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RSS2010 Vol. 22, No. 05
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2010,
22.
Abstract:
A “one pot” procedure of synthesis of GeO2/SiO2 binary composite aerogel was presented. The precursors of GeO2 and SiO2 were vigorously stirred into homogenous mixture in alcohol solution and the stoichiometric calculation water was added to co-hydrolyze the solution at 0 ℃. After the clear sol obtained, ammonium was introduced into the sol to gelatinize the system. The solvent in gel pores was removed by supercritical CO2 to prepare composite aerogels. The as-synthesized aerogels were characterized by field-emission scanning electron microscopy(FESEM), high-resolution transmission electron microscopy(HRTEM) and Brunauer-Emmett-Teller(BET) N2 isothermal adsorption method. The FESEM micrograph shows that, the aerogels are made up of
A “one pot” procedure of synthesis of GeO2/SiO2 binary composite aerogel was presented. The precursors of GeO2 and SiO2 were vigorously stirred into homogenous mixture in alcohol solution and the stoichiometric calculation water was added to co-hydrolyze the solution at 0 ℃. After the clear sol obtained, ammonium was introduced into the sol to gelatinize the system. The solvent in gel pores was removed by supercritical CO2 to prepare composite aerogels. The as-synthesized aerogels were characterized by field-emission scanning electron microscopy(FESEM), high-resolution transmission electron microscopy(HRTEM) and Brunauer-Emmett-Teller(BET) N2 isothermal adsorption method. The FESEM micrograph shows that, the aerogels are made up of
2010,
22.
Abstract:
The perfectly matched layer(PML) medium equations for Gaussian unit were derived based on the basic idea of Benrenger’s PML and the numerical validation and parameter optimization were done. The corresponding absorbing boundary module was added into the 2D3V PIC software PLASIM, achieving good absorption with low reflection. In addition, this module is proved applicable by simulating the propagation of a nanosecond laser prepulse in an underdense plasma.
The perfectly matched layer(PML) medium equations for Gaussian unit were derived based on the basic idea of Benrenger’s PML and the numerical validation and parameter optimization were done. The corresponding absorbing boundary module was added into the 2D3V PIC software PLASIM, achieving good absorption with low reflection. In addition, this module is proved applicable by simulating the propagation of a nanosecond laser prepulse in an underdense plasma.
2010,
22.
Abstract:
Good radiation-driven symmetry is crucial for forming center hot spot in the indirect-driven inertial fusion. In this paper, our goal is to assess quantitatively the impacts of the radiation-driven asymmetry on the capsule compression. For the time-independent asymmetry, the 2D simulations show that the impact of the radiation-driven asymmetry on the capsule distortion and neutron yield will reduce as the convergence ratio of the capsule decreases. The neutron yield will degrade by 30% when the capsule distortion is about 2.0. In the hohlraums utilized in experiments, the asymmetry varies in space and time with different hohlraum lengths. For the length of 1 350 μm, the subsequent reversal of flux nonuniformity will be adequate to eliminate the effects of the earlier asymmetry, thus the c
Good radiation-driven symmetry is crucial for forming center hot spot in the indirect-driven inertial fusion. In this paper, our goal is to assess quantitatively the impacts of the radiation-driven asymmetry on the capsule compression. For the time-independent asymmetry, the 2D simulations show that the impact of the radiation-driven asymmetry on the capsule distortion and neutron yield will reduce as the convergence ratio of the capsule decreases. The neutron yield will degrade by 30% when the capsule distortion is about 2.0. In the hohlraums utilized in experiments, the asymmetry varies in space and time with different hohlraum lengths. For the length of 1 350 μm, the subsequent reversal of flux nonuniformity will be adequate to eliminate the effects of the earlier asymmetry, thus the c
2010,
22.
Abstract:
A relatively simple and accurate photometric method was presented to calculate the optical constants of the weak absorption coatings on weak absorption substrate materials . And the optical constants of the JGS1 fused silica substrate, MgF2 and LaF3 films were calculated according to the above method. The results show that, at the wavelength of 200 nm, the absorption of the JGS1 fused silica substrate is relatively obvious with the extinction coefficient of 10-8 level. Therefore, the weak absorption of the substrate should be taken into account to improve the calculation precision of the film’s optical constants.
A relatively simple and accurate photometric method was presented to calculate the optical constants of the weak absorption coatings on weak absorption substrate materials . And the optical constants of the JGS1 fused silica substrate, MgF2 and LaF3 films were calculated according to the above method. The results show that, at the wavelength of 200 nm, the absorption of the JGS1 fused silica substrate is relatively obvious with the extinction coefficient of 10-8 level. Therefore, the weak absorption of the substrate should be taken into account to improve the calculation precision of the film’s optical constants.
2010,
22.
Abstract:
In order to study the effects of CO2 laser pretreatment parameters on surface roughness of fused silica, the fused silica samples were irradiated by a 100 Hz CO2 laser with a spot size of 1 mm2. Repairing degrees were defined as mild, moderate and severe. Surface roughnesses under different repairing degrees were statistically studied. Besides, surface roughness was investigated for the samples after single shot irradiation by CO2 laser at different pulse durations and duty cycles. The results show that the sample’s surface roughness and crater depth increase with the increasing duration and duty cycle. The rate of increase rises gradually as the duration increases, while descends gradually as the duty cycle increases.
In order to study the effects of CO2 laser pretreatment parameters on surface roughness of fused silica, the fused silica samples were irradiated by a 100 Hz CO2 laser with a spot size of 1 mm2. Repairing degrees were defined as mild, moderate and severe. Surface roughnesses under different repairing degrees were statistically studied. Besides, surface roughness was investigated for the samples after single shot irradiation by CO2 laser at different pulse durations and duty cycles. The results show that the sample’s surface roughness and crater depth increase with the increasing duration and duty cycle. The rate of increase rises gradually as the duration increases, while descends gradually as the duty cycle increases.
2010,
22.
Abstract:
Numerical simulations have been conducted on the propagation of a long proton beam in the background plasma with the help of 2D3V PIC code. The simulations show that the plasma improves the propagation of the proton beam obviously. And for long distance propagation, the proton beam has a more stationary profile when propagating in the bulk plasma compared to propagating in the plasma slab. The plasma wave excited by the beam can modulate the density of the proton beam, influencing the beam’s stable propagation, and the results of the simulations confirm that the proton beam with a smooth edge-density profile can minimize the excitation of plasma waves．
Numerical simulations have been conducted on the propagation of a long proton beam in the background plasma with the help of 2D3V PIC code. The simulations show that the plasma improves the propagation of the proton beam obviously. And for long distance propagation, the proton beam has a more stationary profile when propagating in the bulk plasma compared to propagating in the plasma slab. The plasma wave excited by the beam can modulate the density of the proton beam, influencing the beam’s stable propagation, and the results of the simulations confirm that the proton beam with a smooth edge-density profile can minimize the excitation of plasma waves．
2010,
22.
Abstract:
Ray trace and filtered random phase can be used as initial phase to design continuous phase plates (CPPs).The performance of the CPPs designed with the two ways was studied. The results show that the CPP with filtered random phase as initial phase has better defocusing and amplitude aberration tolerance compared with that with ray trace as initial phase. What’s more, wavefront aberration is the primary factor affecting the CPP’s performance and the tolerance to it is related with focal spot size. Thus relative phase aberration factor was introduced to quantify wavefront aberration and focal spot size and with the defined CPP performance standard the tolerance was 0.5 aberration factor.
Ray trace and filtered random phase can be used as initial phase to design continuous phase plates (CPPs).The performance of the CPPs designed with the two ways was studied. The results show that the CPP with filtered random phase as initial phase has better defocusing and amplitude aberration tolerance compared with that with ray trace as initial phase. What’s more, wavefront aberration is the primary factor affecting the CPP’s performance and the tolerance to it is related with focal spot size. Thus relative phase aberration factor was introduced to quantify wavefront aberration and focal spot size and with the defined CPP performance standard the tolerance was 0.5 aberration factor.
2010,
22.
Abstract:
The glow discharge polymer (GDP) coating were prepared by low-pressure plasma chemical vapor deposition (LPPCVD) at different T2B/H2 flow ratios varying from 0.04 to 3.00. The hydrogen bonding and microstructure of GDP coatings were studied by Fourier transform infrared absorption spectroscopy. The ratio of C(sp2)-Hx to C(sp3)-Hx decreases as the T2B/H2 flow ratio increases. The thermal properties of the coatings were investigated by thermogravimetry at a high purity argon atmosphere. The influence of the T2B/H2 flow ratio on the thermal stability of GDP coatings was discussed. It is found that the thermal stability deteriorates with increasing the T2B/H2 flow ratio. The GDP coatin
The glow discharge polymer (GDP) coating were prepared by low-pressure plasma chemical vapor deposition (LPPCVD) at different T2B/H2 flow ratios varying from 0.04 to 3.00. The hydrogen bonding and microstructure of GDP coatings were studied by Fourier transform infrared absorption spectroscopy. The ratio of C(sp2)-Hx to C(sp3)-Hx decreases as the T2B/H2 flow ratio increases. The thermal properties of the coatings were investigated by thermogravimetry at a high purity argon atmosphere. The influence of the T2B/H2 flow ratio on the thermal stability of GDP coatings was discussed. It is found that the thermal stability deteriorates with increasing the T2B/H2 flow ratio. The GDP coatin
2010,
22.
Abstract:
A simple method is introduced to reconstruct the nearfield wave-front from intensity distribution near foal plane, which is treated in this paper as an optimization problem. Proper orthogonal decomposition technique is applied to describe the wave-front to be reconstructed. By optimizing the coefficients of the polynomial to minimize the differences between simulated intensity distributions and the real intensity distributions, nearfield wave-front can be reconstructed and characterized. Simulations are carried out upon square-aperture beam using Legendre polynomial. Conjugate gradient method is used and optimization is performed for several steps to reduce executing time. The results show that the reconstructed wave-front are consistent well with the reference wave-front.
A simple method is introduced to reconstruct the nearfield wave-front from intensity distribution near foal plane, which is treated in this paper as an optimization problem. Proper orthogonal decomposition technique is applied to describe the wave-front to be reconstructed. By optimizing the coefficients of the polynomial to minimize the differences between simulated intensity distributions and the real intensity distributions, nearfield wave-front can be reconstructed and characterized. Simulations are carried out upon square-aperture beam using Legendre polynomial. Conjugate gradient method is used and optimization is performed for several steps to reduce executing time. The results show that the reconstructed wave-front are consistent well with the reference wave-front.
2010,
22.
Abstract:
A view-factor method for calculating the radiation drive from hohlraum walls to the capsule in indirect inertial confinement fusion (ICF) has been presented, with which asymmetry conditions for implosion experiments on laser prototype were evaluated. X-ray intensity distribution on the hohlraum walls was calculated as well as the radiation drive on the capsule located in the center of the cylindrical gold target. The drive nonuniformity varying with the laser-spot locus and the hohlraum geometry were also given. The results show that this method helps to assess the main parameters of indirect ICF targets and provides useful information for experiment design.
A view-factor method for calculating the radiation drive from hohlraum walls to the capsule in indirect inertial confinement fusion (ICF) has been presented, with which asymmetry conditions for implosion experiments on laser prototype were evaluated. X-ray intensity distribution on the hohlraum walls was calculated as well as the radiation drive on the capsule located in the center of the cylindrical gold target. The drive nonuniformity varying with the laser-spot locus and the hohlraum geometry were also given. The results show that this method helps to assess the main parameters of indirect ICF targets and provides useful information for experiment design.
2010,
22.
Abstract:
The influence of Coulomb damping on vibration absorber. The model of Coulomb damping was introduced concerning Coulomb damping in the vibration absorber, two relative motions between the master vibration system and the addition mass, sticking and sliding, were analyzed, and the conditions in which two motions and alternate were discussed, as well as the freezing of the degree of freedom due to coulomb damping. Numerical simulation was conducted using Simulink of MATLAB to study the vibration absorbing excited by harmonic and white noise and the equivalence between coulomb damping and linear damping.
The influence of Coulomb damping on vibration absorber. The model of Coulomb damping was introduced concerning Coulomb damping in the vibration absorber, two relative motions between the master vibration system and the addition mass, sticking and sliding, were analyzed, and the conditions in which two motions and alternate were discussed, as well as the freezing of the degree of freedom due to coulomb damping. Numerical simulation was conducted using Simulink of MATLAB to study the vibration absorbing excited by harmonic and white noise and the equivalence between coulomb damping and linear damping.
2010,
22.
Abstract:
Using tetraethoxylsilane as precursor and ammonia as catalyst, the fluoroalkylsilane was doped when the silica sol was growing, and the fluorin-doped silica antireflective coating was prepared by sol-gel process on K9 substrate. The properties of the coatings with and without fluorin were characterized with infared spectrometer, spectrophotometer, atomic force microscope, ellipsometer, contact angle measurement and N2-adsorption/desorption analysis. The results indicate that the peak transmittance of the fluorin-doped coating is 99.7%, and its water contact angle and polydimethyl siloxane oil contact angle are 129° and 86°, respectively. The contamination-resistant capability of the fluorin-doped antireflective coating is much better than the common one．
Using tetraethoxylsilane as precursor and ammonia as catalyst, the fluoroalkylsilane was doped when the silica sol was growing, and the fluorin-doped silica antireflective coating was prepared by sol-gel process on K9 substrate. The properties of the coatings with and without fluorin were characterized with infared spectrometer, spectrophotometer, atomic force microscope, ellipsometer, contact angle measurement and N2-adsorption/desorption analysis. The results indicate that the peak transmittance of the fluorin-doped coating is 99.7%, and its water contact angle and polydimethyl siloxane oil contact angle are 129° and 86°, respectively. The contamination-resistant capability of the fluorin-doped antireflective coating is much better than the common one．
2010,
22.
Abstract:
In the stability design of a high-power laser facility, if equiprobable allocation results are chosen as the stability design indexes, there are often much difficulty in structure design and great waste in building. Thus, a stability reallocation way based on the finite element analysis (FEA) is put forward. That is, computing the linear weighted coefficients with the target orientation errors brought by the vibration responses of optical elements in a beam, and then reallocating the stability indexes by the linear weighted method. The safety factors are equal in the beam after the reallocation. Stability indexes in a beam of centain large laser facility’s target area are reallocated by this method, and all beams’ safety factors are 1.229, satisfying the requirement of stability design.
In the stability design of a high-power laser facility, if equiprobable allocation results are chosen as the stability design indexes, there are often much difficulty in structure design and great waste in building. Thus, a stability reallocation way based on the finite element analysis (FEA) is put forward. That is, computing the linear weighted coefficients with the target orientation errors brought by the vibration responses of optical elements in a beam, and then reallocating the stability indexes by the linear weighted method. The safety factors are equal in the beam after the reallocation. Stability indexes in a beam of centain large laser facility’s target area are reallocated by this method, and all beams’ safety factors are 1.229, satisfying the requirement of stability design.
2010,
22.
Abstract:
Based on home-made amorphous cores and semiconductor switch, an all-solid-state exciter(ASSE) for pumping a corona preionized mini TEA CO2 laser has been developed, which uses silicon controlled rectifier, pulse transformer and a two-stage magnetic pulse compression system. Analysis and measurements of energy transfer efficiency are made to optimize system performance and minimize system volume. Energy transfer efficiency is over 83% for the magnetic pulse compression, and over 75% for the ASSE. Interfacing to the laser with discharge volume of 29 cm3， at 100 kPa, 22 kV discharge peak voltage and 100 ns discharge current rise time are observed. Output laser pulse with energy of 109 mJ and pulse width of 70 ns is gained. The laser is capable of operating at 100 Hz und
Based on home-made amorphous cores and semiconductor switch, an all-solid-state exciter(ASSE) for pumping a corona preionized mini TEA CO2 laser has been developed, which uses silicon controlled rectifier, pulse transformer and a two-stage magnetic pulse compression system. Analysis and measurements of energy transfer efficiency are made to optimize system performance and minimize system volume. Energy transfer efficiency is over 83% for the magnetic pulse compression, and over 75% for the ASSE. Interfacing to the laser with discharge volume of 29 cm3， at 100 kPa, 22 kV discharge peak voltage and 100 ns discharge current rise time are observed. Output laser pulse with energy of 109 mJ and pulse width of 70 ns is gained. The laser is capable of operating at 100 Hz und
2010,
22.
Abstract:
This paper presents fundamental theory on how to synchronize and control signals with different frequency in TW Ti:sapphire amplifier, and introduces three homemade TW laser systems with different repetition rate. Both Jiguang Ⅱ and Titan are two-stage amplifier, in former system, both pre-amplifier and main amplifier operate at same repetition rate of 10 Hz; in latter one, pre-amplifier operates at 1 kHz and main amplifier at 10 Hz repetition rate. Jiguang Ⅲ is multi-stage amplifier, in which pre-amplifier operates at 10 Hz, 1st-satge main amplifier 1 Hz and 2nd-stage one single shot every 15 min. The synchronization systems are specially designed for controlling above three TW laser systems, which enable these amplifiers working stably with synchronization precision up to 200 ps．
This paper presents fundamental theory on how to synchronize and control signals with different frequency in TW Ti:sapphire amplifier, and introduces three homemade TW laser systems with different repetition rate. Both Jiguang Ⅱ and Titan are two-stage amplifier, in former system, both pre-amplifier and main amplifier operate at same repetition rate of 10 Hz; in latter one, pre-amplifier operates at 1 kHz and main amplifier at 10 Hz repetition rate. Jiguang Ⅲ is multi-stage amplifier, in which pre-amplifier operates at 10 Hz, 1st-satge main amplifier 1 Hz and 2nd-stage one single shot every 15 min. The synchronization systems are specially designed for controlling above three TW laser systems, which enable these amplifiers working stably with synchronization precision up to 200 ps．
2010,
22.
Abstract:
Anderson's relaxation model of two modes and three vibrational temperatures was combined with Yan Haixing’s vibrational relaxation data to simulate 2D non-equilibrium nozzle flows in a gasdynamic laser. Two different minimum-length nozzles with supersonic area ratios of 50∶1 and 20∶1 were studied by numerically solving the conservational equations. The small signal gains of the simulation results agree very well with J. S. Vamos's experiments for both nozzles. This analysis method solves the problem of matching the non-equilibrium nozzle flow analysis results of gasdynamic laser nozzles with the experimental data, which conventional quasi-one-dimensional simulation cannot do well. By this way, highly accurate method of evaluating a gasdynamic laser nozzle’s performance was realized.
Anderson's relaxation model of two modes and three vibrational temperatures was combined with Yan Haixing’s vibrational relaxation data to simulate 2D non-equilibrium nozzle flows in a gasdynamic laser. Two different minimum-length nozzles with supersonic area ratios of 50∶1 and 20∶1 were studied by numerically solving the conservational equations. The small signal gains of the simulation results agree very well with J. S. Vamos's experiments for both nozzles. This analysis method solves the problem of matching the non-equilibrium nozzle flow analysis results of gasdynamic laser nozzles with the experimental data, which conventional quasi-one-dimensional simulation cannot do well. By this way, highly accurate method of evaluating a gasdynamic laser nozzle’s performance was realized.
2010,
22.
Abstract:
The principle, structure and parameters of the diode-laser lidar used to measure visibility were introduced, and a steady iteration algorithm was proposed to calculate the extinction coefficient. The intercomparison experiment with this lidar and the Belfort model 6230A made in America was conducted for horizontal and slant visibility detection. The results show that the possibilities of average relative error below 10%, 20% and 30% for horizontal visibility measurements are 45.6%, 84.7% and 91.2%, respectively. For slant visibility measurement, the change of the visibility is obvious, which demonstrates the difference and significance of the slant and horizontal visibility measurements on various weather conditions. It is sufficiently shown that this lidar system is capable of measuring t
The principle, structure and parameters of the diode-laser lidar used to measure visibility were introduced, and a steady iteration algorithm was proposed to calculate the extinction coefficient. The intercomparison experiment with this lidar and the Belfort model 6230A made in America was conducted for horizontal and slant visibility detection. The results show that the possibilities of average relative error below 10%, 20% and 30% for horizontal visibility measurements are 45.6%, 84.7% and 91.2%, respectively. For slant visibility measurement, the change of the visibility is obvious, which demonstrates the difference and significance of the slant and horizontal visibility measurements on various weather conditions. It is sufficiently shown that this lidar system is capable of measuring t
2010,
22.
Abstract:
CO2 laser was utilized to clean the dimethylsilicone contamination on the surface of gilded K9 glass. In the case of point to point laser cleaning, the effects of laser power and radiation time were studied, respectively. Then the laser cleaning effect was studied in the scanning mode. Optical microscope and Fourier transform infrared spectrometer were used to characterize the cleaning effects. The results showed that CO2 laser could effectively remove the dimethylsilicone by properly controlling the laser parameters. In addition, this non-contact cleaning method can clean the gold films on the K9 glass without damage. Finite element analysis code was used to simulate the effects of laser power and radiation time on the temperature of samples. The simulation results w
CO2 laser was utilized to clean the dimethylsilicone contamination on the surface of gilded K9 glass. In the case of point to point laser cleaning, the effects of laser power and radiation time were studied, respectively. Then the laser cleaning effect was studied in the scanning mode. Optical microscope and Fourier transform infrared spectrometer were used to characterize the cleaning effects. The results showed that CO2 laser could effectively remove the dimethylsilicone by properly controlling the laser parameters. In addition, this non-contact cleaning method can clean the gold films on the K9 glass without damage. Finite element analysis code was used to simulate the effects of laser power and radiation time on the temperature of samples. The simulation results w
2010,
22.
Abstract:
This paper proposes the novel concept of coherent beam combining using stimulated annealing algorithm. Numerical simulation on coherent beam combining of multiple fiber amplifiers is carried out; the dependence of convergence rate on laser numbers is analyzed. Coherent beam combining of two watt-level fiber amplifiers is experimentally achieved. Experimental result shows that the whole system in close-loop performs well for long-time observation. The average energy encircled in the target pinhole is 1.8 times higher than that in the case of open-loop. The probability of energy encircled in the main-lobe to be more than 80% of its ideal value is increased from 19.4% to 51.3% when the system evolves from open-loop to close-loop.
This paper proposes the novel concept of coherent beam combining using stimulated annealing algorithm. Numerical simulation on coherent beam combining of multiple fiber amplifiers is carried out; the dependence of convergence rate on laser numbers is analyzed. Coherent beam combining of two watt-level fiber amplifiers is experimentally achieved. Experimental result shows that the whole system in close-loop performs well for long-time observation. The average energy encircled in the target pinhole is 1.8 times higher than that in the case of open-loop. The probability of energy encircled in the main-lobe to be more than 80% of its ideal value is increased from 19.4% to 51.3% when the system evolves from open-loop to close-loop.
2010,
22.
Abstract:
A high-resolution and long working distance digital holographic microscopy is proposed based on synthetic aperture method. A series of digital holograms are successively recorded, which cover different spatial frequency ranges scattered from the object, with different tilted object illuminations. Subsequently, the intensity image is numerically reconstructed and magnified for each digital hologram. Finally, a synthetic image with the resolution improved and speckle noise suppressed is obtained by synthesizing the reconstructed images. The theory and experimental results show that the proposed method can be easily used in in-situ microscopy at a long working distance.
A high-resolution and long working distance digital holographic microscopy is proposed based on synthetic aperture method. A series of digital holograms are successively recorded, which cover different spatial frequency ranges scattered from the object, with different tilted object illuminations. Subsequently, the intensity image is numerically reconstructed and magnified for each digital hologram. Finally, a synthetic image with the resolution improved and speckle noise suppressed is obtained by synthesizing the reconstructed images. The theory and experimental results show that the proposed method can be easily used in in-situ microscopy at a long working distance.
2010,
22.
Abstract:
The selection of atmospheric model and aerosol type is very important in the radiation transfer calculation of quantitative remote sensing. However, the selection is commonly empiric, and its influence on the calculation is usually neglected. Thus a method based on the measurement of sun photometer was proposed to study the selection of atmospheric model and aerosol type. Meanwhile, a calibrated spectral radiometer was used to measure the spectral radiance to check the results above at the ground level. Experiments have been done in Kunming. Choosing middle altitude summer atmospheric and land aerosol type, the relative error between calculation and measurement is below 3.3% in the spectral range of 0.50 to 0.68 μm. Changing atmospheric model only, the relative error can be up to 10%, whi
The selection of atmospheric model and aerosol type is very important in the radiation transfer calculation of quantitative remote sensing. However, the selection is commonly empiric, and its influence on the calculation is usually neglected. Thus a method based on the measurement of sun photometer was proposed to study the selection of atmospheric model and aerosol type. Meanwhile, a calibrated spectral radiometer was used to measure the spectral radiance to check the results above at the ground level. Experiments have been done in Kunming. Choosing middle altitude summer atmospheric and land aerosol type, the relative error between calculation and measurement is below 3.3% in the spectral range of 0.50 to 0.68 μm. Changing atmospheric model only, the relative error can be up to 10%, whi
2010,
22.
Abstract:
In order to evaluate the performance of the gain generator in a chemical laser, the small signal gain has been measured using the variable output coupling method. The stable resonator was composed of two mirrors, one concave mirror and one outcoupling mirror. The ternary coupling problem about saturation intensity, non-output wasting and small signal gain in measured data was translated into a dualistic numerical problem. Processing results, which met engineering requirements, were derived through numerical fitting, and the errors in experiment and data processing were analyzed. Through the variance analysis, it was found that the fitting curves of the average two accorded with experiment results better than the fitting curves of the average one. There existed a maximum output power in the
In order to evaluate the performance of the gain generator in a chemical laser, the small signal gain has been measured using the variable output coupling method. The stable resonator was composed of two mirrors, one concave mirror and one outcoupling mirror. The ternary coupling problem about saturation intensity, non-output wasting and small signal gain in measured data was translated into a dualistic numerical problem. Processing results, which met engineering requirements, were derived through numerical fitting, and the errors in experiment and data processing were analyzed. Through the variance analysis, it was found that the fitting curves of the average two accorded with experiment results better than the fitting curves of the average one. There existed a maximum output power in the
2010,
22.
Abstract:
The thermal-mechanical response of the internally pressured cylindrical shell under laser irradiation is simulated by finite element method. Under different working conditions, the temperature and stress distributions of the cylindrical shell are gained, and the failure time of the shell is determined according to the theory of material strength. A numerical method is put forward to predicting the failure energy threshold of the cylindrical shell under laser irradiation. The influences of shell thickness and internal pressure on the failure energy threshold are investigated, and the relationship between the failure energy threshold of the cylindrical shell and the two parameters are given. It is found that failure energy threshold has an approximately linear relation with shell thickness a
The thermal-mechanical response of the internally pressured cylindrical shell under laser irradiation is simulated by finite element method. Under different working conditions, the temperature and stress distributions of the cylindrical shell are gained, and the failure time of the shell is determined according to the theory of material strength. A numerical method is put forward to predicting the failure energy threshold of the cylindrical shell under laser irradiation. The influences of shell thickness and internal pressure on the failure energy threshold are investigated, and the relationship between the failure energy threshold of the cylindrical shell and the two parameters are given. It is found that failure energy threshold has an approximately linear relation with shell thickness a
2010,
22.
Abstract:
By the very high speed camera technology and numerical calculation, the relation between dimensionless distance and bubble dynamics in a rigid half sphere is determined. The conception of optimum dimensionless distance is presented, and the conflict between cavitation erosion and utility ratio of sound energy is solved. The result shows that, when the ratio of the half sphere radius to the maximum bubble radius is smaller than 1.1, the laser-induced bubble will jump out of the half sphere in the first expanding, and cavitation may appear. The cavitation bubble and cavitation erosion have adverse effects on the transmission of the laser-induced sound. When the ratio is bigger than 1.1 and smaller than 3.3, the laser induced bubble will meet the half sphere before the third collapsing, which
By the very high speed camera technology and numerical calculation, the relation between dimensionless distance and bubble dynamics in a rigid half sphere is determined. The conception of optimum dimensionless distance is presented, and the conflict between cavitation erosion and utility ratio of sound energy is solved. The result shows that, when the ratio of the half sphere radius to the maximum bubble radius is smaller than 1.1, the laser-induced bubble will jump out of the half sphere in the first expanding, and cavitation may appear. The cavitation bubble and cavitation erosion have adverse effects on the transmission of the laser-induced sound. When the ratio is bigger than 1.1 and smaller than 3.3, the laser induced bubble will meet the half sphere before the third collapsing, which
2010,
22.
Abstract:
The generation of proton beams from thin-foil targets on SILEX-Ⅰ is studied. It shows that prepulse has a profound effect on the maximum proton energy. The thinner the target is, the more sensitive it is to the prepulse. Under the laser intensity of 1018 to 3×1019 W/cm2, the maximum proton energy is 0.54 MeV with 190 nm CH target and 3.15 MeV with 3 μm Cu target (back surface plated with 4 μm CH) respectively. Besides, the effect of laser polarization on proton acceleration is also studied. The maximum proton energy accelerated by a circularly polarized laser pulse is a little lower than that by a P-polarized laser pulse with the same laser power density. The mechanism is consistent with target normal sheath acceleration.
The generation of proton beams from thin-foil targets on SILEX-Ⅰ is studied. It shows that prepulse has a profound effect on the maximum proton energy. The thinner the target is, the more sensitive it is to the prepulse. Under the laser intensity of 1018 to 3×1019 W/cm2, the maximum proton energy is 0.54 MeV with 190 nm CH target and 3.15 MeV with 3 μm Cu target (back surface plated with 4 μm CH) respectively. Besides, the effect of laser polarization on proton acceleration is also studied. The maximum proton energy accelerated by a circularly polarized laser pulse is a little lower than that by a P-polarized laser pulse with the same laser power density. The mechanism is consistent with target normal sheath acceleration.
2010,
22.
Abstract:
An ant colony algorithm is presented for infrared image segmentation. The core idea is to use the fuzzy membership function as enlightening information, which guides the ant colony with the pheromone together. By updating the distribution of pheromones on the routes that the ants have passed, the pheromones on the target route are increased, and the searching routes will converge on the segmented image progressively. Finally, the segmentation results can be extracted according to the intensity of the pheromones. Simulations and experiments show that the infrared image can be segmented well.
An ant colony algorithm is presented for infrared image segmentation. The core idea is to use the fuzzy membership function as enlightening information, which guides the ant colony with the pheromone together. By updating the distribution of pheromones on the routes that the ants have passed, the pheromones on the target route are increased, and the searching routes will converge on the segmented image progressively. Finally, the segmentation results can be extracted according to the intensity of the pheromones. Simulations and experiments show that the infrared image can be segmented well.
2010,
22.
Abstract:
To reduce the high dynamic range requirement on high speed amplifier, a probe for measuring the far field characteristics of narrow pulsed laser was designed based on using double detectors instead of the traditional single detector. From radiometric analysis on the probe’s optical structure, the illuminance transfer coefficient was deduced when the probe was irradiated evenly, and the model’s possible maximal error was also investigated when the probe was irradiated unevenly. From the aspect of minimizing the model’s error, both increasing the distance between translucent ceramic and detector and reducing the aperture are helpful, and reducing the two detectors’ abaxial distance can improve their measurement uniformity. The test result using 10 ns-width 1.064 μm laser shows that, the
To reduce the high dynamic range requirement on high speed amplifier, a probe for measuring the far field characteristics of narrow pulsed laser was designed based on using double detectors instead of the traditional single detector. From radiometric analysis on the probe’s optical structure, the illuminance transfer coefficient was deduced when the probe was irradiated evenly, and the model’s possible maximal error was also investigated when the probe was irradiated unevenly. From the aspect of minimizing the model’s error, both increasing the distance between translucent ceramic and detector and reducing the aperture are helpful, and reducing the two detectors’ abaxial distance can improve their measurement uniformity. The test result using 10 ns-width 1.064 μm laser shows that, the
2010,
22.
Abstract:
The dispersion curves of the coaxial slow-wave structure (SWS) with the trapezoidal corrugation are obtained by numerical calculation. The electric field vector of π mode of the quasi-TEM mode and the influence of the inner-conductor radius on resonance frequency are calculated using the electromagnetic software Superfish. In addition, a compact L-band relativistic backward wave oscillator (RBWO) is investigated and optimized in detail with particle-in-cell (PIC) methods (Karat code) to explain effects of the inner-conductor radius. In experiment, the operation frequencies are 1.64 GHz, 1.63 GHz and 1.61 GHz when the inner-conductor radii are 0.50 cm, 0.75 cm and 1.00 cm respectiuely, which shows that the operation frequency decreases with the enlargement of the inner-conductor radius. T
The dispersion curves of the coaxial slow-wave structure (SWS) with the trapezoidal corrugation are obtained by numerical calculation. The electric field vector of π mode of the quasi-TEM mode and the influence of the inner-conductor radius on resonance frequency are calculated using the electromagnetic software Superfish. In addition, a compact L-band relativistic backward wave oscillator (RBWO) is investigated and optimized in detail with particle-in-cell (PIC) methods (Karat code) to explain effects of the inner-conductor radius. In experiment, the operation frequencies are 1.64 GHz, 1.63 GHz and 1.61 GHz when the inner-conductor radii are 0.50 cm, 0.75 cm and 1.00 cm respectiuely, which shows that the operation frequency decreases with the enlargement of the inner-conductor radius. T
2010,
22.
Abstract:
A focusing system, consisting of horn antenna and lens, has been designed for the laboratory experiment of millimeter wave induced bioeffects. It adopts quasi-optical techniques, and can operate at 95 GHz and radiate GW-level power. For the millimeter wave source at W-level, the power density and area of its focal spot are 0.01～2 W·cm-2 and 0.8～30 cm2, respectively. In addition, the system has been applied successfully to the laboratory experiment of millimeter wave induced bioeffects.
A focusing system, consisting of horn antenna and lens, has been designed for the laboratory experiment of millimeter wave induced bioeffects. It adopts quasi-optical techniques, and can operate at 95 GHz and radiate GW-level power. For the millimeter wave source at W-level, the power density and area of its focal spot are 0.01～2 W·cm-2 and 0.8～30 cm2, respectively. In addition, the system has been applied successfully to the laboratory experiment of millimeter wave induced bioeffects.
2010,
22.
Abstract:
The one-dimensional microwave photonic crystal (MPC) composed of alternating multilayer media is studied. Transmission matrix technique is used to theoretically analyze the influence of period number, wave incidence angle, medium’s relative dielectric constant and dielectric sheet thickness on its frequency selection characteristics. Finally, a feasible MPC frequency selective surface is designed, whose energy reflectance in 3.2～4.0 GHz and transmittance in 9.5～9.7 GHz are greater than 0.99 and 0.98, respectively.
The one-dimensional microwave photonic crystal (MPC) composed of alternating multilayer media is studied. Transmission matrix technique is used to theoretically analyze the influence of period number, wave incidence angle, medium’s relative dielectric constant and dielectric sheet thickness on its frequency selection characteristics. Finally, a feasible MPC frequency selective surface is designed, whose energy reflectance in 3.2～4.0 GHz and transmittance in 9.5～9.7 GHz are greater than 0.99 and 0.98, respectively.
2010,
22.
Abstract:
The physics of modulation and RF extraction of an S-band, long pulse, relativistic extended-interaction-cavity oscillator (REICO) is studied in this paper via experiment, theory and simulation. The origin of pulse shortening and mode competition of the REICO driven by the long-pulsed intense relativistic electron beams (IREBs) is explored. The modified cavity structure with coupler is proposed for the first time to suppress the pulse shortening and mode competition. The pulse width of the modulated IREBs is increased from 60 ns to 140 ns, and the magnitude of the modulated IREBs is increased from 2 kA to 5 kA. The radiation microwave power and efficiency are promoted obviously after adjusting the parameters of the IREBs and the leading magnetic field. Using a 500 kV, 4.2 kA, 210 ns, 20 Hz
The physics of modulation and RF extraction of an S-band, long pulse, relativistic extended-interaction-cavity oscillator (REICO) is studied in this paper via experiment, theory and simulation. The origin of pulse shortening and mode competition of the REICO driven by the long-pulsed intense relativistic electron beams (IREBs) is explored. The modified cavity structure with coupler is proposed for the first time to suppress the pulse shortening and mode competition. The pulse width of the modulated IREBs is increased from 60 ns to 140 ns, and the magnitude of the modulated IREBs is increased from 2 kA to 5 kA. The radiation microwave power and efficiency are promoted obviously after adjusting the parameters of the IREBs and the leading magnetic field. Using a 500 kV, 4.2 kA, 210 ns, 20 Hz
2010,
22.
Abstract:
The folded waveguide is widely studied in the world due to its broad band. The transition waveguides between folded waveguide slow-wave structure and 8 mm waveguide are studied by using numerical method. Three transition waveguides, i.e. linearly tapered waveguide, dualarc waveguide and Chebyshev stepped waveguide, are designed for millimeter wave folded waveguide traveling wave tubes, and their merits and demerits are analyzed. The relationship between the dimensions and performance of the waveguides is obtained. The simulation results show that the reflectivity is below 0.05 within 28~40 GHz for the three structures with rational optimization．
The folded waveguide is widely studied in the world due to its broad band. The transition waveguides between folded waveguide slow-wave structure and 8 mm waveguide are studied by using numerical method. Three transition waveguides, i.e. linearly tapered waveguide, dualarc waveguide and Chebyshev stepped waveguide, are designed for millimeter wave folded waveguide traveling wave tubes, and their merits and demerits are analyzed. The relationship between the dimensions and performance of the waveguides is obtained. The simulation results show that the reflectivity is below 0.05 within 28~40 GHz for the three structures with rational optimization．
2010,
22.
Abstract:
A novel dual-band feeder is investigated. The structure converts two TM01 modes from two separate non-coaxial microwave sources effectively, and coaxial radiation has been achieved. A dual-bend circular waveguide mode converter is designed with parallel axes of both input and output ports, realizing the conversion from TM10 to TE11 circular waveguide mode at high band. Another mode converter is designed to realize axes superposition of different radiation systems and mode conversion from TM011 to TE11 coaxial waveguide mode based on intermediate TE10 rectangular waveguide mode at low band. Simulations have verified the design.
A novel dual-band feeder is investigated. The structure converts two TM01 modes from two separate non-coaxial microwave sources effectively, and coaxial radiation has been achieved. A dual-bend circular waveguide mode converter is designed with parallel axes of both input and output ports, realizing the conversion from TM10 to TE11 circular waveguide mode at high band. Another mode converter is designed to realize axes superposition of different radiation systems and mode conversion from TM011 to TE11 coaxial waveguide mode based on intermediate TE10 rectangular waveguide mode at low band. Simulations have verified the design.
2010,
22.
Abstract:
A type of bend coaxial waveguide has been proposed. Its application background and principle were introduced, and the design and numerical simulation of a bend coaxial waveguide at the center frequency 4.0 GHz were conducted, as well as the experiment research. The experiment result indicates that, at the center frequency of 4.0 GHz, the loss is about 0.17 dB and the voltage standing wave ratio (VSWR) is about 1.20. In the range of 3.8 GHz to 4.2 GHz, the loss and the VSWR are below 0.20 dB and 1.25 respectively. The bend coaxial waveguide has the advantages of small volume, simple structure, no dielectric support and easy to machining, which can be applied to coaxial waveguide connection and bend in the feed network of high power microwave．
A type of bend coaxial waveguide has been proposed. Its application background and principle were introduced, and the design and numerical simulation of a bend coaxial waveguide at the center frequency 4.0 GHz were conducted, as well as the experiment research. The experiment result indicates that, at the center frequency of 4.0 GHz, the loss is about 0.17 dB and the voltage standing wave ratio (VSWR) is about 1.20. In the range of 3.8 GHz to 4.2 GHz, the loss and the VSWR are below 0.20 dB and 1.25 respectively. The bend coaxial waveguide has the advantages of small volume, simple structure, no dielectric support and easy to machining, which can be applied to coaxial waveguide connection and bend in the feed network of high power microwave．
2010,
22.
Abstract:
A method to widen the microwave spectrum with radiating dual-pulse is presented. Based upon this method, a high power ultrawide band dual-pulse radiating antenna is developed. The antenna consists of a half-paraboloidal reflector, a ground plane, and three TEM horn feeds. Simulation analysis and experiments on the antenna are taken. Short-time Fourier transform (STFT) have been conducted to assist with the characterization of the combined pulses. Results show that the combined radiation pulses more effective to widen the microwave spectrum than a single radiation pulse.
A method to widen the microwave spectrum with radiating dual-pulse is presented. Based upon this method, a high power ultrawide band dual-pulse radiating antenna is developed. The antenna consists of a half-paraboloidal reflector, a ground plane, and three TEM horn feeds. Simulation analysis and experiments on the antenna are taken. Short-time Fourier transform (STFT) have been conducted to assist with the characterization of the combined pulses. Results show that the combined radiation pulses more effective to widen the microwave spectrum than a single radiation pulse.
2010,
22.
Abstract:
Accurate analysis on over voltage in a superconducting magnet during quench process is the basis of quench protection system design for the superconducting magnet. For multi-sectioned superconducting solenoid, based on the classical assumption of ellipsoidal normal zone, three-dimensional temperatures are mapped to one dimension along the conductor and then the temperature distribution along the conductor and the resistances of each turn are obtained. The coil is treated as a circuit composed of turn resistance and turn inductance, and resistive voltage, inductive voltage and resultant voltage along the conductor are calculated, thus the peak coil-to-ground voltage, layer-to-layer voltage and turn-to-turn voltage are better estimated. This method was applied to analysis of a multi-sectione
Accurate analysis on over voltage in a superconducting magnet during quench process is the basis of quench protection system design for the superconducting magnet. For multi-sectioned superconducting solenoid, based on the classical assumption of ellipsoidal normal zone, three-dimensional temperatures are mapped to one dimension along the conductor and then the temperature distribution along the conductor and the resistances of each turn are obtained. The coil is treated as a circuit composed of turn resistance and turn inductance, and resistive voltage, inductive voltage and resultant voltage along the conductor are calculated, thus the peak coil-to-ground voltage, layer-to-layer voltage and turn-to-turn voltage are better estimated. This method was applied to analysis of a multi-sectione
2010,
22.
Abstract:
Working principle and structure and debugging process of a mobile accelerator are introduced. The mobile accelerator, compact and light-weighted, can produce beam currents with high stability and small spot, and it is used in experiment of fast neutron imaging in our academy for the first time. In application process, some parameters including the beam current stability parameter are measured. Successive neutron yield is measured using concomitance particle means. Elementary images are acquired to fit the accelerator and the digital imaging system together．
Working principle and structure and debugging process of a mobile accelerator are introduced. The mobile accelerator, compact and light-weighted, can produce beam currents with high stability and small spot, and it is used in experiment of fast neutron imaging in our academy for the first time. In application process, some parameters including the beam current stability parameter are measured. Successive neutron yield is measured using concomitance particle means. Elementary images are acquired to fit the accelerator and the digital imaging system together．
2010,
22.
Abstract:
The restriction of tantalum target expansion along axis bombarded by high-current pulsed electron beams was studied. The vaporized tantalum target can be blocked by the titanium foil partially vaporized due to the difference of energy deposition in both materials by the electron beam, and furthermore, the energy in tantalum can be absorbed by titanium to lower the expansion speed. By comparison of the holes in the targets formed by the electron beam and the target expansion pictures captured by high speed camera, the restriction of the titanium foil to the tantalum target has been confirmed, and such effect is distinct within 1 μs after the electron beam reaching the target.
The restriction of tantalum target expansion along axis bombarded by high-current pulsed electron beams was studied. The vaporized tantalum target can be blocked by the titanium foil partially vaporized due to the difference of energy deposition in both materials by the electron beam, and furthermore, the energy in tantalum can be absorbed by titanium to lower the expansion speed. By comparison of the holes in the targets formed by the electron beam and the target expansion pictures captured by high speed camera, the restriction of the titanium foil to the tantalum target has been confirmed, and such effect is distinct within 1 μs after the electron beam reaching the target.
2010,
22.
Abstract:
With its equivalent RLC circuit, the coupling factor of a sub-harmonic cavity as a function of the cavity’s parameters are derived. This paper presents the design points of the coupler, which is an important part of the sub-harmonic cavity working at 499.654 MHz in the linac of the Shanghai synchrotron radiation facility (SSRF). The structure, the depth into the cavity and the direction of the coupler have been optimized with the three-dimensional finite element method software CST, as well as the coupling factor of the cavity. The cavity has been tested at low RF level. The measurement agrees well with the design values. And some methods on installation and test are given.
With its equivalent RLC circuit, the coupling factor of a sub-harmonic cavity as a function of the cavity’s parameters are derived. This paper presents the design points of the coupler, which is an important part of the sub-harmonic cavity working at 499.654 MHz in the linac of the Shanghai synchrotron radiation facility (SSRF). The structure, the depth into the cavity and the direction of the coupler have been optimized with the three-dimensional finite element method software CST, as well as the coupling factor of the cavity. The cavity has been tested at low RF level. The measurement agrees well with the design values. And some methods on installation and test are given.
2010,
22.
Abstract:
The Dragon-I linear induction accelerator produces the single-pulse high current electron beam, which interacts with bremsstrahlung converter target to generate pulsed intense X-ray. The tantalum target may be ablated or even penetrated after the beam-target interaction. This paper introduces a laser detection system to detect the destruction process of the converter target. The experiment shows that the laser beam began penetrating the 0.4 mm thick target about 240 μs after the electron beam striking the target, and the penetrating process lasted 1.5 ms．
The Dragon-I linear induction accelerator produces the single-pulse high current electron beam, which interacts with bremsstrahlung converter target to generate pulsed intense X-ray. The tantalum target may be ablated or even penetrated after the beam-target interaction. This paper introduces a laser detection system to detect the destruction process of the converter target. The experiment shows that the laser beam began penetrating the 0.4 mm thick target about 240 μs after the electron beam striking the target, and the penetrating process lasted 1.5 ms．
2010,
22.
Abstract:
A coil measurement system has been designed to measure the magnetic induction intensity of the weak magnetic field generated by hypervelocity impact. Coil designing, equivalent circuit analysis, and the choice and function of the differential operational amplifier were expounded. The influence on measurement frequency of self-integration resistor was explored in theory. Finally, weak magnetic field signals generated by hypervelocity impact were obtained through experiments, and the recorded signals were smooth, which showed that the measurement system had a good anti-interference performance.
A coil measurement system has been designed to measure the magnetic induction intensity of the weak magnetic field generated by hypervelocity impact. Coil designing, equivalent circuit analysis, and the choice and function of the differential operational amplifier were expounded. The influence on measurement frequency of self-integration resistor was explored in theory. Finally, weak magnetic field signals generated by hypervelocity impact were obtained through experiments, and the recorded signals were smooth, which showed that the measurement system had a good anti-interference performance.
2010,
22.
Abstract:
Magnetic proton recoil (MPR) spectrometer is a novel diagnostic instrument with high performance for measurements of the neutron spectra from inertial confinement fusion (ICF) experiments and high power fusion devices. The design of the magnetic analysis system, which is a key part of the compact MPR-type spectrometer, has been completed through two-dimensional beam transport simulations and three-dimensional particle transport simulations. The analysis of the system’s parameters and performances was performed, as well as system designs based on preferential principles of energy resolution, detection efficiency, and count rate, respectively. The results indicate that the magnetic analysis system can achieve a detection efficiency of 10-5～10-4 level at the resolution range of 1.5% to 3.0%
Magnetic proton recoil (MPR) spectrometer is a novel diagnostic instrument with high performance for measurements of the neutron spectra from inertial confinement fusion (ICF) experiments and high power fusion devices. The design of the magnetic analysis system, which is a key part of the compact MPR-type spectrometer, has been completed through two-dimensional beam transport simulations and three-dimensional particle transport simulations. The analysis of the system’s parameters and performances was performed, as well as system designs based on preferential principles of energy resolution, detection efficiency, and count rate, respectively. The results indicate that the magnetic analysis system can achieve a detection efficiency of 10-5～10-4 level at the resolution range of 1.5% to 3.0%
2010,
22.
Abstract:
The gas heating of microhollow cathode discharge (MHCD) is found to have a strong relation with overall discharge behavior in the experimental investigation. It provides crucial understanding to support the application and preliminary design of MHCD thruster. The thruster produced by this kind of propulsion system is predicted in the range of several tens to several thousands μN and the specific impulse is evaluated on the order of 600～1 000 N·s/kg using argon or on the order of 3000 N·s/kg using helium as the propellant gas respectively. The main performance of the MHCD thruster proves that MHCD can be applied as a new microplasma propulsion system for attitude control and station keeping of nano-satellites.
The gas heating of microhollow cathode discharge (MHCD) is found to have a strong relation with overall discharge behavior in the experimental investigation. It provides crucial understanding to support the application and preliminary design of MHCD thruster. The thruster produced by this kind of propulsion system is predicted in the range of several tens to several thousands μN and the specific impulse is evaluated on the order of 600～1 000 N·s/kg using argon or on the order of 3000 N·s/kg using helium as the propellant gas respectively. The main performance of the MHCD thruster proves that MHCD can be applied as a new microplasma propulsion system for attitude control and station keeping of nano-satellites.
2010,
22.
Abstract:
This paper describes the thermal behaviour of hollow cathodes as core components in an ion thruster. Warm-up time and steady-state temperature distributions for the cases of the cathode keeper open/closed are simulated using the finite element software ANSYS. The heat of the interior hollow cathode is lost in the heater and orifice plate. Cathode keeper and heat shield are the important components to decrease the heat loss and to improve the heat efficiency. The temperature of hollow cathode with cathode keeper and heat shield increases by 2.3%～13.2% with emitter’s temperature increasing by 2.3%～4.2%.The simulation results are in agreement with experiment results, providing a reference for the optimum design of the hollow cathode for ion thrusters．
This paper describes the thermal behaviour of hollow cathodes as core components in an ion thruster. Warm-up time and steady-state temperature distributions for the cases of the cathode keeper open/closed are simulated using the finite element software ANSYS. The heat of the interior hollow cathode is lost in the heater and orifice plate. Cathode keeper and heat shield are the important components to decrease the heat loss and to improve the heat efficiency. The temperature of hollow cathode with cathode keeper and heat shield increases by 2.3%～13.2% with emitter’s temperature increasing by 2.3%～4.2%.The simulation results are in agreement with experiment results, providing a reference for the optimum design of the hollow cathode for ion thrusters．
2010,
22.
Abstract:
Under the slowly-varying-envelope approximation, the three coupled-wave equations were resolved and the storage of optical pulses was demonstrated theoretically. The variation of readout efficiency of date pulses versus acoustic lifetime, Brillouin gain coefficient, date pulse intensity and control pulse intensity were studied. The results show that, better readout efficiency and longer storage time of date pulses can be obtained with longer acoustic lifetime. Both Brillouin gain coefficient and the intensity of date pulses have no effect on readout efficiency. However, for a given readout efficiency, the intensity of control pulses decreases with increasing the Brillouin gain coefficient. Compared with long pulses, this optical storage method is more applicable for short ones.
Under the slowly-varying-envelope approximation, the three coupled-wave equations were resolved and the storage of optical pulses was demonstrated theoretically. The variation of readout efficiency of date pulses versus acoustic lifetime, Brillouin gain coefficient, date pulse intensity and control pulse intensity were studied. The results show that, better readout efficiency and longer storage time of date pulses can be obtained with longer acoustic lifetime. Both Brillouin gain coefficient and the intensity of date pulses have no effect on readout efficiency. However, for a given readout efficiency, the intensity of control pulses decreases with increasing the Brillouin gain coefficient. Compared with long pulses, this optical storage method is more applicable for short ones.
2010,
22.
Abstract:
The emission spectra of Cl plasma are calculated by solving the rate equations under conditions with and without M-shell high-energy photons at different temperatures and densities. The influences of the M-shell high-energy photons on the emission spectra are studied. It is found that the M-shell high-energy photons hardly affect the important ionic stage of the plasma, but they can excite or ionize the inner-shell electrons (e.g. 1s electron) of the ions in the plasma, hence affect the emission spectra. Therefore, if there are M-shell high-energy photons, the influence of temperature, density and M-shell high-energy photons on the emission spectra should be considered simultaneously.
The emission spectra of Cl plasma are calculated by solving the rate equations under conditions with and without M-shell high-energy photons at different temperatures and densities. The influences of the M-shell high-energy photons on the emission spectra are studied. It is found that the M-shell high-energy photons hardly affect the important ionic stage of the plasma, but they can excite or ionize the inner-shell electrons (e.g. 1s electron) of the ions in the plasma, hence affect the emission spectra. Therefore, if there are M-shell high-energy photons, the influence of temperature, density and M-shell high-energy photons on the emission spectra should be considered simultaneously.
2010,
22.
Abstract:
An energy spectrometer use to measured the intense γ-ray was developed and preliminary experimental results was obtained at rod pinch diode on inductive voltage adder (IVA). Si-PIN detectors array and Pb attenuator were used to design the energy spectrometer. The intensity of pulse γ-ray on IVA was measured by placing different thickness Pb plate in front of the energy spectrometer. Using the Monte-Carlo code, the energy deposition in sensitive region of Si-PIN detectors was calculated when the photons of different energies transmitted through the Pb plate. The sensitive curve of the detectors was obtained. Using correlation of theoretical quantity of electric charge and experimental waveform, the primal energy spectrum was calculated. The highest energy of the photons on IVA was 1.44
An energy spectrometer use to measured the intense γ-ray was developed and preliminary experimental results was obtained at rod pinch diode on inductive voltage adder (IVA). Si-PIN detectors array and Pb attenuator were used to design the energy spectrometer. The intensity of pulse γ-ray on IVA was measured by placing different thickness Pb plate in front of the energy spectrometer. Using the Monte-Carlo code, the energy deposition in sensitive region of Si-PIN detectors was calculated when the photons of different energies transmitted through the Pb plate. The sensitive curve of the detectors was obtained. Using correlation of theoretical quantity of electric charge and experimental waveform, the primal energy spectrum was calculated. The highest energy of the photons on IVA was 1.44
2010,
22.
Abstract:
A repetitive pulsed magnetic field serving as the guiding magnetic field for the repetitive high-power microwave source has been proposed, which makes the source compact with low loss and small heat. The design started from the expression of the current producing the pulsed magnetic field, and was based on the following principles: low eddy current loss, small capacitive energy storage and large quality factor. The optimization method of the storage capacitor and charging voltage of the field producing system was presented. Applying this method to the design of a Ka-band back-wave oscillator (BWO), the circuit parameters were determined, corresponding simulation and experiment were conducted, and the measured results accorded with the calculated requirements. The BWO worked steadily at a r
A repetitive pulsed magnetic field serving as the guiding magnetic field for the repetitive high-power microwave source has been proposed, which makes the source compact with low loss and small heat. The design started from the expression of the current producing the pulsed magnetic field, and was based on the following principles: low eddy current loss, small capacitive energy storage and large quality factor. The optimization method of the storage capacitor and charging voltage of the field producing system was presented. Applying this method to the design of a Ka-band back-wave oscillator (BWO), the circuit parameters were determined, corresponding simulation and experiment were conducted, and the measured results accorded with the calculated requirements. The BWO worked steadily at a r
2010,
22.
Abstract:
A theoretical analysis of the working mechanism and process has been presented for a magnetic switch based on metglas magnetic core. The volume of the magnetic core and the condition for multiple stage magnetic pulse compression circuit were deduced. Then the working process of the magnetic switch was simulated by Pspice. For validation a magnetic switch with 10 kV output voltage and 8.3 compression ratio was designed according to the theoretical analysis and simulation result. The experimental results reveal that the 10 kV, 9.2 μs electric pulse is compressed to 10 kV, 1.3 μs, which is in agreement with the theoretical design. At last, a novel testing method for the hysteresis loop of the magnetic core has been proposed according to this experimental platform. And the hysteresis loop o
A theoretical analysis of the working mechanism and process has been presented for a magnetic switch based on metglas magnetic core. The volume of the magnetic core and the condition for multiple stage magnetic pulse compression circuit were deduced. Then the working process of the magnetic switch was simulated by Pspice. For validation a magnetic switch with 10 kV output voltage and 8.3 compression ratio was designed according to the theoretical analysis and simulation result. The experimental results reveal that the 10 kV, 9.2 μs electric pulse is compressed to 10 kV, 1.3 μs, which is in agreement with the theoretical design. At last, a novel testing method for the hysteresis loop of the magnetic core has been proposed according to this experimental platform. And the hysteresis loop o
2010,
22.
Abstract:
This paper elucidates our understanding of the key characteristic quantity of high energy laser(HEL) system which is rapidly advancing in the world. Factors influencing the key characteristic quantity are analysed: the evolution history of principal laser and its reasons; as beam quality is the lifeline of HEL system, and to gain a better beam quality is a multilink-chain scientific engineering, technical challenges in the upper, middle and lower reaches along the technical chain, as well as the stability of the whole HEL system are discussed. In the end, by combining all the factors of contribution, the key characteristic quantity is expressed as the laser beam brightness on the target.
This paper elucidates our understanding of the key characteristic quantity of high energy laser(HEL) system which is rapidly advancing in the world. Factors influencing the key characteristic quantity are analysed: the evolution history of principal laser and its reasons; as beam quality is the lifeline of HEL system, and to gain a better beam quality is a multilink-chain scientific engineering, technical challenges in the upper, middle and lower reaches along the technical chain, as well as the stability of the whole HEL system are discussed. In the end, by combining all the factors of contribution, the key characteristic quantity is expressed as the laser beam brightness on the target.
2010,
22.
Abstract:
The triggered breakdown delay time distribution of the gas switch was presented for the 1 MA/100 ns fast linear transformer driver (FLTD), consisting of 40 parallel bricks. The delay time and switch jitter were simulated by random arrays generated by MATLAB program. The influence of the switch jitter on the rise time and amplitude of the FLTD’s output current has been studied based on the simplified second-order circuit of the FLTD brick. Simulated results indicate that the peak of the output current is about 996 kA at 90 ns with a rise time of about 54 ns (10% to 90%) in the ideal situation of 0 ns switch jitter. The rise time of the output current increases by about 14% and the peak decreases by 2% when the switch jitter is about 10 ns. The rise time increases by about 38% and the peak
The triggered breakdown delay time distribution of the gas switch was presented for the 1 MA/100 ns fast linear transformer driver (FLTD), consisting of 40 parallel bricks. The delay time and switch jitter were simulated by random arrays generated by MATLAB program. The influence of the switch jitter on the rise time and amplitude of the FLTD’s output current has been studied based on the simplified second-order circuit of the FLTD brick. Simulated results indicate that the peak of the output current is about 996 kA at 90 ns with a rise time of about 54 ns (10% to 90%) in the ideal situation of 0 ns switch jitter. The rise time of the output current increases by about 14% and the peak decreases by 2% when the switch jitter is about 10 ns. The rise time increases by about 38% and the peak
2010,
22.
Abstract:
The mutli-gap mutli-channel spark switch is of low induance and low jitter, thus it has important application in the pulse power technology. This paper presents a ± 100 kV mutli-gap mutli-channel spark switch used for fast linear transformer driver(LTD) . The experiment studies the influence of the switch triggering breakdown characteristic of the switch with different trigger voltage polarity and different trigger voltage, then analyzes different phases delay time and jitter of the gas spark switch under different voltage. Typical results are: the influence of the switch triggering breakdown characteristic of the switch with the trigger voltage polarity is small; the delay time as well as its jitter is decreasing while the trigger voltage is increasing. The paper also analyzes the tr
The mutli-gap mutli-channel spark switch is of low induance and low jitter, thus it has important application in the pulse power technology. This paper presents a ± 100 kV mutli-gap mutli-channel spark switch used for fast linear transformer driver(LTD) . The experiment studies the influence of the switch triggering breakdown characteristic of the switch with different trigger voltage polarity and different trigger voltage, then analyzes different phases delay time and jitter of the gas spark switch under different voltage. Typical results are: the influence of the switch triggering breakdown characteristic of the switch with the trigger voltage polarity is small; the delay time as well as its jitter is decreasing while the trigger voltage is increasing. The paper also analyzes the tr
