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RSS2013 Vol. 25, No. 05
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2013,
25: 1073-1074.
doi: 10.3788/HPLPB20132505.1073
Abstract:
The obstacles of scaling the average output power of the supercontinuum source based on single core photonic crystal fiber are analyzed. Adopting multi-core photonic crystal fiber as the nonlinear medium would be a potential solution. A 42.3 W high power supercontinuum source, spanning from 750 to 1700 nm, is demonstrated by pumping a piece of self-made multi-core photonic crystal fiber with a self-made picosecond fiber laser.
The obstacles of scaling the average output power of the supercontinuum source based on single core photonic crystal fiber are analyzed. Adopting multi-core photonic crystal fiber as the nonlinear medium would be a potential solution. A 42.3 W high power supercontinuum source, spanning from 750 to 1700 nm, is demonstrated by pumping a piece of self-made multi-core photonic crystal fiber with a self-made picosecond fiber laser.
2013,
25: 1075-1080.
doi: 10.3788/HPLPB20132505.1075
Abstract:
The irradiation effects of 976 nm continuous wave laser on glass fiber reinforced E-51 resin matrix composite are studied experimentally, with a 0.4 Ma tangential airflow, a 0.4 Ma tangential nitrogen flow and no gas flow on the target surface, respectively. Experimental results show that, the incoming laser beam will be severely affected by the gaseous pyrolysis products while without gas flow on the target surface, and the loading of tangential gas flow will reduce the influence. The failure mode of glass fiber is that it melts and then is blown away by gas flow, when laser irradiation happens in the presence of a gas flow parallel to the specimen surface. The main function of the tangential airflow is to enhance the convection cooling effect for a low laser irradiance, thus the tangential airflow is not conductive to the laser damage of glass fiber composite. When the laser irradiance increases, the main functions of the airflow are to reduce the shielding effect of the gaseous pyrolysis products on the incoming laser beam and to supply oxygen, thus the loading of the tangential airflow is advantageous to the laser damage of glass fiber composite. Under three different gas flow states, the mass loss increases with the increasing incident power density. The utilization ratio of laser beam increases up to a saturation value as the incident power density in the range of 100-600 W/cm2.
The irradiation effects of 976 nm continuous wave laser on glass fiber reinforced E-51 resin matrix composite are studied experimentally, with a 0.4 Ma tangential airflow, a 0.4 Ma tangential nitrogen flow and no gas flow on the target surface, respectively. Experimental results show that, the incoming laser beam will be severely affected by the gaseous pyrolysis products while without gas flow on the target surface, and the loading of tangential gas flow will reduce the influence. The failure mode of glass fiber is that it melts and then is blown away by gas flow, when laser irradiation happens in the presence of a gas flow parallel to the specimen surface. The main function of the tangential airflow is to enhance the convection cooling effect for a low laser irradiance, thus the tangential airflow is not conductive to the laser damage of glass fiber composite. When the laser irradiance increases, the main functions of the airflow are to reduce the shielding effect of the gaseous pyrolysis products on the incoming laser beam and to supply oxygen, thus the loading of the tangential airflow is advantageous to the laser damage of glass fiber composite. Under three different gas flow states, the mass loss increases with the increasing incident power density. The utilization ratio of laser beam increases up to a saturation value as the incident power density in the range of 100-600 W/cm2.
2013,
25: 1081-1086.
doi: 10.3788/HPLPB20132505.1081
Abstract:
Numerical experiments have been conducted to simulate the sky background brightness for various aerosol scale heights in order to study the effect of vertical distribution of aerosol on the sky background brightness. A homogeneous model and a vertically inhomogeneous distributed model are utilized to estimate the sky background brightness under the conditions of different ground surface reflectances. The relative differences of sky background brightness as well as the sensitivity of sky background brightness to ground surface reflectance are also shown. The results indicate that the sky background brightness is much different under various aerosol scale heights for given aerosol optical thickness and ground surface reflectance. Moreover,the sky background brightness is also sensitive to the ground surface reflectance and aerosol optical thickness, and the degree of sensitivity is dependent on solar-observation geometry.
Numerical experiments have been conducted to simulate the sky background brightness for various aerosol scale heights in order to study the effect of vertical distribution of aerosol on the sky background brightness. A homogeneous model and a vertically inhomogeneous distributed model are utilized to estimate the sky background brightness under the conditions of different ground surface reflectances. The relative differences of sky background brightness as well as the sensitivity of sky background brightness to ground surface reflectance are also shown. The results indicate that the sky background brightness is much different under various aerosol scale heights for given aerosol optical thickness and ground surface reflectance. Moreover,the sky background brightness is also sensitive to the ground surface reflectance and aerosol optical thickness, and the degree of sensitivity is dependent on solar-observation geometry.
2013,
25: 1087-1090.
doi: 10.3788/HPLPB20132505.1087
Abstract:
As the heart of chemical oxygen iodine laser (COIL), the singlet oxygen generator (SOG) has been focus of research for many years. A novel eject singlet oxygen generator was designed based on research of industrial ejectors and cyclone separators. Simulations and experiments were performed on the chemical reaction of O2(1). This eject SOG can make larger gas-liquid surface area through nozzle compared with traditional SOGs, and therefore it has a high chemical efficiency. Gas and liquid were separated by a cyclone separator which was designed to fit for the high separation efficiency and low residence time. This SOG has a chlorine utilization of 97%-99% and O2(1) yield of 40%-50%.
As the heart of chemical oxygen iodine laser (COIL), the singlet oxygen generator (SOG) has been focus of research for many years. A novel eject singlet oxygen generator was designed based on research of industrial ejectors and cyclone separators. Simulations and experiments were performed on the chemical reaction of O2(1). This eject SOG can make larger gas-liquid surface area through nozzle compared with traditional SOGs, and therefore it has a high chemical efficiency. Gas and liquid were separated by a cyclone separator which was designed to fit for the high separation efficiency and low residence time. This SOG has a chlorine utilization of 97%-99% and O2(1) yield of 40%-50%.
2013,
25: 1091-1096.
doi: 10.3788/HPLPB20132505.1091
Abstract:
Based on residual turbulent scintillation(RTS) theory, many lidar component parameters were analyzed, and the ones related to atmospheric turbulence detecting were obtained and optimized. An RTS lidar was then developed for acquiring atmospheric turbulence information. It is suggested that the lidar works normally and the data are reliable according to some performance tests of baseline, linearity characteristic and so on. The relationships of scintillation index and atmospheric refractive index structure constant with propagation distance and time in horizontal direction were experimentally obtained. The scintillation index increases from 0.001 to 0.35 with the propagation distance changing from 450 m to 2000 m, and the refractive index structure constant is between 1.010-16 and 1.010-15 m-2/3 and basically maintains homogenous in that distance range. From 10:00 am to 09:00 pm, the refractive index structure constant rises in the morning, falls in the afternoon and then rises in the evening approximately. On the whole, the variations of scintillation index and refractive index structure constant with propagation distance and time are similar to the theoretical results and practical measurements. The results suggest that the RTS lidar has the capability of extracting atmospheric turbulence information that varies with propagation distance and time in the lidar echo signal.
Based on residual turbulent scintillation(RTS) theory, many lidar component parameters were analyzed, and the ones related to atmospheric turbulence detecting were obtained and optimized. An RTS lidar was then developed for acquiring atmospheric turbulence information. It is suggested that the lidar works normally and the data are reliable according to some performance tests of baseline, linearity characteristic and so on. The relationships of scintillation index and atmospheric refractive index structure constant with propagation distance and time in horizontal direction were experimentally obtained. The scintillation index increases from 0.001 to 0.35 with the propagation distance changing from 450 m to 2000 m, and the refractive index structure constant is between 1.010-16 and 1.010-15 m-2/3 and basically maintains homogenous in that distance range. From 10:00 am to 09:00 pm, the refractive index structure constant rises in the morning, falls in the afternoon and then rises in the evening approximately. On the whole, the variations of scintillation index and refractive index structure constant with propagation distance and time are similar to the theoretical results and practical measurements. The results suggest that the RTS lidar has the capability of extracting atmospheric turbulence information that varies with propagation distance and time in the lidar echo signal.
2013,
25: 1097-1099.
doi: 10.3788/HPLPB20132505.1097
Abstract:
Based on the self-stimulated Raman scattering of Nd:YVO4 laser crystal, combined with Cr:YAG passive mode-locking technology and frequency doubling technology, compact 1176 nm and 588 nm yellow laser mode locking was realized. A folded laser cavity with three mirrors and an output coupler with 10% transmittance were designed in the laser diode end-pumped laser. The Nd3+ concentration and length of the Nd:YVO4 crystal were 0.2% and 10 mm, respectively, and the initial transmission of Cr:YAG at 1064 nm was 67%. At 10 W incident pump power the average output power was 123 mW and the duration of Q-switched envelope was only 6.0 ns with the mode-locked pulse repetition rate of 1.0 GHz. The average output power of 588.2 nm yellow laser was about 8 mW. An effective method for achieving mode-locked yellow lasers was provided.
Based on the self-stimulated Raman scattering of Nd:YVO4 laser crystal, combined with Cr:YAG passive mode-locking technology and frequency doubling technology, compact 1176 nm and 588 nm yellow laser mode locking was realized. A folded laser cavity with three mirrors and an output coupler with 10% transmittance were designed in the laser diode end-pumped laser. The Nd3+ concentration and length of the Nd:YVO4 crystal were 0.2% and 10 mm, respectively, and the initial transmission of Cr:YAG at 1064 nm was 67%. At 10 W incident pump power the average output power was 123 mW and the duration of Q-switched envelope was only 6.0 ns with the mode-locked pulse repetition rate of 1.0 GHz. The average output power of 588.2 nm yellow laser was about 8 mW. An effective method for achieving mode-locked yellow lasers was provided.
2013,
25: 1100-1104.
doi: 10.3788/HPLPB20132505.1100
Abstract:
A curvature threshold based target searching method is reported in order to reduce the high false alarm rate in staring infrared warning system. A staring infrared warning system with view field of 5.34 is chosen to simulate the infrared search process in MATLAB, proving the feasibility of the proposed algorithm. Target scene with a large amount of random noise is simulated according to Monte-Carlo method to compare the search performance of the proposed algorithm with the classical 3D matched-filter method. The number of search frames is discussed to expand the proposed algorithm, and the search performance and temporal limit are also reported for different search frames.
A curvature threshold based target searching method is reported in order to reduce the high false alarm rate in staring infrared warning system. A staring infrared warning system with view field of 5.34 is chosen to simulate the infrared search process in MATLAB, proving the feasibility of the proposed algorithm. Target scene with a large amount of random noise is simulated according to Monte-Carlo method to compare the search performance of the proposed algorithm with the classical 3D matched-filter method. The number of search frames is discussed to expand the proposed algorithm, and the search performance and temporal limit are also reported for different search frames.
2013,
25: 1105-1109.
doi: 10.3788/HPLPB20132505.1105
Abstract:
To reduce the impact of noise on infrared spectral signal measurement, a denoising method based on non-subsampled wavelet transform(NSWT) is proposed. In this method, original spectrum signal is decomposed in multi-scale with NSWT. According to the difference between signal and noise in the scales, sub-band coefficients from the decomposition are adjusted by resolving correlated variational partial differential equations. Signal and noise can then be separated in re-composing the sub-bands. Experiments were conducted for denoising performance comparison between traditional wavelet method and our method. The experiment results show that our method is much better in denoising and signal shapes keeping. The mean square error of our method is also less than that of the traditional method.
To reduce the impact of noise on infrared spectral signal measurement, a denoising method based on non-subsampled wavelet transform(NSWT) is proposed. In this method, original spectrum signal is decomposed in multi-scale with NSWT. According to the difference between signal and noise in the scales, sub-band coefficients from the decomposition are adjusted by resolving correlated variational partial differential equations. Signal and noise can then be separated in re-composing the sub-bands. Experiments were conducted for denoising performance comparison between traditional wavelet method and our method. The experiment results show that our method is much better in denoising and signal shapes keeping. The mean square error of our method is also less than that of the traditional method.
2013,
25: 1110-1114.
doi: 10.3788/HPLPB20132505.1110
Abstract:
Laser radiation has been considered as one kind of feasible methods to clean space debris. Impulse coupling coefficient is an important parameter to calculate the clean effects. An analytical model for calculating laser ablation impulse coupling coefficient is put forward. The impulse coupling coefficients in vapor mechanism and plasma mechanismare connected by the ionization fraction. Therefore, a unified model of impulse coupling coefficient is set up. The relationship of laser intensity, ionization fraction and impulse coupling coefficient is obtained with Al, the most common material of space debris, as the calculation example. The transition between vapor mechanism and plasma mechanism progressively changes with the increase of laser intensity. The ionization fraction is also increasing until the vapor is totallyionized. The impulse coupling coefficient increases at first, then reaches the maximum, and decreases at last. The optimum impulse coupling coefficient is obtained when the plasma mechanism dominates.
Laser radiation has been considered as one kind of feasible methods to clean space debris. Impulse coupling coefficient is an important parameter to calculate the clean effects. An analytical model for calculating laser ablation impulse coupling coefficient is put forward. The impulse coupling coefficients in vapor mechanism and plasma mechanismare connected by the ionization fraction. Therefore, a unified model of impulse coupling coefficient is set up. The relationship of laser intensity, ionization fraction and impulse coupling coefficient is obtained with Al, the most common material of space debris, as the calculation example. The transition between vapor mechanism and plasma mechanism progressively changes with the increase of laser intensity. The ionization fraction is also increasing until the vapor is totallyionized. The impulse coupling coefficient increases at first, then reaches the maximum, and decreases at last. The optimum impulse coupling coefficient is obtained when the plasma mechanism dominates.
2013,
25: 1115-1119.
doi: 10.3788/HPLPB20132505.1115
Abstract:
In order to implement the laser shock peening (LSP) technology on the TC6 titanium alloy aero-engine blade, TC6 titanium alloy was treated by LSP. Microstructural characteristics, microhardness and residual stress on the cross-section of TC6 titanium alloy after LSP were tested with X-ray diffraction (XRD), transmission electron microscope (TEM), microhardness tester and residual stress tester, and vibration fatigue limit was obtained by high-cycle fatigue test. The results demonstrated that the original structure was refined, with high density dislocation, dislocation cell, subgrain and nanocrystallite generated with laser impact increasing. Besides, on the aspect of mechanics performance, the surface microhardness was increased by 19% with a 700-m-depth affected layer under one laser impact. The greatest residual stress value was -608.5 MPa on the surface in ten impacts and at 500 m depth the value was still above -100 MPa. With three impacts, the fatigue limit of standard fatigue specimens was improved by about 20%.
In order to implement the laser shock peening (LSP) technology on the TC6 titanium alloy aero-engine blade, TC6 titanium alloy was treated by LSP. Microstructural characteristics, microhardness and residual stress on the cross-section of TC6 titanium alloy after LSP were tested with X-ray diffraction (XRD), transmission electron microscope (TEM), microhardness tester and residual stress tester, and vibration fatigue limit was obtained by high-cycle fatigue test. The results demonstrated that the original structure was refined, with high density dislocation, dislocation cell, subgrain and nanocrystallite generated with laser impact increasing. Besides, on the aspect of mechanics performance, the surface microhardness was increased by 19% with a 700-m-depth affected layer under one laser impact. The greatest residual stress value was -608.5 MPa on the surface in ten impacts and at 500 m depth the value was still above -100 MPa. With three impacts, the fatigue limit of standard fatigue specimens was improved by about 20%.
2013,
25: 1120-1124.
doi: 10.3788/HPLPB20132505.1120
Abstract:
Multi-beam combination is an effective way to improve the laser output power. In this paper beam alignment influences on the character of focal spot in energy synthetic cases are discussed. By using two beams with rectangular aperture, we analyze the focal spot characteristics of the two beams in different alignment cases. When the two beams are completely aligned, their focal spots overlap completely, and the focal spot energy is the sum of the two beams. We also discuss three common alignment errors, and compare their influences on the character of focal spot in the actual beam alignment system. ZEMAX software is used to simulate the design system and the results are proved by experiments. The results show that the component position error will reduce the energy and increase the root-mean-square radius of focal spot.
Multi-beam combination is an effective way to improve the laser output power. In this paper beam alignment influences on the character of focal spot in energy synthetic cases are discussed. By using two beams with rectangular aperture, we analyze the focal spot characteristics of the two beams in different alignment cases. When the two beams are completely aligned, their focal spots overlap completely, and the focal spot energy is the sum of the two beams. We also discuss three common alignment errors, and compare their influences on the character of focal spot in the actual beam alignment system. ZEMAX software is used to simulate the design system and the results are proved by experiments. The results show that the component position error will reduce the energy and increase the root-mean-square radius of focal spot.
2013,
25: 1125-1128.
doi: 10.3788/HPLPB20132505.1125
Abstract:
The coherent combination system of two fiber lasers based on heterodyne method has been constructed using a 1064 nm, 1 W seed laser. In this system, two graded index (GRIN) lenses with polarization maintaining (PM) fiber is used to receive interference signals for getting better high-contrast strips, compared with interference signals directly received by detectors. The phase noise is studied, and the influence of phase noise on phase control precision is discussed. The phase noise is found to result from electrical crosstalk and environmental perturbation. When the phase noise bandwidth increases, the phase control precision drops. The ways to improve phase control precision are shown. When the phase of two fiber lasers is locked in the experiment, the power in the bucket(PIB) is 21.3%, the Strehl ratio is 79%, and the phase control precision is 0.008.
The coherent combination system of two fiber lasers based on heterodyne method has been constructed using a 1064 nm, 1 W seed laser. In this system, two graded index (GRIN) lenses with polarization maintaining (PM) fiber is used to receive interference signals for getting better high-contrast strips, compared with interference signals directly received by detectors. The phase noise is studied, and the influence of phase noise on phase control precision is discussed. The phase noise is found to result from electrical crosstalk and environmental perturbation. When the phase noise bandwidth increases, the phase control precision drops. The ways to improve phase control precision are shown. When the phase of two fiber lasers is locked in the experiment, the power in the bucket(PIB) is 21.3%, the Strehl ratio is 79%, and the phase control precision is 0.008.
2013,
25: 1129-1133.
doi: 10.3788/HPLPB20132505.1129
Abstract:
In order to recover the noisy wrapped phase map rapidly and accurately, four typical algorithms based on fast Fourier transform, i.e. the algorithms respectively based on fourfast Fourier transforms (4-FFT algorithm), two fast Fourier transforms (2-FFT algorithm), four discrete cosine transforms (4-DCT algorithm) and combination of lateral shearing and Fourier transform (LS-FFT algorithm), are compared through theoretical analysis, computer simulation and experimental verification. The results show that, the 2-FFT algorithm is the fastest, followed by the 4-FFT algorithm, and the LS-FFT algorithm is the slowest. For the strong noisy and slightly under-sampled wrapped phase map obtained by digital holographic experiments, the 4-FFT algorithm performs the best, while the LS-FFT algorithm does the worst.
In order to recover the noisy wrapped phase map rapidly and accurately, four typical algorithms based on fast Fourier transform, i.e. the algorithms respectively based on fourfast Fourier transforms (4-FFT algorithm), two fast Fourier transforms (2-FFT algorithm), four discrete cosine transforms (4-DCT algorithm) and combination of lateral shearing and Fourier transform (LS-FFT algorithm), are compared through theoretical analysis, computer simulation and experimental verification. The results show that, the 2-FFT algorithm is the fastest, followed by the 4-FFT algorithm, and the LS-FFT algorithm is the slowest. For the strong noisy and slightly under-sampled wrapped phase map obtained by digital holographic experiments, the 4-FFT algorithm performs the best, while the LS-FFT algorithm does the worst.
2013,
25: 1134-1138.
doi: 10.3788/HPLPB20132505.1134
Abstract:
By using the method of finite element combined with Fox-Li iteration algorithm, the eigenmode in positive-branch confocal unstable resonators has been calculated and simulated, with considering the coupling effect between the eigenmodes of resonators and the thermal distortions of cavity mirrors. The effect of thermal distortions of cavity mirrors on output beam quality of high-power laser has also been analyzed quantitatively. Furthermore, the changes of eigenmode phase characteristics caused by thermal distortions of cavity mirrors have been discussed, and the phase characteristics of output beam with and without thermal distortions have been compared and analyzed from the aspects of the wavefront power spectral density (PSD), Zernike coefficients and factors of output laser beams. The results show that the output beam quality would be influenced by the thermal distortions of cavity mirrors. The proportion of high frequency part in distorted phase and the high order Zernike aberrations increase with the increasing of output laser power, resulting in the degradation of beam quality of output laser beams.
By using the method of finite element combined with Fox-Li iteration algorithm, the eigenmode in positive-branch confocal unstable resonators has been calculated and simulated, with considering the coupling effect between the eigenmodes of resonators and the thermal distortions of cavity mirrors. The effect of thermal distortions of cavity mirrors on output beam quality of high-power laser has also been analyzed quantitatively. Furthermore, the changes of eigenmode phase characteristics caused by thermal distortions of cavity mirrors have been discussed, and the phase characteristics of output beam with and without thermal distortions have been compared and analyzed from the aspects of the wavefront power spectral density (PSD), Zernike coefficients and factors of output laser beams. The results show that the output beam quality would be influenced by the thermal distortions of cavity mirrors. The proportion of high frequency part in distorted phase and the high order Zernike aberrations increase with the increasing of output laser power, resulting in the degradation of beam quality of output laser beams.
2013,
25: 1139-1143.
doi: 10.3788/HPLPB20132505.1139
Abstract:
Sodium guide-star laser research needs laser linewidth tunable within a range. The numerical simulation of linewidth compressing by Fabry-Perot etalon has been done, using an all-solid-state 1064 nm laser with high beam quality and linear polarization output as the experiment device, the spectrum of laser is test and put into the calculation. Linewidth discrete tuning in the range of 0.75-2.83 GHz is achieved by inserting different single etalons and combinations of etalons selected by the simulation results in the cavity. Without temperature control of etalon, the central wavelength of laser is fixed to 1 064.58 nm in linewidth tuning, and the wavelength excursion is less than 3 pm in 30 minutes.
Sodium guide-star laser research needs laser linewidth tunable within a range. The numerical simulation of linewidth compressing by Fabry-Perot etalon has been done, using an all-solid-state 1064 nm laser with high beam quality and linear polarization output as the experiment device, the spectrum of laser is test and put into the calculation. Linewidth discrete tuning in the range of 0.75-2.83 GHz is achieved by inserting different single etalons and combinations of etalons selected by the simulation results in the cavity. Without temperature control of etalon, the central wavelength of laser is fixed to 1 064.58 nm in linewidth tuning, and the wavelength excursion is less than 3 pm in 30 minutes.
2013,
25: 1144-1146.
doi: 10.3788/HPLPB20132505.1144
Abstract:
A set of airborne high-resolution all-sphere midwave infrared optical system was designed based on the advanced staring focal plane array which had a format of 640480 and the pixel pitch of 15 m. The working wavelength is in 3-5 m, the full field of view is 8.58, the relative aperture is 1/2, and the efficient focal length is 80 mm. The optical system adopted four lenses with three kinds of materialGe, ZnSe and Si. All surfaces are spherical, instead of the diffractive surface and aspheric surface used in traditional systems, and it is more easy to process and test. The design results prove that, the midwave infrared optical system has compact structure, small volume, high resolution, and excellent image quality, meeting the design requirements, and it could be used in airborne photoelectric detection and tracking systems.
A set of airborne high-resolution all-sphere midwave infrared optical system was designed based on the advanced staring focal plane array which had a format of 640480 and the pixel pitch of 15 m. The working wavelength is in 3-5 m, the full field of view is 8.58, the relative aperture is 1/2, and the efficient focal length is 80 mm. The optical system adopted four lenses with three kinds of materialGe, ZnSe and Si. All surfaces are spherical, instead of the diffractive surface and aspheric surface used in traditional systems, and it is more easy to process and test. The design results prove that, the midwave infrared optical system has compact structure, small volume, high resolution, and excellent image quality, meeting the design requirements, and it could be used in airborne photoelectric detection and tracking systems.
2013,
25: 1147-1151.
doi: 10.3788/HPLPB20132505.1147
Abstract:
The contamination control method covering the whole process of laser driver construction is proposed to ensure the safe operation of high-power solid-state laser driver. The technical means for improving cleanliness level including high pressure washing, cleanliness detection and protection are described, and a technical approach is proposed for improving cleanliness of the slab amplifiers of SG-Ⅲ laser driver. The illuminating cleaning experiment by flashlamp light is introduced. The results indicate that the cleanliness of SG-Ⅲ laser driver is close to NIF, and better than other similar devices.
The contamination control method covering the whole process of laser driver construction is proposed to ensure the safe operation of high-power solid-state laser driver. The technical means for improving cleanliness level including high pressure washing, cleanliness detection and protection are described, and a technical approach is proposed for improving cleanliness of the slab amplifiers of SG-Ⅲ laser driver. The illuminating cleaning experiment by flashlamp light is introduced. The results indicate that the cleanliness of SG-Ⅲ laser driver is close to NIF, and better than other similar devices.
2013,
25: 1152-1156.
doi: 10.3788/HPLPB20132505.1152
Abstract:
Fusion reaction bang time is an important parameter for measuring compression during the implosion in inertial confinement fusion experiment. A system for fusion reaction bang time measurement with high temporal resolution was developed at the SG-Ⅲ prototype. Through the introduction of timing fiducial, the fusion reaction bang time for different CH ablation layer thickness was obtained. For the first time, fusion reaction bang time was measured for deuterium-tritium (DT) filled targets. The results indicate that the fusion reaction bang time is 0.7~1.0 ns after laser pulses, and increasing the thickness of CH or the pressure of DT gas leads to delay of the fusion reaction bang time.
Fusion reaction bang time is an important parameter for measuring compression during the implosion in inertial confinement fusion experiment. A system for fusion reaction bang time measurement with high temporal resolution was developed at the SG-Ⅲ prototype. Through the introduction of timing fiducial, the fusion reaction bang time for different CH ablation layer thickness was obtained. For the first time, fusion reaction bang time was measured for deuterium-tritium (DT) filled targets. The results indicate that the fusion reaction bang time is 0.7~1.0 ns after laser pulses, and increasing the thickness of CH or the pressure of DT gas leads to delay of the fusion reaction bang time.
2013,
25: 1157-1160.
doi: 10.3788/HPLPB20132505.1157
Abstract:
In capsule compression experiments on SG-Ⅱ facility, the variation of the hohlraum length affects the radiant intensity of the capsule equator and poles, thus the fuel is compressed to different shapes. We introduced the radiation hydrodynamics equations and numerical methods used in radiation multi-group diffusion modeling. Using the recently developed two-dimensional LARED-integration code, we accomplished the integrated simulation of compression distortion experiments of SG-Ⅱ hohlraums with different lengths in radiation multi-group diffusion approximation. The shapes of fuel simulated agree well with those in the SG-Ⅱ experiments, which shows that the radiation multi-group diffusion approximation could reflect the radiation uniformity in the hohlraum.
In capsule compression experiments on SG-Ⅱ facility, the variation of the hohlraum length affects the radiant intensity of the capsule equator and poles, thus the fuel is compressed to different shapes. We introduced the radiation hydrodynamics equations and numerical methods used in radiation multi-group diffusion modeling. Using the recently developed two-dimensional LARED-integration code, we accomplished the integrated simulation of compression distortion experiments of SG-Ⅱ hohlraums with different lengths in radiation multi-group diffusion approximation. The shapes of fuel simulated agree well with those in the SG-Ⅱ experiments, which shows that the radiation multi-group diffusion approximation could reflect the radiation uniformity in the hohlraum.
2013,
25: 1161-1165.
doi: 10.3788/HPLPB20132505.1161
Abstract:
Multiwall carbon nanotubes (MWCNTs) encapsuled with iron nanowires were fabricated by chemical vapor deposition (CVD) methods in furnace using ferrocene and xylene as catalyzer and carbon source. The MWCNTs were characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The results indicate that the MWCNTs have good alignment and fine multilayer graphite form, and a small number of iron(Fe) catalyzer nanowires and nanoparticles remaining in the MWCNTs consist of Fe and Fe3C, whichare the outcomes of continuous supply of carbon source and iron catalyst particles. According to the synthesis process and characterization results, the possible growth mechanism of the MWCNTs is believed to accord with the base-growth model, which follows the cyclic process of catalyst nucleation on the open ends of MWCNTs from active gas phase cluster and then diffusion and formation of particles along inner surface of MWCNTs.
Multiwall carbon nanotubes (MWCNTs) encapsuled with iron nanowires were fabricated by chemical vapor deposition (CVD) methods in furnace using ferrocene and xylene as catalyzer and carbon source. The MWCNTs were characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The results indicate that the MWCNTs have good alignment and fine multilayer graphite form, and a small number of iron(Fe) catalyzer nanowires and nanoparticles remaining in the MWCNTs consist of Fe and Fe3C, whichare the outcomes of continuous supply of carbon source and iron catalyst particles. According to the synthesis process and characterization results, the possible growth mechanism of the MWCNTs is believed to accord with the base-growth model, which follows the cyclic process of catalyst nucleation on the open ends of MWCNTs from active gas phase cluster and then diffusion and formation of particles along inner surface of MWCNTs.
2013,
25: 1166-1170.
doi: 10.3788/HPLPB20132505.1166
Abstract:
A layered structure imaging model is developed in order to reconstruct emission coefficients and absorption coefficients simultaneously, in laser fusion core plasma diagnostics. A novel axially symmetric reconstruction method that utilizes the LM(Levenberg-Marquardt) nonlinear least squares minimization algorithm is proposed based on the layered structure. Numerical simulation results demonstrate that the proposed method is sufficiently accurate to reconstruct emission coefficients and absorption coefficients, and when the standard deviation of noise is 0.01, the errors of emission coefficients and absorption coefficients are 0.17, 0.22, respectively. Furthermore, this method could perform much better on reconstruction effect compared with traditional inverse Abel transform algorithms.
A layered structure imaging model is developed in order to reconstruct emission coefficients and absorption coefficients simultaneously, in laser fusion core plasma diagnostics. A novel axially symmetric reconstruction method that utilizes the LM(Levenberg-Marquardt) nonlinear least squares minimization algorithm is proposed based on the layered structure. Numerical simulation results demonstrate that the proposed method is sufficiently accurate to reconstruct emission coefficients and absorption coefficients, and when the standard deviation of noise is 0.01, the errors of emission coefficients and absorption coefficients are 0.17, 0.22, respectively. Furthermore, this method could perform much better on reconstruction effect compared with traditional inverse Abel transform algorithms.
2013,
25: 1171-1175.
doi: 10.3788/HPLPB20132505.1171
Abstract:
Based on the fractal theory, this paper analyzed statistical distribution features of middle-high frequency phase distortion of the optics for Shenguang-Ⅲ laser facility. The middle-high frequency phase distribution is found to be consistent with the model of fractional Brownian random field. The fractal dimension was calculated by structure function. The fractal dimension of large-aperture neodymium-doped phosphate amplifier glass is distributed between 2.34 and 2.43. A method of phase simulation by random midpoint-displacement was presented. In this method, the fractal dimension can be viewed as a parameter for estimating phase distortion, which helps to evaluate the high laser optics.
Based on the fractal theory, this paper analyzed statistical distribution features of middle-high frequency phase distortion of the optics for Shenguang-Ⅲ laser facility. The middle-high frequency phase distribution is found to be consistent with the model of fractional Brownian random field. The fractal dimension was calculated by structure function. The fractal dimension of large-aperture neodymium-doped phosphate amplifier glass is distributed between 2.34 and 2.43. A method of phase simulation by random midpoint-displacement was presented. In this method, the fractal dimension can be viewed as a parameter for estimating phase distortion, which helps to evaluate the high laser optics.
2013,
25: 1176-1178.
doi: 10.3788/HPLPB20132505.1176
Abstract:
The diagnosis of X-ray flux with high temporal and spatial resolutions is important in the researches of hohlraum physics, and spectral response coupling and design of spectrum rebuilding unit are key issues in the design of flat-response streak camera. Based on the study of the spectral response characteristics of streak camera and X-ray transmission photocathode, compound filter is adopted to realize the M-band band-pass flat-response of streak camera. The calculation shows that the flatness of spectral response is better than 2.7% with an acceptable band pass effect.
The diagnosis of X-ray flux with high temporal and spatial resolutions is important in the researches of hohlraum physics, and spectral response coupling and design of spectrum rebuilding unit are key issues in the design of flat-response streak camera. Based on the study of the spectral response characteristics of streak camera and X-ray transmission photocathode, compound filter is adopted to realize the M-band band-pass flat-response of streak camera. The calculation shows that the flatness of spectral response is better than 2.7% with an acceptable band pass effect.
2013,
25: 1179-1183.
doi: 10.3788/HPLPB20132505.1179
Abstract:
In order to explore the diffusion of gas in the polymer chain and solid surface, molecular dynamics (MD) method is used to simulate the diffusion of H2, D2, T2 in the interface of polystyrene-Cu (PS-Cu). Their diffusion coefficients are obtained from the mean square displacement (MSD) of these gases in different metal surfaces and polystyrene interfaces. Results show that the diffusion coefficients of these gases in the interface are smaller than those in polystyrene itself, and the diffusion coefficients of these gases in PS-Cu (110) interface are the largest, while in PS-Cu (111) interface they are the smallest. Through calculation and analysis of interaction between PS and metal surface, we also found that the bigger the interaction energy is, the smaller the diffusion coefficient of gas in the interface becomes. Moreover, crystal density of the metal surface has a certain effect on the diffusion of gas in the interface.
In order to explore the diffusion of gas in the polymer chain and solid surface, molecular dynamics (MD) method is used to simulate the diffusion of H2, D2, T2 in the interface of polystyrene-Cu (PS-Cu). Their diffusion coefficients are obtained from the mean square displacement (MSD) of these gases in different metal surfaces and polystyrene interfaces. Results show that the diffusion coefficients of these gases in the interface are smaller than those in polystyrene itself, and the diffusion coefficients of these gases in PS-Cu (110) interface are the largest, while in PS-Cu (111) interface they are the smallest. Through calculation and analysis of interaction between PS and metal surface, we also found that the bigger the interaction energy is, the smaller the diffusion coefficient of gas in the interface becomes. Moreover, crystal density of the metal surface has a certain effect on the diffusion of gas in the interface.
2013,
25: 1184-1188.
doi: 10.3788/HPLPB20132505.1184
Abstract:
A C-band and X-band dual-frequency coaxial relativistic backward-wave oscillator (CRBWO) with an asymmetric resonant reflector and a single annular electron beam structure is designed and investigated in this paper. The improved slow wave structure (SWS) with stepwise variable coupling impedance is employed, and the particle-in-cell (PIC) simulation code is used to investigate the device. The PIC simulation results indicate that the axial electric field in the SWS is enhanced and the energy scatter of the relativistic electron beam (REB) is improved. With an electron beam of 511 kV and 8.95 kA and an axial magnetic field of 0.73 T, an average power of 1.0 GW with power conversion efficiency of 21.9% is obtained and the two dominant frequencies are 8.09 GHz and 9.91 GHz. The efficiency is higher than dual-band non-coaxial RBWO and other dual-band high-power microwave (HPM) generators. A more clear and stable beat radiation microwave power with beat frequency of 1.82 GHz is acquired, and the dual frequencies both demonstrate periodic-like dependence on the length of the tapered waveguide between the two SWS sections.
A C-band and X-band dual-frequency coaxial relativistic backward-wave oscillator (CRBWO) with an asymmetric resonant reflector and a single annular electron beam structure is designed and investigated in this paper. The improved slow wave structure (SWS) with stepwise variable coupling impedance is employed, and the particle-in-cell (PIC) simulation code is used to investigate the device. The PIC simulation results indicate that the axial electric field in the SWS is enhanced and the energy scatter of the relativistic electron beam (REB) is improved. With an electron beam of 511 kV and 8.95 kA and an axial magnetic field of 0.73 T, an average power of 1.0 GW with power conversion efficiency of 21.9% is obtained and the two dominant frequencies are 8.09 GHz and 9.91 GHz. The efficiency is higher than dual-band non-coaxial RBWO and other dual-band high-power microwave (HPM) generators. A more clear and stable beat radiation microwave power with beat frequency of 1.82 GHz is acquired, and the dual frequencies both demonstrate periodic-like dependence on the length of the tapered waveguide between the two SWS sections.
2013,
25: 1189-1194.
doi: 10.3788/HPLPB20132505.1189
Abstract:
The effect of periodic rectangular grooves on output window multipactor of horn antennas is analyzed theoretically. Dynamic calculation is applied to the research of the electron transit time and collision energy under groove surface. It is found that dielectric window with suitable grooves can effectively suppress the emission of secondary electrons. Using electromagnetic wave simulation software, the radiation pattern and transmission efficiency of the windows with and without the grooves have been investigated. Results show that, for the dielectric window with grooves with 2 mm in period, 1 mm in width, and 1 mm in depth, the influence of the grooves can be neglected.
The effect of periodic rectangular grooves on output window multipactor of horn antennas is analyzed theoretically. Dynamic calculation is applied to the research of the electron transit time and collision energy under groove surface. It is found that dielectric window with suitable grooves can effectively suppress the emission of secondary electrons. Using electromagnetic wave simulation software, the radiation pattern and transmission efficiency of the windows with and without the grooves have been investigated. Results show that, for the dielectric window with grooves with 2 mm in period, 1 mm in width, and 1 mm in depth, the influence of the grooves can be neglected.
2013,
25: 1195-1199.
doi: 10.3788/HPLPB20132505.1195
Abstract:
In order to suppress oscillation and maintain stability in the development of W-band folded waveguide traveling wave tube, this paper presents the analysis of reflection, backward wave and band edge oscillations. Periodic step structure together with other design and fabrication research improvement was applied to increasing the oscillation threshold. The investigation on oscillation suppression for W-band folded waveguide was carried out by simulation and experiment. After the methods mentioned above were applied as the most important key technologies to improving the output power and broadening the bandwidth, the developed W-band folded waveguide traveling wave tube could maintain stability from possible oscillations and reach over 100 Woutputpower with 5 GHz bandwidth at 20% duty cycle.
In order to suppress oscillation and maintain stability in the development of W-band folded waveguide traveling wave tube, this paper presents the analysis of reflection, backward wave and band edge oscillations. Periodic step structure together with other design and fabrication research improvement was applied to increasing the oscillation threshold. The investigation on oscillation suppression for W-band folded waveguide was carried out by simulation and experiment. After the methods mentioned above were applied as the most important key technologies to improving the output power and broadening the bandwidth, the developed W-band folded waveguide traveling wave tube could maintain stability from possible oscillations and reach over 100 Woutputpower with 5 GHz bandwidth at 20% duty cycle.
2013,
25: 1200-1204.
doi: 10.3788/HPLPB20132505.1200
Abstract:
Based on the basic principle of semiconductor physics, an analytical theoretical model was proposed to show the relationship between the microwave pulse power threshold triggering the internal transient latch-up in the CMOS inverter and pulse width quantitatively by solving the continuity equations for minority carriers. By comparing the proposed theoretical model with simulated results and experimental data reported in literatures, the correctness of the theoretical model was verified. Furthermore, the model suggests that the power threshold triggering the internal transient latch-up in the CMOS inverter is a decreasing function of pulse width as the pulse width is short. However, there is an inflexion range and the power threshold varies little when the pulse width exceeds the inflexion range.
Based on the basic principle of semiconductor physics, an analytical theoretical model was proposed to show the relationship between the microwave pulse power threshold triggering the internal transient latch-up in the CMOS inverter and pulse width quantitatively by solving the continuity equations for minority carriers. By comparing the proposed theoretical model with simulated results and experimental data reported in literatures, the correctness of the theoretical model was verified. Furthermore, the model suggests that the power threshold triggering the internal transient latch-up in the CMOS inverter is a decreasing function of pulse width as the pulse width is short. However, there is an inflexion range and the power threshold varies little when the pulse width exceeds the inflexion range.
2013,
25: 1205-1210.
doi: 10.3788/HPLPB20132505.1205
Abstract:
Using an ultra high-speed framing camera Hsfc-Pro, the development of vacuum surface flashover of grooved dielectrics is investigated. Variations in flashover images between the plane and grooved dielectric samples are compared. Then the capability of grooved dielectrics in strengthening the insulation strength is discussed. It is found that the introduction of periodical grooves alters obviously the flashover channel. With respect to the plane samples, their flashover channel develops along a straight line across the A-K gap, while for the grooved dielectrics, their flashover channel locates at the circular edge of the samples. Such a bended path increases obviously the flashover distance, therefore, the flashover time delay of grooved dielectrics is at least /2 times that of plane ones. This certifies that grooved dielectrics can increase promisingly the insulation strength without increasing their physical dimension.
Using an ultra high-speed framing camera Hsfc-Pro, the development of vacuum surface flashover of grooved dielectrics is investigated. Variations in flashover images between the plane and grooved dielectric samples are compared. Then the capability of grooved dielectrics in strengthening the insulation strength is discussed. It is found that the introduction of periodical grooves alters obviously the flashover channel. With respect to the plane samples, their flashover channel develops along a straight line across the A-K gap, while for the grooved dielectrics, their flashover channel locates at the circular edge of the samples. Such a bended path increases obviously the flashover distance, therefore, the flashover time delay of grooved dielectrics is at least /2 times that of plane ones. This certifies that grooved dielectrics can increase promisingly the insulation strength without increasing their physical dimension.
2013,
25: 1211-1214.
doi: 10.3788/HPLPB20132505.1211
Abstract:
A method based on quasi-optical technology is presented for designing high power miter bend. It can realize high efficiency transmission in bend circular waveguide for TE0m mode. A conical Gaussian mode is generated from the propagated mode TE0m with the help of mode converter and then converted back to the propagated mode TE0m after the bend. Efficient transmission of the propagated mode is achieved since the conical Gaussian mode could decrease the diffraction losses at the mirror. A megawatt, TE01 mode miter bend with an operating frequency at Ka band is designed with this method. The HFSS results show that the transmission efficiency higher than 98% is obtained in the frequency band of 6.5%.
A method based on quasi-optical technology is presented for designing high power miter bend. It can realize high efficiency transmission in bend circular waveguide for TE0m mode. A conical Gaussian mode is generated from the propagated mode TE0m with the help of mode converter and then converted back to the propagated mode TE0m after the bend. Efficient transmission of the propagated mode is achieved since the conical Gaussian mode could decrease the diffraction losses at the mirror. A megawatt, TE01 mode miter bend with an operating frequency at Ka band is designed with this method. The HFSS results show that the transmission efficiency higher than 98% is obtained in the frequency band of 6.5%.
2013,
25: 1215-1220.
doi: 10.3788/HPLPB20132505.1215
Abstract:
For investigating the influence of high-power microwave and material characteristic parameters on flashover and breakdown on dielectric surfaces, a 1D3V PIC-MCC code is adopted in this simulation. By using this code, the number of electrons and ions, electron and ion density distributions, time and space distribution of space charge field, average electron energy, discharge power, deposited power, excitation and ionization loss power, and ionization frequency are studied numerically in detail. Ionization frequency increases with electric-field increasing, and then reaches to saturation and decreases slowly; higher value of electric-field causes more secondary electrons to form higher deposited power. Ionization frequency increases with microwave frequency decreasing, and then reaches to saturation and decreases slowly; higher frequency may suppress multipactor discharge. Thus high-power microwaves with higher value of electric-field and lower frequency is easier to induce breakdown. Reflection causes electric-field decrease and magnetic-filed increase on dielectric surfaces, which leads to the decrease of ionization frequency and secondary electron decrease, the shortening of the oscillation time of multipactor discharge, and the breakdown risk increase of the inner region of device. Compared with linear polarization, circular polarization causes more secondary electrons to form higher deposited power, and the breakdown risk increases. Shorter pulses produce fewer electrons and ions with lower average energy, which form lower deposited power, so high-power microwaves with long pulses are easier to induce breakdown. Longer rise time of pulses causes longer breakdown time, but could not decrease the breakdown risk. Compared with surface roughness, higher value of materials secondary emission yield increases breakdown risk markedly. Ionization frequency and average electron energy increase firstly, and then decrease with gas pressure increasing. Multipactor discharge dominates at low pressure, and ionization dominates at high pressure.
For investigating the influence of high-power microwave and material characteristic parameters on flashover and breakdown on dielectric surfaces, a 1D3V PIC-MCC code is adopted in this simulation. By using this code, the number of electrons and ions, electron and ion density distributions, time and space distribution of space charge field, average electron energy, discharge power, deposited power, excitation and ionization loss power, and ionization frequency are studied numerically in detail. Ionization frequency increases with electric-field increasing, and then reaches to saturation and decreases slowly; higher value of electric-field causes more secondary electrons to form higher deposited power. Ionization frequency increases with microwave frequency decreasing, and then reaches to saturation and decreases slowly; higher frequency may suppress multipactor discharge. Thus high-power microwaves with higher value of electric-field and lower frequency is easier to induce breakdown. Reflection causes electric-field decrease and magnetic-filed increase on dielectric surfaces, which leads to the decrease of ionization frequency and secondary electron decrease, the shortening of the oscillation time of multipactor discharge, and the breakdown risk increase of the inner region of device. Compared with linear polarization, circular polarization causes more secondary electrons to form higher deposited power, and the breakdown risk increases. Shorter pulses produce fewer electrons and ions with lower average energy, which form lower deposited power, so high-power microwaves with long pulses are easier to induce breakdown. Longer rise time of pulses causes longer breakdown time, but could not decrease the breakdown risk. Compared with surface roughness, higher value of materials secondary emission yield increases breakdown risk markedly. Ionization frequency and average electron energy increase firstly, and then decrease with gas pressure increasing. Multipactor discharge dominates at low pressure, and ionization dominates at high pressure.
2013,
25: 1221-1225.
doi: 10.3788/HPLPB20132505.1221
Abstract:
The HPM UWB dual-reflector antenna has been optimized by Taguchis method, and simulated by FEKO software. The radiation efficiency, reflectance and high voltage insulation have been considered. The antenna reflectance was decreased by increasing the thickness of TEM horn plates. The simulation result shows that the VSWR of combined feeding horn at 800 MHz-1.25 GHz decreases from 3.5 to no more than 1.5.The electric field of screws which connect the sub-reflector and insulation nylon box is decreased by70% by optimizing the structure of sub-reflector and insulation box. The antenna can be fed with 81 GW UWB pulse without high power breakdown. The radiation field-range product has been improved by .2 times. The ratio of the radiation field-range product and source voltage reaches 11. The high power antenna experiments have been conducted. The experiment results verified that the high power capacitance of antenna is more than 30 GW, the field-range product exceeds 8 MV, the spectrum of radiation is from 182 MHz to 1.69 GHz, and the 3 dB widths of power of H- and E-plane of radiation are 2.35 and 2.27 respectively.
The HPM UWB dual-reflector antenna has been optimized by Taguchis method, and simulated by FEKO software. The radiation efficiency, reflectance and high voltage insulation have been considered. The antenna reflectance was decreased by increasing the thickness of TEM horn plates. The simulation result shows that the VSWR of combined feeding horn at 800 MHz-1.25 GHz decreases from 3.5 to no more than 1.5.The electric field of screws which connect the sub-reflector and insulation nylon box is decreased by70% by optimizing the structure of sub-reflector and insulation box. The antenna can be fed with 81 GW UWB pulse without high power breakdown. The radiation field-range product has been improved by .2 times. The ratio of the radiation field-range product and source voltage reaches 11. The high power antenna experiments have been conducted. The experiment results verified that the high power capacitance of antenna is more than 30 GW, the field-range product exceeds 8 MV, the spectrum of radiation is from 182 MHz to 1.69 GHz, and the 3 dB widths of power of H- and E-plane of radiation are 2.35 and 2.27 respectively.
2013,
25: 1226-1230.
doi: 10.3788/HPLPB20132505.1226
Abstract:
We have designed a single gap cylindrical coaxial cavity operating at transverse magnetic TM310-mode with low external quality factor for X-band klystron. Under the condition of the gap impedance imaginary part being zero at the working center frequency, the equivalent gap center of drift tubes at TM310 in the coaxial cavity is calculated with equivalent circuit theory, and then the equivalent length between the center and the transverse diaphragms in output waveguide is calculated. The equivalent gap impedance of the cylindrical coaxial cavity coupled with a waveguide filter containing a pair of transverse diaphragms is calculated with MATLAB and the result is coinciding with that of the cold test. This indicates that the equivalent length calculation method is correct. Thus the microwave equivalent circuit theory is not only applicable to analyzing TM010 mode in cylindrical cavity, but alsosuitable for studying the output circuit of high order transverse magnetic mode in single gap cylindrical coaxial cavity. Furthermore, its process is speedier compared with traditional cold test simulation and field analysis methods.
We have designed a single gap cylindrical coaxial cavity operating at transverse magnetic TM310-mode with low external quality factor for X-band klystron. Under the condition of the gap impedance imaginary part being zero at the working center frequency, the equivalent gap center of drift tubes at TM310 in the coaxial cavity is calculated with equivalent circuit theory, and then the equivalent length between the center and the transverse diaphragms in output waveguide is calculated. The equivalent gap impedance of the cylindrical coaxial cavity coupled with a waveguide filter containing a pair of transverse diaphragms is calculated with MATLAB and the result is coinciding with that of the cold test. This indicates that the equivalent length calculation method is correct. Thus the microwave equivalent circuit theory is not only applicable to analyzing TM010 mode in cylindrical cavity, but alsosuitable for studying the output circuit of high order transverse magnetic mode in single gap cylindrical coaxial cavity. Furthermore, its process is speedier compared with traditional cold test simulation and field analysis methods.
2013,
25: 1231-1235.
doi: 10.3788/HPLPB20132505.1231
Abstract:
An inductively-loaded two-cavity wide-gap klystron amplifier (WKA) with high power injection driven by a relativistic backward wave oscillator (RBWO) is studied theoretically and experimentally for solving the problem of power insufficiency of existing seed sources. The electric power of the amplifier and oscillator is supplied by a single accelerator capable of producing dual electron beams. The main switch is electrically triggered to stabilize the diode voltage and the frequency of the RBWO. In the experiments, the frequency and phase of the WKA are locked by the RBWO. The relative phase difference of the applied microwave devices is locked within 16 in a single shot, and a phase jitter of 11 is obtained within a series of 4 shots with a duration of about 40 ns. Under a diode voltage of 530 kV and injection power of about 22 MW, an output power of 230 MW is achieved from the RBWO-WKA system with a conversion efficiency of approximately 11% and power gain of approximately 10 dB.
An inductively-loaded two-cavity wide-gap klystron amplifier (WKA) with high power injection driven by a relativistic backward wave oscillator (RBWO) is studied theoretically and experimentally for solving the problem of power insufficiency of existing seed sources. The electric power of the amplifier and oscillator is supplied by a single accelerator capable of producing dual electron beams. The main switch is electrically triggered to stabilize the diode voltage and the frequency of the RBWO. In the experiments, the frequency and phase of the WKA are locked by the RBWO. The relative phase difference of the applied microwave devices is locked within 16 in a single shot, and a phase jitter of 11 is obtained within a series of 4 shots with a duration of about 40 ns. Under a diode voltage of 530 kV and injection power of about 22 MW, an output power of 230 MW is achieved from the RBWO-WKA system with a conversion efficiency of approximately 11% and power gain of approximately 10 dB.
2013,
25: 1236-1240.
doi: 10.3788/HPLPB20132505.1236
Abstract:
The paper drew a comparison between the Fowler-Nordheim (FN) field emission current density which is applicable at low temperature and the general integral expression for field emission current density. A slender cylindrical microprotrusion model was adopted, two main factors－joule heating and heat conduction were both taken into account, and the temperature distribution in microprotrusion and the time-dependence of temperature at different points on microprotrusion were obtained using the code developed by ourselves. The results show that it is necessary to consider the influence of temperature effect of field emission on explosive electron emission. The temperature in microprotrusion increases nonlinearly with time when the temperature effect is included, and the increasing rate of the temperature grows more and more quickly. At low microwave electric field, the time delay of explosive electron emission will be shortened if the FN current density of electron emission is used instead of the general integral expression which can include the temperature effect of field emission; the temperature effect has little influence on time delay of explosive electron emission at high microwave electric field.
The paper drew a comparison between the Fowler-Nordheim (FN) field emission current density which is applicable at low temperature and the general integral expression for field emission current density. A slender cylindrical microprotrusion model was adopted, two main factors－joule heating and heat conduction were both taken into account, and the temperature distribution in microprotrusion and the time-dependence of temperature at different points on microprotrusion were obtained using the code developed by ourselves. The results show that it is necessary to consider the influence of temperature effect of field emission on explosive electron emission. The temperature in microprotrusion increases nonlinearly with time when the temperature effect is included, and the increasing rate of the temperature grows more and more quickly. At low microwave electric field, the time delay of explosive electron emission will be shortened if the FN current density of electron emission is used instead of the general integral expression which can include the temperature effect of field emission; the temperature effect has little influence on time delay of explosive electron emission at high microwave electric field.
2013,
25: 1241-1246.
doi: 10.3788/HPLPB20132505.1241
Abstract:
In order to quantitatively study the coupling terminal response electromagnetic wave and microstrip line, a coupling analysis method was proposed based on the BLT equation. It greatly improve the computational efficiency and occupies less memory, compared with traditional methods. The microstrip line on the printed circuit board (PCB) was equivalent to a lossy transmission line, and the plane wave vector was analyzed and the effective excitation source was solved, The influence of different incident waves and incidence angles on the microstrip line terminal was investigated using the BLT equation. The time-domain and frequency-domain analyses on the incident wave and terminal response were performed. The results show that, when the frequency of the incident wave has a certain relationship with the microstrip line, the peak coupling voltage reaches a maximum of 2.4 mV; the terminal peak voltage, when electric field is parallel to the microstrip line, is twice that for electric field perpendicular to the PCB; the peak coupling voltage of the microstrip line caused by rectangular pulses is larger than those for Gaussian pulses and triangular pulse with the same amplitude and pulse width; the terminal coupling voltage could reach millivolt level by adjusting the pulse width of different pulses.
In order to quantitatively study the coupling terminal response electromagnetic wave and microstrip line, a coupling analysis method was proposed based on the BLT equation. It greatly improve the computational efficiency and occupies less memory, compared with traditional methods. The microstrip line on the printed circuit board (PCB) was equivalent to a lossy transmission line, and the plane wave vector was analyzed and the effective excitation source was solved, The influence of different incident waves and incidence angles on the microstrip line terminal was investigated using the BLT equation. The time-domain and frequency-domain analyses on the incident wave and terminal response were performed. The results show that, when the frequency of the incident wave has a certain relationship with the microstrip line, the peak coupling voltage reaches a maximum of 2.4 mV; the terminal peak voltage, when electric field is parallel to the microstrip line, is twice that for electric field perpendicular to the PCB; the peak coupling voltage of the microstrip line caused by rectangular pulses is larger than those for Gaussian pulses and triangular pulse with the same amplitude and pulse width; the terminal coupling voltage could reach millivolt level by adjusting the pulse width of different pulses.
2013,
25: 1247-1250.
doi: 10.3788/HPLPB20132505.1247
Abstract:
Microwave imaging reflectometry (MIR) is a kind of important means in plasma turbulence diagnosis, which is used to obtain the 2-D/3-D image of the turbulences and instabilities with high space and time resolutions, so that visualized real-time observation of plasma turbulence field can be achieved and more accurate information can be gained. This paper presents the theoretical calculation and optical simulation of an 8 mm MIR with quasi-optical system according to the parameters of the HL-2A Tokamak. And the quasi-optical system in the MIR is then designed.
Microwave imaging reflectometry (MIR) is a kind of important means in plasma turbulence diagnosis, which is used to obtain the 2-D/3-D image of the turbulences and instabilities with high space and time resolutions, so that visualized real-time observation of plasma turbulence field can be achieved and more accurate information can be gained. This paper presents the theoretical calculation and optical simulation of an 8 mm MIR with quasi-optical system according to the parameters of the HL-2A Tokamak. And the quasi-optical system in the MIR is then designed.
2013,
25: 1251-1255.
doi: 10.3788/HPLPB20132505.1251
Abstract:
The requirements of part of power supply control systems for the heavy ion accelerator were analyzed, and a real-time, efficient, multi-function control system was proposed and achieved. The key processing architecture of this system is based on a combination of a digital signal processor (DSP) and two field programmable gate array (FPGA) chips. The back-end of the system exchanges data with the system controller and other components in the industrial control chassis by the PXI bus interface and the FPGA. The front-end of the system can process control parameters of different power supplies and output the power through the direct digital synthesizer, analog to digital converter, digital to analog converter, and the control algorithm and mechanism realized in the DSP and FPGA. The two groups of fiber optical modules corresponding with the front-end FPGA can achieve the receiving and sending efficiently for the real-time data like synchronous event signal and the debugging of the platform.
The requirements of part of power supply control systems for the heavy ion accelerator were analyzed, and a real-time, efficient, multi-function control system was proposed and achieved. The key processing architecture of this system is based on a combination of a digital signal processor (DSP) and two field programmable gate array (FPGA) chips. The back-end of the system exchanges data with the system controller and other components in the industrial control chassis by the PXI bus interface and the FPGA. The front-end of the system can process control parameters of different power supplies and output the power through the direct digital synthesizer, analog to digital converter, digital to analog converter, and the control algorithm and mechanism realized in the DSP and FPGA. The two groups of fiber optical modules corresponding with the front-end FPGA can achieve the receiving and sending efficiently for the real-time data like synchronous event signal and the debugging of the platform.
2013,
25: 1256-1260.
doi: 10.3788/HPLPB20132505.1256
Abstract:
The beam transport system of the Dragon-Ⅰ linear induction accelerator(LIA) consists of hundreds of solenoid coils and dipole steering coils, which are designed to reduce corkscrew amplitude and transverse motion of electron beam. In order to improve the beam quality, a genetic optimization model of solenoid currents is proposed in this paper and the optimization code GABC based on genetic algorithm and beam transport models is designed, which contains both beam centroid track and the beam envelope model. The matched magnetic field in five blocks of the Dragon-Ⅰ LIA, including twenty induction acceleration cells and five connection cells, are analyzed using the optimization code. The numerical results reveal that the GABC is effective to solve transport magnetic field optimization problems and could play an important role for beam tuning simulation and experiment.
The beam transport system of the Dragon-Ⅰ linear induction accelerator(LIA) consists of hundreds of solenoid coils and dipole steering coils, which are designed to reduce corkscrew amplitude and transverse motion of electron beam. In order to improve the beam quality, a genetic optimization model of solenoid currents is proposed in this paper and the optimization code GABC based on genetic algorithm and beam transport models is designed, which contains both beam centroid track and the beam envelope model. The matched magnetic field in five blocks of the Dragon-Ⅰ LIA, including twenty induction acceleration cells and five connection cells, are analyzed using the optimization code. The numerical results reveal that the GABC is effective to solve transport magnetic field optimization problems and could play an important role for beam tuning simulation and experiment.
2013,
25: 1261-1264.
doi: 10.3788/HPLPB20132505.1261
Abstract:
A kind of narrow-gap opposed-contact photoconductive semiconductor switch(PCSS) is described in this paper, and it will be used in the dielectric wall accelerator(DWA) in a near future. The switch we used in the experiment is an opposed contact GaAs PCSS whose electrode gap is 5 mm. When the bias pulsed voltage is between 15 kV and 22 kV, it works in the nonlinear mode. The pulsed laser, triggering the PCSS, is from the laser diode, and it has the wavelength, FWHM, rise-time, and peak power of about 905 nm, 20 ns, 3.1 ns and 90 W, respectively. As a result, when the PCSS works at a low voltage, it has a long lifetime but poor performance; while, when the PCSS works at a high voltage and is triggered by a high peak power pulsed laser, it works well but has a shorter lifetime.
A kind of narrow-gap opposed-contact photoconductive semiconductor switch(PCSS) is described in this paper, and it will be used in the dielectric wall accelerator(DWA) in a near future. The switch we used in the experiment is an opposed contact GaAs PCSS whose electrode gap is 5 mm. When the bias pulsed voltage is between 15 kV and 22 kV, it works in the nonlinear mode. The pulsed laser, triggering the PCSS, is from the laser diode, and it has the wavelength, FWHM, rise-time, and peak power of about 905 nm, 20 ns, 3.1 ns and 90 W, respectively. As a result, when the PCSS works at a low voltage, it has a long lifetime but poor performance; while, when the PCSS works at a high voltage and is triggered by a high peak power pulsed laser, it works well but has a shorter lifetime.
2013,
25: 1265-1269.
doi: 10.3788/HPLPB20132505.1265
Abstract:
A general laser-beam synchronization method based on coherent radiation measurement is introduced. Fundamental principles and detailed steps to achieve spatial and temporal synchronization are described. Sub-picosecond level synchronization between the seed laser and the electron beam has been achieved with this method at the Shanghai Deep-Ultraviolet Free-Electron Laser (SDUV-FEL) test facility, which lays a solid foundation for seeding experiments such as high-gain harmonic-generation (HGHG), echo-enabled harmonic-generation (EEHG) and cascaded HGHG. Moreover, longitudinal profiles of the electron beam under different conditions are measured and analyzed.
A general laser-beam synchronization method based on coherent radiation measurement is introduced. Fundamental principles and detailed steps to achieve spatial and temporal synchronization are described. Sub-picosecond level synchronization between the seed laser and the electron beam has been achieved with this method at the Shanghai Deep-Ultraviolet Free-Electron Laser (SDUV-FEL) test facility, which lays a solid foundation for seeding experiments such as high-gain harmonic-generation (HGHG), echo-enabled harmonic-generation (EEHG) and cascaded HGHG. Moreover, longitudinal profiles of the electron beam under different conditions are measured and analyzed.
2013,
25: 1270-1274.
doi: 10.3788/HPLPB20132505.1270
Abstract:
Large number and variety of instruments with complex interfaces are the main characteristics of the measurement and control system in multi-pulse and high-current linear induction accelerator(LIA). The instruments are divided into distinct subsystems according to their function, and the instruments in each subsystem are joined to the model of protocol transition, and then linked with the local server in the network of the measurement and control system. The software of communication and control for instruments is programmed based on LabVIEW. VISA library and UDP protocol are applied to the software in local server, and DataSocket protocol is applied to the remote communication. Circuits of power supply and charger to Marx are heavily insulated against the electromagnetic disturbance and high voltage strike. For improving reliability, network structure and data flows are optimized, UDP protocols are applied, and master-slave pattern is also applied to bus arbitration. The system runs steadily and reliably in multi-pulse and high-current LIA by this time.
Large number and variety of instruments with complex interfaces are the main characteristics of the measurement and control system in multi-pulse and high-current linear induction accelerator(LIA). The instruments are divided into distinct subsystems according to their function, and the instruments in each subsystem are joined to the model of protocol transition, and then linked with the local server in the network of the measurement and control system. The software of communication and control for instruments is programmed based on LabVIEW. VISA library and UDP protocol are applied to the software in local server, and DataSocket protocol is applied to the remote communication. Circuits of power supply and charger to Marx are heavily insulated against the electromagnetic disturbance and high voltage strike. For improving reliability, network structure and data flows are optimized, UDP protocols are applied, and master-slave pattern is also applied to bus arbitration. The system runs steadily and reliably in multi-pulse and high-current LIA by this time.
2013,
25: 1275-1278.
doi: 10.3788/HPLPB20132505.1275
Abstract:
Pin power distributions in the China Experimental Fast Reactor(CEFR) should be calculated for thermal hydraulics calculation. Monte Carlo program was used to calculate the pin power distributions and the statistical error of the calculation results is guaranteed to be less than 0.8%. Another program based on nodal diffusion theory, NAS, was used to provide reference for the Monte Carlo results of pin power distributions. It is indicated that the maximum deviation of pin power distributions obtained with the two programs is less than 3%. Thus, application of Monte Carlo program to calculation of pin power distributions in the fuel subassembly of CEFR is credible, and moreover can be generalized to reactor design.
Pin power distributions in the China Experimental Fast Reactor(CEFR) should be calculated for thermal hydraulics calculation. Monte Carlo program was used to calculate the pin power distributions and the statistical error of the calculation results is guaranteed to be less than 0.8%. Another program based on nodal diffusion theory, NAS, was used to provide reference for the Monte Carlo results of pin power distributions. It is indicated that the maximum deviation of pin power distributions obtained with the two programs is less than 3%. Thus, application of Monte Carlo program to calculation of pin power distributions in the fuel subassembly of CEFR is credible, and moreover can be generalized to reactor design.
2013,
25: 1279-1282.
doi: 10.3788/HPLPB20132505.1279
Abstract:
In neutron depth profiling(NDP), the recorded ions have a spread of energies because of energy straggling, geometrical acceptance angles and detector energy resolution effects. In common conditions, a physical model predicting the observed energy spectrum of a sample with target nuclide in prearranged depth changes is built on the basis of Gaussian function. The predicted ion spectrum derived from the above model is well accorded with the observed energy spectrum in peak position and FWHM. So the model can be applied to deconvolution of NDP spectra.
In neutron depth profiling(NDP), the recorded ions have a spread of energies because of energy straggling, geometrical acceptance angles and detector energy resolution effects. In common conditions, a physical model predicting the observed energy spectrum of a sample with target nuclide in prearranged depth changes is built on the basis of Gaussian function. The predicted ion spectrum derived from the above model is well accorded with the observed energy spectrum in peak position and FWHM. So the model can be applied to deconvolution of NDP spectra.
2013,
25: 1283-1287.
doi: 10.3788/HPLPB20132505.1283
Abstract:
Dust particles were produced in situ using reactive mixtures (SiH4/C2H4/Ar) in radio-frequency(RF) discharge. To get more information about dusty plasma, Langmuir probe and optical emission spectroscopy diagnoses were introduced. Then the emission intensities of Si+ 390.6 nm, Si2+ 380.6 nm and C+ 426.7 nm as a function of pressure, RF power, and flow rates of SiH4/C2H4 were presented. The emission intensities of Si+, Si2+ and C+ are enhanced with the increase of gas pressure and RF power. But as the flow rates of SiH4/C2H4 increase, the emission intensities are weakened. By using Langmuir probe, the density of dust particles was calculated from electron density and ion density, and then variation of the dust particle density with RF power was derived, which is basically consistent with the trend of SiH4/C2H4 dissociation.
Dust particles were produced in situ using reactive mixtures (SiH4/C2H4/Ar) in radio-frequency(RF) discharge. To get more information about dusty plasma, Langmuir probe and optical emission spectroscopy diagnoses were introduced. Then the emission intensities of Si+ 390.6 nm, Si2+ 380.6 nm and C+ 426.7 nm as a function of pressure, RF power, and flow rates of SiH4/C2H4 were presented. The emission intensities of Si+, Si2+ and C+ are enhanced with the increase of gas pressure and RF power. But as the flow rates of SiH4/C2H4 increase, the emission intensities are weakened. By using Langmuir probe, the density of dust particles was calculated from electron density and ion density, and then variation of the dust particle density with RF power was derived, which is basically consistent with the trend of SiH4/C2H4 dissociation.
2013,
25: 1288-1292.
doi: 10.3788/HPLPB20132505.1288
Abstract:
Ensemble empirical mode decomposition (EEMD) of the lightning negative return strokes was conducted and a set of almost complete and orthogonal components named intrinsic mode functions (IMFs) having physical meaning were obtained. The results show that IMF1 is the high frequency noise item and the residual item is mainly due to the electrostatic field. IMF2-IMF11 represent the discharge characteristics of the lightning channel in different scales, respectively. According to the calculation of the fractal dimension of different IMFs, the fractal dimension will increase with the increasing IMF order, indicating that the IMF with higher order corresponds to the discharge channel with increasing tortuosity. It is also found that EEMD-based Hilbert-Huang transform (HHT) spectrum can ameliorate mode mixing and it is more suitable for analyzing the lightning than EMD-based HHT analysis and wavelet analysis.
Ensemble empirical mode decomposition (EEMD) of the lightning negative return strokes was conducted and a set of almost complete and orthogonal components named intrinsic mode functions (IMFs) having physical meaning were obtained. The results show that IMF1 is the high frequency noise item and the residual item is mainly due to the electrostatic field. IMF2-IMF11 represent the discharge characteristics of the lightning channel in different scales, respectively. According to the calculation of the fractal dimension of different IMFs, the fractal dimension will increase with the increasing IMF order, indicating that the IMF with higher order corresponds to the discharge channel with increasing tortuosity. It is also found that EEMD-based Hilbert-Huang transform (HHT) spectrum can ameliorate mode mixing and it is more suitable for analyzing the lightning than EMD-based HHT analysis and wavelet analysis.
2013,
25: 1293-1297.
doi: 10.3788/HPLPB20132505.1293
Abstract:
A switch-trigger system for a 2.0 MJ pulsed power supply module has been developed. This paper discusses the design, construction and testing of this switch-trigger system. In the section about the mathematical principles, the equations of the lifetime and stability of the spark gap switch and its trigger generator are given. Extensive testing has proved the operating parameters of the switch-trigger system. The measured discharge current of the 2.0 MJ capacitive pulsed power supply module is demonstrated to be over 500 kA and the transfer charge per shot is over 150 C. The switch trigger system can support more than 200 kC transfer charge, and it can support simultaneous operation of 20 pairs of xeon flash lamps in theory. Moreover, the lifetime of this switch can be extended by replacing the graphite electrodes adopted.
A switch-trigger system for a 2.0 MJ pulsed power supply module has been developed. This paper discusses the design, construction and testing of this switch-trigger system. In the section about the mathematical principles, the equations of the lifetime and stability of the spark gap switch and its trigger generator are given. Extensive testing has proved the operating parameters of the switch-trigger system. The measured discharge current of the 2.0 MJ capacitive pulsed power supply module is demonstrated to be over 500 kA and the transfer charge per shot is over 150 C. The switch trigger system can support more than 200 kC transfer charge, and it can support simultaneous operation of 20 pairs of xeon flash lamps in theory. Moreover, the lifetime of this switch can be extended by replacing the graphite electrodes adopted.
2013,
25: 1298-1302.
doi: 10.3788/HPLPB20132505.1298
Abstract:
A test stand of one-meter long coaxial magnetically-insulated-transmission line (MITL) with 2 cm anode-cathode gap was designed and constructed based on the Qiangguang-Ⅰ facility. Current-loss characteristics of MITL with the load resistance of 0, 2.07, 4.12 and 5.68 were experimentally studied. Experimental results show that current loss along the MITL which fits in with the principle of magnetic insulation mainly occurred in the areas with abrupt change of geometrical impedance. And it is also shown that with the load resistance of 2.07 , the ratio of the vacuum electron flow between anode and cathode gap to the transmission-line current is close to 17.4%, and it increases gradually with the enhancement of the load resistance. Finally, based on theories of the space-charge flow, the experimental phenomena mentioned above were qualitatively analyzed and discussed.
A test stand of one-meter long coaxial magnetically-insulated-transmission line (MITL) with 2 cm anode-cathode gap was designed and constructed based on the Qiangguang-Ⅰ facility. Current-loss characteristics of MITL with the load resistance of 0, 2.07, 4.12 and 5.68 were experimentally studied. Experimental results show that current loss along the MITL which fits in with the principle of magnetic insulation mainly occurred in the areas with abrupt change of geometrical impedance. And it is also shown that with the load resistance of 2.07 , the ratio of the vacuum electron flow between anode and cathode gap to the transmission-line current is close to 17.4%, and it increases gradually with the enhancement of the load resistance. Finally, based on theories of the space-charge flow, the experimental phenomena mentioned above were qualitatively analyzed and discussed.
2013,
25: 1303-1306.
doi: 10.3788/HPLPB20132505.1303
Abstract:
Closure jitter versus voltage ratio and trigger voltage was experimentally measured for a six-stage gas switch. An ultra-violet fiber system was used to diagnose the discharge process influencing the closure jitter, and a pre-ionizing measure was employed to decrease the trigger voltage. It is found that the switch closure jitter declines exponentially with the product of trigger voltage and voltage ratio. The trigger gap accounts for 30%-40% of the closure jitter while the other five gaps account for 60%-70%. The trigger voltage and voltage ratio have more influences on the jitter of the trigger gap which breaks down first, than on that of the three gaps discharging subsequently, and hardly affects the last two gaps. For the switch with a voltage ratio greater than 57%, the pre-ionizing measure finally lowers the trigger voltage by over 10 kV.
Closure jitter versus voltage ratio and trigger voltage was experimentally measured for a six-stage gas switch. An ultra-violet fiber system was used to diagnose the discharge process influencing the closure jitter, and a pre-ionizing measure was employed to decrease the trigger voltage. It is found that the switch closure jitter declines exponentially with the product of trigger voltage and voltage ratio. The trigger gap accounts for 30%-40% of the closure jitter while the other five gaps account for 60%-70%. The trigger voltage and voltage ratio have more influences on the jitter of the trigger gap which breaks down first, than on that of the three gaps discharging subsequently, and hardly affects the last two gaps. For the switch with a voltage ratio greater than 57%, the pre-ionizing measure finally lowers the trigger voltage by over 10 kV.
2013,
25: 1307-1310.
doi: 10.3788/HPLPB20132505.1307
Abstract:
The visible radiation has been studied in wire array Z-pinch experiments on Yang accelerator using a silicone photodiode with 1 ns rise time, multi-mode optical fiber and quartz filter. Experimental data show that the visible radiation detected at implosion initial phase is different from X-ray radiation profile and there is a inflexion in front of the profile peak. The visible radiation is owed significantly to single wire pinch and precursor plasma before implosion stagnation, while the inflexion of the radiation profile is formed because the local magnetic field near the single wire disappears just before the whole implosion.
The visible radiation has been studied in wire array Z-pinch experiments on Yang accelerator using a silicone photodiode with 1 ns rise time, multi-mode optical fiber and quartz filter. Experimental data show that the visible radiation detected at implosion initial phase is different from X-ray radiation profile and there is a inflexion in front of the profile peak. The visible radiation is owed significantly to single wire pinch and precursor plasma before implosion stagnation, while the inflexion of the radiation profile is formed because the local magnetic field near the single wire disappears just before the whole implosion.
2013,
25: 1311-1314.
doi: 10.3788/HPLPB20132505.1311
Abstract:
A kind of ceramic slab with high energy storage density is appropriate to be employed in parallel-plate stacked Blumlein lines (SBLs). In this paper, we propose the design concept of a parallel-plate SBL using ceramic slabs. A stacked rail-gap triggered switch (SRTS) is designed for achieving a fast rise-time of less than 10 ns. For verifying this design concept, the prototype of a 2-stage SBL has been developed and tested. Experimental results demonstrate that the SBL design depicted here is suitable for a modularized pulsed power system.
A kind of ceramic slab with high energy storage density is appropriate to be employed in parallel-plate stacked Blumlein lines (SBLs). In this paper, we propose the design concept of a parallel-plate SBL using ceramic slabs. A stacked rail-gap triggered switch (SRTS) is designed for achieving a fast rise-time of less than 10 ns. For verifying this design concept, the prototype of a 2-stage SBL has been developed and tested. Experimental results demonstrate that the SBL design depicted here is suitable for a modularized pulsed power system.
2013,
25: 1315-1319.
doi: 10.3788/HPLPB20132505.1315
Abstract:
In order to achieve the series connection of insulated gate bipolar transistors (IGBTs), resistor-capacitor-diode (RCD) snubber circuit, which was chosen for active voltage sharing, was analyzed by mathematical methods, then the RCD snubber circuit parameters were modeled and proved by PSpice simulations. Based on optical fiber transmission and M57962L, the drive circuit and fault feedback circuit controlled by digital signal processor (DSP) were designed to drive 32 series connected IGBTs and for overcurrent and short circuit protection. The maximum break-over time in 32 IGBTs was 90 ns, while failure protection completion time was 6 s. Eight independent isolated sources were designed for the isolation voltageof 50 kV. Based on the above research achievements, the 32 IGBTs series connected circuit can work safely under the voltage of 20 kV.
In order to achieve the series connection of insulated gate bipolar transistors (IGBTs), resistor-capacitor-diode (RCD) snubber circuit, which was chosen for active voltage sharing, was analyzed by mathematical methods, then the RCD snubber circuit parameters were modeled and proved by PSpice simulations. Based on optical fiber transmission and M57962L, the drive circuit and fault feedback circuit controlled by digital signal processor (DSP) were designed to drive 32 series connected IGBTs and for overcurrent and short circuit protection. The maximum break-over time in 32 IGBTs was 90 ns, while failure protection completion time was 6 s. Eight independent isolated sources were designed for the isolation voltageof 50 kV. Based on the above research achievements, the 32 IGBTs series connected circuit can work safely under the voltage of 20 kV.
2013,
25: 1320-1324.
doi: 10.3788/HPLPB20132505.1320
Abstract:
When a pulse forming line (PFL) is being charged, the voltage will be not the same on the PFL for the short charging time and certain length of the PFL. Therefore, the output voltage on the load resistance is also changed. This is researched in theory and simulation in this paper. First, the mechanism of nonuniform charging is studied, and output voltage is calculated in this situation based on the telegraph equation with the initial condition of nonuniform charging. Then, the circuit simulation is carried out to verify the results of theoretical analysis. It is shown that, the flat of the output voltage turns to be up-and-down due to nonuniform charging.
When a pulse forming line (PFL) is being charged, the voltage will be not the same on the PFL for the short charging time and certain length of the PFL. Therefore, the output voltage on the load resistance is also changed. This is researched in theory and simulation in this paper. First, the mechanism of nonuniform charging is studied, and output voltage is calculated in this situation based on the telegraph equation with the initial condition of nonuniform charging. Then, the circuit simulation is carried out to verify the results of theoretical analysis. It is shown that, the flat of the output voltage turns to be up-and-down due to nonuniform charging.
2013,
25: 1325-1331.
doi: 10.3788/HPLPB20132505.1325
Abstract:
Terahertz (THz) pulses after spatiotemporal shaping have been widely applied to THz spectroscopy and imaging. We simulate the shaping effect of rectangular and circular apertures by employing the three-dimensional (3D) finite-difference-time-domain (FDTD) method. The simulation results show that we can realize effective shaping and filtering of THz pulses using rectangular and circular conductive apertures of finite thickness. When the long side of the rectangular aperture is perpendicular to the polarization direction of the incident wave, the rectangular aperture has a good influence on the shaping and filtering of THz pulses. However, when the long side of the rectangular aperture is parallel to the polarization direction of the incident wave, it almost has no obvious effect on the shaping and filtering of THz pulses. The circular aperture has more obvious effect on shaping of THz pulses than the rectangular aperture. Moreover, these simulation results can be interpreted qualitatively by the theory of planar waveguides.
Terahertz (THz) pulses after spatiotemporal shaping have been widely applied to THz spectroscopy and imaging. We simulate the shaping effect of rectangular and circular apertures by employing the three-dimensional (3D) finite-difference-time-domain (FDTD) method. The simulation results show that we can realize effective shaping and filtering of THz pulses using rectangular and circular conductive apertures of finite thickness. When the long side of the rectangular aperture is perpendicular to the polarization direction of the incident wave, the rectangular aperture has a good influence on the shaping and filtering of THz pulses. However, when the long side of the rectangular aperture is parallel to the polarization direction of the incident wave, it almost has no obvious effect on the shaping and filtering of THz pulses. The circular aperture has more obvious effect on shaping of THz pulses than the rectangular aperture. Moreover, these simulation results can be interpreted qualitatively by the theory of planar waveguides.
2013,
25: 1332-1336.
doi: 10.3788/HPLPB20132505.1332
Abstract:
A fourstage cascade terahertz mesh bandpass filter has been designed according to the atmospheric absorption windows of terahertz waves. The center frequency of the filter is 0.25 THz, the bandwidth is 0.1 THz at 3 dB, the transmittance is greater than 80%, the ripple factor is less than 0.5 dB in the passband, and both of the center frequency and the bandwidth can be adjusted by scaling the size of mesh slot. The HFSS simulation conducted under periodic boundary conditions and absorbing boundary condition of perfectly matched layers shows the transmittance and insertion loss of this filter with different mesh arrangements anddielectric substrates, under incident waves of different incidence angles and different polarizations.
A fourstage cascade terahertz mesh bandpass filter has been designed according to the atmospheric absorption windows of terahertz waves. The center frequency of the filter is 0.25 THz, the bandwidth is 0.1 THz at 3 dB, the transmittance is greater than 80%, the ripple factor is less than 0.5 dB in the passband, and both of the center frequency and the bandwidth can be adjusted by scaling the size of mesh slot. The HFSS simulation conducted under periodic boundary conditions and absorbing boundary condition of perfectly matched layers shows the transmittance and insertion loss of this filter with different mesh arrangements anddielectric substrates, under incident waves of different incidence angles and different polarizations.
2013,
25: 1337-1340.
doi: 10.3788/HPLPB20132505.1337
Abstract:
The existing input structure for confocal waveguide is narrow-banded. Thus a quasi-optical input structure for 0.4 THz confocal waveguide gyro-TWT is designed based on Gaussian transformation, and the input mode is HE06 mode. This structure is composed of a corrugated waveguide mode converter, Gaussian transformation mirrors and a receiving antenna. The structure is validated through 3D electromagnetic simulation. The simulation result indicates that, the input efficiency exceeds 50% in the 8 GHz working band of the gyro-TWT and the highest efficiency is 68%.
The existing input structure for confocal waveguide is narrow-banded. Thus a quasi-optical input structure for 0.4 THz confocal waveguide gyro-TWT is designed based on Gaussian transformation, and the input mode is HE06 mode. This structure is composed of a corrugated waveguide mode converter, Gaussian transformation mirrors and a receiving antenna. The structure is validated through 3D electromagnetic simulation. The simulation result indicates that, the input efficiency exceeds 50% in the 8 GHz working band of the gyro-TWT and the highest efficiency is 68%.
