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RSS2018 Vol. 30, No. 3
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2018,
30: 031001.
doi: 10.11884/HPLPB201830.170299
Abstract:
Thermal-mechanical failure behavior of the internally pressurized cylinder shell under laser irradiation is investigated by numerical approach. The dynamic bursting processes are simulated, and the obtained failure modes are validated by experiment. Three typical failure modes are found and the corresponding parameter ranges are listed, and formation mechanisms of each failure mode are discussed. The effect of thermal softening on the threshold of internal pressure at different laser spot sizes and shell thicknesses are explored, and the relation between internal pressure and failure time is discussed. The results show that the threshold of internal pressure decreases with the increasing laser spot size and the extent of thermal softening, and it is in linear relationship with the shell thickness. At given laser parameters and shell parameters, the failure time declines in a quadratic function of internal pressure. A method to predict the failure time of internally pressurized cylinder shell under laser irradiation based on thermal softening factor is proposed and presented.
Thermal-mechanical failure behavior of the internally pressurized cylinder shell under laser irradiation is investigated by numerical approach. The dynamic bursting processes are simulated, and the obtained failure modes are validated by experiment. Three typical failure modes are found and the corresponding parameter ranges are listed, and formation mechanisms of each failure mode are discussed. The effect of thermal softening on the threshold of internal pressure at different laser spot sizes and shell thicknesses are explored, and the relation between internal pressure and failure time is discussed. The results show that the threshold of internal pressure decreases with the increasing laser spot size and the extent of thermal softening, and it is in linear relationship with the shell thickness. At given laser parameters and shell parameters, the failure time declines in a quadratic function of internal pressure. A method to predict the failure time of internally pressurized cylinder shell under laser irradiation based on thermal softening factor is proposed and presented.
2018,
30: 031002.
doi: 10.11884/HPLPB201830.170312
Abstract:
An integrated ultrafast laser manufacturing system, which is based on LabVIEW software, has been designed to improve the integration level of three-dimensional translation stage controlling software and optical microscope software. This system is consisted of six units: femtosecond laser, translation stage, CCD camera, shutter, power meter, and computer. The main design idea is based on the multi-thread programming method in LabVIEW software: (1) the synchro control between the laser beam on or off and translation stage has been achieved; (2) the laser manufacturing process is monitored via a CCD camera; (3) the laser parameters such as laser average power are monitored via a power meter. And these separate modules are controlled in an integration interface. Compared with usual ultrafast laser manufacturing systems, this system has the advantages of high stability, simple operation, integrated control interface, strong scalability and high regulation efficiency.
An integrated ultrafast laser manufacturing system, which is based on LabVIEW software, has been designed to improve the integration level of three-dimensional translation stage controlling software and optical microscope software. This system is consisted of six units: femtosecond laser, translation stage, CCD camera, shutter, power meter, and computer. The main design idea is based on the multi-thread programming method in LabVIEW software: (1) the synchro control between the laser beam on or off and translation stage has been achieved; (2) the laser manufacturing process is monitored via a CCD camera; (3) the laser parameters such as laser average power are monitored via a power meter. And these separate modules are controlled in an integration interface. Compared with usual ultrafast laser manufacturing systems, this system has the advantages of high stability, simple operation, integrated control interface, strong scalability and high regulation efficiency.
2018,
30: 032001.
doi: 10.11884/HPLPB201830.170264
Abstract:
Focusing on the design and running condition of the reflectors in the lamp boxes, an experiment has been designed to confirm the quantization of the reflector's influence on the flash lamps radiation and neodymium glass fluorescence. The flash lamp radiation is measured by the high current diode. The neodymium glass fluorescence is recorded by the measurement system designed and manufactured by ourselves. Meanwhile, a high speed camera is used to observe the discharge channel. Results indicate that the reflector can improve the flash lamp radiation by 89% and the neodymium glass fluorescence by 78%. More important, the reason of flash lamp's "turning white" while running has been found. The reflector will induce the discharge channel forming near the reflector, making the lamp wall near the reflector be ablated excessively.
Focusing on the design and running condition of the reflectors in the lamp boxes, an experiment has been designed to confirm the quantization of the reflector's influence on the flash lamps radiation and neodymium glass fluorescence. The flash lamp radiation is measured by the high current diode. The neodymium glass fluorescence is recorded by the measurement system designed and manufactured by ourselves. Meanwhile, a high speed camera is used to observe the discharge channel. Results indicate that the reflector can improve the flash lamp radiation by 89% and the neodymium glass fluorescence by 78%. More important, the reason of flash lamp's "turning white" while running has been found. The reflector will induce the discharge channel forming near the reflector, making the lamp wall near the reflector be ablated excessively.
2018,
30: 032002.
doi: 10.11884/HPLPB201830.170368
Abstract:
In order to investigate the irradiation effects of heavy particles on hollow glass microspheres (HGMs) used in inertial confinement fusion (ICF) and the mechanism during filling gas, the molecular dynamics method was used to simulate the formation of micro-channels before and after irradiation in silica glass. The simulation results show the irradiation of heavy particles have produced obvious channels in silica glasses, which will be better for filling argon gas; the particle channels produced by irradiation have gradually closed under high temperature and high pressure, and the irradiation defects have recovered in some degree. Therefore, the irradiation of heavy particles can produce micro-channels for filling gas, and they can be closed under high temperature and high pressure, which plays the role of a switch. The results provide theoretical support for the experiment of gas filling and barrier properties of microspheres, and also testify the feasibility of the method.
In order to investigate the irradiation effects of heavy particles on hollow glass microspheres (HGMs) used in inertial confinement fusion (ICF) and the mechanism during filling gas, the molecular dynamics method was used to simulate the formation of micro-channels before and after irradiation in silica glass. The simulation results show the irradiation of heavy particles have produced obvious channels in silica glasses, which will be better for filling argon gas; the particle channels produced by irradiation have gradually closed under high temperature and high pressure, and the irradiation defects have recovered in some degree. Therefore, the irradiation of heavy particles can produce micro-channels for filling gas, and they can be closed under high temperature and high pressure, which plays the role of a switch. The results provide theoretical support for the experiment of gas filling and barrier properties of microspheres, and also testify the feasibility of the method.
2018,
30: 033001.
doi: 10.11884/HPLPB201830.170328
Abstract:
In this paper, the configuration design of a novel multipacting cathode driven by pulsed power source is put forward and its dynamic process is theoretically investigated in detail. Firstly, the dynamic model is established for this novel multipacting cathode, the displacement and velocity expressions are obtained by solving the dynamic equation of secondary electrons. The influences of electron with different initial energy emitted from each direction on electron trajectory, velocity, and impact energy are discussed. The approximate expressions of electron transit time and impact energy are obtained and discussed theoretically. Secondly, to find the multipacting cathode working range, the multipacting susceptibility diagram is obtained and discussed in detail by solving electron dynamic equation coupling Vaughan's empirical formula (secondary electron yield model). Theoretical results demonstrate that the conception of the novel multipacting cathode is feasible. By applying an appropriate electric field (about MV/m) in axial and radial directions and a proper magnetic field (T) in axial direction on a cylindrical dielectric surface coated by high secondary emission yield coefficient material, the electrons move with spiral trajectories along axial direction. Electron number could be increased effectively by each impact with multipacting interaction. This phenomenon could achieve electron current amplification until multipacting comes to saturation. Finally, the deposit phenomenon of positive charges and multipacting saturation are analyzed and discussed. The roughly theoretical estimation indicates that the novel multipacting cathode has the performance of high emission current density, and the emission current density can run up to the level of kA/cm2. Enhancing the magnitude of applied electrostatic field in radial direction can effectively improve the emission current density.
In this paper, the configuration design of a novel multipacting cathode driven by pulsed power source is put forward and its dynamic process is theoretically investigated in detail. Firstly, the dynamic model is established for this novel multipacting cathode, the displacement and velocity expressions are obtained by solving the dynamic equation of secondary electrons. The influences of electron with different initial energy emitted from each direction on electron trajectory, velocity, and impact energy are discussed. The approximate expressions of electron transit time and impact energy are obtained and discussed theoretically. Secondly, to find the multipacting cathode working range, the multipacting susceptibility diagram is obtained and discussed in detail by solving electron dynamic equation coupling Vaughan's empirical formula (secondary electron yield model). Theoretical results demonstrate that the conception of the novel multipacting cathode is feasible. By applying an appropriate electric field (about MV/m) in axial and radial directions and a proper magnetic field (T) in axial direction on a cylindrical dielectric surface coated by high secondary emission yield coefficient material, the electrons move with spiral trajectories along axial direction. Electron number could be increased effectively by each impact with multipacting interaction. This phenomenon could achieve electron current amplification until multipacting comes to saturation. Finally, the deposit phenomenon of positive charges and multipacting saturation are analyzed and discussed. The roughly theoretical estimation indicates that the novel multipacting cathode has the performance of high emission current density, and the emission current density can run up to the level of kA/cm2. Enhancing the magnitude of applied electrostatic field in radial direction can effectively improve the emission current density.
2018,
30: 033002.
doi: 10.11884/HPLPB201830.170364
Abstract:
In conventional High Power Microwave(HPM) waveguide arrays of longitudinal shunt slots, the mutual coupling of slots in different waveguide can badly decrease the capability of wide-angle scanning of array. For this reason, an L-band HPM waveguide array of longitudinal shunt slots was designed. The choke groove was adopted to restrain the mutual coupling of slots of the HPM array antenna. The results of simulation are: the scanning angle of array without choke groove structure with the gain of antenna decreased 3 dB is only 24.7°, and it is 33.0° for array with choke groove structure; the wideband of active reflection of array have been improved with choke groove structure, the bandwidth of VSWR ≤3 of array with choke groove is 6.6%, and that is 5.0% without choke groove; the power-handling capacity of array antenna with scanning angle of 35° can reach 957 MW, which is a little less than that of array without scanning(1008 MW).
In conventional High Power Microwave(HPM) waveguide arrays of longitudinal shunt slots, the mutual coupling of slots in different waveguide can badly decrease the capability of wide-angle scanning of array. For this reason, an L-band HPM waveguide array of longitudinal shunt slots was designed. The choke groove was adopted to restrain the mutual coupling of slots of the HPM array antenna. The results of simulation are: the scanning angle of array without choke groove structure with the gain of antenna decreased 3 dB is only 24.7°, and it is 33.0° for array with choke groove structure; the wideband of active reflection of array have been improved with choke groove structure, the bandwidth of VSWR ≤3 of array with choke groove is 6.6%, and that is 5.0% without choke groove; the power-handling capacity of array antenna with scanning angle of 35° can reach 957 MW, which is a little less than that of array without scanning(1008 MW).
2018,
30: 033003.
doi: 10.11884/HPLPB201830.170314
Abstract:
A broadband Wilkinson power divider with circular micro-strip line structure is presented. Firstly, the design equation is derived based on the analysis of the odd-even mode. Secondly, particle swarm optimization is used to obtain the design parameters of the Wilkinson power divider. This method improves the efficiency and accuracy of the power divider design. The results show that, in the frequency range of 8-12 GHz, the return loss is less than －20 dB, the ports transmission loss is less than 3.4 dB, and the isolation degree is less than －20 dB. The simulation results are in good agreement with the measured results, which verifies the feasibility of this design.
A broadband Wilkinson power divider with circular micro-strip line structure is presented. Firstly, the design equation is derived based on the analysis of the odd-even mode. Secondly, particle swarm optimization is used to obtain the design parameters of the Wilkinson power divider. This method improves the efficiency and accuracy of the power divider design. The results show that, in the frequency range of 8-12 GHz, the return loss is less than －20 dB, the ports transmission loss is less than 3.4 dB, and the isolation degree is less than －20 dB. The simulation results are in good agreement with the measured results, which verifies the feasibility of this design.
2018,
30: 033201.
doi: 10.11884/HPLPB201830.170177
Abstract:
Monopole antenna is widely used as HF/VHF radio in vehicle system. Its response characteristics exposed to high-altitude nuclear electromagnetic pulse(HEMP) is simulated using CST in this paper. The time-domain and frequency-domain response voltages of antenna terminal's 50 Ω load are calculated. And its their variation with angle of incidence of electromagnetic pulse, top area of vehicle and antenna position in top surface are explored. The simulation results show that the maximum response voltage at feeding point increases as the increase of the angle between electric field vector of incident pulse and horizontal plane, and the increases of effective reflection area to incident pulse. The simulation results have important guiding significance for the antennas layout and the selection of electromagnetic pulse protection device for the antenna system.
Monopole antenna is widely used as HF/VHF radio in vehicle system. Its response characteristics exposed to high-altitude nuclear electromagnetic pulse(HEMP) is simulated using CST in this paper. The time-domain and frequency-domain response voltages of antenna terminal's 50 Ω load are calculated. And its their variation with angle of incidence of electromagnetic pulse, top area of vehicle and antenna position in top surface are explored. The simulation results show that the maximum response voltage at feeding point increases as the increase of the angle between electric field vector of incident pulse and horizontal plane, and the increases of effective reflection area to incident pulse. The simulation results have important guiding significance for the antennas layout and the selection of electromagnetic pulse protection device for the antenna system.
2018,
30: 033202.
doi: 10.11884/HPLPB201830.170427
Abstract:
Sometimes we can not obtain the interference signal information, but can easily obtain the input signal and output signal information when FM signal has got single-tone interference. So we propose to modify the mean square error and make it be associated with jamming to signal ratio(JSR), then we evaluate indirectly the FM signal single-tone interference. First, we establish the simulation model of FM signal and analyze distortion of FM demodulated signal under different SNR and different JSR. And we analyze the relation between JSR and mean square error which is used to express analog signal distortion. Then we modify the formula of the mean square error and obtain the new evaluation index after the simulation. Finally, we analyze the relation among the new evaluation index, the JSR and the duty cycle and get the conclusion.
Sometimes we can not obtain the interference signal information, but can easily obtain the input signal and output signal information when FM signal has got single-tone interference. So we propose to modify the mean square error and make it be associated with jamming to signal ratio(JSR), then we evaluate indirectly the FM signal single-tone interference. First, we establish the simulation model of FM signal and analyze distortion of FM demodulated signal under different SNR and different JSR. And we analyze the relation between JSR and mean square error which is used to express analog signal distortion. Then we modify the formula of the mean square error and obtain the new evaluation index after the simulation. Finally, we analyze the relation among the new evaluation index, the JSR and the duty cycle and get the conclusion.
2018,
30: 033203.
doi: 10.11884/HPLPB201830.170395
Abstract:
Traditional spectrum sensing based on compressed sensing assumes that the sparsity is known, while actually, it is unknown. To solve the problem, we proposed a modified sparsity adaptive matching pursuit (MSAMP) algorithm. The MSAMP algorithm pre-estimates the value of sparsity in the process of choosing the support set. A cooperative wideband spectrum compressed sensing method is developed based on the MSAMP algorithm and sequential compression inspection technique. Theoretical analysis and simulation results show that the method can enhance the spectrum sensing capability without a priori knowledge of sparsity.
Traditional spectrum sensing based on compressed sensing assumes that the sparsity is known, while actually, it is unknown. To solve the problem, we proposed a modified sparsity adaptive matching pursuit (MSAMP) algorithm. The MSAMP algorithm pre-estimates the value of sparsity in the process of choosing the support set. A cooperative wideband spectrum compressed sensing method is developed based on the MSAMP algorithm and sequential compression inspection technique. Theoretical analysis and simulation results show that the method can enhance the spectrum sensing capability without a priori knowledge of sparsity.
2018,
30: 034001.
doi: 10.11884/HPLPB201830.170278
Abstract:
The detection efficiency of ϕ75 mm×25 mm of 241Am standard samples were studied by using laboratory HPGe detection. When we used detectors with the same type of structure to measure a given volume source, the linearity function between the virtual point source and the virtual point detector was established by using LabSOCS software and Monte Carlo method. For a detector, the position of virtual point detector can be fixed by a point source placed at different height, and then, the position of virtual point source can be fixed by using their linearity function. The real calibration process will be carried out by placing a point source at its virtual position, namely, the volume source is replaced with the point source. In conclusion, the position of virtual point source can be obtained through the virtual point detector. This is a completely new technology method, which will be widely applied in radioactive measurement.
The detection efficiency of ϕ75 mm×25 mm of 241Am standard samples were studied by using laboratory HPGe detection. When we used detectors with the same type of structure to measure a given volume source, the linearity function between the virtual point source and the virtual point detector was established by using LabSOCS software and Monte Carlo method. For a detector, the position of virtual point detector can be fixed by a point source placed at different height, and then, the position of virtual point source can be fixed by using their linearity function. The real calibration process will be carried out by placing a point source at its virtual position, namely, the volume source is replaced with the point source. In conclusion, the position of virtual point source can be obtained through the virtual point detector. This is a completely new technology method, which will be widely applied in radioactive measurement.
2018,
30: 034002.
doi: 10.11884/HPLPB201830.170239
Abstract:
Owing to the effect of non-ideal factors in the imaging process, X-ray photographic image quality is degraded, resulting in a shift of image boundary position relative to that of the object. In this paper, the Monte Carlo method is used to simulate the flash photography process, and the influence of fuzzy and scattering on the boundary detection is studied. The result shows that the relationship between the blur size and the boundary deviation is dependent on the material, density and size of adjacent layers; under the same object structure, the larger the blur, the greater the boundary deviation; when the object structure is different, the boundary deviation is also different with the same blur size. The greater the ratio of scatter to direct, the greater the effect of scattering on the boundary detection results. When the ratio is greater than 50, the boundary detection error caused by scattering is more than one pixel.
Owing to the effect of non-ideal factors in the imaging process, X-ray photographic image quality is degraded, resulting in a shift of image boundary position relative to that of the object. In this paper, the Monte Carlo method is used to simulate the flash photography process, and the influence of fuzzy and scattering on the boundary detection is studied. The result shows that the relationship between the blur size and the boundary deviation is dependent on the material, density and size of adjacent layers; under the same object structure, the larger the blur, the greater the boundary deviation; when the object structure is different, the boundary deviation is also different with the same blur size. The greater the ratio of scatter to direct, the greater the effect of scattering on the boundary detection results. When the ratio is greater than 50, the boundary detection error caused by scattering is more than one pixel.
2018,
30: 034101.
doi: 10.11884/HPLPB201830.170423
Abstract:
In view of the incompatibility of PET material with the standard microfabrication due to its low intolerance to high temperature, an effective fabrication process including lithography, metal deposition and reactive ion etching have been developed which paves the way for direct micro processing on PET. Based on such a method, thin film graphene layer was grown and transferred to 0.5 mm thick PET substrate and the graphene strain sensor was successfully fabricated. According to the measurement results, the piezoresistive gauge factor of the graphene can be estimated about 1.3, which is in good accordance with the value given in literature. Such fabrication method can also be applied in the domain where flexible micro devices are required.
In view of the incompatibility of PET material with the standard microfabrication due to its low intolerance to high temperature, an effective fabrication process including lithography, metal deposition and reactive ion etching have been developed which paves the way for direct micro processing on PET. Based on such a method, thin film graphene layer was grown and transferred to 0.5 mm thick PET substrate and the graphene strain sensor was successfully fabricated. According to the measurement results, the piezoresistive gauge factor of the graphene can be estimated about 1.3, which is in good accordance with the value given in literature. Such fabrication method can also be applied in the domain where flexible micro devices are required.
2018,
30: 034102.
doi: 10.11884/HPLPB201830.170294
Abstract:
In this paper, the linewidth of femtosecond laser two-photon polymerization is studied by the theory of free radical density and the effect of optical tweezers. Based on the relationship between free radical density and time in the process of two-photon polymerization, the expression of linewidth of two-photon femtosecond laser processing is deduced considering the effect of optical tweezers. The relationship of linewidth with scanning speed and laser power is studied and the influence of different light initiators on the linewidth is also discussed. The theoreticial result agrees well with the experimental one in the literature. The result of this paper gives a new idea for the study of femtosecond laser two-photon processing, and provides a theoretical formula for the study of the influence of optical tweezers on linewidth.
In this paper, the linewidth of femtosecond laser two-photon polymerization is studied by the theory of free radical density and the effect of optical tweezers. Based on the relationship between free radical density and time in the process of two-photon polymerization, the expression of linewidth of two-photon femtosecond laser processing is deduced considering the effect of optical tweezers. The relationship of linewidth with scanning speed and laser power is studied and the influence of different light initiators on the linewidth is also discussed. The theoreticial result agrees well with the experimental one in the literature. The result of this paper gives a new idea for the study of femtosecond laser two-photon processing, and provides a theoretical formula for the study of the influence of optical tweezers on linewidth.
2018,
30: 035001.
doi: 10.11884/HPLPB201830.170351
Abstract:
Fast Linear Transformer Drivers (FLTDs) can directly produce high-power pulse with the rise time 70-200 ns, which are based on magnetic coupling by many bricks connected in parallel in a circular annulus to output MA current and tens of cavities connected in series to output MV voltage. FLTDs are regarded as the next petawatt drivers for Z-pinch by international scientific community. At present, mega-ampere scale FLTD cavities need two or four triggering pulses with 100 kV and rise time of 25 ns in general, so the petawatt FLTD drivers consist of several thousand cavities require ten thousands of the triggering pulses and should be arrived the different position cavities at accurate sequences in order to realize the secondary pulses to superpose inductively and efficiently, which is the bottleneck of the FLTD development. The paper presents a creative FLTD module with four stages in series sharing induction cavity shell and a novel trigger method achieving nearly ideal IVA triggering sequence for each FLTD module. The FLTD module with mega-ampere current output consisting of 16-cavities in series is designed. The circuit model of the new structure of 16-stage FLTD is developed. The influences of the switches' prefire of main bricks, the triggering brick switches' closing sequences and jitter, and the secondary transmission line impedances are simulated based on the circuit model.
Fast Linear Transformer Drivers (FLTDs) can directly produce high-power pulse with the rise time 70-200 ns, which are based on magnetic coupling by many bricks connected in parallel in a circular annulus to output MA current and tens of cavities connected in series to output MV voltage. FLTDs are regarded as the next petawatt drivers for Z-pinch by international scientific community. At present, mega-ampere scale FLTD cavities need two or four triggering pulses with 100 kV and rise time of 25 ns in general, so the petawatt FLTD drivers consist of several thousand cavities require ten thousands of the triggering pulses and should be arrived the different position cavities at accurate sequences in order to realize the secondary pulses to superpose inductively and efficiently, which is the bottleneck of the FLTD development. The paper presents a creative FLTD module with four stages in series sharing induction cavity shell and a novel trigger method achieving nearly ideal IVA triggering sequence for each FLTD module. The FLTD module with mega-ampere current output consisting of 16-cavities in series is designed. The circuit model of the new structure of 16-stage FLTD is developed. The influences of the switches' prefire of main bricks, the triggering brick switches' closing sequences and jitter, and the secondary transmission line impedances are simulated based on the circuit model.
2018,
30: 035002.
doi: 10.11884/HPLPB201830.170340
Abstract:
With the development of pulse power technology, the pulse power supply modules (PPSMs) are widely used in areas of scientific research, medical treatment, industry, military, and geological exploration. In these areas, more and more energy is needed and the number of PPSMs is increasing rapidly, and accurate pulse discharging waveforms are required. How to control the numerous PPSMs to discharge in precise time sequence effectively to obtain the waveforms becomes one of the key problems in the pulse power technology.According to the requirements of a pulse discharging velocity source, a time sequence discharging control system is designed, which can control 30 PPSMs to discharge in a precise time sequence. In this control system, the digital signal processor (DSP) is used as the main control chip and the high speed photoelectric converters and optical fibers are used as the trigger signals transmission system. The time sequence can be set by using the upper computer software and the accuracy of the trigger pulses can reach microsecond level. This control system has been used in the actual experiments of the acceleration source and the results prove that the control system is effective.
With the development of pulse power technology, the pulse power supply modules (PPSMs) are widely used in areas of scientific research, medical treatment, industry, military, and geological exploration. In these areas, more and more energy is needed and the number of PPSMs is increasing rapidly, and accurate pulse discharging waveforms are required. How to control the numerous PPSMs to discharge in precise time sequence effectively to obtain the waveforms becomes one of the key problems in the pulse power technology.According to the requirements of a pulse discharging velocity source, a time sequence discharging control system is designed, which can control 30 PPSMs to discharge in a precise time sequence. In this control system, the digital signal processor (DSP) is used as the main control chip and the high speed photoelectric converters and optical fibers are used as the trigger signals transmission system. The time sequence can be set by using the upper computer software and the accuracy of the trigger pulses can reach microsecond level. This control system has been used in the actual experiments of the acceleration source and the results prove that the control system is effective.
2018,
30: 035003.
doi: 10.11884/HPLPB201830.170353
Abstract:
The accurate control technology for 24 modules of the Primary Test Stand (PTS) and the experimental results are given in this paper. The synchronicity of 24 lines pulsed current is controlled by 24 laser trigger switches. The current waveform can form through adjusting laser time easily. 24 laser trigger switches are triggered by 12 Q- switched Nd: YAG fourth harmonic 266 nm laser, i.e., two laser switches are triggered by one laser. The experimental results show that the jitter of the laser trigger system is less than 1.0 ns, the jitter of switch is less than 1.5 ns. The load current is 9.8 MA and the rising time of current is 75 ns under 65 kV charging voltage, when 24 modules are triggered synchronously. The adjusting range of rising time of current get to about 600 ns, 5.5 MA in PTS. The measured result of current waveform is consistent with the simulation result. The current waveform is repeatable for same load.
The accurate control technology for 24 modules of the Primary Test Stand (PTS) and the experimental results are given in this paper. The synchronicity of 24 lines pulsed current is controlled by 24 laser trigger switches. The current waveform can form through adjusting laser time easily. 24 laser trigger switches are triggered by 12 Q- switched Nd: YAG fourth harmonic 266 nm laser, i.e., two laser switches are triggered by one laser. The experimental results show that the jitter of the laser trigger system is less than 1.0 ns, the jitter of switch is less than 1.5 ns. The load current is 9.8 MA and the rising time of current is 75 ns under 65 kV charging voltage, when 24 modules are triggered synchronously. The adjusting range of rising time of current get to about 600 ns, 5.5 MA in PTS. The measured result of current waveform is consistent with the simulation result. The current waveform is repeatable for same load.
2018,
30: 035004.
doi: 10.11884/HPLPB201830.170349
Abstract:
A high current device for dense plasma focus (DPF) is developed. It uses eight 12 μF pulse capacitors with low inductance and low resistance as primary energy storage bank, and each capacitor is connected with a large current high voltage switch. When the switch synchronous trigger system triggers the eight high voltage switches synchronously, high current is delivered into the load through eight plate transmission lines. The pulse capacitor and the high voltage switch are integrated. With such a structure, the device is compact and it has a minimized connection inductance. The plate transmission line is a sector structure, which can make the transmission inductance smaller, and help the transmission of high current. The following technical parameters of the device were achieved on the dummy load: output current amplitude of ~500 kA when primary capacitors are charged with 20 kV.
A high current device for dense plasma focus (DPF) is developed. It uses eight 12 μF pulse capacitors with low inductance and low resistance as primary energy storage bank, and each capacitor is connected with a large current high voltage switch. When the switch synchronous trigger system triggers the eight high voltage switches synchronously, high current is delivered into the load through eight plate transmission lines. The pulse capacitor and the high voltage switch are integrated. With such a structure, the device is compact and it has a minimized connection inductance. The plate transmission line is a sector structure, which can make the transmission inductance smaller, and help the transmission of high current. The following technical parameters of the device were achieved on the dummy load: output current amplitude of ~500 kA when primary capacitors are charged with 20 kV.
2018,
30: 035005.
doi: 10.11884/HPLPB201830.170392
Abstract:
For the application requirements of the high voltage pulse generator based on the pulse forming network(PFN) in the microwave driver and the solid-state modulator, the theory of the PFN with the trapezoidal pulse output was developed. First, the analytical expression of the trapezoidal pulse was obtained by the Prony algorithm. Secondly, the waveform parameters were optimized by using the best uniform approximation algorithm based on the equations of the optimal control with the maximum and minimum of the output wave, and solving these nonlinear equations with the Newton iteration method or other numerical methods. Then, the initial parameters of the PFN were worked out with the method of impedance matching. The final components parameters were obtained by rejecting some secondary parameters and adjusting a few of the main parameters. The method and criteria of the design for a PFN with the low ripple trapezoidal pulse output were proposed by theoretical analysis and numerical simulation. The results show that the proposed method can be used to design the PFN with any order and low ripple, and it can be used to design not only the pulse source with trapezoidal pulse output, but also the pulse sources with other pulse output.
For the application requirements of the high voltage pulse generator based on the pulse forming network(PFN) in the microwave driver and the solid-state modulator, the theory of the PFN with the trapezoidal pulse output was developed. First, the analytical expression of the trapezoidal pulse was obtained by the Prony algorithm. Secondly, the waveform parameters were optimized by using the best uniform approximation algorithm based on the equations of the optimal control with the maximum and minimum of the output wave, and solving these nonlinear equations with the Newton iteration method or other numerical methods. Then, the initial parameters of the PFN were worked out with the method of impedance matching. The final components parameters were obtained by rejecting some secondary parameters and adjusting a few of the main parameters. The method and criteria of the design for a PFN with the low ripple trapezoidal pulse output were proposed by theoretical analysis and numerical simulation. The results show that the proposed method can be used to design the PFN with any order and low ripple, and it can be used to design not only the pulse source with trapezoidal pulse output, but also the pulse sources with other pulse output.
2018,
30: 035006.
doi: 10.11884/HPLPB201830.170280
Abstract:
Surface micro structure is a key influence factor on surface flashover of insulators. This paper studied the construction methods of micro-structure on polymer insulators as well as its effect on surface flashover characteristics. Firstly, taking SiO2 micro balls as template, the method of chemical templating was applied to realize the construction of micro holes on the surface of CLPS. The effect of diameters of SiO2 ball and volume of addition on the morphology was also studied. Secondly, laser micro treatment was used to construct triangular grooves in hundreds of microns on the surface of PMMA insulators and the influence of laser parameters on the morphology and structure of micro grooves was explored as well. Surface flashover test of the insulators with the aforementioned micro structure in different scales was conducted on a short-pulsed high voltage platform. The results show there was a big increase in surface hole-off voltage. Compared with the traditional surface roughness treatment by polishing, the construction of micro structure on the surface of polymer in this paper is controllable and the increase of flashover voltages is stable.
Surface micro structure is a key influence factor on surface flashover of insulators. This paper studied the construction methods of micro-structure on polymer insulators as well as its effect on surface flashover characteristics. Firstly, taking SiO2 micro balls as template, the method of chemical templating was applied to realize the construction of micro holes on the surface of CLPS. The effect of diameters of SiO2 ball and volume of addition on the morphology was also studied. Secondly, laser micro treatment was used to construct triangular grooves in hundreds of microns on the surface of PMMA insulators and the influence of laser parameters on the morphology and structure of micro grooves was explored as well. Surface flashover test of the insulators with the aforementioned micro structure in different scales was conducted on a short-pulsed high voltage platform. The results show there was a big increase in surface hole-off voltage. Compared with the traditional surface roughness treatment by polishing, the construction of micro structure on the surface of polymer in this paper is controllable and the increase of flashover voltages is stable.
2018,
30: 035007.
doi: 10.11884/HPLPB201830.170400
Abstract:
Explosion-driven ferroelectric generator (EDFEG) has important applications due to its excellent properties of high energy density and small volume. The output of EDFEG is based on the depolarization of ferroelectric during shock wave compression. In the present work, a new experiment method was developed to investigate dynamic resistivity of PZT95/5 under shock wave compression, in which a pulse capacitor was used as an output load. A current leakage in shocked PZT95/5 was observed in the experiment at a shock stress of 3.5 GPa after the depolarization of all ferroelectrics. This current leakage was just related to the resistance of shocked PZT95/5 and the voltage applied. The resistivity of shocked PZT95/5 was calculated for a longer time than the shock transit time of the sample. The factors that reduced the efficiency of output charge were analyzed. Furthermore, new experiments were designed to eliminate the effect on depolarization of ferroelectrics from boundary rarefaction. Two shots of experiments with different capacitance loads produced different voltages across the PZT95/5 ferroelectrics stack. These experimental results show that efficiency of output charge was improved obviously, and that the higher the electric field was, the more the resistance of PZT95/5 ferroelectrics decreased. In conclusion, the resistivity of ferroelectric ceramics has little effect on the efficiency of output charge from ferroelectric ceramics.
Explosion-driven ferroelectric generator (EDFEG) has important applications due to its excellent properties of high energy density and small volume. The output of EDFEG is based on the depolarization of ferroelectric during shock wave compression. In the present work, a new experiment method was developed to investigate dynamic resistivity of PZT95/5 under shock wave compression, in which a pulse capacitor was used as an output load. A current leakage in shocked PZT95/5 was observed in the experiment at a shock stress of 3.5 GPa after the depolarization of all ferroelectrics. This current leakage was just related to the resistance of shocked PZT95/5 and the voltage applied. The resistivity of shocked PZT95/5 was calculated for a longer time than the shock transit time of the sample. The factors that reduced the efficiency of output charge were analyzed. Furthermore, new experiments were designed to eliminate the effect on depolarization of ferroelectrics from boundary rarefaction. Two shots of experiments with different capacitance loads produced different voltages across the PZT95/5 ferroelectrics stack. These experimental results show that efficiency of output charge was improved obviously, and that the higher the electric field was, the more the resistance of PZT95/5 ferroelectrics decreased. In conclusion, the resistivity of ferroelectric ceramics has little effect on the efficiency of output charge from ferroelectric ceramics.
2018,
30: 035101.
doi: 10.11884/HPLPB201830.170363
Abstract:
Thermionic cathode is widely used in accelerators, FELs and all kinds of vacuum electronics. For better performance and long stable running, low emittance with notable contribution from cathode is needed. Emittance of perfect thermal cathode only depends on radius and temperature. However, emission non-uniformity exists due to cathode surface profile, material distribution, temperature variation, crystal orientation, etc., which may cause intrinsic emittance growth, brightness decline, envelop size augment, device performance deterioration or even failure. To understand how intrinsic emittance is manipulated by temperature variation, a general intrinsic emittance model consisting of contributions from surface non-uniformity is developed based on general thermal emission. Numerical calculation for a cathode with radial temperature variation shows that RMS emittance declines about 15% when non-uniformity reaches 10%, which well conforms to FDTD-PIC simulation result.
Thermionic cathode is widely used in accelerators, FELs and all kinds of vacuum electronics. For better performance and long stable running, low emittance with notable contribution from cathode is needed. Emittance of perfect thermal cathode only depends on radius and temperature. However, emission non-uniformity exists due to cathode surface profile, material distribution, temperature variation, crystal orientation, etc., which may cause intrinsic emittance growth, brightness decline, envelop size augment, device performance deterioration or even failure. To understand how intrinsic emittance is manipulated by temperature variation, a general intrinsic emittance model consisting of contributions from surface non-uniformity is developed based on general thermal emission. Numerical calculation for a cathode with radial temperature variation shows that RMS emittance declines about 15% when non-uniformity reaches 10%, which well conforms to FDTD-PIC simulation result.
2018,
30: 035102.
doi: 10.11884/HPLPB201830.170372
Abstract:
A different on-line beam radius diagnosis structure based on the principle of diamagnetic loops was proposed. This structure can distinguish beam information from magnetic field at the same time, from which we can obtain beams' radius and currents. This paper focuses on the probe structure, equivalent circuit and experiment simulation platform. It analyzes the homogeneity of electric field information and puts forward the improvement measures, then compares the measurement results before and after improvement to illustrate the effectiveness of the structure. It shows that the consistency of the electric field signals increases from 94.08% to 99.60%. The simulated screwrods' radius errors are within 1 mm.
A different on-line beam radius diagnosis structure based on the principle of diamagnetic loops was proposed. This structure can distinguish beam information from magnetic field at the same time, from which we can obtain beams' radius and currents. This paper focuses on the probe structure, equivalent circuit and experiment simulation platform. It analyzes the homogeneity of electric field information and puts forward the improvement measures, then compares the measurement results before and after improvement to illustrate the effectiveness of the structure. It shows that the consistency of the electric field signals increases from 94.08% to 99.60%. The simulated screwrods' radius errors are within 1 mm.
2018,
30: 036001.
doi: 10.11884/HPLPB201830.170099
Abstract:
The subcritical energy blanket is an important component of the fusion-fission hybrid reactor. The mechanical characteristic analysis of the subcritical energy blanket is the key to ensure the normal operation of the whole reactor. In this paper, the preliminary mechanical analysis for the parts including the first wall and the support structure of the subcritical energy blanket is carried out. Accordingly, the maximal stress value, the stress distribution contours and the deformation distribution contours are obtained. The maximal stress of the support structure is located at the connection between the stiffener and the cylindrical pin and the value is 310.2 MPa. The maximal Tresca stress of the first wall is located at the corner of the U shaped flow channel and the value is 240.7 MPa. In the light of the strength and stiffness norms, the calculation results show that the structure of the subcritical energy blanket can satisfy the strength and stiffness requirements.
The subcritical energy blanket is an important component of the fusion-fission hybrid reactor. The mechanical characteristic analysis of the subcritical energy blanket is the key to ensure the normal operation of the whole reactor. In this paper, the preliminary mechanical analysis for the parts including the first wall and the support structure of the subcritical energy blanket is carried out. Accordingly, the maximal stress value, the stress distribution contours and the deformation distribution contours are obtained. The maximal stress of the support structure is located at the connection between the stiffener and the cylindrical pin and the value is 310.2 MPa. The maximal Tresca stress of the first wall is located at the corner of the U shaped flow channel and the value is 240.7 MPa. In the light of the strength and stiffness norms, the calculation results show that the structure of the subcritical energy blanket can satisfy the strength and stiffness requirements.
2018,
30: 036002.
doi: 10.11884/HPLPB201830.170293
Abstract:
In order to trace strictly the changes of nuclide density with burnup in a fission reactor, the independently developed codes by Chebyshev Rational Approximate Method (CRAM) and widely applied ORIGEN2 were adopted to solve large depletion chains to solve depletion equations based on Burnup Matrix Methods. The values are compared and analyzed with the aspects of computational accuracy, efficiency and step stability. The results show that CRAM can provide similar density solutions of important nuclides with a little slower speed and a much better step stability than those of ORIGEN2.
In order to trace strictly the changes of nuclide density with burnup in a fission reactor, the independently developed codes by Chebyshev Rational Approximate Method (CRAM) and widely applied ORIGEN2 were adopted to solve large depletion chains to solve depletion equations based on Burnup Matrix Methods. The values are compared and analyzed with the aspects of computational accuracy, efficiency and step stability. The results show that CRAM can provide similar density solutions of important nuclides with a little slower speed and a much better step stability than those of ORIGEN2.
2018,
30: 036003.
doi: 10.11884/HPLPB201830.170249
Abstract:
Deuteron ion transportation, fusion reaction sampling and neutron transportation simulation are included in the numerical calculation of accelerator driven neutron generator. As well known, the nuclear reaction cross section is much smaller than Coulomb cross section of charged particle transportation, and the mean free path of nuclear reaction is far longer than the depth of target, compared to deuteron ion transportation, the direct sampling efficiency of fusion reaction is almost zero. In this paper, a "forced" fusion arithmetic is introduced and embedded into MCNPX program. By the "forced" fusion arithmetic, fusion reaction must happen for every source deuteron ion. The position, energy and flight direction of deuteron ion that interact with tritium are sampled from all energy steps. The position, energy and flight direction of fusion source neutron are sampled according to that of deuteron ion. The deuteron ion and neutron coupling transportation can be calculated with the revised MCNPX.
Deuteron ion transportation, fusion reaction sampling and neutron transportation simulation are included in the numerical calculation of accelerator driven neutron generator. As well known, the nuclear reaction cross section is much smaller than Coulomb cross section of charged particle transportation, and the mean free path of nuclear reaction is far longer than the depth of target, compared to deuteron ion transportation, the direct sampling efficiency of fusion reaction is almost zero. In this paper, a "forced" fusion arithmetic is introduced and embedded into MCNPX program. By the "forced" fusion arithmetic, fusion reaction must happen for every source deuteron ion. The position, energy and flight direction of deuteron ion that interact with tritium are sampled from all energy steps. The position, energy and flight direction of fusion source neutron are sampled according to that of deuteron ion. The deuteron ion and neutron coupling transportation can be calculated with the revised MCNPX.
2018,
30: 036004.
doi: 10.11884/HPLPB201830.170228
Abstract:
Burnup calculation is one of the core contents in physical analysis of nuclear reactors. In Monte Carlo burnup calculation, power oscillation might occur periodically in certain geometrical dimension and certain step length, namely xenon oscillation. Xenon oscillations might result in a serious deviation from the actual situation. The fundamental reason for the xenon oscillation is that the neutron flux and xenon concentration in the regions of burn-up do not match. According to the mechanism of xenon oscillation, we classify xenon oscillations as physical xenon oscillations produced in short step conditions and numerical xenon oscillations produced in long time step conditions. Balanced xenon oscillation suppression method is forced to balance neutron flux with xenon concentration. In the RMC transport the article uses module a balanced xenon method for the calculation of iodine and xenon. In the RMC transport module, the equilibrium xenon method was used to continuously update the concentration of iodine and xenon. In the case of convergence, the occurrence of xenon oscillation is suppressed.
Burnup calculation is one of the core contents in physical analysis of nuclear reactors. In Monte Carlo burnup calculation, power oscillation might occur periodically in certain geometrical dimension and certain step length, namely xenon oscillation. Xenon oscillations might result in a serious deviation from the actual situation. The fundamental reason for the xenon oscillation is that the neutron flux and xenon concentration in the regions of burn-up do not match. According to the mechanism of xenon oscillation, we classify xenon oscillations as physical xenon oscillations produced in short step conditions and numerical xenon oscillations produced in long time step conditions. Balanced xenon oscillation suppression method is forced to balance neutron flux with xenon concentration. In the RMC transport the article uses module a balanced xenon method for the calculation of iodine and xenon. In the RMC transport module, the equilibrium xenon method was used to continuously update the concentration of iodine and xenon. In the case of convergence, the occurrence of xenon oscillation is suppressed.
2018,
30: 036005.
doi: 10.11884/HPLPB201830.170315
Abstract:
Single layer and laminated (double layer) CdZnTe detectors were prepared and their gamma spectrum characteristics were tested using 241Am@59.54 keV and 57Co@122 keV gamma ray sources. Compared with the single layer detector, for the higher energy gamma rays of 57Co@122 keV, the laminated CdZnTe detectors exhibited higher detection efficiency and light peak efficiency, and improved the Compton continuum, showing similar performance to that of a single-layered CdZnTe detector of the same thickness; but charge carriers collection efficiency became worse, and the peak position of the energy spectrum shifted to lower channel area; energy resolution was not improved. The experimental results show that it is feasible to prepare the laminated CdZnTe detector by stacking method, and it can be inferred that the preparation of stacked detectors of larger thickness will be beneficial for mid- and high-energy gamma ray spectrometry.
Single layer and laminated (double layer) CdZnTe detectors were prepared and their gamma spectrum characteristics were tested using 241Am@59.54 keV and 57Co@122 keV gamma ray sources. Compared with the single layer detector, for the higher energy gamma rays of 57Co@122 keV, the laminated CdZnTe detectors exhibited higher detection efficiency and light peak efficiency, and improved the Compton continuum, showing similar performance to that of a single-layered CdZnTe detector of the same thickness; but charge carriers collection efficiency became worse, and the peak position of the energy spectrum shifted to lower channel area; energy resolution was not improved. The experimental results show that it is feasible to prepare the laminated CdZnTe detector by stacking method, and it can be inferred that the preparation of stacked detectors of larger thickness will be beneficial for mid- and high-energy gamma ray spectrometry.
2018,
30: 039001.
doi: 10.11884/HPLPB201830.170366
Abstract:
Transient temperature field distribution is important for laser sintering graphene reinforced copper matrix composites. It is still difficult to measure the temperature field directly today. Numerical simulation was normally utilized to study the distribution of temperature field. Finite element models were employed to simulate the laser sintering of graphene and copper mixture coatings on 42CrMo base plate. The temperature distribution, the geometrical parameters of the melting pool, the width of metallurgical bonding were investigated. In order to verify simulation results, single-track experiments were performed with the same laser sintering parameters as used in simulation. It was proved that convection and radiation heat transfer, and the latent heat of phase transition play the major roles in the laser sintering process. Simulation results are consistent with experiment results under the same processing parameters. Based on simulation results, the temperature field distribution and the geometrical parameters of the melting pool can be predicted. Thus, according to these guidelines, the optimal laser sintering parameters can be decided.
Transient temperature field distribution is important for laser sintering graphene reinforced copper matrix composites. It is still difficult to measure the temperature field directly today. Numerical simulation was normally utilized to study the distribution of temperature field. Finite element models were employed to simulate the laser sintering of graphene and copper mixture coatings on 42CrMo base plate. The temperature distribution, the geometrical parameters of the melting pool, the width of metallurgical bonding were investigated. In order to verify simulation results, single-track experiments were performed with the same laser sintering parameters as used in simulation. It was proved that convection and radiation heat transfer, and the latent heat of phase transition play the major roles in the laser sintering process. Simulation results are consistent with experiment results under the same processing parameters. Based on simulation results, the temperature field distribution and the geometrical parameters of the melting pool can be predicted. Thus, according to these guidelines, the optimal laser sintering parameters can be decided.
2018,
30: 030000.
