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RSS2022 Vol. 34, No. 7
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2022,
34: 1-2.
2022,
34: 074001.
doi: 10.11884/HPLPB202234.210515
Abstract:
A magnetic field regulating ion source introduces strong pulsed magnetic field in the discharge plasma region of the ion source. On one hand, it forms Penning discharge effect to enhance the collision ionization efficiency of the atoms and gas molecules due to the magnetic field. On the other hand, the light ions are restrained along the axis by the strong magnetic field, but it can’t restrain the heavy metal ions. This phenomenon results in the heavy ions loss by colliding wall of the plasma expansion extraction channel, so it promotes the ratio of the light ions. Discharge structure of a magnetic field regulating ion source and strong pulsed solenoid magnetic field, as well as the optic structure of extraction beam are designed and depicted in this paper. Intensity of extraction ion beam and beam spot on the target measured by scintillator screen are analyzed in this paper. The results show that the strong axial magnetic field increases the proportion of light ion components as the result of filtering effect for plasma with mixed ion component.
A magnetic field regulating ion source introduces strong pulsed magnetic field in the discharge plasma region of the ion source. On one hand, it forms Penning discharge effect to enhance the collision ionization efficiency of the atoms and gas molecules due to the magnetic field. On the other hand, the light ions are restrained along the axis by the strong magnetic field, but it can’t restrain the heavy metal ions. This phenomenon results in the heavy ions loss by colliding wall of the plasma expansion extraction channel, so it promotes the ratio of the light ions. Discharge structure of a magnetic field regulating ion source and strong pulsed solenoid magnetic field, as well as the optic structure of extraction beam are designed and depicted in this paper. Intensity of extraction ion beam and beam spot on the target measured by scintillator screen are analyzed in this paper. The results show that the strong axial magnetic field increases the proportion of light ion components as the result of filtering effect for plasma with mixed ion component.
2022,
34: 074002.
doi: 10.11884/HPLPB202234.210458
Abstract:
Based on GEANT4 simulation, a feasible numerical simulation method is provided for the beam dynamics design of cyclotron. Through the electromagnetic field simulation software Opera, the corresponding electromagnetic field data are imported into GEANT4 for interpolation calculation. The equilibrium orbit, oscillation frequency and acceleration orbit of particles are calculated by using the electromagnetic field differential equation and differential equation solver of GEANT4. The results show that: for the transverse motion, GEANT4 calculation results and the traditional numerical method calculation results tend to be consistent; for the axial motion, due to the difference of the magnetic field interpolation method, there is a certain difference between the two. For the acceleration of the non-equilibrium particle, its energy changes around the equilibrium particle. For the beam loss, the simulation is closer to the actual experimental situation by limiting the particle motion time, accelerating the calculation efficiency by axial displacement and adding the determination of electrode collision.
Based on GEANT4 simulation, a feasible numerical simulation method is provided for the beam dynamics design of cyclotron. Through the electromagnetic field simulation software Opera, the corresponding electromagnetic field data are imported into GEANT4 for interpolation calculation. The equilibrium orbit, oscillation frequency and acceleration orbit of particles are calculated by using the electromagnetic field differential equation and differential equation solver of GEANT4. The results show that: for the transverse motion, GEANT4 calculation results and the traditional numerical method calculation results tend to be consistent; for the axial motion, due to the difference of the magnetic field interpolation method, there is a certain difference between the two. For the acceleration of the non-equilibrium particle, its energy changes around the equilibrium particle. For the beam loss, the simulation is closer to the actual experimental situation by limiting the particle motion time, accelerating the calculation efficiency by axial displacement and adding the determination of electrode collision.
2022,
34: 074003.
doi: 10.11884/HPLPB202234.210513
Abstract:
Based on the principle of Induction Synchrotron (IS), the high-repetition pulse induction acceleration module can replace the radio frequency acceleration cavity in circular accelerators, thereby obtaining more application prospects. In this paper, a set of MHz continuous repetition bipolar pulse induction acceleration module suitable for IS is developed, and its circuit design and experimental results are introduced. Compared with the induction acceleration module of KEK, which is the only IS acceleration module in use at present, this induction module adopts different circuit structures to make the longitudinal dimension of the induction cell be reduced by 5 times at the same pulse flat voltage drop, which can effectively improve the adjustment ability of the accelerating voltage in a limited space, reduce the power consumption and the cost of system cooling, and improve the reliability of continuous operation of the pulse power system.
Based on the principle of Induction Synchrotron (IS), the high-repetition pulse induction acceleration module can replace the radio frequency acceleration cavity in circular accelerators, thereby obtaining more application prospects. In this paper, a set of MHz continuous repetition bipolar pulse induction acceleration module suitable for IS is developed, and its circuit design and experimental results are introduced. Compared with the induction acceleration module of KEK, which is the only IS acceleration module in use at present, this induction module adopts different circuit structures to make the longitudinal dimension of the induction cell be reduced by 5 times at the same pulse flat voltage drop, which can effectively improve the adjustment ability of the accelerating voltage in a limited space, reduce the power consumption and the cost of system cooling, and improve the reliability of continuous operation of the pulse power system.
2022,
34: 075001.
doi: 10.11884/HPLPB202234.210483
Abstract:
The pulse forming network (PFN)-Marx generator can realize both integration of pulse modulation and pulse voltage accumulation, exhibiting a the natural “gene” of compactness. In recent years, the pulsed energy storage technology has been developing rapidly, which makes it a reality to use PFN-Marx generators to drive various loads directly. The PFN-Marx generator has gradually become a worldwide research focus. The research progress of high-power compact PFN-Marx generators are systematically introduced in this paper. In summary, judging from the development over time, PFN-Marx generators adopt high-energy-density components and thus improve the energy density level themselves, which makes the generator more and more compact. In the pursuit of compactness, the effect of optimal design of PFN-Marx generator spatial structure is better than optimal design of PFN network topology parameters. The waveform optimization method of the PFN-Marx generator has obvious benefits, which can effectively reduce the negative impact of stray parameters strongly coupling between stages caused by small size of generator. In the meanwhile, this paper discusses the development trend of PFN-Marx generator.
2022,
34: 075002.
doi: 10.11884/HPLPB202234.210433
Abstract:
Based on the Lagrangian description, a single temperature magneto-hydrodynamics model of underwater electrical wire explosion is established, and a high-order mixed finite element method is used to solve this model. For the Lagrangian compressible fluid equations, velocity is discretized using the continuous high-order basis function in the H1 space, and internal energy is discretized using a L2 piecewise discontinuous high-order basis function for the precise capture of the material interface. A tensor artificial viscosity is introduced to suppress the numerical oscillation. Only the azimuthal magnetic flux density is contained in the magnetic diffusion equation, which is simplified to a scalar equation, and is discretized using continuous basis function. Joule heating and Lorenz force are introduced to couple hydrodynamics equations with magnetic field. Numerical results show that the magneto-diffusion solver can solve a multi-material magnetic diffusion problem, and the hydrodynamics solver can track the material interface and shock wave. Underwater electrical wire explosion is simulated based on the magneto-hydrodynamics solver coupled with RLC circuit, including phase transition, shock wave and different discharge modes.
Based on the Lagrangian description, a single temperature magneto-hydrodynamics model of underwater electrical wire explosion is established, and a high-order mixed finite element method is used to solve this model. For the Lagrangian compressible fluid equations, velocity is discretized using the continuous high-order basis function in the H1 space, and internal energy is discretized using a L2 piecewise discontinuous high-order basis function for the precise capture of the material interface. A tensor artificial viscosity is introduced to suppress the numerical oscillation. Only the azimuthal magnetic flux density is contained in the magnetic diffusion equation, which is simplified to a scalar equation, and is discretized using continuous basis function. Joule heating and Lorenz force are introduced to couple hydrodynamics equations with magnetic field. Numerical results show that the magneto-diffusion solver can solve a multi-material magnetic diffusion problem, and the hydrodynamics solver can track the material interface and shock wave. Underwater electrical wire explosion is simulated based on the magneto-hydrodynamics solver coupled with RLC circuit, including phase transition, shock wave and different discharge modes.
2022,
34: 075003.
doi: 10.11884/HPLPB202234.220002
Abstract:
The thermal erosion of arc is the main cause of electrode loss in the spark gap switch. The graphite electrode will evaporate and constantly undergo mass loss under the effect of the arc, which changes the gas environment in switch and the electrode distance, resulting in decreased reliability of the switch operation. To obtain erosion characteristics of graphite electrode under high-current pulse arc, the energy coupling model between the switching arc and graphite electrode is established based on the switching arc transient diffusion characteristics and graphite material parameters, and the heat transfer characteristics of plasma-solid region is obtained. Considering the phase change characteristics of graphite electrode, the heating range and critical phase change point of graphite electrode under transient thermal effect is calculated, and the phase change mechanism of graphite electrode under transient thermal shock of the arc is studied. The study results indicate that the heat flux of the arc-electrode interface is mainly concentrated in the center of the arc contact surface, and the energy density of arc deposition can reach up to 109 W/m2. Graphite is basically in a heating state at the beginning of the current rise, under the effect of energy accumulation, the graphite transforms into sublimation state. The heat transfer intensity decreases sharply with the radius decreasing, and the evaporation radius is slightly smaller than the arc radius. The ablation morphology and mass loss of graphite electrode under five different switching conditions were recorded through experiments. The experimental results show that the electrode mass loss is linearly related to the energy deposited on the electrode surface by the arc, approximately 0.015 mg/J. This paper studies the influence of arc key parameters on electrode mass-loss rate, and provides a theoretical and experimental basis for slowing electrode loss.
The thermal erosion of arc is the main cause of electrode loss in the spark gap switch. The graphite electrode will evaporate and constantly undergo mass loss under the effect of the arc, which changes the gas environment in switch and the electrode distance, resulting in decreased reliability of the switch operation. To obtain erosion characteristics of graphite electrode under high-current pulse arc, the energy coupling model between the switching arc and graphite electrode is established based on the switching arc transient diffusion characteristics and graphite material parameters, and the heat transfer characteristics of plasma-solid region is obtained. Considering the phase change characteristics of graphite electrode, the heating range and critical phase change point of graphite electrode under transient thermal effect is calculated, and the phase change mechanism of graphite electrode under transient thermal shock of the arc is studied. The study results indicate that the heat flux of the arc-electrode interface is mainly concentrated in the center of the arc contact surface, and the energy density of arc deposition can reach up to 109 W/m2. Graphite is basically in a heating state at the beginning of the current rise, under the effect of energy accumulation, the graphite transforms into sublimation state. The heat transfer intensity decreases sharply with the radius decreasing, and the evaporation radius is slightly smaller than the arc radius. The ablation morphology and mass loss of graphite electrode under five different switching conditions were recorded through experiments. The experimental results show that the electrode mass loss is linearly related to the energy deposited on the electrode surface by the arc, approximately 0.015 mg/J. This paper studies the influence of arc key parameters on electrode mass-loss rate, and provides a theoretical and experimental basis for slowing electrode loss.
2022,
34: 075004.
doi: 10.11884/HPLPB202234.210538
Abstract:
There are significant differences between the calculation results and experimental results by using J. C. Martin empirical formula to estimate the breakdown electric field for hundreds of kV/cm electric field and nanosecond pulse. To improve the design of pulsed gas switch and adjustment of working conditions, the relationships between the breakdown electric field and time delay and the experimental parameters based on the classical empirical formula is established. The empirical formula of breakdown electric field and time delay for SF6 gas switch under nanosecond pulse and hundreds of kV/cm electric field is presented. It is indicated that the slope of pulse will affect the breakdown characteristics of nanosecond pulse in high electric field and the breakdown electric field is correlated with the breakdown time delay. The differences between the calculation results and experimental results are caused by the experimental conditions. The fitting expression of empirical formula can give more guidance for the design of output switch in the electromagnetic pulse simulator.
There are significant differences between the calculation results and experimental results by using J. C. Martin empirical formula to estimate the breakdown electric field for hundreds of kV/cm electric field and nanosecond pulse. To improve the design of pulsed gas switch and adjustment of working conditions, the relationships between the breakdown electric field and time delay and the experimental parameters based on the classical empirical formula is established. The empirical formula of breakdown electric field and time delay for SF6 gas switch under nanosecond pulse and hundreds of kV/cm electric field is presented. It is indicated that the slope of pulse will affect the breakdown characteristics of nanosecond pulse in high electric field and the breakdown electric field is correlated with the breakdown time delay. The differences between the calculation results and experimental results are caused by the experimental conditions. The fitting expression of empirical formula can give more guidance for the design of output switch in the electromagnetic pulse simulator.
2022,
34: 075005.
doi: 10.11884/HPLPB202234.210435
Abstract:
The voltage droop of high-voltage pulses is required to be as low as possible in many industrial applications including particle accelerators. The commonly used method of reducing the droop is to increase the capacitance of the energy storage capacitors at the price of lower energy efficiency, bigger size, and higher power of the system. Another method is to insert some special stages to compensate for the voltage droop. When a resonant inductor and a switch in series are connected in parallel with the capacitor in a common stage in solid-state Marx generators (SSMGs), a compensation stage is obtained. In this paper, four compensation stages based on resonant circuit have been inserted into a 16-stage SSMG to compensate for the voltage droop with different loads and different pulse widths. The nearly linear part of the sinusoidal voltage is precisely added to the load during discharge as compensation and the rectangular pulsed voltage with little droop can be realized. Different numbers of compensation stages can compensate the droop to different levels, which means the compensation effect is also adjustable. Moreover, these compensation stages can also operate as common stages in Marx generators as long as the resonant circuits are open. Since the capacitors in resonant compensation stages are also charged in parallel with capacitors in common stages, no auxiliary power supply is required. Experimental results show that the droop of 2.5 kV and 10.5 kV pulses can be ideally compensated over 400 Ω and 5 kΩ resistive loads, respectively. The pulse widths should be shorter than the length of the nearly linear part of sinusoidal voltage for better compensation effect.
The voltage droop of high-voltage pulses is required to be as low as possible in many industrial applications including particle accelerators. The commonly used method of reducing the droop is to increase the capacitance of the energy storage capacitors at the price of lower energy efficiency, bigger size, and higher power of the system. Another method is to insert some special stages to compensate for the voltage droop. When a resonant inductor and a switch in series are connected in parallel with the capacitor in a common stage in solid-state Marx generators (SSMGs), a compensation stage is obtained. In this paper, four compensation stages based on resonant circuit have been inserted into a 16-stage SSMG to compensate for the voltage droop with different loads and different pulse widths. The nearly linear part of the sinusoidal voltage is precisely added to the load during discharge as compensation and the rectangular pulsed voltage with little droop can be realized. Different numbers of compensation stages can compensate the droop to different levels, which means the compensation effect is also adjustable. Moreover, these compensation stages can also operate as common stages in Marx generators as long as the resonant circuits are open. Since the capacitors in resonant compensation stages are also charged in parallel with capacitors in common stages, no auxiliary power supply is required. Experimental results show that the droop of 2.5 kV and 10.5 kV pulses can be ideally compensated over 400 Ω and 5 kΩ resistive loads, respectively. The pulse widths should be shorter than the length of the nearly linear part of sinusoidal voltage for better compensation effect.
2022,
34: 075006.
doi: 10.11884/HPLPB202234.210569
Abstract:
Agile high repetition rate discharge technology has important applications in improving plasma uniformity. SiC photoconductive semiconductor switch (PCSS) has the advantages of high breakdown field strength, high saturated carrier rate, high radiation resistance, high thermal conductivity and high temperature stability. It is an important solid-state electronic device to produce high repetition rate, high power and short width pulse. Operation characteristics of the MHz repetition frequency sub-nanosecond pulse generator based on vanadium-compensated semi-insulating (VCSI) 4H-SiC PCSS under high electric field are presented in this paper. 1 MHz, 1030 nm laser cluster driver with tunable optical pulse width is used for VCSI 4H-SiC PCSS response test. The 0.8 mm thick 4H-SiC PCSS can work with electric fields up to 200 kV/cm and the electrical power capacity up to 176 kW without failure for long time. The minimum photocurrent pulse width is about 365 ps and the jitter is less than 100 ps.
Agile high repetition rate discharge technology has important applications in improving plasma uniformity. SiC photoconductive semiconductor switch (PCSS) has the advantages of high breakdown field strength, high saturated carrier rate, high radiation resistance, high thermal conductivity and high temperature stability. It is an important solid-state electronic device to produce high repetition rate, high power and short width pulse. Operation characteristics of the MHz repetition frequency sub-nanosecond pulse generator based on vanadium-compensated semi-insulating (VCSI) 4H-SiC PCSS under high electric field are presented in this paper. 1 MHz, 1030 nm laser cluster driver with tunable optical pulse width is used for VCSI 4H-SiC PCSS response test. The 0.8 mm thick 4H-SiC PCSS can work with electric fields up to 200 kV/cm and the electrical power capacity up to 176 kW without failure for long time. The minimum photocurrent pulse width is about 365 ps and the jitter is less than 100 ps.
2022,
34: 075007.
doi: 10.11884/HPLPB202234.210519
Abstract:
To measure the transition section and outlet current of LTD single branch verification device, a B-dot current probe is designed and calibrated. The radial transmission line is used to calibrate the current probe offline, and the corresponding verification experiments are carried out to verify the effectiveness of the calibration. The experimental results show that the sensitivity deviation of the probe is about 1% due to the errors of probe installation depth and angle. When the distance between the cathode and the anode is greater than the diameter of the probe hole, the B-dot calibration result is independent of the distance. For the coaxial transmission line with large diameter involved in the device, the simulation and calibration results of radial transmission line are effective. According to the experimental results of the LTD single channel verification device, the difference of anode current from the four transition sections to the outlet is very small, while the cathode current decreases gradually.
To measure the transition section and outlet current of LTD single branch verification device, a B-dot current probe is designed and calibrated. The radial transmission line is used to calibrate the current probe offline, and the corresponding verification experiments are carried out to verify the effectiveness of the calibration. The experimental results show that the sensitivity deviation of the probe is about 1% due to the errors of probe installation depth and angle. When the distance between the cathode and the anode is greater than the diameter of the probe hole, the B-dot calibration result is independent of the distance. For the coaxial transmission line with large diameter involved in the device, the simulation and calibration results of radial transmission line are effective. According to the experimental results of the LTD single channel verification device, the difference of anode current from the four transition sections to the outlet is very small, while the cathode current decreases gradually.
2022,
34: 075008.
doi: 10.11884/HPLPB202234.210484
Abstract:
With the development of pulse power technology to high repetition rate and long life, it is necessary to test the stability of energy storage and switching components under transient intense field. This paper presents a solid-state platform for transient intense field test at several tens kilovolts with charging and discharging time in microsecond region. The platform consists of a high voltage power supply, a primary unit, a core-type pulse transformer, a magnetic compression network, core reset power supplies and a test cavity, hence it has an integrated structure and is easy to use. A circuit model is presented to optimize the electrical parameters of the platform. Then, the test platform is built up and experimented. A group of serial connected thyristors are used as control switch in the primary unit for pulse charging and high power magnetic switch is used for discharging in the test cavity. Preliminary results are obtained with ceramic capacitors of 40 nF under test, of which the test voltage is 50 kV, the pulse width is 1 μs with repetitive rate of 10 Hz and operation time of 85 min (51 000 pulses), indicating the platform is stable and reliable. The research results could setup good foundation for further investigation into related test.
With the development of pulse power technology to high repetition rate and long life, it is necessary to test the stability of energy storage and switching components under transient intense field. This paper presents a solid-state platform for transient intense field test at several tens kilovolts with charging and discharging time in microsecond region. The platform consists of a high voltage power supply, a primary unit, a core-type pulse transformer, a magnetic compression network, core reset power supplies and a test cavity, hence it has an integrated structure and is easy to use. A circuit model is presented to optimize the electrical parameters of the platform. Then, the test platform is built up and experimented. A group of serial connected thyristors are used as control switch in the primary unit for pulse charging and high power magnetic switch is used for discharging in the test cavity. Preliminary results are obtained with ceramic capacitors of 40 nF under test, of which the test voltage is 50 kV, the pulse width is 1 μs with repetitive rate of 10 Hz and operation time of 85 min (51 000 pulses), indicating the platform is stable and reliable. The research results could setup good foundation for further investigation into related test.
2022,
34: 075009.
doi: 10.11884/HPLPB202234.210486
Abstract:
An electromagnetic loading system is designed to be applied to a separate Hopkinson rod experimental device. It can overcome the shortcomings of traditional pneumatic drive and achieve the purpose of accurately controlling the incident stress. The low-voltage loading method is determined through the investigation of electromagnetic loading technology, then the system equivalent RLC loop is constructed, and the functional relationship between the loop parameters and the incident stress wave is derived. Combining theoretical calculation results, using finite element software for coupling field simulation, the simulation shows that the number of turns of the active coil has a great impact on the pulse width and amplitude of the incident stress. At the same time, to ensure the utilization efficiency of electromagnetic energy, it is necessary to ensure that the thickness of the inductive coil is greater than the depth of magnetic penetration, and determine the parameters of the electromagnetic loading system according to the experimental requirements. An experimental platform was built to carry out the Hopkinson bar impact experiment, and the correctness of the theoretical calculation and software simulation was verified through the measurement of the incident stress.
An electromagnetic loading system is designed to be applied to a separate Hopkinson rod experimental device. It can overcome the shortcomings of traditional pneumatic drive and achieve the purpose of accurately controlling the incident stress. The low-voltage loading method is determined through the investigation of electromagnetic loading technology, then the system equivalent RLC loop is constructed, and the functional relationship between the loop parameters and the incident stress wave is derived. Combining theoretical calculation results, using finite element software for coupling field simulation, the simulation shows that the number of turns of the active coil has a great impact on the pulse width and amplitude of the incident stress. At the same time, to ensure the utilization efficiency of electromagnetic energy, it is necessary to ensure that the thickness of the inductive coil is greater than the depth of magnetic penetration, and determine the parameters of the electromagnetic loading system according to the experimental requirements. An experimental platform was built to carry out the Hopkinson bar impact experiment, and the correctness of the theoretical calculation and software simulation was verified through the measurement of the incident stress.
2022,
34: 075010.
doi: 10.11884/HPLPB202234.210459
Abstract:
Influence factors of the breakdown delay jitter of a self-triggered UV-illuminated switch are studied. It indicates that the switch electric field at the injection time of pre-ionization is the decisive factor of the time jitter when the capacitor discharge stage of the trigger gap works. Increasing the operating coefficient and using electrode material with lower working function cannot remarkably reduce the time jitter when the switch breaks down near the peak time. The improvement method is to reduce the value of parallel resistors, which can extend the duration of sufficient arcing of the trigger gap and eliminate the influence of pre-ionization injection time and its jitter. By adapting this method, the time jitter is less than 1.3 ns or 2.8 ns under a pulse rise time of 100 ns or 180 ns when the operating voltage is 300−800 kV.
Influence factors of the breakdown delay jitter of a self-triggered UV-illuminated switch are studied. It indicates that the switch electric field at the injection time of pre-ionization is the decisive factor of the time jitter when the capacitor discharge stage of the trigger gap works. Increasing the operating coefficient and using electrode material with lower working function cannot remarkably reduce the time jitter when the switch breaks down near the peak time. The improvement method is to reduce the value of parallel resistors, which can extend the duration of sufficient arcing of the trigger gap and eliminate the influence of pre-ionization injection time and its jitter. By adapting this method, the time jitter is less than 1.3 ns or 2.8 ns under a pulse rise time of 100 ns or 180 ns when the operating voltage is 300−800 kV.
2022,
34: 075011.
doi: 10.11884/HPLPB202234.210457
Abstract:
A dynamic model for high voltage Child-sheath of mixed multi-component plasmas is built up, and the characteristics of high voltage Child-sheath of mixed D+ and Ti2+ plasmas is numerically studied. The theoretical and numerical results demonstrate as follows. The depth of Child-sheath will increase and electric field intensity on target will decrease by increasing the ratio of D+ to Ti2+, decreasing the sheath-entering velocity of D+ or Ti2+, and decreasing the density of mixed plasmas. Through the above ways, ions could achieve convergent transportation and breakdown risk on target could also be reduced. As the increase of accelerating voltage, the range of stable ion-extraction operating region will firstly increase and then decrease. By increasing the ratio of D+ to Ti2+ and decreasing the sheath-entering velocity of D+ or Ti2+, the range of stable ion-extraction operating region could be notably increased.
A dynamic model for high voltage Child-sheath of mixed multi-component plasmas is built up, and the characteristics of high voltage Child-sheath of mixed D+ and Ti2+ plasmas is numerically studied. The theoretical and numerical results demonstrate as follows. The depth of Child-sheath will increase and electric field intensity on target will decrease by increasing the ratio of D+ to Ti2+, decreasing the sheath-entering velocity of D+ or Ti2+, and decreasing the density of mixed plasmas. Through the above ways, ions could achieve convergent transportation and breakdown risk on target could also be reduced. As the increase of accelerating voltage, the range of stable ion-extraction operating region will firstly increase and then decrease. By increasing the ratio of D+ to Ti2+ and decreasing the sheath-entering velocity of D+ or Ti2+, the range of stable ion-extraction operating region could be notably increased.
2022,
34: 075012.
doi: 10.11884/HPLPB202234.210442
Abstract:
The thermal-mechanical damage induced by high current pulsed electron beam striking on anode targets is a key factor affecting the stability and lifetime of high current diodes. This problem is mostly addressed by replacing the anode target and cleaning the cavity and cathode to ensure the normal operation of the diode. In this paper, a diode anode target temperature and thermal deformation simulation method is established using the energy deposition profile of the electron beam in the target as a bridge. The method can be used to determine the temperature distribution and thermal deformation of the target under various diode operating conditions, provide basic data for the investigation of thermal-mechanical damage to the target, and provide technical support for diode configuration design and life enhancement. With application of this method to the “Qiangguang-I” accelerator, the simulation results show that the surface temperature of the target can reach 5500−6000 ℃ and the thermal deformation can reach about 4.5 mm when the ion density is more than 1014 cm−3 (tight-pinched). The temperature is about 4500 ℃ and the thermal deformation is 2.8−3.2 mm when there is no ion flow (weak-pinched).
The thermal-mechanical damage induced by high current pulsed electron beam striking on anode targets is a key factor affecting the stability and lifetime of high current diodes. This problem is mostly addressed by replacing the anode target and cleaning the cavity and cathode to ensure the normal operation of the diode. In this paper, a diode anode target temperature and thermal deformation simulation method is established using the energy deposition profile of the electron beam in the target as a bridge. The method can be used to determine the temperature distribution and thermal deformation of the target under various diode operating conditions, provide basic data for the investigation of thermal-mechanical damage to the target, and provide technical support for diode configuration design and life enhancement. With application of this method to the “Qiangguang-I” accelerator, the simulation results show that the surface temperature of the target can reach 5500−6000 ℃ and the thermal deformation can reach about 4.5 mm when the ion density is more than 1014 cm−3 (tight-pinched). The temperature is about 4500 ℃ and the thermal deformation is 2.8−3.2 mm when there is no ion flow (weak-pinched).
2022,
34: 075013.
doi: 10.11884/HPLPB202234.210468
Abstract:
Aiming at the problem that the stability of the flat-top pulsed magnetic field generated by open-loop control of capacitor discharge is difficult to meet the requirements of nuclear magnetic resonance, this paper proposes a closed-loop continuous micro-control scheme for the flat-top magnetic field. A compensation coil is placed in the pulse magnet, which is powered by batteries, adopts the strategy of feedforward control and feedback control, uses the IGBT active region to linearly regulate the magnetic field of the compensation coil, compensates for the fluctuation of the background magnetic field, and forms a highly stable flat-top magnetic field. To this end, this paper designs a driving circuit for IGBTs working in the active region, and builds a prototype for experiments. The results show that the method proposed can increase the magnetic field stability to 50×10−6, which verifies the feasibility of the scheme.
Aiming at the problem that the stability of the flat-top pulsed magnetic field generated by open-loop control of capacitor discharge is difficult to meet the requirements of nuclear magnetic resonance, this paper proposes a closed-loop continuous micro-control scheme for the flat-top magnetic field. A compensation coil is placed in the pulse magnet, which is powered by batteries, adopts the strategy of feedforward control and feedback control, uses the IGBT active region to linearly regulate the magnetic field of the compensation coil, compensates for the fluctuation of the background magnetic field, and forms a highly stable flat-top magnetic field. To this end, this paper designs a driving circuit for IGBTs working in the active region, and builds a prototype for experiments. The results show that the method proposed can increase the magnetic field stability to 50×10−6, which verifies the feasibility of the scheme.
2022,
34: 075014.
doi: 10.11884/HPLPB202234.220007
Abstract:
Using electrical explosion of wires to produce nanopowders has attracted wide interest because of the considerable overheat of the metal and the non-equilibrium process and it is considered to be an effective method to prepare expensive or difficult materials and powders with new properties. An experimental study on exploding Ti wire in atmosphere under a microsecond time-scale pulsed current was conducted. The influences of different collection methods on preparing Ti nanoparticles via electrical explosion were investigated. The reasons for different products characteristics were studied combined with the methods of electrical, radiant, self-emission images and the morphology characterization. Experimental results indicate that Ti explosion belongs to periodical discharge mode, the products channel expands to 1.7 cm before the end of discharge (about 40 μs), and then there develops cuspate protrusions with a speed of 55 m/s. To investigate the formation characteristics of nanoparticles under different states of exploded products, three methods were used for collecting products, namely: ① Placing a silicon wafer at 1.5 cm in radial direction; ② Placing a silicon wafer on the exit of the cavity; ③ Collecting by directional spraying on one electrode of the wire. The characterization results of products morphology show that products have prominent discrepancies under different collection methods. Products of the former two methods mix with ambient medium and then sedimentate to the silicon, producing dispersive and catenulate nanoparticles and dense and stacked clusters respectively. For the last method, the exploded products possess relatively greater density and directed velocity (toward silicon wafer), presenting two forms as powders and sintered chunks (near the wire axis).
Using electrical explosion of wires to produce nanopowders has attracted wide interest because of the considerable overheat of the metal and the non-equilibrium process and it is considered to be an effective method to prepare expensive or difficult materials and powders with new properties. An experimental study on exploding Ti wire in atmosphere under a microsecond time-scale pulsed current was conducted. The influences of different collection methods on preparing Ti nanoparticles via electrical explosion were investigated. The reasons for different products characteristics were studied combined with the methods of electrical, radiant, self-emission images and the morphology characterization. Experimental results indicate that Ti explosion belongs to periodical discharge mode, the products channel expands to 1.7 cm before the end of discharge (about 40 μs), and then there develops cuspate protrusions with a speed of 55 m/s. To investigate the formation characteristics of nanoparticles under different states of exploded products, three methods were used for collecting products, namely: ① Placing a silicon wafer at 1.5 cm in radial direction; ② Placing a silicon wafer on the exit of the cavity; ③ Collecting by directional spraying on one electrode of the wire. The characterization results of products morphology show that products have prominent discrepancies under different collection methods. Products of the former two methods mix with ambient medium and then sedimentate to the silicon, producing dispersive and catenulate nanoparticles and dense and stacked clusters respectively. For the last method, the exploded products possess relatively greater density and directed velocity (toward silicon wafer), presenting two forms as powders and sintered chunks (near the wire axis).
2022,
34: 075015.
doi: 10.11884/HPLPB202234.220008
Abstract:
Underwater electrical wire explosion igniting energetic materials can generate stronger shock waves (SW), which is also considered as an important direction for the development of controllable shock wave technology. Compared with other energetic materials, the liquid-phase aluminum powder suspension has more advantages in terms of safety and uniformity that is easy to obtain and has a high reaction heat. It has great potential for civil applications. This paper reports an experimental study on the detonation of aluminum powder suspension by underwater electrical wire explosion. The aluminum powder suspension was confined in a plexiglass tube and passed through a 200 μm metal copper wire in the coaxial direction. After being driven by a high-voltage pulse source, it rapidly phased transformation and explosion, providing reaction conditions for aluminum powder. By comparing the discharge parameters and SW pressure signals of different quality aluminum powder suspensions, the electric explosion-driven aluminum powder discharge characteristics and the law of SW enhancement effect are obtained. The experiment shows that SW has two obvious peaks, which correspond to the evaporation SW (the first peak) and the breakup of the tube (the second peak). The effect of aluminum powder deflagration on the second SW is very significant. In the 300 mg aluminum powder suspension environment, the peak value of the second SW reaches 2.77 MPa, increased by 2.25 times compared to an optimal underwater electrical wire explosion, and the impulse of the SW is increased by about 50%. This paper also compares the SW signals in the suspension environment of 200 mg aluminum powder under different energy storage. It is found that with the increase of energy storage, both of two peaks of SW increase, reaching 3.17 MPa and 1.91 MPa respectively at 600 J. The impulse of SW also increases with the increase of energy storage. The impulse at 600 J energy storage is 41.12 Pa·s, which is twice as high as that at 300 J energy storage.
Underwater electrical wire explosion igniting energetic materials can generate stronger shock waves (SW), which is also considered as an important direction for the development of controllable shock wave technology. Compared with other energetic materials, the liquid-phase aluminum powder suspension has more advantages in terms of safety and uniformity that is easy to obtain and has a high reaction heat. It has great potential for civil applications. This paper reports an experimental study on the detonation of aluminum powder suspension by underwater electrical wire explosion. The aluminum powder suspension was confined in a plexiglass tube and passed through a 200 μm metal copper wire in the coaxial direction. After being driven by a high-voltage pulse source, it rapidly phased transformation and explosion, providing reaction conditions for aluminum powder. By comparing the discharge parameters and SW pressure signals of different quality aluminum powder suspensions, the electric explosion-driven aluminum powder discharge characteristics and the law of SW enhancement effect are obtained. The experiment shows that SW has two obvious peaks, which correspond to the evaporation SW (the first peak) and the breakup of the tube (the second peak). The effect of aluminum powder deflagration on the second SW is very significant. In the 300 mg aluminum powder suspension environment, the peak value of the second SW reaches 2.77 MPa, increased by 2.25 times compared to an optimal underwater electrical wire explosion, and the impulse of the SW is increased by about 50%. This paper also compares the SW signals in the suspension environment of 200 mg aluminum powder under different energy storage. It is found that with the increase of energy storage, both of two peaks of SW increase, reaching 3.17 MPa and 1.91 MPa respectively at 600 J. The impulse of SW also increases with the increase of energy storage. The impulse at 600 J energy storage is 41.12 Pa·s, which is twice as high as that at 300 J energy storage.
2022,
34: 075016.
doi: 10.11884/HPLPB202234.210534
Abstract:
Development trends of pulsed power technology is high power density, compactness and high reliabilities. Liquid dielectric, because of its high insulation, easy flow, fast recovery and good heat dispersion, is widely used in the pulse power source based on liquid pulse forming line as energy storage medium. Research focuses are put on the key techniques of the ARC series of pulse power sources. Studies are carried out on pulsed breakdown characteristics, system development and its application. Firstly, a pulse formation line is proposed based on high-energy-density-storage liquid dielectric and slow wave structure. By using the method of electromagnetic field uniformity and insulation technology to solve the high-voltage insulation problems, the compact pulse power sources ARC-01/02 are developed. They can output 1−2 GW power, 5−30 ns duration, 1−100 Hz rep-rate, and their maximum compact level is increased by 2 times that of the international advanced similar devices. Through the research on the pulsed insulation characteristics of liquid dielectric in the microsecond regime, the database is established by statistical analysis method. And then, by using the ultrafast camera optical diagnosis method, based on the images of generation, propagation, cut-off for shock wave, sub-microscopic fracture surface, a liquid dielectric breakdown model is established, combined with amorphous energy band and Griffith tension theory. Finally, the pulsed power source is applied to drive wide band/narrow band microwave source and test the stability and life of carbon fiber cathode.
Development trends of pulsed power technology is high power density, compactness and high reliabilities. Liquid dielectric, because of its high insulation, easy flow, fast recovery and good heat dispersion, is widely used in the pulse power source based on liquid pulse forming line as energy storage medium. Research focuses are put on the key techniques of the ARC series of pulse power sources. Studies are carried out on pulsed breakdown characteristics, system development and its application. Firstly, a pulse formation line is proposed based on high-energy-density-storage liquid dielectric and slow wave structure. By using the method of electromagnetic field uniformity and insulation technology to solve the high-voltage insulation problems, the compact pulse power sources ARC-01/02 are developed. They can output 1−2 GW power, 5−30 ns duration, 1−100 Hz rep-rate, and their maximum compact level is increased by 2 times that of the international advanced similar devices. Through the research on the pulsed insulation characteristics of liquid dielectric in the microsecond regime, the database is established by statistical analysis method. And then, by using the ultrafast camera optical diagnosis method, based on the images of generation, propagation, cut-off for shock wave, sub-microscopic fracture surface, a liquid dielectric breakdown model is established, combined with amorphous energy band and Griffith tension theory. Finally, the pulsed power source is applied to drive wide band/narrow band microwave source and test the stability and life of carbon fiber cathode.
2022,
34: 075017.
doi: 10.11884/HPLPB202234.210471
Abstract:
To develop a light and small high voltage pulsed power source, an innovative fast pulse technology based on an explosive driven ferroelectric generator (EDFEG) is investigated. An EDFEG is used as the primary power supply, inductive energy storage technology and an electrical exploding opening switch (EEOS) are used to generate a high-voltage fast pulse. On the basis of full-circuit simulation model of EDFEGs and the material properties of ferroelectric ceramics, the circuit simulation research on this fast pulse technology is carried out. The simulation results reveal the influence of circuit parameters on high voltage pulse generation. The research shows that the high-voltage mode of EDFEGs is more suitable for generating high-voltage fast pulse combined with EEOS technology. As a result, the principle of this technology is verified in experiments. In the experiment, the output current of an EDFEG was about 360 A and its pulse width was about 3.8 μs. The charging voltage of a 17.5 nF capacitor was 75 kV. After the capacitor was discharged, a pulse current with a peak value greater than 12 kA was generated in an EEOS. Finally, a high-voltage fast pulse with a voltage peak value greater than 180 kV, a rise time of 3 ns, a pulse width of 30 ns and a current peak of 3.4 kA was obtained on an X-ray diode load.
To develop a light and small high voltage pulsed power source, an innovative fast pulse technology based on an explosive driven ferroelectric generator (EDFEG) is investigated. An EDFEG is used as the primary power supply, inductive energy storage technology and an electrical exploding opening switch (EEOS) are used to generate a high-voltage fast pulse. On the basis of full-circuit simulation model of EDFEGs and the material properties of ferroelectric ceramics, the circuit simulation research on this fast pulse technology is carried out. The simulation results reveal the influence of circuit parameters on high voltage pulse generation. The research shows that the high-voltage mode of EDFEGs is more suitable for generating high-voltage fast pulse combined with EEOS technology. As a result, the principle of this technology is verified in experiments. In the experiment, the output current of an EDFEG was about 360 A and its pulse width was about 3.8 μs. The charging voltage of a 17.5 nF capacitor was 75 kV. After the capacitor was discharged, a pulse current with a peak value greater than 12 kA was generated in an EEOS. Finally, a high-voltage fast pulse with a voltage peak value greater than 180 kV, a rise time of 3 ns, a pulse width of 30 ns and a current peak of 3.4 kA was obtained on an X-ray diode load.
2022,
34: 075018.
doi: 10.11884/HPLPB202234.210556
Abstract:
Under the condition of refrequency, the resonant circuit of the capacitor charging power supply oscillates abnormally due to the residual voltage, which leads to switching overcurrent and power failure. To address this issue, on the basis of analyzing the working principle of resonant circuit, we put forward a method of releasing the residual voltage of the resonant capacitor by controlling part of the switching of the power supply itself at the end of each charging cycle. The method not only keeps the initial voltage of the resonant capacitor at zero in each period, but also avoids the defect of adding the discharge circuit. The control method is simple and universal. The circuit simulation and experiment carried out on a 800 V/6 A charging power supply show that the proposed method reduces the residual voltage of the resonant capacitor to zero rapidly after the charging cycle, and the resonant current tends to be stable, which effectively inhibits the abnormal oscillation of the resonant circuit, thus verifying the effectiveness and practicability of the proposed method.
Under the condition of refrequency, the resonant circuit of the capacitor charging power supply oscillates abnormally due to the residual voltage, which leads to switching overcurrent and power failure. To address this issue, on the basis of analyzing the working principle of resonant circuit, we put forward a method of releasing the residual voltage of the resonant capacitor by controlling part of the switching of the power supply itself at the end of each charging cycle. The method not only keeps the initial voltage of the resonant capacitor at zero in each period, but also avoids the defect of adding the discharge circuit. The control method is simple and universal. The circuit simulation and experiment carried out on a 800 V/6 A charging power supply show that the proposed method reduces the residual voltage of the resonant capacitor to zero rapidly after the charging cycle, and the resonant current tends to be stable, which effectively inhibits the abnormal oscillation of the resonant circuit, thus verifying the effectiveness and practicability of the proposed method.
2022,
34: 075019.
doi: 10.11884/HPLPB202234.210465
Abstract:
A 50 kV compact automatic nanosecond pulse source was developed. The working principle of the pulse source, its structure design and the development of automatic control system are introduced. The typical electric field waveform of a pulse source connected to a guided wave antenna is given. The output voltage of the pulse source can be adjusted continuously by DC capacitor charging method, and the output pulse width can be adjusted by changing the storage capacitance. The pulse source can be used to generate electromagnetic environment and test the breakdown characteristics of insulating materials. The output of higher voltage can be realized by selecting and designing higher voltage storage capacitors and charging insulators.
A 50 kV compact automatic nanosecond pulse source was developed. The working principle of the pulse source, its structure design and the development of automatic control system are introduced. The typical electric field waveform of a pulse source connected to a guided wave antenna is given. The output voltage of the pulse source can be adjusted continuously by DC capacitor charging method, and the output pulse width can be adjusted by changing the storage capacitance. The pulse source can be used to generate electromagnetic environment and test the breakdown characteristics of insulating materials. The output of higher voltage can be realized by selecting and designing higher voltage storage capacitors and charging insulators.
2022,
34: 079001.
doi: 10.11884/HPLPB202234.210568
Abstract:
The use of aluminum alloy high-voltage wire harnesses instead of copper wire harnesses can reduce the weight of electric vehicles, increase battery endurance, and reduce cost. Aiming at the difficulty of reliable and effective connection between aluminum alloy high-voltage wire harness and copper alloy terminal, this paper proposes to use electromagnetic pulse crimping technology (EMPC) to connect aluminum alloy high-voltage wire harness and copper alloy terminal. A set of EMPC device suitable for the connection has been developed. The EMPW device has a maximum discharge energy of 28 kJ. During the crimping process, with the increase of the discharge voltage, the temperature of the terminal surface increases. The aluminum alloy high-voltage wire harness and the copper alloy terminal can be connected reliably at 12 kV. An optical microscope was used to analyze the microstructure of the connection interface, and the electrical and mechanical properties of the interface were tested. The analysis shows that the electromagnetic pulse crimping technology can realize metallurgical combination between the aluminum alloy high-voltage wire harness and the terminal as well as the aluminum alloy core wires. The connection interface has a corrugated morphology and a vortex morphology. The test results show that the contact resistance, vibration test and tensile load test of the joint meet the industrial standards of automobile and the national standards of cable joint.
The use of aluminum alloy high-voltage wire harnesses instead of copper wire harnesses can reduce the weight of electric vehicles, increase battery endurance, and reduce cost. Aiming at the difficulty of reliable and effective connection between aluminum alloy high-voltage wire harness and copper alloy terminal, this paper proposes to use electromagnetic pulse crimping technology (EMPC) to connect aluminum alloy high-voltage wire harness and copper alloy terminal. A set of EMPC device suitable for the connection has been developed. The EMPW device has a maximum discharge energy of 28 kJ. During the crimping process, with the increase of the discharge voltage, the temperature of the terminal surface increases. The aluminum alloy high-voltage wire harness and the copper alloy terminal can be connected reliably at 12 kV. An optical microscope was used to analyze the microstructure of the connection interface, and the electrical and mechanical properties of the interface were tested. The analysis shows that the electromagnetic pulse crimping technology can realize metallurgical combination between the aluminum alloy high-voltage wire harness and the terminal as well as the aluminum alloy core wires. The connection interface has a corrugated morphology and a vortex morphology. The test results show that the contact resistance, vibration test and tensile load test of the joint meet the industrial standards of automobile and the national standards of cable joint.
2022,
34: 079002.
doi: 10.11884/HPLPB202234.210540
Abstract:
The gain of silicon photomultiplier tube will drift greatly due to temperature variation, which will affect the gain accuracy of silicon photomultiplier tube. To realize that silicon photomultiplier tube gain does not change greatly with temperature variation, an automatic gain correction system for silicon photomultiplier tube is designed, including the design of a high voltage power supply and an acquisition system based on single chip microcomputer.The high voltage module can accurately operate in the temperature range of −10 ℃ to 60 ℃, and the power noise is about 30 mV, which can meet the requirements of silicon photomultiplier tube performance testing.Through frequency sweep test and laser irradiation test, the acquisition system can better pass the 60 MHz AC signal, and transform the optical signal into a more obvious electrical signal.The system provides a working voltage and acquisition circuit to Jingbon Compony’s silicon photomultiplier tube array JARY-TP3050-8X8C.
The gain of silicon photomultiplier tube will drift greatly due to temperature variation, which will affect the gain accuracy of silicon photomultiplier tube. To realize that silicon photomultiplier tube gain does not change greatly with temperature variation, an automatic gain correction system for silicon photomultiplier tube is designed, including the design of a high voltage power supply and an acquisition system based on single chip microcomputer.The high voltage module can accurately operate in the temperature range of −10 ℃ to 60 ℃, and the power noise is about 30 mV, which can meet the requirements of silicon photomultiplier tube performance testing.Through frequency sweep test and laser irradiation test, the acquisition system can better pass the 60 MHz AC signal, and transform the optical signal into a more obvious electrical signal.The system provides a working voltage and acquisition circuit to Jingbon Compony’s silicon photomultiplier tube array JARY-TP3050-8X8C.
