cathode support cylinder is optimized by studying the relationship between heating power and cathode temperature under different slot width, thickness and material. Simulation results show that the optimized cathode-heater assemblys heating power is reduced from 8.2 W to 6.7 W.
The structure of the cathode-heater assembly has been changed appropriately in order to reduce the heating power of some X-band space pulsed TWT. Thermal characters of cathode-heater assembly are analyzed using finite element software ANSYS, and its steady-state temperature distribution, cathode temperature transient solution and the relationship between heating power and cathode temperature are obtained. Simulation results are compared with test data, which shows that the calculation error of cathode temperature is within 1.3%, indicating the model and the methods have been correctly used. Then the structure of the cathode support cylinder is optimized by studying the relationship between heating power and cathode temperature under different slot width, thickness and material. Simulation results show that the optimized cathode-heater assemblys heating power is reduced from 8.2 W to 6.7 W.
2015,
27: 053101.
doi: 10.11884/HPLPB201527.053101
Abstract:
In this paper, the analytical equations based on mode-coupling theory are derived to facilitate the design process of rectangular transition structure in folded waveguide devices. As an important component of the power coupler, two common categories of structures are considered to match the TE10 modes in rectangular waveguide in folded waveguide slow wave structure into the TE10 mode in the standard rectangular waveguide port. By comparison, the tapered transition structure is much longer than the laddered transition structure with the same reflection requirement, whereas the former has a naturally much broader frequency bandwidth and less sensitivity to configuration errors. As an example, both the laddered and tapered rectangular transitions are designed and error-analyzed for 220 GHz FW Backward Wave Oscillator (BWO). The theoretical method adopted in design process is finally verified by numeric simulation, which shows excellent agreement. The design period based on the accurate theoretical method is only several minutes.
In this paper, the analytical equations based on mode-coupling theory are derived to facilitate the design process of rectangular transition structure in folded waveguide devices. As an important component of the power coupler, two common categories of structures are considered to match the TE10 modes in rectangular waveguide in folded waveguide slow wave structure into the TE10 mode in the standard rectangular waveguide port. By comparison, the tapered transition structure is much longer than the laddered transition structure with the same reflection requirement, whereas the former has a naturally much broader frequency bandwidth and less sensitivity to configuration errors. As an example, both the laddered and tapered rectangular transitions are designed and error-analyzed for 220 GHz FW Backward Wave Oscillator (BWO). The theoretical method adopted in design process is finally verified by numeric simulation, which shows excellent agreement. The design period based on the accurate theoretical method is only several minutes.
2015,
27: 053102.
doi: 10.11884/HPLPB201527.053102
Abstract:
To minimize the inaccuracy of Schottky diode pair circuit model for sub-millimeter wave band mixer, full-wave analysis and circuit simulation were carried out to classify the signals in and out of diodes. Then a more precise modeling of the anti-parallel diode pair was proposed and applied to the circuits of sub-millimeter wave sub-harmonic mixers. To enhance the efficiency of simulation and optimization, a globally lumped element equivalent circuit of the mixer has been built based on the accurate diode model. A 183 GHz sub-harmonic mixer was designed and fabricated. The mixer exhibited less than 6.8 dB double side-band conversion loss and a mixer temperature of lower than 800 K over an RF band of 176-192 GHz using 2 mW of local oscillator power at 92 GHz. A minimum double side-band mixer conversion loss of 4.9 dB was measured at 182 GHz. The measured results agree well with the simulated ones.
To minimize the inaccuracy of Schottky diode pair circuit model for sub-millimeter wave band mixer, full-wave analysis and circuit simulation were carried out to classify the signals in and out of diodes. Then a more precise modeling of the anti-parallel diode pair was proposed and applied to the circuits of sub-millimeter wave sub-harmonic mixers. To enhance the efficiency of simulation and optimization, a globally lumped element equivalent circuit of the mixer has been built based on the accurate diode model. A 183 GHz sub-harmonic mixer was designed and fabricated. The mixer exhibited less than 6.8 dB double side-band conversion loss and a mixer temperature of lower than 800 K over an RF band of 176-192 GHz using 2 mW of local oscillator power at 92 GHz. A minimum double side-band mixer conversion loss of 4.9 dB was measured at 182 GHz. The measured results agree well with the simulated ones.
2015,
27: 053103.
doi: 10.11884/HPLPB201527.053103
Abstract:
Two-dimensional THz imaging can be used for safety inspection and quality control. This paper presents the design of a wide field off-axis three-mirror optical system for two-dimensional THz imaging. The surface types of the three-mirror system are analyzed according to the Petzvals condition and an off-axis three-mirror system based on the retrofocus configuration is proposed. And an off-axis three-mirror system with a field of view of 2020 , a focal length of 70 mm and F number of 3.5 is designed. The result indicates that MTF of the optical system is close to the diffraction limit. In each field of view, the RMS radius of the spot diagram is much smaller than the radius of the Airy disk. The optical system with a good image quality meets the design requirements.
Two-dimensional THz imaging can be used for safety inspection and quality control. This paper presents the design of a wide field off-axis three-mirror optical system for two-dimensional THz imaging. The surface types of the three-mirror system are analyzed according to the Petzvals condition and an off-axis three-mirror system based on the retrofocus configuration is proposed. And an off-axis three-mirror system with a field of view of 2020 , a focal length of 70 mm and F number of 3.5 is designed. The result indicates that MTF of the optical system is close to the diffraction limit. In each field of view, the RMS radius of the spot diagram is much smaller than the radius of the Airy disk. The optical system with a good image quality meets the design requirements.
2015,
27: 053201.
doi: 10.11884/HPLPB201527.053201
Abstract:
A 1.575 GHz integrated GPS magneto window antenna which aimed to reduce communication interruption of hypersonic aerial vehicle was designed, and a static verification experiment was done. The designed magneto window antenna was composed of a microstrip antenna and a permanent magnet. Its size was 100 mm100 mm75 mm, and a protection structure was designed. The microstrip antenna would not influence the magnetic field of the permanent magnet, and the permanent magnet would not change the resonant frequency of the microstrip antenna; the designed protection structure could eliminate all magnetic field in the non-propagation direction, and would not reduce the intensity of the magnetic field in the propagation direction. When tests were performed on plasmas of 25.5 mm in thickness and the electron density changed from 61010/cm3 to 11011/cm3 , the designed magneto window antenna raised the transmission coefficient from ［－19, －23.5］ dB to ［－11, －16］ dB. The results indicate that the designed GPS magneto window antenna could reduce the influence of plasma on the communication, the magneto window antenna size is miniaturized and the safety in communication is enhanced.
A 1.575 GHz integrated GPS magneto window antenna which aimed to reduce communication interruption of hypersonic aerial vehicle was designed, and a static verification experiment was done. The designed magneto window antenna was composed of a microstrip antenna and a permanent magnet. Its size was 100 mm100 mm75 mm, and a protection structure was designed. The microstrip antenna would not influence the magnetic field of the permanent magnet, and the permanent magnet would not change the resonant frequency of the microstrip antenna; the designed protection structure could eliminate all magnetic field in the non-propagation direction, and would not reduce the intensity of the magnetic field in the propagation direction. When tests were performed on plasmas of 25.5 mm in thickness and the electron density changed from 61010/cm3 to 11011/cm3 , the designed magneto window antenna raised the transmission coefficient from ［－19, －23.5］ dB to ［－11, －16］ dB. The results indicate that the designed GPS magneto window antenna could reduce the influence of plasma on the communication, the magneto window antenna size is miniaturized and the safety in communication is enhanced.
2015,
27: 053202.
doi: 10.11884/HPLPB201527.053202
Abstract:
Two X-band low sidelobe slotted waveguide antenna arrays are designed and tested. The excitation amplitude of aperture unit is based on the Taylor distribution. Using the Stevenson equivalent circuit method, aperture offset is calculated with different excitation amplitude distributions. With a resonant length extraction model of multiple cracks, the aperture resonance length is calculated in mutual coupling environment. It is found that the slotted waveguide antenna array can be easily designed using the Stevenson formula and the resonance length obtained from mutual coupling environment. The measured gain of the linear antenna array is 17. 83 dB and the simulation result is 18. 2 dB. The measured sidelobe is -28. 12 dB and the simulation result is -29. 97 dB. The measured gain of the planar antenna array is 27 dB and the simulation result is 27. 9 dB. The measured sidelobe of H-plane is -27. 2 dB and the simulation result is -29. 9. The measured sidelobe of E-plane is -22 dB and the simulation result is -22 dB. The test results of the antennas are highly consistent with the simulation results.
Two X-band low sidelobe slotted waveguide antenna arrays are designed and tested. The excitation amplitude of aperture unit is based on the Taylor distribution. Using the Stevenson equivalent circuit method, aperture offset is calculated with different excitation amplitude distributions. With a resonant length extraction model of multiple cracks, the aperture resonance length is calculated in mutual coupling environment. It is found that the slotted waveguide antenna array can be easily designed using the Stevenson formula and the resonance length obtained from mutual coupling environment. The measured gain of the linear antenna array is 17. 83 dB and the simulation result is 18. 2 dB. The measured sidelobe is -28. 12 dB and the simulation result is -29. 97 dB. The measured gain of the planar antenna array is 27 dB and the simulation result is 27. 9 dB. The measured sidelobe of H-plane is -27. 2 dB and the simulation result is -29. 9. The measured sidelobe of E-plane is -22 dB and the simulation result is -22 dB. The test results of the antennas are highly consistent with the simulation results.
2015,
27: 054001.
doi: 10.11884/HPLPB201527.054001
Abstract:
The particle trajectory varies exponentially at turning points in orthogonal electromagnetic field, causing the obvious difference of variety mass ion trajectories. So a new nuclides electromagnetic separation method can be created. From the Newton motion equation and based on the single particle track method, the article discusses the movement law of nuclide separated in orthogonal electromagnetic field and focuses on finding the turning point of the trajectories. The mass focusing characteristics of the multi-mass beam flowing in the orthogonal electromagnetic field are given. As an example, the particle trajectories of Li ion are simulated by MATLAB. The result shows the possibility of the mass separation for the multi-mass particle beam in the orthogonal electromagnetic field. According to the characteristics of the trajectory equation, the particles moving along a circular trajectory are summarized. Parameters such as space dimension for the engineering realization of multi-mass particle beam separation structure are provided. The research result can be applied to the development of some devices, such as the mass separator, the spectrum analyzer and the materials purification device. At the same time, it has certain reference significance for the related fields research of the special configuration electromagnetic field controlling multi-mass beam flow.
The particle trajectory varies exponentially at turning points in orthogonal electromagnetic field, causing the obvious difference of variety mass ion trajectories. So a new nuclides electromagnetic separation method can be created. From the Newton motion equation and based on the single particle track method, the article discusses the movement law of nuclide separated in orthogonal electromagnetic field and focuses on finding the turning point of the trajectories. The mass focusing characteristics of the multi-mass beam flowing in the orthogonal electromagnetic field are given. As an example, the particle trajectories of Li ion are simulated by MATLAB. The result shows the possibility of the mass separation for the multi-mass particle beam in the orthogonal electromagnetic field. According to the characteristics of the trajectory equation, the particles moving along a circular trajectory are summarized. Parameters such as space dimension for the engineering realization of multi-mass particle beam separation structure are provided. The research result can be applied to the development of some devices, such as the mass separator, the spectrum analyzer and the materials purification device. At the same time, it has certain reference significance for the related fields research of the special configuration electromagnetic field controlling multi-mass beam flow.
2015,
27: 054002.
doi: 10.11884/HPLPB201527.054002
Abstract:
A kind of small Faraday cup array used for measuring the intense current distribution was designed. The diameter of the Faraday cup array is 22 mm, and it consists of 5 small Faraday cups. The maximum current density which the array can measure is 38 A/mm2.The precise current density distribution on the anode target was obtained by the array. The result shows that the density on the middle of the target was higher than that on any other part of the target. A weak pinch existed during the diode working time. The uniformity of the electron beam on the target was partial. The current density distribution on the target was radially symmetrical. The experiment result is consistent with theoretical expectation and simulation result.
A kind of small Faraday cup array used for measuring the intense current distribution was designed. The diameter of the Faraday cup array is 22 mm, and it consists of 5 small Faraday cups. The maximum current density which the array can measure is 38 A/mm2.The precise current density distribution on the anode target was obtained by the array. The result shows that the density on the middle of the target was higher than that on any other part of the target. A weak pinch existed during the diode working time. The uniformity of the electron beam on the target was partial. The current density distribution on the target was radially symmetrical. The experiment result is consistent with theoretical expectation and simulation result.
2015,
27: 054003.
doi: 10.11884/HPLPB201527.054003
Abstract:
In order to optimize the feeding way of the propellant into the 20 cm diameter ion thrusters discharge chamber, the fluid velocity and pressure at the interface of the thruster anode and main cathode were studied without discharge process, and then the fluid field inside the discharge chamber was calculated. The results indicate that the pressure at the outlet of the thrusters anode gas feeding component is in the range of 4-158 Pa, the exiting velocity of the gas flow is approximately in the range of 0.1-47 m/s. The pressure at the outlet of the cathode aperture is approximately 33.1 Pa, and the velocity is approximately 12 m/s. considering the backstreaming of the vacuum system, the pressure inside the discharge chamber in the range of 0.001-0.4 Pa, the density distribution of Xe atom is not uniform and in the range of (0.2-3)1018 m-3, the density near grids assembly is about 91019 m-3. With the addition of a number of anode feeding pipes, the exiting velocity of the anode gas feeding component is in the range of 18-40 m/s, and the pressure inside the discharge chamber in the range of 0.03-0.1 Pa. When the density of Xe atoms in most part of the discharge chamber is about (0.72-2.4)1019 m-3, the atom density in a small part near the anode and the main cathodes gas-in end is of the order of 21017 m-3 and the discharge has a relatively overall uniform density distribution.
In order to optimize the feeding way of the propellant into the 20 cm diameter ion thrusters discharge chamber, the fluid velocity and pressure at the interface of the thruster anode and main cathode were studied without discharge process, and then the fluid field inside the discharge chamber was calculated. The results indicate that the pressure at the outlet of the thrusters anode gas feeding component is in the range of 4-158 Pa, the exiting velocity of the gas flow is approximately in the range of 0.1-47 m/s. The pressure at the outlet of the cathode aperture is approximately 33.1 Pa, and the velocity is approximately 12 m/s. considering the backstreaming of the vacuum system, the pressure inside the discharge chamber in the range of 0.001-0.4 Pa, the density distribution of Xe atom is not uniform and in the range of (0.2-3)1018 m-3, the density near grids assembly is about 91019 m-3. With the addition of a number of anode feeding pipes, the exiting velocity of the anode gas feeding component is in the range of 18-40 m/s, and the pressure inside the discharge chamber in the range of 0.03-0.1 Pa. When the density of Xe atoms in most part of the discharge chamber is about (0.72-2.4)1019 m-3, the atom density in a small part near the anode and the main cathodes gas-in end is of the order of 21017 m-3 and the discharge has a relatively overall uniform density distribution.
2015,
27: 054004.
doi: 10.11884/HPLPB201527.054004
Abstract:
The typical conventional CT system employs the digital integrating sensor. It is difficult to identify X-ray attenuation characteristics for different materials. This paper focuses on color CT imaging technique based on MARS X-ray spectral CT system to analyze different materials. In experimental study, we scan the rubber tube corroded by iodine solution and a mouse injected with a contrast agent (Gold Nanoparticles (GNP)) in different energy ranges, and extract and quantify X-ray energy spectrum information to reconstructed color projection images of the rubber tube and color CT image of the mouse chest. The picturesdemonstrate the complex structure of the rubber tube and concentration information of the gold particles in the mouse chest. X-ray spectral CT could represent more richer structure information and different composition of materials.
The typical conventional CT system employs the digital integrating sensor. It is difficult to identify X-ray attenuation characteristics for different materials. This paper focuses on color CT imaging technique based on MARS X-ray spectral CT system to analyze different materials. In experimental study, we scan the rubber tube corroded by iodine solution and a mouse injected with a contrast agent (Gold Nanoparticles (GNP)) in different energy ranges, and extract and quantify X-ray energy spectrum information to reconstructed color projection images of the rubber tube and color CT image of the mouse chest. The picturesdemonstrate the complex structure of the rubber tube and concentration information of the gold particles in the mouse chest. X-ray spectral CT could represent more richer structure information and different composition of materials.
2015,
27: 054101.
doi: 10.11884/HPLPB201527.054101
Abstract:
The counter-Meshing Gears (CMG) mechanism is a discrimination mechanism which can be used in combination locks for high-consequence system surety. For an arbitrary binary Unlocking Symbol Sequence composed of equal number symbols of A and B, i.e. NA+NB, how to realize the binary discrimination teeth coding of its corresponding CMG mechanism with minimum fixed gear levels C and gear divisions D, is an important practical problem which is firstly well defined as the Optimal Normalizing CMG Coding Problem. With the toolbox comprising previously reported terms and methods, e.g. the CMG classification method, the 2-D Maze Map and the 3-color circular alternant coloring method for Critical Trap Grids (CTGs), optimal normalizing coding theory and methods for CMG Mechanisms are systematically discussed. Two optional coding methods, and their minimum requirement for the coding space (characterized with CD) and coding algorithm, are all presented. A Figure of Merit (FoM) which characterizes the CMG coding efficiency is defined on the coding space and the symbol length of the Unlocking Symbol Sequence which dedicated for. By the FoM with clear physical meanings, the two optional Optimal Normalizing CMG Coding methods are compared, and it is concluded that the first type CMG mechanism with a coding space of C=3 and D=N+2 is the preferred method. As to the first type CMG mechanism, there is no difference between the Optimal Normalizing Coding, the previously reported Optimized coding with minimum gear levels, thus the minimum coding space of C=3 and D=N+2 are both needed and the 3-color circular alternant CTGs coloring method is a suitable coding method for both two. With application of the 3-color circular alternant CTGs coloring method, a distinct fingerprint feature can be revealed in the 2-D verification maze map that all CTGs are circular regularly allotted to only three color sets, i.e. the predesigned gear-teeth meshing between the two coupled composite gear A and B for error-locking function will alternately happen in only three discrimination gear levels.
The counter-Meshing Gears (CMG) mechanism is a discrimination mechanism which can be used in combination locks for high-consequence system surety. For an arbitrary binary Unlocking Symbol Sequence composed of equal number symbols of A and B, i.e. NA+NB, how to realize the binary discrimination teeth coding of its corresponding CMG mechanism with minimum fixed gear levels C and gear divisions D, is an important practical problem which is firstly well defined as the Optimal Normalizing CMG Coding Problem. With the toolbox comprising previously reported terms and methods, e.g. the CMG classification method, the 2-D Maze Map and the 3-color circular alternant coloring method for Critical Trap Grids (CTGs), optimal normalizing coding theory and methods for CMG Mechanisms are systematically discussed. Two optional coding methods, and their minimum requirement for the coding space (characterized with CD) and coding algorithm, are all presented. A Figure of Merit (FoM) which characterizes the CMG coding efficiency is defined on the coding space and the symbol length of the Unlocking Symbol Sequence which dedicated for. By the FoM with clear physical meanings, the two optional Optimal Normalizing CMG Coding methods are compared, and it is concluded that the first type CMG mechanism with a coding space of C=3 and D=N+2 is the preferred method. As to the first type CMG mechanism, there is no difference between the Optimal Normalizing Coding, the previously reported Optimized coding with minimum gear levels, thus the minimum coding space of C=3 and D=N+2 are both needed and the 3-color circular alternant CTGs coloring method is a suitable coding method for both two. With application of the 3-color circular alternant CTGs coloring method, a distinct fingerprint feature can be revealed in the 2-D verification maze map that all CTGs are circular regularly allotted to only three color sets, i.e. the predesigned gear-teeth meshing between the two coupled composite gear A and B for error-locking function will alternately happen in only three discrimination gear levels.
2015,
27: 054102.
doi: 10.11884/HPLPB201527.054102
Abstract:
The MEMS bionic vector hydrophone developed by North University of China has advantages of low frequency, miniaturization, high sensitivity, etc. But the sensitivity of the hydrophone is still low for detecting the week acoustic signals. How to enhance the sensitivity is a critical problem to the future developments. So a type of central buoyant microstructure is proposed, expecting to improve the sensitivity. And based on the acoustic research, the parameters of the central buoyant sphere is finally determined. The influences of the central buoyant microstructure on the sensitivity and the frequency band are analyzed by static analysis and fluid-structure interaction respectively. In order to verify the feasibility and performance, the hydrophone is tested in the standing wave field and in the real environment. Results show that the sensitivity of the hydrophone is -175 dB, the frequency ranges from 20 Hz to 500 Hz, which satisfies the requirement of detecting the ship radiation noise over a long distance, and the fluctuation range of frequency response curve is 1.5 dB. The directivity pattern of 8-shape is good(48.8 dB).
The MEMS bionic vector hydrophone developed by North University of China has advantages of low frequency, miniaturization, high sensitivity, etc. But the sensitivity of the hydrophone is still low for detecting the week acoustic signals. How to enhance the sensitivity is a critical problem to the future developments. So a type of central buoyant microstructure is proposed, expecting to improve the sensitivity. And based on the acoustic research, the parameters of the central buoyant sphere is finally determined. The influences of the central buoyant microstructure on the sensitivity and the frequency band are analyzed by static analysis and fluid-structure interaction respectively. In order to verify the feasibility and performance, the hydrophone is tested in the standing wave field and in the real environment. Results show that the sensitivity of the hydrophone is -175 dB, the frequency ranges from 20 Hz to 500 Hz, which satisfies the requirement of detecting the ship radiation noise over a long distance, and the fluctuation range of frequency response curve is 1.5 dB. The directivity pattern of 8-shape is good(48.8 dB).
2015,
27: 055002.
doi: 10.11884/HPLPB201527.055002
Abstract:
Based on Blumlein pulse forming network(PFN), a compact module for long-pulse power generator is designed. Two Blumlein PFNs with 20 impedance are symmetrically connected with a linear transformer driver（LTD）s primary coil, and driven by an identical high voltage gas switch which ensures two Blumlein PFNs synchronizing operation. The Blumlein PFN uses L-type configuration. The design ensures PFN and gas switch being compactly connected and the horizontal size of the module being the smallest. Meanwhile, the L-type configuration has little impact on the waveform of the output pulse. The output pulse of the long-pulse module connected witha 10 load is about 135 kV in amplitude and 180 ns in full width at half maximum with a rise time of about 50 ns and a flat top of about 100 ns.
Based on Blumlein pulse forming network(PFN), a compact module for long-pulse power generator is designed. Two Blumlein PFNs with 20 impedance are symmetrically connected with a linear transformer driver（LTD）s primary coil, and driven by an identical high voltage gas switch which ensures two Blumlein PFNs synchronizing operation. The Blumlein PFN uses L-type configuration. The design ensures PFN and gas switch being compactly connected and the horizontal size of the module being the smallest. Meanwhile, the L-type configuration has little impact on the waveform of the output pulse. The output pulse of the long-pulse module connected witha 10 load is about 135 kV in amplitude and 180 ns in full width at half maximum with a rise time of about 50 ns and a flat top of about 100 ns.
2015,
27: 055003.
doi: 10.11884/HPLPB201527.055003
Abstract:
The lateral geometry 4H-SiC photoconductive semiconductor switches (PCSS) were fabricated on the vanadium compensated semi-insulating 4H-SiC substrate with the Si (0001) Ni/Au contacts deposited by magnetron sputtering. The effect of laser excitation energy on the photoelectric response and that on the state resistance of PCSS were investigated. The experimental results showed that a nano-second pulse electric signal was obtained when the PCSS was triggered with a 532 nm wavelength laser light. The on state resistance decreased from 295 to 197 when the laser excitation energy increased from 26.7 mJ to 43.9 mJ. Based on the combination theory, the relationship between the carrier concentration and time deduced when the PCSS was irradiated. The on state resistance simulated from the MATLAB is consistent with the experimental results. Finally, the two ways to reduce the on resistance of the switch are put forward.
The lateral geometry 4H-SiC photoconductive semiconductor switches (PCSS) were fabricated on the vanadium compensated semi-insulating 4H-SiC substrate with the Si (0001) Ni/Au contacts deposited by magnetron sputtering. The effect of laser excitation energy on the photoelectric response and that on the state resistance of PCSS were investigated. The experimental results showed that a nano-second pulse electric signal was obtained when the PCSS was triggered with a 532 nm wavelength laser light. The on state resistance decreased from 295 to 197 when the laser excitation energy increased from 26.7 mJ to 43.9 mJ. Based on the combination theory, the relationship between the carrier concentration and time deduced when the PCSS was irradiated. The on state resistance simulated from the MATLAB is consistent with the experimental results. Finally, the two ways to reduce the on resistance of the switch are put forward.
2015,
27: 055004.
doi: 10.11884/HPLPB201527.055004
Abstract:
In the blocked state, the position of the armature of a single synchronous induction coilgun (SSICG) is fixed. Hence the mutual inductance and mutual inductance gradient between armature and coil are fixed and there is a linear relation between the electromagnetic force and the square of the current of the coil. The current filament equivalent circuit model and the finite element model were created by means of Matlab and Ansoft softwares respectively, and the forces of the armature at different discharging voltages were analyzed by means of the two models respectively. Finally the force was measured by the SSICG prototype in the laboratory and experimental results show a good agreement with the simulation results. It verifies the linear relation between the electromagnetic force and the square of the current of the coil, which provides experimental basis for the dynamic launch of the SSICG.
In the blocked state, the position of the armature of a single synchronous induction coilgun (SSICG) is fixed. Hence the mutual inductance and mutual inductance gradient between armature and coil are fixed and there is a linear relation between the electromagnetic force and the square of the current of the coil. The current filament equivalent circuit model and the finite element model were created by means of Matlab and Ansoft softwares respectively, and the forces of the armature at different discharging voltages were analyzed by means of the two models respectively. Finally the force was measured by the SSICG prototype in the laboratory and experimental results show a good agreement with the simulation results. It verifies the linear relation between the electromagnetic force and the square of the current of the coil, which provides experimental basis for the dynamic launch of the SSICG.
2015,
27: 055005.
doi: 10.11884/HPLPB201527.055005
Abstract:
One type of 100 kV repetitive fast trigger generator based on Tesla transformer and PFL is developed. The generator has characteristic of good reliability and compact construction. The factors which influence the system jitter are theoretically analyzed and improved methods are proposed. The design and numerical simulation of Tesla transformer are described, The experimental results show that the trigger generator can output 100 kV at 40 matched load with a duration of 4 ns(FWHM) and 0.5 ns rise time, the overall jitter is less than 10 ns at 50 Hz repetitive frequency.
One type of 100 kV repetitive fast trigger generator based on Tesla transformer and PFL is developed. The generator has characteristic of good reliability and compact construction. The factors which influence the system jitter are theoretically analyzed and improved methods are proposed. The design and numerical simulation of Tesla transformer are described, The experimental results show that the trigger generator can output 100 kV at 40 matched load with a duration of 4 ns(FWHM) and 0.5 ns rise time, the overall jitter is less than 10 ns at 50 Hz repetitive frequency.
2015,
27: 055006.
doi: 10.11884/HPLPB201527.055006
Abstract:
Flash X-ray generator comprises a pulsed power driver and a diode. Pulse forming line (PFL) and transmission line are utilized to generate high voltage with several MV on diode, and the function of the latter is to compress the pulse rise time and match the impedance of PFL to diodes. Impedance and capacitance of these coaxial lines are calculated to get the highest voltage and certain pre-pulse on load, respectively. Configuration of diode insulators are designed based on radial grading rings, and the layout of a flash X-ray generator is proposed. The results show that a voltage of 4 MV is generated on 40 load when 2.6 MV and 3.3 MV voltage charging to immediate storage energy and PFL, respectively. Meanwhile the pre-pulse is about 1.2% of charging voltage to PFL.
Flash X-ray generator comprises a pulsed power driver and a diode. Pulse forming line (PFL) and transmission line are utilized to generate high voltage with several MV on diode, and the function of the latter is to compress the pulse rise time and match the impedance of PFL to diodes. Impedance and capacitance of these coaxial lines are calculated to get the highest voltage and certain pre-pulse on load, respectively. Configuration of diode insulators are designed based on radial grading rings, and the layout of a flash X-ray generator is proposed. The results show that a voltage of 4 MV is generated on 40 load when 2.6 MV and 3.3 MV voltage charging to immediate storage energy and PFL, respectively. Meanwhile the pre-pulse is about 1.2% of charging voltage to PFL.
2015,
27: 055007.
doi: 10.11884/HPLPB201527.055007
Abstract:
In solid electromagnetic rail launcher, electric and thermal characteristics of sliding electric contact between armature and rails are related to contact status, current conduction and energy dissipation of sliding interface, influencing launcher system efficiency and rail lifespan. Many repeated launch test groups under different maximum linear current density were designed and carried out. Through iterative computation with test electric parameters, dynamic variation rule of sliding contact resistance and interface joule heat power were obtained, and effect of melt deposition evolvement and linear current density on electro-thermal properties were further analyzed. With inspection of melting deposition on rails after repeated tests, interface evolution process of sliding electric contact in gun bore was discussed. Results show that the steady critical point of sliding electric contact resistance and peak point of interface joule heat power both came up during current falling-edge. Contact resistance value of steady phase can be reduced in 10-2 m, and the maximum value of joule heat power can reach 10-1 MW. Contact resistance and heat power were affected hardly by repeated tests shows that deposition would re-melt and play positive role in sliding electric contact characteristic. Interface joule heat power was enlarged evidently by increasing linear current density even under the same input energy.
In solid electromagnetic rail launcher, electric and thermal characteristics of sliding electric contact between armature and rails are related to contact status, current conduction and energy dissipation of sliding interface, influencing launcher system efficiency and rail lifespan. Many repeated launch test groups under different maximum linear current density were designed and carried out. Through iterative computation with test electric parameters, dynamic variation rule of sliding contact resistance and interface joule heat power were obtained, and effect of melt deposition evolvement and linear current density on electro-thermal properties were further analyzed. With inspection of melting deposition on rails after repeated tests, interface evolution process of sliding electric contact in gun bore was discussed. Results show that the steady critical point of sliding electric contact resistance and peak point of interface joule heat power both came up during current falling-edge. Contact resistance value of steady phase can be reduced in 10-2 m, and the maximum value of joule heat power can reach 10-1 MW. Contact resistance and heat power were affected hardly by repeated tests shows that deposition would re-melt and play positive role in sliding electric contact characteristic. Interface joule heat power was enlarged evidently by increasing linear current density even under the same input energy.
2015,
27: 055101.
doi: 10.11884/HPLPB201527.055101
Abstract:
The superconducting (SC) linac driven free-electron laser (FEL) is an important development direction in the near future. The present statuses of the worldwide SC linac-driven hard X-ray FEL (SC-HXFEL) facilities, including Euro-XFEL and LCLS-II, are overviewed. A candidate scheme of a constructing SC-HXFEL in China based on a 7 GeV SC linac is proposed. The main parameters of the SC-HXFEL are given and the technical routes to achieve FEL power of up to 1000 GW by increasing peak current and adopting tapering technology are discussed.
The superconducting (SC) linac driven free-electron laser (FEL) is an important development direction in the near future. The present statuses of the worldwide SC linac-driven hard X-ray FEL (SC-HXFEL) facilities, including Euro-XFEL and LCLS-II, are overviewed. A candidate scheme of a constructing SC-HXFEL in China based on a 7 GeV SC linac is proposed. The main parameters of the SC-HXFEL are given and the technical routes to achieve FEL power of up to 1000 GW by increasing peak current and adopting tapering technology are discussed.
2015,
27: 055102.
doi: 10.11884/HPLPB201527.055102
Abstract:
In order to achieve high-level collimation and the complete conservation of the flyer boundary in high energy flash radiographic experiment, this paper proposes a new kind of design method of the collimator. The coupling transport process of photons and electrons, taking FTO as the object, is simulated by the means of Monte Carlo method to validate the characteristics of the improved collimator. And the deduction method of the optical path of the improved collimator is investigated. The result shows that the scatter exposure at the core region of the object is reduced by 99.8%. The dynamic range of the signal is reduced by 99.7%,which is great benefit for designing the detector. And the outer boundary is completely preserved in the image. The optical path of the object with relative error less than 0.1 is obtained by the way of layering the secondary collimator along the axial direction.
In order to achieve high-level collimation and the complete conservation of the flyer boundary in high energy flash radiographic experiment, this paper proposes a new kind of design method of the collimator. The coupling transport process of photons and electrons, taking FTO as the object, is simulated by the means of Monte Carlo method to validate the characteristics of the improved collimator. And the deduction method of the optical path of the improved collimator is investigated. The result shows that the scatter exposure at the core region of the object is reduced by 99.8%. The dynamic range of the signal is reduced by 99.7%,which is great benefit for designing the detector. And the outer boundary is completely preserved in the image. The optical path of the object with relative error less than 0.1 is obtained by the way of layering the secondary collimator along the axial direction.
2015,
27: 055103.
doi: 10.11884/HPLPB201527.055103
Abstract:
An accurate quantum efficiency (QE) map is very important in characterizing the performances of semiconductor photocathodes. This paper presents the study of a QE mapping system built on a DC high-voltage GaAs photocathode injector. A focusing lens is used to move the laser spot to different locations on the photocathode and to map the quantum efficiency. The control system and the data acquisition are established by LabVIEW. With a single sampling time of 2.3 s and a resolution of 0.32 mm, several quantum efficiency maps of the GaAs photocathode have been measured during 330 h. Both the distribution and the decay of the quantum efficiency have been observed from these maps as non-uniform. The quantum efficiency in the high quantum efficiency region decays slower than that in other regions. This QE mapping system is critically useful in improving the preparation technique of the photocathode.
An accurate quantum efficiency (QE) map is very important in characterizing the performances of semiconductor photocathodes. This paper presents the study of a QE mapping system built on a DC high-voltage GaAs photocathode injector. A focusing lens is used to move the laser spot to different locations on the photocathode and to map the quantum efficiency. The control system and the data acquisition are established by LabVIEW. With a single sampling time of 2.3 s and a resolution of 0.32 mm, several quantum efficiency maps of the GaAs photocathode have been measured during 330 h. Both the distribution and the decay of the quantum efficiency have been observed from these maps as non-uniform. The quantum efficiency in the high quantum efficiency region decays slower than that in other regions. This QE mapping system is critically useful in improving the preparation technique of the photocathode.
2015,
27: 055104.
doi: 10.11884/HPLPB201527.055104
Abstract:
The collimator at the end of the ring to target beam transport (RTBT) line is one of the key devices in the Chinese Spallation Neutron Source (CSNS) project. Design reliability of the collimator is extremely important since the high radiation on it due to its closeness to the target station. According to the working principle of the collimator and CSNS physical design requirements, comparing the design experience of similar foreign accelerator, the collimator is designed. Considering strict requirements of thermal deposition, power loss and material performance in the design process, the specific scheme is expounded. Using the result compared between Bethe-Bloch formula and SRIM software to determine the reliability of the simulation tool and simulation methods. According to the result of ANSYS finite element software simulation, the reliability of the collimator structure design is verified.
The collimator at the end of the ring to target beam transport (RTBT) line is one of the key devices in the Chinese Spallation Neutron Source (CSNS) project. Design reliability of the collimator is extremely important since the high radiation on it due to its closeness to the target station. According to the working principle of the collimator and CSNS physical design requirements, comparing the design experience of similar foreign accelerator, the collimator is designed. Considering strict requirements of thermal deposition, power loss and material performance in the design process, the specific scheme is expounded. Using the result compared between Bethe-Bloch formula and SRIM software to determine the reliability of the simulation tool and simulation methods. According to the result of ANSYS finite element software simulation, the reliability of the collimator structure design is verified.
2015,
27: 055105.
doi: 10.11884/HPLPB201527.055105
Abstract:
In order to fully understand the electron beam current amplification characteristic in diamond used in the diamond amplified photocathode as well as the relationship with other factors, a PIC module of VSIM was used to simulate the amplification characteristic of the electron beam current in diamond. The relationships among the secondary electron yield and the energy of the primary electrons, the internal field in diamond, the diamond film thickness and some other factors were obtained from the simulation results. The secondary electron yield could reach two orders of magnitude when appropriate primary electrons energy and internal field in diamond film were chosen.
In order to fully understand the electron beam current amplification characteristic in diamond used in the diamond amplified photocathode as well as the relationship with other factors, a PIC module of VSIM was used to simulate the amplification characteristic of the electron beam current in diamond. The relationships among the secondary electron yield and the energy of the primary electrons, the internal field in diamond, the diamond film thickness and some other factors were obtained from the simulation results. The secondary electron yield could reach two orders of magnitude when appropriate primary electrons energy and internal field in diamond film were chosen.
2015,
27: 056001.
doi: 10.11884/HPLPB201527.056001
Abstract:
By MCNP5 program, we used the Monte Carlo method to calculate the scatter contribution and neutron scattering distribution produced by different scattering bodies in experimental hall. The results show that the scattered neutron intensity decreases with the distance between the critical assembly and the measuring position at first, then increases near the hall walls, forming a W shape. The experiments are designed and conducted to verify the correctness of simulation results. The consistency of the calculated results and the measured results demonstrates the reliability of the calculated results.
By MCNP5 program, we used the Monte Carlo method to calculate the scatter contribution and neutron scattering distribution produced by different scattering bodies in experimental hall. The results show that the scattered neutron intensity decreases with the distance between the critical assembly and the measuring position at first, then increases near the hall walls, forming a W shape. The experiments are designed and conducted to verify the correctness of simulation results. The consistency of the calculated results and the measured results demonstrates the reliability of the calculated results.
2015,
27: 059001.
doi: 10.11884/HPLPB201527.059001
Abstract:
Vanadium oxide (VO2) thin films were successfully deposited using pulsed laser deposition (PLD) method. The samples were identified as polycrystalline thin films by analysis of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) . Phase transition properties of VO2 films irradiated by nanosecond laser were investigated by pump-probe technique. The results show that the minimum response time is 12 ns at repetition rate of 160 Hz. Moreover, the recovery time of phase transition varies with laser energy according to natural exponential law. Our simulation results suggest that the recovery time of phase transition correlates with thermal conductivity and thermal diffusion coefficient of substrates for the same laser energy.
Vanadium oxide (VO2) thin films were successfully deposited using pulsed laser deposition (PLD) method. The samples were identified as polycrystalline thin films by analysis of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) . Phase transition properties of VO2 films irradiated by nanosecond laser were investigated by pump-probe technique. The results show that the minimum response time is 12 ns at repetition rate of 160 Hz. Moreover, the recovery time of phase transition varies with laser energy according to natural exponential law. Our simulation results suggest that the recovery time of phase transition correlates with thermal conductivity and thermal diffusion coefficient of substrates for the same laser energy.
2015,
27: 059002.
doi: 10.11884/HPLPB201527.059002
Abstract:
Bi2WO6 nanosheets with different morphologies were synthesized by adjusting the ratios of CH3CH2OH to H2O using solvothermal method. Meanwhile, the effects of morphology on photoluminescence of Bi2WO6 nanosheets were explored. The crystalline, edges, and interlayer spacings of Bi2WO6 nanosheets were first enhanced and then reduced with the increase in proportion of CH3CH2OH in the solvent. When the ratio of CH3CH2OH to H2O was 1∶1, the values of edges, interlayer spacings and specific surface areas for the Bi2WO6 nanosheets were attained maximum, which contributed to the excellent photoluminescence. However, when the ratio was more than 1∶1, the values of edges, interlayer spacings and specific surface areas for Bi2WO6 nanosheets were reduced, which went against the improvement of photoluminescence. The results indicated that there was a synergistic effect of CH3CH2OH and H2O on the formation of morphology and the improvement of photoluminescence for Bi2WO6 nanosheets.
Bi2WO6 nanosheets with different morphologies were synthesized by adjusting the ratios of CH3CH2OH to H2O using solvothermal method. Meanwhile, the effects of morphology on photoluminescence of Bi2WO6 nanosheets were explored. The crystalline, edges, and interlayer spacings of Bi2WO6 nanosheets were first enhanced and then reduced with the increase in proportion of CH3CH2OH in the solvent. When the ratio of CH3CH2OH to H2O was 1∶1, the values of edges, interlayer spacings and specific surface areas for the Bi2WO6 nanosheets were attained maximum, which contributed to the excellent photoluminescence. However, when the ratio was more than 1∶1, the values of edges, interlayer spacings and specific surface areas for Bi2WO6 nanosheets were reduced, which went against the improvement of photoluminescence. The results indicated that there was a synergistic effect of CH3CH2OH and H2O on the formation of morphology and the improvement of photoluminescence for Bi2WO6 nanosheets.
2015,
27: 059003.
doi: 10.11884/HPLPB201527.059003
Abstract:
The micro-CT has been an increasingly important tool in researching core pore structure. In this study, a domestically self-developed high-resolution micro-CT equipment is used to capture the CT images of a core sample. Based on the results from digital image analysis of pore core CT images, this paper reconstructs a three-dimensional model of core pore. Then fractal dimension of two-dimension image and three-dimension reconstructed model are calculated based on fractal theory. Finally, the fractal characteristics between the two-dimension image and the three-dimension reconstructed model of the sample are verified by fractal model of porous media. Wherein, the mean difference between the two-dimensional fractal dimension and the three-dimensional fractal dimension is 1.000 3, and the maximum deviation is 0.004. The results well satisfy the relations between the two-dimension and the three-dimension fractal dimension of the fractal model of porous media.
The micro-CT has been an increasingly important tool in researching core pore structure. In this study, a domestically self-developed high-resolution micro-CT equipment is used to capture the CT images of a core sample. Based on the results from digital image analysis of pore core CT images, this paper reconstructs a three-dimensional model of core pore. Then fractal dimension of two-dimension image and three-dimension reconstructed model are calculated based on fractal theory. Finally, the fractal characteristics between the two-dimension image and the three-dimension reconstructed model of the sample are verified by fractal model of porous media. Wherein, the mean difference between the two-dimensional fractal dimension and the three-dimensional fractal dimension is 1.000 3, and the maximum deviation is 0.004. The results well satisfy the relations between the two-dimension and the three-dimension fractal dimension of the fractal model of porous media.
2015,
27: 055001.
doi: 10.11884/HPLPB201527.055001
Abstract:
In order to prevent the flash and shutter failure occurred in the high speed imaging of detonation experiments, this article presented a robust and reliable method by improving the test control devices and circuit of xenon lamp power supply of the high-speed imaging in experiment. Firstly, a circuit for performing logical operations was added on control signals to supervise the experiment. Secondly, the technology of a pseudospark switch and multi-section pulse forming line was used in the xenon flash lamp power supply, so that it could solve the xenon lamps self-flash, non-ignite and light intensity uneven problems. Finally, the pseudospark switch solved the process-encountered electromagnetic interference and synchronization ignition problems. In conclusion, this method effectively prevented the high-speed photography optical image missing and uneven film exposure in the detonation test. And the current article introduced the main components, circuits, systems, as well as the development process and the results of the experiment of this method.
In order to prevent the flash and shutter failure occurred in the high speed imaging of detonation experiments, this article presented a robust and reliable method by improving the test control devices and circuit of xenon lamp power supply of the high-speed imaging in experiment. Firstly, a circuit for performing logical operations was added on control signals to supervise the experiment. Secondly, the technology of a pseudospark switch and multi-section pulse forming line was used in the xenon flash lamp power supply, so that it could solve the xenon lamps self-flash, non-ignite and light intensity uneven problems. Finally, the pseudospark switch solved the process-encountered electromagnetic interference and synchronization ignition problems. In conclusion, this method effectively prevented the high-speed photography optical image missing and uneven film exposure in the detonation test. And the current article introduced the main components, circuits, systems, as well as the development process and the results of the experiment of this method.
2015,
27: 053203.
doi: 10.11884/HPLPB201527.053203
Abstract:
The transmission line equivalent circuit method(TLM) is one of the frequently used quick algorithms for shielding effectiveness (SE) prediction of an enclosure. Electromagnetic field modes at the aperture are taken into consideration in the coupling coefficient calculation to improve the accuracy of SE at higher frequencies. Then TLM algorithm is developed to calculate the shielding effectiveness of double metal enclosures with apertures on the common wall. The shielding effectiveness of the inner cavity can be predicted by using the voltage at any position inside the outer cavity to derive the equivalent voltage source at the apertures on the common wall. The results calculated by the proposed method are in good agreement with the simulated results using commercial software CST.
The transmission line equivalent circuit method(TLM) is one of the frequently used quick algorithms for shielding effectiveness (SE) prediction of an enclosure. Electromagnetic field modes at the aperture are taken into consideration in the coupling coefficient calculation to improve the accuracy of SE at higher frequencies. Then TLM algorithm is developed to calculate the shielding effectiveness of double metal enclosures with apertures on the common wall. The shielding effectiveness of the inner cavity can be predicted by using the voltage at any position inside the outer cavity to derive the equivalent voltage source at the apertures on the common wall. The results calculated by the proposed method are in good agreement with the simulated results using commercial software CST.
2015,
27: 052002.
Abstract:
As a novel ignition method, shock ignition has many advantages comparing to fast ignition. The resolvability experiments of shock ignition in China implemented on the Shenguang Ⅲ prototype laser facility is put forward in the paper. Based on the shaping ability of the laser pulse of the facility, a shock laser pulse and a square-topped laser pulse are employed as the drive source. This paper introduces the design of the targets and beam smoothing ability of the laser. The main configurations and measurement precision of two typical diagnostic equipment-the back scattering light diagnostic system and imaging VISAR, are also expounded. The main purpose of the experiment focuses on the laser plasma interaction and the generation and transmitting of the shock wave in the CH polymer layer. Experimental results with the energy and spectrum of back scattering light prove that the fraction of back scattering light has risen and mainly been generated in the wider density region of the plasma after using the shock laser pulse. The simulations and experiment results of the main transmitting progress of the shock wave in CH layer agree well with each other.
As a novel ignition method, shock ignition has many advantages comparing to fast ignition. The resolvability experiments of shock ignition in China implemented on the Shenguang Ⅲ prototype laser facility is put forward in the paper. Based on the shaping ability of the laser pulse of the facility, a shock laser pulse and a square-topped laser pulse are employed as the drive source. This paper introduces the design of the targets and beam smoothing ability of the laser. The main configurations and measurement precision of two typical diagnostic equipment-the back scattering light diagnostic system and imaging VISAR, are also expounded. The main purpose of the experiment focuses on the laser plasma interaction and the generation and transmitting of the shock wave in the CH polymer layer. Experimental results with the energy and spectrum of back scattering light prove that the fraction of back scattering light has risen and mainly been generated in the wider density region of the plasma after using the shock laser pulse. The simulations and experiment results of the main transmitting progress of the shock wave in CH layer agree well with each other.
