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RSS2020 Vol. 32, No. 10
Recommend Articles
2020, 32: 103001.
doi: 10.11884/HPLPB202032.200228
2020, 32: 103003.
doi: 10.11884/HPLPB202032.200195
column
- Cover and Contents
- Feature Issue on Klystron Amplifier
- High Power Laser Physics and Technology•Research Letter
- High Power Laser Physics and Technology
- Inertial Confinement Fusion Physics and Technology
- High Power Microwave Technology
- Particle Beams and Accelerator Technology
- Pulsed Power Technology
- Nuclear Science and Engineering
Display Method:
2020,
32: 1-2.
2020,
32: 1-1.
2020,
32: 103001.
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 became 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 became saturated.
2020,
32: 103002.
doi: 10.11884/HPLPB202032.200167
Abstract:
To improve the stability of frequency and phase of the output microwave on condition of repetitive operation, an S-band, long-pulse relativistic klystron amplifier (RKA) is investigated by theoretical modeling, numerical simulation and experimental measurement. Description and analysis are made on the physical origins of self-oscillation, output microwave pulse shortening, the instability in the repetitive operation and the phase fluctuation of output microwave in the RKA. Measures are taken to solve or alleviate these problems, which are demonstrated by the simulation and experiment. It is confirmed that the electrons reflected from the gaps of idler cavity and output cavity of RKA result in the self-oscillation and the output microwave pulse shortening, and the electron dispersion and bombardment on the noses of the output cavity and idler cavity affect the stability of repetitive operation. It is validated that enlarging the drifting tube radius, adding some microwave absorber in the drifting tube between those cavities and optimizing the structure of the input cavity, output cavity and collector of the electron beams can alleviate the problem of self-oscillation and pulse shortening obviously and improve the stability of repetitive operation and phase fluctuation of output microwave. Using an 830 kV, 7.7 kA, 190 ns electron beam and an input microwave of 80 kW, an output power of 1.55 GW, pulse width of 163 ns, and phase fluctuation of 18° are generated by the S-band three-cavity RKA operating at 25 Hz.
To improve the stability of frequency and phase of the output microwave on condition of repetitive operation, an S-band, long-pulse relativistic klystron amplifier (RKA) is investigated by theoretical modeling, numerical simulation and experimental measurement. Description and analysis are made on the physical origins of self-oscillation, output microwave pulse shortening, the instability in the repetitive operation and the phase fluctuation of output microwave in the RKA. Measures are taken to solve or alleviate these problems, which are demonstrated by the simulation and experiment. It is confirmed that the electrons reflected from the gaps of idler cavity and output cavity of RKA result in the self-oscillation and the output microwave pulse shortening, and the electron dispersion and bombardment on the noses of the output cavity and idler cavity affect the stability of repetitive operation. It is validated that enlarging the drifting tube radius, adding some microwave absorber in the drifting tube between those cavities and optimizing the structure of the input cavity, output cavity and collector of the electron beams can alleviate the problem of self-oscillation and pulse shortening obviously and improve the stability of repetitive operation and phase fluctuation of output microwave. Using an 830 kV, 7.7 kA, 190 ns electron beam and an input microwave of 80 kW, an output power of 1.55 GW, pulse width of 163 ns, and phase fluctuation of 18° are generated by the S-band three-cavity RKA operating at 25 Hz.
2020,
32: 103003.
doi: 10.11884/HPLPB202032.200195
Abstract:
High power generation in terahertz frequency band is limited by physical mechanism. 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. 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 show that more than 500 W of power output can be obtained with the actual cavity loss considered, and the electron efficiency and gain are 3.65% and 38.2 dB respectively. It is found that the power and efficiency are 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. 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. 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 show that more than 500 W of power output can be obtained with the actual cavity loss considered, and the electron efficiency and gain are 3.65% and 38.2 dB respectively. It is found that the power and efficiency are 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.
2020,
32: 103004.
doi: 10.11884/HPLPB202032.200188
Abstract:
To meet the high power and high gain requirements in engineering applications, we've designed a three-dimensional whole tube model for an X-band high-power high-gain multi-beam relativistic klystron amplifier. This paper presents the high frequency characteristic analysis and the tube with the integrated model. 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. A 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 average microwave power was generated with 550 kV electron beam voltage, 5.1 kA current, 35% efficiency and 53 dB amplification gain.
To meet the high power and high gain requirements in engineering applications, we've designed a three-dimensional whole tube model for an X-band high-power high-gain multi-beam relativistic klystron amplifier. This paper presents the high frequency characteristic analysis and the tube with the integrated model. 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. A 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 average microwave power was generated with 550 kV electron beam voltage, 5.1 kA current, 35% efficiency and 53 dB amplification gain.
2020,
32: 103005.
doi: 10.11884/HPLPB202032.200202
Abstract:
This paper introduces the development of a new ultra-wideband (relative bandwidth ≥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, 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 peak power 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 3 ms pulse length and continuous 24 h of steady work have been realized. To achieve full power output with in 3 min and 2000 h life time, 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 introduces the development of a new ultra-wideband (relative bandwidth ≥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, 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 peak power 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 3 ms pulse length and continuous 24 h of steady work have been realized. To achieve full power output with in 3 min and 2000 h life time, 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.
2020,
32: 103006.
doi: 10.11884/HPLPB202032.200227
Abstract:
High-frequency relativistic klystron amplifier is one of the 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. This paper presents the design of a novel Ku-band radial-line klystron amplifier, which consists of an input cavity, two groups of double-gap bunching cavities and a three-gap extraction cavity. By comparing the coupling coefficient of single-gap bunching cavity with that 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 a 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. PIC simulationshows that 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 microwaves with frequency of 14.25 GHz and output power of 825 MW are obtained.
High-frequency relativistic klystron amplifier is one of the 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. This paper presents the design of a novel Ku-band radial-line klystron amplifier, which consists of an input cavity, two groups of double-gap bunching cavities and a three-gap extraction cavity. By comparing the coupling coefficient of single-gap bunching cavity with that 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 a 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. PIC simulationshows that 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 microwaves with frequency of 14.25 GHz and output power of 825 MW are obtained.
2020,
32: 103007.
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 five 5-gap buncher cavities and one 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 the 5-gap (or 11-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 duty cycle of 5%.
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 five 5-gap buncher cavities and one 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 the 5-gap (or 11-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 duty cycle of 5%.
2020,
32: 103008.
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 region. 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 region. 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.
2020,
32: 103009.
doi: 10.11884/HPLPB202032.200193
Abstract:
This paper proposes a Ka-band coaxial multi-gap cavity operating in the TM51-2π mode. 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 studies the start-oscillation characteristics of the high-order mode coaxial multi-gap cavity using the multi-beam excitation method. And it analyzes the mode stability and beam-wave interaction characteristics of the coaxial multi-gap cavity operating in the high-order mode. 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 proposes a Ka-band coaxial multi-gap cavity operating in the TM51-2π mode. 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 studies the start-oscillation characteristics of the high-order mode coaxial multi-gap cavity using the multi-beam excitation method. And it analyzes the mode stability and beam-wave interaction characteristics of the coaxial multi-gap cavity operating in the high-order mode. 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.
2020,
32: 103010.
doi: 10.11884/HPLPB202032.200171
Abstract:
This paper applies the theory of kinematics and space charge wave to conclude an experiential formula for calculating the phase of the modulated current at the entrance of the gap of the middle cavity. It also applies a nonlinear theory of cavity excitation by modulated electron beam to calculate the amplitude and the phase of the gap voltage of the middle cavity and the output cavity, and presents an experimential formula for calculating the phase of the modulated current at the entrance of the gap of the output cavity. With these theories and 2D PIC, it estimates the phase of the modulated current at the entrance of the gap of the middle cavity and the output cavity as well as the amplitude and the phase of gap voltage in the middle cavity and the output cavity. The errors of the phase of the modulated current at the entrance of the gap of the middle cavity and the output cavity are 2.627° (model 1) and 3.857° (model 2); the relativistic errors of the amplitude of gap voltage in the middle cavity and the output cavity are 1.47% and 5.42%, the error of the phase of gap voltage in the middle cavity are 4.017° (model 2) and 5.427° (model 3), and the error of the phase of gap voltage in the output cavity is 12.32°. Finally, the paper analyzes the phase of the modulated current versus the propagation distance in three models by 2D PIC simulation.
This paper applies the theory of kinematics and space charge wave to conclude an experiential formula for calculating the phase of the modulated current at the entrance of the gap of the middle cavity. It also applies a nonlinear theory of cavity excitation by modulated electron beam to calculate the amplitude and the phase of the gap voltage of the middle cavity and the output cavity, and presents an experimential formula for calculating the phase of the modulated current at the entrance of the gap of the output cavity. With these theories and 2D PIC, it estimates the phase of the modulated current at the entrance of the gap of the middle cavity and the output cavity as well as the amplitude and the phase of gap voltage in the middle cavity and the output cavity. The errors of the phase of the modulated current at the entrance of the gap of the middle cavity and the output cavity are 2.627° (model 1) and 3.857° (model 2); the relativistic errors of the amplitude of gap voltage in the middle cavity and the output cavity are 1.47% and 5.42%, the error of the phase of gap voltage in the middle cavity are 4.017° (model 2) and 5.427° (model 3), and the error of the phase of gap voltage in the output cavity is 12.32°. Finally, the paper analyzes the phase of the modulated current versus the propagation distance in three models by 2D PIC simulation.
2020,
32: 101001.
doi: 10.11884/HPLPB202032.200143
Abstract:
This paper demonstrates an all-fiber high-power Yb-doped 1064 nm fiber laser based on master oscillator power amplifier structure. The record output power up to 2625 W was achieved, along with a slope efficiency of 76%. The beam quality factor is Mx2＝1.273, My2＝1.255, and full width at half maximum is 21.7 GHz at maximum power level. The fiber laser has the highest output power of all-fiber lasers with 22 GHz linewidth.
2020,
32: 101002.
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. For the laser at T = 3%, the maximum output power of 98 mW was received under the pump power of 6.70 W, with the shortest pulse width of 436 ns and the pulse repetition rate of 206 kHz. 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. For the laser at T = 3%, the maximum output power of 98 mW was received under the pump power of 6.70 W, with the shortest pulse width of 436 ns and the pulse repetition rate of 206 kHz. 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.
2020,
32: 102001.
doi: 10.11884/HPLPB202032.200217
Abstract:
The theoretical analysis method is used to calculate the adsorption behavior of water molecules on the surface of lithium hydride, and analyze the influence of surface modification of lithium hydride on its hydrophobic performance. The results show that after constructing groove structure and columnar structure on LiH-111 surface and LiH-100 surface, the adsorption force to water molecules of the modified surface is stronger than that of the complete surface, indicating that the introduction of surface microstructure does change the potential energy distribution. There is a superposition of potential energy at the intersection of the walls, which strengthens the ability to adsorb water molecules, but does not cause changes in the hydrophilic properties of the surface. Water molecules can be stably adsorbed on the perfect LiH (001) surface, and its dissociation energy barrier is only 0.386 eV. This dissociation reaction can be carried out at room temperature. Water molecules are easily dissociated on the LiH surface with structural defects, which is the fundamental reason why LiH decomposes easily in a certain humidity air and water environment.
The theoretical analysis method is used to calculate the adsorption behavior of water molecules on the surface of lithium hydride, and analyze the influence of surface modification of lithium hydride on its hydrophobic performance. The results show that after constructing groove structure and columnar structure on LiH-111 surface and LiH-100 surface, the adsorption force to water molecules of the modified surface is stronger than that of the complete surface, indicating that the introduction of surface microstructure does change the potential energy distribution. There is a superposition of potential energy at the intersection of the walls, which strengthens the ability to adsorb water molecules, but does not cause changes in the hydrophilic properties of the surface. Water molecules can be stably adsorbed on the perfect LiH (001) surface, and its dissociation energy barrier is only 0.386 eV. This dissociation reaction can be carried out at room temperature. Water molecules are easily dissociated on the LiH surface with structural defects, which is the fundamental reason why LiH decomposes easily in a certain humidity air and water environment.
2020,
32: 103011.
doi: 10.11884/HPLPB202032.200225
Abstract:
Based on the fundamental principle oriented from the single beam klystron, multi-beam klystron can make higher peak output power under a lower working voltage with the help of parallel working mode combining several low perveance electron beams. Lower working voltage also makes 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 of the source power can shorten the linac tube dramatically, thus make the brand-new application scenarios possible such as the high-degree freedom cancer treatment or the compact nondestructive testing system. The C-band multi-beam klystron in this article mainly targets 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 higher peak output power under a lower working voltage with the help of parallel working mode combining several low perveance electron beams. Lower working voltage also makes 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 of the source power can shorten the linac tube dramatically, thus make the brand-new application scenarios possible such as the high-degree freedom cancer treatment or the compact nondestructive testing system. The C-band multi-beam klystron in this article mainly targets 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%).
2020,
32: 103012.
doi: 10.11884/HPLPB202032.200211
Abstract:
This paper introduces a technical scheme of X-band high peak power klystron. At present, this klystron has achieved 50 MW pulse output power and 57% efficiency at X band. The pulse width is up to 3.6 μs. By using some key techniques, such as COM method, circle waveguide travelling-wave window, Anticorona ring and coating thin film on ceramic, some problems such as high efficiency, high peak power capacity and high reliability are solved. In particular, COM method can be used to optimize electron beam bunching. Compared with the second harmonic bunching method, the interaction efficiency can be further improved by about 10% under the same length of high frequency tube body. Because of the successfully developed klystron, the peak power level of domestic X-band klystron has been raised from 3 MW to 50 MW, and the performance of the klystron has reached the international leading level.
This paper introduces a technical scheme of X-band high peak power klystron. At present, this klystron has achieved 50 MW pulse output power and 57% efficiency at X band. The pulse width is up to 3.6 μs. By using some key techniques, such as COM method, circle waveguide travelling-wave window, Anticorona ring and coating thin film on ceramic, some problems such as high efficiency, high peak power capacity and high reliability are solved. In particular, COM method can be used to optimize electron beam bunching. Compared with the second harmonic bunching method, the interaction efficiency can be further improved by about 10% under the same length of high frequency tube body. Because of the successfully developed klystron, the peak power level of domestic X-band klystron has been raised from 3 MW to 50 MW, and the performance of the klystron has reached the international leading level.
2020,
32: 103013.
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 time of the klystron. The size of millimeter wave klystron is small. 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 electron optical system designed can meet the requirement of 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 time of the klystron. The size of millimeter wave klystron is small. 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 electron optical system designed can meet the requirement of engineering realization of klystron.
2020,
32: 103014.
doi: 10.11884/HPLPB202032.200097
Abstract:
In this work, the response characteristics of the microwave limiter under various high power microwave irradiation are investigated via both simulation and experiment, and the simulation results match those of the experiment well. When the input power exceeds 6 dBm, a spike leakage phenomenon is observed. As the input power increases, the rise time and pulse width of the leakage peak decrease, whereas the leakage power gradually increases. However, the leakage power of the plateau firstly linearly increases, then gradually decreases, and finally slightly increases. Moreover, the pulse width and repetition frequency have almost no influence on the characteristics of leakage pulse, and the leakage energy decreases as the injection power increases.
In this work, the response characteristics of the microwave limiter under various high power microwave irradiation are investigated via both simulation and experiment, and the simulation results match those of the experiment well. When the input power exceeds 6 dBm, a spike leakage phenomenon is observed. As the input power increases, the rise time and pulse width of the leakage peak decrease, whereas the leakage power gradually increases. However, the leakage power of the plateau firstly linearly increases, then gradually decreases, and finally slightly increases. Moreover, the pulse width and repetition frequency have almost no influence on the characteristics of leakage pulse, and the leakage energy decreases as the injection power increases.
2020,
32: 103015.
doi: 10.11884/HPLPB202032.200226
Abstract:
In common medical/industrial linac systems, ordinary magnetron as the power source has been adopted for about 20 years. Despite of 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 have taken 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 engineering. To meet the demands from medical and industrial applications, high-power klystrons were developed for cancer treatment, nondestructive inspection and industrial irradiation. This paper introduces an X-band high-power multi-beam klystron with 3 MW output power at 9300 MHz. Compared with the magnetron power source, the linac cavity could be reduced by 30%. 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 common medical/industrial linac systems, ordinary magnetron as the power source has been adopted for about 20 years. Despite of 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 have taken 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 engineering. To meet the demands from medical and industrial applications, high-power klystrons were developed for cancer treatment, nondestructive inspection and industrial irradiation. This paper introduces an X-band high-power multi-beam klystron with 3 MW output power at 9300 MHz. Compared with the magnetron power source, the linac cavity could be reduced by 30%. 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.
2020,
32: 104001.
doi: 10.11884/HPLPB202032.200158
Abstract:
In BEPCⅡ, button BPM and stripline BPM cannot reach sufficient precise resolution for beam transverse displacement. This project aims at 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 direction and 2503 MHz in vertical direction. 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. Offline caliberation test results showed that CBPM has excellent measurement value of linearity area, which is over 10 mm. After frequency spectrum analysis and linear fitting, the position resolution of CBPM is 2.87 μm in horizontal direction and 2.16 μm in vertical direction.
In BEPCⅡ, button BPM and stripline BPM cannot reach sufficient precise resolution for beam transverse displacement. This project aims at 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 direction and 2503 MHz in vertical direction. 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. Offline caliberation test results showed that CBPM has excellent measurement value of linearity area, which is over 10 mm. After frequency spectrum analysis and linear fitting, the position resolution of CBPM is 2.87 μm in horizontal direction and 2.16 μm in vertical direction.
2020,
32: 104002.
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.
2020,
32: 105001.
doi: 10.11884/HPLPB202032.200114
Abstract:
Gas spark switch is the most commonly used key device in pulse power device. The difficult problem of electrode erosion, which affects the performance of gas spark switches, has always become a bottleneck restricting the development and application of gas switch. 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.
2020,
32: 105002.
doi: 10.11884/HPLPB202032.200102
Abstract:
This paper presents a solid-state pulse generator based on drift step recovery diode (DSRD) - a new high-power, ultra-fast semiconductor opening switch, and a 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 kΩ-resistive load with amplitude 38.2 kV, rise time 7.1 ns, pulse width 14.1 ns, output peak power 29.2kW, 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) - a new high-power, ultra-fast semiconductor opening switch, and a 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 kΩ-resistive load with amplitude 38.2 kV, rise time 7.1 ns, pulse width 14.1 ns, output peak power 29.2kW, and it could work stably at the repetition frequency of 400 kHz.
2020,
32: 105003.
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 caliber. Under the same cross-sectional area, the thickness of the additional rails should be reduced to increase the inductance gradient of the system, and the height of the additional rails should be reduced 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 caliber. Under the same cross-sectional area, the thickness of the additional rails should be reduced to increase the inductance gradient of the system, and the height of the additional rails should be reduced to alleviate the proximity effect. Concave cross-section additional rail can obviously improve the current proximity effect.
2020,
32: 106001.
doi: 10.11884/HPLPB202032.200118
Abstract:
Energy spectrum data analysis is the main source of nuclide identification. Aiming at the slow recognition speed and low accuracy of the emerging energy spectrum nuclide identification method in the noisy environment of mixed radionuclides, an energy spectrum nuclide recognition method based on long short-term memory neural network (LSTM) is proposed. In the experiment, a LaBr3 crystal detector was used to measure the 60Co and 137Cs radioactive sources in the environment to obtain a gamma spectrum data set. First, the experiment used data smoothing and normalization methods for data preprocessing. Then, the energy spectrum data was grouped in time series to obtain a usable input sequence array. Finally, the prediction results were 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 has performed well in the nuclide identification 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 slow recognition speed and low accuracy of the emerging energy spectrum nuclide identification method in the noisy environment of mixed radionuclides, an energy spectrum nuclide recognition method based on long short-term memory neural network (LSTM) is proposed. In the experiment, a LaBr3 crystal detector was used to measure the 60Co and 137Cs radioactive sources in the environment to obtain a gamma spectrum data set. First, the experiment used data smoothing and normalization methods for data preprocessing. Then, the energy spectrum data was grouped in time series to obtain a usable input sequence array. Finally, the prediction results were 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 has performed well in the nuclide identification and can be used in fast energy spectrum nuclide identification equipment.
2020,
32: 106002.
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 are fulfilled. The major in-pile performance of CF2 fuel assembly are studied on the basis 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, the growth of grid, etc. The results show that the major in-pile performance of the CF2 fuel assembly has reached the expectations, and the fuel has fulfilled the requirements of the 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 are fulfilled. The major in-pile performance of CF2 fuel assembly are studied on the basis 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, the growth of grid, etc. The results show that the major in-pile performance of the CF2 fuel assembly has reached the expectations, and the fuel has fulfilled the requirements of the reactor system.
