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RSS2022 Vol. 34, No. 12
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2022,
34: 121001.
doi: 10.11884/HPLPB202234.220247
Abstract:
Fiber-coupled semiconductor laser (LD)-pumped fiber laser amplifiers have the advantages of small size, high power-to-mass ratio, and good stability. However, limited by the level of device fabrication and the stimulated Raman scattering effect and mode instability (MI) effect inside the fiber, it is difficult for LD-pumped fiber laser amplifiers to achieve high-power and high-brightness laser output at the same time. To achieve higher power and higher brightness fiber laser output, it is necessary to combine the existing device technology and simultaneously realize effective suppression of the SRS and MI effect in the amplifier. Based on this, this paper reports the successful realization of 13 kW power and high beam quality laser output based on a homemade large-mode-area (LMA) gain fiber. The laser adopts the main oscillation power amplifier structure, and the LMA gain fiber is counter-pumped by 981 nm LDs in the amplification stage. When the total pump power is 15 kW, the output power reaches 12.94 kW, and the beam quality M2 factor is about 2.85. By further optimizing the device performance and fiber mode control, it is expected to achieve higher power and higher brightness fiber laser output.
2022,
34: 121002.
doi: 10.11884/HPLPB202234.220267
Abstract:
High-power narrow-linewidth fiber lasers are highly desired for nonlinear frequency conversion, spectral combination, and coherent combination. In this work, a 5 kW near single mode narrow-linewidth fiber laser system is established based on a composite fiber oscillator seed. By optimizing temporal characteristic of seed and structure of amplifier, the stimulated Raman scattering, spectral broadening, and transverse mode instability effects are suppressed comprehensively. Consequently, the output power is scaled up to 5 kW with a slope efficiency as high as approximately 86.1%. The peak signal to noise ratio is about 28.3 dB compared with the Raman Stokes light. The 3 dB and 20 dB linewidths are 0.48 nm and 2.1 nm, respectively. The beam quality (M2 factor) is about 1.35. This work shows a amplification potential of narrow-linewidth fiber lasers based on such a simple structure.
Real time phase calculation of phase shifted structured light based on one-dimensional look-up table
2022,
34: 121003.
doi: 10.11884/HPLPB202234.220159
Abstract:
We propose a fast phase decoding algorithm based on a one-dimensional look-up table. Firstly, according to the property of the arctangent function in the phase calculation formula, the phase relationship between the four quadrants is obtained. A linear function is used to map the coordinate points in the first quadrant to a discrete integer interval, and a one-dimensional look-up table of phases is established in advance by combining the interval with the linear function. In the process of phase calculation, firstly, the index of the one-dimensional look-up table is calculated by using relevant information to directly obtain the phase value, and then the phase value is adjusted by the linear interpolation method and phase relationship to obtain the final real phase. Experiments have verified the effectiveness of the proposed algorithm. Compared with the traditional phase calculation method, the proposed method can improve the speed by 3.97 times, 1.29 times compared with the traditional polynomial approximation algorithm, and 1.20 times compared with the traditional one-dimensional look-up table algorithm.
We propose a fast phase decoding algorithm based on a one-dimensional look-up table. Firstly, according to the property of the arctangent function in the phase calculation formula, the phase relationship between the four quadrants is obtained. A linear function is used to map the coordinate points in the first quadrant to a discrete integer interval, and a one-dimensional look-up table of phases is established in advance by combining the interval with the linear function. In the process of phase calculation, firstly, the index of the one-dimensional look-up table is calculated by using relevant information to directly obtain the phase value, and then the phase value is adjusted by the linear interpolation method and phase relationship to obtain the final real phase. Experiments have verified the effectiveness of the proposed algorithm. Compared with the traditional phase calculation method, the proposed method can improve the speed by 3.97 times, 1.29 times compared with the traditional polynomial approximation algorithm, and 1.20 times compared with the traditional one-dimensional look-up table algorithm.
2022,
34: 121004.
doi: 10.11884/HPLPB202234.220119
Abstract:
Vacuum window (VW) damage is the bottleneck restricting the load capacity of high-power laser device, and the influence of vacuum environment is worthy of attention. Firstly, based on the fluororubber ring seal, the laser-induced damage threshold (LIDT) of fused silica VW irradiated by the 351 nm laser was measured. It is found that the LIDT of the VW decreases by about 50% after the close contact with the fluororubber ring. After repeated extrusion, the influence of the fluororubber ring on the LIDT of the VW is significantly weakened. On this basis, the LIDTs of the VW under atmosphere, 103 Pa and 10−2～10−1 Pa are compared. The results show that the LIDT of vacuum window decreases significantly with the decrease of air pressure, and the LIDT does not increase after the air pressure rises again. In addition, the LIDT of the VW under different air pressure is tested based on indium ring sealing, while the effect of air pressure difference on the LIDT is not found. Comparing the results of the two sealing materials, it is considered that the LIDT decreasing of the VW is mainly caused by the release of organic contamination from fluororubber ring and the release of organic matter will be intensified under low pressure.
Vacuum window (VW) damage is the bottleneck restricting the load capacity of high-power laser device, and the influence of vacuum environment is worthy of attention. Firstly, based on the fluororubber ring seal, the laser-induced damage threshold (LIDT) of fused silica VW irradiated by the 351 nm laser was measured. It is found that the LIDT of the VW decreases by about 50% after the close contact with the fluororubber ring. After repeated extrusion, the influence of the fluororubber ring on the LIDT of the VW is significantly weakened. On this basis, the LIDTs of the VW under atmosphere, 103 Pa and 10−2～10−1 Pa are compared. The results show that the LIDT of vacuum window decreases significantly with the decrease of air pressure, and the LIDT does not increase after the air pressure rises again. In addition, the LIDT of the VW under different air pressure is tested based on indium ring sealing, while the effect of air pressure difference on the LIDT is not found. Comparing the results of the two sealing materials, it is considered that the LIDT decreasing of the VW is mainly caused by the release of organic contamination from fluororubber ring and the release of organic matter will be intensified under low pressure.
2022,
34: 121005.
doi: 10.11884/HPLPB202234.220205
Abstract:
To solve the problems of dissolution and surface fragmentation of Cr12MoV steel, laser cladding experiments were carried out on Cr12MoV steel using Al-Ni and Nd-Ni powders. The effects of Al and Nd on the macro and micro morphology, microstructure and surface properties of nickel base cladding were studied. The results show that Al can reduce the crack generation of cladding layer and reduce the hardness of cladding layer, so that the hard phase Al2O3 with anti-wear effect is generated in cladding layer, and the wear amount of cladding layer is reduced. The wear amount of 14% Al cladding layer is 44.5% lower than that of 2% Al cladding layer, and the optimal Al content is 14%. The grain refinement effect of Nd is obvious, and the microhardness of the coating is significantly increased. The average hardness of the coating is 36.8% higher than that of the substrate, and the optimal content of Nd is 2.5%.
To solve the problems of dissolution and surface fragmentation of Cr12MoV steel, laser cladding experiments were carried out on Cr12MoV steel using Al-Ni and Nd-Ni powders. The effects of Al and Nd on the macro and micro morphology, microstructure and surface properties of nickel base cladding were studied. The results show that Al can reduce the crack generation of cladding layer and reduce the hardness of cladding layer, so that the hard phase Al2O3 with anti-wear effect is generated in cladding layer, and the wear amount of cladding layer is reduced. The wear amount of 14% Al cladding layer is 44.5% lower than that of 2% Al cladding layer, and the optimal Al content is 14%. The grain refinement effect of Nd is obvious, and the microhardness of the coating is significantly increased. The average hardness of the coating is 36.8% higher than that of the substrate, and the optimal content of Nd is 2.5%.
2022,
34: 121006.
doi: 10.11884/HPLPB202234.220233
Abstract:
The refractive index profile of optical fiber preform can be measured by beam scanning method. Due to the requirements of the refractometer for the length, diameter and shape of preforms, the refractive index profile of special-shaped preforms cannot be measured directly. Thus the sleeve-assistant method is produced. A quarts sleeve is needed to expand the measuring range of the refractometer. The refractive index profile of the same round preform is measured directly by refractometer and by sleeve-assistant method respectively. And the results obtained are consistent, confirming the accuracy of the sleeve-assistant method. The refractive index profiles of the neck-down region of the preform measured confirm that the sleeve-assistant method can improve the test ability of refractometer.
The refractive index profile of optical fiber preform can be measured by beam scanning method. Due to the requirements of the refractometer for the length, diameter and shape of preforms, the refractive index profile of special-shaped preforms cannot be measured directly. Thus the sleeve-assistant method is produced. A quarts sleeve is needed to expand the measuring range of the refractometer. The refractive index profile of the same round preform is measured directly by refractometer and by sleeve-assistant method respectively. And the results obtained are consistent, confirming the accuracy of the sleeve-assistant method. The refractive index profiles of the neck-down region of the preform measured confirm that the sleeve-assistant method can improve the test ability of refractometer.
2022,
34: 122001.
doi: 10.11884/HPLPB202234.220186
Abstract:
To measure the areal density distribution of cold fuel at the maximum compression time during the stagnation phase of implosion in inertial confinement fusion (ICF), we have established the ps-laser driven high-energy X-ray radiography using source-coded technique. This paper describes the design and employment of the object including character-object and pinhole array. Based on the object, the source distribution and the object radiography was obtained at the same shot and same angle of view, and therefore the source-coded radiography of ps-laser driven X-ray has been established in experiments for the first time. From the experimental work on Xingguang-III facility, the spatial resolution of the inversion image with W wire-array target is 5.4 μm±0.7 μm. The efficiency of converting laser energy to high-energy bremsstrahlung (50−200 keV) is 5.4×10−4 in W wire-array target and 4.8×10−4 in Au single-wire target, respectively. It is possible that the the source-coded radiography of ps-laser driven X-ray in this work could account for overcoming the balance between spatial resolution and brightness in traditional X-ray backlight by ps-laser. The source-coded radiography provides an important method for ICF implosion backlight to get high resolution high signal-to-noise ratio images under the strong background.
To measure the areal density distribution of cold fuel at the maximum compression time during the stagnation phase of implosion in inertial confinement fusion (ICF), we have established the ps-laser driven high-energy X-ray radiography using source-coded technique. This paper describes the design and employment of the object including character-object and pinhole array. Based on the object, the source distribution and the object radiography was obtained at the same shot and same angle of view, and therefore the source-coded radiography of ps-laser driven X-ray has been established in experiments for the first time. From the experimental work on Xingguang-III facility, the spatial resolution of the inversion image with W wire-array target is 5.4 μm±0.7 μm. The efficiency of converting laser energy to high-energy bremsstrahlung (50−200 keV) is 5.4×10−4 in W wire-array target and 4.8×10−4 in Au single-wire target, respectively. It is possible that the the source-coded radiography of ps-laser driven X-ray in this work could account for overcoming the balance between spatial resolution and brightness in traditional X-ray backlight by ps-laser. The source-coded radiography provides an important method for ICF implosion backlight to get high resolution high signal-to-noise ratio images under the strong background.
2022,
34: 122002.
doi: 10.11884/HPLPB202234.220238
Abstract:
A recording design of wide-angle velocity interferometer system for any reflector (VISAR) fringe that loading shaped optical fiber panel or ring-to-line fiber bundle in front of the streak camera is presented, and the coordinates of recording position are located at a certain circle on pellet. To realize implosion symmetry analysis, the phase of wide-angle VISAR fringes is obtained by using coordinate transformation, Fourier transformation and Legendre expansion, and its feasibility is verified by examples. The diagnostic characteristics, optical design, equipment development and data processing of the method are discussed, and the development direction of implosion symmetry diagnosis based on wide-angle VISAR is introduced. Using this method to record and analyze the wide-angle VISAR fringe data can make implosion symmetry diagnosis accurate, intuitive and vivid, and can provide support for studying laser plasma instability and fluid instability in inertial confinement fusion research.
A recording design of wide-angle velocity interferometer system for any reflector (VISAR) fringe that loading shaped optical fiber panel or ring-to-line fiber bundle in front of the streak camera is presented, and the coordinates of recording position are located at a certain circle on pellet. To realize implosion symmetry analysis, the phase of wide-angle VISAR fringes is obtained by using coordinate transformation, Fourier transformation and Legendre expansion, and its feasibility is verified by examples. The diagnostic characteristics, optical design, equipment development and data processing of the method are discussed, and the development direction of implosion symmetry diagnosis based on wide-angle VISAR is introduced. Using this method to record and analyze the wide-angle VISAR fringe data can make implosion symmetry diagnosis accurate, intuitive and vivid, and can provide support for studying laser plasma instability and fluid instability in inertial confinement fusion research.
2022,
34: 122003.
doi: 10.11884/HPLPB202234.220199
Abstract:
To establish a monochromatic high-energy proton photography platform on high power laser device with hundreds of kilojoules, D3He gas-filled spherical SiO2 glass pellets, irradiated by an absorbed laser intensity of 1015 W/cm2 have been considered and the exploding pusher target simulation has been conducted with Helios-CR to design an optimum target, which couples to the incident laser light more effectively to produce the optimum number of protons. By varying the inner radius of the target, the laser intensity and the thickness of the spherical shell, the optimal laser conditions and target parameters for photography under the condition of our laser device are obtained. The simulation results give a suitable experimental parameter of 300 μm target ball radius, 1.8 MPa filled D3He gas and 3.5 μm SiO2 spherical shell thickness. In addition, we also considered the influence of laser driving symmetry and kinetic effect on the simulation results. Taking the optimal parameters obtained by simulation as the input, it is expected that 109–1010 proton yield can be obtained experimentally. The law of proton yield variation obtained through simulation provides a reference for the formal establishment of the proton photography platform and the selection of experimental parameters.
To establish a monochromatic high-energy proton photography platform on high power laser device with hundreds of kilojoules, D3He gas-filled spherical SiO2 glass pellets, irradiated by an absorbed laser intensity of 1015 W/cm2 have been considered and the exploding pusher target simulation has been conducted with Helios-CR to design an optimum target, which couples to the incident laser light more effectively to produce the optimum number of protons. By varying the inner radius of the target, the laser intensity and the thickness of the spherical shell, the optimal laser conditions and target parameters for photography under the condition of our laser device are obtained. The simulation results give a suitable experimental parameter of 300 μm target ball radius, 1.8 MPa filled D3He gas and 3.5 μm SiO2 spherical shell thickness. In addition, we also considered the influence of laser driving symmetry and kinetic effect on the simulation results. Taking the optimal parameters obtained by simulation as the input, it is expected that 109–1010 proton yield can be obtained experimentally. The law of proton yield variation obtained through simulation provides a reference for the formal establishment of the proton photography platform and the selection of experimental parameters.
2022,
34: 122004.
doi: 10.11884/HPLPB202234.220327
Abstract:
In this paper, a transmission curved crystal spectrometer is developed . The transmission curved crystal spectrometer employs a quartz crystal with radius of 200 mm covering the measuring range of 8 keV to 60 keV. We have applied the spectrometer to measure X-ray sources driven by picosecond laser both at XG-III and the SGII-Updated laser facility. The characteristic Kα and Kβ line emissions from Cu, Mo, Ag, and Zr were measured. Specifically, the L-shell emissions from Au targets irradiated by the picosecond lasers with different pulse duration were compared. The spectra show good signal-to-noise ratio, which indicates the spectrometer is suitable for the diagnostic of picosecond laser produced X-ray sources.
2022,
34: 122005.
doi: 10.11884/HPLPB202234.220288
Abstract:
In indirect-drive inertial confinement fusion experiments with vacuum or low-gas-fill hohlraums, collisionless electrostatic shocks can be launched in the hohlraum wall/alblator (or the low-density fill-gas) interpenetration region, which reflect ions at twice the shock velocity. A low-energy Thomson ion spectrometer was designed to measure the energy spectra of the reflected ions on the order of 10 keV generated by nanosecond-laser-driven non-relativistic collisionless electrostatic shocks. Monte Carlo simulations of ion measurement were carried out with Geant4 modeling to evaluate the influence of residual gas in the vacuum chamber and gas jet on the measurement of the low-energy ions. Simulation results show that the residual gas in the vacuum chamber causes the signal of D ions on the order of 10 keV to broaden in both the electric and magnetic deflection of the spectrometer. The broadening of the electric deflection will increase the risk of overlapping of ion spectral lines of different charge-to-mass ratios, while the broadening of the magnetic deflection will lead to the broadening of the energy spectra of the ions. The gas jet causes the ion signal to move and tail into the lower energy region, causing the measured ion spectra to deviate from the actual energy spectra of the reflected ions.
In indirect-drive inertial confinement fusion experiments with vacuum or low-gas-fill hohlraums, collisionless electrostatic shocks can be launched in the hohlraum wall/alblator (or the low-density fill-gas) interpenetration region, which reflect ions at twice the shock velocity. A low-energy Thomson ion spectrometer was designed to measure the energy spectra of the reflected ions on the order of 10 keV generated by nanosecond-laser-driven non-relativistic collisionless electrostatic shocks. Monte Carlo simulations of ion measurement were carried out with Geant4 modeling to evaluate the influence of residual gas in the vacuum chamber and gas jet on the measurement of the low-energy ions. Simulation results show that the residual gas in the vacuum chamber causes the signal of D ions on the order of 10 keV to broaden in both the electric and magnetic deflection of the spectrometer. The broadening of the electric deflection will increase the risk of overlapping of ion spectral lines of different charge-to-mass ratios, while the broadening of the magnetic deflection will lead to the broadening of the energy spectra of the ions. The gas jet causes the ion signal to move and tail into the lower energy region, causing the measured ion spectra to deviate from the actual energy spectra of the reflected ions.
2022,
34: 123001.
doi: 10.11884/HPLPB202234.220172
Abstract:
The electromagnetic radiation of pantograph-catenary offline discharge has the characteristics of transient and broadband. We can use the D-dot sensor to measure its transient electric field in time domain. However, the direct integral operation of the differential signal seriously distorts the original signal. To solve this problem, a transient electric field time-domain waveform restoration system including a pulse electric field generating device and a measuring device is built in the laboratory firstly. Then, we propose a time-domain waveform restoration method for transient electric field including DC removal, numerical integration, elimination of trend items and low frequency compensation. Finally, the method is used to test the electric field time domain waveform of electromagnetic radiation of pantograph- catenary offline discharge under different voltages. Theoretical and experimental results show that the proposed method can accurately and stably restore the original time-domain waveform of the transient electric field radiated by off-line discharge of the pantograph. The main frequency components of the reduced signal and the measured differential signal are both at 7.5MHz, and the correlation coefficient between them is more than 93%.
The electromagnetic radiation of pantograph-catenary offline discharge has the characteristics of transient and broadband. We can use the D-dot sensor to measure its transient electric field in time domain. However, the direct integral operation of the differential signal seriously distorts the original signal. To solve this problem, a transient electric field time-domain waveform restoration system including a pulse electric field generating device and a measuring device is built in the laboratory firstly. Then, we propose a time-domain waveform restoration method for transient electric field including DC removal, numerical integration, elimination of trend items and low frequency compensation. Finally, the method is used to test the electric field time domain waveform of electromagnetic radiation of pantograph- catenary offline discharge under different voltages. Theoretical and experimental results show that the proposed method can accurately and stably restore the original time-domain waveform of the transient electric field radiated by off-line discharge of the pantograph. The main frequency components of the reduced signal and the measured differential signal are both at 7.5MHz, and the correlation coefficient between them is more than 93%.
2022,
34: 123002.
doi: 10.11884/HPLPB202234.220219
Abstract:
A design method for broadband reflective linearizer with specific gain and phase compensation is proposed, and a predistortion linearizer for solid-state power amplifiers is designed by this method. Nonlinear compensation is produced using the Schottky diode. The MATLAB optimization tool is utilized to calculate the shunt load’s impedance at a single frequency point with the specified gain and phase compensation in accordance with the circuit topology. To obtain the variation of the shunt load with frequency necessary for a specific gain and phase compensation, i.e. the ZL-f curve, the frequency point is changed, and the aforementioned procedures are repeated. The circuit is optimized using the ADS software so that the change in impedance of the diode's parallel load with frequency is approximated by the ZL-f curve. The gain compensation and phase compensation of the circuit simulated in this paper are 6 dB and −40°, respectively. The final measurement reveals that the frequency band characteristics are good when the frequency range is 9.4–11.4 GHz, the gain expansion is 3.9–4.4 dB, and the phase compensation is −32.3°–41.5°. Additionally, the relative bandwidth of linearizer is 19.2%. By changing the DC bias voltage of the diode, the slope of the compensation curve is also adjustable.
A design method for broadband reflective linearizer with specific gain and phase compensation is proposed, and a predistortion linearizer for solid-state power amplifiers is designed by this method. Nonlinear compensation is produced using the Schottky diode. The MATLAB optimization tool is utilized to calculate the shunt load’s impedance at a single frequency point with the specified gain and phase compensation in accordance with the circuit topology. To obtain the variation of the shunt load with frequency necessary for a specific gain and phase compensation, i.e. the ZL-f curve, the frequency point is changed, and the aforementioned procedures are repeated. The circuit is optimized using the ADS software so that the change in impedance of the diode's parallel load with frequency is approximated by the ZL-f curve. The gain compensation and phase compensation of the circuit simulated in this paper are 6 dB and −40°, respectively. The final measurement reveals that the frequency band characteristics are good when the frequency range is 9.4–11.4 GHz, the gain expansion is 3.9–4.4 dB, and the phase compensation is −32.3°–41.5°. Additionally, the relative bandwidth of linearizer is 19.2%. By changing the DC bias voltage of the diode, the slope of the compensation curve is also adjustable.
2022,
34: 123003.
doi: 10.11884/HPLPB202234.220094
Abstract:
EMP simulators are used to test and harden electronic systems in an intense electromagnetic pulse. A horizontally polarized bounded-wave EMP simulator is designed based on a bicone-plate antenna structure, which combines the strengths of traditional bounded-wave simulators and radiating-wave simulators. Simulation and experiments are conducted to study the characteristics and the distribution of the radiation field. The results show that the simulator can generate horizontally polarized electromagnetic pulse and the waveform is double-exponential with a rise time of (2.5±0.5) ns and a pulse width of (23±5) ns. The simulator has a working volume of 5 m×3 m×2 m in which the electric field is no less than 50 kV/m within a 6 dB tolerance. Moreover, the simulator is flexible to increase the working volume while decreasing the field intensity.
EMP simulators are used to test and harden electronic systems in an intense electromagnetic pulse. A horizontally polarized bounded-wave EMP simulator is designed based on a bicone-plate antenna structure, which combines the strengths of traditional bounded-wave simulators and radiating-wave simulators. Simulation and experiments are conducted to study the characteristics and the distribution of the radiation field. The results show that the simulator can generate horizontally polarized electromagnetic pulse and the waveform is double-exponential with a rise time of (2.5±0.5) ns and a pulse width of (23±5) ns. The simulator has a working volume of 5 m×3 m×2 m in which the electric field is no less than 50 kV/m within a 6 dB tolerance. Moreover, the simulator is flexible to increase the working volume while decreasing the field intensity.
2022,
34: 123004.
doi: 10.11884/HPLPB202234.220241
Abstract:
For the first time, a highly isolated common aperture low-profile microstrip antenna is designed and realized to work in four frequency bands—L/S/C/X, simultaneously. The overall structure is made by stacking microstrip antennas of four bands from bottom to top according to the order of frequency from low to high, using coaxial probes through the low-frequency radiation patch to form an over-hole to feed the high-frequency antenna and using the lower-frequency antenna as the ground of the higher-frequency one in turn to improve the antenna index and performance. Among them, each radiation patch of L/S/C band adopts the way of adding branches around a rectangular radiation patch, which is conducive to impedance adjustment. The X band radiation patch is placed at the top layer, and by slotting the rectangular patch, the radiation blocking to other bands is avoided. By adopting the method of neutralizing line decoupling and orthogonally feeding, the gain in the four bands is finally realized as 6.85 dBi, 7.48 dBi, 6.13 dBi, and 6.62 dBi respectively. The isolation between each port is greater than 30 dB. The antenna size is 85 mm×85 mm×9.07 mm. By means of the physical processing , the test results and simulation ones match well, which verifies the validity and reliability of the design.
For the first time, a highly isolated common aperture low-profile microstrip antenna is designed and realized to work in four frequency bands—L/S/C/X, simultaneously. The overall structure is made by stacking microstrip antennas of four bands from bottom to top according to the order of frequency from low to high, using coaxial probes through the low-frequency radiation patch to form an over-hole to feed the high-frequency antenna and using the lower-frequency antenna as the ground of the higher-frequency one in turn to improve the antenna index and performance. Among them, each radiation patch of L/S/C band adopts the way of adding branches around a rectangular radiation patch, which is conducive to impedance adjustment. The X band radiation patch is placed at the top layer, and by slotting the rectangular patch, the radiation blocking to other bands is avoided. By adopting the method of neutralizing line decoupling and orthogonally feeding, the gain in the four bands is finally realized as 6.85 dBi, 7.48 dBi, 6.13 dBi, and 6.62 dBi respectively. The isolation between each port is greater than 30 dB. The antenna size is 85 mm×85 mm×9.07 mm. By means of the physical processing , the test results and simulation ones match well, which verifies the validity and reliability of the design.
2022,
34: 124001.
doi: 10.11884/HPLPB202234.220322
Abstract:
Based on the photocathode S-band electron linac, a high-energy (9 MeV) micro-focus CT system named “Jingwei” was built. The focal-point is less than 100 μm, and the 7 h dose fluctuation is as low as 1.6%. An initial imaging experiment was also carried out. The focal spot of the dual-wire image quality meter clearly distinguished the 13D wire with a wire diameter of 0.05 mm, and the CT spatial resolution measured by a test card is better than 10 lp/mm. The electron beam energy of the system is also adjustable from 6 MeV to 18 MeV.
2022,
34: 124002.
doi: 10.11884/HPLPB202234.220180
Abstract:
The 270° beam deflection system with magnets is widely used in medical electron linear accelerators and high-energy electron industrial irradiation accelerators. In this paper, three common structures of 270° deflection magnet are systematically analyzed and discussed. Numerical calculation and simulation methods are used for the two-magnet asymmetric deflection structure, the three 90° magnets deflection structure and the 70°+130°+70° deflection structure. The achromatic transmission conditions of the deflection systems are given, and the changes of beam envelope in the deflection and exit beam line are analyzed. After analysis and comparison, the advantages and disadvantages of the three structures are listed in detail, which has certain guiding significance for the selection of structures in specific application fields. The two-magnet asymmetric deflection structure is suitable for medical accelerators. The three 90° magnets deflection structure is suitable for irradiation accelerators that require long-distance drift at the exit. The 70°+130°+70° deflection structure can satisfy the non-destructive drift of a certain distance from the exit, and it achieves relatively low cost, therefore, it which is a more economical and suitable choice for industrial irradiation accelerators.
The 270° beam deflection system with magnets is widely used in medical electron linear accelerators and high-energy electron industrial irradiation accelerators. In this paper, three common structures of 270° deflection magnet are systematically analyzed and discussed. Numerical calculation and simulation methods are used for the two-magnet asymmetric deflection structure, the three 90° magnets deflection structure and the 70°+130°+70° deflection structure. The achromatic transmission conditions of the deflection systems are given, and the changes of beam envelope in the deflection and exit beam line are analyzed. After analysis and comparison, the advantages and disadvantages of the three structures are listed in detail, which has certain guiding significance for the selection of structures in specific application fields. The two-magnet asymmetric deflection structure is suitable for medical accelerators. The three 90° magnets deflection structure is suitable for irradiation accelerators that require long-distance drift at the exit. The 70°+130°+70° deflection structure can satisfy the non-destructive drift of a certain distance from the exit, and it achieves relatively low cost, therefore, it which is a more economical and suitable choice for industrial irradiation accelerators.
2022,
34: 124003.
doi: 10.11884/HPLPB202234.220195
Abstract:
As the precise sensor system for monitoring the relative difference in height among multiple points, the hydrostatic leveling system (HLS) is widely used in particle accelerators. At present, the HLS system is mainly used for the measurement of relative altitude changes. To expand the application of HLS system in accelerator alignment, the research on the issue of HLS system for altitude difference measurement based on the horizontal plane between multiple points is carried out. Firstly, the measurement principle of capacitive HLS sensor is introduced briefly. Based on the working principle of the sensor, a comparison system composed of dual-frequency laser interferometer, high-precision Z stage, HLS sensors and others is designed and manufactured. The system is used to control multiple sensors to observe the same liquid level in the same coordinate system. The zero-position difference between multiple sensors based on the sensor coordinate system are obtained by comparison, and the absolute height difference measurement with respect to a hydrostatic surface between the multi-sensor coordinate systems is realized, and it is verified that the measurement accuracy is better than 5 μm. In addition, by installing the target holder above the HLS sensor, and using the coordinate measuring machine (CMM) to strictly calibrate the distance between the sensor surface to the center of the target of each sensor, the absolute height difference measurement of the position of the multi-target centers with respect to the hydrostatic surface is realized, and its measurement accuracy is better than 30 μm.
As the precise sensor system for monitoring the relative difference in height among multiple points, the hydrostatic leveling system (HLS) is widely used in particle accelerators. At present, the HLS system is mainly used for the measurement of relative altitude changes. To expand the application of HLS system in accelerator alignment, the research on the issue of HLS system for altitude difference measurement based on the horizontal plane between multiple points is carried out. Firstly, the measurement principle of capacitive HLS sensor is introduced briefly. Based on the working principle of the sensor, a comparison system composed of dual-frequency laser interferometer, high-precision Z stage, HLS sensors and others is designed and manufactured. The system is used to control multiple sensors to observe the same liquid level in the same coordinate system. The zero-position difference between multiple sensors based on the sensor coordinate system are obtained by comparison, and the absolute height difference measurement with respect to a hydrostatic surface between the multi-sensor coordinate systems is realized, and it is verified that the measurement accuracy is better than 5 μm. In addition, by installing the target holder above the HLS sensor, and using the coordinate measuring machine (CMM) to strictly calibrate the distance between the sensor surface to the center of the target of each sensor, the absolute height difference measurement of the position of the multi-target centers with respect to the hydrostatic surface is realized, and its measurement accuracy is better than 30 μm.
2022,
34: 124004.
doi: 10.11884/HPLPB202234.220123
Abstract:
Neutral beam has potential applications in space debris cleanup and space exploration. As that neutral beam prepared by ion source is not ideal in practice, this paper simulates the long-range transmission effect of non-ideal hydrogen beam in vacuum environment. According to the degree of neutralization, non-ideal beams are divided into under-neutral beams and over-neutral beams. The effects of beam density, neutralization factor, spatial magnetic field and elastic scattering on the nonideal hydrogen beam are studied by establishing a quasi-electromagnetic model of beam transmission. The results show that the presence of negative hydrogen ions has no effect on the transmission of hydrogen atoms in the under-neutral beam, thus the bias magnetic field can be removed to reduce the volume and mass of the device. For the over-neutral beam, the loss ratio is related to the beam density and neutralization factor, that is, the higher the beam density, the greater the beam loss; the higher the neutralization factor, the higher the beam loss. The magnetic field and the elastic scattering between particles have no effect on the propagation of either the under-neutral or over-neutral beams.
Neutral beam has potential applications in space debris cleanup and space exploration. As that neutral beam prepared by ion source is not ideal in practice, this paper simulates the long-range transmission effect of non-ideal hydrogen beam in vacuum environment. According to the degree of neutralization, non-ideal beams are divided into under-neutral beams and over-neutral beams. The effects of beam density, neutralization factor, spatial magnetic field and elastic scattering on the nonideal hydrogen beam are studied by establishing a quasi-electromagnetic model of beam transmission. The results show that the presence of negative hydrogen ions has no effect on the transmission of hydrogen atoms in the under-neutral beam, thus the bias magnetic field can be removed to reduce the volume and mass of the device. For the over-neutral beam, the loss ratio is related to the beam density and neutralization factor, that is, the higher the beam density, the greater the beam loss; the higher the neutralization factor, the higher the beam loss. The magnetic field and the elastic scattering between particles have no effect on the propagation of either the under-neutral or over-neutral beams.
2022,
34: 125001.
doi: 10.11884/HPLPB202234.220213
Abstract:
To suppress the surface charge accumulation and improve the surface pressure resistance of polytetrafluoroethene (PTFE), the plasma immersion ion implantation was carried out on the surface of PTFE by radio frequency (RF) generation nitrogen plasma. The modification effect of PTFE sample surface was realized by changing RF power, pulse width and pulse amplitude during injection. X-ray photoelectron spectroscopy, surface morphology, surface resistivity, surface potential attenuation characteristics, surface trap energy level and density distribution were measured before and after injection. The effects of different injection parameters on surface composition, surface charge accumulation and dissipation characteristics of PTFE samples were systematically studied. The results show that nitrogen ions can achieve surface modification mainly through their own kinetic energy, rather than introducing new components through chemical reaction. The kinetic energy and quantity of nitrogen ions are the main factors determining the surface modification effect. With the increase of RF source power, nitrogen utilization efficiency of RF source is improved, the saturation point of treatment effect increases from 20 cm3/min at 100 W RF power to 30 cm3/min at 400 W RF power. The corresponding surface resistivity decreases from the maximum value\begin{document}$ 3.3\times {10}^{16}\;\mathrm{\Omega }/\mathrm{m}{\mathrm{m}}^{2} $\end{document} ![]()
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\begin{document}$ 1\times {10}^{15}\;\mathrm{\Omega }/\mathrm{m}{\mathrm{m}}^{2} $\end{document} ![]()
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To suppress the surface charge accumulation and improve the surface pressure resistance of polytetrafluoroethene (PTFE), the plasma immersion ion implantation was carried out on the surface of PTFE by radio frequency (RF) generation nitrogen plasma. The modification effect of PTFE sample surface was realized by changing RF power, pulse width and pulse amplitude during injection. X-ray photoelectron spectroscopy, surface morphology, surface resistivity, surface potential attenuation characteristics, surface trap energy level and density distribution were measured before and after injection. The effects of different injection parameters on surface composition, surface charge accumulation and dissipation characteristics of PTFE samples were systematically studied. The results show that nitrogen ions can achieve surface modification mainly through their own kinetic energy, rather than introducing new components through chemical reaction. The kinetic energy and quantity of nitrogen ions are the main factors determining the surface modification effect. With the increase of RF source power, nitrogen utilization efficiency of RF source is improved, the saturation point of treatment effect increases from 20 cm3/min at 100 W RF power to 30 cm3/min at 400 W RF power. The corresponding surface resistivity decreases from the maximum value
2022,
34: 125002.
doi: 10.11884/HPLPB202234.220128
Abstract:
The influences of switch prefire in different LTD cavities on the other cavities with shorted or open load have been researched based on the 50 stages linear transformer driver module. It is shown that the induced voltage in the other cavities is very low, and the amplitude of voltage signal will decrease with increase of distance. The maximal induced voltage is 2.43 kV when switch prefire occurred in neighbouring cavity at voltage of ±83 kV. The results will contribute to reliability model constructing, analysis and assessment of large scale LTD generator.
The influences of switch prefire in different LTD cavities on the other cavities with shorted or open load have been researched based on the 50 stages linear transformer driver module. It is shown that the induced voltage in the other cavities is very low, and the amplitude of voltage signal will decrease with increase of distance. The maximal induced voltage is 2.43 kV when switch prefire occurred in neighbouring cavity at voltage of ±83 kV. The results will contribute to reliability model constructing, analysis and assessment of large scale LTD generator.
2022,
34: 125003.
doi: 10.11884/HPLPB202234.220284
Abstract:
A new large research infrastructure for fundamental researches on the space environment, Space Environment Simulation Research Infrastructure (SESRI), is being constructed. When studying the three-dimensional magnetic reconnection of the earth’s magnetotail, the dipole coil and two magnetic mirror coils in vacuum environment are used to provide the simulated background magnetic field required for the study. To generate the amplitude and duration of the background magnetic field required by the experiment, two sets of pulsed power supplies with a total energy of 3.36 MJ are developed and tested. The pulsed power supply used to drive the dipole coil can provide a peak current of more than 9 kA when the charging voltage is not more than 20 kV, and the duration of 95% peak current is more than 5 ms, the time from peak time to 10% peak time does not exceed 130 ms; According to the experimental requirements, the pulsed power supply used to drive the magnetic mirror coil can provide a peak current of more than 8 kA when the charging voltage is not more than 20 kV, the duration of 95% peak current is more than 5 ms, and the time from peak time to 10% peak time does not exceed 130 ms. The two sets of pulsed power supplies need to work simultaneously in the three-dimensional magnetic reconnection experiment of the earth’s magnetotail.
A new large research infrastructure for fundamental researches on the space environment, Space Environment Simulation Research Infrastructure (SESRI), is being constructed. When studying the three-dimensional magnetic reconnection of the earth’s magnetotail, the dipole coil and two magnetic mirror coils in vacuum environment are used to provide the simulated background magnetic field required for the study. To generate the amplitude and duration of the background magnetic field required by the experiment, two sets of pulsed power supplies with a total energy of 3.36 MJ are developed and tested. The pulsed power supply used to drive the dipole coil can provide a peak current of more than 9 kA when the charging voltage is not more than 20 kV, and the duration of 95% peak current is more than 5 ms, the time from peak time to 10% peak time does not exceed 130 ms; According to the experimental requirements, the pulsed power supply used to drive the magnetic mirror coil can provide a peak current of more than 8 kA when the charging voltage is not more than 20 kV, the duration of 95% peak current is more than 5 ms, and the time from peak time to 10% peak time does not exceed 130 ms. The two sets of pulsed power supplies need to work simultaneously in the three-dimensional magnetic reconnection experiment of the earth’s magnetotail.
2022,
34: 126001.
doi: 10.11884/HPLPB202234.220156
Abstract:
The heat pipe cooled reactor adopts the solid-state reactor design concept, and it has the characteristics of high power density, compact structure and high inherent safety. It has been extensively used for deep space exploration, deep sea exploration, remote areas electricity markets and other scenarios. Nuclear fuel is an important part of the heat pipe cooling reactor, different types of nuclear fuel will reflect different neutronics performance on the reactor burnup analysis. In this paper, based on the heat pipe cooled reactor INL Design A proposed by the Idaho National Laboratory (INL), the burnup calculation is done by selecting six nuclear fuels : UO2, (U0.9Pu0.1)O2, U-10Zr, U-8Pu-10Zr, UN and UC. The effects of different nuclear fuel and power levels on the burnup performance of heat pipe cooled reactor core were analyzed. The calculation results show that under the same core burnup depth (20.8 GW·d·t−1), the core loaded with U-8Pu-10Zr fuel requires the lowest 235U enrichment (9.8%), and has better U-Pu breeding. For the heat pipe cooling reactor with the core power of 5 MW, the presence of 241Pu in the fuel does not increase the core burnup depth, but leads to the increase of residual reactivity of the core and the yield of the secondary actinides nuclides (MAs) in the core end of life, which affects the safety and economy of the reactor. Therefore, for the low-power and long-life heat pipe cooled reactor loaded with Pu fuel, it is necessary to focus on the influence of 241Pu on the core burnup performance.
The heat pipe cooled reactor adopts the solid-state reactor design concept, and it has the characteristics of high power density, compact structure and high inherent safety. It has been extensively used for deep space exploration, deep sea exploration, remote areas electricity markets and other scenarios. Nuclear fuel is an important part of the heat pipe cooling reactor, different types of nuclear fuel will reflect different neutronics performance on the reactor burnup analysis. In this paper, based on the heat pipe cooled reactor INL Design A proposed by the Idaho National Laboratory (INL), the burnup calculation is done by selecting six nuclear fuels : UO2, (U0.9Pu0.1)O2, U-10Zr, U-8Pu-10Zr, UN and UC. The effects of different nuclear fuel and power levels on the burnup performance of heat pipe cooled reactor core were analyzed. The calculation results show that under the same core burnup depth (20.8 GW·d·t−1), the core loaded with U-8Pu-10Zr fuel requires the lowest 235U enrichment (9.8%), and has better U-Pu breeding. For the heat pipe cooling reactor with the core power of 5 MW, the presence of 241Pu in the fuel does not increase the core burnup depth, but leads to the increase of residual reactivity of the core and the yield of the secondary actinides nuclides (MAs) in the core end of life, which affects the safety and economy of the reactor. Therefore, for the low-power and long-life heat pipe cooled reactor loaded with Pu fuel, it is necessary to focus on the influence of 241Pu on the core burnup performance.
2022,
34: 126002.
doi: 10.11884/HPLPB202234.220192
Abstract:
To study the influence of different pulse parameters on the melting and resolidification behavior of tungsten after its temperature reaches the melting point under transient heat flow, the differences in morphology and structure of tungsten after melting and resolidification under IPEB (5 ms) and CPF (0.1 ms) were experimentally observed. The dependence of hierarchical structure and columnar crystal grain on pulse parameters was analyzed considering the driving force of molten layer motion, cooling rate, temperature gradient and other factors. The reason why the columnar crystal grains appear on tungsten at pulse width of 0.1 ms but not at pulse width of 5 ms was analyzed by calculating the thermal action characteristics for two heat sources. It is found that the beam with high current intensity and short pulse width is easy to promote the formation of hierarchical structure. The reason is that the high current intensity of the pulse beam can cause the molten layer motion on the surface of the material, while the short pulse width of the pulse beam can make the molten traces too late to recover and be quickly cooled and solidified. When the sample melts under transient heat flow, short pulse width is beneficial to the formation of columnar crystal grains and long pulse width is beneficial to the formation of equiaxed grains and grain growth.
To study the influence of different pulse parameters on the melting and resolidification behavior of tungsten after its temperature reaches the melting point under transient heat flow, the differences in morphology and structure of tungsten after melting and resolidification under IPEB (5 ms) and CPF (0.1 ms) were experimentally observed. The dependence of hierarchical structure and columnar crystal grain on pulse parameters was analyzed considering the driving force of molten layer motion, cooling rate, temperature gradient and other factors. The reason why the columnar crystal grains appear on tungsten at pulse width of 0.1 ms but not at pulse width of 5 ms was analyzed by calculating the thermal action characteristics for two heat sources. It is found that the beam with high current intensity and short pulse width is easy to promote the formation of hierarchical structure. The reason is that the high current intensity of the pulse beam can cause the molten layer motion on the surface of the material, while the short pulse width of the pulse beam can make the molten traces too late to recover and be quickly cooled and solidified. When the sample melts under transient heat flow, short pulse width is beneficial to the formation of columnar crystal grains and long pulse width is beneficial to the formation of equiaxed grains and grain growth.
2022,
34: 129001.
doi: 10.11884/HPLPB202234.220086
Abstract:
Evaluation function of automatic focusing system is the key to evaluate image quality. In multi-depth-of-field scenarios, when the target is located in the center of the image, the sensitivity of the traditional focusing evaluation curve is low; when the target deviates from the center, the focus evaluation function curve is prone to local maximum, which affects the accuracy of the automatic focusing system. In view of these two situations, this paper proposes a method based on U-Net neural network and sets the corresponding window and evaluation function. When the object is located in the center of the image, a new focusing evaluation function, SMD-Roberts function, is proposed. When the target is not in the center of the image, the corresponding window is set for the image and the SML evaluation function is selected to evaluate the image quality. Experimental results show that , compared with traditional focused evaluation function and central window method, this method can effectively solve the problem that the focus evaluation function is not accurate in judging the clearest position of the object and the double peak of the focusing evaluation function curve in multi-depth-of-field scenes and obviously improve the unbiasedness, unimodal and sensitivity of the focused evaluation function. This method has strong universality and is more suitable for focused evaluation system.
Evaluation function of automatic focusing system is the key to evaluate image quality. In multi-depth-of-field scenarios, when the target is located in the center of the image, the sensitivity of the traditional focusing evaluation curve is low; when the target deviates from the center, the focus evaluation function curve is prone to local maximum, which affects the accuracy of the automatic focusing system. In view of these two situations, this paper proposes a method based on U-Net neural network and sets the corresponding window and evaluation function. When the object is located in the center of the image, a new focusing evaluation function, SMD-Roberts function, is proposed. When the target is not in the center of the image, the corresponding window is set for the image and the SML evaluation function is selected to evaluate the image quality. Experimental results show that , compared with traditional focused evaluation function and central window method, this method can effectively solve the problem that the focus evaluation function is not accurate in judging the clearest position of the object and the double peak of the focusing evaluation function curve in multi-depth-of-field scenes and obviously improve the unbiasedness, unimodal and sensitivity of the focused evaluation function. This method has strong universality and is more suitable for focused evaluation system.
