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RSS2012 Vol. 24, No. 05
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2012,
24: 1009-1010.
Abstract:
A master oscillator power amplifier(MOPA) structured pulsed Yb fiber laser is set up. The single-frequency pulsed seed, with a repetition rate of 10 MHz, a pulse duration of about 8 ns, and an average power of 0.5 mW, is obtained by externally modulating a continuous wave laser with line width of 20 kHz. The pulsed seed is amplified to 300.8 W of average power with four Yb-doped fiber amplifiers. Further power-scaling of this MOPA structure can be realized since our experiment is only pump-power limited.
A master oscillator power amplifier(MOPA) structured pulsed Yb fiber laser is set up. The single-frequency pulsed seed, with a repetition rate of 10 MHz, a pulse duration of about 8 ns, and an average power of 0.5 mW, is obtained by externally modulating a continuous wave laser with line width of 20 kHz. The pulsed seed is amplified to 300.8 W of average power with four Yb-doped fiber amplifiers. Further power-scaling of this MOPA structure can be realized since our experiment is only pump-power limited.
2012,
24: 1011-1012.
Abstract:
The paper investigates the relationship between the change of nuclear sample enrichment and the relative position of detectors of the 252Cf source-driven noise analysis system. A Monte Carlo numerical simulation with varied 235U enrichment (85.15%, 90.15%, 93.15%) and different relative positions has been conducted, and the cross-covariance between data of paired detectors was calculated. The results show that the amplitude of cross-covariance improves with 235U enrichment, which coincides with reference results. Thus it is feasible to estimate the nuclear material enrichment based on the cross-covariance amplitude of detectors.
The paper investigates the relationship between the change of nuclear sample enrichment and the relative position of detectors of the 252Cf source-driven noise analysis system. A Monte Carlo numerical simulation with varied 235U enrichment (85.15%, 90.15%, 93.15%) and different relative positions has been conducted, and the cross-covariance between data of paired detectors was calculated. The results show that the amplitude of cross-covariance improves with 235U enrichment, which coincides with reference results. Thus it is feasible to estimate the nuclear material enrichment based on the cross-covariance amplitude of detectors.
2012,
24: 1013-1014.
doi: 10.3788/HPLPB20122405.1013
Abstract:
Gyrotron traveling-wave tube (gyro-TWT) with helical waveguide has wider instantaneous frequency bandwidth than that with smooth waveguide. This paper introduces the linear theory of its beam-wave interaction, and calculates the influence on linear gain of Ka-band gyro-TWT caused by changing the applied magnetic field and the amplitude of the groove. The results accord with those reported, indicating that the theory can be used to preliminarily determine the parameters of gyro-TWT assembly.
Gyrotron traveling-wave tube (gyro-TWT) with helical waveguide has wider instantaneous frequency bandwidth than that with smooth waveguide. This paper introduces the linear theory of its beam-wave interaction, and calculates the influence on linear gain of Ka-band gyro-TWT caused by changing the applied magnetic field and the amplitude of the groove. The results accord with those reported, indicating that the theory can be used to preliminarily determine the parameters of gyro-TWT assembly.
2012,
24: 1019-1023.
doi: 10.3788/HPLPB20122405.1019
Abstract:
Analytical expressions for the propagation of nonparaxial radial array Gaussian laser beams in coherent and incoherent combinations are derived and used to study their propagation properties in free space, where the effect of array beam parameters on the intensity distribution of the resulting beam is stressed. It is shown that the ratio of array radius to waist width is a key parameter. The intensity distribution of the resulting beam in both coherent and incoherent combinations remain unchanged under the condition that the ratio of array radius to waist width is kept fixed, while the intensity distribution and the axial intensity maximum in the far field of the resulting beam depend on the combination scheme.
Analytical expressions for the propagation of nonparaxial radial array Gaussian laser beams in coherent and incoherent combinations are derived and used to study their propagation properties in free space, where the effect of array beam parameters on the intensity distribution of the resulting beam is stressed. It is shown that the ratio of array radius to waist width is a key parameter. The intensity distribution of the resulting beam in both coherent and incoherent combinations remain unchanged under the condition that the ratio of array radius to waist width is kept fixed, while the intensity distribution and the axial intensity maximum in the far field of the resulting beam depend on the combination scheme.
2012,
24: 1024-1028.
doi: 10.3788/HPLPB20122405.1024
Abstract:
By using a legible and comprehensive physical model describing the generation and evolvement of ion densities in the plasma channel induced by intense femtosecond laser pulse, the work studied the temporal evolution of the plasma densities in femtosecond light filaments. It shows that the contribution of the ionization of oxygen and nitrogen molecules to the total electron densities varies much for different laser pulse shapes, and the pulse shapes have more effects on the lifetime of the higher density plasma. It is necessary to control the pulse shape for efficient using of the plasma channel. Pulses of long duration and short wavelength can obtain a plasma channel with higher electron density, but the channel lifetime thoroughly depends on the later evolution of the self-guided channel.
By using a legible and comprehensive physical model describing the generation and evolvement of ion densities in the plasma channel induced by intense femtosecond laser pulse, the work studied the temporal evolution of the plasma densities in femtosecond light filaments. It shows that the contribution of the ionization of oxygen and nitrogen molecules to the total electron densities varies much for different laser pulse shapes, and the pulse shapes have more effects on the lifetime of the higher density plasma. It is necessary to control the pulse shape for efficient using of the plasma channel. Pulses of long duration and short wavelength can obtain a plasma channel with higher electron density, but the channel lifetime thoroughly depends on the later evolution of the self-guided channel.
2012,
24: 1029-1032.
doi: 10.3788/HPLPB20122405.1029
Abstract:
By using the least square method, the phase fitting effects of deformable mirror are investigated with different actuator position deviations, and arrangements, coupling coefficients and numbers of actuators. The results show that, for the random low frequency phase, the anti-disturbance ability of the deformable mirror with square arrangement of actuators is better than that with triangle arrangement, and the ability can be improved by increasing the coupling coefficient and the number of actuators.
By using the least square method, the phase fitting effects of deformable mirror are investigated with different actuator position deviations, and arrangements, coupling coefficients and numbers of actuators. The results show that, for the random low frequency phase, the anti-disturbance ability of the deformable mirror with square arrangement of actuators is better than that with triangle arrangement, and the ability can be improved by increasing the coupling coefficient and the number of actuators.
2012,
24: 1033-1037.
doi: 10.3788/HPLPB20122405.1033
Abstract:
The paper studies the influence of gain module aspect ratio on output power and extraction efficiency in MOPA-structured HF chemical laser. A finite difference method based on coordinate system transformation is used to calculate the output power of master oscillator, the extraction efficiency of amplifier and the total output power of the HF laser under different gain module aspect ratio. The results show that for the MOPA-structured HF chemical laser, when the gain volume and the small-signal gain curve are fixed, with the decrease of the aspect ratio, the output power of master oscillator and the output power amplified by amplifier will increase, but the extraction efficiency of amplifier will reduce. When the aspect ratio is less than 5, its change has little influence on the extraction efficiency and the total output power.
The paper studies the influence of gain module aspect ratio on output power and extraction efficiency in MOPA-structured HF chemical laser. A finite difference method based on coordinate system transformation is used to calculate the output power of master oscillator, the extraction efficiency of amplifier and the total output power of the HF laser under different gain module aspect ratio. The results show that for the MOPA-structured HF chemical laser, when the gain volume and the small-signal gain curve are fixed, with the decrease of the aspect ratio, the output power of master oscillator and the output power amplified by amplifier will increase, but the extraction efficiency of amplifier will reduce. When the aspect ratio is less than 5, its change has little influence on the extraction efficiency and the total output power.
2012,
24: 1038-1042.
doi: 10.3788/HPLPB20122405.1038
Abstract:
A fast and memory-saving registration algorithm is proposed for image sequence-based computer vision applications. First, a new scheme, which is independent of the image content, is adopted to generate a series of feature points. Then, a forward-and-backward tracking approach is used to obtain the reliable feature point pairs. In the approach, the forward tracking is performed to get all the potential feature point pairs, and the backward tracking is utilized to measure the forward-backward discrepancies which enable selection of the final reliable point pairs. Finally, building upon these reliable pairs, the homography is computed by using normalized direct linear transformation. Due to the intensive exploitation of the interframe continuity existing in image sequences, the proposed registration algorithm provides comparable experimental results to current state-of-the-art techniques, while using a fraction of the computation time and a fraction of the memory as well. Specifically, with a memory usage of 421 kB only, this algorithm runs at 32 frames per second for a sequence with an image resolution of 480360.
A fast and memory-saving registration algorithm is proposed for image sequence-based computer vision applications. First, a new scheme, which is independent of the image content, is adopted to generate a series of feature points. Then, a forward-and-backward tracking approach is used to obtain the reliable feature point pairs. In the approach, the forward tracking is performed to get all the potential feature point pairs, and the backward tracking is utilized to measure the forward-backward discrepancies which enable selection of the final reliable point pairs. Finally, building upon these reliable pairs, the homography is computed by using normalized direct linear transformation. Due to the intensive exploitation of the interframe continuity existing in image sequences, the proposed registration algorithm provides comparable experimental results to current state-of-the-art techniques, while using a fraction of the computation time and a fraction of the memory as well. Specifically, with a memory usage of 421 kB only, this algorithm runs at 32 frames per second for a sequence with an image resolution of 480360.
2012,
24: 1043-1046.
doi: 10.3788/HPLPB20122405.1043
Abstract:
For supersonic-supersonic ejector, the design model and corresponding analysis were presented, and the relation of design parameters and the performance was partly revealed. The results revealed the confliction of two performance objectives and the complexity of the design problem. To clarify the entangled relation of design parameters and objectives and to afford facilities for the design process, the Pareto front(PF) concept was introduced and an MOEA/D algorithm was programmed to calculate the PFs of specific supersonic-supersonic ejector multi-objective optimization problems. The methodology adopted here proved to be effective and efficient for the supersonic-supersonic ejector design problem.
For supersonic-supersonic ejector, the design model and corresponding analysis were presented, and the relation of design parameters and the performance was partly revealed. The results revealed the confliction of two performance objectives and the complexity of the design problem. To clarify the entangled relation of design parameters and objectives and to afford facilities for the design process, the Pareto front(PF) concept was introduced and an MOEA/D algorithm was programmed to calculate the PFs of specific supersonic-supersonic ejector multi-objective optimization problems. The methodology adopted here proved to be effective and efficient for the supersonic-supersonic ejector design problem.
2012,
24: 1047-1051.
doi: 10.3788/HPLPB20122405.1047
Abstract:
A six-rod series connection pulsed Nd:YAG laser was presented. 44 matrices were used to theoretically analyze the deviation of optical axis affected by the offset angle of Nd:YAG rods in the resonator, and the tolerance of the offset angle is given. A plane-plane symmetrical resonator has been used in the experiment, and through adjusting the offset angle of all rods within the tolerance, the six-rod series connection pulsed Nd:YAG laser was achieved. With an input electric power of 86 kW and a duty cycle of 17%, an output laser with an average power of 3 018 W, a peak power of 17.75 kW, the maximum single pulse energy of 66 J and a beam parameters product of 26.3 mmmrad was obtained. The electro-optical conversion efficiency was 3.5%, and the instability of the laser was less than 2%.
A six-rod series connection pulsed Nd:YAG laser was presented. 44 matrices were used to theoretically analyze the deviation of optical axis affected by the offset angle of Nd:YAG rods in the resonator, and the tolerance of the offset angle is given. A plane-plane symmetrical resonator has been used in the experiment, and through adjusting the offset angle of all rods within the tolerance, the six-rod series connection pulsed Nd:YAG laser was achieved. With an input electric power of 86 kW and a duty cycle of 17%, an output laser with an average power of 3 018 W, a peak power of 17.75 kW, the maximum single pulse energy of 66 J and a beam parameters product of 26.3 mmmrad was obtained. The electro-optical conversion efficiency was 3.5%, and the instability of the laser was less than 2%.
2012,
24: 1052-1056.
doi: 10.3788/HPLPB20122405.1052
Abstract:
According to the theory of optical fiber transmission mode, combined with the structure of single-mode tapered fiber, the paper uses finite difference beam propagation method (FD-BPM) to simulate the transmission of fiber mode at 1 550 nm wavelength, and analyzes the influence of the mode in cladding on the mode in fiber core. The results show that, because of the existence of cladding mode, with the reduction of cladding mode number and the change of the constraint state of mode field in fiber core, the mode field distribution within different regions of tapered fiber core changes significantly, and the root-mean-square(RMS) widths of mode field within different regions have different degrees of ups and downs. The distribution of mode field energy is obtained by using numerical method and the existence of cladding mode is found to slower the reduction of mode field energy.
According to the theory of optical fiber transmission mode, combined with the structure of single-mode tapered fiber, the paper uses finite difference beam propagation method (FD-BPM) to simulate the transmission of fiber mode at 1 550 nm wavelength, and analyzes the influence of the mode in cladding on the mode in fiber core. The results show that, because of the existence of cladding mode, with the reduction of cladding mode number and the change of the constraint state of mode field in fiber core, the mode field distribution within different regions of tapered fiber core changes significantly, and the root-mean-square(RMS) widths of mode field within different regions have different degrees of ups and downs. The distribution of mode field energy is obtained by using numerical method and the existence of cladding mode is found to slower the reduction of mode field energy.
2012,
24: 1057-1062.
doi: 10.3788/HPLPB20122405.1057
Abstract:
The paper studies the initiated damage morphology and the subsequent damage growth on fused silicas exit-surface and input-surface in air under nanosecond laser irradiation at 1 064 nm and 532 nm. The results demonstrate a significant dependence of the initiated damage on laser parameters and surface defects characters, and of the damage growth on the laser wavelength, location and fluence. Exponential growth behavior appears for exit-surface and linear growth one for input-surface in the lateral side of the damage site with the increase of shot number. Possible reasons for the observed initiated damages and damage growth behaviors are discussed.
The paper studies the initiated damage morphology and the subsequent damage growth on fused silicas exit-surface and input-surface in air under nanosecond laser irradiation at 1 064 nm and 532 nm. The results demonstrate a significant dependence of the initiated damage on laser parameters and surface defects characters, and of the damage growth on the laser wavelength, location and fluence. Exponential growth behavior appears for exit-surface and linear growth one for input-surface in the lateral side of the damage site with the increase of shot number. Possible reasons for the observed initiated damages and damage growth behaviors are discussed.
2012,
24: 1063-1066.
doi: 10.3788/HPLPB20122405.1063
Abstract:
Complex natural background(e.g. clouds and ground)suppression is a difficult problem for dim and small target detection in infrared image sequences. A dim and small target background suppression method based on wave atoms as a variant of two-dimensional (2D) wavelet packets, is proposed to solve the problem. It adopts kernel local normalization after wave atoms analysis, to suppress background details which contain edge, contour and texture, and enhance target information, and then modified coefficients are reconstructed using wave atoms inverse transform for suppression background. Experimental results demonstrate that, compared with wavelet transform (WT) and max-median (MMed) filter methods, the proposed method can suppress complex background in dim and small target images effectively. The improvement in signal-to-clutter ratio (ISCR) and background suppression factor (BSF) increase more than 3 times and 4 times, respectively.
Complex natural background(e.g. clouds and ground)suppression is a difficult problem for dim and small target detection in infrared image sequences. A dim and small target background suppression method based on wave atoms as a variant of two-dimensional (2D) wavelet packets, is proposed to solve the problem. It adopts kernel local normalization after wave atoms analysis, to suppress background details which contain edge, contour and texture, and enhance target information, and then modified coefficients are reconstructed using wave atoms inverse transform for suppression background. Experimental results demonstrate that, compared with wavelet transform (WT) and max-median (MMed) filter methods, the proposed method can suppress complex background in dim and small target images effectively. The improvement in signal-to-clutter ratio (ISCR) and background suppression factor (BSF) increase more than 3 times and 4 times, respectively.
2012,
24: 1067-1070.
doi: 10.3788/HPLPB20122405.1067
Abstract:
Laser-induced cavitation bubble collapse sound waves in liquid are measured by the PZT hydrophone, and the bubble content of laser-induced cavitation bubble during the first oscillating cycle is calculated. In combination with the analysis of the effect on the maximum bubble radius and oscillating duration of the bubble content, the effect on sound wave spectrum properties of the bubble content is investigated. The results indicate that the bubble content increases with the increase of laser energy. The bubble content influences the intensity of bubble collapse, and larger bubble content leads to shorter oscillating duration. Moreover, the peak frequency decreases with the increase of the bubble content.
Laser-induced cavitation bubble collapse sound waves in liquid are measured by the PZT hydrophone, and the bubble content of laser-induced cavitation bubble during the first oscillating cycle is calculated. In combination with the analysis of the effect on the maximum bubble radius and oscillating duration of the bubble content, the effect on sound wave spectrum properties of the bubble content is investigated. The results indicate that the bubble content increases with the increase of laser energy. The bubble content influences the intensity of bubble collapse, and larger bubble content leads to shorter oscillating duration. Moreover, the peak frequency decreases with the increase of the bubble content.
2012,
24: 1071-1075.
doi: 10.3788/HPLPB20122405.1071
Abstract:
In numerical simulation of laser propagation through atmospheric turbulence considering time characteristics, the generation of long turbulent phase screen is critical. In this paper, the multi-point prediction interpolation algorithm based on the phase covariance method is proposed. The algorithm predicts the phase value of the new interpolation point according to given points which are known. The prediction matrix and the residual variance expression of the interpolation point are derived, and the spatial statistical properties of the generated phase screen are verified. The results show that the statistical properties of generated phase screen agree well with theoretical ones of atmospheric turbulence. With the increase of known points, the generated turbulence phase screen will have better accuracy. In addition, the method can generate infinitely long turbulence phase screen through successive interpolation.
In numerical simulation of laser propagation through atmospheric turbulence considering time characteristics, the generation of long turbulent phase screen is critical. In this paper, the multi-point prediction interpolation algorithm based on the phase covariance method is proposed. The algorithm predicts the phase value of the new interpolation point according to given points which are known. The prediction matrix and the residual variance expression of the interpolation point are derived, and the spatial statistical properties of the generated phase screen are verified. The results show that the statistical properties of generated phase screen agree well with theoretical ones of atmospheric turbulence. With the increase of known points, the generated turbulence phase screen will have better accuracy. In addition, the method can generate infinitely long turbulence phase screen through successive interpolation.
2012,
24: 1076-1080.
doi: 10.3788/HPLPB20122405.1076
Abstract:
A one-dimensional KBA microscope for diagnosis of planar targets, working at 4.75 keV, has been experimentally studied. According to the requirements of spatial resolution and working environments, the optical structure of one-dimensional KBA microscope was designed, and compared with conventional Kirkpatrick-Baez microscope. A double-periodic multilayer KBA mirror simultaneously working at 8 keV and 4.75 keV was adopted and manufactured to complete the system alignment. The 4.75 keV X-ray imaging experiment in XRL chamber of Shenguang Ⅱ shows that the resolution is about 4 m in all the illumination area of backlighter, and the effective field of the one-dimensional KBA microscope is limited by backlighter size.
A one-dimensional KBA microscope for diagnosis of planar targets, working at 4.75 keV, has been experimentally studied. According to the requirements of spatial resolution and working environments, the optical structure of one-dimensional KBA microscope was designed, and compared with conventional Kirkpatrick-Baez microscope. A double-periodic multilayer KBA mirror simultaneously working at 8 keV and 4.75 keV was adopted and manufactured to complete the system alignment. The 4.75 keV X-ray imaging experiment in XRL chamber of Shenguang Ⅱ shows that the resolution is about 4 m in all the illumination area of backlighter, and the effective field of the one-dimensional KBA microscope is limited by backlighter size.
2012,
24: 1081-1084.
doi: 10.3788/HPLPB20122405.1081
Abstract:
An in-chamber, mini X-ray imager employing a pinhole and a logarithmic spiral crystal has been manufactured to obtain the K-shell emission monochromatic X-ray images. The imager was tested on the Yang accelerator and successfully obtained the hydrogenlike line and heliumlike line images of the imploding Al wire array. The results show that the imager has excellent monochromacity (the energy band width is less than 1 eV) and is very suitable for acquiring the characteristic X-ray emission images of the medium or low Z imploding Z-pinch loads.
An in-chamber, mini X-ray imager employing a pinhole and a logarithmic spiral crystal has been manufactured to obtain the K-shell emission monochromatic X-ray images. The imager was tested on the Yang accelerator and successfully obtained the hydrogenlike line and heliumlike line images of the imploding Al wire array. The results show that the imager has excellent monochromacity (the energy band width is less than 1 eV) and is very suitable for acquiring the characteristic X-ray emission images of the medium or low Z imploding Z-pinch loads.
2012,
24: 1085-1088.
doi: 10.3788/HPLPB20122405.1085
Abstract:
For further understanding of the proton acceleration by target normal sheath acceleration (TNSA), the effect of the proton initial locations on the quality of the proton beam is investigated by two-dimensional particle-in-cell (2D-PIC) code Flips2D. The simulation results show that the effect of the proton initial locations on the proton quality is very significant. The divergence of protons is related to their initial locations in transverse direction. The farther away the protons is from the laser axis, the larger the proton divergence can be received.
For further understanding of the proton acceleration by target normal sheath acceleration (TNSA), the effect of the proton initial locations on the quality of the proton beam is investigated by two-dimensional particle-in-cell (2D-PIC) code Flips2D. The simulation results show that the effect of the proton initial locations on the proton quality is very significant. The divergence of protons is related to their initial locations in transverse direction. The farther away the protons is from the laser axis, the larger the proton divergence can be received.
2012,
24: 1089-1092.
doi: 10.3788/HPLPB20122405.1089
Abstract:
Potassium dihydrogen phosphate (KDP) crystals were baked at different temperatures in the same procedure. Samples from similar locations of as-grown 500-mm-class KDP crystals were used to measure the transmission spectra and laser damage thresholds. The results prove that the transmission spectra are not affected by thermal conditioning, and the laser damage thresholds of samples after annealing at 140 ℃and 160 ℃ are not significantly different from that of the unconditioned sample. However, for samples annealing at 150 ℃ a 1.4 times increase in the laser damage threshold is observed at 1, indicating that the annealing temperature of150 ℃ is the best for elevating the laser damage threshold of KDP crystals.
Potassium dihydrogen phosphate (KDP) crystals were baked at different temperatures in the same procedure. Samples from similar locations of as-grown 500-mm-class KDP crystals were used to measure the transmission spectra and laser damage thresholds. The results prove that the transmission spectra are not affected by thermal conditioning, and the laser damage thresholds of samples after annealing at 140 ℃and 160 ℃ are not significantly different from that of the unconditioned sample. However, for samples annealing at 150 ℃ a 1.4 times increase in the laser damage threshold is observed at 1, indicating that the annealing temperature of150 ℃ is the best for elevating the laser damage threshold of KDP crystals.
2012,
24: 1093-1097.
doi: 10.3788/HPLPB20122405.1093
Abstract:
In chirped pulse amplification laser systems, the damage threshold of the final grating in the pulse compressor seriously limits the energy output. This paper proposes a measurement, by which the exact correlation between the local fluence and local damage characteristics can be established. This method collects the near-field intensity distribution of a cm-sized beam spot and its corresponding raster damage image through on-line monitoring and image processing, and then matches the pixels on the two images to each other. Finally the gray level in the damage image is converted in terms of damage density by microscope observation. It does not strictly require the spatial uniformity of the beam. Moreover, since the intensity fluctuation is taken into account, the damage densities versus the fluence can be extracted within one shot.
In chirped pulse amplification laser systems, the damage threshold of the final grating in the pulse compressor seriously limits the energy output. This paper proposes a measurement, by which the exact correlation between the local fluence and local damage characteristics can be established. This method collects the near-field intensity distribution of a cm-sized beam spot and its corresponding raster damage image through on-line monitoring and image processing, and then matches the pixels on the two images to each other. Finally the gray level in the damage image is converted in terms of damage density by microscope observation. It does not strictly require the spatial uniformity of the beam. Moreover, since the intensity fluctuation is taken into account, the damage densities versus the fluence can be extracted within one shot.
2012,
24: 1098-1102.
doi: 10.3788/HPLPB20122405.1098
Abstract:
The paper investigates the resolution of soft X-ray KBA microscope and analyzes its influencing factors, including diffractive effect, geometrical aberration, slope error and surface roughness of specula. A calculation model of the KBA microscope is obtained according to these analyses. A 2.5 keV X-ray imaging experiment is performed and the resolution agrees with the simulated data of the model in large visual field. The incompleteness of this model is also analyzed.
The paper investigates the resolution of soft X-ray KBA microscope and analyzes its influencing factors, including diffractive effect, geometrical aberration, slope error and surface roughness of specula. A calculation model of the KBA microscope is obtained according to these analyses. A 2.5 keV X-ray imaging experiment is performed and the resolution agrees with the simulated data of the model in large visual field. The incompleteness of this model is also analyzed.
2012,
24: 1103-1106.
doi: 10.3788/HPLPB20122405.1103
Abstract:
The Monte Carlo code SRIM was used to simulate the process of Hf ion plasma source ion implantation in Cu substrate. The relationship between energy and stopping power, the relationship between ion energy and range, and ion distribution of different implantation conditions were simulated. The results show that, nuclear stopping power dominates when the energy is lower than 6 MeV, otherwise electronic stopping power dominates. There are a Bragg peak of the energy deposition process and the phenomenon that the mass deposition area concentrates, and the range generally increases as the energy increases.
The Monte Carlo code SRIM was used to simulate the process of Hf ion plasma source ion implantation in Cu substrate. The relationship between energy and stopping power, the relationship between ion energy and range, and ion distribution of different implantation conditions were simulated. The results show that, nuclear stopping power dominates when the energy is lower than 6 MeV, otherwise electronic stopping power dominates. There are a Bragg peak of the energy deposition process and the phenomenon that the mass deposition area concentrates, and the range generally increases as the energy increases.
2012,
24: 1107-1110.
doi: 10.3788/HPLPB20122405.1107
Abstract:
Using electron trace program and CST electromagnetic studio, the paper investigated a key component of mini bremsstrahlung X-ray source, perturbator, designed the distribution of the perturbator magnetic field, and studied its effect on the electron trajectory when the perturbator was placed in different angular positions. When the angular position of the perturbator is close to the position where the electrons cross the center trajectory, the amplitude of the electron after being captured is smallest, but the strength of the magnetic field needed is greatest. Moreover, the analysis on the transverse and longitudinal acceptance shows that the transverse acceptance is 3 mm0.23 mrad andthe energy acceptance is 0.1%.
Using electron trace program and CST electromagnetic studio, the paper investigated a key component of mini bremsstrahlung X-ray source, perturbator, designed the distribution of the perturbator magnetic field, and studied its effect on the electron trajectory when the perturbator was placed in different angular positions. When the angular position of the perturbator is close to the position where the electrons cross the center trajectory, the amplitude of the electron after being captured is smallest, but the strength of the magnetic field needed is greatest. Moreover, the analysis on the transverse and longitudinal acceptance shows that the transverse acceptance is 3 mm0.23 mrad andthe energy acceptance is 0.1%.
2012,
24: 1117-1120.
doi: 10.3788/HPLPB20122405.1117
Abstract:
The aluminum wedge target was produced by diamond turning technology. The actual profile of the wedge targets inclined surface is found to be a conical one. The surface roughness was characterized by Veeco NT1100 white light interferometer. The results indicate that the surface root-mean-square roughness of the plane part is less than 50 nm and the maximum peak-to-valley height there is less than 100 nm. The surface roughness of the inclined part is less than 200 nm. The larger measurement value of roughness appearing at the inclined part can be explained by the following two reasons: one is the variation of working angles of tool, which increases the roughness, the other is that the measurement profile is not the generatrix of cone, which enlarges the measurement results.
The aluminum wedge target was produced by diamond turning technology. The actual profile of the wedge targets inclined surface is found to be a conical one. The surface roughness was characterized by Veeco NT1100 white light interferometer. The results indicate that the surface root-mean-square roughness of the plane part is less than 50 nm and the maximum peak-to-valley height there is less than 100 nm. The surface roughness of the inclined part is less than 200 nm. The larger measurement value of roughness appearing at the inclined part can be explained by the following two reasons: one is the variation of working angles of tool, which increases the roughness, the other is that the measurement profile is not the generatrix of cone, which enlarges the measurement results.
2012,
24: 1121-1125.
doi: 10.3788/HPLPB20122405.1121
Abstract:
Sc films have been successfully grown on Si substrates by electron beam deposition (EBD). The microstructure and surface morphology of Sc films prepared with different deposition parameters were examined by X-ray diffraction and scanning electron microscopy. The observations show that, in the substrate temperature range of 350 to 550 ℃, the films are mainly composed by Sc, and higher substrate temperature leads to more compact films with larger grain sizes. With the temperature increasing up to 650 ℃, the reaction between Sc and Si makes a film of ScSi. At lower temperature, the effects of deposition rate on the morphologies and structures of Sc films are weak. While at the higher temperature of 650 ℃,micro cracks appear and the number of ScSi peaks increases with increasing the deposition rate.
Sc films have been successfully grown on Si substrates by electron beam deposition (EBD). The microstructure and surface morphology of Sc films prepared with different deposition parameters were examined by X-ray diffraction and scanning electron microscopy. The observations show that, in the substrate temperature range of 350 to 550 ℃, the films are mainly composed by Sc, and higher substrate temperature leads to more compact films with larger grain sizes. With the temperature increasing up to 650 ℃, the reaction between Sc and Si makes a film of ScSi. At lower temperature, the effects of deposition rate on the morphologies and structures of Sc films are weak. While at the higher temperature of 650 ℃,micro cracks appear and the number of ScSi peaks increases with increasing the deposition rate.
2012,
24: 1126-1130.
doi: 10.3788/HPLPB20122405.1126
Abstract:
To acquire temporal and spatial distribution characteristics of particle density for plasma generated by hypervelocity impact, the paper synthetically considered the laws of mass conservation, momentum conservation, and energy conservation, and Maxwell equations. Temporal and spatial distribution of particle density was derived in expanding plasma cloud by using one-dimension theoretical model of field strength of point charge. The temporal and spatial evolution rules of particle density in expanding plasma cloud generated by hypervelocity impacting 2024-T4 aluminum targets were obtained based on the analysis of original data from 2024-T4 aluminum target impacting experiments.
To acquire temporal and spatial distribution characteristics of particle density for plasma generated by hypervelocity impact, the paper synthetically considered the laws of mass conservation, momentum conservation, and energy conservation, and Maxwell equations. Temporal and spatial distribution of particle density was derived in expanding plasma cloud by using one-dimension theoretical model of field strength of point charge. The temporal and spatial evolution rules of particle density in expanding plasma cloud generated by hypervelocity impacting 2024-T4 aluminum targets were obtained based on the analysis of original data from 2024-T4 aluminum target impacting experiments.
2012,
24: 1131-1136.
doi: 10.3788/HPLPB20122405.1131
Abstract:
This article investigates the efficiency optimization of harmonic gyroklystron. The electron beam-wave interaction is characterized by a nonlinear pendulum equation with two dimensionless parameters: a bunching parameter and a relative phase. The efficiencies for the gyroklystron operating at fundamental through fourth harmonic are presented. The numerical results show that the perpendicular efficiencies are higher than 55%, 40%, 30%, and 15% for the fundamental, second, third, and fourth harmonics, respectively, when the harmonic gyroklystron operates in amplifier region; and the perpendicular efficiencies are as high as 93.9%, 88.2%, 81.8%, and 62.7% for the fundamental, second, third, and fourth harmonics, respectively, when the harmonic gyroklystron operates in oscillator region.
This article investigates the efficiency optimization of harmonic gyroklystron. The electron beam-wave interaction is characterized by a nonlinear pendulum equation with two dimensionless parameters: a bunching parameter and a relative phase. The efficiencies for the gyroklystron operating at fundamental through fourth harmonic are presented. The numerical results show that the perpendicular efficiencies are higher than 55%, 40%, 30%, and 15% for the fundamental, second, third, and fourth harmonics, respectively, when the harmonic gyroklystron operates in amplifier region; and the perpendicular efficiencies are as high as 93.9%, 88.2%, 81.8%, and 62.7% for the fundamental, second, third, and fourth harmonics, respectively, when the harmonic gyroklystron operates in oscillator region.
2012,
24: 1137-1140.
doi: 10.3788/HPLPB20122405.1137
Abstract:
A series of experiments have been performed to study the radiation characteristics of single-source monopole plasma antenna. The radiation intensity and pattern were measured carefully, and then the antennas main lobe beamwidth and direction factor were derived. Through the comparison with metal antenna, the radiation efficiency of plasma antenna was fingered out. The impedance of the antenna was also measured and analyzed. The results show that plasma antenna has a similar radiation pattern and impedance as metal antenna does, and in most cases its direction factor is better than the laters. However, its radiation efficiency is lower and its stability is weaker.
A series of experiments have been performed to study the radiation characteristics of single-source monopole plasma antenna. The radiation intensity and pattern were measured carefully, and then the antennas main lobe beamwidth and direction factor were derived. Through the comparison with metal antenna, the radiation efficiency of plasma antenna was fingered out. The impedance of the antenna was also measured and analyzed. The results show that plasma antenna has a similar radiation pattern and impedance as metal antenna does, and in most cases its direction factor is better than the laters. However, its radiation efficiency is lower and its stability is weaker.
2012,
24: 1141-1145.
doi: 10.3788/HPLPB20122405.1141
Abstract:
This paper proposes a finite-difference time-domain(FDTD) method to calculate the internal electromagnetic pulse (IEMP) within cavities of any shapes in three-dimensional rectangular coordinate system. By adopting conformal FDTD techniques, this method can analyze the IEMP within cavities of any shapes, even when there is an asymmetric border in the cavity. The finite-difference equations have been deduced when the cavity is under oblique incidence of rays. The IEMP within a cylindrical cavity under oblique incidence is calculated by the method proposed in this paper and the FDTD method in cylindrical coordinate system, respectively. The results of the two methods agree well with each other, proving the accuracy of the FDTD method proposed.
This paper proposes a finite-difference time-domain(FDTD) method to calculate the internal electromagnetic pulse (IEMP) within cavities of any shapes in three-dimensional rectangular coordinate system. By adopting conformal FDTD techniques, this method can analyze the IEMP within cavities of any shapes, even when there is an asymmetric border in the cavity. The finite-difference equations have been deduced when the cavity is under oblique incidence of rays. The IEMP within a cylindrical cavity under oblique incidence is calculated by the method proposed in this paper and the FDTD method in cylindrical coordinate system, respectively. The results of the two methods agree well with each other, proving the accuracy of the FDTD method proposed.
2012,
24: 1146-1150.
doi: 10.3788/HPLPB20122405.1146
Abstract:
The time-resolved measurement system which can work at very high speed is necessary in electron beam parameter diagnosis for Dragon-Ⅰ linear induction accelerator（LIA）. A two-frame gated camera system has been developed and put into operation. The camera system adopts the optical principle of splitting the imaging light beam into two parts in the imaging space of a lens with long focus length. It includes lens coupled gated image intensifier, CCD camera, high speed shutter trigger device based on large scale field programmable gate array. The minimum exposure time for each image is about 3 ns， and the interval time between two images can be adjusted with a step of about 0.5 ns. The exposure time and the interval time can be independently adjusted and can reach about 1 s. The camera system features good linearity， good response uniformity， equivalent background illumination(EBI) as low as about 5 electrons per pixel per second, large adjustment range of sensitivity, and excellent flexibility and adaptability in applications. The camera system can capture two frame images at one time with the image size of 1 0241 024. It meets the requirements of measurement for Dragon-Ⅰ LIA.
The time-resolved measurement system which can work at very high speed is necessary in electron beam parameter diagnosis for Dragon-Ⅰ linear induction accelerator（LIA）. A two-frame gated camera system has been developed and put into operation. The camera system adopts the optical principle of splitting the imaging light beam into two parts in the imaging space of a lens with long focus length. It includes lens coupled gated image intensifier, CCD camera, high speed shutter trigger device based on large scale field programmable gate array. The minimum exposure time for each image is about 3 ns， and the interval time between two images can be adjusted with a step of about 0.5 ns. The exposure time and the interval time can be independently adjusted and can reach about 1 s. The camera system features good linearity， good response uniformity， equivalent background illumination(EBI) as low as about 5 electrons per pixel per second, large adjustment range of sensitivity, and excellent flexibility and adaptability in applications. The camera system can capture two frame images at one time with the image size of 1 0241 024. It meets the requirements of measurement for Dragon-Ⅰ LIA.
2012,
24: 1151-1154.
doi: 10.3788/HPLPB20122405.1151
Abstract:
The neutron sensitivity of a helium scintillation fission neutron detector was investigated through theoretical and experimental methods. The energy deposition of neutrons with different energy and fragments of fission targets with different thickness in helium scintillator was calculated based on Monte Carlo method. The energy deposition curves of neutrons and fragments are complementary to each other, so the total energy deposition curve is relatively flatter. The neutron sensitivity was calculated to be 10-15 Ccm2 level. The neutron sensitivity was measured and the theoretical results of neutron sensitivity are consistent with experimental results.
The neutron sensitivity of a helium scintillation fission neutron detector was investigated through theoretical and experimental methods. The energy deposition of neutrons with different energy and fragments of fission targets with different thickness in helium scintillator was calculated based on Monte Carlo method. The energy deposition curves of neutrons and fragments are complementary to each other, so the total energy deposition curve is relatively flatter. The neutron sensitivity was calculated to be 10-15 Ccm2 level. The neutron sensitivity was measured and the theoretical results of neutron sensitivity are consistent with experimental results.
2012,
24: 1155-1159.
doi: 10.3788/HPLPB20122405.1155
Abstract:
During beam injection in Hefei Light Source(HLS), the amplitude of betatron oscillation varies rapidly, and the frequency varies greatly. It is a typical non-stationary process. Using the traditional method to process the time series signal acquired by the bunch-by-bunch measurement system may result in amplitude distortion and phase deviation. Wavelet analysis provides multi-resolution representations of the bunch signal. Subsequently, the oscillation component and baseline drift component can be separated. The locations on timeline and the linear relationships of the components remain the same as the original signal. Compared with the traditional method, the data processing method based on wavelet analysis is capable of analyzing a non-stationary signal and de-noising a signal without appreciable degradation. It will not bring about conspicuous amplitude distortion and phase deviation, and ensures that the subsequent tracking of the evolution of oscillation amplitude, phase, frequency and mode in the time domain is more reliable. Furthermore, the method has been successfully used to extract the amplitude envelope of betatron oscillation and to calculate growth rate and damping rate. It provides an accurate foundation for machine studies, beam diagnosis and the commissioning of bunch-by-bunch feedback system.
During beam injection in Hefei Light Source(HLS), the amplitude of betatron oscillation varies rapidly, and the frequency varies greatly. It is a typical non-stationary process. Using the traditional method to process the time series signal acquired by the bunch-by-bunch measurement system may result in amplitude distortion and phase deviation. Wavelet analysis provides multi-resolution representations of the bunch signal. Subsequently, the oscillation component and baseline drift component can be separated. The locations on timeline and the linear relationships of the components remain the same as the original signal. Compared with the traditional method, the data processing method based on wavelet analysis is capable of analyzing a non-stationary signal and de-noising a signal without appreciable degradation. It will not bring about conspicuous amplitude distortion and phase deviation, and ensures that the subsequent tracking of the evolution of oscillation amplitude, phase, frequency and mode in the time domain is more reliable. Furthermore, the method has been successfully used to extract the amplitude envelope of betatron oscillation and to calculate growth rate and damping rate. It provides an accurate foundation for machine studies, beam diagnosis and the commissioning of bunch-by-bunch feedback system.
2012,
24: 1160-1164.
doi: 10.3788/HPLPB20122405.1160
Abstract:
The dissipative dynamics of a two-level system interacting with a reservoir has been solved by Markovian and non-Markovian approaches. The results in conditions of two different spectral densities, namely the detuning spectral density and a photonic gap distributed density, are compared with the exact solutions. In the first case, the population of excitation state in the non-Markovian and Markovian reservoirs is discussed. For both weak coupling regime in short time and a long period of strong coupling regime, the result of non-Markovian approaches is more consistent with the exact solution, while the Markovian approximation is mainly applicable to weak coupling condition. In the second case, the population in small gap width is considered. The Markovian approach is applied in weak coupling condition, but in strong condition the non-Markovian approximation is exploited. Therefore, through appropriate choice of Markovian and non-Markovian approaches, the dynamics of a system can be described exactly for different spectral densities and coupling regimes.
The dissipative dynamics of a two-level system interacting with a reservoir has been solved by Markovian and non-Markovian approaches. The results in conditions of two different spectral densities, namely the detuning spectral density and a photonic gap distributed density, are compared with the exact solutions. In the first case, the population of excitation state in the non-Markovian and Markovian reservoirs is discussed. For both weak coupling regime in short time and a long period of strong coupling regime, the result of non-Markovian approaches is more consistent with the exact solution, while the Markovian approximation is mainly applicable to weak coupling condition. In the second case, the population in small gap width is considered. The Markovian approach is applied in weak coupling condition, but in strong condition the non-Markovian approximation is exploited. Therefore, through appropriate choice of Markovian and non-Markovian approaches, the dynamics of a system can be described exactly for different spectral densities and coupling regimes.
2012,
24: 1165-1168.
doi: 10.3788/HPLPB20122405.1165
Abstract:
The measurement of DD neutron yield by activation is presented. This method is based on the inelastic scattering reaction of 115In with DD neutron, and the activated spectrum is counted by HPGe detector. The relation between the counts of detected rays and the neutron yield is analyzed. The optimal thickness of sample is given by Monte Carlo simulation, which is 1 cm. The entire counting system has been calibrated on the K-400 accelerator. The result shows that the DD neutron measurement by indium activation can be used in the ICF experiment when the neutron yield is above 2109. The total error of the system is below 10% in this condition. The total error will reduce when the neutron yield is larger.
The measurement of DD neutron yield by activation is presented. This method is based on the inelastic scattering reaction of 115In with DD neutron, and the activated spectrum is counted by HPGe detector. The relation between the counts of detected rays and the neutron yield is analyzed. The optimal thickness of sample is given by Monte Carlo simulation, which is 1 cm. The entire counting system has been calibrated on the K-400 accelerator. The result shows that the DD neutron measurement by indium activation can be used in the ICF experiment when the neutron yield is above 2109. The total error of the system is below 10% in this condition. The total error will reduce when the neutron yield is larger.
2012,
24: 1169-1172.
doi: 10.3788/HPLPB20122405.1169
Abstract:
The thermal desorption behavior of ion-implanted helium in erbium and scandium films was investigated by means of thermal helium desorption spectrometry. The peak positions of ion-implanted helium desorption are the same for erbium films with different surface morphologies. The degree of denseness of films, however, will affect the amount of released helium as the implanted helium releases through the path of cavities existing in the loose film before thermal desorption. The difference in peak positions of helium desorption from erbium and scandium films may be related to the depth distribution of helium and the degree of denseness of films. The helium implantation depths measured by enhanced proton backscattering spectrometry are 210 and 308 nm, respectively, for erbium and scandium films with the implantation energy of 60 keV.
The thermal desorption behavior of ion-implanted helium in erbium and scandium films was investigated by means of thermal helium desorption spectrometry. The peak positions of ion-implanted helium desorption are the same for erbium films with different surface morphologies. The degree of denseness of films, however, will affect the amount of released helium as the implanted helium releases through the path of cavities existing in the loose film before thermal desorption. The difference in peak positions of helium desorption from erbium and scandium films may be related to the depth distribution of helium and the degree of denseness of films. The helium implantation depths measured by enhanced proton backscattering spectrometry are 210 and 308 nm, respectively, for erbium and scandium films with the implantation energy of 60 keV.
2012,
24: 1173-1176.
doi: 10.3788/HPLPB20122405.1173
Abstract:
(PrNd)32.3Nb0.70Al0.60Cu0.20B1.03Fe65.17 (weight percent) alloys were prepared via different powdering processes, i.e. air classification(AC) and hydrogenation decomposition(HD). Their microstrutures and magnetic properties were investigated. The results show that, HD produces monodispersed fine powders, with which the magnets prepared have uniform microstructure. Moreover, the maximum magnetic energy product, remanence and intrinsic coercivity of the magnets prepared with HD-produced powders are 24.6 kJm-3, 0.047 T and 193.4 kAm-1 higher than those of the magnets prepared with AC-produced powders, and thus the former magnets are better applicable to devices like laser head and magnetron.
(PrNd)32.3Nb0.70Al0.60Cu0.20B1.03Fe65.17 (weight percent) alloys were prepared via different powdering processes, i.e. air classification(AC) and hydrogenation decomposition(HD). Their microstrutures and magnetic properties were investigated. The results show that, HD produces monodispersed fine powders, with which the magnets prepared have uniform microstructure. Moreover, the maximum magnetic energy product, remanence and intrinsic coercivity of the magnets prepared with HD-produced powders are 24.6 kJm-3, 0.047 T and 193.4 kAm-1 higher than those of the magnets prepared with AC-produced powders, and thus the former magnets are better applicable to devices like laser head and magnetron.
2012,
24: 1177-1180.
doi: 10.3788/HPLPB20122405.1177
Abstract:
This paper investigates the breakdown characteristics of high pressure nitrogen dielectric gas spark switch from the aspects of theoretical analysis, experimental study and software simulation. The theoretical pressure of the high pressure spark switch can reach 10 MPa, which is designed and manufactured according to the strength theoretical calculation. During the experiments of the high pressure spark switch, the nitrogen delay is less than 14 ns and the jitter is less than 1 ns under the conditions of 2, 4, or 6 MPa pressure and 0.1, 0.5, or1.0 mm electrode gap. The 50%-breakdown voltage is 34 kV with 2 MPa pressure and 0.1 mm electrode gap. The high pressure spark switch has better stability and insulating property than atmospheric air switch.
This paper investigates the breakdown characteristics of high pressure nitrogen dielectric gas spark switch from the aspects of theoretical analysis, experimental study and software simulation. The theoretical pressure of the high pressure spark switch can reach 10 MPa, which is designed and manufactured according to the strength theoretical calculation. During the experiments of the high pressure spark switch, the nitrogen delay is less than 14 ns and the jitter is less than 1 ns under the conditions of 2, 4, or 6 MPa pressure and 0.1, 0.5, or1.0 mm electrode gap. The 50%-breakdown voltage is 34 kV with 2 MPa pressure and 0.1 mm electrode gap. The high pressure spark switch has better stability and insulating property than atmospheric air switch.
2012,
24: 1181-1185.
doi: 10.3788/HPLPB20122405.1181
Abstract:
Based on a compact (2 m1 m1.5 m) pulsed current generator (~100 kA, 60 ns), a table-top X-pinch device was constructed and tested. The load current was almost unchanged for X-pinches made using different wires (5 m, 8 m, 10 m and 13 m Wu wires, 13 m and 25 m Mo wires), which means that the impedance of the wires is much lower than the total impedance of the load section. When the above mentioned wires were used as two-wire load, X-ray pulses from X-pinch were always observed. As the mass of the two-wire load increases, the time delay of the X-ray emission relative to the beginning of the load current increases. The X-ray pulse consists of single peak or two overlapping peaks of subnanosecond pulsewidth. Two X-ray pulses with a time interval on the order of 10 ns were often observed for a small mass load when the load current was high enough. The appearance of the second X-ray pulse is attributed to the second pinch of the plasma.
Based on a compact (2 m1 m1.5 m) pulsed current generator (~100 kA, 60 ns), a table-top X-pinch device was constructed and tested. The load current was almost unchanged for X-pinches made using different wires (5 m, 8 m, 10 m and 13 m Wu wires, 13 m and 25 m Mo wires), which means that the impedance of the wires is much lower than the total impedance of the load section. When the above mentioned wires were used as two-wire load, X-ray pulses from X-pinch were always observed. As the mass of the two-wire load increases, the time delay of the X-ray emission relative to the beginning of the load current increases. The X-ray pulse consists of single peak or two overlapping peaks of subnanosecond pulsewidth. Two X-ray pulses with a time interval on the order of 10 ns were often observed for a small mass load when the load current was high enough. The appearance of the second X-ray pulse is attributed to the second pinch of the plasma.
2012,
24: 1186-1190.
doi: 10.3788/HPLPB20122405.1186
Abstract:
This paper introduces a type of program-controlled pulse generator, which can adjust the amplitude, width and frequency of the output pulses, and precisely control the delay time of the ten-channel output pulsesequences. The pulse generator includes the main and auxiliary power supplies, power amplifier circuit, controlling system, digital keyboard and liquid crystal display. The output pulses have parameters adjustable within following ranges: frequency range 1 Hz-30 kHz, pulse width range 1-30 s, and pulse amplitude range 1-15 V; the delay of ten branches can be precisely adjusted within 0-1 ms. The pulse generator can provide delay triggers for pulse sources in parallel, and synchronized triggers for IGBT switches in series.
This paper introduces a type of program-controlled pulse generator, which can adjust the amplitude, width and frequency of the output pulses, and precisely control the delay time of the ten-channel output pulsesequences. The pulse generator includes the main and auxiliary power supplies, power amplifier circuit, controlling system, digital keyboard and liquid crystal display. The output pulses have parameters adjustable within following ranges: frequency range 1 Hz-30 kHz, pulse width range 1-30 s, and pulse amplitude range 1-15 V; the delay of ten branches can be precisely adjusted within 0-1 ms. The pulse generator can provide delay triggers for pulse sources in parallel, and synchronized triggers for IGBT switches in series.
2012,
24: 1191-1194.
doi: 10.3788/HPLPB20122405.1191
Abstract:
This paper presents a switch assembly based on reversely switched dynistor(RSD). The RSD-based assembly has been tested with the working voltage of 10 kV, repetition frequency of 0.2 Hz and peak current of about 107 kA. The peak power is larger than 1 GW. The transferred charge and energy per shot are about 20 C and 100 kJ, respectively, and the total experimental shot number is more than 50 000. The lifetime of RSD switch was investigated with the static volt-ampere character. The lifetime model of RSD switch under high current for long pulse application was established with numerical fitting. According to the failure criterion, the preliminarily estimated lifetime is about 107 shots.
This paper presents a switch assembly based on reversely switched dynistor(RSD). The RSD-based assembly has been tested with the working voltage of 10 kV, repetition frequency of 0.2 Hz and peak current of about 107 kA. The peak power is larger than 1 GW. The transferred charge and energy per shot are about 20 C and 100 kJ, respectively, and the total experimental shot number is more than 50 000. The lifetime of RSD switch was investigated with the static volt-ampere character. The lifetime model of RSD switch under high current for long pulse application was established with numerical fitting. According to the failure criterion, the preliminarily estimated lifetime is about 107 shots.
2012,
24: 1195-1200.
doi: 10.3788/HPLPB20122405.1195
Abstract:
The plasma source (cable guns) of the plasma opening switch(POS) on QiangguangⅠgenerator was chosen as the study object. The plasma source performance was investigated by using charge collectors. Experimental results show that the plasma ejection density is positively correlated with the structural parameter, the distance between gun core tip and muzzle plane, and the plasma ejection velocity is negatively correlated with the parameter. The increasing rate of plasma ejection density is less than that of drive current. As far as a plasma source with tens of cable plasma guns is concerned, the influence of single cable guns discharge dispersancy on plasma uniformity is little. Analysis of uncertainty shows that the uncertainty of measurement can be reduced by increasing the number of experiments and averaging the results. The combined standard uncertainty of plasma ejection density is less than 10%.
The plasma source (cable guns) of the plasma opening switch(POS) on QiangguangⅠgenerator was chosen as the study object. The plasma source performance was investigated by using charge collectors. Experimental results show that the plasma ejection density is positively correlated with the structural parameter, the distance between gun core tip and muzzle plane, and the plasma ejection velocity is negatively correlated with the parameter. The increasing rate of plasma ejection density is less than that of drive current. As far as a plasma source with tens of cable plasma guns is concerned, the influence of single cable guns discharge dispersancy on plasma uniformity is little. Analysis of uncertainty shows that the uncertainty of measurement can be reduced by increasing the number of experiments and averaging the results. The combined standard uncertainty of plasma ejection density is less than 10%.
2012,
24: 1201-1205.
doi: 10.3788/HPLPB20122405.1201
Abstract:
According to the physical design and electrical parameters of the 300 kA single induction cavity developed for linear transformer drivers, a more detailed circuit model for single induction cavity has been proposed, in consideration of gas spark switch channel resistance, electromagnetic-coupling effect among discharge bricks, hysteresis losses and saturation characteristics of cores, and secondary power transmission. Experimental results have verified the effectiveness of the model. The simulation results for cavity working normally or with single brick in self-discharge states agree well with the waveforms acquired by experiment. It indicates that the circuit model is capable of simulating operating characteristics of induction cavity even though there are devices in abnormal states in it.
According to the physical design and electrical parameters of the 300 kA single induction cavity developed for linear transformer drivers, a more detailed circuit model for single induction cavity has been proposed, in consideration of gas spark switch channel resistance, electromagnetic-coupling effect among discharge bricks, hysteresis losses and saturation characteristics of cores, and secondary power transmission. Experimental results have verified the effectiveness of the model. The simulation results for cavity working normally or with single brick in self-discharge states agree well with the waveforms acquired by experiment. It indicates that the circuit model is capable of simulating operating characteristics of induction cavity even though there are devices in abnormal states in it.
2012,
24: 1206-1210.
doi: 10.3788/HPLPB20122405.1206
Abstract:
A dielectric barrier discharge (DBD) plasma jet source is presented, which is low-cost and small in size, fed with neon and driven by the a self-developed microsecond pulse power supply with a peak voltage of 0-35 kV and a frequency of 1 kHz. Influences of applied voltage amplitude and gas flow rate on the discharge characteristics of the plasma jet are studied by measuring the waveforms of voltage and current, taking the light emission images and measuring the optical emission spectra. Results show that, the DBD in neon at atmospheric pressure driven by a microsecond pulse voltage can generate a cone-shaped flaming plasma jet, and the intensity of plasma is moderate. The fast rise of the applied pulse voltage can apply a higher overvoltage instantly to the gas gap, and thus can promotes the increases of discharge power, electron density and excitation temperature efficiently; while the increase of gas flow rate results in the decrease of these parameters but little variation of the jet length. Under certain operating conditions, the plasma jet with long length can be generated.
A dielectric barrier discharge (DBD) plasma jet source is presented, which is low-cost and small in size, fed with neon and driven by the a self-developed microsecond pulse power supply with a peak voltage of 0-35 kV and a frequency of 1 kHz. Influences of applied voltage amplitude and gas flow rate on the discharge characteristics of the plasma jet are studied by measuring the waveforms of voltage and current, taking the light emission images and measuring the optical emission spectra. Results show that, the DBD in neon at atmospheric pressure driven by a microsecond pulse voltage can generate a cone-shaped flaming plasma jet, and the intensity of plasma is moderate. The fast rise of the applied pulse voltage can apply a higher overvoltage instantly to the gas gap, and thus can promotes the increases of discharge power, electron density and excitation temperature efficiently; while the increase of gas flow rate results in the decrease of these parameters but little variation of the jet length. Under certain operating conditions, the plasma jet with long length can be generated.
2012,
24: 1211-1216.
doi: 10.3788/HPLPB20122405.1211
Abstract:
A method to calculate power flow for magnetically-insulated inductive voltage adder was developed based on the transmission line algorithm, in which space charge limited flow and magnetic insulation flow were introduced. This method can estimate the power flow of a 10 stage LTD system faster than PIC simulation. The description of flow impedance in magnetic insulation phase is the key to the accuracy of this method, and the numerical stability is an important prerequisite for its application.
A method to calculate power flow for magnetically-insulated inductive voltage adder was developed based on the transmission line algorithm, in which space charge limited flow and magnetic insulation flow were introduced. This method can estimate the power flow of a 10 stage LTD system faster than PIC simulation. The description of flow impedance in magnetic insulation phase is the key to the accuracy of this method, and the numerical stability is an important prerequisite for its application.
2012,
24: 1217-1220.
doi: 10.3788/HPLPB20122405.1217
Abstract:
The basic theory and experimental results of measuring diode voltage with differential absorption method were reported. With the MCNP model of 'bremsstrahlung-attenuation-detector' system, the relation curve of the radiation dose and the diode voltage was fitted. The measurement system of diode voltage with differential absorption method was established, and the waveforms of diode voltage were gained by putting absorbing films of different thicknesses in front of the detectors. By using the fitted curves and the experimental waveforms, the diode voltage of Chenguang accelerator was obtained through iterative method. The peak value of diode voltage was 0.58 MV. The results derived with differential absorption method agree with those measured with the conventional method.
The basic theory and experimental results of measuring diode voltage with differential absorption method were reported. With the MCNP model of 'bremsstrahlung-attenuation-detector' system, the relation curve of the radiation dose and the diode voltage was fitted. The measurement system of diode voltage with differential absorption method was established, and the waveforms of diode voltage were gained by putting absorbing films of different thicknesses in front of the detectors. By using the fitted curves and the experimental waveforms, the diode voltage of Chenguang accelerator was obtained through iterative method. The peak value of diode voltage was 0.58 MV. The results derived with differential absorption method agree with those measured with the conventional method.
2012,
24: 1221-1224.
doi: 10.3788/HPLPB20122405.1221
Abstract:
The circuit equations of variable-impedance transmission lines are usually solved by numerical circuit simulation with simulation code such as PSpice. The commonly-used method is the equal-length segmentation method which divides the transmission line into many small sections with equal length. The paper proposes a different segmentation method, in which the small sections are with equal impedance difference. A transmission line with exponential impedance change is simulated with the two methods. The results show that, with the proposed method, the simulation converges to the true solution more quickly.
The circuit equations of variable-impedance transmission lines are usually solved by numerical circuit simulation with simulation code such as PSpice. The commonly-used method is the equal-length segmentation method which divides the transmission line into many small sections with equal length. The paper proposes a different segmentation method, in which the small sections are with equal impedance difference. A transmission line with exponential impedance change is simulated with the two methods. The results show that, with the proposed method, the simulation converges to the true solution more quickly.
2012,
24: 1225-1228.
doi: 10.3788/HPLPB20122405.1225
Abstract:
A test stand was developed to measure magnetic properties of toroidal magnetic cores at a constant magnetization rate of 8-12 T/s. The test stand consists of pulse forming network(PFN), discharge switches, load and magnetic core. On the basis of the test stand, the magnetization curves of domestic nanocrystalline magnetic core were measured. The energy losses and relative permeability at 200-300 ns pulse width of toroidal magnetic cores were also tested. The experiment results show that the relative pulse permeability of the nanocrystalline magnetic core decreases with increasing the magnetic induction increment and decreasing the pulse width, while the energy loss increases.
A test stand was developed to measure magnetic properties of toroidal magnetic cores at a constant magnetization rate of 8-12 T/s. The test stand consists of pulse forming network(PFN), discharge switches, load and magnetic core. On the basis of the test stand, the magnetization curves of domestic nanocrystalline magnetic core were measured. The energy losses and relative permeability at 200-300 ns pulse width of toroidal magnetic cores were also tested. The experiment results show that the relative pulse permeability of the nanocrystalline magnetic core decreases with increasing the magnetic induction increment and decreasing the pulse width, while the energy loss increases.
2012,
24: 1229-1233.
doi: 10.3788/HPLPB20122405.1229
Abstract:
When dry-type pulsed capacitors of large capacitance are used in vacuum, flashover in low pressure area is inevitable. This paper analyzes the mechanism and solution for the flashover of the capacitors in vacuum. The surface flashover voltage of three different insulating materials is theoretically and experimentally studied. Finally, an overall-encapsulated capacitor is put forward, which uses solid insulation to prevent discharge in low pressure area in vacuum. Experimental tests show that this type of capacitor has strong mechanical strength and excellent electrical performance, and thus can work reliably in vacuum (lower than 10-2 Pa).
When dry-type pulsed capacitors of large capacitance are used in vacuum, flashover in low pressure area is inevitable. This paper analyzes the mechanism and solution for the flashover of the capacitors in vacuum. The surface flashover voltage of three different insulating materials is theoretically and experimentally studied. Finally, an overall-encapsulated capacitor is put forward, which uses solid insulation to prevent discharge in low pressure area in vacuum. Experimental tests show that this type of capacitor has strong mechanical strength and excellent electrical performance, and thus can work reliably in vacuum (lower than 10-2 Pa).
2012,
24: 1234-1238.
doi: 10.3788/HPLPB20122405.1234
Abstract:
A coaxial field distortion gas spark switch was designed and experiments were carried out to study the effect of trigger pulse peak on discharge channel number of the switch gaps in N2 in two cases. In the first case, only the trigger pulse was applied to the switch, while in the second, the inner and outer electrodes were connected to two capacitors with positive and negative charge respectively. The numbers of discharge channels in the two cases were compared. In the first case, discharge channels carry lower current. The average number of channels in the switch inner gap increases obviously with increasing trigger pulse peak in the first case, while the average number of channels in the switch inner gap increases and the average number of channels in the switch outer gap decreases in the second case. Under similar overvoltage multiples, the average number of channels in the second case is smaller.
A coaxial field distortion gas spark switch was designed and experiments were carried out to study the effect of trigger pulse peak on discharge channel number of the switch gaps in N2 in two cases. In the first case, only the trigger pulse was applied to the switch, while in the second, the inner and outer electrodes were connected to two capacitors with positive and negative charge respectively. The numbers of discharge channels in the two cases were compared. In the first case, discharge channels carry lower current. The average number of channels in the switch inner gap increases obviously with increasing trigger pulse peak in the first case, while the average number of channels in the switch inner gap increases and the average number of channels in the switch outer gap decreases in the second case. Under similar overvoltage multiples, the average number of channels in the second case is smaller.
2012,
24: 1239-1243.
doi: 10.3788/HPLPB20122405.1239
Abstract:
The paper proposes a mixed-mode LTD(linear transformer driver) module. Each brick of the mixed-mode LTD module is a multi-stage Marx circuit, where only the switches of the first several stages need external trigger, and the others work in self-breakdown mode. The analysis indicates that, the mixed-mode LTD module can effectively reduce the demand for external trigger; the independent structure of each brick can improve the maintainability of the module, and coupling trigger between Marx bricks can improve the reliability. The paper also discusses the effects of circuit resistance, magnetic core loss and self-breakdown switch jitter on the modules parameter design.
The paper proposes a mixed-mode LTD(linear transformer driver) module. Each brick of the mixed-mode LTD module is a multi-stage Marx circuit, where only the switches of the first several stages need external trigger, and the others work in self-breakdown mode. The analysis indicates that, the mixed-mode LTD module can effectively reduce the demand for external trigger; the independent structure of each brick can improve the maintainability of the module, and coupling trigger between Marx bricks can improve the reliability. The paper also discusses the effects of circuit resistance, magnetic core loss and self-breakdown switch jitter on the modules parameter design.
2012,
24: 1244-1246.
doi: 10.3788/HPLPB20122405.1244
Abstract:
Dark current initiated by field emission and multipacting caused by secondary emission have been observed in various radio frequency or microwave components. These phenomena are believed to be major limitations on the stable operation of the particle accelerators, communication satellites and microwave payloads of spacecrafts. This work extends OPAL, a parallel framework for charged particle optics in accelerator structures and beam lines, with the necessary physics models to simulate dark current and multipacting phenomena. Careful benchmark has been performed by code to code comparison with TxPhysics library. After benchmarking, the dark current in highgradient linac structures was evaluated and the post processing capability of OPAL was shown.
Dark current initiated by field emission and multipacting caused by secondary emission have been observed in various radio frequency or microwave components. These phenomena are believed to be major limitations on the stable operation of the particle accelerators, communication satellites and microwave payloads of spacecrafts. This work extends OPAL, a parallel framework for charged particle optics in accelerator structures and beam lines, with the necessary physics models to simulate dark current and multipacting phenomena. Careful benchmark has been performed by code to code comparison with TxPhysics library. After benchmarking, the dark current in highgradient linac structures was evaluated and the post processing capability of OPAL was shown.
2012,
24: 1247-1250.
doi: 10.3788/HPLPB20122405.1247
Abstract:
Experimental data of magnetic core under repeated magnetization, usually used during the design of high power pulsed equipment, can not accurately reflect its performance under pulsed magnetization. A method of magnetic core test and data processing under pulsed magnetization is given. The loss characteristics of a kind of glassy alloy magnetic core under pulsed magnetization are experimentally studied. The relationship between magnetic core loss and magnetization rates is presented. The saturation time ranges from 67 to 1 410 ns and the magnetization rate ranges from 1 to 40 T/s. The percentages of hysteresis loss and eddy loss are analyzed. The experimental results show that the relationship between magnetic core loss and magnetization rates accords with the saturation wave model. Moreover, the core loss is directly proportional to the magnetization rate.
Experimental data of magnetic core under repeated magnetization, usually used during the design of high power pulsed equipment, can not accurately reflect its performance under pulsed magnetization. A method of magnetic core test and data processing under pulsed magnetization is given. The loss characteristics of a kind of glassy alloy magnetic core under pulsed magnetization are experimentally studied. The relationship between magnetic core loss and magnetization rates is presented. The saturation time ranges from 67 to 1 410 ns and the magnetization rate ranges from 1 to 40 T/s. The percentages of hysteresis loss and eddy loss are analyzed. The experimental results show that the relationship between magnetic core loss and magnetization rates accords with the saturation wave model. Moreover, the core loss is directly proportional to the magnetization rate.
2012,
24: 1251-1255.
doi: 10.3788/HPLPB20122405.1251
Abstract:
In order to trigger the two-electrode gas switch without a trigger electrode, not only a high magnitude, fast rise time output pulse is needed but also high reliability is required for the switch trigger in high power system. A six-stage Marx trigger was introduced to solve the above technical and reliability problems. A pulse voltage with fast rise time and high magnitude was obtained by establishing a multi-stage pulse forming circuit and the operating parameters were determined by the method combining experiment measurement with probability model analysis. The results demonstrate that, both the self-trigger rate of Marx trigger and the success rate of triggering gas switch accord with the two-parameter Weibull distribution model established based on experimental data. The output voltages magnitude can reach 120 kV and rise time is less than 20 ns, when the under-voltage ratio is 65%, the operating voltage is 13.5 kV, and the absolute gas pressure is 0.35 MPa. The calculated self-trigger rate is less than 0.000 1% and the calculated success rate of triggering gas switch is higher than 99.999 9%.
In order to trigger the two-electrode gas switch without a trigger electrode, not only a high magnitude, fast rise time output pulse is needed but also high reliability is required for the switch trigger in high power system. A six-stage Marx trigger was introduced to solve the above technical and reliability problems. A pulse voltage with fast rise time and high magnitude was obtained by establishing a multi-stage pulse forming circuit and the operating parameters were determined by the method combining experiment measurement with probability model analysis. The results demonstrate that, both the self-trigger rate of Marx trigger and the success rate of triggering gas switch accord with the two-parameter Weibull distribution model established based on experimental data. The output voltages magnitude can reach 120 kV and rise time is less than 20 ns, when the under-voltage ratio is 65%, the operating voltage is 13.5 kV, and the absolute gas pressure is 0.35 MPa. The calculated self-trigger rate is less than 0.000 1% and the calculated success rate of triggering gas switch is higher than 99.999 9%.
2012,
24: 1256-1260.
doi: 10.3788/HPLPB20122405.1256
Abstract:
For single-use and cost-effective pulsed power system such as exploding foil initiators, a micro planar gas spark switch is designed and fabricated based on microfabrication. The size of the switch is only about 1.5 cm0.5 cm. Device testing of the switch gives an output of peak current 3 450 A and rise time 164 ns, which satisfies the demand of exploding foil initiators and ordinary pulsed power systems. System modeling based on experimental data shows that the inductance and resistance of the switch circuit are 26.5 nH and 0.066 , respectively. Compared with the conventional stereo spark gap switch, the parameters of the device are greatly optimized.
For single-use and cost-effective pulsed power system such as exploding foil initiators, a micro planar gas spark switch is designed and fabricated based on microfabrication. The size of the switch is only about 1.5 cm0.5 cm. Device testing of the switch gives an output of peak current 3 450 A and rise time 164 ns, which satisfies the demand of exploding foil initiators and ordinary pulsed power systems. System modeling based on experimental data shows that the inductance and resistance of the switch circuit are 26.5 nH and 0.066 , respectively. Compared with the conventional stereo spark gap switch, the parameters of the device are greatly optimized.
2012,
24: 1015-1018.
doi: 10.3788/HPLPB20122405.1015
Abstract:
设计并搭建了化学激光器1/4环柱型增益发生器的实验系统。按设计流量进行了出光实验，功率计探测到的出光功率在60 W左右。测量了燃烧室温度及压力，与Alpha激光器HL911-3实验数据类似，燃烧室温度及压力曲线都存在一个爬升阶段。环柱型增益发生器沿角向扩张的特点使得光腔区压力很低，仅为0.5 kPa左右。为验证环柱状增益区的有效形成，对3对取光孔分别进行了出光实验，结果表明每对取光孔都有功率输出，证明设计的增益发生器运行正常。
2012,
24: 1111-1116.
doi: 10.3788/HPLPB20122405.1111
Abstract:
将 5,5-二甲基乙内酰脲(DMH)新型无氰电镀体系应用于惯性约束聚变金空腔靶制备中。利用扫描电镜和库仑计法研究了以DMH为配位剂的镀液组成和工艺条件对电镀金层质量等的影响。结果表明:该镀液体系具有良好的稳定性，控制镀液中金盐质量浓度为8 g/L，DMH质量浓度为80 g/L时，在阴极电流密度1.5 A/dm2、pH值9~10、温度45 ℃的条件下，可制得结晶致密、厚度均一的金镀层。
