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2020, 32: 092002.
doi: 10.11884/HPLPB202032.200090
Just Accepted manuscripts are peer-reviewed and accepted for publication. They are posted online prior to technical editing formatting for publication and author proofing.
Display Method:
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200235
Abstract:
In recent years, the study of kinetic effects is a hot issue in the field of laser inertial confinement fusion, which helps to understand the deviation between experimental results and traditional fluid simulation. The temperature and density of the plasma in indirect-drive hohlraum span multiple orders of magnitude, and the composition of capsule is complex. In the local high temperature and low density region, the thermal non-equilibrium effect of particles becomes significant, which may indirectly affect the implosion performance. In this paper, the concept and some progress of kinetic effects in the ICF field are briefly reviewed.
In recent years, the study of kinetic effects is a hot issue in the field of laser inertial confinement fusion, which helps to understand the deviation between experimental results and traditional fluid simulation. The temperature and density of the plasma in indirect-drive hohlraum span multiple orders of magnitude, and the composition of capsule is complex. In the local high temperature and low density region, the thermal non-equilibrium effect of particles becomes significant, which may indirectly affect the implosion performance. In this paper, the concept and some progress of kinetic effects in the ICF field are briefly reviewed.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200203
Abstract:
There are many kinds of nonlinear effects in the interaction between high power laser and matter. The beam of laser fusion driver is highly coherent, which greatly enhances the effects, and inevitably limits the laser power and efficient utilization. Looking back on the development history of laser fusion driver, there is a dark line runing through the main line of improving laser output capability, which is struggling with beam coherence. The control status of beam coherence in laser fusion driver is reviewed from two aspects: restraining the nonlinear transmission effect of high power laser and suppressing the interaction between laser and plasma. In view of the potential demand, innovative technologies for the future development of high power lasers are proposed.
There are many kinds of nonlinear effects in the interaction between high power laser and matter. The beam of laser fusion driver is highly coherent, which greatly enhances the effects, and inevitably limits the laser power and efficient utilization. Looking back on the development history of laser fusion driver, there is a dark line runing through the main line of improving laser output capability, which is struggling with beam coherence. The control status of beam coherence in laser fusion driver is reviewed from two aspects: restraining the nonlinear transmission effect of high power laser and suppressing the interaction between laser and plasma. In view of the potential demand, innovative technologies for the future development of high power lasers are proposed.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200226
Abstract:
In a common medical/industrial linac system, an ordinary magnetron power source was adopted which stays the same for about 20 years. Despite the low power level and the short life time, magnetron is the only choice to drive the compact linac system due to its size and weight. With the development of multi-beam klystron technique, working voltage and the system size can be reduced dramatically while the power level and average power is taking a big step forward. Typically, a magnetron in X-band can supply a 2 MW microwave power maximum, which gives great challenge for the linac system engineer. Based on the studies in this article, new applications will emerge across the medical and industrial field. To meet the demands from medical and industrial applications, high-power klystrons were developed in cancer treatment, nondestructive inspection and industrial irradiation. In this article, an X-band high-power multi-beam klystron with 3 MW output power in 9300 MHz was introduced. Compared with the magnetron power source, the linac cavity could be reduced by 30% due to the power supply. Based on the integrated coil and oil cooling system, the boundary dimension could be reduced to ϕ200 mm×400 mm with the total weight of 25 kg.
In a common medical/industrial linac system, an ordinary magnetron power source was adopted which stays the same for about 20 years. Despite the low power level and the short life time, magnetron is the only choice to drive the compact linac system due to its size and weight. With the development of multi-beam klystron technique, working voltage and the system size can be reduced dramatically while the power level and average power is taking a big step forward. Typically, a magnetron in X-band can supply a 2 MW microwave power maximum, which gives great challenge for the linac system engineer. Based on the studies in this article, new applications will emerge across the medical and industrial field. To meet the demands from medical and industrial applications, high-power klystrons were developed in cancer treatment, nondestructive inspection and industrial irradiation. In this article, an X-band high-power multi-beam klystron with 3 MW output power in 9300 MHz was introduced. Compared with the magnetron power source, the linac cavity could be reduced by 30% due to the power supply. Based on the integrated coil and oil cooling system, the boundary dimension could be reduced to ϕ200 mm×400 mm with the total weight of 25 kg.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200225
Abstract:
Based on the fundamental principle oriented from the single beam klystron, multi-beam klystron can make the higher peak output power possible under a lower working voltage with the help of parallel working mode combining several low perveance electron beams. Lower working voltage also make a contribution to the compact design of the whole system. In the linac system design, input power source is the key factor that determines the composition of the whole system. The increasement on the power source can shorten the linac tube dramatically, thus make the brand-new application scenarios possible such like the high-degree freedom cancer treatment or the compact nondestructive testing system. The C-band multi-beam klystron in this article mainly target on the low and medium energy accelerator applications, which can give out the microwave power at higher rep-rate (500 Hz) and higher working ratio (0.2%).
Based on the fundamental principle oriented from the single beam klystron, multi-beam klystron can make the higher peak output power possible under a lower working voltage with the help of parallel working mode combining several low perveance electron beams. Lower working voltage also make a contribution to the compact design of the whole system. In the linac system design, input power source is the key factor that determines the composition of the whole system. The increasement on the power source can shorten the linac tube dramatically, thus make the brand-new application scenarios possible such like the high-degree freedom cancer treatment or the compact nondestructive testing system. The C-band multi-beam klystron in this article mainly target on the low and medium energy accelerator applications, which can give out the microwave power at higher rep-rate (500 Hz) and higher working ratio (0.2%).
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200135
Abstract:
The inductance gradient of the background field enhancement scheme of the four-rail electromagnetic launcher is simulated. Based on the principle of virtual work, the formula of the inductance gradient of the four-rail launchers under the background field is derived. A three-dimensional background field simulation model is established to analyze the variation law of inductance gradient under different main and additional rail parameters. The simulation results show that the inductance gradient of the system can be improved by increasing the launcher caliber, reducing the distance between the main and additional rails and the cross-sectional area of the additional rails. With the enhancement of background field, the proximity effect becomes obvious when the height of main rail reaches 57% of the diameter. Under the same cross-sectional area, the thickness of the additional rails should be reduced in order to increase the inductance gradient of the system, and the height of the additional rails should be reduced in order to alleviate the proximity effect. Concave cross - section additional rail can obviously improve the current proximity effect.
The inductance gradient of the background field enhancement scheme of the four-rail electromagnetic launcher is simulated. Based on the principle of virtual work, the formula of the inductance gradient of the four-rail launchers under the background field is derived. A three-dimensional background field simulation model is established to analyze the variation law of inductance gradient under different main and additional rail parameters. The simulation results show that the inductance gradient of the system can be improved by increasing the launcher caliber, reducing the distance between the main and additional rails and the cross-sectional area of the additional rails. With the enhancement of background field, the proximity effect becomes obvious when the height of main rail reaches 57% of the diameter. Under the same cross-sectional area, the thickness of the additional rails should be reduced in order to increase the inductance gradient of the system, and the height of the additional rails should be reduced in order to alleviate the proximity effect. Concave cross - section additional rail can obviously improve the current proximity effect.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200159
Abstract:
The mechanical performance of CF2 lead fuel assembly and the thermal-mechanical performance of the fuel rod are evaluated considering the irradiation condition of the irradiation program and the criteria is fulfilled. The major in pile performance of CF2 fuel assembly are studied on the base of the poolside examination results, including the burnup dependent parameters such as the growth of fuel assembly and fuel rod, the bow of fuel assembly and fuel rod and the growth of grid etc. The results show that the major in pile performance of CF2 fuel assembly reach the target, and the fuel fulfill the requirement of reactor system.
The mechanical performance of CF2 lead fuel assembly and the thermal-mechanical performance of the fuel rod are evaluated considering the irradiation condition of the irradiation program and the criteria is fulfilled. The major in pile performance of CF2 fuel assembly are studied on the base of the poolside examination results, including the burnup dependent parameters such as the growth of fuel assembly and fuel rod, the bow of fuel assembly and fuel rod and the growth of grid etc. The results show that the major in pile performance of CF2 fuel assembly reach the target, and the fuel fulfill the requirement of reactor system.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200127
Abstract:
Using gold nanocages (GNCs) as saturable absorbers (SAs), passively Q-switched Nd:GAGG lasers at 1106 nm were demonstrated. Q-switched pulse with the shortest pulse duration of 370 ns, pulse repetition rate of 170 kHz was achieved at transmittance T＝7% under the pump power of 7.69 W with the maximum average output power of 121 mW. These results indicate a great potential of the GNCs as SA in the near-infrared lasers.
Using gold nanocages (GNCs) as saturable absorbers (SAs), passively Q-switched Nd:GAGG lasers at 1106 nm were demonstrated. Q-switched pulse with the shortest pulse duration of 370 ns, pulse repetition rate of 170 kHz was achieved at transmittance T＝7% under the pump power of 7.69 W with the maximum average output power of 121 mW. These results indicate a great potential of the GNCs as SA in the near-infrared lasers.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200118
Abstract:
Energy spectrum data analysis is the main source of nuclide identification. Aiming at the emerging energy spectrum nuclide identification method, in the noisy environment of mixed radionuclides, there are problems such as slow recognition speed and low accuracy, an energy spectrum nuclide recognition method based on Long short-term memory neural network (LSTM) is proposed. In the experiment, a LaBr3 crystal detector is used to measure the 60Co and 137Cs radioactive sources in the environment to obtain a gamma spectrum data set. First, the experiment uses data smoothing and normalization methods for data preprocessing. Then, the energy spectrum data is grouped in time series to obtain a usable input sequence array. Finally, the prediction results are obtained through the LSTM model. By comparing two energy spectrum recognition models based on BP neural network and convolutional neural network (CNN), the average recognition rates in the test set are 83.45% and 86.21% respectively, while the average recognition rate of the LSTM model is 93.04%. The experimental results show that the energy spectrum model performs well in the nuclide identification effect and can be used in fast energy spectrum nuclide identification equipment.
Energy spectrum data analysis is the main source of nuclide identification. Aiming at the emerging energy spectrum nuclide identification method, in the noisy environment of mixed radionuclides, there are problems such as slow recognition speed and low accuracy, an energy spectrum nuclide recognition method based on Long short-term memory neural network (LSTM) is proposed. In the experiment, a LaBr3 crystal detector is used to measure the 60Co and 137Cs radioactive sources in the environment to obtain a gamma spectrum data set. First, the experiment uses data smoothing and normalization methods for data preprocessing. Then, the energy spectrum data is grouped in time series to obtain a usable input sequence array. Finally, the prediction results are obtained through the LSTM model. By comparing two energy spectrum recognition models based on BP neural network and convolutional neural network (CNN), the average recognition rates in the test set are 83.45% and 86.21% respectively, while the average recognition rate of the LSTM model is 93.04%. The experimental results show that the energy spectrum model performs well in the nuclide identification effect and can be used in fast energy spectrum nuclide identification equipment.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200114
Abstract:
Gas spark switch is the most commonly used key device in pulse power device. The difficult pooblem of electrode erosion, which affects the performance of gas spark switches, has always been attracting the attention of scholars at home and abroad. This article reviews the existing electrode erosion theory and experimental research results, introduces the basic mechanism and simulation model of electrode erosion, summarizes the factors affecting the switching electrode erosion and the research progress of erosion-resistant electrode materials, and finally discusses the problems faced by the erosion research and the direction of optimizing the erosion resistance of the electrode materials, so as to provide references for subsequent research.
Gas spark switch is the most commonly used key device in pulse power device. The difficult pooblem of electrode erosion, which affects the performance of gas spark switches, has always been attracting the attention of scholars at home and abroad. This article reviews the existing electrode erosion theory and experimental research results, introduces the basic mechanism and simulation model of electrode erosion, summarizes the factors affecting the switching electrode erosion and the research progress of erosion-resistant electrode materials, and finally discusses the problems faced by the erosion research and the direction of optimizing the erosion resistance of the electrode materials, so as to provide references for subsequent research.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200102
Abstract:
This paper presents a solid-state pulse generator based on drift step recovery diode (DSRD, Drift Step Recovery Diode), a new high-power, ultra-fast semiconductor opening switch, and saturable pulse transformer. The topology structure of circuit is designed, the operating principle of the pulse generator is analyzed theoretically. And the influence of several key circuit parameters on the output waveform of the pulse generator is studied, including the coil winding turns, the magnetic core layers, the load resistance, and the trigger pulse width. The experimental results show that the pulse generator can produce a pulse at a 50 k-resistive load with amplitude 38.2 kV, rise time 7.1 ns, pulse width 14.1 ns and it could work stably at the repetition frequency of 400 kHz.
This paper presents a solid-state pulse generator based on drift step recovery diode (DSRD, Drift Step Recovery Diode), a new high-power, ultra-fast semiconductor opening switch, and saturable pulse transformer. The topology structure of circuit is designed, the operating principle of the pulse generator is analyzed theoretically. And the influence of several key circuit parameters on the output waveform of the pulse generator is studied, including the coil winding turns, the magnetic core layers, the load resistance, and the trigger pulse width. The experimental results show that the pulse generator can produce a pulse at a 50 k-resistive load with amplitude 38.2 kV, rise time 7.1 ns, pulse width 14.1 ns and it could work stably at the repetition frequency of 400 kHz.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200097
Abstract:
In this work, the response characteristics of the microwave limiter with various high power microwave parameters are investigated via both simulation and experiment, the simulation matches the experiment well. When the input power exceeds 6 dBm, a spike leakage phenomenon is observed. As the input power is increased, the rise time and pulse width of the leakage peak is decreased, whereas the leakage power is gradually increased. However, the leakage power of the plateau is firstly linearly increased, then is gradually decreased, and finally is slightly increased. Moreover, the pulse width and repetition frequency have almost no influence on the characteristics of leakage pulse, and leakage energy is decreased as the injection power is increased.
In this work, the response characteristics of the microwave limiter with various high power microwave parameters are investigated via both simulation and experiment, the simulation matches the experiment well. When the input power exceeds 6 dBm, a spike leakage phenomenon is observed. As the input power is increased, the rise time and pulse width of the leakage peak is decreased, whereas the leakage power is gradually increased. However, the leakage power of the plateau is firstly linearly increased, then is gradually decreased, and finally is slightly increased. Moreover, the pulse width and repetition frequency have almost no influence on the characteristics of leakage pulse, and leakage energy is decreased as the injection power is increased.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200053
Abstract:
Considering the neutral particle beams can help cleaning effect in space debris in low-Earth orbit and their potential application prospects in space exploration, this paper analyzes several major mechanisms that cause beam energy loss and density loss during the long-range transmission of neutral particle beams in sub-orbital space, and focuses on analyzing the effect of stripping effects on beam loss. The neutral beam stripping effects include self-stripping effects caused by collisions of stripped particles with beam particles and stripping effects caused by collisions of beam particles with atmospheric particles. Based on the equation that the beam density changes with the propagation distance, this paper introduces a geometric factor to characterize the intensity of the self-stripping effect of the beam, and derives the functional relationship between the transmission distance and the geometric factor. By normalizing the transmission distance under a certain particle survival ratio, it evaluates the relative importance of the effect of beam self-stripping on the transmission distance in the long-range transmission of neutral beams. The results show that at a fixed height, when the neutral beam density is greater than the density of air particles, the self-stripping effect will be very strong. With the increase of the transmission height, even if the beam density and the air density decrease at the same time with the same order of magnitude, the effect of self stripping on the transmission distance will increase with a large geometric factor.
Considering the neutral particle beams can help cleaning effect in space debris in low-Earth orbit and their potential application prospects in space exploration, this paper analyzes several major mechanisms that cause beam energy loss and density loss during the long-range transmission of neutral particle beams in sub-orbital space, and focuses on analyzing the effect of stripping effects on beam loss. The neutral beam stripping effects include self-stripping effects caused by collisions of stripped particles with beam particles and stripping effects caused by collisions of beam particles with atmospheric particles. Based on the equation that the beam density changes with the propagation distance, this paper introduces a geometric factor to characterize the intensity of the self-stripping effect of the beam, and derives the functional relationship between the transmission distance and the geometric factor. By normalizing the transmission distance under a certain particle survival ratio, it evaluates the relative importance of the effect of beam self-stripping on the transmission distance in the long-range transmission of neutral beams. The results show that at a fixed height, when the neutral beam density is greater than the density of air particles, the self-stripping effect will be very strong. With the increase of the transmission height, even if the beam density and the air density decrease at the same time with the same order of magnitude, the effect of self stripping on the transmission distance will increase with a large geometric factor.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200195
Abstract:
High power generation in terahertz frequency band is limited by physical mechanism. In this paper, a G-band sheet beam extended-interaction klystron was designed to demonstrate the power level and the physical factors that affect the performance of the klystron. An elliptical electron beam with a voltage of 24.5 kV, a current of 0.6 A and the dimension of 1 mm×0.15 mm was used. In order to match the size of the sheet beam and obtain high efficiency and high gain, the transverse-oversized barbell type multi-gap resonant cavity was used as the interaction circuit. The 3D PIC simulation results showed that more than 500 W of power output can be obtained with the actual cavity loss is considered, and the electron efficiency and gain are 3.65% and 38.2 dB respectively. It is found that the power and efficiency is largely restricted by the mode stability of the multi-gap cavity as well as the ohmic loss. The ohmic loss of the output cavity has a significant effect on the final output power which should be given special consideration in engineering design. The research in this paper has laid a good foundation for the development of high frequency sheet beam extended-interaction devices.
High power generation in terahertz frequency band is limited by physical mechanism. In this paper, a G-band sheet beam extended-interaction klystron was designed to demonstrate the power level and the physical factors that affect the performance of the klystron. An elliptical electron beam with a voltage of 24.5 kV, a current of 0.6 A and the dimension of 1 mm×0.15 mm was used. In order to match the size of the sheet beam and obtain high efficiency and high gain, the transverse-oversized barbell type multi-gap resonant cavity was used as the interaction circuit. The 3D PIC simulation results showed that more than 500 W of power output can be obtained with the actual cavity loss is considered, and the electron efficiency and gain are 3.65% and 38.2 dB respectively. It is found that the power and efficiency is largely restricted by the mode stability of the multi-gap cavity as well as the ohmic loss. The ohmic loss of the output cavity has a significant effect on the final output power which should be given special consideration in engineering design. The research in this paper has laid a good foundation for the development of high frequency sheet beam extended-interaction devices.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200170
Abstract:
In the multipactor investigation of dielectric window, the effect of low energy electron is usually neglected. In this paper, a homemade Monte Carlo model was developed to simulate the multipactor mechanism of the RF window. By comparing the multipactor susceptibility curves obtained under the classical Vaughan secondary electron emission model and two modified Vaughan models (fitted by Rice and Vincent respectively), the influence of low-energy electrons on the multipactor effect of the dielectric window was obtained. The simulation results demonstrate that under effect of the tangential electric field, the susceptibility curves obtained by the three emission models almost overlap. Low-energy electrons have little effect on the susceptibility curves, and the Rice model has the largest discharge area. In comparison, under effect of the normal electric field, the susceptibility area fitted by the Vincent model is much larger than the other two models. These characteristics should be taken into account in the research on the breakdown phenomenon of high-power dielectric window and breakdown suppression technology.
In the multipactor investigation of dielectric window, the effect of low energy electron is usually neglected. In this paper, a homemade Monte Carlo model was developed to simulate the multipactor mechanism of the RF window. By comparing the multipactor susceptibility curves obtained under the classical Vaughan secondary electron emission model and two modified Vaughan models (fitted by Rice and Vincent respectively), the influence of low-energy electrons on the multipactor effect of the dielectric window was obtained. The simulation results demonstrate that under effect of the tangential electric field, the susceptibility curves obtained by the three emission models almost overlap. Low-energy electrons have little effect on the susceptibility curves, and the Rice model has the largest discharge area. In comparison, under effect of the normal electric field, the susceptibility area fitted by the Vincent model is much larger than the other two models. These characteristics should be taken into account in the research on the breakdown phenomenon of high-power dielectric window and breakdown suppression technology.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200158
Abstract:
In BEPCⅡ, button BPM and stripline BPM cannot reach to sufficient precise resolution for beam transverse displacement. This project aims to the design of cavity BPM for BEPCⅡ linac. Position cavity in cavity beam position monitor (CBPM) is an re-entrant resonator with four rectangular waveguides. TM110 mode frequency is chosen in S band, and the radius of beam pipe is 23 mm. TM010 mode in reference cavity is almost as same as TM110 mode in position cavity. According to the results of offline test, characterized parameters of CBPM coincided with computer simulated data. The frquency of TM110 mode are 2502 MHz in horizontal and 2503 MHz in vertical. Cross-talk isolation for position cavity is better than -44.7 dB. Ratio front circuits included filtration, amplification and down-convertion when signals extracted from CBPM. After finishing offline caliberation test, the results showed that CBPM has excellent measurement of linearity area, which is over 10 mm. After frequency spectrum analyzing and linear fitting, the position resolution of CBPM are 2.87 μm in horizontal and 2.16 μm in vertical.
In BEPCⅡ, button BPM and stripline BPM cannot reach to sufficient precise resolution for beam transverse displacement. This project aims to the design of cavity BPM for BEPCⅡ linac. Position cavity in cavity beam position monitor (CBPM) is an re-entrant resonator with four rectangular waveguides. TM110 mode frequency is chosen in S band, and the radius of beam pipe is 23 mm. TM010 mode in reference cavity is almost as same as TM110 mode in position cavity. According to the results of offline test, characterized parameters of CBPM coincided with computer simulated data. The frquency of TM110 mode are 2502 MHz in horizontal and 2503 MHz in vertical. Cross-talk isolation for position cavity is better than -44.7 dB. Ratio front circuits included filtration, amplification and down-convertion when signals extracted from CBPM. After finishing offline caliberation test, the results showed that CBPM has excellent measurement of linearity area, which is over 10 mm. After frequency spectrum analyzing and linear fitting, the position resolution of CBPM are 2.87 μm in horizontal and 2.16 μm in vertical.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200228
Abstract:
To achieve GW-level amplification output radiation at X-band, a relativistic triaxial klystron amplifier （TKA） with two-stage cascaded double-gap bunching cavities is investigated. The input cavity is optimized to obtain a high absorption rate of the external injection microwave. The cascaded bunching cavities are optimized to achieve a high depth of the fundamental harmonic current. A double-gap standing wave extractor is designed to improve the beam wave conversion efficiency. Two reflectors with high reflection coefficients both to the asymmetric mode and the TEM mode are employed to suppress the asymmetric mode competition and TEM mode microwave leakage. Particle-in-cell simulation results show that a high power microwave with a power of 2.53 GW and a frequency of 8.4 GHz is generated with a 690 kV, 9.3 kA electron beam excitation and a 25 kW radio-frequency signal injection. Meanwhile, there is insignificant self-excitation of parasitic mode in the proposed structure by adopting the reflectors. The relative phase difference between the injected signals and the output microwaves keeps locked after the amplifier becomes saturated.
To achieve GW-level amplification output radiation at X-band, a relativistic triaxial klystron amplifier （TKA） with two-stage cascaded double-gap bunching cavities is investigated. The input cavity is optimized to obtain a high absorption rate of the external injection microwave. The cascaded bunching cavities are optimized to achieve a high depth of the fundamental harmonic current. A double-gap standing wave extractor is designed to improve the beam wave conversion efficiency. Two reflectors with high reflection coefficients both to the asymmetric mode and the TEM mode are employed to suppress the asymmetric mode competition and TEM mode microwave leakage. Particle-in-cell simulation results show that a high power microwave with a power of 2.53 GW and a frequency of 8.4 GHz is generated with a 690 kV, 9.3 kA electron beam excitation and a 25 kW radio-frequency signal injection. Meanwhile, there is insignificant self-excitation of parasitic mode in the proposed structure by adopting the reflectors. The relative phase difference between the injected signals and the output microwaves keeps locked after the amplifier becomes saturated.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200208
Abstract:
In millimeter wave klystron, the electron optics system is very important. The electron optics system is related to the realization and the life of the klystron. The size of millimeter wave klystron is small. In order to achieve kW output power in Ka-band and W-band, the higher electron passing rate and lower cathode load are required. The paper analyzes the characteristics of electron Optics system for Ka-band and W-band klystron. The design schemes of Ka-band 10 kW klystron and W- band 1 kW klystron are determined. The structures of electron gun and focusing system are calculated by software, and the state of electron gun in focusing magnetic field is optimized by CST. Ka-band klystron and W-band klystron have been made, and the design electron optical system can meet the engineering realization of klystron.
In millimeter wave klystron, the electron optics system is very important. The electron optics system is related to the realization and the life of the klystron. The size of millimeter wave klystron is small. In order to achieve kW output power in Ka-band and W-band, the higher electron passing rate and lower cathode load are required. The paper analyzes the characteristics of electron Optics system for Ka-band and W-band klystron. The design schemes of Ka-band 10 kW klystron and W- band 1 kW klystron are determined. The structures of electron gun and focusing system are calculated by software, and the state of electron gun in focusing magnetic field is optimized by CST. Ka-band klystron and W-band klystron have been made, and the design electron optical system can meet the engineering realization of klystron.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200207
Abstract:
This paper briefly introduces the design of a W-band extended interaction klystron(EIK), and gives the test results. The high frequency extended interaction circuit consisted of 5-gap buncher cavities and 11-gap output cavity which can obtain wider bandwidth. This ladder-type multi-gap cavity circuit is easy to fabricate and supports greater energy margins. The π-mode is selected as the operating mode of 5-gap (or 13-gap) cavities. By now, with an electron beam of 17 kV and 0.78 A, the EIK has achieved a peak output power of 2 kW, bandwidth of 500 MHz, gain of 40 dB, and 5% duty.
This paper briefly introduces the design of a W-band extended interaction klystron(EIK), and gives the test results. The high frequency extended interaction circuit consisted of 5-gap buncher cavities and 11-gap output cavity which can obtain wider bandwidth. This ladder-type multi-gap cavity circuit is easy to fabricate and supports greater energy margins. The π-mode is selected as the operating mode of 5-gap (or 13-gap) cavities. By now, with an electron beam of 17 kV and 0.78 A, the EIK has achieved a peak output power of 2 kW, bandwidth of 500 MHz, gain of 40 dB, and 5% duty.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200202
Abstract:
This paper introduce the research of a new ultra-wideband (wideband ≥17%) S-band multi-beam klystron (MBK) for the first time in China. By optimizing the electronic optics system, gun construction, high-frequency system、heat removal system and so on many measures, the electronic passing rate can be improved and the heat dissipation pressure in the high frequency part can be reduced. These measures enabled the MBK to achieve 120 kW with 30% efficiency and 40 kW average power. At the same time, through low cathode load design and many process measures, the steady working with 3mspulse length and continuous 24 h of steady work have been realized. To achieve full power output with 3 min and 2000 h life, we have optimized the working parameters of cathode and structure and technology of electron gun for many times. This project has completed the all index, the small-batch production and vehicle-mounted environmental testing, with engineering application conditions, which can provide effective technical reference for subsequent similar designs.
This paper introduce the research of a new ultra-wideband (wideband ≥17%) S-band multi-beam klystron (MBK) for the first time in China. By optimizing the electronic optics system, gun construction, high-frequency system、heat removal system and so on many measures, the electronic passing rate can be improved and the heat dissipation pressure in the high frequency part can be reduced. These measures enabled the MBK to achieve 120 kW with 30% efficiency and 40 kW average power. At the same time, through low cathode load design and many process measures, the steady working with 3mspulse length and continuous 24 h of steady work have been realized. To achieve full power output with 3 min and 2000 h life, we have optimized the working parameters of cathode and structure and technology of electron gun for many times. This project has completed the all index, the small-batch production and vehicle-mounted environmental testing, with engineering application conditions, which can provide effective technical reference for subsequent similar designs.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200193
Abstract:
This paper has proposed a Ka-band coaxial multi-gap cavity operating in the TM51-2πmode. The CST eigenmode solver is used to study the characteristics of the electric field distribution, and the mode characteristics of this cavity have been analyzed based on the all-pass coupling structure at the outer radius. By combining space-charge wave theory and 3-D particle-in-cell (PIC) simulation analysis, this paper has studied the start-oscillation characteristics of the high-order mode coaxial multi-gap cavity under the multi-beam excitation method. And the mode stability and beam-wave interaction characteristics of the coaxial multi-gap cavity operating in the high-order mode have been analyzed. The results show that the coaxial multi-gap cavity operating in the TM51-2π mode adopting the coupling method at the outer radius possesses high mode stability. In this structure, multiple beams can not only uniformly inspire the operating mode but also non-uniformly inspire the competition mode. Different from the multi-beam extended-interaction klystron (EIK) operating in the fundamental mode, the high-order mode EIK with this structure establishes the gap voltages separately. Therefore, the peak electric fields with different phases can interact with the beams respectively. While keeping the same total beam current and beam voltage, the operating method driven by more beams requires a smaller focusing magnetic field.
This paper has proposed a Ka-band coaxial multi-gap cavity operating in the TM51-2πmode. The CST eigenmode solver is used to study the characteristics of the electric field distribution, and the mode characteristics of this cavity have been analyzed based on the all-pass coupling structure at the outer radius. By combining space-charge wave theory and 3-D particle-in-cell (PIC) simulation analysis, this paper has studied the start-oscillation characteristics of the high-order mode coaxial multi-gap cavity under the multi-beam excitation method. And the mode stability and beam-wave interaction characteristics of the coaxial multi-gap cavity operating in the high-order mode have been analyzed. The results show that the coaxial multi-gap cavity operating in the TM51-2π mode adopting the coupling method at the outer radius possesses high mode stability. In this structure, multiple beams can not only uniformly inspire the operating mode but also non-uniformly inspire the competition mode. Different from the multi-beam extended-interaction klystron (EIK) operating in the fundamental mode, the high-order mode EIK with this structure establishes the gap voltages separately. Therefore, the peak electric fields with different phases can interact with the beams respectively. While keeping the same total beam current and beam voltage, the operating method driven by more beams requires a smaller focusing magnetic field.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200171
Abstract:
First the theory of kinematics and space charge wave are applied to conclude an experiential formula for calculating the phase of the modulated current at the entrance of the gap of the middle cavity. Second a nonlinear theory of cavity excitation by modulated electron beam is applied to calculate the amplitude and the phase of the gap voltage of the middle cavity and the output cavity, and an experiential formula for calculating the phase of the modulated current at the entrance of the gap of the output cavity is presented. These theories and 2D PIC are applied to estimate the phase of the modulated current at the entrance of the gap of the middle cavity and the output cavity、the amplitude and the phase of gap voltage in the middle cavity and the output cavity. The error of the phase of the modulated current at the entrance of the gap of the middle cavity and the output cavity is 2.627° (model 1) and 3.857° (model 2); the relativistic error of the amplitude gap voltage in the middle cavity and the output cavity is 1.47% and 5.42%, the error of the phase of gap voltage in the middle cavity is 4.017° (model 2) and 5.427° (model 3) the error of the phase of gap voltage in the output cavity is 12.32°. Finally, the phase of the modulated current versus the propagation distance in three models is analyzed by 2D PIC simulation.
First the theory of kinematics and space charge wave are applied to conclude an experiential formula for calculating the phase of the modulated current at the entrance of the gap of the middle cavity. Second a nonlinear theory of cavity excitation by modulated electron beam is applied to calculate the amplitude and the phase of the gap voltage of the middle cavity and the output cavity, and an experiential formula for calculating the phase of the modulated current at the entrance of the gap of the output cavity is presented. These theories and 2D PIC are applied to estimate the phase of the modulated current at the entrance of the gap of the middle cavity and the output cavity、the amplitude and the phase of gap voltage in the middle cavity and the output cavity. The error of the phase of the modulated current at the entrance of the gap of the middle cavity and the output cavity is 2.627° (model 1) and 3.857° (model 2); the relativistic error of the amplitude gap voltage in the middle cavity and the output cavity is 1.47% and 5.42%, the error of the phase of gap voltage in the middle cavity is 4.017° (model 2) and 5.427° (model 3) the error of the phase of gap voltage in the output cavity is 12.32°. Finally, the phase of the modulated current versus the propagation distance in three models is analyzed by 2D PIC simulation.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200227
Abstract:
High-frequency relativistic klystron amplifier is one of research hotspots in the field of high power microwave in recent years, and its development is mainly limited by mode competition, phase jitter and low efficiency. We design a novel Ku-band radial-line klystron amplifier in this paper, which consist of input cavity, two groups of double-gap bunching cavity and three-gap extraction cavity. By comparing the coupling coefficient of single-gap bunching cavity with its of non-uniform double-gap bunching cavities, it is proved that non-uniform double-gap bunching cavity has stronger modulation ability to the electron beam. The working mode of non-uniform double-gap bunching cavity with a TEM reflector is TM01-π mode, which has large Q value and benefit from energy isolation between resonant cavities. When the injection power is only 10 kW, the modulation depth of fundamental current is about 110% by cascading two groups of double-gap cavities. In PIC simulation results, this device has high efficiency. When electron beam voltage is 400 kV, beam current is 5 kA and magnetic field is only 0.4 T, high power microwave with a frequency of 14.25 GHz and output power of 825 MW are obtained.
High-frequency relativistic klystron amplifier is one of research hotspots in the field of high power microwave in recent years, and its development is mainly limited by mode competition, phase jitter and low efficiency. We design a novel Ku-band radial-line klystron amplifier in this paper, which consist of input cavity, two groups of double-gap bunching cavity and three-gap extraction cavity. By comparing the coupling coefficient of single-gap bunching cavity with its of non-uniform double-gap bunching cavities, it is proved that non-uniform double-gap bunching cavity has stronger modulation ability to the electron beam. The working mode of non-uniform double-gap bunching cavity with a TEM reflector is TM01-π mode, which has large Q value and benefit from energy isolation between resonant cavities. When the injection power is only 10 kW, the modulation depth of fundamental current is about 110% by cascading two groups of double-gap cavities. In PIC simulation results, this device has high efficiency. When electron beam voltage is 400 kV, beam current is 5 kA and magnetic field is only 0.4 T, high power microwave with a frequency of 14.25 GHz and output power of 825 MW are obtained.
Accepted Manuscript
, Available online ,
doi: 10.11884/HPLPB202032.200188
Abstract:
In order to meet the high power and high gain requirements in engineering applications, a three-dimensional whole tube model for an X-band high-power high-gain multi-beam relativistic klystron amplifier is designed. With the integrated model, the high frequency characteristic analysis and the tube are presented. The input cavity structure with bilateral symmetric coupling hole is designed to reduce the influence of the input waveguide on the field uniformity of the input cavity gap. The multi-cavity and multi-gap modulation structure is adopted to reduce the requirement of input microwave power and improve the amplification gain. Moreover, the multi-gap spreading interaction extraction structure is analyzed and designed to improve the power conversion efficiency and reduce the surface electric field intensity, so as to control the risk of RF breakdown of the device. A three-dimensional full electromagnetic particle in cell code is used to simulate the absorption of injected microwave, and the fundamental harmonic modulated current when electron beams propagate through the input cavity and middle cavity gaps have also been simulated. A 3.2 GW averaged microwave power over the oscillator period is generated by simulation with 900 kV electron beam voltage, 9 kA current and 1 T leading magnetic induction intensity, the efficiency is 40% and the amplification gain is 60 dB. In the experiment, a 0.99 GW averaged microwave power is generated with 550 kV electron beam voltage, 5.1 kA current, the efficiency is 35% and the amplification gain is 53 dB.
In order to meet the high power and high gain requirements in engineering applications, a three-dimensional whole tube model for an X-band high-power high-gain multi-beam relativistic klystron amplifier is designed. With the integrated model, the high frequency characteristic analysis and the tube are presented. The input cavity structure with bilateral symmetric coupling hole is designed to reduce the influence of the input waveguide on the field uniformity of the input cavity gap. The multi-cavity and multi-gap modulation structure is adopted to reduce the requirement of input microwave power and improve the amplification gain. Moreover, the multi-gap spreading interaction extraction structure is analyzed and designed to improve the power conversion efficiency and reduce the surface electric field intensity, so as to control the risk of RF breakdown of the device. A three-dimensional full electromagnetic particle in cell code is used to simulate the absorption of injected microwave, and the fundamental harmonic modulated current when electron beams propagate through the input cavity and middle cavity gaps have also been simulated. A 3.2 GW averaged microwave power over the oscillator period is generated by simulation with 900 kV electron beam voltage, 9 kA current and 1 T leading magnetic induction intensity, the efficiency is 40% and the amplification gain is 60 dB. In the experiment, a 0.99 GW averaged microwave power is generated with 550 kV electron beam voltage, 5.1 kA current, the efficiency is 35% and the amplification gain is 53 dB.
Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
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Corrected proofs
, Available online ,
doi: 10.11884/HPLPB202133.200173
Abstract:
Laser fusion, likely the ultimate solution to the crisis of human energy, is highly valued by the international community and has always been the focus of international research. It turns out that the biggest scientific obstacle of laser fusion is the effective control of the high-energy-density nonlinear flows during implosions. The research of high-energy-density nonlinear flows covers many different fields, such as high-energy-density physics, plasma physics, fluid mechanics, computing science, strong impact physics, and high pressure atomic physics, meanwhile, the capability of multi-material and multi-scale numerical simulations as well as large laser facility with high output power is also needed. As an emerging research filed, it is full of all kinds of novel phenomena to be explored. In addition, hydrodynamic instabilities and the subsequent turbulent mixing in high-energy-density flows, are also important processes in astrophysical phenomena (e.g., galaxy collision and merging, stellar evolution, formation of protostars and supernova explosion) and involve with the core content of astrophysics. In this paper, firstly, the status and progress, as well as the challenges and opportunities of high-energy-density nonlinear flows research are reviewed. Secondly, hydrodynamic instabilities during implosions in central ignition laser fusion are introduced, among which, key factors related to the bottleneck of implosion performance of the National Ignition Facility (NIF) in the United States are condensed. Next, the development of hydrodynamic instability experiments in laser fusion abroad is summarized. Finally, some keyachievements are listedon the fundamental issues of hydrodynamic instabilitiesby the laser fusion implosion physics team in China over the last three years. This team has been engaged in the research and control of nonlinear flowsin laser fusion implosions, as well as the research and design of target physics. A lot of improvements have been made in recent yearson the theoretical analysis andnumerical simulation of outstanding issues for hydrodynamic instabilities in laser fusion implosions, and the design and analysis of experiments on large lasers, which greatly promoted the development of this research direction in China.
Laser fusion, likely the ultimate solution to the crisis of human energy, is highly valued by the international community and has always been the focus of international research. It turns out that the biggest scientific obstacle of laser fusion is the effective control of the high-energy-density nonlinear flows during implosions. The research of high-energy-density nonlinear flows covers many different fields, such as high-energy-density physics, plasma physics, fluid mechanics, computing science, strong impact physics, and high pressure atomic physics, meanwhile, the capability of multi-material and multi-scale numerical simulations as well as large laser facility with high output power is also needed. As an emerging research filed, it is full of all kinds of novel phenomena to be explored. In addition, hydrodynamic instabilities and the subsequent turbulent mixing in high-energy-density flows, are also important processes in astrophysical phenomena (e.g., galaxy collision and merging, stellar evolution, formation of protostars and supernova explosion) and involve with the core content of astrophysics. In this paper, firstly, the status and progress, as well as the challenges and opportunities of high-energy-density nonlinear flows research are reviewed. Secondly, hydrodynamic instabilities during implosions in central ignition laser fusion are introduced, among which, key factors related to the bottleneck of implosion performance of the National Ignition Facility (NIF) in the United States are condensed. Next, the development of hydrodynamic instability experiments in laser fusion abroad is summarized. Finally, some keyachievements are listedon the fundamental issues of hydrodynamic instabilitiesby the laser fusion implosion physics team in China over the last three years. This team has been engaged in the research and control of nonlinear flowsin laser fusion implosions, as well as the research and design of target physics. A lot of improvements have been made in recent yearson the theoretical analysis andnumerical simulation of outstanding issues for hydrodynamic instabilities in laser fusion implosions, and the design and analysis of experiments on large lasers, which greatly promoted the development of this research direction in China.
Corrected proofs
, Available online ,
doi: 10.11884/HPLPB202133.200140
Abstract:
In laser indirect-drive inertial confinement fusion (ICF), the interaction of high-intensity laser and under-dense plasmas will excite two stimulated scattering processes: stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). These processes are detrimental to ignition since they consume laser energy, break symmetry of the X-ray radiation, and produce energetic electrons. Therefore, comprehending the basic physics of the stimulated scattering processes and hence finding effective approaches to suppress them are great concerns in ICF research. This article introduces several theoretical models developed by Chinese researchers for studying stimulated scattering processes, as well as their applications in analysis of experimental data. These theoretical models, together with the experiments, play important roles in improving the physical understanding of the stimulated scattering processes.
In laser indirect-drive inertial confinement fusion (ICF), the interaction of high-intensity laser and under-dense plasmas will excite two stimulated scattering processes: stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). These processes are detrimental to ignition since they consume laser energy, break symmetry of the X-ray radiation, and produce energetic electrons. Therefore, comprehending the basic physics of the stimulated scattering processes and hence finding effective approaches to suppress them are great concerns in ICF research. This article introduces several theoretical models developed by Chinese researchers for studying stimulated scattering processes, as well as their applications in analysis of experimental data. These theoretical models, together with the experiments, play important roles in improving the physical understanding of the stimulated scattering processes.
Corrected proofs
, Available online ,
doi: 10.11884/HPLPB202133.200137
Abstract:
Hydrogen is the most abundant element in nature and an important object of astrophysics and ICF research. This paper briefly presents an overview of the research progress in wide-range equation of state and especially comments assessment of the most recent shock compression experiments on Omega laser facility and the theoretical models. Based on the previous work, the wide-range equation of state of hydrogen is constructed by using the improved chemical free energy model, the first-principle numerical simulation results and the multi-parameter equation of state model, which is applicable in the temperature range of 20−108 K and the density range of 10−7−2000 g/cm3. Compared with experimental results, such as those of shock compression experiment, static high pressure isotherm experiment and sound velocity experiment, the newly-constructed wide-range equation of state for hydrogen has high confidence and provides high precision data for astrophysics, inertial confinement fusion, international thermonuclear experimental reactor and other engineering physics designs. The construction and validation method of the hydrogen wide-range equation of state can also be applied to its isotope deuterium. In comparison with current models published abroad, the deuterium wide-range equation of state constructed by this method is in better agreement with the experimental data of principal and secondary Hugoniot published in 2019. This paper also points out the temperature-density regimesthat need attention in future research.
Hydrogen is the most abundant element in nature and an important object of astrophysics and ICF research. This paper briefly presents an overview of the research progress in wide-range equation of state and especially comments assessment of the most recent shock compression experiments on Omega laser facility and the theoretical models. Based on the previous work, the wide-range equation of state of hydrogen is constructed by using the improved chemical free energy model, the first-principle numerical simulation results and the multi-parameter equation of state model, which is applicable in the temperature range of 20−108 K and the density range of 10−7−2000 g/cm3. Compared with experimental results, such as those of shock compression experiment, static high pressure isotherm experiment and sound velocity experiment, the newly-constructed wide-range equation of state for hydrogen has high confidence and provides high precision data for astrophysics, inertial confinement fusion, international thermonuclear experimental reactor and other engineering physics designs. The construction and validation method of the hydrogen wide-range equation of state can also be applied to its isotope deuterium. In comparison with current models published abroad, the deuterium wide-range equation of state constructed by this method is in better agreement with the experimental data of principal and secondary Hugoniot published in 2019. This paper also points out the temperature-density regimesthat need attention in future research.
Corrected proofs
, Available online ,
doi: 10.11884/HPLPB202133.200128
Abstract:
The pinch devices based on pulsed power technique can produce extreme conditions of temperature, pressure, density and strong radiation in spatial scale of cm and time scale of 100 ns. Numerous high energy density physics experiments are carried out on the 10 MA level pulsed power facility constructed at Institute of Fluid Physics, CAEP, which utilize a wide range of load configurations. Z-pinch driven dynamic hohlraums produce high temperature radiation field required for conducting inertial confinement fusion (ICF) experiments. Characteristics of implosion dynamics of metallic foils and solid liners are investigated and presented. Implosions using medium and low Z materials produce considerable K-shell line emissions, which are used to perform X-ray thermo-mechanical effect experiments. Magnetically driven isentropic compression and shock loading provide new experimental capabilities for research on dynamic materials properties. Ring diodes and reflex triodes are adopted to produce large X-ray or gamma-ray dose (rate) from bremsstrahlung. Magnetically driven radial metallic foils are used to simulate the formation of stellar jets and its radiation relevant to astrophysics. Additionally, experimental results of formation of preheated magnetized plasma target on a field reverse configuration (FRC) magnetized target fusion device are presented.
The pinch devices based on pulsed power technique can produce extreme conditions of temperature, pressure, density and strong radiation in spatial scale of cm and time scale of 100 ns. Numerous high energy density physics experiments are carried out on the 10 MA level pulsed power facility constructed at Institute of Fluid Physics, CAEP, which utilize a wide range of load configurations. Z-pinch driven dynamic hohlraums produce high temperature radiation field required for conducting inertial confinement fusion (ICF) experiments. Characteristics of implosion dynamics of metallic foils and solid liners are investigated and presented. Implosions using medium and low Z materials produce considerable K-shell line emissions, which are used to perform X-ray thermo-mechanical effect experiments. Magnetically driven isentropic compression and shock loading provide new experimental capabilities for research on dynamic materials properties. Ring diodes and reflex triodes are adopted to produce large X-ray or gamma-ray dose (rate) from bremsstrahlung. Magnetically driven radial metallic foils are used to simulate the formation of stellar jets and its radiation relevant to astrophysics. Additionally, experimental results of formation of preheated magnetized plasma target on a field reverse configuration (FRC) magnetized target fusion device are presented.
Corrected proofs
, Available online ,
doi: 10.11884/HPLPB202032.200125
Abstract:
The issue of laser plasma instabilities (LPIs) including stimulated Raman scattering, stimulated Brillouin scattering and so on is one of the most fascinating subjects in laser plasma physics. In particular, LPIs may cause significant laser energy loss and produce hot electrons to preheat fusion targets, which affect target compression and fusion energy gain in laser-driven inertial confinement fusion. Recent experiments carried out on the National Ignition Facility, the largest laser facility in the world for laser fusion, indicate that the understanding and the control of LPIs are essential to the realization of laser fusion. In this paper, we present a review on recent studies of LPIs. Firstly, we retrospect the classical theoretical model of LPIs, which offers a good estimation of growth rate in the linear development stage. Then, we discuss some progresses on the understanding of LPIs in more complex and real scenarios, such as LPI development in the nonlinear regions, cascaded LPIs, multi-beam LPIs, and nonlinear couplings between LPIs. Following the exploration of LPI physics, we emphasize on the strategies for the control of LPIs, including beam smoothing techniques, temporal profile shaping, broadband laser, laser polarization rotation, external magnetic field and so on.
The issue of laser plasma instabilities (LPIs) including stimulated Raman scattering, stimulated Brillouin scattering and so on is one of the most fascinating subjects in laser plasma physics. In particular, LPIs may cause significant laser energy loss and produce hot electrons to preheat fusion targets, which affect target compression and fusion energy gain in laser-driven inertial confinement fusion. Recent experiments carried out on the National Ignition Facility, the largest laser facility in the world for laser fusion, indicate that the understanding and the control of LPIs are essential to the realization of laser fusion. In this paper, we present a review on recent studies of LPIs. Firstly, we retrospect the classical theoretical model of LPIs, which offers a good estimation of growth rate in the linear development stage. Then, we discuss some progresses on the understanding of LPIs in more complex and real scenarios, such as LPI development in the nonlinear regions, cascaded LPIs, multi-beam LPIs, and nonlinear couplings between LPIs. Following the exploration of LPI physics, we emphasize on the strategies for the control of LPIs, including beam smoothing techniques, temporal profile shaping, broadband laser, laser polarization rotation, external magnetic field and so on.
Display Method:
2020, 32: 092001.
doi: 10.11884/HPLPB202032.200174
Abstract:
An ultra-short ultra-intense laser can excite high-amplitude electron plasma waves or so called laser wakefields when it propagates in under-dense gas plasma. A laser wakefield accelerator makes use of such waves to accelerate charged particles (especially electrons and positrons). These plasma waves can sustain longitudinal acceleration fields over three orders of magnitude higher than conventional radio frequency accelerators. This new type of laser-driven plasma-based accelerator opens the way for compact particle accelerators and radiation sources. It also has the potential to be applied for the construction of future ultra-high energy TeV electron-positron colliders and free electron lasers. In this paper, the principle, characteristics and development history of this new accelerator, especially the main progress in the past ten years, the future development trend and the main challenges will be briefly reviewed and introduced.
An ultra-short ultra-intense laser can excite high-amplitude electron plasma waves or so called laser wakefields when it propagates in under-dense gas plasma. A laser wakefield accelerator makes use of such waves to accelerate charged particles (especially electrons and positrons). These plasma waves can sustain longitudinal acceleration fields over three orders of magnitude higher than conventional radio frequency accelerators. This new type of laser-driven plasma-based accelerator opens the way for compact particle accelerators and radiation sources. It also has the potential to be applied for the construction of future ultra-high energy TeV electron-positron colliders and free electron lasers. In this paper, the principle, characteristics and development history of this new accelerator, especially the main progress in the past ten years, the future development trend and the main challenges will be briefly reviewed and introduced.
2020, 32: 092002.
doi: 10.11884/HPLPB202032.200090
Abstract:
Laser-driven ion acceleration is a frontier of laser plasma physics which has been developed in recent decades. Energetic ion beam generated in the interaction of laser and matter has unique properties such as high brilliance, compact size, ultra-short duration, and low emittance. These advantages are particularly suitable for many potential applications. This paper describes the main physical mechanism of ion acceleration driven by ultrashort laser. It reviews the progress of a series of laser-driven ion acceleration experiments. At last, it provides a brief introduction of several potential applications of laser-driven ion sources.
Laser-driven ion acceleration is a frontier of laser plasma physics which has been developed in recent decades. Energetic ion beam generated in the interaction of laser and matter has unique properties such as high brilliance, compact size, ultra-short duration, and low emittance. These advantages are particularly suitable for many potential applications. This paper describes the main physical mechanism of ion acceleration driven by ultrashort laser. It reviews the progress of a series of laser-driven ion acceleration experiments. At last, it provides a brief introduction of several potential applications of laser-driven ion sources.
2020, 32: 092003.
doi: 10.11884/HPLPB202032.200123
Abstract:
Laboratory astrophysics came into being with the advent of modern high-energy density physics research devices that can be used to create extreme physical conditions in the laboratory similar to those of certain celestial bodies or their surroundings, such as high-power lasers or pinch devices to generate extreme astrophysical plasma conditions. Such experimental conditions are unprecedented and correspond directly to many important and critical physical phenomena in astrophysics. They enable people to study the problems with astrophysical background in the laboratory in a close, active and controllable way. This paper introduces the latest progress in this field in recent years, and presents perspectives on future research directions.
Laboratory astrophysics came into being with the advent of modern high-energy density physics research devices that can be used to create extreme physical conditions in the laboratory similar to those of certain celestial bodies or their surroundings, such as high-power lasers or pinch devices to generate extreme astrophysical plasma conditions. Such experimental conditions are unprecedented and correspond directly to many important and critical physical phenomena in astrophysics. They enable people to study the problems with astrophysical background in the laboratory in a close, active and controllable way. This paper introduces the latest progress in this field in recent years, and presents perspectives on future research directions.
2020, 32: 092004.
doi: 10.11884/HPLPB202032.200130
Abstract:
Currently, laboratory created energy density of laser-driven inertial confinement fusion (ICF) is extremely close to that for ignition, while the divergence between experiment and simulation is increasing. One of the key issues is the lack of advanced knowledge of laser-hohlraum coupling process, which has shown the complexity of hohlraum environment. Optical Thomson scattering (OTS) becomes the standard technique for diagnosing the ICF hohlraum plasma parameters, due to its capability of providing unperturbed, local and precise measurement. The development of OTS in China is closely related with the Shenguang series laser facilities, on which most of the ICF experiments are carried out. In recent years, 4ω(263 nm) Thomson scattering technique has been set up on Shenguang-III prototype and 100 kJ-level laser facility, the corresponding results help the understanding of ICF physics. In the near future, several novel methods will be developed, for high-precision diagnostics of ICF ignition hohlraum plasmas and the research of new physical phenomena.
Currently, laboratory created energy density of laser-driven inertial confinement fusion (ICF) is extremely close to that for ignition, while the divergence between experiment and simulation is increasing. One of the key issues is the lack of advanced knowledge of laser-hohlraum coupling process, which has shown the complexity of hohlraum environment. Optical Thomson scattering (OTS) becomes the standard technique for diagnosing the ICF hohlraum plasma parameters, due to its capability of providing unperturbed, local and precise measurement. The development of OTS in China is closely related with the Shenguang series laser facilities, on which most of the ICF experiments are carried out. In recent years, 4ω(263 nm) Thomson scattering technique has been set up on Shenguang-III prototype and 100 kJ-level laser facility, the corresponding results help the understanding of ICF physics. In the near future, several novel methods will be developed, for high-precision diagnostics of ICF ignition hohlraum plasmas and the research of new physical phenomena.
2020, 32: 092005.
doi: 10.11884/HPLPB202032.200094
Abstract:
The fast Z-pinch can highly efficiently convert the electrical energy stored in the pulsed power generator to X-ray radiation, creating high temperature, high density and high pressure environments. Significant progress in Z-pinch driven inertial confinement fusion and high energy density physics have been achieved in the last two decades. This paper outlines researches in indirect radiation driven fusion and magnetically direct driven fusion briefly, and introduces recent works on the dynamic hohlraum and the relative radiation source experiments on the 7−8 MA facility in China. It reviews progress of several Z-pinch applications in high energy density physics, such as the radiation-material interaction, opacity, dynamic material, laboratory astrophysics, as well as other domains. The paper also expects futher researches and developments of Z-pinch driven fusion and the corresponding applications in high energy density physics in China.
The fast Z-pinch can highly efficiently convert the electrical energy stored in the pulsed power generator to X-ray radiation, creating high temperature, high density and high pressure environments. Significant progress in Z-pinch driven inertial confinement fusion and high energy density physics have been achieved in the last two decades. This paper outlines researches in indirect radiation driven fusion and magnetically direct driven fusion briefly, and introduces recent works on the dynamic hohlraum and the relative radiation source experiments on the 7−8 MA facility in China. It reviews progress of several Z-pinch applications in high energy density physics, such as the radiation-material interaction, opacity, dynamic material, laboratory astrophysics, as well as other domains. The paper also expects futher researches and developments of Z-pinch driven fusion and the corresponding applications in high energy density physics in China.
2020, 32: 092006.
doi: 10.11884/HPLPB202032.200121
Abstract:
With the establishment of high-power laser facilities and the development of precise measurement technology, the interaction between high-power lasers and solids has become an important path to generate warm dense matter in laboratories. The structural complexity, transients and non-equilibrium of warm dense matter have brought great challenges to theoretical modeling and experimental measurements. This paper systematically reviews the important advances in the experimental methods and theoretical simulation methods in laser-generating warm dense matter, analyzes the physical processes such as electron excitation dynamics, electron-ion energy relaxation, and ionic dynamics. It summarizes the experimental techniques and theoretical methods of state diagnosis of warm dense matter, and discusses the development trend of laser-generating warm dense matter.
With the establishment of high-power laser facilities and the development of precise measurement technology, the interaction between high-power lasers and solids has become an important path to generate warm dense matter in laboratories. The structural complexity, transients and non-equilibrium of warm dense matter have brought great challenges to theoretical modeling and experimental measurements. This paper systematically reviews the important advances in the experimental methods and theoretical simulation methods in laser-generating warm dense matter, analyzes the physical processes such as electron excitation dynamics, electron-ion energy relaxation, and ionic dynamics. It summarizes the experimental techniques and theoretical methods of state diagnosis of warm dense matter, and discusses the development trend of laser-generating warm dense matter.
2020, 32: 092007.
doi: 10.11884/HPLPB202032.200134
Abstract:
In the study of inertial confinement fusion physics, the characteristics, temporal and spatial evolution of kinetic effects at the plasma interfaces attract crucial interest recently because they can affect the laser energy deposition, laser plasma instabilities, radiation asymmetry and implosion performance. A successful design of inertial confinement fusion requires the accurate description of the temporal and spatial evolution of the kinetic effects at the plasma interfaces, which is also a very challenging and unresolved problem in high energy density physics. In this paper, we will review our recent researches on the kinetic effects and their influence on laser plasma instabilities and implosion performance: (1) Electrostatic field arisen in the hohlraum wall/ablator (or the low-density fill-gas) interpenetration region will result in efficient acceleration of high energy ions, which is a source of the low-mode asymmetry of the implosion capsule. (2) The mechanism for the electrostatic field generation and the anomalous mix in the interpenetration layer at the high-Z and low-Z plasma interface and its effects on the laser plasma instabilities. (3) Reconstruction of the spontaneous electric and magnetic fields through proton radiography.
In the study of inertial confinement fusion physics, the characteristics, temporal and spatial evolution of kinetic effects at the plasma interfaces attract crucial interest recently because they can affect the laser energy deposition, laser plasma instabilities, radiation asymmetry and implosion performance. A successful design of inertial confinement fusion requires the accurate description of the temporal and spatial evolution of the kinetic effects at the plasma interfaces, which is also a very challenging and unresolved problem in high energy density physics. In this paper, we will review our recent researches on the kinetic effects and their influence on laser plasma instabilities and implosion performance: (1) Electrostatic field arisen in the hohlraum wall/ablator (or the low-density fill-gas) interpenetration region will result in efficient acceleration of high energy ions, which is a source of the low-mode asymmetry of the implosion capsule. (2) The mechanism for the electrostatic field generation and the anomalous mix in the interpenetration layer at the high-Z and low-Z plasma interface and its effects on the laser plasma instabilities. (3) Reconstruction of the spontaneous electric and magnetic fields through proton radiography.
2020, 32: 092008.
doi: 10.11884/HPLPB202032.200139
Abstract:
In order to carry out scientific research on the properties of materials under extremely high pressure conditions, a series of laser-driven high pressure loading technology based on Hügoniot, quasi-isentropic compression and “shock+quasi-isentropic” composite thermodynamic path compression have been developed on 10 kJ-level laser facility. The practical high-pressure loading design method has been established and optimization research on planarity, cleanness of compression wave has been performed. High-pressure state generation capability in wide parameter area which covers from above 1011 Pa of quasi-isentropic compression to above 1012 Pa of Hügoniot compression has been implemented, which provides an important technical foundation for the study of the high-pressure state equation and phase transition dynamics on the laser device.
In order to carry out scientific research on the properties of materials under extremely high pressure conditions, a series of laser-driven high pressure loading technology based on Hügoniot, quasi-isentropic compression and “shock+quasi-isentropic” composite thermodynamic path compression have been developed on 10 kJ-level laser facility. The practical high-pressure loading design method has been established and optimization research on planarity, cleanness of compression wave has been performed. High-pressure state generation capability in wide parameter area which covers from above 1011 Pa of quasi-isentropic compression to above 1012 Pa of Hügoniot compression has been implemented, which provides an important technical foundation for the study of the high-pressure state equation and phase transition dynamics on the laser device.
2020, 32: 092009.
doi: 10.11884/HPLPB202032.200122
Abstract:
The nonlinear evolution of stimulated Brillouin scattering (SBS) in inhomogeneous flowing plasmas is self-consistently investigated by the Vlasov-Maxwell simulations. In the physical regime where ion trapping is dominant, simulations show that the evolution of SBS includes a linear convective stage and a nonlinear stage. In the linear stage, the reflectivity is in good agreement with the theoretical prediction from the Rosenbluth gain. In the nonlinear stage, the reflectivity shows a continuous increase and becomes much larger than the theoretical value. And the auto-resonant growing of ion acoustic wave (IAW) shows a nature of absolute instability, which can be explained as the compensation of the negative kinetic frequency shift from trapped ions and the detuning due to the flow velocity gradient. Methods using the incoherence in the pump waves to mitigate the enhanced SBS are proposed. The saturation of SBS by the decay to solitary turbulence of the IAW is demonstrated in the fluid dominant regime. The formation of solitary structures is due to the generation of harmonics of IAW.
The nonlinear evolution of stimulated Brillouin scattering (SBS) in inhomogeneous flowing plasmas is self-consistently investigated by the Vlasov-Maxwell simulations. In the physical regime where ion trapping is dominant, simulations show that the evolution of SBS includes a linear convective stage and a nonlinear stage. In the linear stage, the reflectivity is in good agreement with the theoretical prediction from the Rosenbluth gain. In the nonlinear stage, the reflectivity shows a continuous increase and becomes much larger than the theoretical value. And the auto-resonant growing of ion acoustic wave (IAW) shows a nature of absolute instability, which can be explained as the compensation of the negative kinetic frequency shift from trapped ions and the detuning due to the flow velocity gradient. Methods using the incoherence in the pump waves to mitigate the enhanced SBS are proposed. The saturation of SBS by the decay to solitary turbulence of the IAW is demonstrated in the fluid dominant regime. The formation of solitary structures is due to the generation of harmonics of IAW.
2020, 32: 092010.
doi: 10.11884/HPLPB202032.200111
Abstract:
For ignition and high fusion gain, it’s the key issue to achieve high implosion velocity in inertial confinement fusion. The important implosion dynamics quantities like implosion velocity and residual mass can be diagnosed by implosion ablated convergence measurement. The measured results will be used to modify the point design, optimizing the ablator materials, thickness and laser pulse profiles. In recent years, we demonstrated the conventional implosion ablated convergence measurement on Shenguang laser facilities with the slit imaging technique. The high spatial resolution monochromatic imaging technique based on the spherically bent crystal was developed and used for the implosion ablated convergence measurement. With the continuing improvements of the imaging system and the modification of the diagnostics, a high spatial resolution implosion trajectory diagnosis has been implemented. The implosion velocities are measured with high precision while the uncertainties are not greater than 2.1%.
For ignition and high fusion gain, it’s the key issue to achieve high implosion velocity in inertial confinement fusion. The important implosion dynamics quantities like implosion velocity and residual mass can be diagnosed by implosion ablated convergence measurement. The measured results will be used to modify the point design, optimizing the ablator materials, thickness and laser pulse profiles. In recent years, we demonstrated the conventional implosion ablated convergence measurement on Shenguang laser facilities with the slit imaging technique. The high spatial resolution monochromatic imaging technique based on the spherically bent crystal was developed and used for the implosion ablated convergence measurement. With the continuing improvements of the imaging system and the modification of the diagnostics, a high spatial resolution implosion trajectory diagnosis has been implemented. The implosion velocities are measured with high precision while the uncertainties are not greater than 2.1%.
