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RSS2021 Vol. 33, No. 2
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2021,
: 1-3.
2021,
33: 021001.
doi: 10.11884/HPLPB202133.200309
Abstract:
To enhance the thresholds of both stimulated Raman scattering and transverse mode instability, we proposed a novel active Yb-doped fiber with a spindle-shaped core and inner-cladding. An all-fiber main oscillator power amplifier (MOPA) was experimentally established based on this homemade fiber. A maximum power of 5 kW was achieved with the optical-to-optical efficiency of 66.6%, Raman-suppression ratio of ＞45 dB and M2 factor of about 2.0. We believe that the brightness and the efficiency of the laser can be improved by optimizing the structure of the Yb-doped fiber.
2021,
33: 021002.
doi: 10.11884/HPLPB202133.200305
Abstract:
An all-fiber supercontinuum generation system is built based on a long tapered photonic crystal fiber with small core diameter, large duty cycle and gragual core change. The system uses high power picoseconds seed source pumping to achieve 314.7 W high power supercontinuum output covering all visible light with spectrum coverage 388−2400 nm. It takes into account high power and blue shift enhancement in the shortwave direction at the same time, and it has the highest power of supercontinuum covering full visible spectrum publicly reported at home and abroad.
Experimental investigation of the package of diode laser chip based on lateral heat flow suppression
2021,
33: 021003.
doi: 10.11884/HPLPB202133.200241
Abstract:
To improve slow axis beam quality of diode laser (LD) and decrease slow axis divergence angle, a new package with lateral heat flow suppression was designed utilizing the difference in thermal conductivity between air and heat sink. The finite element analysis software was used to analyze the temperature distribution with lateral flow suppression package. It is shown that diode laser chip soldered on trough heat sink with width W=120 μm and length L=4000 μm can reduce slow axis divergence angle about 14%, from 12.25° to 10.49°, when working current was 15A. Correspondingly, beam parameter product (BPP) can reduce from 5.344 mm·mrad to 4.5763 mm·mrad and the brightness of slow axis increased about 5.5% than before. According to the result, the lateral flow suppression package can weaken higher order mode caused by thermal lens effect of diode laser so that decrease slow axis divergence angle effectively.
To improve slow axis beam quality of diode laser (LD) and decrease slow axis divergence angle, a new package with lateral heat flow suppression was designed utilizing the difference in thermal conductivity between air and heat sink. The finite element analysis software was used to analyze the temperature distribution with lateral flow suppression package. It is shown that diode laser chip soldered on trough heat sink with width W=120 μm and length L=4000 μm can reduce slow axis divergence angle about 14%, from 12.25° to 10.49°, when working current was 15A. Correspondingly, beam parameter product (BPP) can reduce from 5.344 mm·mrad to 4.5763 mm·mrad and the brightness of slow axis increased about 5.5% than before. According to the result, the lateral flow suppression package can weaken higher order mode caused by thermal lens effect of diode laser so that decrease slow axis divergence angle effectively.
2021,
33: 021004.
doi: 10.11884/HPLPB202133.200242
Abstract:
Structured light technology is a typical method for capturing the three-dimensional point cloud data of realistic objects. Structured light images are projected on the surface of the object, which are modulated by the height of the object. Then, the modulated structured light is captured by the camera. Finally, the triangulation principle is used to calculate the three-dimensional surface shape data. To scan the high-precision three-dimensional point cloud of the object, this paper proposes a structured light technology based on Gray code and six-step phase shift method. The structured light based on Gray code is composed of 7 black and white fringe periodic images, and the image can be divided into 128 areas through the gray code decoding operation; the structured light based on six-step phase shift is composed of 6 cosine periodic images with phase difference. Phase shift decoding can subdivide each of the 128 areas into a single pixel. Compared with the cumbersome calculation of six Moiré fringes, the proposed structured light technology based on six-step phase-shift method has less calculation. In the simulation experiment and actual test, the proposed structured light technology showed excellent performance.
Structured light technology is a typical method for capturing the three-dimensional point cloud data of realistic objects. Structured light images are projected on the surface of the object, which are modulated by the height of the object. Then, the modulated structured light is captured by the camera. Finally, the triangulation principle is used to calculate the three-dimensional surface shape data. To scan the high-precision three-dimensional point cloud of the object, this paper proposes a structured light technology based on Gray code and six-step phase shift method. The structured light based on Gray code is composed of 7 black and white fringe periodic images, and the image can be divided into 128 areas through the gray code decoding operation; the structured light based on six-step phase shift is composed of 6 cosine periodic images with phase difference. Phase shift decoding can subdivide each of the 128 areas into a single pixel. Compared with the cumbersome calculation of six Moiré fringes, the proposed structured light technology based on six-step phase-shift method has less calculation. In the simulation experiment and actual test, the proposed structured light technology showed excellent performance.
2021,
33: 021005.
doi: 10.11884/HPLPB202133.200182
Abstract:
To realize of passive-cooling high power fiber cladding light stripper, it is important to optimize the thermal management of both the fiber and the package. By using Teflon capillaries to make segmental etching configuration on fiber, using copper as the package material, and optimizing the package structure through finite element thermal simulations, cladding light stripper capable of handling 500 W power was designed and fabricated. It was experimentally verified that the stripping efficiency reached 23.7 dB and the temperature increase rate on the bare fiber of cladding light stripper was as low as 0.007 ℃/W. In addition, at 540 W of power injection, cladding light stripper could work continuously if mounted on water-cooled cold plate, and could work for 50 s each time if mounted on cold plate filled with phase-change material, with the maximum temperature of package being 58.7 ℃ and 80 ℃ respectively. The researches and results could provide valuable information to the design and development of high power fiber lasers.
To realize of passive-cooling high power fiber cladding light stripper, it is important to optimize the thermal management of both the fiber and the package. By using Teflon capillaries to make segmental etching configuration on fiber, using copper as the package material, and optimizing the package structure through finite element thermal simulations, cladding light stripper capable of handling 500 W power was designed and fabricated. It was experimentally verified that the stripping efficiency reached 23.7 dB and the temperature increase rate on the bare fiber of cladding light stripper was as low as 0.007 ℃/W. In addition, at 540 W of power injection, cladding light stripper could work continuously if mounted on water-cooled cold plate, and could work for 50 s each time if mounted on cold plate filled with phase-change material, with the maximum temperature of package being 58.7 ℃ and 80 ℃ respectively. The researches and results could provide valuable information to the design and development of high power fiber lasers.
2021,
33: 021006.
doi: 10.11884/HPLPB202133.200181
Abstract:
High power double cladding fiber Bragg grating (FBG) fabrication based on ultraviolet laser and phase mask method was introduced. A pair of chirped FBGs with 1080 nm central wavelength was made. The reflection spectrum bandwidths were 2 nm and 1 nm, respectively. We adopted these FBGs to construct a fiber oscillator. whose output signal power is up to 502 W.
High power double cladding fiber Bragg grating (FBG) fabrication based on ultraviolet laser and phase mask method was introduced. A pair of chirped FBGs with 1080 nm central wavelength was made. The reflection spectrum bandwidths were 2 nm and 1 nm, respectively. We adopted these FBGs to construct a fiber oscillator. whose output signal power is up to 502 W.
2021,
33: 022001.
doi: 10.11884/HPLPB202133.200200
Abstract:
The pulse power device will produce a strong electromagnetic environment in the process of discharge, which interferes with diagnostic systems in the experiment, leading to their failure to work properly. By selecting, transforming and delaying the time correlated signals, a trigger network has been established for diagnostic instruments in high energy density experiments on an 8 MA pulsed power device. The jitter of time interval between the trigger signal and the X-ray pulse is less than 2 ns, which meets the requirement to synchronize diagnostics with time resolution of nanosecond. Shielding and grounding techniques are used and effectively eliminate the jamming of strong electromagnetic environment and other stray signals produced by the discharge of the device, which also ensure the normal operation of diagnostic instruments and the quality of the experimental data.
The pulse power device will produce a strong electromagnetic environment in the process of discharge, which interferes with diagnostic systems in the experiment, leading to their failure to work properly. By selecting, transforming and delaying the time correlated signals, a trigger network has been established for diagnostic instruments in high energy density experiments on an 8 MA pulsed power device. The jitter of time interval between the trigger signal and the X-ray pulse is less than 2 ns, which meets the requirement to synchronize diagnostics with time resolution of nanosecond. Shielding and grounding techniques are used and effectively eliminate the jamming of strong electromagnetic environment and other stray signals produced by the discharge of the device, which also ensure the normal operation of diagnostic instruments and the quality of the experimental data.
2021,
33: 023001.
doi: 10.11884/HPLPB202133.200257
Abstract:
High-power waveguide window is a critical component of high-power klystron and accelerator. The RF breakdown of the waveguide window always cause the failure of the high-power klystron. In this paper, the research progress of high-power waveguide window in the international vacuum electronics field is introduced. The research status, manufacturing requirement, and RF breakdown mechanism of the classical pill-box window are presented at first. Then the characters of some new type waveguide windows such as the tapered window, travelling wave in ceramic window, mixed-mode window, and over-mode window are summarized. Some breakdown suppression technologies like changing the material character of the window disk, changing the surface configuration of the window disk, using the positive dielectric angle, applying DC electric field or DC magnetic field, changing the waveform of transverse electric field are emphasized at the end.
2021,
33: 023002.
doi: 10.11884/HPLPB202133.200252
Abstract:
High power helical array antenna fed from planar waveguide is a new type antenna to realize the directional radiation of circularly polarized microwave, which works in C-band. The complexity and the height of the feed structure are reduced by using the planar waveguide. The structure of the basic electric probe is improved, and the coupling quantity is adjusted by controlling the central angle of the sector gap, and the reflection is eliminated by the upper and lower ridge structure. A new structure of short helical antenna is designed to optimize the axial ratio and reflection by separating the parameters, and the axial ratio of the antenna is less than 0.5 dB in the range of −7° to 7°. A 20 units linear feed array is constructed to realize equal amplitude feed by coupling energy from the planar waveguide through the electric probe structure. Finally, a helical array antenna with 20×20 units working in 4.3 GHz is simulated, and the results show that the gain of the antenna is 31.6 dB, and the aperture efficiency is 74%. The reflection is less than −16 dB within the frequency band range of 4.11−4.43 GHz and the power capacity is 3.6 GW.
High power helical array antenna fed from planar waveguide is a new type antenna to realize the directional radiation of circularly polarized microwave, which works in C-band. The complexity and the height of the feed structure are reduced by using the planar waveguide. The structure of the basic electric probe is improved, and the coupling quantity is adjusted by controlling the central angle of the sector gap, and the reflection is eliminated by the upper and lower ridge structure. A new structure of short helical antenna is designed to optimize the axial ratio and reflection by separating the parameters, and the axial ratio of the antenna is less than 0.5 dB in the range of −7° to 7°. A 20 units linear feed array is constructed to realize equal amplitude feed by coupling energy from the planar waveguide through the electric probe structure. Finally, a helical array antenna with 20×20 units working in 4.3 GHz is simulated, and the results show that the gain of the antenna is 31.6 dB, and the aperture efficiency is 74%. The reflection is less than −16 dB within the frequency band range of 4.11−4.43 GHz and the power capacity is 3.6 GW.
2021,
33: 023003.
doi: 10.11884/HPLPB202133.200233
Abstract:
The effect of plasma on the transmission properties of electromagnetic waves and its application have always been one of the key research directions of electromagnetic theory and technology and plasma physics. The enhancement effect of collisional plasma on electromagnetic waves is a classic subject of the interaction between electromagnetic waves and plasma. Based on the transmission characteristics of electromagnetic waves in medium, this paper takes plasma as a special medium, and carries out experimental, theoretical and simulation studies on the transmission characteristics of high power microwave (HPM) atmospheric plasma and a certain range of electromagnetic waves under certain experimental conditions. The study found that the plasma formed by the S-band HPM under a vacuum of 50 Pa has a great influence on the electromagnetic wave transmission characteristics of different frequencies, and the electromagnetic wave transmission signal enhancement effect occurs regularly within a certain frequency range. A series of transmission waveforms of continuous electromagnetic waves of different frequencies passing through the HPM plasma area were obtained, and the waveforms were normalized. At 32.4 GHz, the transmission coefficient of continuous electromagnetic waves passing through the plasma area with plasma is about twice as high as that through the area without plasma. A simulation model was established, and the transmission coefficient distribution curve in the range of 31.5−32.5 GHz was obtained. The electromagnetic wave passing through the plasma showed a transmission enhancement effect, and at some frequency points, there was a transmission enhancement of about 1.9 times. The research results provides important technical support for the application of plasma in stealth, emergency communications, and black barrier communications.
The effect of plasma on the transmission properties of electromagnetic waves and its application have always been one of the key research directions of electromagnetic theory and technology and plasma physics. The enhancement effect of collisional plasma on electromagnetic waves is a classic subject of the interaction between electromagnetic waves and plasma. Based on the transmission characteristics of electromagnetic waves in medium, this paper takes plasma as a special medium, and carries out experimental, theoretical and simulation studies on the transmission characteristics of high power microwave (HPM) atmospheric plasma and a certain range of electromagnetic waves under certain experimental conditions. The study found that the plasma formed by the S-band HPM under a vacuum of 50 Pa has a great influence on the electromagnetic wave transmission characteristics of different frequencies, and the electromagnetic wave transmission signal enhancement effect occurs regularly within a certain frequency range. A series of transmission waveforms of continuous electromagnetic waves of different frequencies passing through the HPM plasma area were obtained, and the waveforms were normalized. At 32.4 GHz, the transmission coefficient of continuous electromagnetic waves passing through the plasma area with plasma is about twice as high as that through the area without plasma. A simulation model was established, and the transmission coefficient distribution curve in the range of 31.5−32.5 GHz was obtained. The electromagnetic wave passing through the plasma showed a transmission enhancement effect, and at some frequency points, there was a transmission enhancement of about 1.9 times. The research results provides important technical support for the application of plasma in stealth, emergency communications, and black barrier communications.
2021,
33: 023004.
doi: 10.11884/HPLPB202133.200206
Abstract:
At present, China’s Q/V band low orbit satellite internet project is being vigorously carried out, broadband communications are gradually developing. But the domestic linearization technology is generally limited to narrow band, the related research is not mature. Therefore, it is necessary to design broadband linearizer as soon as possible. In this paper, a Q-band linearizer of traveling-wave tube amplifier (TWTA) for satellite communication has been designed using an analog predistortion technique suitable for space environment. Using the new microstrip transmission structure and the Schottky diode, the ultra-wide instantaneous frequency band can be linearized in the millimeter-wave frequency band. The amplitude distortion and phase distortion of TWTA are greatly improved in the 38−43 GHz (5 GHz) instantaneous frequency band. The linearizer has an in-band amplitude gain of about 4.8−7.2 dB and a phase expansion of about 70°−88° in the input power range of −17−13 dBm. Compared with other linearizers of the same type, this linearizer has higher corresponding frequency and can realize stable linearization of TWTA in a wide instantaneous frequency band.
At present, China’s Q/V band low orbit satellite internet project is being vigorously carried out, broadband communications are gradually developing. But the domestic linearization technology is generally limited to narrow band, the related research is not mature. Therefore, it is necessary to design broadband linearizer as soon as possible. In this paper, a Q-band linearizer of traveling-wave tube amplifier (TWTA) for satellite communication has been designed using an analog predistortion technique suitable for space environment. Using the new microstrip transmission structure and the Schottky diode, the ultra-wide instantaneous frequency band can be linearized in the millimeter-wave frequency band. The amplitude distortion and phase distortion of TWTA are greatly improved in the 38−43 GHz (5 GHz) instantaneous frequency band. The linearizer has an in-band amplitude gain of about 4.8−7.2 dB and a phase expansion of about 70°−88° in the input power range of −17−13 dBm. Compared with other linearizers of the same type, this linearizer has higher corresponding frequency and can realize stable linearization of TWTA in a wide instantaneous frequency band.
2021,
33: 023005.
doi: 10.11884/HPLPB202133.200198
Abstract:
Based on the consideration of power capacity and aperture matching to extend the low-frequency operating bandwidth, an ultra-wideband TEM horn antenna with a distributed impedance end-loading structure was designed. First, the gradual coaxial-flat balun structure was optimized, which expands the working bandwidth of the feed structure and improves the feed efficiency. Secondly, the distributed impedance matching design was performed on the exponential TEM horn antenna, and its port characteristics and radiation characteristics were significantly improved. The power pattern and energy pattern were used to evaluate the radiation effect of the antenna. The experimental results show that, compared with the exponential TEM horn antenna, after the distributed impedance matching structure is loaded, the antenna low-frequency bandwidth is widened by 330 MHz, the peak-to-peak value of the antenna main axis radiated electric field is increased by 10%, and the feed efficiency is increased by 17%.
Based on the consideration of power capacity and aperture matching to extend the low-frequency operating bandwidth, an ultra-wideband TEM horn antenna with a distributed impedance end-loading structure was designed. First, the gradual coaxial-flat balun structure was optimized, which expands the working bandwidth of the feed structure and improves the feed efficiency. Secondly, the distributed impedance matching design was performed on the exponential TEM horn antenna, and its port characteristics and radiation characteristics were significantly improved. The power pattern and energy pattern were used to evaluate the radiation effect of the antenna. The experimental results show that, compared with the exponential TEM horn antenna, after the distributed impedance matching structure is loaded, the antenna low-frequency bandwidth is widened by 330 MHz, the peak-to-peak value of the antenna main axis radiated electric field is increased by 10%, and the feed efficiency is increased by 17%.
2021,
33: 023006.
doi: 10.11884/HPLPB202133.200153
Abstract:
For the application requirements of high integration and high selectivity of balanced filters, this paper proposes a novel balanced tri-band filter with high selectivity, which is based on an improved asymmetric stepped impedance resonator structure with self-coupling. Firstly, through the differential mode and common mode equivalent circuits of the balanced filter, the resonant characteristics of the resonator structure are specifically analyzed, and the first three resonance modes under the differential mode equivalent circuit are used to form three passbands respectively. In addition, by loading capacitors and resistance elements on the symmetrical surface of the circuit, the suppression of CM signals can be improved without affecting DM signals based on the proposed multimode balanced filter structure and design method, and a balanced tri-band filter with passband frequencies of 2.75/4.46/6.21 GHz was designed, processed and tested. The results show that the structure can achieve a compact size and high selection characteristics, and has good common mode rejection characteristics.
For the application requirements of high integration and high selectivity of balanced filters, this paper proposes a novel balanced tri-band filter with high selectivity, which is based on an improved asymmetric stepped impedance resonator structure with self-coupling. Firstly, through the differential mode and common mode equivalent circuits of the balanced filter, the resonant characteristics of the resonator structure are specifically analyzed, and the first three resonance modes under the differential mode equivalent circuit are used to form three passbands respectively. In addition, by loading capacitors and resistance elements on the symmetrical surface of the circuit, the suppression of CM signals can be improved without affecting DM signals based on the proposed multimode balanced filter structure and design method, and a balanced tri-band filter with passband frequencies of 2.75/4.46/6.21 GHz was designed, processed and tested. The results show that the structure can achieve a compact size and high selection characteristics, and has good common mode rejection characteristics.
2021,
33: 023007.
doi: 10.11884/HPLPB202133.200149
Abstract:
The interaction between space plasma and spacecraft results into the onset of spacecraft surface charging and the resultant electrostatic discharging events. The computation of spacecraft surface charging is commonly accomplished using the secondary electron yield of spacecraft surface irradiated by mono-energetic electrons. To depict the charging environment more precisely and obtain more reliable computation results, focusing the spacecraft charging problem under the worst charging condition and taking into accounts the double-Maxwellian plasma distribution, the threshold equation controlling the onset charging is derived based on the averaged secondary electron yield. This equation is useful to analyze spacecraft charging under the condition of election irradiation with a continuous energy spectrum. Besides, the adoption of double-Maxwellian plasma distribution could better model the space plasma condition in the case of magnetospheric substorm. By theoretical analysis, the ambient plasma is divided into two typical situations according to the charging characteristics of spacecraft surface charging. Through simulation computation, the trend of spacecraft surface charging versus plasma parameters fluctuations is obtained for these two typical situations. Results show that higher electron temperature corresponds to more severe charging with higher negative potential; meanwhile, the density ratio of the two electron components in double-Maxwellian plasma distribution plays an important role in spacecraft surface charging. The obtained conclusions could provide useful reference for quantitative analysis of spacecraft surface severe charging events.
The interaction between space plasma and spacecraft results into the onset of spacecraft surface charging and the resultant electrostatic discharging events. The computation of spacecraft surface charging is commonly accomplished using the secondary electron yield of spacecraft surface irradiated by mono-energetic electrons. To depict the charging environment more precisely and obtain more reliable computation results, focusing the spacecraft charging problem under the worst charging condition and taking into accounts the double-Maxwellian plasma distribution, the threshold equation controlling the onset charging is derived based on the averaged secondary electron yield. This equation is useful to analyze spacecraft charging under the condition of election irradiation with a continuous energy spectrum. Besides, the adoption of double-Maxwellian plasma distribution could better model the space plasma condition in the case of magnetospheric substorm. By theoretical analysis, the ambient plasma is divided into two typical situations according to the charging characteristics of spacecraft surface charging. Through simulation computation, the trend of spacecraft surface charging versus plasma parameters fluctuations is obtained for these two typical situations. Results show that higher electron temperature corresponds to more severe charging with higher negative potential; meanwhile, the density ratio of the two electron components in double-Maxwellian plasma distribution plays an important role in spacecraft surface charging. The obtained conclusions could provide useful reference for quantitative analysis of spacecraft surface severe charging events.
2021,
33: 024001.
doi: 10.11884/HPLPB202133.200216
Abstract:
Vertical tests are very important for superconducting cavity after its post-processing. The aim is to obtain the quality factor versus accelerating gradient curve to evaluate a cavity’s performance. Because of its narrow bandwidth, the superconducting cavity should work stably in the resonant state during the vertical tests. The digital self-excited loop system for the vertical test stand of Peking University is introduced in this paper. The methods of avoiding crosstalk during multi-cell superconducting cavity test were brought out. The influence of deviation from quadruple frequency sampling on amplitude and phase was analyzed. The system is stable and reliable, can effectively distinguish\begin{document}$ {\text{π}} $\end{document} ![]()
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Vertical tests are very important for superconducting cavity after its post-processing. The aim is to obtain the quality factor versus accelerating gradient curve to evaluate a cavity’s performance. Because of its narrow bandwidth, the superconducting cavity should work stably in the resonant state during the vertical tests. The digital self-excited loop system for the vertical test stand of Peking University is introduced in this paper. The methods of avoiding crosstalk during multi-cell superconducting cavity test were brought out. The influence of deviation from quadruple frequency sampling on amplitude and phase was analyzed. The system is stable and reliable, can effectively distinguish
2021,
33: 024002.
doi: 10.11884/HPLPB202133.200162
Abstract:
Hybrid bunching-accelerating structure (HBaS) is a novel RF structure integrating a standing-wave(SW) pre-buncher (PB), a traveling-wave (TW) buncher (B) and a standard accelerating structure together. This paper presents the design results, including beam dynamic optimization, microwave design and the cold test of the S-band HBaS prototype, and explicates the reason of transverse emittance increasement caused by the hybrid structure. The low RF power results are in good agreement with the RF design. The measured S11 at operation frequency is less than −45 dB, the phase shift deviation is less than ±2° and the bandwidth is more than 5 MHz (VSWR≤1.2). The axis field distribution fully meets the dynamic requirements.
Hybrid bunching-accelerating structure (HBaS) is a novel RF structure integrating a standing-wave(SW) pre-buncher (PB), a traveling-wave (TW) buncher (B) and a standard accelerating structure together. This paper presents the design results, including beam dynamic optimization, microwave design and the cold test of the S-band HBaS prototype, and explicates the reason of transverse emittance increasement caused by the hybrid structure. The low RF power results are in good agreement with the RF design. The measured S11 at operation frequency is less than −45 dB, the phase shift deviation is less than ±2° and the bandwidth is more than 5 MHz (VSWR≤1.2). The axis field distribution fully meets the dynamic requirements.
2021,
33: 024003.
doi: 10.11884/HPLPB202133.200197
Abstract:
In one high repetition frequency X-ray free electron laser (XFEL) equipment, the electron gun and compensate solenoid have special structure in the photoinjector, thus the electric field and the magnetic field overlaps near the cathode. The thermal emittance of the cathode should be measured in the experiment. The solenoid scan method used to measure the thermal emittance is not suitable for the overlapping field, because it works effectively only when the rms emittance keeps constant. As the normalized phase space can avoid the influence of the electric field, we tried to use the solenoid scan method in normalized phase space. Using simulation code to do simulations and analysis, we finally demonstrate that this method is feasible for measurement of thermal emittance of the photoinjector which has overlapping field.
In one high repetition frequency X-ray free electron laser (XFEL) equipment, the electron gun and compensate solenoid have special structure in the photoinjector, thus the electric field and the magnetic field overlaps near the cathode. The thermal emittance of the cathode should be measured in the experiment. The solenoid scan method used to measure the thermal emittance is not suitable for the overlapping field, because it works effectively only when the rms emittance keeps constant. As the normalized phase space can avoid the influence of the electric field, we tried to use the solenoid scan method in normalized phase space. Using simulation code to do simulations and analysis, we finally demonstrate that this method is feasible for measurement of thermal emittance of the photoinjector which has overlapping field.
2021,
33: 024004.
doi: 10.11884/HPLPB202133.200107
Abstract:
By studying the principle of characteristic impedance mismatch of uniform transmission line, it is found that the characteristic impedance mismatch of transmission cable will lead to the distortion of excitation current amplitude of load terminal. The key parameters of main circuit for power supply are analyzed, the amplitude and rise time of the excitation current at the magnet are decreased, when the matching impedance of the uniform transmission line is mismatched. By establishing the equivalent model of barrier point in uniform transmission line, the reflection coefficient at the barrier point of the uniform transmission line is derived. Based on the analysis of series resistance and parallel resistance at the barrier, it is found that the mismatch of transmission line characteristic impedance will lead to the decrease of active power at matching load. It is verified by the breakdown of high voltage cable.
By studying the principle of characteristic impedance mismatch of uniform transmission line, it is found that the characteristic impedance mismatch of transmission cable will lead to the distortion of excitation current amplitude of load terminal. The key parameters of main circuit for power supply are analyzed, the amplitude and rise time of the excitation current at the magnet are decreased, when the matching impedance of the uniform transmission line is mismatched. By establishing the equivalent model of barrier point in uniform transmission line, the reflection coefficient at the barrier point of the uniform transmission line is derived. Based on the analysis of series resistance and parallel resistance at the barrier, it is found that the mismatch of transmission line characteristic impedance will lead to the decrease of active power at matching load. It is verified by the breakdown of high voltage cable.
2021,
33: 024005.
doi: 10.11884/HPLPB202133.200229
Abstract:
To study the influence of ion beam perveance condition on the grids erosion velocity for 30 cm diameter ion thruster, we established a beam perveance model and calculated the grids erosion velocity caused by CEX (charge exchange) ions by PIC-MCC method, and then compared and analyzed the calculation results with 1500 h short time life test results. The results show that under the normal beam perveance condition, the mass erosion velocity of the accelerator grid and the decelerator grid are (1.11−1.72)×10−15 kg/s and (1.22−1.26)×10−17 kg/s in 3 kW and 5 kW working modes, respectively. Under 5 kW working mode, when the upstream plasma density of the screen grid reaches 4.03×1017 m−3, the beam is under perveance condition, and the maximum ion erosion velocity of the accelerator grid and the decelerator grid is about 4.33×10−15 kg/s and 4.02×10−15 kg/s respectively. Under 3 kW working mode, when the upstream plasma density of the screen grid reaches 0.22×1017 m−3, the beam is in over perveance condition. Meanwhile, the maximum ion erosion velocity of the accelerator grid and the decelerator grid is about 3.24×10−15 kg/s and 5.01×10−15 kg/s respectively. The life test results show that the calculation value of mass erosion velocity of the accelerator grid hole has a small error to the test value. However, the calculation results of erosion velocity of the decelerator grid hole differ greatly from the test results, which is mainly because of the direct bombardment of the beam ions on the decelerator grid hole. From the current research conclusions, it is considered that the variable aperture design for the screen grid hole is an effective measure to reduce the erosion velocity of the accelerator grid hole and the decelerator grid hole caused by CEX ions when the beam is in under or over perveance condition. In addition, variable aperture design of the grids can significantly improve the working life of the thruster.
To study the influence of ion beam perveance condition on the grids erosion velocity for 30 cm diameter ion thruster, we established a beam perveance model and calculated the grids erosion velocity caused by CEX (charge exchange) ions by PIC-MCC method, and then compared and analyzed the calculation results with 1500 h short time life test results. The results show that under the normal beam perveance condition, the mass erosion velocity of the accelerator grid and the decelerator grid are (1.11−1.72)×10−15 kg/s and (1.22−1.26)×10−17 kg/s in 3 kW and 5 kW working modes, respectively. Under 5 kW working mode, when the upstream plasma density of the screen grid reaches 4.03×1017 m−3, the beam is under perveance condition, and the maximum ion erosion velocity of the accelerator grid and the decelerator grid is about 4.33×10−15 kg/s and 4.02×10−15 kg/s respectively. Under 3 kW working mode, when the upstream plasma density of the screen grid reaches 0.22×1017 m−3, the beam is in over perveance condition. Meanwhile, the maximum ion erosion velocity of the accelerator grid and the decelerator grid is about 3.24×10−15 kg/s and 5.01×10−15 kg/s respectively. The life test results show that the calculation value of mass erosion velocity of the accelerator grid hole has a small error to the test value. However, the calculation results of erosion velocity of the decelerator grid hole differ greatly from the test results, which is mainly because of the direct bombardment of the beam ions on the decelerator grid hole. From the current research conclusions, it is considered that the variable aperture design for the screen grid hole is an effective measure to reduce the erosion velocity of the accelerator grid hole and the decelerator grid hole caused by CEX ions when the beam is in under or over perveance condition. In addition, variable aperture design of the grids can significantly improve the working life of the thruster.
2021,
33: 025001.
doi: 10.11884/HPLPB202133.200223
Abstract:
With the wide application of all-solid-state high-voltage pulse generators in the fields of material modification, biomedicine and industry, all-solid-state pulse generators are developing in the direction of miniaturization, intelligence and modularization. To further reduce the volume and cost of the power supply, this paper proposes a positive self-triggering all-solid-state Marx generator topology. It only needs to provide an isolated signal to control the turn-on and turn-off of discharging switch in the first stage, and the gates of the adjacent-stage discharging switches will be automatically charged and discharged through the inter-stage capacitors, so that they turn on and off one by one. This topology makes the driving circuit of the multiple switches in the Marx generators much simpler and does not need to provide a multi-channel driving power supply with isolated power supplies, and also avoids the dynamic and static voltage balancing problems of the switches. Based on this topology, a 17-stage positive polarity Marx generator prototype is built, and the voltage amplitudes and pulse widths are continuously adjustable. It outputs 10 kV positive high-voltage pulses at a repetition frequency of 100 Hz over a 10 kΩ resistive load. The leading edge is approximately 328 ns. The prototype is small in size and stable in work, which verifies the feasibility of this topology.
With the wide application of all-solid-state high-voltage pulse generators in the fields of material modification, biomedicine and industry, all-solid-state pulse generators are developing in the direction of miniaturization, intelligence and modularization. To further reduce the volume and cost of the power supply, this paper proposes a positive self-triggering all-solid-state Marx generator topology. It only needs to provide an isolated signal to control the turn-on and turn-off of discharging switch in the first stage, and the gates of the adjacent-stage discharging switches will be automatically charged and discharged through the inter-stage capacitors, so that they turn on and off one by one. This topology makes the driving circuit of the multiple switches in the Marx generators much simpler and does not need to provide a multi-channel driving power supply with isolated power supplies, and also avoids the dynamic and static voltage balancing problems of the switches. Based on this topology, a 17-stage positive polarity Marx generator prototype is built, and the voltage amplitudes and pulse widths are continuously adjustable. It outputs 10 kV positive high-voltage pulses at a repetition frequency of 100 Hz over a 10 kΩ resistive load. The leading edge is approximately 328 ns. The prototype is small in size and stable in work, which verifies the feasibility of this topology.
2021,
33: 025002.
doi: 10.11884/HPLPB202133.200142
Abstract:
Aiming at the arc-drawing problem of rail gun armature at muzzle exit, a muzzle arc suppression scheme based on shunt is proposed in this paper. Taking solid armature as the research object, the simulation model of electromagnetic rail launching system with arc suppression device is established by using Simulink software. The purpose is to achieve the best match between the electrical parameters of the arc suppression device and the electrical parameters of the launch system through the simulation calculation of the different impedance values of the arc suppression device, so as to reduce the influence of the arc suppression branch on the speed of the armature outlet, and at the same time effectively restrain the arc of the muzzle. By optimizing the parameters of resistance and inductance of the arc suppression device, the impedance of the arc suppression branch is far greater than that of the armature branch in bore, and the launch current mostly flows through the armature, which has the least effect on the armature speed. After the armature is out of the muzzle, the impedance of the arc suppression branch is less than that of the arc, thus a reasonable arc rapid elimination is established. The residual energy of the launching system can be released by the arc suppression device to reduce the influence of the muzzle arcing on the launching performance. After the calculation and analysis of the multi parameter values of the resistance and the inductance of the arc suppression device, it is determined that the arc suppression resistance matching the transmission system in this paper is about 1 mΩ, and the inductance is about 1 μH. Combined with the structure of the launching device, the resistance and inductance of the arc suppression device are 1.32 mΩ and 0.124 μH respectively. In the simulation model of the launching system, the launching simulation calculation of the charging voltage 3 kV is carried out. Under the energy level of the charging voltage 3 kV, the arc suppression launching test is carried out. The simulation results are in good agreement with the test results, and the arc suppression effect is good.
Aiming at the arc-drawing problem of rail gun armature at muzzle exit, a muzzle arc suppression scheme based on shunt is proposed in this paper. Taking solid armature as the research object, the simulation model of electromagnetic rail launching system with arc suppression device is established by using Simulink software. The purpose is to achieve the best match between the electrical parameters of the arc suppression device and the electrical parameters of the launch system through the simulation calculation of the different impedance values of the arc suppression device, so as to reduce the influence of the arc suppression branch on the speed of the armature outlet, and at the same time effectively restrain the arc of the muzzle. By optimizing the parameters of resistance and inductance of the arc suppression device, the impedance of the arc suppression branch is far greater than that of the armature branch in bore, and the launch current mostly flows through the armature, which has the least effect on the armature speed. After the armature is out of the muzzle, the impedance of the arc suppression branch is less than that of the arc, thus a reasonable arc rapid elimination is established. The residual energy of the launching system can be released by the arc suppression device to reduce the influence of the muzzle arcing on the launching performance. After the calculation and analysis of the multi parameter values of the resistance and the inductance of the arc suppression device, it is determined that the arc suppression resistance matching the transmission system in this paper is about 1 mΩ, and the inductance is about 1 μH. Combined with the structure of the launching device, the resistance and inductance of the arc suppression device are 1.32 mΩ and 0.124 μH respectively. In the simulation model of the launching system, the launching simulation calculation of the charging voltage 3 kV is carried out. Under the energy level of the charging voltage 3 kV, the arc suppression launching test is carried out. The simulation results are in good agreement with the test results, and the arc suppression effect is good.
2021,
33: 026001.
doi: 10.11884/HPLPB202133.200168
Abstract:
Aiming at the radiation protection and safety requirements of HLS-II (HLS-Ⅱ), a neutron monitor based on embedded EPICS was developed for neutron monitoring of radiation field and environment. The control system of HLS-II is based on EPICS (Experimental Physics and Industrial Control System) architecture. In order to reduce the middle link of the radiation monitoring system and improve the reliability of the personal safety chain of HLS-II, a neutron monitor based on embedded EPICS control system was developed. The key component of the neutron monitor-detector is the BF3 proportional counter tube. By adding a 2 kV positive high voltage bias to the weak electrical signal generated by the proportional counter tube, the AC coupling intervenes in the preamplifier for amplification, and then outputs a pulse signal with a fixed width. The signal is counted by the CORTEX-M3 circuit, and then processed by the CORTEX-A8 circuit to publish the data to the local area network. The performance of the developed monitor has been preliminarily tested by using Am-Be neutron source and on-site radiation environment of HLS-II. The results show that the monitor meets the design requirements and can be used for neutron monitoring.
Aiming at the radiation protection and safety requirements of HLS-II (HLS-Ⅱ), a neutron monitor based on embedded EPICS was developed for neutron monitoring of radiation field and environment. The control system of HLS-II is based on EPICS (Experimental Physics and Industrial Control System) architecture. In order to reduce the middle link of the radiation monitoring system and improve the reliability of the personal safety chain of HLS-II, a neutron monitor based on embedded EPICS control system was developed. The key component of the neutron monitor-detector is the BF3 proportional counter tube. By adding a 2 kV positive high voltage bias to the weak electrical signal generated by the proportional counter tube, the AC coupling intervenes in the preamplifier for amplification, and then outputs a pulse signal with a fixed width. The signal is counted by the CORTEX-M3 circuit, and then processed by the CORTEX-A8 circuit to publish the data to the local area network. The performance of the developed monitor has been preliminarily tested by using Am-Be neutron source and on-site radiation environment of HLS-II. The results show that the monitor meets the design requirements and can be used for neutron monitoring.
2021,
33: 026002.
doi: 10.11884/HPLPB202133.200152
Abstract:
The 4.6 GHz low hybrid current drive (LHCD) system is an important part in the EAST tokamak auxiliary heating system. Its cathode high voltage dc power supply is based on pulse stepped modulation (PSM) technology. 64 DC modules are used to output 50 kV dc voltage in series. As the modulation frequency of PSM single module is 50 Hz, the regulation speed of system is limited. In the face of the interference caused by the voltage fluctuation of the network side in the actual operation, the power supply cannot make more rapid response and feedback regulation. It leads to large fluctuation of the output voltage and affects the output performance. To improve the regulation speed and anti-interference capability of system, the high-frequency PSM module with 1 kHz modulation frequency capability was designed to replace some of the original low-frequency modules. The fluctuation of output voltage was suppressed by the rapid regulation capability of the high frequency module. The experimental results show that the output voltage fluctuation of the upgraded power supply is reduced by 50%, which better meets the control requirements of klystron for voltage accuracy and stability, and guarantees the reliability of the system operation.
The 4.6 GHz low hybrid current drive (LHCD) system is an important part in the EAST tokamak auxiliary heating system. Its cathode high voltage dc power supply is based on pulse stepped modulation (PSM) technology. 64 DC modules are used to output 50 kV dc voltage in series. As the modulation frequency of PSM single module is 50 Hz, the regulation speed of system is limited. In the face of the interference caused by the voltage fluctuation of the network side in the actual operation, the power supply cannot make more rapid response and feedback regulation. It leads to large fluctuation of the output voltage and affects the output performance. To improve the regulation speed and anti-interference capability of system, the high-frequency PSM module with 1 kHz modulation frequency capability was designed to replace some of the original low-frequency modules. The fluctuation of output voltage was suppressed by the rapid regulation capability of the high frequency module. The experimental results show that the output voltage fluctuation of the upgraded power supply is reduced by 50%, which better meets the control requirements of klystron for voltage accuracy and stability, and guarantees the reliability of the system operation.
2021,
33: 029001.
doi: 10.11884/HPLPB202133.200221
Abstract:
Compared with a point laser scanning method, a surface exposure laser melting has advantages of high forming efficiency and low residual stress, which has become a promising new generation selective laser melting of additive manufacturing technology. In this paper, a principle device platform of new generation surface exposure selective laser melting were developed with a light source of 915 nm diode laser, combined with an electrically addressed reflective pure phase liquid crystal spatial light modulator. Its principle experimental verification of surface exposure selective laser melting were implemented. A sample of surface exposure selective laser melting with a “○”-shaped pattern were obtained by using a low melting point metal powder.
Compared with a point laser scanning method, a surface exposure laser melting has advantages of high forming efficiency and low residual stress, which has become a promising new generation selective laser melting of additive manufacturing technology. In this paper, a principle device platform of new generation surface exposure selective laser melting were developed with a light source of 915 nm diode laser, combined with an electrically addressed reflective pure phase liquid crystal spatial light modulator. Its principle experimental verification of surface exposure selective laser melting were implemented. A sample of surface exposure selective laser melting with a “○”-shaped pattern were obtained by using a low melting point metal powder.
2021,
33: 029002.
doi: 10.11884/HPLPB202133.200224
Abstract:
To achieve high-power white LED system with high uniformity and narrow beam, an optical system composed of Chips On Board (COB), compound parabolic reflector, Fresnel lens and aspheric lens is designed. In the design, based on the COB light distribution curve, the light source simulation model of the optical system is built firstly. Then the light source beam is converged by the compound parabolic reflector, and the spill light is controlled by the Fresnel lens. finally, an aspheric lens is used for collimating light source beam. The TracePro software is used for ray tracing simulation. According to the simulated results, an experimental setup is developed for experimental testing. The testing results show that the divergence angle of the optical system is ±7.9°, and the circular uniformity is 96% with the distance of 0.7 m, and the overall light efficiency reaches 60%.
To achieve high-power white LED system with high uniformity and narrow beam, an optical system composed of Chips On Board (COB), compound parabolic reflector, Fresnel lens and aspheric lens is designed. In the design, based on the COB light distribution curve, the light source simulation model of the optical system is built firstly. Then the light source beam is converged by the compound parabolic reflector, and the spill light is controlled by the Fresnel lens. finally, an aspheric lens is used for collimating light source beam. The TracePro software is used for ray tracing simulation. According to the simulated results, an experimental setup is developed for experimental testing. The testing results show that the divergence angle of the optical system is ±7.9°, and the circular uniformity is 96% with the distance of 0.7 m, and the overall light efficiency reaches 60%.
