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RSS2020 Vol. 32, No. 7
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2020,
32: 1-2.
2020,
32: 071001.
doi: 10.11884/HPLPB202032.200012
Abstract:
Charge coupled device(CCD) is one kind of photoelectric solid-state imaging device with excellent performance. It has the features of large array and good image quality. Working under very complex driving timing, it usually has low frame frequency and can not meet the demand of high imaging frame rate. The method of equivalent high frame rate imaging technique is introduced based on normal CCD in this paper. Some CCDs can be drived via electrodes separately. To meet the imaging demands of high frame rate, high resolution and high quality of two frame imaging technique for pulse light images, the right kind of CCDs should be adopted. The most important is that the CCD electrodes must be controlled directly and respectively. The charge transfer period is a key point while designing CCD driving timing for separate pulse light integration, charge package transfer and readout for two pulse light images. The validation experiments for the principle of equivalent high frame rate exposure of two pulse light images has been accomplished. It is shown that two pulse light images with interval of about 2 μs can be distinguished while all CCD’s inherent excellent performance are retained. A kind of two framing camera system with simple structure can be developed based on this principle.
Charge coupled device(CCD) is one kind of photoelectric solid-state imaging device with excellent performance. It has the features of large array and good image quality. Working under very complex driving timing, it usually has low frame frequency and can not meet the demand of high imaging frame rate. The method of equivalent high frame rate imaging technique is introduced based on normal CCD in this paper. Some CCDs can be drived via electrodes separately. To meet the imaging demands of high frame rate, high resolution and high quality of two frame imaging technique for pulse light images, the right kind of CCDs should be adopted. The most important is that the CCD electrodes must be controlled directly and respectively. The charge transfer period is a key point while designing CCD driving timing for separate pulse light integration, charge package transfer and readout for two pulse light images. The validation experiments for the principle of equivalent high frame rate exposure of two pulse light images has been accomplished. It is shown that two pulse light images with interval of about 2 μs can be distinguished while all CCD’s inherent excellent performance are retained. A kind of two framing camera system with simple structure can be developed based on this principle.
2020,
32: 071002.
doi: 10.11884/HPLPB202032.200006
Abstract:
Annealing is one of the most accessible post-treatment techniques in high power laser coatings, however, the impact of annealing on laser resistance of the coatings is not clear until today. In this experiment, HfO2 films have been prepared by EBE, IBS and ALD techniques, respectively. The laser resistance of each film before and after annealing has been tested with the 1 064 nm Nd: YAG laser according to ISO 21254. It is found that the ALD HfO2 film has the highest LIDT, while the IBS HfO2 film has the lowest. It is also found that the laser resistance of all the samples does not benefit from the 300 ℃ annealing, moreover, the laser resistance of the ALD HfO2 film decreases tremendously after annealing at 500 ℃. The experimental results are discussed and analyzed.
Annealing is one of the most accessible post-treatment techniques in high power laser coatings, however, the impact of annealing on laser resistance of the coatings is not clear until today. In this experiment, HfO2 films have been prepared by EBE, IBS and ALD techniques, respectively. The laser resistance of each film before and after annealing has been tested with the 1 064 nm Nd: YAG laser according to ISO 21254. It is found that the ALD HfO2 film has the highest LIDT, while the IBS HfO2 film has the lowest. It is also found that the laser resistance of all the samples does not benefit from the 300 ℃ annealing, moreover, the laser resistance of the ALD HfO2 film decreases tremendously after annealing at 500 ℃. The experimental results are discussed and analyzed.
2020,
32: 071003.
doi: 10.11884/HPLPB202032.190474
Abstract:
To study the pressure recovery ability of the diffuser of chemical lasers, an equipment that can simulate different background pressure is designed. The simulated background pressure can be changed by changing the valve’s pass area. The influence of the straight part’s length before the valve being considered, different length models are simulated and the validation test is carried out, whose result is consistent with that of the simulation. The result shows the feasibility of simulating different background pressure with a flashboard valve. The equipment will redound to the investigation of the diffuser’s recovery pressure in chemical lasers.
To study the pressure recovery ability of the diffuser of chemical lasers, an equipment that can simulate different background pressure is designed. The simulated background pressure can be changed by changing the valve’s pass area. The influence of the straight part’s length before the valve being considered, different length models are simulated and the validation test is carried out, whose result is consistent with that of the simulation. The result shows the feasibility of simulating different background pressure with a flashboard valve. The equipment will redound to the investigation of the diffuser’s recovery pressure in chemical lasers.
2020,
32: 071004.
doi: 10.11884/HPLPB202032.200021
Abstract:
Aiming at the requirements of efficient heat dissipation and uniform cooling for high heat flux laser medium, an experimental platform of open single nozzle spray was designed and established by using the deionized water as cooling medium. The spray cooling heat transfer coefficients and cooling uniformity effect in the single-phase region were obtained at different heat flux (16～110 W/cm2), flow rates (200～300 mL/min) and spray heights (15～25 mm). It is concluded from the experimental results that the cooling efficiency and temperature uniformity were significantly affected by the spray height and flow rate under different heat flux. The maximal heat transfer coefficient of 5.93 W/(cm2·K) was got at the spray height of 15 mm and flow rate of 200 mL/min, while the temperature uniformity could be greater than 0.6 ℃ with the heating area of 20 mm×20 mm at the spray height of 15 mm and flow rate of 250 mL/min.
Aiming at the requirements of efficient heat dissipation and uniform cooling for high heat flux laser medium, an experimental platform of open single nozzle spray was designed and established by using the deionized water as cooling medium. The spray cooling heat transfer coefficients and cooling uniformity effect in the single-phase region were obtained at different heat flux (16～110 W/cm2), flow rates (200～300 mL/min) and spray heights (15～25 mm). It is concluded from the experimental results that the cooling efficiency and temperature uniformity were significantly affected by the spray height and flow rate under different heat flux. The maximal heat transfer coefficient of 5.93 W/(cm2·K) was got at the spray height of 15 mm and flow rate of 200 mL/min, while the temperature uniformity could be greater than 0.6 ℃ with the heating area of 20 mm×20 mm at the spray height of 15 mm and flow rate of 250 mL/min.
2020,
32: 071005.
doi: 10.11884/HPLPB202032.200007
Abstract:
To further improve the output power of the multi-single emitters diode laser, based on the analysis of the common stepped multi-single emitters diode laser array, this paper proposes to fill the beam in the slow axis direction with small spot size, and under the same coupling condition, more laser energy is coupled into the fiber to achieve higher power output. The beam-parameter product is used as the index to evaluate the beam quality, and the feasibility of slow axis beam filling is demonstrated. By using ZEMAX simulation software, the comparison simulation of 8-way ladder type multi-single emitters diode laser array and 12-way filling array is carried out. On the premise of not affecting the coupling efficiency, the 12 single emitters diode laser with center wavelength of 860 nm and output power of 3 W is coupled into a fiber with core diameter of 105 um and numerical aperture of 0.22, the output power is 33.4 W and the coupling efficiency is 92.78%. The simulation results show that the slow axis beam filling can improve the power output of the diode laser to a certain extent.
To further improve the output power of the multi-single emitters diode laser, based on the analysis of the common stepped multi-single emitters diode laser array, this paper proposes to fill the beam in the slow axis direction with small spot size, and under the same coupling condition, more laser energy is coupled into the fiber to achieve higher power output. The beam-parameter product is used as the index to evaluate the beam quality, and the feasibility of slow axis beam filling is demonstrated. By using ZEMAX simulation software, the comparison simulation of 8-way ladder type multi-single emitters diode laser array and 12-way filling array is carried out. On the premise of not affecting the coupling efficiency, the 12 single emitters diode laser with center wavelength of 860 nm and output power of 3 W is coupled into a fiber with core diameter of 105 um and numerical aperture of 0.22, the output power is 33.4 W and the coupling efficiency is 92.78%. The simulation results show that the slow axis beam filling can improve the power output of the diode laser to a certain extent.
2020,
32: 071006.
doi: 10.11884/HPLPB202032.200028
Abstract:
Nodular defect is one of the most common defects that affect the laser damage resistance of optical thin films. It has been an important research object in the field of high power laser thin films at home and abroad. 45° multilayer mirrors with a central wavelength of 1 064 nm were designed and fabricated. Through numerical simulations and experiments, the electric field enhancement effect(EFEE) caused by nodular defect and its influence on the laser damage resistance of the film were studied. The results show that when the 1 064 nm laser is incident obliquely from right to left at 45°, the EFEE mainly appears in the surface layer of the nodular defect and the middle of its left profile. The EFEE increases with the size of nodule defect. In the experiment, mono-disperse SiO2 microspheres were sprayed on the surface of clean substrates as the artificial nodule seeds, the multilayer high reflection coatings were prepared by electron beam evaporation, and the laser damage resistance of the samples was tested by R-on-1 method. By comprehensively analyzing the experiment results, it is concluded that the damage threshold reduction of coatings is due to the nodular defects and micro-defects in the coatings, and the damage threshold of coatings decreases with the increase of nodular defect size.
Nodular defect is one of the most common defects that affect the laser damage resistance of optical thin films. It has been an important research object in the field of high power laser thin films at home and abroad. 45° multilayer mirrors with a central wavelength of 1 064 nm were designed and fabricated. Through numerical simulations and experiments, the electric field enhancement effect(EFEE) caused by nodular defect and its influence on the laser damage resistance of the film were studied. The results show that when the 1 064 nm laser is incident obliquely from right to left at 45°, the EFEE mainly appears in the surface layer of the nodular defect and the middle of its left profile. The EFEE increases with the size of nodule defect. In the experiment, mono-disperse SiO2 microspheres were sprayed on the surface of clean substrates as the artificial nodule seeds, the multilayer high reflection coatings were prepared by electron beam evaporation, and the laser damage resistance of the samples was tested by R-on-1 method. By comprehensively analyzing the experiment results, it is concluded that the damage threshold reduction of coatings is due to the nodular defects and micro-defects in the coatings, and the damage threshold of coatings decreases with the increase of nodular defect size.
2020,
32: 071007.
doi: 10.11884/HPLPB202032.200061
Abstract:
Femtosecond laser can ablate explosives to generate a high-temperature, high-pressure plasma in extremely short time. The femtosecond laser can be used to precisely process energetic materials or assemblies containing energetic materials. Deep understanding of the thermal effects within the explosives during femtosecond laser ablation is the basis for the development of the safe processing technology of explosives using femtosecond laser. A fluid-solid coupling calculation model of single-pulse femtosecond laser ablation of explosives was established to study the combined thermal effect of the thermal radiation of the plasma and the autothermal reaction of the explosives. The hydrodynamic process of femtosecond laser ablation on TNT was calculated. The results show that in the unablated zones of the explosive, significant thermal effect was detected, and the peak temperature is higher than that of ignition. Due to the small zones affected by the thermal effect and its extremely short duration time, the temperature in the explosive drops quickly, thus the explosive is not ignited.
Femtosecond laser can ablate explosives to generate a high-temperature, high-pressure plasma in extremely short time. The femtosecond laser can be used to precisely process energetic materials or assemblies containing energetic materials. Deep understanding of the thermal effects within the explosives during femtosecond laser ablation is the basis for the development of the safe processing technology of explosives using femtosecond laser. A fluid-solid coupling calculation model of single-pulse femtosecond laser ablation of explosives was established to study the combined thermal effect of the thermal radiation of the plasma and the autothermal reaction of the explosives. The hydrodynamic process of femtosecond laser ablation on TNT was calculated. The results show that in the unablated zones of the explosive, significant thermal effect was detected, and the peak temperature is higher than that of ignition. Due to the small zones affected by the thermal effect and its extremely short duration time, the temperature in the explosive drops quickly, thus the explosive is not ignited.
2020,
32: 071008.
doi: 10.11884/HPLPB202032.200078
Abstract:
To reduce the complexity and cost of partially coherent optical system, increase the convenience of partially coherent laser beam application, in this paper, we presents a method to control the coherence and divergence angle of laser beam complexly, using a liquid crystal spatial light modulator (LC-SLM). First, we introduce the basic theory and method to control the coherence and divergence angle of laser beam complexly using an LC-SLM; then, we put forward the experiment to test the coherence and divergence angle controlling accuracy. The experiment results show that, for a partially coherent laser beam with the coherence and divergence angle of 0.9 mm, 7.5 mrad and 1.5 mm, 3.8 mrad, the error of coherence is less than 5%, the root-mean-square errors of the degree of coherence are 0.027 386 and 0.031 314, and the peak-to-valley values are 0.084 658 and 0.089 103 respectively; the error of divergence angle is less than 5%, the root-mean-square errors of the divergence angle are 0.022 478 and 0.023 186, and the peak-to-valley values are 0.081 201 and 0.092 130 respectively. This method can control degree of coherence and divergence angle with high accuracy.
To reduce the complexity and cost of partially coherent optical system, increase the convenience of partially coherent laser beam application, in this paper, we presents a method to control the coherence and divergence angle of laser beam complexly, using a liquid crystal spatial light modulator (LC-SLM). First, we introduce the basic theory and method to control the coherence and divergence angle of laser beam complexly using an LC-SLM; then, we put forward the experiment to test the coherence and divergence angle controlling accuracy. The experiment results show that, for a partially coherent laser beam with the coherence and divergence angle of 0.9 mm, 7.5 mrad and 1.5 mm, 3.8 mrad, the error of coherence is less than 5%, the root-mean-square errors of the degree of coherence are 0.027 386 and 0.031 314, and the peak-to-valley values are 0.084 658 and 0.089 103 respectively; the error of divergence angle is less than 5%, the root-mean-square errors of the divergence angle are 0.022 478 and 0.023 186, and the peak-to-valley values are 0.081 201 and 0.092 130 respectively. This method can control degree of coherence and divergence angle with high accuracy.
2020,
32: 072001.
doi: 10.11884/HPLPB202032.200069
Abstract:
The guide-slider joint of the transmission mechanism with a long stroke has a great effect on the dynamic characteristic of the structure. Aiming at the dynamic modeling on the joint part of the LM linear rolling guide in some large laser facility, the finite element (FE) model of the transmission mechanism with a long stroke is established based on the thin layer element and spring element. The modulus of the thin element and the stiffness of the spring element are identified by the model updating method and the modal experimental results. After the model update, the maximal error of the first three modal frequencies between simulation and experiment is 2.29%, and the maximal error of the point’s displacement response between simulation and experiment is 7.61% under the ambient vibration. The results of simulation and experiment are consistent, which shows that the model is effective and reasonable. The study provides a theoretical basis for the high confidence dynamic modeling on other structure with such a the joint.
The guide-slider joint of the transmission mechanism with a long stroke has a great effect on the dynamic characteristic of the structure. Aiming at the dynamic modeling on the joint part of the LM linear rolling guide in some large laser facility, the finite element (FE) model of the transmission mechanism with a long stroke is established based on the thin layer element and spring element. The modulus of the thin element and the stiffness of the spring element are identified by the model updating method and the modal experimental results. After the model update, the maximal error of the first three modal frequencies between simulation and experiment is 2.29%, and the maximal error of the point’s displacement response between simulation and experiment is 7.61% under the ambient vibration. The results of simulation and experiment are consistent, which shows that the model is effective and reasonable. The study provides a theoretical basis for the high confidence dynamic modeling on other structure with such a the joint.
2020,
32: 072002.
doi: 10.11884/HPLPB202032.200117
Abstract:
Advances in basic and applied research of conventional grating have been attracting much attention from optical engineering community. However, the higher orders diffraction contamination degrades the spectral purity obtained by conventional gratings seriously. Many designs of single-order or quasi-single-order gratings have been proposed to suppress higher-order diffraction contributions, however, their inhibitive effects on the higher order diffractions are restrained by the processing accuracy unavoidably. In this paper, we propose a grating that incorporates a quasi-periodical array of rectangular holes, and achieves larger tolerance of processing errors compared with the previously designed gratings by optimizing the probability density distribution function of the holes. This paper describes an analytical study of the diffraction property of this grating. Theoretical calculations reveal that the grating completely suppresses the 2nd, 3rd, and 4th orders diffractions, and the ratio of the 5th order diffraction efficiency to that of the 1st is as low as 0.01% even if relative errors for hole sizes exceed 20%, which greatly decreases the required processing accuracy.
Advances in basic and applied research of conventional grating have been attracting much attention from optical engineering community. However, the higher orders diffraction contamination degrades the spectral purity obtained by conventional gratings seriously. Many designs of single-order or quasi-single-order gratings have been proposed to suppress higher-order diffraction contributions, however, their inhibitive effects on the higher order diffractions are restrained by the processing accuracy unavoidably. In this paper, we propose a grating that incorporates a quasi-periodical array of rectangular holes, and achieves larger tolerance of processing errors compared with the previously designed gratings by optimizing the probability density distribution function of the holes. This paper describes an analytical study of the diffraction property of this grating. Theoretical calculations reveal that the grating completely suppresses the 2nd, 3rd, and 4th orders diffractions, and the ratio of the 5th order diffraction efficiency to that of the 1st is as low as 0.01% even if relative errors for hole sizes exceed 20%, which greatly decreases the required processing accuracy.
2020,
32: 073001.
doi: 10.11884/HPLPB202032.200095
Abstract:
Microwave power amplifiers are divided into vacuum and solid devices. This paper analyzes the principles, advantages and disadvantages of these two types of devices, and then introduces their development history, current technical research status and future development trends. This paper mainly introduces the microwave power module as it is the combination of these two devices, including its evolution process and current development status both home and abroad, and analyzes and predictes its future development.
Research on several test issues of electromagnetic radiation susceptibility for electronic equipment
2020,
32: 073002.
doi: 10.11884/HPLPB202032.200088
Abstract:
According to the practical problem that some electronic equipments still exist electromagnetic incompatibility phenomenon in training and fighting stage after passing the normal electromagnetic compatibility test required by National Military Standard of China, on the basis of systematically analyzing the technical requirements and test methods in the current military standard, considering the technology accumulation of our research team on the electronic information equipment electromagnetic environment effects in recent years, the influence the several conditions on the electronic information equipment electromagnetic radiation susceptibility test results were discussed. These conditions contain not searching the sensitive receiving direction of the equipment under test(EUT), lacking of electromagnetic radiation susceptibility test in in-band frequency, multi-source radiation causing remarkable reduction of the susceptibility threshold of the EUT and so on. On the basis of the discussion, the measures and suggestions which can solve the above related problems were given. The development tendency of the high intensity electromagnetic radiation effect test technology and the complex electromagnetic environment adaptability evaluation technology for electronic equipment were discussed.
According to the practical problem that some electronic equipments still exist electromagnetic incompatibility phenomenon in training and fighting stage after passing the normal electromagnetic compatibility test required by National Military Standard of China, on the basis of systematically analyzing the technical requirements and test methods in the current military standard, considering the technology accumulation of our research team on the electronic information equipment electromagnetic environment effects in recent years, the influence the several conditions on the electronic information equipment electromagnetic radiation susceptibility test results were discussed. These conditions contain not searching the sensitive receiving direction of the equipment under test(EUT), lacking of electromagnetic radiation susceptibility test in in-band frequency, multi-source radiation causing remarkable reduction of the susceptibility threshold of the EUT and so on. On the basis of the discussion, the measures and suggestions which can solve the above related problems were given. The development tendency of the high intensity electromagnetic radiation effect test technology and the complex electromagnetic environment adaptability evaluation technology for electronic equipment were discussed.
2020,
32: 073003.
doi: 10.11884/HPLPB202032.200092
Abstract:
By coupling with cables, the high electromagnetic pulse poses a serious threat to the electronic control unit of vehicle platform, which affects the performance of the vehicle. Based on a typical vehicle platform, the effect mechanism of electronic control unit(ECU) in the environment of high electromagnetic pulses is analyzed. The relationship between the working state of the engine on the vehicle platform and the coupling voltage on the power supply line of the ECU is analyzed through the wide-band high electromagnetic pulse irradiation test of the vehicle platform. The test results show that the wide-band electromagnetic pulses cause electromagnetic interference to the vehicle ECU through the power cable, which leads to the engine flameout. According to the analysis results, a multi-level protection circuit is designed for the DC power supply of the ECU. The electromagnetic safety protection is realized by cutting off the transmission path of electromagnetic pulse energy, and the effectiveness of the protection circuit is verified.
By coupling with cables, the high electromagnetic pulse poses a serious threat to the electronic control unit of vehicle platform, which affects the performance of the vehicle. Based on a typical vehicle platform, the effect mechanism of electronic control unit(ECU) in the environment of high electromagnetic pulses is analyzed. The relationship between the working state of the engine on the vehicle platform and the coupling voltage on the power supply line of the ECU is analyzed through the wide-band high electromagnetic pulse irradiation test of the vehicle platform. The test results show that the wide-band electromagnetic pulses cause electromagnetic interference to the vehicle ECU through the power cable, which leads to the engine flameout. According to the analysis results, a multi-level protection circuit is designed for the DC power supply of the ECU. The electromagnetic safety protection is realized by cutting off the transmission path of electromagnetic pulse energy, and the effectiveness of the protection circuit is verified.
2020,
32: 073004.
doi: 10.11884/HPLPB202032.190441
Abstract:
To evaluate Electromagnetic Environment Effects (E3) of the vehicle ignition pulses on High Frequency Receiving Station (HFRS), a model of the vehicle ignition circuit has been analyzed, and frequency spectrums of the noises induced by a car and a truck at the moment of their engine being ignited were measured. Using the method-of-moments-based electromagnetic simulation tool, we have modeled the ignition-equivalent antennas by a car and a truck respectively and obtained their transmission loss fluctuation curves in the transmission path to a 10 m long monopole receiving antenna. In comparison, E3 of the engine ignition by two cars and a truck on HFRS in the countryside was measured. Simulation shows that the least transmission loss from the car and truck to the 10 m monopole antenna located 30 and 100 m away occurs at 7.5 MHz, which is 24 dB and 32.2 dB respectively. This measurement indicates that the emitting signal induced by the engine ignition of the truck is 14 dB higher than that of the car. In the distance of 30 m from the vehicle, the noise floor in the low frequency band is raised 1−2 dB. When the distance is increased to 100 m, the effect can be neglected.
To evaluate Electromagnetic Environment Effects (E3) of the vehicle ignition pulses on High Frequency Receiving Station (HFRS), a model of the vehicle ignition circuit has been analyzed, and frequency spectrums of the noises induced by a car and a truck at the moment of their engine being ignited were measured. Using the method-of-moments-based electromagnetic simulation tool, we have modeled the ignition-equivalent antennas by a car and a truck respectively and obtained their transmission loss fluctuation curves in the transmission path to a 10 m long monopole receiving antenna. In comparison, E3 of the engine ignition by two cars and a truck on HFRS in the countryside was measured. Simulation shows that the least transmission loss from the car and truck to the 10 m monopole antenna located 30 and 100 m away occurs at 7.5 MHz, which is 24 dB and 32.2 dB respectively. This measurement indicates that the emitting signal induced by the engine ignition of the truck is 14 dB higher than that of the car. In the distance of 30 m from the vehicle, the noise floor in the low frequency band is raised 1−2 dB. When the distance is increased to 100 m, the effect can be neglected.
2020,
32: 074001.
doi: 10.11884/HPLPB202032.200018
Abstract:
A digital delay and pulse generator with high precision delay control, short rise time and flexible parameter adjustment is designed to meet the needs of BPM electronics for external trigger signals in the process of upgrading the BEPC II linear accelerator. An FPGA is used as the main controller. This paper mainly introduces the design principle and simulation results of edge detection module and multi-channel delay processing module based on FPGA software platform, and describes the design of FPGA and drive circuit, and its application in linear accelerator. The test results show that the output pulse of the digital delay generator has an adjustable delay range of 4 ns～4 μs, a minimum step of 4 ns, an adjustable error of 0.125%, a rise time of 2 ns, and a delay jitter of 135.4 ps.
A digital delay and pulse generator with high precision delay control, short rise time and flexible parameter adjustment is designed to meet the needs of BPM electronics for external trigger signals in the process of upgrading the BEPC II linear accelerator. An FPGA is used as the main controller. This paper mainly introduces the design principle and simulation results of edge detection module and multi-channel delay processing module based on FPGA software platform, and describes the design of FPGA and drive circuit, and its application in linear accelerator. The test results show that the output pulse of the digital delay generator has an adjustable delay range of 4 ns～4 μs, a minimum step of 4 ns, an adjustable error of 0.125%, a rise time of 2 ns, and a delay jitter of 135.4 ps.
Signal processing algorithm optimization of bunch-by-bunch phase measurement system for storage ring
2020,
32: 074002.
doi: 10.11884/HPLPB202032.200033
Abstract:
To further improve the accuracy of phase measurement, the Shanghai Synchrotron Radiation Facility (SSRF) Beam Instrumentation (BI) Group proposed a new signal processing method, the correlation function method, based on the bunch-by-bunch phase measurement system. This method calculates the bunch-by-bunch phase by performing pattern matching directly on all sampling points of the oscilloscope in the time domain. The advantage is that the data processing is only limited by the oscilloscope bandwidth, and more BPM (Beam Position Monitor) harmonic signals can be retained. The results show that increasing the BPM signal processing bandwidth can effectively remove the crosstalk between bunches and reduce the system measurement error caused by signal reflection. The principal component analysis (PCA) method is used to evaluate the phase measurement resolution, the larger bunch charge, the better the resolution. The precise phase dependence between the bunches can also be used to analyze the beam wake field and impedance in the storage ring.
To further improve the accuracy of phase measurement, the Shanghai Synchrotron Radiation Facility (SSRF) Beam Instrumentation (BI) Group proposed a new signal processing method, the correlation function method, based on the bunch-by-bunch phase measurement system. This method calculates the bunch-by-bunch phase by performing pattern matching directly on all sampling points of the oscilloscope in the time domain. The advantage is that the data processing is only limited by the oscilloscope bandwidth, and more BPM (Beam Position Monitor) harmonic signals can be retained. The results show that increasing the BPM signal processing bandwidth can effectively remove the crosstalk between bunches and reduce the system measurement error caused by signal reflection. The principal component analysis (PCA) method is used to evaluate the phase measurement resolution, the larger bunch charge, the better the resolution. The precise phase dependence between the bunches can also be used to analyze the beam wake field and impedance in the storage ring.
2020,
32: 075001.
doi: 10.11884/HPLPB202032.200045
Abstract:
To suppress the accumulation of charge on the surface of polytetrafluoroethylene (PTFE) material, radio frequency nitrogen plasma was generated to perform plasma immersion ion implantation (PIII) on the PTFE surface to improve its surface properties. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), water contact angle measurement, surface resistivity measurement and surface potential attenuation measurement were performed on the samples of PTFE material before and after injection to analyze the changes in surface composition and physical properties of PTFE samples after ion implantation treatment. Based on the theory of isothermal surface potential attenuation, the energy levels and density distributions of the surface traps were calculated. The results show that after nitrogen ion implantation, the main change in the chemical composition of the surface of the PTFE material is the destruction and conversion of its own molecular structure, and part of the CF2 structure is transformed into the CF and CF3 structures, resulting in shallower trap levels on the sample surface. The results also show that the water contact angle rose to about 140°, which is about 27° higher than that of the unprocessed sample. The surface resistivity drops to 3×1015 Ω, which is two orders of magnitude lower than that of the unprocessed samples. After 1 min of corona discharge on the surface, the amount of accumulated charge on the surface of the PTFE material processed with nitrogen ion implantation decreased, and the rate of dissipation increased. This is because the lower surface trap level is conducive to surface charge trapping, and the reduction in surface resistivity also promotes the dissipation process of surface charge along the surface. The curve of trap level distribution on the surface of PTFE sample also confirmed this.
To suppress the accumulation of charge on the surface of polytetrafluoroethylene (PTFE) material, radio frequency nitrogen plasma was generated to perform plasma immersion ion implantation (PIII) on the PTFE surface to improve its surface properties. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), water contact angle measurement, surface resistivity measurement and surface potential attenuation measurement were performed on the samples of PTFE material before and after injection to analyze the changes in surface composition and physical properties of PTFE samples after ion implantation treatment. Based on the theory of isothermal surface potential attenuation, the energy levels and density distributions of the surface traps were calculated. The results show that after nitrogen ion implantation, the main change in the chemical composition of the surface of the PTFE material is the destruction and conversion of its own molecular structure, and part of the CF2 structure is transformed into the CF and CF3 structures, resulting in shallower trap levels on the sample surface. The results also show that the water contact angle rose to about 140°, which is about 27° higher than that of the unprocessed sample. The surface resistivity drops to 3×1015 Ω, which is two orders of magnitude lower than that of the unprocessed samples. After 1 min of corona discharge on the surface, the amount of accumulated charge on the surface of the PTFE material processed with nitrogen ion implantation decreased, and the rate of dissipation increased. This is because the lower surface trap level is conducive to surface charge trapping, and the reduction in surface resistivity also promotes the dissipation process of surface charge along the surface. The curve of trap level distribution on the surface of PTFE sample also confirmed this.
2020,
32: 075002.
doi: 10.11884/HPLPB202032.190439
Abstract:
It is of great significance for the development and application of pulse power technology to explore ways to improve the vacuum breakdown threshold of metal surface. Based on the theoretical analysis of electron on metal surface, the variation of surface electric field of cathode rod with diode voltage is calculated by finite element method. Experimental system is designed and experimental research is carried out. The experiment compares the vacuum breakdown threshold of TC4 of titanium alloy under different kinds of dielectric films (film thickness 30−60 μm), when the pulse width is about 30 ns and the gap between cathode rod and anode tube is 12 mm. The TC4 cathode rods with a surface roughness Rz (maximum outline height) of 0.8 μm are plated with epoxy resin and acrylic acid film respectively. The experimental results show that the breakdown threshold of the acrylic acid coated cathode rod is about 505 kV/cm. Compared with the uncoated cathode rod, the breakdown field strength is increased by about 20.6%; The TC4 cathode rods with surface roughness Rz of 0.2 μm are plated with polyimide film and polyether-ether-ketol film respectively. The experimental results show that the breakdown threshold of the polyimide film coated rod is about 584 kV/cm. The breakdown field strength is enhanced by approximately 28.1%, relative to the non-coated cathode rod. Therefore, coating acrylic acid film and polyimide film on the surface of metal cathode rod can effectively improve the vacuum breakdown threshold of metal rod.
It is of great significance for the development and application of pulse power technology to explore ways to improve the vacuum breakdown threshold of metal surface. Based on the theoretical analysis of electron on metal surface, the variation of surface electric field of cathode rod with diode voltage is calculated by finite element method. Experimental system is designed and experimental research is carried out. The experiment compares the vacuum breakdown threshold of TC4 of titanium alloy under different kinds of dielectric films (film thickness 30−60 μm), when the pulse width is about 30 ns and the gap between cathode rod and anode tube is 12 mm. The TC4 cathode rods with a surface roughness Rz (maximum outline height) of 0.8 μm are plated with epoxy resin and acrylic acid film respectively. The experimental results show that the breakdown threshold of the acrylic acid coated cathode rod is about 505 kV/cm. Compared with the uncoated cathode rod, the breakdown field strength is increased by about 20.6%; The TC4 cathode rods with surface roughness Rz of 0.2 μm are plated with polyimide film and polyether-ether-ketol film respectively. The experimental results show that the breakdown threshold of the polyimide film coated rod is about 584 kV/cm. The breakdown field strength is enhanced by approximately 28.1%, relative to the non-coated cathode rod. Therefore, coating acrylic acid film and polyimide film on the surface of metal cathode rod can effectively improve the vacuum breakdown threshold of metal rod.
2020,
32: 075003.
doi: 10.11884/HPLPB202032.190429
Abstract:
Considering the application requirement of compact and miniaturized pulse source, the design technique of the quasi-square wave pulse forming network with adjacent mutual coupling inductors is studied. Firstly, the network optimization technique based on the univariate search method is introduced, and the values of the inductance and capacitance and the analytical expressions of quasi-square wave are obtained. Then the equivalent decoupling circuit of the network with adjacent mutual coupling inductors is deduced. Based on the backtracking algorithm, the method for calculating the values of each element in the network is given. Finally, in cases of equal capacitance and constrained capacitance, the parameters of each element in the network are given. The numerical results show that the ideal quasi-square-wave pulse with a certain width flat-top can be produced by using the designed PFN with adjacent mutual coupling inductors. The ingenious design based on mutual coupling inductance is beneficial to the design of compact quasi-square wave pulse forming network.
Considering the application requirement of compact and miniaturized pulse source, the design technique of the quasi-square wave pulse forming network with adjacent mutual coupling inductors is studied. Firstly, the network optimization technique based on the univariate search method is introduced, and the values of the inductance and capacitance and the analytical expressions of quasi-square wave are obtained. Then the equivalent decoupling circuit of the network with adjacent mutual coupling inductors is deduced. Based on the backtracking algorithm, the method for calculating the values of each element in the network is given. Finally, in cases of equal capacitance and constrained capacitance, the parameters of each element in the network are given. The numerical results show that the ideal quasi-square-wave pulse with a certain width flat-top can be produced by using the designed PFN with adjacent mutual coupling inductors. The ingenious design based on mutual coupling inductance is beneficial to the design of compact quasi-square wave pulse forming network.
2020,
32: 075004.
doi: 10.11884/HPLPB202032.200074
Abstract:
This paper studies a new type of LCC-LC resonant converter for the application background of high voltage storage capacitor charging of pulsed plasma thruster (PPT). While keeping the basic characteristics of LCC resonant network, the converter is provided with zero gain point, which makes the converter have the functions of load short-circuit protection and slow start. Compared with LCC resonant converter, the new converter’s working frequency adjustment range is narrower, which is conducive to magnetic integration and power density improvement. The characteristics of high-order LCC-LC resonator are analyzed by fundamental wave analysis and impedance analysis. Based on the analysis, the working range is divided to ensure that the LCC-LC resonant converter can realize soft switch in a wide load range. Aiming at efficient operation of the LCC-LC resonant converter, parameters are optimized. Finally, the functions of the converter are verified by the simulation and the experimental data of the 1 kW prototype.
This paper studies a new type of LCC-LC resonant converter for the application background of high voltage storage capacitor charging of pulsed plasma thruster (PPT). While keeping the basic characteristics of LCC resonant network, the converter is provided with zero gain point, which makes the converter have the functions of load short-circuit protection and slow start. Compared with LCC resonant converter, the new converter’s working frequency adjustment range is narrower, which is conducive to magnetic integration and power density improvement. The characteristics of high-order LCC-LC resonator are analyzed by fundamental wave analysis and impedance analysis. Based on the analysis, the working range is divided to ensure that the LCC-LC resonant converter can realize soft switch in a wide load range. Aiming at efficient operation of the LCC-LC resonant converter, parameters are optimized. Finally, the functions of the converter are verified by the simulation and the experimental data of the 1 kW prototype.
2020,
32: 075005.
doi: 10.11884/HPLPB202032.200066
Abstract:
As electron transportation in vacuum convolute structure plays a quite important role during current converging process on pulsed power facility, fully three-dimensional (3D) particle-in-cell (PIC) simulations are performed using NEPTUNE3D code to explore this process. Simulated region (34 cm×34 cm×18 cm) including the double post-hole convolute (DPHC) structure is modeled and calculated with the help of high-performance computing clusters. The calculated results including the distributions of magnetic field nulls, trajectory of electron transportation, electrons lost on surfaces of anode posts, and time-integrated electron energy deposition damaging around the magnetic null areas between posts and holes, agree with the experimental ones from the large-scale pulsed power facility. According to the calculations, maximum current loss (437 kA, 27%) happens at early time (about 15 ns), while the loss drops dramatically to only 0.48% (34 kA) when current peaks at 53 ns (7.12 MA), at this time the magnetic insulations of transforming lines have been fully established, which also proves that the DPHC structure has especially high efficiency on high-density current converging.
As electron transportation in vacuum convolute structure plays a quite important role during current converging process on pulsed power facility, fully three-dimensional (3D) particle-in-cell (PIC) simulations are performed using NEPTUNE3D code to explore this process. Simulated region (34 cm×34 cm×18 cm) including the double post-hole convolute (DPHC) structure is modeled and calculated with the help of high-performance computing clusters. The calculated results including the distributions of magnetic field nulls, trajectory of electron transportation, electrons lost on surfaces of anode posts, and time-integrated electron energy deposition damaging around the magnetic null areas between posts and holes, agree with the experimental ones from the large-scale pulsed power facility. According to the calculations, maximum current loss (437 kA, 27%) happens at early time (about 15 ns), while the loss drops dramatically to only 0.48% (34 kA) when current peaks at 53 ns (7.12 MA), at this time the magnetic insulations of transforming lines have been fully established, which also proves that the DPHC structure has especially high efficiency on high-density current converging.
2020,
32: 075006.
doi: 10.11884/HPLPB202032.200020
Abstract:
During the launching of electromagnetic railgun, movement of the armature will be influenced by many factors, such as electromagnetic force, armature initial positive pressure, friction force, air resistance and electrical erosion resistance when the armature is moving in the bore. The muzzle velocity of the armature will fluctuate in a certain range. To improve the precision of the muzzle velocity of the armature, based on the character of the uncertainty of friction and ablation degree of armature and rail, this paper presents a simulation model for the open loop control of the armature in the bore, considering the dynamic characteristics of the circuit model and armature. The relationship between the discharge time interval and muzzle velocity of the armature is obtained by simulation, the armature velocity closed loop control model is put forward, and the feasible scheme of armature velocity control is explored. The simulation results show that the closed-loop control can improve the control precision of the muzzle velocity of the armature.
During the launching of electromagnetic railgun, movement of the armature will be influenced by many factors, such as electromagnetic force, armature initial positive pressure, friction force, air resistance and electrical erosion resistance when the armature is moving in the bore. The muzzle velocity of the armature will fluctuate in a certain range. To improve the precision of the muzzle velocity of the armature, based on the character of the uncertainty of friction and ablation degree of armature and rail, this paper presents a simulation model for the open loop control of the armature in the bore, considering the dynamic characteristics of the circuit model and armature. The relationship between the discharge time interval and muzzle velocity of the armature is obtained by simulation, the armature velocity closed loop control model is put forward, and the feasible scheme of armature velocity control is explored. The simulation results show that the closed-loop control can improve the control precision of the muzzle velocity of the armature.
