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RSS2013 Vol. 25, No. 04
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2013,
25: 805-806.
Abstract:
A new approach to outputting 2 m light was proposed based on non-critical phase matching KTA-OPO intra-cavity pumped by Nd:YVO4 crystal laser. A signal light with a power exceeding 1 W at 2093 nm is obtained with a diode-to-signal efficiency up to 10%. The short pulse width is about 3.4 ns at 30 kHz and the spectrum width at 2 m waveband is only about 1 nm. The results show that this approach is also an efficient way to achieve 2 m pulsed laser with high peak power.
A new approach to outputting 2 m light was proposed based on non-critical phase matching KTA-OPO intra-cavity pumped by Nd:YVO4 crystal laser. A signal light with a power exceeding 1 W at 2093 nm is obtained with a diode-to-signal efficiency up to 10%. The short pulse width is about 3.4 ns at 30 kHz and the spectrum width at 2 m waveband is only about 1 nm. The results show that this approach is also an efficient way to achieve 2 m pulsed laser with high peak power.
2013,
25: 807-812.
Abstract:
A experiment of laser ablating aluminum target was conducted. A schlieren photography technique was employed for visualizing temporal evolution of detonation waves and analyzing detonation wave attenuation law. Based on similitude theory of shockwave motion, a point explosion model was used to describe detonation-wave evolution induced by laser ablating aluminum target. The propagation speed, pressure and temperature of the wave front were calculated. The results show that the detonation wave has a high speed towards laser source. The wave front transform from half-elliptical in early evolution stage into half-spherical. The disturbed zone has a complicated structure and multi-density discontinuities during the flow-field evolution. In the initial stage of detonation-wave propagation, the shockwave has a high pressure and temperature, but they decrease rapidly.
A experiment of laser ablating aluminum target was conducted. A schlieren photography technique was employed for visualizing temporal evolution of detonation waves and analyzing detonation wave attenuation law. Based on similitude theory of shockwave motion, a point explosion model was used to describe detonation-wave evolution induced by laser ablating aluminum target. The propagation speed, pressure and temperature of the wave front were calculated. The results show that the detonation wave has a high speed towards laser source. The wave front transform from half-elliptical in early evolution stage into half-spherical. The disturbed zone has a complicated structure and multi-density discontinuities during the flow-field evolution. In the initial stage of detonation-wave propagation, the shockwave has a high pressure and temperature, but they decrease rapidly.
2013,
25: 813-816.
Abstract:
The density and decay kinetics of a plasma channel produced in air by a self-guided intense femtosecond laser pulse is investigated by numerical simulation method. The two-body, three-body dissociation attachment and the recombination of the free electrons, positive and negative ions are considered in the theoretical model. The influence of dissociation attachment caused by the subsequently incident laser on the generated plasma channel has been studied and the effective control parameters of the subsequent laser can be obtained. The calculation shows that the lifetime of the channel is sensitive to the initial conditions of the subsequent laser and the relative delay between the subsequent laser and the maximum plasma density. The corresponding lifetime of the revived plasma channel can be efficiently extended to more than 25 s, in the case that the subsequent laser is sufficiently controlled under optimum parameters.
The density and decay kinetics of a plasma channel produced in air by a self-guided intense femtosecond laser pulse is investigated by numerical simulation method. The two-body, three-body dissociation attachment and the recombination of the free electrons, positive and negative ions are considered in the theoretical model. The influence of dissociation attachment caused by the subsequently incident laser on the generated plasma channel has been studied and the effective control parameters of the subsequent laser can be obtained. The calculation shows that the lifetime of the channel is sensitive to the initial conditions of the subsequent laser and the relative delay between the subsequent laser and the maximum plasma density. The corresponding lifetime of the revived plasma channel can be efficiently extended to more than 25 s, in the case that the subsequent laser is sufficiently controlled under optimum parameters.
2013,
25: 817-821.
Abstract:
The strength gradient in bright and dark rings of the non-diffracting Bessel beam for three kinds of different spectral width source (the laser, green LED and white LED sources) is analyzed. The profile of optical intensity distribution in different propagation distances is simulated, and the intensity of the bright and dark rings is calculated. The contrast of the bright and dark rings of the Bessel beam generated by the three different spectral width sources is calculated using the contrast formula. We find that the contrast and the strength gradient of the bright and dark rings reduce with the increase of the spectrum width. Therefore, the trapping ability of the Bessel beam is reduced. An optical system is designed according to the character of these three sources, and the profile of optical intensity distribution of the non-diffracting beam from these three different spectral width sources is captured. By calculating the contrast of the experimental result, we know that the contrast ratio of cross-sectional intensity declines, the ability of the trapping particles reduces with the increase of the spectral width. The experimental results agree well with the theoretical analysis.
The strength gradient in bright and dark rings of the non-diffracting Bessel beam for three kinds of different spectral width source (the laser, green LED and white LED sources) is analyzed. The profile of optical intensity distribution in different propagation distances is simulated, and the intensity of the bright and dark rings is calculated. The contrast of the bright and dark rings of the Bessel beam generated by the three different spectral width sources is calculated using the contrast formula. We find that the contrast and the strength gradient of the bright and dark rings reduce with the increase of the spectrum width. Therefore, the trapping ability of the Bessel beam is reduced. An optical system is designed according to the character of these three sources, and the profile of optical intensity distribution of the non-diffracting beam from these three different spectral width sources is captured. By calculating the contrast of the experimental result, we know that the contrast ratio of cross-sectional intensity declines, the ability of the trapping particles reduces with the increase of the spectral width. The experimental results agree well with the theoretical analysis.
2013,
25: 822-826.
Abstract:
The Nd:YAG slab end-pumped by laser diode arrays features small thermal effect and wavefront distortion. The theoretical analyses show that inhomogeneity of the temperature field and stress field is the main cause of wavefront distortion in the slab gain medium. For the end-pumped conduction cooled slab gain module, we optimized the pump and thermal uniformity by reasonable design and obtained the static wavefront distortion with a peak-valley (PV) value of 0.22 m. We tested the wavefront distortion of this module in the double-amplifier experiment device, deriving the PV values of 3.49 m without the signal power injection and 0.59 m after energy extraction. At the injection power of 3120 W, we obtained an output power of 4660 W and a beam quality value of 3.88 times the diffraction limit, with an optical-optical efficiency of 27%.
The Nd:YAG slab end-pumped by laser diode arrays features small thermal effect and wavefront distortion. The theoretical analyses show that inhomogeneity of the temperature field and stress field is the main cause of wavefront distortion in the slab gain medium. For the end-pumped conduction cooled slab gain module, we optimized the pump and thermal uniformity by reasonable design and obtained the static wavefront distortion with a peak-valley (PV) value of 0.22 m. We tested the wavefront distortion of this module in the double-amplifier experiment device, deriving the PV values of 3.49 m without the signal power injection and 0.59 m after energy extraction. At the injection power of 3120 W, we obtained an output power of 4660 W and a beam quality value of 3.88 times the diffraction limit, with an optical-optical efficiency of 27%.
2013,
25: 827-831.
Abstract:
A calibration method of fundamental frequency wavelength of space heterodyne spectrometer(SHS) is presented according to the operating principle of SHS and the generation mechanism of interferograms. Pixel phases along the normal direction of interferograms were calculated and linearly fitted to get the phase slopes corresponding to the space frequencies along the normal direction of interference fringes. When the phase slopes of laser interferograms for two known wavelengths were obtained, and then the fundamental frequency wavelength of the SHS was determined. The data test results of four groups of wavelengths show fundamental frequency wavelengths calibrated by this method have good consistency, and the standard deviation is 0.044 nm. In addition, the spectrum from simulated calibration results and that from actual measurement are consistent at a high degree, which implies the feasibility of the method.
A calibration method of fundamental frequency wavelength of space heterodyne spectrometer(SHS) is presented according to the operating principle of SHS and the generation mechanism of interferograms. Pixel phases along the normal direction of interferograms were calculated and linearly fitted to get the phase slopes corresponding to the space frequencies along the normal direction of interference fringes. When the phase slopes of laser interferograms for two known wavelengths were obtained, and then the fundamental frequency wavelength of the SHS was determined. The data test results of four groups of wavelengths show fundamental frequency wavelengths calibrated by this method have good consistency, and the standard deviation is 0.044 nm. In addition, the spectrum from simulated calibration results and that from actual measurement are consistent at a high degree, which implies the feasibility of the method.
2013,
25: 832-840.
Abstract:
A novel laser model with active gain medium and open-resonator boundary condition was developed, which is applicable to both stable and unstable resonators. Based on the equivalency between the Schrdinger equation and Helmholtz equation, quantum mechanics method was used to solve the Helmholtz equation of resonators, and the eigen equation and eigen solution were obtained, which fully satisfy the wave equations, boundary condtions, matrix optics, and stability criterion. Based on the eigen equation, the relationship between transverse mode number and output coupling ratio was derived. Futhermore, the relationship of the output power and output coupling ratio to magnification was deduced. This model not only can regress into the exact form of the traditional formula in case of small output couplings, but also consists with the curve-fittings of experimental data very well in case of large output couplings.
A novel laser model with active gain medium and open-resonator boundary condition was developed, which is applicable to both stable and unstable resonators. Based on the equivalency between the Schrdinger equation and Helmholtz equation, quantum mechanics method was used to solve the Helmholtz equation of resonators, and the eigen equation and eigen solution were obtained, which fully satisfy the wave equations, boundary condtions, matrix optics, and stability criterion. Based on the eigen equation, the relationship between transverse mode number and output coupling ratio was derived. Futhermore, the relationship of the output power and output coupling ratio to magnification was deduced. This model not only can regress into the exact form of the traditional formula in case of small output couplings, but also consists with the curve-fittings of experimental data very well in case of large output couplings.
2013,
25: 841-846.
Abstract:
Based on the weak guidance approximation, the condition for realizing single mode operation of annular core fiber (ACF) and the energy distribution in far-field are discussed. The theoretical results demonstrate that when an ACF realizes single-mode operation, the annular beam emitted from the end of ACF diffracts to a central circular area in the far-field with good energy focusability. Besides, the beam width gets smaller when the thickness of the guiding section and the refractive index difference between the cladding and fiber core are reduced.
Based on the weak guidance approximation, the condition for realizing single mode operation of annular core fiber (ACF) and the energy distribution in far-field are discussed. The theoretical results demonstrate that when an ACF realizes single-mode operation, the annular beam emitted from the end of ACF diffracts to a central circular area in the far-field with good energy focusability. Besides, the beam width gets smaller when the thickness of the guiding section and the refractive index difference between the cladding and fiber core are reduced.
2013,
25: 847-852.
Abstract:
The axial drift of ring laser gyroscopes (RLGs) is a major factor that impacts the performance of the single-axis rotation inertial navigation system. A square support vector machine (SVM) algorithm to forecast the axial RLG drift is proposed in the paper. Latitude and temperature variation during the identification stage are adopted as inputs of model. Employing polynomial, radial basis function (RBF) and wavelet function as the kernel functions, we construct three kinds of support vector machine (SVM), which are SVM, least square support vector machine (LSSVM) and forgetting factor least square support vector machine (FFLSSVM) and compare their capability to forecast the axial RLG drift. The navigational results show that the FFLSSVM method is an effective approach and has the best identification precision. The experimental result of navigation can meet the practical demand.
The axial drift of ring laser gyroscopes (RLGs) is a major factor that impacts the performance of the single-axis rotation inertial navigation system. A square support vector machine (SVM) algorithm to forecast the axial RLG drift is proposed in the paper. Latitude and temperature variation during the identification stage are adopted as inputs of model. Employing polynomial, radial basis function (RBF) and wavelet function as the kernel functions, we construct three kinds of support vector machine (SVM), which are SVM, least square support vector machine (LSSVM) and forgetting factor least square support vector machine (FFLSSVM) and compare their capability to forecast the axial RLG drift. The navigational results show that the FFLSSVM method is an effective approach and has the best identification precision. The experimental result of navigation can meet the practical demand.
2013,
25: 853-857.
Abstract:
Focusing on the random vibration phenomena in infrared video sequences taken from moving vehicles, a BRISK characteristic point matching based high-precision global motion estimation algorithm is proposed. For mismatch in feature point matching and moving objects in the scene, fuzzy clustering method is used to separate global motion and local motion, which improves the robustness of the algorithm. A Kalman particle filter is used to separate the complex scanning movements and random vibration effectively. Meanwhile, we use bilinear interpolation for image compensation. Finally, a panoramic image is acquired by processing the undefined region with fast image alignment. A series of experiments have been carried out using video sequences taken on vehicle-borne thermal camera and the experimental results illustrate that the video sequences are well stabilized, which meet the requirements for practical use.
Focusing on the random vibration phenomena in infrared video sequences taken from moving vehicles, a BRISK characteristic point matching based high-precision global motion estimation algorithm is proposed. For mismatch in feature point matching and moving objects in the scene, fuzzy clustering method is used to separate global motion and local motion, which improves the robustness of the algorithm. A Kalman particle filter is used to separate the complex scanning movements and random vibration effectively. Meanwhile, we use bilinear interpolation for image compensation. Finally, a panoramic image is acquired by processing the undefined region with fast image alignment. A series of experiments have been carried out using video sequences taken on vehicle-borne thermal camera and the experimental results illustrate that the video sequences are well stabilized, which meet the requirements for practical use.
2013,
25: 858-862.
Abstract:
Due to the random fluctuation of thickness of layers in the deposition process, the robustness of thickness of narrowband filters for far infrared is calculated. The results show that the omnidirectional band gap and the gap ratio of the narrowband filter change little in accordance with the value of random degree less than 0.05. However, the transmission ratio can only reach to about 1/3 of the original one in the defect layer. Both the omnidirectional band gap and the gap ratio of the narrowband filter decrease with the increase of random fluctuation of thickness when the random degree is over 0.1. The first omnidirectional band gap disappears while the second one obviously transfers to the shortwave direction when the value of random degree reaches to 0.2. Meanwhile, the transmission ratio also reaches to about 1/3 of the original one in the defect layer.The two omnidirectional band gaps disappear totally when the value of random degree reaches to 0.5. A kind of narrowband filter for far infrared is prepared, and the results preferably demonstrate the effect of random fluctuation of thickness on the narrowband filter.
Due to the random fluctuation of thickness of layers in the deposition process, the robustness of thickness of narrowband filters for far infrared is calculated. The results show that the omnidirectional band gap and the gap ratio of the narrowband filter change little in accordance with the value of random degree less than 0.05. However, the transmission ratio can only reach to about 1/3 of the original one in the defect layer. Both the omnidirectional band gap and the gap ratio of the narrowband filter decrease with the increase of random fluctuation of thickness when the random degree is over 0.1. The first omnidirectional band gap disappears while the second one obviously transfers to the shortwave direction when the value of random degree reaches to 0.2. Meanwhile, the transmission ratio also reaches to about 1/3 of the original one in the defect layer.The two omnidirectional band gaps disappear totally when the value of random degree reaches to 0.5. A kind of narrowband filter for far infrared is prepared, and the results preferably demonstrate the effect of random fluctuation of thickness on the narrowband filter.
2013,
25: 863-866.
Abstract:
As the gain coefficient of XeF(C-A) blue-green lasers is low, it is difficult to obtain a laser pulse with both high energy and narrow spectrum. In this paper, a dispersive prism is used in the resonator to compress the laser spectrum and to get high laser pulse energy. The experimental results show that, using a concave output mirror, the laser spectrum can be compressed to about 2.5 nm and the maximal laser energy is 3.47 J. As a comparison, using a plane output mirror, the laser spectrum can be compressed to about 0.7 nm with the laser pulse energy of 2.93 J. In the expriment, the laser spectrum can be tunable between 460 nm and 520 nm and the tunable width is about 60 nm.
As the gain coefficient of XeF(C-A) blue-green lasers is low, it is difficult to obtain a laser pulse with both high energy and narrow spectrum. In this paper, a dispersive prism is used in the resonator to compress the laser spectrum and to get high laser pulse energy. The experimental results show that, using a concave output mirror, the laser spectrum can be compressed to about 2.5 nm and the maximal laser energy is 3.47 J. As a comparison, using a plane output mirror, the laser spectrum can be compressed to about 0.7 nm with the laser pulse energy of 2.93 J. In the expriment, the laser spectrum can be tunable between 460 nm and 520 nm and the tunable width is about 60 nm.
2013,
25: 867-871.
Abstract:
The automatic alignment system is a large system that obtains the beam position by processing the images with particular image processing algorithm, and the position information is used to drive the motors and adjust the beam to the specified position, however, the image quality has a great influence on the accuracy of beam positioning. To avoid the images seriously affected by the noise and beam distortion entering into the automatic alignment process which could generate the misjudgement of alignment results, and to ensure the accuracy of image processing results, this paper tries to describe a simple method to recognize these images, and three main far-field noise evaluation models are established based on the Monte-Carlo simulation. The uncertainty of measurement is regarded as the characteristic parameter to determine whether the image should be processed, and we plot the parameter results to a statistical chart as judgement condition. The experimental results show that, in the case of setting a reasonable threshold, the automatic alignment systems can reject most of the not-good images, and greatly improve the reliability of the alignment system.
The automatic alignment system is a large system that obtains the beam position by processing the images with particular image processing algorithm, and the position information is used to drive the motors and adjust the beam to the specified position, however, the image quality has a great influence on the accuracy of beam positioning. To avoid the images seriously affected by the noise and beam distortion entering into the automatic alignment process which could generate the misjudgement of alignment results, and to ensure the accuracy of image processing results, this paper tries to describe a simple method to recognize these images, and three main far-field noise evaluation models are established based on the Monte-Carlo simulation. The uncertainty of measurement is regarded as the characteristic parameter to determine whether the image should be processed, and we plot the parameter results to a statistical chart as judgement condition. The experimental results show that, in the case of setting a reasonable threshold, the automatic alignment systems can reject most of the not-good images, and greatly improve the reliability of the alignment system.
2013,
25: 872-874.
Abstract:
Polyvinylidene fluoride (PVDF) patch sensors were pasted beside the laser shock spot to measure the dynamic strain on the 2024 aluminum alloy surface induced by pulse lasers, and then the characteristics of the dynamic strain curves were analyzed. The results indicate that PVDF patch sensors have the characteristics of quick dynamic response and high sensitivity, and can be applied effectively to real-time measurement of laser-induced dynamic strain. During laser shock processing, the material around the shock spot of 2024 aluminum alloy is compressed first, then the compressive strain decreases. After laser shock processing, the surface particles around the shock spot of 2024 aluminum alloy are doing reciprocating motion constantly under the action of unloading rarefaction wave and surface rarefaction wave. The material around the shock spot is even in the tension. Finally, the dynamic response of the surface particles tends to stability.
Polyvinylidene fluoride (PVDF) patch sensors were pasted beside the laser shock spot to measure the dynamic strain on the 2024 aluminum alloy surface induced by pulse lasers, and then the characteristics of the dynamic strain curves were analyzed. The results indicate that PVDF patch sensors have the characteristics of quick dynamic response and high sensitivity, and can be applied effectively to real-time measurement of laser-induced dynamic strain. During laser shock processing, the material around the shock spot of 2024 aluminum alloy is compressed first, then the compressive strain decreases. After laser shock processing, the surface particles around the shock spot of 2024 aluminum alloy are doing reciprocating motion constantly under the action of unloading rarefaction wave and surface rarefaction wave. The material around the shock spot is even in the tension. Finally, the dynamic response of the surface particles tends to stability.
2013,
25: 875-878.
Abstract:
Since the Rb D2 absorption linewidth is much narrower than that of commercially available diode lasers, linewidth reduction of diode laser is one of the key technologies in Rb vapor laser. In this paper, a 40 W laser diode array (LDA) with linewidth of 0.14 nm and wavelength of 780 nm was realized through external cavity technology of volume Bragg grating (VBG). By controlling the temperature of the VBG with a thermoelectric cooler (TEC), the central wavelength of the LDA was tunable from 779.39 nm to 780.10 nm (in air). That means the LDA can be used as an efficient pumping source for Rb vapor lasers.
Since the Rb D2 absorption linewidth is much narrower than that of commercially available diode lasers, linewidth reduction of diode laser is one of the key technologies in Rb vapor laser. In this paper, a 40 W laser diode array (LDA) with linewidth of 0.14 nm and wavelength of 780 nm was realized through external cavity technology of volume Bragg grating (VBG). By controlling the temperature of the VBG with a thermoelectric cooler (TEC), the central wavelength of the LDA was tunable from 779.39 nm to 780.10 nm (in air). That means the LDA can be used as an efficient pumping source for Rb vapor lasers.
2013,
25: 879-884.
Abstract:
A method for reverse design of the resonance-domain rectangular-groove dielectric grating based on modal method is presented. The design of the polarization (non-polarization) beam splitter and blazed grating is discussed. As an example, the -1st transmitted order blazed grating with fused-silica is designed with the reverse design method. The basic idea behind the method is the excitation and propagation of the propagating modes in gratings. As different phase difference is accumulated for the first two propagating modes excited in gratings, the incident light can be diffracted into the -1st or 0th order with about 100% diffraction efficiency for TE or TM polarization. The diffraction efficiency of the -1st transmitted order blazed grating is calculated with the rigorous couple-wave analysis (RCWA) method. The geometrical parameters of the blazed grating calculated by the modal method agree well with the results simulated by RCWA.
A method for reverse design of the resonance-domain rectangular-groove dielectric grating based on modal method is presented. The design of the polarization (non-polarization) beam splitter and blazed grating is discussed. As an example, the -1st transmitted order blazed grating with fused-silica is designed with the reverse design method. The basic idea behind the method is the excitation and propagation of the propagating modes in gratings. As different phase difference is accumulated for the first two propagating modes excited in gratings, the incident light can be diffracted into the -1st or 0th order with about 100% diffraction efficiency for TE or TM polarization. The diffraction efficiency of the -1st transmitted order blazed grating is calculated with the rigorous couple-wave analysis (RCWA) method. The geometrical parameters of the blazed grating calculated by the modal method agree well with the results simulated by RCWA.
2013,
25: 885-889.
Abstract:
Due to the constraint of thyratron life, thyratron-based excimer lasers are not available in some situation where high repetition rate is desired, such as in the ophthalmic treatment equipment. We designed a solid state pulsed power module (SSPPM) based on two-stage magnetic pulse compression technology, which uses solid-state switches and magnetic pulse compression to generate a high-voltage pulse of 0.1 microseconds. In discharging on the 193 nm ArF excimer laser, the rise time of the obtained excitation pulse is about 90 ns, the discharge voltage is 16.5 kV, the repetition rate is up to 1 kHz, and the overall transfer efficiency of two-stage magnetic pulse compression switches is 59.1%.
Due to the constraint of thyratron life, thyratron-based excimer lasers are not available in some situation where high repetition rate is desired, such as in the ophthalmic treatment equipment. We designed a solid state pulsed power module (SSPPM) based on two-stage magnetic pulse compression technology, which uses solid-state switches and magnetic pulse compression to generate a high-voltage pulse of 0.1 microseconds. In discharging on the 193 nm ArF excimer laser, the rise time of the obtained excitation pulse is about 90 ns, the discharge voltage is 16.5 kV, the repetition rate is up to 1 kHz, and the overall transfer efficiency of two-stage magnetic pulse compression switches is 59.1%.
2013,
25: 890-894.
Abstract:
The laser induced damage threshold (LIDT) and the particle contaminations of the large-aperture optics such as beam sampling grating (BSG) which is likely to generate stimulated Brillouin scattering, were measured after chemical etching and ultraviolet (UV) laser cleaning, with the BSG side under the radiation of 355 nm laser. The results show that the LIDT of the BSG side increases by 78% after chemical etching, which is almost equal to that of light pass surface, but it is only about 56% after UV laser cleaning. By comparing the particle contaminations coming from the side of the optics in two ways, it is found that the UV laser cleaning can also improve the laser threshold for the particle contamination generating, and has little influence on the optics performance. Also, we prove that the UV laser cleaning has a better security and applicability than the chemical etching through the analysis of morphologies and the influence of optical clear aperture.
The laser induced damage threshold (LIDT) and the particle contaminations of the large-aperture optics such as beam sampling grating (BSG) which is likely to generate stimulated Brillouin scattering, were measured after chemical etching and ultraviolet (UV) laser cleaning, with the BSG side under the radiation of 355 nm laser. The results show that the LIDT of the BSG side increases by 78% after chemical etching, which is almost equal to that of light pass surface, but it is only about 56% after UV laser cleaning. By comparing the particle contaminations coming from the side of the optics in two ways, it is found that the UV laser cleaning can also improve the laser threshold for the particle contamination generating, and has little influence on the optics performance. Also, we prove that the UV laser cleaning has a better security and applicability than the chemical etching through the analysis of morphologies and the influence of optical clear aperture.
2013,
25: 895-897.
Abstract:
Boron carbide films were deposited on Si and Ge substrates using KrF eximer laser. Influences of laser energy, distance between the target and substrate, and bias voltage were studied. A Fourier transform infrared spectroscope and a nano-indenter were used to test the optical transmission and hardness of the samples. Furthermore, the adhesion performance of the film and substrate was tested according to the common criterion of optical films. The largest transmission of Si and Ge advanced 10% after only one surface of substrates was coated by boron carbide films. The nano-hardness of the coated substrates reached more than 3 times that of the uncoated substrates and the adhesion was also satisfactory. The results show that boron carbide films are useful as anti-reflective and protective films for optical substrates.
Boron carbide films were deposited on Si and Ge substrates using KrF eximer laser. Influences of laser energy, distance between the target and substrate, and bias voltage were studied. A Fourier transform infrared spectroscope and a nano-indenter were used to test the optical transmission and hardness of the samples. Furthermore, the adhesion performance of the film and substrate was tested according to the common criterion of optical films. The largest transmission of Si and Ge advanced 10% after only one surface of substrates was coated by boron carbide films. The nano-hardness of the coated substrates reached more than 3 times that of the uncoated substrates and the adhesion was also satisfactory. The results show that boron carbide films are useful as anti-reflective and protective films for optical substrates.
2013,
25: 898-902.
Abstract:
A new formula was proposed to investigate the relationship between reaction time and tetraethylorthosilicate (TEOS) conversion rate for preparation of silica sol with Stber method, by studying the reaction kinetics of TEOS hydrolytic process. An appropriate conversion rate was then determined and used to calculate the theoretical optimal reaction time. Meanwhile, silica sols were prepared by sol-gel process using TEOS as precursor and ammonia as catalyst. It was found that the reaction time decreases with an increasing amount of ammonia and water. The values of experimental optimal reaction time were obtained, and agree with the theoretical results (the errors are within 5%), which shows good applicability of our formula.
A new formula was proposed to investigate the relationship between reaction time and tetraethylorthosilicate (TEOS) conversion rate for preparation of silica sol with Stber method, by studying the reaction kinetics of TEOS hydrolytic process. An appropriate conversion rate was then determined and used to calculate the theoretical optimal reaction time. Meanwhile, silica sols were prepared by sol-gel process using TEOS as precursor and ammonia as catalyst. It was found that the reaction time decreases with an increasing amount of ammonia and water. The values of experimental optimal reaction time were obtained, and agree with the theoretical results (the errors are within 5%), which shows good applicability of our formula.
2013,
25: 903-907.
Abstract:
To meet the requirement of framing diagnosis of CH cylindrical target implosion experiments, a four-channel 4.75 keV KB microscope was developed. The optical structure and imaging quality of the four-channel KB microscope were analyzed. With the size limit of framing camera taken into account, the problem of assembly of the four-channel KB microscope has been solved using reference cone core. The assembly and alignment experiments of the four-channel KB microscope were performed in the laboratory. The clear image of four-quadrant grid with a spatial resolution of 3 m in central field was obtained in Shenguang-Ⅱ laser facility, and the image spacing meets the design requirements, indicating that inertial confinement fusion framing experiments could be carried out.
To meet the requirement of framing diagnosis of CH cylindrical target implosion experiments, a four-channel 4.75 keV KB microscope was developed. The optical structure and imaging quality of the four-channel KB microscope were analyzed. With the size limit of framing camera taken into account, the problem of assembly of the four-channel KB microscope has been solved using reference cone core. The assembly and alignment experiments of the four-channel KB microscope were performed in the laboratory. The clear image of four-quadrant grid with a spatial resolution of 3 m in central field was obtained in Shenguang-Ⅱ laser facility, and the image spacing meets the design requirements, indicating that inertial confinement fusion framing experiments could be carried out.
2013,
25: 908-912.
Abstract:
Nanoporous Cu is synthesized by dealloying Mn-Cu precursors with the selective corrosion. The effects of time of heat treatment，the corrosion time and the temperature of dealloying on the porous morphology and the residual Mn content are investigated. It is revealed that the heat treatment can drive the composition to distribute homogeneously in the bulk alloy with increasing the time and consequently results in more fully dealloying for forming nanoporous Cu. There is no distinct decrease of the residual Mn content in the nanoporous Cu made from 95 h-heat-treated precursors with increasing the corrosion time. The residual Mn content in nanoporous Cu decreases from 3.54% at 25 ℃ corrosion temperature to 1.14% at 60 ℃ corrosion temperature. But the pore and the ligament sizes of the samples obviously coarsen after60 ℃ corrosion of the samples, and the samples are frangible. The resultant nanoporous copper possesses uniform porous structure in the three-dimensional network, with the residual Mn content of 1.23% and the average pore size of 40 nm.
Nanoporous Cu is synthesized by dealloying Mn-Cu precursors with the selective corrosion. The effects of time of heat treatment，the corrosion time and the temperature of dealloying on the porous morphology and the residual Mn content are investigated. It is revealed that the heat treatment can drive the composition to distribute homogeneously in the bulk alloy with increasing the time and consequently results in more fully dealloying for forming nanoporous Cu. There is no distinct decrease of the residual Mn content in the nanoporous Cu made from 95 h-heat-treated precursors with increasing the corrosion time. The residual Mn content in nanoporous Cu decreases from 3.54% at 25 ℃ corrosion temperature to 1.14% at 60 ℃ corrosion temperature. But the pore and the ligament sizes of the samples obviously coarsen after60 ℃ corrosion of the samples, and the samples are frangible. The resultant nanoporous copper possesses uniform porous structure in the three-dimensional network, with the residual Mn content of 1.23% and the average pore size of 40 nm.
2013,
25: 913-917.
Abstract:
A series of melamine-formaldehyde(MF) organic aerogel templates were prepared with different categories and concentration of catalyst. Their molecular structure, thermal stability and pore structure were tested by Fourier transform infrared spectroscopy, thermogravimetric analysis and nitrogen adsorption. It is indicated that the type and concentration of catalyst do not affect molecular structure and thermal stability of the MF organic aerogel template. The specific surface area and pore volume of the MF organic aerogel template using Na2CO3 as catalyst are higher than those using NaOH, NaHCO3 as catalyst. When the ratio of the concentration of melamine to that of catalyst is 500, the specific surface area is maximized.
A series of melamine-formaldehyde(MF) organic aerogel templates were prepared with different categories and concentration of catalyst. Their molecular structure, thermal stability and pore structure were tested by Fourier transform infrared spectroscopy, thermogravimetric analysis and nitrogen adsorption. It is indicated that the type and concentration of catalyst do not affect molecular structure and thermal stability of the MF organic aerogel template. The specific surface area and pore volume of the MF organic aerogel template using Na2CO3 as catalyst are higher than those using NaOH, NaHCO3 as catalyst. When the ratio of the concentration of melamine to that of catalyst is 500, the specific surface area is maximized.
2013,
25: 918-922.
Abstract:
With the increase of capsule requirement, a method for batch characterization of the diameter and sphericity of poly (-methyl styrene) (PAMS) mandrels is developed based on the VMR microscope system. The sources of uncertainty in characterizing the diameter are analyzed and every uncertainty component is evaluated. The 95% results of a 1 mm standard ball are in the range of (998.2-1.2) m to (998.2+1.2) m, showing excellent precision and stability of batch characterization. The characterization method is also used in measuring the PAMS mandrels. Compared with the results characterized on MM-400 microscope by hand, the deviation of the diameters of PAMS shells characterized by batch shows unidirectionality, and the maximum value is about 10 m, within the requirement of 15 m.
With the increase of capsule requirement, a method for batch characterization of the diameter and sphericity of poly (-methyl styrene) (PAMS) mandrels is developed based on the VMR microscope system. The sources of uncertainty in characterizing the diameter are analyzed and every uncertainty component is evaluated. The 95% results of a 1 mm standard ball are in the range of (998.2-1.2) m to (998.2+1.2) m, showing excellent precision and stability of batch characterization. The characterization method is also used in measuring the PAMS mandrels. Compared with the results characterized on MM-400 microscope by hand, the deviation of the diameters of PAMS shells characterized by batch shows unidirectionality, and the maximum value is about 10 m, within the requirement of 15 m.
2013,
25: 923-928.
Abstract:
The field reversed configuration(FRC) is a toroidal magnetic confinement system in which a pre-heated and magnetized plasma target can be produced in a -pinch coil. FRC is the main approach to the so-called magnetic target fusion. To understand the physical mechanism of its plasma equilibrium better, this paper focuses on the classical rigid rotor(RR) model of the FRC and analytically solved the equilibrium distribution functions. Based on the comparison with the standard two-dimensional magnetohydrodynamics(MHD) simulation, the influences of the various RR model assumptions on the equilibrium distribution functions have been discussed, and a calculated expression of the model profile variable with the relative radius was derivated. The results show that the FRC plasma RR model can describe the parameter distribution well within the plasma separatrix.
The field reversed configuration(FRC) is a toroidal magnetic confinement system in which a pre-heated and magnetized plasma target can be produced in a -pinch coil. FRC is the main approach to the so-called magnetic target fusion. To understand the physical mechanism of its plasma equilibrium better, this paper focuses on the classical rigid rotor(RR) model of the FRC and analytically solved the equilibrium distribution functions. Based on the comparison with the standard two-dimensional magnetohydrodynamics(MHD) simulation, the influences of the various RR model assumptions on the equilibrium distribution functions have been discussed, and a calculated expression of the model profile variable with the relative radius was derivated. The results show that the FRC plasma RR model can describe the parameter distribution well within the plasma separatrix.
2013,
25: 929-934.
Abstract:
Single-step and multi-step laser conditioning methods for HfO2/SiO2 multilayer high-reflective (HR) coatings prepared by electron-beam evaporation were introduced, with the use of different beam increment between pulses. In order not to damage the coating, the maximum conditioning fluence can not exceed 90% of its unconditioned laser induced damage threshold (LIDT). The LIDT enhancement of the coating after single-step conditioning is more than that after multi-step conditioning under the same conditioning efficiency. After two-step laser conditioning with a beam increment between pulses equal to the beam diameter at 98.4% of the peak intensity, the LIDT of the coating attains 181% of that of the unconditioned coating. The starting material composition for the hafnia layers has a direct impact on the concentration of defects imbedded in the coating, it is believed that coatings deposited from hafnium have defect-seeds at a significantly lower density.
Single-step and multi-step laser conditioning methods for HfO2/SiO2 multilayer high-reflective (HR) coatings prepared by electron-beam evaporation were introduced, with the use of different beam increment between pulses. In order not to damage the coating, the maximum conditioning fluence can not exceed 90% of its unconditioned laser induced damage threshold (LIDT). The LIDT enhancement of the coating after single-step conditioning is more than that after multi-step conditioning under the same conditioning efficiency. After two-step laser conditioning with a beam increment between pulses equal to the beam diameter at 98.4% of the peak intensity, the LIDT of the coating attains 181% of that of the unconditioned coating. The starting material composition for the hafnia layers has a direct impact on the concentration of defects imbedded in the coating, it is believed that coatings deposited from hafnium have defect-seeds at a significantly lower density.
2013,
25: 935-939.
Abstract:
Polytetrafluoroethylene(PTFE), polyethylene(PE), polymethyl methacrylate(PMMA) and other similar medium materials are widely used for making of output window of high power microwave(HPM), due to their favorable wave-transparent and mechanical properties. But there are few studies conducted on the influence of different processing technologies on dielectric properties of these materials. In this article, the basic dielectric parameters of different medium materials processed with different technologies are measured with high-pressure bridges and high resistance meters, and the surface electrical trap densities of these materials at the low energy level of 0.8-0.9 eV are measured with the adoption of electrostatic induction method. Medium breakdown experiments with waveguides under S band, 800 MW and 100 ns microwave pulse are conducted, and the effects of different material surface finishes on window surface breakdown are studied. The results show that, the baking technology to some extent reduces materials resistance to breakdown, and causes more dielectric losses; the scratches parallel to the direction of electric field form the channel for material surface breakdown, leading to more serious breakdown.
Polytetrafluoroethylene(PTFE), polyethylene(PE), polymethyl methacrylate(PMMA) and other similar medium materials are widely used for making of output window of high power microwave(HPM), due to their favorable wave-transparent and mechanical properties. But there are few studies conducted on the influence of different processing technologies on dielectric properties of these materials. In this article, the basic dielectric parameters of different medium materials processed with different technologies are measured with high-pressure bridges and high resistance meters, and the surface electrical trap densities of these materials at the low energy level of 0.8-0.9 eV are measured with the adoption of electrostatic induction method. Medium breakdown experiments with waveguides under S band, 800 MW and 100 ns microwave pulse are conducted, and the effects of different material surface finishes on window surface breakdown are studied. The results show that, the baking technology to some extent reduces materials resistance to breakdown, and causes more dielectric losses; the scratches parallel to the direction of electric field form the channel for material surface breakdown, leading to more serious breakdown.
2013,
25: 940-944.
Abstract:
Quantum chaos theory is used to study a reverberation chamber (RC). We evaluate the chaotic characteristics of a numerical RC by analyzing the eigenfrequency spacing distribution with the finite element method. Based on the electromagnetic chaotic features and the hypothesis, the electric field vector eigenfunction in the RC could be expressed as linear superposition of random plane waves. Then the electric field in the RC can be expressed as the vector eigenfunction expansion. The Rayleigh distribution model of probability density function of electric field in the RC is derived by statistical approach. The electric field intensity measurement in an actual mechanical stirring RC is completed with ETS HI-6105 prober. The electric field distribution in the chamber is in close agreement with the result from the statistical model, which proves the validity of the theoretical model.
Quantum chaos theory is used to study a reverberation chamber (RC). We evaluate the chaotic characteristics of a numerical RC by analyzing the eigenfrequency spacing distribution with the finite element method. Based on the electromagnetic chaotic features and the hypothesis, the electric field vector eigenfunction in the RC could be expressed as linear superposition of random plane waves. Then the electric field in the RC can be expressed as the vector eigenfunction expansion. The Rayleigh distribution model of probability density function of electric field in the RC is derived by statistical approach. The electric field intensity measurement in an actual mechanical stirring RC is completed with ETS HI-6105 prober. The electric field distribution in the chamber is in close agreement with the result from the statistical model, which proves the validity of the theoretical model.
2013,
25: 945-949.
Abstract:
Based on the helical coordinate system, using the approximate field matching method, we studied the high-frequency characteristics of thicker helical slow wave structure, obtained the dispersion equation, and analyzed the influence of the thickness of the helix slow wave on the phase velocity. The results show that the dispersion curve of the slow-wave structure becomes flat with the increase of helix thickness, and also the dispersion becomes weaker, the bandwidth broadens. The calculation results of our method agree well with the results obtained by CST simulation, which proves that the theoretical method has a higher accuracy than the Hooks model in analysis of the thicker helix.
Based on the helical coordinate system, using the approximate field matching method, we studied the high-frequency characteristics of thicker helical slow wave structure, obtained the dispersion equation, and analyzed the influence of the thickness of the helix slow wave on the phase velocity. The results show that the dispersion curve of the slow-wave structure becomes flat with the increase of helix thickness, and also the dispersion becomes weaker, the bandwidth broadens. The calculation results of our method agree well with the results obtained by CST simulation, which proves that the theoretical method has a higher accuracy than the Hooks model in analysis of the thicker helix.
2013,
25: 950-958.
Abstract:
For investigating the mechanism of high power microwave flashover and breakdown on dielectric surface, the theoretical modeling is put forward, including dynamic equations, particle-in-cell method, secondary emission and Monte-Carlo collision between electrons and gas atoms. Based on the theoretical model, the 1D3V PIC-MCC code is programmed. By using this code, we numerically study vacuum multipactor discharge, volume breakdown under high-pressure gas and surface breakdown under low-pressure gas course, including the number of electrons and ions, electron trajectories, electron and ion density distributions, the time and space distribution of space charge field, the average electron energy, the average energy of impact electrons, the number of impact electrons, electron energy distribution functions, average secondary emission ratio and energy balance. The numerical results are concluded as follows: vacuum multipactor could not cause breakdown for low deposited power (about 1% microwave power); volume breakdown is caused by high-level number of electrons with low energy, the breakdown position is far from dielectric surface, and the forming time is at the level of microseconds; flashover and breakdown on dielectric surface are caused by the continuous increase of deposited power resulting from many high-energy electrons, the breakdown position is near to dielectric surface, and the forming time is at the level of nanoseconds.
For investigating the mechanism of high power microwave flashover and breakdown on dielectric surface, the theoretical modeling is put forward, including dynamic equations, particle-in-cell method, secondary emission and Monte-Carlo collision between electrons and gas atoms. Based on the theoretical model, the 1D3V PIC-MCC code is programmed. By using this code, we numerically study vacuum multipactor discharge, volume breakdown under high-pressure gas and surface breakdown under low-pressure gas course, including the number of electrons and ions, electron trajectories, electron and ion density distributions, the time and space distribution of space charge field, the average electron energy, the average energy of impact electrons, the number of impact electrons, electron energy distribution functions, average secondary emission ratio and energy balance. The numerical results are concluded as follows: vacuum multipactor could not cause breakdown for low deposited power (about 1% microwave power); volume breakdown is caused by high-level number of electrons with low energy, the breakdown position is far from dielectric surface, and the forming time is at the level of microseconds; flashover and breakdown on dielectric surface are caused by the continuous increase of deposited power resulting from many high-energy electrons, the breakdown position is near to dielectric surface, and the forming time is at the level of nanoseconds.
2013,
25: 959-962.
Abstract:
The paper presents the potential problem in traditional microwave extractor design in the magnetically insulated line oscillator (MILO). Through high frequency electromagnetic simulation, the dependence of TEM mode transmission efficiency on frequency is obtained at different impedance of the microwave extractor. Simulation results show that the microwave extractor designed in traditional way can not meet the demand of TEM transmission. In order to conquer the transmission difficulty of TEM mode, the paper introduces the scheme using ladder load. Further simulation results indicate that the ladder load conquers the transmission difficulty of TEM mode and improves the adaptability of the microwave extractor to frequency drifting of the MILO.
The paper presents the potential problem in traditional microwave extractor design in the magnetically insulated line oscillator (MILO). Through high frequency electromagnetic simulation, the dependence of TEM mode transmission efficiency on frequency is obtained at different impedance of the microwave extractor. Simulation results show that the microwave extractor designed in traditional way can not meet the demand of TEM transmission. In order to conquer the transmission difficulty of TEM mode, the paper introduces the scheme using ladder load. Further simulation results indicate that the ladder load conquers the transmission difficulty of TEM mode and improves the adaptability of the microwave extractor to frequency drifting of the MILO.
2013,
25: 963-967.
Abstract:
In order to evaluate the stirring efficiency in the reverberation chamber under different stirring modes, and improve the accuracy of the measurement, the method for calculating the number of independent samples which is an important indicator is introduced briefly. The frequencies of 200, 500 and 1000 MHz are chosen to evaluate the stirring efficiency of mechanical stirring and frequency stirring. The calculated number of independent samples shows that the stirring efficiency of the two stirring modes is proportional to the operating frequency. In the mechanical stirring mode, the stirring efficiency can be significantly improved when stirrers work at different speed ratios, and the larger stirring bandwidth is chosen, the higher stirring efficiency can be obtained in the frequency stirring mode, but the number of independent samples has an upper limit in the order of hundreds. Thus the combined stirring method based on mechanical stirring and frequency stirring is proposed, and the stirring efficiency is analyzed deeply, also the formula for calculating the independent samples is given. The test results show that the number of independent samples can be drastically increased under the combined stirring mode.
In order to evaluate the stirring efficiency in the reverberation chamber under different stirring modes, and improve the accuracy of the measurement, the method for calculating the number of independent samples which is an important indicator is introduced briefly. The frequencies of 200, 500 and 1000 MHz are chosen to evaluate the stirring efficiency of mechanical stirring and frequency stirring. The calculated number of independent samples shows that the stirring efficiency of the two stirring modes is proportional to the operating frequency. In the mechanical stirring mode, the stirring efficiency can be significantly improved when stirrers work at different speed ratios, and the larger stirring bandwidth is chosen, the higher stirring efficiency can be obtained in the frequency stirring mode, but the number of independent samples has an upper limit in the order of hundreds. Thus the combined stirring method based on mechanical stirring and frequency stirring is proposed, and the stirring efficiency is analyzed deeply, also the formula for calculating the independent samples is given. The test results show that the number of independent samples can be drastically increased under the combined stirring mode.
2013,
25: 968-972.
Abstract:
It is impossible to ignore the influence of S-parameter characteristics in THz folded waveguide slow wave structures. In this paper, the relation between calculated period numbers and S-parameters is considered, the effect of variations of folded waveguide slow wave structures on loss is discussed, and the influence of roughness on loss is present. The loss of 0.22 THz standard rectangular straight waveguides is measured to certify theoretical analysis. Finally, based on test of the machined 0.22 THz folded waveguide slow wave structures, we obtain the transmission and loss characteristics of these slow wave structures.
It is impossible to ignore the influence of S-parameter characteristics in THz folded waveguide slow wave structures. In this paper, the relation between calculated period numbers and S-parameters is considered, the effect of variations of folded waveguide slow wave structures on loss is discussed, and the influence of roughness on loss is present. The loss of 0.22 THz standard rectangular straight waveguides is measured to certify theoretical analysis. Finally, based on test of the machined 0.22 THz folded waveguide slow wave structures, we obtain the transmission and loss characteristics of these slow wave structures.
2013,
25: 973-976.
Abstract:
Based on twodimensional electromagnetic bandgap (2D EBG) structure, both straight and 90curving waveguide transmission lines working at 0.22 THz were designed. The numerical simulation result shows that the S21 parameters of straight and curving waveguides are both above 10-5 dB at 0.22 THz, they are above -0.001 dB and -0.003 5 dB respectively in the 20 GHz simulation frequency band, and the bandgap has good inhibition to the electromagnetic wave. Based on the EBG waveguide, 3 dB power divider and H plane horn array antenna were designed. Their numerical simulation result shows that the S21 parameter of the power divider is -3 dB at 0.14 THz, the array antenna has the directivity of 17.1 dBi with small side and back lobe, and both E plane and H plane patterns are symmetrical.
Based on twodimensional electromagnetic bandgap (2D EBG) structure, both straight and 90curving waveguide transmission lines working at 0.22 THz were designed. The numerical simulation result shows that the S21 parameters of straight and curving waveguides are both above 10-5 dB at 0.22 THz, they are above -0.001 dB and -0.003 5 dB respectively in the 20 GHz simulation frequency band, and the bandgap has good inhibition to the electromagnetic wave. Based on the EBG waveguide, 3 dB power divider and H plane horn array antenna were designed. Their numerical simulation result shows that the S21 parameter of the power divider is -3 dB at 0.14 THz, the array antenna has the directivity of 17.1 dBi with small side and back lobe, and both E plane and H plane patterns are symmetrical.
2013,
25: 977-980.
Abstract:
A 100 MeV proton cyclotron, referred to as CYCIAE-100, is designed to provide proton beams with energy up to 200 A. When the cyclotron is under commissioning, a beam dump is required to measure the beam with a power of 20 kW. The paper introduces the beam line, target material selecting, target configuration, cooling calculation and the local shielding structure. The calculation result of the beam line matching is given. After comparing the neutron yield, flux angle and thermal activation of the targets of different materials by the proton targeting, the aluminum is selected as the target material. Based on the extraction beam energy and power of the cyclotron, a layered target configuration is designed, and the cooling calculation result is presented. The average energy of the emergent particle produced by the proton targeting is relatively high, so it will produce large radiation dose. Considering the harmful effect on the environment and personnel, the local shielding is selected for use. The calculation result and configuration of the local shielding are also presented in the paper.
A 100 MeV proton cyclotron, referred to as CYCIAE-100, is designed to provide proton beams with energy up to 200 A. When the cyclotron is under commissioning, a beam dump is required to measure the beam with a power of 20 kW. The paper introduces the beam line, target material selecting, target configuration, cooling calculation and the local shielding structure. The calculation result of the beam line matching is given. After comparing the neutron yield, flux angle and thermal activation of the targets of different materials by the proton targeting, the aluminum is selected as the target material. Based on the extraction beam energy and power of the cyclotron, a layered target configuration is designed, and the cooling calculation result is presented. The average energy of the emergent particle produced by the proton targeting is relatively high, so it will produce large radiation dose. Considering the harmful effect on the environment and personnel, the local shielding is selected for use. The calculation result and configuration of the local shielding are also presented in the paper.
2013,
25: 981-984.
Abstract:
IQT files, the spectrum data files of Tektronix real-time spectrum analyzer with special structure are found hardly to manipulate in late experimental data processing. The structure and offline processing of IQT files are analyzed, and the signal contrast is mathematically improved in this paper. As an application example in experimental data processing, the longitudinal electron cooling force of an 36Ar18+21.7 MeV/u beam at different ion-electron relative velocity is obtained. This processing method contributes to the offline processing of real-time spectrum data in experiments.
IQT files, the spectrum data files of Tektronix real-time spectrum analyzer with special structure are found hardly to manipulate in late experimental data processing. The structure and offline processing of IQT files are analyzed, and the signal contrast is mathematically improved in this paper. As an application example in experimental data processing, the longitudinal electron cooling force of an 36Ar18+21.7 MeV/u beam at different ion-electron relative velocity is obtained. This processing method contributes to the offline processing of real-time spectrum data in experiments.
2013,
25: 985-988.
Abstract:
For the safety issue for top-up injection, the trajectory of the injection beam was tracked to find out in what kinds of conditions the injection beam would get through the synchrotron light beam pipe and cause radiation hazards. The forward tracking method is used with Accelerator Toolbox (AT) code. We enlarge injection beam phase space volume and reduce the beam line element to simplify the calculation while covering all the possibility. According to this simulation, the interlock criteria are set up for top-up operation.
For the safety issue for top-up injection, the trajectory of the injection beam was tracked to find out in what kinds of conditions the injection beam would get through the synchrotron light beam pipe and cause radiation hazards. The forward tracking method is used with Accelerator Toolbox (AT) code. We enlarge injection beam phase space volume and reduce the beam line element to simplify the calculation while covering all the possibility. According to this simulation, the interlock criteria are set up for top-up operation.
2013,
25: 989-993.
Abstract:
A direct plasma injection scheme (DPIS) project has been developed since 2007 at the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS). In this paper, the test methods and results of radio frequency (RF) characteristics are presented, and especially a new approach, which can calibrate a directional coupler by the RF instrument, is introduced to measure the pulsed power precisely. Furthermore, we present the conditioning situation of the whole radio frequency quadrupole (RFQ) system including the analysis of and the solutions to the sparking of the cavity and amplifier. Finally, the result from the beam experiment proves that the design and measurement can meet the commissioning demand.
A direct plasma injection scheme (DPIS) project has been developed since 2007 at the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS). In this paper, the test methods and results of radio frequency (RF) characteristics are presented, and especially a new approach, which can calibrate a directional coupler by the RF instrument, is introduced to measure the pulsed power precisely. Furthermore, we present the conditioning situation of the whole radio frequency quadrupole (RFQ) system including the analysis of and the solutions to the sparking of the cavity and amplifier. Finally, the result from the beam experiment proves that the design and measurement can meet the commissioning demand.
2013,
25: 994-1000.
Abstract:
A new accelerator dedicated to hadron therapy, the Heavy-Ion Therapy Facility in Lanzhou (HITFiL), is under construction. As the main accelerator of HITFiL, a heavy-ion synchrotron is designed with special attention paid to compact structure, high reliability and low cost. Stripping injection scheme is adopted for the synchrotron, which is more efficient than single-turn injection and less costly than multi-turn injection supported by electron-cooling. Carbon beams are adopted for HITFiL cancer therapy: C5+ ions from an electron cyclotron resonance ion source, are pre-accelerated by a cyclotron, stripped into C6+ ions by a carbon foil located in a main dipole of the ring and injected into the central orbit of the ring at the same time. The detailed injection scheme for the synchrotron is presented, and the stripping injection process is simulated. The injection efficiency, complete beam loss factors and the particle number gain are investigated. In addition, beam properties including beam distribution in real and phase space and emittance growth due to foil traversal are studied, and the required beam intensity is achieved.
A new accelerator dedicated to hadron therapy, the Heavy-Ion Therapy Facility in Lanzhou (HITFiL), is under construction. As the main accelerator of HITFiL, a heavy-ion synchrotron is designed with special attention paid to compact structure, high reliability and low cost. Stripping injection scheme is adopted for the synchrotron, which is more efficient than single-turn injection and less costly than multi-turn injection supported by electron-cooling. Carbon beams are adopted for HITFiL cancer therapy: C5+ ions from an electron cyclotron resonance ion source, are pre-accelerated by a cyclotron, stripped into C6+ ions by a carbon foil located in a main dipole of the ring and injected into the central orbit of the ring at the same time. The detailed injection scheme for the synchrotron is presented, and the stripping injection process is simulated. The injection efficiency, complete beam loss factors and the particle number gain are investigated. In addition, beam properties including beam distribution in real and phase space and emittance growth due to foil traversal are studied, and the required beam intensity is achieved.
2013,
25: 1001-1004.
Abstract:
Insertion devices are key components of modern light sources such as Shanghai Synchrotron Radiation Facility (SSRF). The control system of insertion devices is mainly composed of motion control of high precision motor, position feedback, correction coil power supply control, front-end feedback and human interface. To implement all these functions and enable insertion devices to be interactive with SSRFS EPICS control system smoothly, a control system based on EPICS has been designed for the insertion devices. Then, all EPICS components have been integrated into one embedded controller by using embedded EPICS technology. With this method, the control system architecture has been simplified, which is more convenient for the maintenance. It has been demonstrated that this control system has integrated functions and good real-time feedback characteristics. With this control system, the insertion devices can enhance the stability of beam orbit and guarantee high quality of synchrotron radiation light for the SSRFs beam line stations.
Insertion devices are key components of modern light sources such as Shanghai Synchrotron Radiation Facility (SSRF). The control system of insertion devices is mainly composed of motion control of high precision motor, position feedback, correction coil power supply control, front-end feedback and human interface. To implement all these functions and enable insertion devices to be interactive with SSRFS EPICS control system smoothly, a control system based on EPICS has been designed for the insertion devices. Then, all EPICS components have been integrated into one embedded controller by using embedded EPICS technology. With this method, the control system architecture has been simplified, which is more convenient for the maintenance. It has been demonstrated that this control system has integrated functions and good real-time feedback characteristics. With this control system, the insertion devices can enhance the stability of beam orbit and guarantee high quality of synchrotron radiation light for the SSRFs beam line stations.
2013,
25: 1005-1008.
Abstract:
The second medium energy beam transport (MEBT2) line is of great importance in the front-end part of the 1.5 GeV accelerator in the China Accelerator Driven System (CADS) project. In this paper, we describe the design considerations and the beam dynamics of the 10 MeV MEBT2 line. The design and simulation of the MEBT2 were carried out with the multi-particle tracking program TraceWin. The simulation results show that an emittance growth of 5% in the transverse planes and 13% in the longitudinal plane is observable after beam transportation in the MEBT2.
The second medium energy beam transport (MEBT2) line is of great importance in the front-end part of the 1.5 GeV accelerator in the China Accelerator Driven System (CADS) project. In this paper, we describe the design considerations and the beam dynamics of the 10 MeV MEBT2 line. The design and simulation of the MEBT2 were carried out with the multi-particle tracking program TraceWin. The simulation results show that an emittance growth of 5% in the transverse planes and 13% in the longitudinal plane is observable after beam transportation in the MEBT2.
2013,
25: 1009-1012.
Abstract:
The dispersion relation of transverse oscillation in the unmagnetized, collisionless, isotropic and relativistic electronpositron plasma is discussed in the context of q distribution. The dispersion equations in connection with q parameter are derived and then the analytical dispersion laws for ultrarelativistic electronpositron plasma are obtained under the longwavelength approximation and the shortwavelength condition. The dispersion equations are numerically simulated with the purpose of getting the full dispersion curve, and the numerical solutions are coincident with the analytical results in the cases of longwavelength and shortwavelength for ultrarelativistic electronpositron plasma. It is shown that the dispersion relation in the context of q distribution is related to q parameter and temperature, and in the limiting case (q1), the classical dispersion relation based on the Maxwellian distribution is recovered.
The dispersion relation of transverse oscillation in the unmagnetized, collisionless, isotropic and relativistic electronpositron plasma is discussed in the context of q distribution. The dispersion equations in connection with q parameter are derived and then the analytical dispersion laws for ultrarelativistic electronpositron plasma are obtained under the longwavelength approximation and the shortwavelength condition. The dispersion equations are numerically simulated with the purpose of getting the full dispersion curve, and the numerical solutions are coincident with the analytical results in the cases of longwavelength and shortwavelength for ultrarelativistic electronpositron plasma. It is shown that the dispersion relation in the context of q distribution is related to q parameter and temperature, and in the limiting case (q1), the classical dispersion relation based on the Maxwellian distribution is recovered.
2013,
25: 1013-1016.
Abstract:
Some techniques of beam profile measurements such as wire rotating scan, Faraday cups array and infrared imagingwere investigated. A measurement device was built based on scintillating screen to cater for the demand of accelerator beam profile diagnostics. The device was bombarded under several tens to hundred nanoampere Fen+(n~512) ion beam. The Fen+ ion beam experiment shows that the imaging saturation is mainly caused by light intensity rather than scintillating screen. A way to solve the saturation problem with a specially developed lens was mentioned. The grayscale of beam profile imaging is approximately linear with respect to the beam intensity, and the reason for formation of this relationship was analyzed.
Some techniques of beam profile measurements such as wire rotating scan, Faraday cups array and infrared imagingwere investigated. A measurement device was built based on scintillating screen to cater for the demand of accelerator beam profile diagnostics. The device was bombarded under several tens to hundred nanoampere Fen+(n~512) ion beam. The Fen+ ion beam experiment shows that the imaging saturation is mainly caused by light intensity rather than scintillating screen. A way to solve the saturation problem with a specially developed lens was mentioned. The grayscale of beam profile imaging is approximately linear with respect to the beam intensity, and the reason for formation of this relationship was analyzed.
2013,
25: 1017-1020.
Abstract:
A self-adaptive identification method is proposed for realizing more accurate and efficient judgment about the inner and outer contours of industrial computed tomography (CT) slice images. The convexity-concavity of the single-pixel-wide closed contour is identified with angle method at first. Then, contours with concave vertices are distinguished to be inner or outer contours with ray method, and contours without concave vertices are distinguished with extreme coordinate value method. The method was chosen to automatically distinguish contours by means of identifying the convexity and concavity of the contours. Thus, the disadvantages of single distinguishing methods, such as ray methods time-consuming and extreme coordinate methods fallibility, can be avoided. The experiments prove the adaptability, efficiency, and accuracy of the self-adaptive method.
A self-adaptive identification method is proposed for realizing more accurate and efficient judgment about the inner and outer contours of industrial computed tomography (CT) slice images. The convexity-concavity of the single-pixel-wide closed contour is identified with angle method at first. Then, contours with concave vertices are distinguished to be inner or outer contours with ray method, and contours without concave vertices are distinguished with extreme coordinate value method. The method was chosen to automatically distinguish contours by means of identifying the convexity and concavity of the contours. Thus, the disadvantages of single distinguishing methods, such as ray methods time-consuming and extreme coordinate methods fallibility, can be avoided. The experiments prove the adaptability, efficiency, and accuracy of the self-adaptive method.
2013,
25: 1021-1025.
Abstract:
The optimized design method based on signal to noise ratio of the image is presented for the object of two-dimensional Gaussian distribution based on the theoretical analysis of the technology of X-ray in-line phase contrast imaging. The imaging systems under the radiation of sub-micrometer focus X-ray source, laser-based micrometer focus X-ray source and synchrotron radiation X-ray source are optimized by means of numerical simulation. The outcome shows that the method based on signal to noise ratio can increase the signal to noise ratio of the image and get more reasonable imaging distance premised by decreasing the contrast slightly when compared with the contrast method.
The optimized design method based on signal to noise ratio of the image is presented for the object of two-dimensional Gaussian distribution based on the theoretical analysis of the technology of X-ray in-line phase contrast imaging. The imaging systems under the radiation of sub-micrometer focus X-ray source, laser-based micrometer focus X-ray source and synchrotron radiation X-ray source are optimized by means of numerical simulation. The outcome shows that the method based on signal to noise ratio can increase the signal to noise ratio of the image and get more reasonable imaging distance premised by decreasing the contrast slightly when compared with the contrast method.
2013,
25: 1026-1030.
Abstract:
In order to enhance the sensitivity of nuclear material identification system(NMIS) against the change of nuclear material enrichment, the principle of high order statistic feature is introduced and applied to traditional NMIS. We present a new enrichment identification method based on cross-correlation and high order spectrum algorithm. By applying the identification method to NMIS, the 3D graphs with nuclear material character are presented and can be used as new signatures to identify the enrichment of nuclear materials. The simulation result shows that the identification method could suppress the background noises, electronic system noises, and improve the sensitivity against enrichment change to exponential order with no system structure modification.
In order to enhance the sensitivity of nuclear material identification system(NMIS) against the change of nuclear material enrichment, the principle of high order statistic feature is introduced and applied to traditional NMIS. We present a new enrichment identification method based on cross-correlation and high order spectrum algorithm. By applying the identification method to NMIS, the 3D graphs with nuclear material character are presented and can be used as new signatures to identify the enrichment of nuclear materials. The simulation result shows that the identification method could suppress the background noises, electronic system noises, and improve the sensitivity against enrichment change to exponential order with no system structure modification.
2013,
25: 1031-1034.
Abstract:
A coupled algorithm is introduced to simulate the long-term radiation effects of MOSFETs, which combines particle transport with semiconductor governing equations. The former is dealt with Monte-Carlo method, and the latter is solved by finite-volume method. The trapped charge in SiO2 and the free charge in Si are both described by the drift-diffusion model, and the deposited energy by incident particles can be coupled with the continuous equations of charge, acting as a source item. The discrete form of governing equations is obtained using the finite-volume method, and the numerical solutions of these equations are the long-term radiation response result of MOSFETs. The threshold voltage shift and off-state leakage current of an irradiated MOSFET are simulated with the coupled algorithm respectively, showing a good accordance with results by other calculations.
A coupled algorithm is introduced to simulate the long-term radiation effects of MOSFETs, which combines particle transport with semiconductor governing equations. The former is dealt with Monte-Carlo method, and the latter is solved by finite-volume method. The trapped charge in SiO2 and the free charge in Si are both described by the drift-diffusion model, and the deposited energy by incident particles can be coupled with the continuous equations of charge, acting as a source item. The discrete form of governing equations is obtained using the finite-volume method, and the numerical solutions of these equations are the long-term radiation response result of MOSFETs. The threshold voltage shift and off-state leakage current of an irradiated MOSFET are simulated with the coupled algorithm respectively, showing a good accordance with results by other calculations.
2013,
25: 1035-1039.
Abstract:
Position sensitive detectors (PSDs) are an important class of optical sensors which utilizes the lateral photovoltaic effect (LPVE). According to the operation principle of PSD, we demonstrate that LPVE can be enhanced by lengthening the lifetime of photo-generated carriers. A PSD based on photonic crystals (PCs) composed of MgF2 and InP is proposed and designed. The transmittances of the defect PC and the reflectance of the perfect PC in the PSD are obtained with transfer matrix method. The theoretical research on the designed device shows that LPVE is enhanced by improving the transmittance of the defect PC and the reflectance of the perfect PC to lengthen the lifetime of photo-generated carriers.
Position sensitive detectors (PSDs) are an important class of optical sensors which utilizes the lateral photovoltaic effect (LPVE). According to the operation principle of PSD, we demonstrate that LPVE can be enhanced by lengthening the lifetime of photo-generated carriers. A PSD based on photonic crystals (PCs) composed of MgF2 and InP is proposed and designed. The transmittances of the defect PC and the reflectance of the perfect PC in the PSD are obtained with transfer matrix method. The theoretical research on the designed device shows that LPVE is enhanced by improving the transmittance of the defect PC and the reflectance of the perfect PC to lengthen the lifetime of photo-generated carriers.
2013,
25: 1040-1044.
Abstract:
The operating principle of stepped transmission lines is introduced, and an ideal rule of output voltage in quasi-Blumlein lines is given. The stepped transmission lines can completely transmit energy and increase the voltage to (n+1)/2 times the input voltage. Also impedance deflection in the stepped transmission lines is researched. The actual impedance is a little bigger than design value, and the impedance deflection ranges from 0 to 20%. By electromagnetic simulation, the relations of impedance deflections and output voltages in three-grade stepped transmission lines are given. In the range of impedance deflection, output voltage coefficient increases with the decrease of impedance, and it ranges from 1.9 to 2.1. The effect of output voltage on transmission lines impedance deflection is discussed. At last, a three-grade stepped transmission line is designed and its experimental results show that the theoretical and experimental data are in good agreement.
The operating principle of stepped transmission lines is introduced, and an ideal rule of output voltage in quasi-Blumlein lines is given. The stepped transmission lines can completely transmit energy and increase the voltage to (n+1)/2 times the input voltage. Also impedance deflection in the stepped transmission lines is researched. The actual impedance is a little bigger than design value, and the impedance deflection ranges from 0 to 20%. By electromagnetic simulation, the relations of impedance deflections and output voltages in three-grade stepped transmission lines are given. In the range of impedance deflection, output voltage coefficient increases with the decrease of impedance, and it ranges from 1.9 to 2.1. The effect of output voltage on transmission lines impedance deflection is discussed. At last, a three-grade stepped transmission line is designed and its experimental results show that the theoretical and experimental data are in good agreement.
2013,
25: 1045-1049.
Abstract:
To realize the compatibility of both high power electromagnetic pulse(EMP) protection and signal receiving and transmitting, a new electromagnetic protection structure, i.e. energy selective surface(ESS), is proposed based on energy selective mechanism. Employing the voltage dependent conductive characteristic of semiconductor, ESS can promptly turn its state from high impendence to low impendence under high power radiation, and therefore has energy low-pass characteristic and wide band. In the design and simulation, PIN diode array was employed, and filed-circuit co-simulation was carried out. The relationship of ESS, PIN diode impedance and incident EMP intensity and rise time has been described, and the results are summarized as follows: the peak leakage power and response time are proportional to thickness of layer Ⅰ and the amplitude of incident EMP electric intensity, and inversely proportional to minority carrier life time.
To realize the compatibility of both high power electromagnetic pulse(EMP) protection and signal receiving and transmitting, a new electromagnetic protection structure, i.e. energy selective surface(ESS), is proposed based on energy selective mechanism. Employing the voltage dependent conductive characteristic of semiconductor, ESS can promptly turn its state from high impendence to low impendence under high power radiation, and therefore has energy low-pass characteristic and wide band. In the design and simulation, PIN diode array was employed, and filed-circuit co-simulation was carried out. The relationship of ESS, PIN diode impedance and incident EMP intensity and rise time has been described, and the results are summarized as follows: the peak leakage power and response time are proportional to thickness of layer Ⅰ and the amplitude of incident EMP electric intensity, and inversely proportional to minority carrier life time.
2013,
25: 1050-1054.
Abstract:
The explosive magnetic flux compression generator (FCG) is a kind of compact pulsed power source with relatively low characteristic impedance. To match the impedance of the generator and the load in kinds of applications, some special power conditioning circuits are always in need. In this paper, a power conditioning circuit based on the electro-exploding opening switch (EEOS) and pulsed transformer is investigated. By analyzing the equivalent circuit of the system where the generator is replaced by a capacitor, a key factor determining the performance of the power conditioning circuit is discussed, as well as its solution. Based on the analysis, the power conditioning circuit with coaxial structure is designed. In the preliminary experiments, the capacitive load was charged to a peak voltage of -267 kV when the crowbar switch used to remove the additional voltage across the fuse kept open, and it was charged to -374 kV when the crowbar switch closed during the opening process of the EEOS. The analysis conclusions are basically proved by these experimental results. And the power conditioning circuit introduced is proved to be efficient to match the impedance of the FCG and high-impedance load
The explosive magnetic flux compression generator (FCG) is a kind of compact pulsed power source with relatively low characteristic impedance. To match the impedance of the generator and the load in kinds of applications, some special power conditioning circuits are always in need. In this paper, a power conditioning circuit based on the electro-exploding opening switch (EEOS) and pulsed transformer is investigated. By analyzing the equivalent circuit of the system where the generator is replaced by a capacitor, a key factor determining the performance of the power conditioning circuit is discussed, as well as its solution. Based on the analysis, the power conditioning circuit with coaxial structure is designed. In the preliminary experiments, the capacitive load was charged to a peak voltage of -267 kV when the crowbar switch used to remove the additional voltage across the fuse kept open, and it was charged to -374 kV when the crowbar switch closed during the opening process of the EEOS. The analysis conclusions are basically proved by these experimental results. And the power conditioning circuit introduced is proved to be efficient to match the impedance of the FCG and high-impedance load
2013,
25: 1055-1058.
Abstract:
The radiation generated by gas-gap switches in the process that intense electron beam accelerator is running with pseudo load may cause the computer to be black screen. The mechanism of electromagnetic radiation induced by the triggered spark-gap switch and main switch is analyzed carefully in this paper. The charging gap of the gas-gap switches is equivalent to electric dipole, and the spatial distribution of the radiation is analyzed theoretically. The radiation signals of the triggered spark-gap switch and main switch are measured, and the result shows that the theoretical analysis is reasonable. At last, the coaxial cable is used to evaluate the interference of the radiation. At the moment that the radiation signal generates in the intense electron beam accelerator, the induced voltage in the coaxial cable reaches to nearly 3 V, which could cause inaccuracy in the measurement of other signals.
The radiation generated by gas-gap switches in the process that intense electron beam accelerator is running with pseudo load may cause the computer to be black screen. The mechanism of electromagnetic radiation induced by the triggered spark-gap switch and main switch is analyzed carefully in this paper. The charging gap of the gas-gap switches is equivalent to electric dipole, and the spatial distribution of the radiation is analyzed theoretically. The radiation signals of the triggered spark-gap switch and main switch are measured, and the result shows that the theoretical analysis is reasonable. At last, the coaxial cable is used to evaluate the interference of the radiation. At the moment that the radiation signal generates in the intense electron beam accelerator, the induced voltage in the coaxial cable reaches to nearly 3 V, which could cause inaccuracy in the measurement of other signals.
2013,
25: 1059-1062.
Abstract:
A four-gap, rail gas switch for fast linear transformer drivers (LTDs) has been developed to be of low jitter and low inductance, by using four horizontal gaps constructed by rail electrodes. The electric field of the switch and the hold-off voltage of the single gap of 8 mm were calculated by using electric field numerical simulation and Meeks Criterion analysis, respectively. A probability analysis method, for predicting self-breakdown voltages of a switch consisting of several gaps in series, is put forward. The calculated self-breakdown voltages were in agreement with the experimental results. The switch inductance of no more than 109 nH provides the LTD brick a measured inductance of 290 nH. The relative standard deviation of self-breakdown voltage is about 1.5%. Under a 60 kV forward voltage pulse, the switch with 48%-74% voltage ratio has a close jitter of 0.9-2.6 ns. Compared with a previously developed switch with toroidal electrodes, the rail gas switch has a lower trigger voltage and self-breakdown stability while operating at the same voltage ratio.
A four-gap, rail gas switch for fast linear transformer drivers (LTDs) has been developed to be of low jitter and low inductance, by using four horizontal gaps constructed by rail electrodes. The electric field of the switch and the hold-off voltage of the single gap of 8 mm were calculated by using electric field numerical simulation and Meeks Criterion analysis, respectively. A probability analysis method, for predicting self-breakdown voltages of a switch consisting of several gaps in series, is put forward. The calculated self-breakdown voltages were in agreement with the experimental results. The switch inductance of no more than 109 nH provides the LTD brick a measured inductance of 290 nH. The relative standard deviation of self-breakdown voltage is about 1.5%. Under a 60 kV forward voltage pulse, the switch with 48%-74% voltage ratio has a close jitter of 0.9-2.6 ns. Compared with a previously developed switch with toroidal electrodes, the rail gas switch has a lower trigger voltage and self-breakdown stability while operating at the same voltage ratio.
2013,
25: 1063-1067.
Abstract:
A nanosecond pulsed power source based on GaAs photoconductive semiconductor switches (PCSSs) and stacked Blumlein line was developed. The pulsed power source consists of four stages of plate Blumlein line, and high-density polyethylene is adopted for energy storage. The full-circuit PSpice model of the pulsed power source with actual circuit parameters was established. Two vertical PCSSs with electrode gaps being 3 mm and 10 mm wide were used. Simulation results and experimental results are given. The rise time of the 10 mm-gap switch at 23.5 kV in experiment is larger than that in simulation. A possible reason is that the transition time of the 10 mm-gap PCSS becomes larger at lower bias electric field. The experiments indicate that the output voltages are respectively up to 39.4 kV and 53 kV with charging voltages up to 13.9 kV for the 3 mm-gap PCSS and 23.5 kV for the 10 mm-gap PCSS. The voltage efficiency with the 3mm-gap PCSS in the above condition is up to 70%. In addition, the voltage efficiency drops firstly and then rises gradually to saturation as the bias enhances.
A nanosecond pulsed power source based on GaAs photoconductive semiconductor switches (PCSSs) and stacked Blumlein line was developed. The pulsed power source consists of four stages of plate Blumlein line, and high-density polyethylene is adopted for energy storage. The full-circuit PSpice model of the pulsed power source with actual circuit parameters was established. Two vertical PCSSs with electrode gaps being 3 mm and 10 mm wide were used. Simulation results and experimental results are given. The rise time of the 10 mm-gap switch at 23.5 kV in experiment is larger than that in simulation. A possible reason is that the transition time of the 10 mm-gap PCSS becomes larger at lower bias electric field. The experiments indicate that the output voltages are respectively up to 39.4 kV and 53 kV with charging voltages up to 13.9 kV for the 3 mm-gap PCSS and 23.5 kV for the 10 mm-gap PCSS. The voltage efficiency with the 3mm-gap PCSS in the above condition is up to 70%. In addition, the voltage efficiency drops firstly and then rises gradually to saturation as the bias enhances.
2013,
25: 1068-1072.
Abstract:
In order to reduce the time-domain simulation time of reverberation chamber (RC), this paper investigates the means to predict time-domain responses of RC. A new kind of matrix pencil method (MPM) is proposed based on the modified MPM. Using the proposed method, a fitting formula for the former part of time-domain responses can be determined, which could be used to predict the later part. When the pencil ratio parameter is 0.62, acceptable results can be obtained using the first 20 000 original records to predict the following 20 000 responses. The relative error between the original and the semi-original semi-predicted signals in frequency domain can be guaranteed below 15%. In this way, the simulation time could be saved about 50% compared to the ordinary
In order to reduce the time-domain simulation time of reverberation chamber (RC), this paper investigates the means to predict time-domain responses of RC. A new kind of matrix pencil method (MPM) is proposed based on the modified MPM. Using the proposed method, a fitting formula for the former part of time-domain responses can be determined, which could be used to predict the later part. When the pencil ratio parameter is 0.62, acceptable results can be obtained using the first 20 000 original records to predict the following 20 000 responses. The relative error between the original and the semi-original semi-predicted signals in frequency domain can be guaranteed below 15%. In this way, the simulation time could be saved about 50% compared to the ordinary
