Email alert
RSS2013 Vol. 25, No. 08
Recommend Articles
Display Method:
2013,
25: 1877-1882.
doi: 10.3788/HPLPB20132508.1877
Abstract:
The pulse adding has been used in super-large pulsed power machines in order to achieve extremely high output power by overcoming the physical limitations of a single pulsed power generator. The inductive voltage adding is an effective way to improve the system flexibility, compactness, and easiness of maintenance. The linear transformer driver (LTD) is a relatively new technology of pulsed power generation based on the concept of pulse adding. In addition, solid-state LTD has further extended this technology to smart pulsed power by introducing the functions of arbitrary waveform synthesis and logical response to the load behavior.
The pulse adding has been used in super-large pulsed power machines in order to achieve extremely high output power by overcoming the physical limitations of a single pulsed power generator. The inductive voltage adding is an effective way to improve the system flexibility, compactness, and easiness of maintenance. The linear transformer driver (LTD) is a relatively new technology of pulsed power generation based on the concept of pulse adding. In addition, solid-state LTD has further extended this technology to smart pulsed power by introducing the functions of arbitrary waveform synthesis and logical response to the load behavior.
2013,
25: 1883-1887.
doi: 10.3788/HPLPB20132508.1883
Abstract:
Considering the four-level rate equations and the effects of pumping rate, loss factor and temperature, this paper theoretically deduced the expression of turn-on delay time for high power thin-disc laser. The numerical simulation results demonstrate the relationship of the pumping rate, loss factor and temperature versus the turn-on delay time. Corresponding experimental research was carried out on a kW-level repetition-frequency V-cavity Nd:YAG thin-disc laser. The relaxation oscillation curves illustrating the variations of photon number and inverted population were measured. The turn-on delay time was measured when the pump current was in the range of 30 A to 80 A. The experiment results show that the turn-on delay time reduces with the increase of pumping rate, which is consistent with the theoretical analysis.
Considering the four-level rate equations and the effects of pumping rate, loss factor and temperature, this paper theoretically deduced the expression of turn-on delay time for high power thin-disc laser. The numerical simulation results demonstrate the relationship of the pumping rate, loss factor and temperature versus the turn-on delay time. Corresponding experimental research was carried out on a kW-level repetition-frequency V-cavity Nd:YAG thin-disc laser. The relaxation oscillation curves illustrating the variations of photon number and inverted population were measured. The turn-on delay time was measured when the pump current was in the range of 30 A to 80 A. The experiment results show that the turn-on delay time reduces with the increase of pumping rate, which is consistent with the theoretical analysis.
2013,
25: 1888-1892.
doi: 10.3788/HPLPB20132508.1888
Abstract:
The research on the laser irradiation effects of composites can expand the field of laser techniques application. A model was proposed to predict the thermal responses of carbon fiber reinforced composites under laser irradiation in time and space domain. An implicit finite volume method was used to solve the governing equation. The boundary conditions were considered in the model, including laser heat flow, heat convection, heat radiation and surface recession rate. The progressive changes in thermo-physical properties including decomposition degree, mass transfer, specific heat capacity, and thermal conductivity were determined. The transient temperature and surface ablation rate of composites under laser irradiation were predicted, and the results were compared to experimental data. Finally the ablation model was modified to simulate the high-velocity airflow removed effects on composites.
The research on the laser irradiation effects of composites can expand the field of laser techniques application. A model was proposed to predict the thermal responses of carbon fiber reinforced composites under laser irradiation in time and space domain. An implicit finite volume method was used to solve the governing equation. The boundary conditions were considered in the model, including laser heat flow, heat convection, heat radiation and surface recession rate. The progressive changes in thermo-physical properties including decomposition degree, mass transfer, specific heat capacity, and thermal conductivity were determined. The transient temperature and surface ablation rate of composites under laser irradiation were predicted, and the results were compared to experimental data. Finally the ablation model was modified to simulate the high-velocity airflow removed effects on composites.
2013,
25: 1893-1896.
doi: 10.3788/HPLPB20132508.1893
Abstract:
The method of controlling mode with which a single mode laser output is achieved under high power is analyzed. Using master-oscillator power amplifier (MOPA), the continuous and single mode laser of 1.08 m wavelength, 1.05 kW maximum output power is obtained. The laser spectrum and beam quality as functions of laser power are studied. The results indicate that the center wavelength and beam quality remain unchanged, and the spectrum width broadens with the increase of laser power. The reason for the broadening of laser spectrum width is that as laser power becomes higher, the change of refractive index of fiber grating core increases, which induces the spectrum broadening of master oscillator stage. Also, the noise induced by the spectrum broadening of master oscillator stage is amplified in amplifier stage, which combined with spontaneous radiation induced by amplifier makes the spectrum width of amplifier stage broaden. Moreover, the reason that the beam quality worsens is that part of the laser transmitting in the fiber core leaks to inner cladding due to fiber bending.
The method of controlling mode with which a single mode laser output is achieved under high power is analyzed. Using master-oscillator power amplifier (MOPA), the continuous and single mode laser of 1.08 m wavelength, 1.05 kW maximum output power is obtained. The laser spectrum and beam quality as functions of laser power are studied. The results indicate that the center wavelength and beam quality remain unchanged, and the spectrum width broadens with the increase of laser power. The reason for the broadening of laser spectrum width is that as laser power becomes higher, the change of refractive index of fiber grating core increases, which induces the spectrum broadening of master oscillator stage. Also, the noise induced by the spectrum broadening of master oscillator stage is amplified in amplifier stage, which combined with spontaneous radiation induced by amplifier makes the spectrum width of amplifier stage broaden. Moreover, the reason that the beam quality worsens is that part of the laser transmitting in the fiber core leaks to inner cladding due to fiber bending.
2013,
25: 1897-1903.
doi: 10.3788/HPLPB20132508.1897
Abstract:
A wavefront reconstruction technique which obtains wavefront from a radial shearing interferometer with high precision based on two-dimensional windowed Fourier transform (WFT) is presented. First, the radial shearing fringe is processed by WFT, and by inverse WFT after setting threshold and frequency range of integration. Then wavefront phase difference distribution is obtained by the treatment of removal-carrier frequency and phase unwrapping. Finally, the actual wavefront can be reconstructed from phase difference by wavefront iterative algorithm. The simulations show that the maximum phase reconstruction error is 0.82%, RMS is 0.020 9 rad. Also corresponding experiments are conducted for comparison. In addition, window function selection, window size and threshold setting are briefly discussed. Compared with the traditional Fourier transform method (FFT), shearing interferometer wavefront measurement based on windowed Fourier transform has higher precision and stability, which provides a new processing method for wavefront measurement.
A wavefront reconstruction technique which obtains wavefront from a radial shearing interferometer with high precision based on two-dimensional windowed Fourier transform (WFT) is presented. First, the radial shearing fringe is processed by WFT, and by inverse WFT after setting threshold and frequency range of integration. Then wavefront phase difference distribution is obtained by the treatment of removal-carrier frequency and phase unwrapping. Finally, the actual wavefront can be reconstructed from phase difference by wavefront iterative algorithm. The simulations show that the maximum phase reconstruction error is 0.82%, RMS is 0.020 9 rad. Also corresponding experiments are conducted for comparison. In addition, window function selection, window size and threshold setting are briefly discussed. Compared with the traditional Fourier transform method (FFT), shearing interferometer wavefront measurement based on windowed Fourier transform has higher precision and stability, which provides a new processing method for wavefront measurement.
2013,
25: 1904-1910.
doi: 10.3788/HPLPB20132508.1904
Abstract:
A three-dimensional thermal model is established for a hard solder packaged, conduction-cooled diode laser array, which contains 19 emitters, its fill factor is 30%, and the width of emitting area is 150 m. The thermal crosstalk among emitters in the diode laser array has been studied systematically. It is found that there is an obvious thermal crosstalk among the emitters in the diode laser array after the device is operated for more than 1.2 ms in continuous wave mode. While the sub-mount material changes from copper-tungsten alloy to copper-diamond composites, the thermal resistance of each emitter and the interactive thermal resistance among adjacent emitters in the diode laser array decrease obviously. It is shown that this package structure design can reduce the thermal crosstalk behavior of the emitters effectively. The effect of the emitter size and pitch on the thermal characteristics of device is analyzed while the output power of the device, the number of the emitters, the cycle of the emitters and the width of the diode laser array are kept constant. The results show that both the thermal resistance of device and the thermal resistance of each emitter decrease exponentially with the increasing of the fill factor of the diode laser array, but the thermal crosstalk characteristics among emitters are not sensitive to the emitter size and pitch. On the other hand, keeping the output power of each single emitter, the emitter size and pitch, and the width of diode laser array constant, the thermal crosstalk behavior of the emitters is heavily influenced by the number of the emitters in diode laser array. Specifically, the higher the fill factor is, the more quickly the temperature of diode laser array rises. But during the first 70 s, the highest temperature difference among these devices containing different number of emitters is about 0.5 ℃，it is benefited to the high-power output of device having high fill factor in this period. This research is significant to the design of the structure of diode laser array, especially to the optimization of the fill factor, the emitter size and pitch of diode laser arrays. More importantly, it also presents necessary references for the package structure design of diode laser array.
A three-dimensional thermal model is established for a hard solder packaged, conduction-cooled diode laser array, which contains 19 emitters, its fill factor is 30%, and the width of emitting area is 150 m. The thermal crosstalk among emitters in the diode laser array has been studied systematically. It is found that there is an obvious thermal crosstalk among the emitters in the diode laser array after the device is operated for more than 1.2 ms in continuous wave mode. While the sub-mount material changes from copper-tungsten alloy to copper-diamond composites, the thermal resistance of each emitter and the interactive thermal resistance among adjacent emitters in the diode laser array decrease obviously. It is shown that this package structure design can reduce the thermal crosstalk behavior of the emitters effectively. The effect of the emitter size and pitch on the thermal characteristics of device is analyzed while the output power of the device, the number of the emitters, the cycle of the emitters and the width of the diode laser array are kept constant. The results show that both the thermal resistance of device and the thermal resistance of each emitter decrease exponentially with the increasing of the fill factor of the diode laser array, but the thermal crosstalk characteristics among emitters are not sensitive to the emitter size and pitch. On the other hand, keeping the output power of each single emitter, the emitter size and pitch, and the width of diode laser array constant, the thermal crosstalk behavior of the emitters is heavily influenced by the number of the emitters in diode laser array. Specifically, the higher the fill factor is, the more quickly the temperature of diode laser array rises. But during the first 70 s, the highest temperature difference among these devices containing different number of emitters is about 0.5 ℃，it is benefited to the high-power output of device having high fill factor in this period. This research is significant to the design of the structure of diode laser array, especially to the optimization of the fill factor, the emitter size and pitch of diode laser arrays. More importantly, it also presents necessary references for the package structure design of diode laser array.
2013,
25: 1911-1915.
doi: 10.3788/HPLPB20132508.1911
Abstract:
Reconstruction of phase perturbation in chirped pulse spectral interferometry is theoretically studied. As for spectral interferogram approximating to the fact, the wavelet transform and Fourier transform are used to reconstruct phase perturbation in time domain. The reconstruction errors are affected by the parameters of filter employing Fourier transform, however, when the wavelet transform is used, it is not necessary to carry on filtering specially, therefore uncertainties of reconstruction errors are avoided.
Reconstruction of phase perturbation in chirped pulse spectral interferometry is theoretically studied. As for spectral interferogram approximating to the fact, the wavelet transform and Fourier transform are used to reconstruct phase perturbation in time domain. The reconstruction errors are affected by the parameters of filter employing Fourier transform, however, when the wavelet transform is used, it is not necessary to carry on filtering specially, therefore uncertainties of reconstruction errors are avoided.
2013,
25: 1916-1920.
doi: 10.3788/HPLPB20132508.1916
Abstract:
Inhomogeneous chemical vapor deposition (CVD) diamond thick films are flatted by a Nd:YAG laser cutting machine with axial offset-focus. The influences of laser voltage, laser frequency and focus position on the diameter and depth of scanning spot are researched respectively. In addition, the influence of scanning step on leveling result, which is characterized by a scanning electron microscope(SEM), a roughmeter and a optical microscope, is studied. The results show that the increase of laser voltage or focus offset contributes to the increase of depth of scanning spot, and the width of scanning groove will increase with the increase of laser voltage. The roughness of the CVD diamond films is reduced significantly after a flatting process, and the graphite on the surface of the diamond film due to laser processing is efficiently removed by etching of hydrogen plasma.
Inhomogeneous chemical vapor deposition (CVD) diamond thick films are flatted by a Nd:YAG laser cutting machine with axial offset-focus. The influences of laser voltage, laser frequency and focus position on the diameter and depth of scanning spot are researched respectively. In addition, the influence of scanning step on leveling result, which is characterized by a scanning electron microscope(SEM), a roughmeter and a optical microscope, is studied. The results show that the increase of laser voltage or focus offset contributes to the increase of depth of scanning spot, and the width of scanning groove will increase with the increase of laser voltage. The roughness of the CVD diamond films is reduced significantly after a flatting process, and the graphite on the surface of the diamond film due to laser processing is efficiently removed by etching of hydrogen plasma.
2013,
25: 1921-1924.
doi: 10.3788/HPLPB20132508.1921
Abstract:
Concerning the noise of spectral-domain optical coherence tomography, a method of interference spectrum decoupling was proposed. The method achieves image denoising by eliminating DC and auto-correlation noise of interference spectrum. The white-light source was used for the imaging experiment of the polystyrene single-layer film. The one-dimensional depth image and the two-dimension cross-sectional image of a single-layer film were obtained. The inner micro-structure and the surface topography of the film can be clearly seen from the image. It was experimentally demonstrated that this method can eliminate the image noise effectively, and improve the signal-to-noise ratio and contrast of the image.
Concerning the noise of spectral-domain optical coherence tomography, a method of interference spectrum decoupling was proposed. The method achieves image denoising by eliminating DC and auto-correlation noise of interference spectrum. The white-light source was used for the imaging experiment of the polystyrene single-layer film. The one-dimensional depth image and the two-dimension cross-sectional image of a single-layer film were obtained. The inner micro-structure and the surface topography of the film can be clearly seen from the image. It was experimentally demonstrated that this method can eliminate the image noise effectively, and improve the signal-to-noise ratio and contrast of the image.
2013,
25: 1925-1929.
doi: 10.3788/HPLPB20132508.1925
Abstract:
The turbulent distribution phase screen along a slant path has been simulated by using the method of power spectrum inversion. By constructing the initial distorted wavefront phase model, the phase characteristics of the laser beam propagating along a slant path has been studied from the view of wavefront peak-valley value and the wavefront power spectral density function. The influences of propagation distance and zenith angle on the phase distortion of laser beams in turbulence have been analyzed. The results show that the wavefront phase of laser beams distorts obviously after propagating along a slant path in the turbulent atmosphere, and the distortion of high frequency phase increases; the wavefront phase of laser beams propagating along a slant path in the turbulent atmosphere is closely related to the propagation distance and zenith angle. The longer the propagation distance or the bigger the zenith angle is, the more distorted the high frequency phase becomes.
The turbulent distribution phase screen along a slant path has been simulated by using the method of power spectrum inversion. By constructing the initial distorted wavefront phase model, the phase characteristics of the laser beam propagating along a slant path has been studied from the view of wavefront peak-valley value and the wavefront power spectral density function. The influences of propagation distance and zenith angle on the phase distortion of laser beams in turbulence have been analyzed. The results show that the wavefront phase of laser beams distorts obviously after propagating along a slant path in the turbulent atmosphere, and the distortion of high frequency phase increases; the wavefront phase of laser beams propagating along a slant path in the turbulent atmosphere is closely related to the propagation distance and zenith angle. The longer the propagation distance or the bigger the zenith angle is, the more distorted the high frequency phase becomes.
2013,
25: 1930-1934.
doi: 10.3788/HPLPB20132508.1930
Abstract:
Investigation on stimulated rotational Raman scattering (SRRS) in air with high power laser to seek suppression methods is one of the key issues which needs to be addressed in the construction of high-power solid-state laser driver. The evolution of SRRS with diverging beam is studied numerically. The threshold of the intensity-path-length product and the criterion to suppress SRRS using diverging beam are established by geometric approximation. The results show that the effect of SRRS grows slowly in diverging beam, choosing proper divergence angle can suppress SRRS effectively, and the angle depends on the beam size, laser intensity and propagation distance.
Investigation on stimulated rotational Raman scattering (SRRS) in air with high power laser to seek suppression methods is one of the key issues which needs to be addressed in the construction of high-power solid-state laser driver. The evolution of SRRS with diverging beam is studied numerically. The threshold of the intensity-path-length product and the criterion to suppress SRRS using diverging beam are established by geometric approximation. The results show that the effect of SRRS grows slowly in diverging beam, choosing proper divergence angle can suppress SRRS effectively, and the angle depends on the beam size, laser intensity and propagation distance.
2013,
25: 1935-1938.
doi: 10.3788/HPLPB20132508.1935
Abstract:
The propagation properties of broadband laser with flattened-Gaussian transverse modes are studied and the influences of the laser bandwidth on intensity distributions are analyzed. The propagation expression of each frequency component of the broadband laser with flattened-Gaussian transverse modes is deduced and then the propagation expression in spatial domain is obtained by Fourier transform. Numerical examples are illustrated to show intensity distributions with different distance and bandwidth. Variations of spatial modes and spatiotemporal effect are investigated and discussed in detail. The results show that the intensity distributions tend to Gaussian mode with increasing of distance. Also, the laser presents stronger spatiotemporal effect when the bandwidth increases and the transverse distributions change evidently. The characteristic of the changes is that the intensity distributions of the wave front are narrowing and those of the wave rear are spreading with decreasing bandwidth.
The propagation properties of broadband laser with flattened-Gaussian transverse modes are studied and the influences of the laser bandwidth on intensity distributions are analyzed. The propagation expression of each frequency component of the broadband laser with flattened-Gaussian transverse modes is deduced and then the propagation expression in spatial domain is obtained by Fourier transform. Numerical examples are illustrated to show intensity distributions with different distance and bandwidth. Variations of spatial modes and spatiotemporal effect are investigated and discussed in detail. The results show that the intensity distributions tend to Gaussian mode with increasing of distance. Also, the laser presents stronger spatiotemporal effect when the bandwidth increases and the transverse distributions change evidently. The characteristic of the changes is that the intensity distributions of the wave front are narrowing and those of the wave rear are spreading with decreasing bandwidth.
2013,
25: 1939-1944.
doi: 10.3788/HPLPB20132508.1939
Abstract:
The confliction between swath width and resolution in the routine space-borne synthetic aperture radar (SAR) can be solved by displaced phase centers multi-beam in azimuth (DPCA) with ScanSAR in across-track direction. However, the pulse repetition frequency, sensor velocity and antenna size underlie a stringent timing requirement and any deviation will result in a non-uniform sampling in space domain. The paper derives an innovative frequency-domain reconstruction algorithm, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling. This algorithm is not iterative and precise, and can improve greatly the flexibility of system and parameters choice. The simulation results which illustrate the algorithms validity show that the spurious image from the non-uniform sampling is suppressed to below -60 dB and the azimuth-ambiguity-to-signal ratio (AASR) is below -23 dB.
The confliction between swath width and resolution in the routine space-borne synthetic aperture radar (SAR) can be solved by displaced phase centers multi-beam in azimuth (DPCA) with ScanSAR in across-track direction. However, the pulse repetition frequency, sensor velocity and antenna size underlie a stringent timing requirement and any deviation will result in a non-uniform sampling in space domain. The paper derives an innovative frequency-domain reconstruction algorithm, which enables a recovery of the unambiguous Doppler spectrum also in case of a non-uniform sampling. This algorithm is not iterative and precise, and can improve greatly the flexibility of system and parameters choice. The simulation results which illustrate the algorithms validity show that the spurious image from the non-uniform sampling is suppressed to below -60 dB and the azimuth-ambiguity-to-signal ratio (AASR) is below -23 dB.
2013,
25: 1945-1950.
doi: 10.3788/HPLPB20132508.1945
Abstract:
By expanding the vectorial Debye theory into the tight focusing of J0-correlated field, the intensity, correlation and polarization properties of J0-correlated azimuthally polarized vortex beams are studied. Expressions are derived for the intensity distribution, the spectral degree of coherence and the degree of polarization in the focal region. It is found that the intensity distributions, the degrees of correlation and the polarization of focused field are dependent not only on the correlation length and the numerical aperture maximal angle but also on the topological charge. It is also shown that such beam in the focal plane can obtain the highly confined focal spot and the focal hole.
By expanding the vectorial Debye theory into the tight focusing of J0-correlated field, the intensity, correlation and polarization properties of J0-correlated azimuthally polarized vortex beams are studied. Expressions are derived for the intensity distribution, the spectral degree of coherence and the degree of polarization in the focal region. It is found that the intensity distributions, the degrees of correlation and the polarization of focused field are dependent not only on the correlation length and the numerical aperture maximal angle but also on the topological charge. It is also shown that such beam in the focal plane can obtain the highly confined focal spot and the focal hole.
2013,
25: 1951-1955.
doi: 10.3788/HPLPB20132508.1951
Abstract:
The discrete phase module in FLUENT is used to build the two-dimensional model of gas-powder flow. The impacts of the amounts of shielding gas, transporting gas and fed powder on the concentration field and velocity field distribution, divergence angle and the focus of powder flow are discussed. The calculated results show that with increase in transporting gas flux, the powder velocity increases and the gas-powder flows divergence angle decreases, and with increase in powder feed amount, the gas-powder flows focus moves down a little and the powder concentration at this focus increases. At the same values of the process parameters as in the calculation, the camera is used to take photos of the powder flow distribution. It is shown that the experimental results agree well with the computational results.
The discrete phase module in FLUENT is used to build the two-dimensional model of gas-powder flow. The impacts of the amounts of shielding gas, transporting gas and fed powder on the concentration field and velocity field distribution, divergence angle and the focus of powder flow are discussed. The calculated results show that with increase in transporting gas flux, the powder velocity increases and the gas-powder flows divergence angle decreases, and with increase in powder feed amount, the gas-powder flows focus moves down a little and the powder concentration at this focus increases. At the same values of the process parameters as in the calculation, the camera is used to take photos of the powder flow distribution. It is shown that the experimental results agree well with the computational results.
2013,
25: 1956-1960.
doi: 10.3788/HPLPB20132508.1956
Abstract:
A numerical simulation was processed to investigate the main factors of droplet diameter formatted in the T-junction microchannel, and to verify from the experiment. The results showed that the main factors influencing droplets diameter were the geometry ratio of discrete phase inlet and the continuous phase inlet (2l10) as well as the velocity ratio (4k16), silicon particles with diameters of 50, 80, 120 m (l=5, k=4, 6, 10) reached spherical degree above 93%, monodispersity, CV5% of statistics. In conclusion, the numerical simulation and experiment were in good consistency.
A numerical simulation was processed to investigate the main factors of droplet diameter formatted in the T-junction microchannel, and to verify from the experiment. The results showed that the main factors influencing droplets diameter were the geometry ratio of discrete phase inlet and the continuous phase inlet (2l10) as well as the velocity ratio (4k16), silicon particles with diameters of 50, 80, 120 m (l=5, k=4, 6, 10) reached spherical degree above 93%, monodispersity, CV5% of statistics. In conclusion, the numerical simulation and experiment were in good consistency.
2013,
25: 1961-1964.
doi: 10.3788/HPLPB20132508.1961
Abstract:
To increase the flexibility of ICF laser facility and meet the requirements of indirect-driven and direct-driven fusions, the beam configuration should be optimized. This paper takes the Shenguang Ⅲ as an example facility which was originally designed for indirect-driven fusion. The beam configuration for direct-driven fusion is optimized through spherical-harmonic mode and three-dimensional irradiation field analysis. The optimization results show that the irradiation uniformity of the sphere target surface is less than 1%. Then irradiation uniformity and coupling efficiency are calculated with different laser profiles. The small and steep spot which direct-driven fusion requires is also obtained based on the beam configuration.
To increase the flexibility of ICF laser facility and meet the requirements of indirect-driven and direct-driven fusions, the beam configuration should be optimized. This paper takes the Shenguang Ⅲ as an example facility which was originally designed for indirect-driven fusion. The beam configuration for direct-driven fusion is optimized through spherical-harmonic mode and three-dimensional irradiation field analysis. The optimization results show that the irradiation uniformity of the sphere target surface is less than 1%. Then irradiation uniformity and coupling efficiency are calculated with different laser profiles. The small and steep spot which direct-driven fusion requires is also obtained based on the beam configuration.
2013,
25: 1965-1969.
doi: 10.3788/HPLPB20132508.1965
Abstract:
The communication blackout caused by the plasma sheath around a hypersonic vehicle flying in atmosphere is a problem to aerospace vehicles. When a vehicle enters the communication blackout phase, it loses all communication including GPS signals, data telemetry, and voice communication. The communication blackout becomes an even more critical issue with development of re-entry vehicles missions. During such missions, the communication loss caused by radio blackout introduces significant problems related to the vehicles safety. This paper analyzes the interaction of electromagnetic waves with plasma in an external magnetic field in theory. The external magnetic field can improve the transmission of electromagnetic waves in plasma from the theoretical analysis. The magnetic window antenna which is designed by integrating the permanent magnet and the helical antenna is proposed. The performance of the helical antenna and magnetic window antenna in plasma is studied. The simulation results show that using the magnetic window antenna can weaken the influence on the antenna performance in plasma. The magnetic window antenna makes it possible for electromagnetic waves to spread in plasma. This provides another way to solve the problem of spacecraft re-entry blackout.
The communication blackout caused by the plasma sheath around a hypersonic vehicle flying in atmosphere is a problem to aerospace vehicles. When a vehicle enters the communication blackout phase, it loses all communication including GPS signals, data telemetry, and voice communication. The communication blackout becomes an even more critical issue with development of re-entry vehicles missions. During such missions, the communication loss caused by radio blackout introduces significant problems related to the vehicles safety. This paper analyzes the interaction of electromagnetic waves with plasma in an external magnetic field in theory. The external magnetic field can improve the transmission of electromagnetic waves in plasma from the theoretical analysis. The magnetic window antenna which is designed by integrating the permanent magnet and the helical antenna is proposed. The performance of the helical antenna and magnetic window antenna in plasma is studied. The simulation results show that using the magnetic window antenna can weaken the influence on the antenna performance in plasma. The magnetic window antenna makes it possible for electromagnetic waves to spread in plasma. This provides another way to solve the problem of spacecraft re-entry blackout.
2013,
25: 1970-1974.
doi: 10.3788/HPLPB20132508.1970
Abstract:
The calculate model ,which is the distribution of temperature field of fast cold of pure copper wire covered glass, was established. Using the finite analysis software, the temperature distribution in the cool process was simulated. We have obtained how nodal point temperature changed as the temperature decreased. the influence of the temperature of the cooling water and the velocity of the water on copper wire was investigated. The results show that the glass layer has a temperature difference up to 45 K/m, the copper core has a temperature difference up to 0.12 K/m; and that as the cooling water flow rate increases, the cooling effect increases, when the flow rate reaches 0.5 m/s, the cooling effect is the best; and that when the cooling water temperature ranges from 283 K to 303 K, the cooling effect almost remains unchanged.
The calculate model ,which is the distribution of temperature field of fast cold of pure copper wire covered glass, was established. Using the finite analysis software, the temperature distribution in the cool process was simulated. We have obtained how nodal point temperature changed as the temperature decreased. the influence of the temperature of the cooling water and the velocity of the water on copper wire was investigated. The results show that the glass layer has a temperature difference up to 45 K/m, the copper core has a temperature difference up to 0.12 K/m; and that as the cooling water flow rate increases, the cooling effect increases, when the flow rate reaches 0.5 m/s, the cooling effect is the best; and that when the cooling water temperature ranges from 283 K to 303 K, the cooling effect almost remains unchanged.
2013,
25: 1975-1978.
doi: 10.3788/HPLPB20132508.1975
Abstract:
The polyhedral oligomeric silsesquioxane(POSS)-zirconia aerogels which contain three different contents of zirconia were successfully prepared from the POSS-［C2H4Si(OEt)3］8 and Zr(OC4H9)4 by the sol-gel process and subsequently supercritical drying with carbon dioxide. Ethanol was used as the solvent during the process. The samples were characterized by FTIR, SEM, XRD and BET. The results indicate that the three samples all have homogeneous Si-O-Ti bonds, and they are amorphous. The BET surface areas decrease with the increasing of the contents of zirconia, the biggest surface area is 491 m2/g, and all the pore distributions of the three samples are broad.
The polyhedral oligomeric silsesquioxane(POSS)-zirconia aerogels which contain three different contents of zirconia were successfully prepared from the POSS-［C2H4Si(OEt)3］8 and Zr(OC4H9)4 by the sol-gel process and subsequently supercritical drying with carbon dioxide. Ethanol was used as the solvent during the process. The samples were characterized by FTIR, SEM, XRD and BET. The results indicate that the three samples all have homogeneous Si-O-Ti bonds, and they are amorphous. The BET surface areas decrease with the increasing of the contents of zirconia, the biggest surface area is 491 m2/g, and all the pore distributions of the three samples are broad.
2013,
25: 1979-1983.
doi: 10.3788/HPLPB20132508.1979
Abstract:
In this experiment, our group studied the preparation methods of inertial confinement fusion polymer microcapsules, and designed a T-junction structure based on dual microchannel device, which was used for the preparation of stable double-emulsion. A glass capillary tube was chosen as the microchannel of middle phase solution, which increased velocity regulation range of three phase solutions, and broadened the size of emulsions. Because of the tiny discrepancy among three phase solutions, the concentricity of the double emulsions improved automatically. Various speeds of solidification were regulated, and the concentricity of the microspheres was optimized under 55 r/min, which was more than 98.7%. Scanning electron microscopy morphology and energy dispersive spectroscopy of dried pellet show that the supercritical drying meets the requirements to remove internal solvent and keeps the pellet structure from destruction. Finally, polyacrylonitrile hollow microcapsules with a size of 300-1000 m and a shell thickness of 20-300 m were successfully fabricated.
In this experiment, our group studied the preparation methods of inertial confinement fusion polymer microcapsules, and designed a T-junction structure based on dual microchannel device, which was used for the preparation of stable double-emulsion. A glass capillary tube was chosen as the microchannel of middle phase solution, which increased velocity regulation range of three phase solutions, and broadened the size of emulsions. Because of the tiny discrepancy among three phase solutions, the concentricity of the double emulsions improved automatically. Various speeds of solidification were regulated, and the concentricity of the microspheres was optimized under 55 r/min, which was more than 98.7%. Scanning electron microscopy morphology and energy dispersive spectroscopy of dried pellet show that the supercritical drying meets the requirements to remove internal solvent and keeps the pellet structure from destruction. Finally, polyacrylonitrile hollow microcapsules with a size of 300-1000 m and a shell thickness of 20-300 m were successfully fabricated.
2013,
25: 1984-1988.
doi: 10.3788/HPLPB20132508.1984
Abstract:
The zinc-based composite aerogel was prepared by the sol-gel method using ZnCl2 as precursor, polyacrylic acid (800, 1800, 5000) as template, and propylene oxide as initiator. The characterization of aerogels was carried out by field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM), and N2 adsorption/desorption. The results suggested that the zinc-based composite aerogel made by polyacrylic acid (1800) had perfectly three-dimensional networks and the skeletal was composed of particles in nanometer and had a high surface area about 236 m2/g. The N2 adsorption/desorption showed the aerogel had an average pore-diameter of 11 nm and a total pore volume of 0.179 cm3/g.
The zinc-based composite aerogel was prepared by the sol-gel method using ZnCl2 as precursor, polyacrylic acid (800, 1800, 5000) as template, and propylene oxide as initiator. The characterization of aerogels was carried out by field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM), and N2 adsorption/desorption. The results suggested that the zinc-based composite aerogel made by polyacrylic acid (1800) had perfectly three-dimensional networks and the skeletal was composed of particles in nanometer and had a high surface area about 236 m2/g. The N2 adsorption/desorption showed the aerogel had an average pore-diameter of 11 nm and a total pore volume of 0.179 cm3/g.
2013,
25: 1989-1994.
doi: 10.3788/HPLPB20132508.1989
Abstract:
Four types of optical polishing pitches with different contents of pitch and rosin were prepared, and the morphology, penetration, glass transition temperature, softening point and viscosity of these polishing pitches were investigated. Three physical states of the polishing pitches were analyzed based on the composition and structure using glass transition temperature and softening point as the transition temperatures of physical states. It was experimentally found that the polishing pitch with the pitch and rosin mass rate of 30% and 70% could be well applied to large-aperture laser glass. It provides an advantage for controlling the astigmatism and surface defect efficiently. Quantitative studies on physical parameters of optical polishing pitch is beneficial for the preparation, quality inspection and stable performance of optical polishing pitch, and could also improve the polishing efficiency of large-aperture laser glass.
Four types of optical polishing pitches with different contents of pitch and rosin were prepared, and the morphology, penetration, glass transition temperature, softening point and viscosity of these polishing pitches were investigated. Three physical states of the polishing pitches were analyzed based on the composition and structure using glass transition temperature and softening point as the transition temperatures of physical states. It was experimentally found that the polishing pitch with the pitch and rosin mass rate of 30% and 70% could be well applied to large-aperture laser glass. It provides an advantage for controlling the astigmatism and surface defect efficiently. Quantitative studies on physical parameters of optical polishing pitch is beneficial for the preparation, quality inspection and stable performance of optical polishing pitch, and could also improve the polishing efficiency of large-aperture laser glass.
2013,
25: 1995-1999.
doi: 10.3788/HPLPB20132508.1995
Abstract:
Using vapor deposition polymerizatioin method, polyimide(PI) thin films were successfully fabricated in different curing conditions. Poly (amic acid) (PAA) thin films at different temperatures and for different retention times at 300 ℃ were analysed by FTIR. The thin films held at 300 ℃ for 3 h were taken off from KBr substrate, and photograghed in interferometry microscope. Also, the thin films were analysed by thermogravimetry (TG) at different heating rates. The results show that the extent of imidization increases with temperature increasing in curing process and retention time increasing at 300 ℃. The thin films can be taken off from KBr for the retention time of 3 h. After curing process surface, the roughness of thin film is good, but Rq is 9.8 nm. The heating rate has a little influence on the ultimate extent of imidization, and low heating rates, 10 ℃/min or even lower, are preferred.
Using vapor deposition polymerizatioin method, polyimide(PI) thin films were successfully fabricated in different curing conditions. Poly (amic acid) (PAA) thin films at different temperatures and for different retention times at 300 ℃ were analysed by FTIR. The thin films held at 300 ℃ for 3 h were taken off from KBr substrate, and photograghed in interferometry microscope. Also, the thin films were analysed by thermogravimetry (TG) at different heating rates. The results show that the extent of imidization increases with temperature increasing in curing process and retention time increasing at 300 ℃. The thin films can be taken off from KBr for the retention time of 3 h. After curing process surface, the roughness of thin film is good, but Rq is 9.8 nm. The heating rate has a little influence on the ultimate extent of imidization, and low heating rates, 10 ℃/min or even lower, are preferred.
2013,
25: 2000-2006.
doi: 10.3788/HPLPB20132508.2000
Abstract:
The Au nanowires were formed in porous aluminum oxide template by AC electrodeposition method, and the influence of the thickness of barrier layer, voltage and frequency in the AC plating progress was discussed. The diameter of Au nanowires was 30 nm, and the average length was 2.1 m. The results show that the thickness of the barrier layer would significantly influence the deposition potential, which turned to be the key factor of the deposition process. The current-time curves were recorded to analyze the AC electrodeposition process, showing that the length of nanowires increased proportionately with the alternating voltage, and the stable current of the reaction increased with the frequency. These facts can be explained by the semiconductor property of the barrier layer.
The Au nanowires were formed in porous aluminum oxide template by AC electrodeposition method, and the influence of the thickness of barrier layer, voltage and frequency in the AC plating progress was discussed. The diameter of Au nanowires was 30 nm, and the average length was 2.1 m. The results show that the thickness of the barrier layer would significantly influence the deposition potential, which turned to be the key factor of the deposition process. The current-time curves were recorded to analyze the AC electrodeposition process, showing that the length of nanowires increased proportionately with the alternating voltage, and the stable current of the reaction increased with the frequency. These facts can be explained by the semiconductor property of the barrier layer.
2013,
25: 2007-2010.
doi: 10.3788/HPLPB20132508.2007
Abstract:
The infrared heating has been demonstrated as an effective technique for preparing uniform fuel ice in ICF cryotargets. A ray tracing program is used to simulate the infrared light propagation in hohlraum, and the volumetric heating rates of shell and fuel are obtained with different focus positions of infrared light. It is found that the volumetric heating rates of the shell and fuel can be adjusted by the focus positions of infrared light. Therefore, the temperature field of fuel required for fuel layering can be achieved by adjusting the focus positions of infrared light. This work is helpful for the future layering experiments of ICF cryotargets by infrared heating.
The infrared heating has been demonstrated as an effective technique for preparing uniform fuel ice in ICF cryotargets. A ray tracing program is used to simulate the infrared light propagation in hohlraum, and the volumetric heating rates of shell and fuel are obtained with different focus positions of infrared light. It is found that the volumetric heating rates of the shell and fuel can be adjusted by the focus positions of infrared light. Therefore, the temperature field of fuel required for fuel layering can be achieved by adjusting the focus positions of infrared light. This work is helpful for the future layering experiments of ICF cryotargets by infrared heating.
2013,
25: 2011-2016.
doi: 10.3788/HPLPB20132508.2011
Abstract:
The numerical simulation is one of the important methods of studying physical process. In this paper, a 3D discrete view factor method is proposed for the equivalent model of two-region uniformly in inertial confinement fusion (ICF). The blocked elements are culled by quadtree data structure when the inner wall of a hohlraum is self-occlusion in irradiation process. The parallelism is analyzed on discrete view factor and then the parallel computation of fluence distribution on target is realized on GPU. The algorithm has been realized in simulation software IRAD3D1.0, and the correctness is verified by comparing with analytical solution. Different simulation results show that the software is versatile and efficient. Finally, the practical application on influencing factors of symmetry distribution is given.
The numerical simulation is one of the important methods of studying physical process. In this paper, a 3D discrete view factor method is proposed for the equivalent model of two-region uniformly in inertial confinement fusion (ICF). The blocked elements are culled by quadtree data structure when the inner wall of a hohlraum is self-occlusion in irradiation process. The parallelism is analyzed on discrete view factor and then the parallel computation of fluence distribution on target is realized on GPU. The algorithm has been realized in simulation software IRAD3D1.0, and the correctness is verified by comparing with analytical solution. Different simulation results show that the software is versatile and efficient. Finally, the practical application on influencing factors of symmetry distribution is given.
2013,
25: 2017-2020.
doi: 10.3788/HPLPB20132508.2017
Abstract:
A relativistic surface wave oscillator based on overmoded structure is simulated with particle-in-cell method. The output signal is generated with a frequency of 0.148 THz and the main output mode of TM01 according to numerical results. The electromagnetic field may leak into diode region because the device is lack of effective reflector. The characteristics of this device and the influence of the parameters of diode on the device are studied via particle simulation. The simulation results indicate that the electromagnetic field leaking to diode region has little impact on the work status of the device but the output power is affected by the structure of diode seriously.
A relativistic surface wave oscillator based on overmoded structure is simulated with particle-in-cell method. The output signal is generated with a frequency of 0.148 THz and the main output mode of TM01 according to numerical results. The electromagnetic field may leak into diode region because the device is lack of effective reflector. The characteristics of this device and the influence of the parameters of diode on the device are studied via particle simulation. The simulation results indicate that the electromagnetic field leaking to diode region has little impact on the work status of the device but the output power is affected by the structure of diode seriously.
Continuously board-waveband tunable all-solid-state CW optical parametric oscillator based on PPMgLN
2013,
25: 2021-2026.
doi: 10.3788/HPLPB20132508.2021
Abstract:
The output characteristics of a multi-wavelength tunable optical parametric oscillator (OPO) pumped by an all-solid-state Nd:YVO4 laser with the 1064 nm wavelength is investigated by quasi-phase-matching period tuning and temperature tuning technology. An experiment is carried out by using an external cavity structure and continuous wave (CW) operation mode, and changing the periods and temperature of a periodically poled MgO:LiNO3 crystal (PPMgLN) from 30 to 100 ℃ with 30.2 m, 30.4 m and 30.6 m grating period. The experimental results indicate that the threshold of the CW PPMgLN OPO is only 0.22 W and the different poling period needs different temperature-tuned range, and the continuously tunable near-infrared spectrum from 1 559.8 to 1 597.2 nm and mid-infrared spectrum from 3 187.3 to 3 347.3 nm are obtained. A continuously tunable PPMgLN-OPO at the signal and idler wavelength is realized.
The output characteristics of a multi-wavelength tunable optical parametric oscillator (OPO) pumped by an all-solid-state Nd:YVO4 laser with the 1064 nm wavelength is investigated by quasi-phase-matching period tuning and temperature tuning technology. An experiment is carried out by using an external cavity structure and continuous wave (CW) operation mode, and changing the periods and temperature of a periodically poled MgO:LiNO3 crystal (PPMgLN) from 30 to 100 ℃ with 30.2 m, 30.4 m and 30.6 m grating period. The experimental results indicate that the threshold of the CW PPMgLN OPO is only 0.22 W and the different poling period needs different temperature-tuned range, and the continuously tunable near-infrared spectrum from 1 559.8 to 1 597.2 nm and mid-infrared spectrum from 3 187.3 to 3 347.3 nm are obtained. A continuously tunable PPMgLN-OPO at the signal and idler wavelength is realized.
2013,
25: 2027-2030.
doi: 10.3788/HPLPB20132508.2027
Abstract:
A compact ultra wide spectrum high power microwave radiation system made up of 100 kV nanosecond pulse generator, subnanosecond gas switch and TEM horn antenna is designed. The output voltage waveform of the pulse generator is a pulse with a rising time of 280 ps, a decaying time of 180 ps and a peak amplitude of 100 kV. The system can work at 100 Hz repetition rate and the peak radiating field on boresight is about 10 kV/m at the distance of 7.5 m. The -3 dB bandwidth of the radiated field is from 230 MHz to 810 MHz and -20 dB bandwidth is from 100 MHz to 1.3 GHz. The system with small volume of 80 cm50 cm26 cm and the weight of 45 kg is expected to find many applications in areas of high power microwave.
A compact ultra wide spectrum high power microwave radiation system made up of 100 kV nanosecond pulse generator, subnanosecond gas switch and TEM horn antenna is designed. The output voltage waveform of the pulse generator is a pulse with a rising time of 280 ps, a decaying time of 180 ps and a peak amplitude of 100 kV. The system can work at 100 Hz repetition rate and the peak radiating field on boresight is about 10 kV/m at the distance of 7.5 m. The -3 dB bandwidth of the radiated field is from 230 MHz to 810 MHz and -20 dB bandwidth is from 100 MHz to 1.3 GHz. The system with small volume of 80 cm50 cm26 cm and the weight of 45 kg is expected to find many applications in areas of high power microwave.
2013,
25: 2031-2034.
doi: 10.3788/HPLPB20132508.2031
Abstract:
In order to develop a RF coupler for the drift tube linac of China Spallation Neutron Source, by improving the conventional RF window structure, we designed a new RF window of the RF coupler. High frequency characteristics of this window were optimized in CST. The calculations of the temperature rising and the thermal stress caused by the high power were performed to avoid the ceramic broken. The fundamental mechanism of the window under vacuum was investigated. Finally a preliminary discussion on the ARC phenomenon was made too. The results show that the in-put power 2 MW of the cavity is less than the critical value 2.355 MW, and the probability of strike arc is very small.
In order to develop a RF coupler for the drift tube linac of China Spallation Neutron Source, by improving the conventional RF window structure, we designed a new RF window of the RF coupler. High frequency characteristics of this window were optimized in CST. The calculations of the temperature rising and the thermal stress caused by the high power were performed to avoid the ceramic broken. The fundamental mechanism of the window under vacuum was investigated. Finally a preliminary discussion on the ARC phenomenon was made too. The results show that the in-put power 2 MW of the cavity is less than the critical value 2.355 MW, and the probability of strike arc is very small.
2013,
25: 2035-2039.
doi: 10.3788/HPLPB20132508.2035
Abstract:
This paper studies the effect of the UV illumination technology on gas switch in principle, analyzing and approving the feasibility of UV pre-ionization to the main switch from transverse capacitance coupling auxiliary spark. UV illumination from auxiliary gap makes initial electrons release from the cathode by photoemission, which can reduce the scatter of breakdown voltage effectively. The factors which affect the intensity of UV pre-ionization are analyzed, such as breakdown current peak, voltage and storage capacity of auxiliary gap. The experiment results show that the UV pre-ionization from transverse auxiliary gap with storage capacitor of pF-order which is apart from the main gap with a distance of 15 cm is feasible among nitrogen. On this basis, a new compact transverse capacity-coupling UV illumination switch is designed.
This paper studies the effect of the UV illumination technology on gas switch in principle, analyzing and approving the feasibility of UV pre-ionization to the main switch from transverse capacitance coupling auxiliary spark. UV illumination from auxiliary gap makes initial electrons release from the cathode by photoemission, which can reduce the scatter of breakdown voltage effectively. The factors which affect the intensity of UV pre-ionization are analyzed, such as breakdown current peak, voltage and storage capacity of auxiliary gap. The experiment results show that the UV pre-ionization from transverse auxiliary gap with storage capacitor of pF-order which is apart from the main gap with a distance of 15 cm is feasible among nitrogen. On this basis, a new compact transverse capacity-coupling UV illumination switch is designed.
2013,
25: 2040-2044.
doi: 10.3788/HPLPB20132508.2040
Abstract:
The phase-locking properties of an S-band relativistic klystron amplifier (RKA) are investigated. In 2.5-dimensional particle-in-cell simulations, the influences of the electron beam voltage waveform on RKA phase-locking are studied. The results show that the spike in the voltage waveform of the electron beam has a positive effect on the RKA phase-locking properties, and it can reduce the time spent to achieve the locked state. A spike of 20% over the original voltage amplitude can cause a change of about 23 in the phase difference. Waveform flat-drops have negative impacts on the phase-locking of the RKA, which make the phase prematurely depart from the steady state. A flat-drop of 5% off the original voltage amplitude can cause a deviation of 50 in the phase difference. The rise time of the voltage waveform influences the RKA phase locked state either, but the trend is not obvious. The influence of the guiding magnetic fields on the phase is studied in a three-dimensional PIC simulation. The results show that the phase differences decrease when the guiding magnetic fields increase in the overall trend when the magnetic fields are below 1.6 T. In detail, the step form is shown, i.e. within a certain range, the changing of the guiding magnetic fields does not result in the changing of the phase differences. Experimental studies show that the phase differences decrease when the guiding magnetic fields increase. In the experiments, the guiding magnetic fields are between 0.6 T and 1.1 T, and the step form of the phase differences is not obvious.
The phase-locking properties of an S-band relativistic klystron amplifier (RKA) are investigated. In 2.5-dimensional particle-in-cell simulations, the influences of the electron beam voltage waveform on RKA phase-locking are studied. The results show that the spike in the voltage waveform of the electron beam has a positive effect on the RKA phase-locking properties, and it can reduce the time spent to achieve the locked state. A spike of 20% over the original voltage amplitude can cause a change of about 23 in the phase difference. Waveform flat-drops have negative impacts on the phase-locking of the RKA, which make the phase prematurely depart from the steady state. A flat-drop of 5% off the original voltage amplitude can cause a deviation of 50 in the phase difference. The rise time of the voltage waveform influences the RKA phase locked state either, but the trend is not obvious. The influence of the guiding magnetic fields on the phase is studied in a three-dimensional PIC simulation. The results show that the phase differences decrease when the guiding magnetic fields increase in the overall trend when the magnetic fields are below 1.6 T. In detail, the step form is shown, i.e. within a certain range, the changing of the guiding magnetic fields does not result in the changing of the phase differences. Experimental studies show that the phase differences decrease when the guiding magnetic fields increase. In the experiments, the guiding magnetic fields are between 0.6 T and 1.1 T, and the step form of the phase differences is not obvious.
2013,
25: 2045-2049.
doi: 10.3788/HPLPB20132508.2045
Abstract:
Based on the traditional TE01n cylindrical cavity, a new resonator is proposed for non-destructive measurements of the complex permittivity of dielectric slabs. It consists of a large planar metal plate, a dielectric slab, and a cylindrical waveguide armed with a flange at one end and a tunable piston at another end. The dielectric slab is sandwiched between the metal plate and the flange. The rigorous mode matching method is employed for analyzing the electric fields in the cavity. Expressions relating the complex permittivity with the cavitys physical dimensions and the measured S21 parameter are developed. Thereafter, several dielectric slabs are tested to demonstrate the usefulness of this proposed method. It is found that by using this cavity, the measurement uncertainty for the relative permittivity is within 1%, while the measurement uncertainty for the dielectric loss could not exceed 10%. This cavity has the advantage of measuring the complex permittivity at multiple resonant modes. Therefore, it could be used as a robust approach for characterizing the frequency dependence of the complex permittivity of dielectric slabs.
Based on the traditional TE01n cylindrical cavity, a new resonator is proposed for non-destructive measurements of the complex permittivity of dielectric slabs. It consists of a large planar metal plate, a dielectric slab, and a cylindrical waveguide armed with a flange at one end and a tunable piston at another end. The dielectric slab is sandwiched between the metal plate and the flange. The rigorous mode matching method is employed for analyzing the electric fields in the cavity. Expressions relating the complex permittivity with the cavitys physical dimensions and the measured S21 parameter are developed. Thereafter, several dielectric slabs are tested to demonstrate the usefulness of this proposed method. It is found that by using this cavity, the measurement uncertainty for the relative permittivity is within 1%, while the measurement uncertainty for the dielectric loss could not exceed 10%. This cavity has the advantage of measuring the complex permittivity at multiple resonant modes. Therefore, it could be used as a robust approach for characterizing the frequency dependence of the complex permittivity of dielectric slabs.
2013,
25: 2050-2054.
doi: 10.3788/HPLPB20132508.2050
Abstract:
In a relativistic klystron amplifier (RKA), the idle cavity can increase the gain of the device, but the oscillation of nonworking modes will occur in the same time, and therefore the performance of RKA will be significantly decreased. We developed a four-cavity relativistic klystron on the basis of three-cavity relativistic klystron to study the mechanism of nonworking modes oscillation. A PIC particle simulation software was used to study the cold cavity structure, beam-microwave interaction and microwave extraction of output cavity. An input cavity with low interaction impedance and a ladder structured drift were adopted in the structure to avoid nonworking modes oscillation. By optimizing the output cavity gap, the returning electrons had been significantly reduced, and thus the oscillation of nonworking modes was not excited. Finally, the output microwave with a power of 3.7 GW, a gain of 56 dB, an efficiency of 22% and 1 dB bandwidth of 74 MHz were achieved in simulation with the discussed structure.
In a relativistic klystron amplifier (RKA), the idle cavity can increase the gain of the device, but the oscillation of nonworking modes will occur in the same time, and therefore the performance of RKA will be significantly decreased. We developed a four-cavity relativistic klystron on the basis of three-cavity relativistic klystron to study the mechanism of nonworking modes oscillation. A PIC particle simulation software was used to study the cold cavity structure, beam-microwave interaction and microwave extraction of output cavity. An input cavity with low interaction impedance and a ladder structured drift were adopted in the structure to avoid nonworking modes oscillation. By optimizing the output cavity gap, the returning electrons had been significantly reduced, and thus the oscillation of nonworking modes was not excited. Finally, the output microwave with a power of 3.7 GW, a gain of 56 dB, an efficiency of 22% and 1 dB bandwidth of 74 MHz were achieved in simulation with the discussed structure.
2013,
25: 2055-2060.
doi: 10.3788/HPLPB20132508.2055
Abstract:
A new output-taper for Ka-band high power gyro-TWT is designed by a function of sine and cosine and using the coupled wave equation to analyze the radius changing circular waveguide. Using the MATLAB code and software HFSS, we analyze the transmission, the reflection coefficient and the coupling coefficient to TE02 mode and TE03 mode. When the length is 80 mm and the diameter changes from 14 mm to 32 mm, the results indicates its transmission coefficient more than -0.000 52 dB, reflection coefficient less than -65 dB, mode purity more than 0.995, the coupling coefficient to TE02 mode and TE03 mode less than -40 dB. Compared with Dolph-Chebyshev output taper, when the length and diameter are the same, the new output tapers transmission, reflection coefficient and mode purity are superior than those in 30 GHz to 33 GHz. The results of cold test for the test-sample show that S11＜-30 dB and S21＞-0.3 dB.
A new output-taper for Ka-band high power gyro-TWT is designed by a function of sine and cosine and using the coupled wave equation to analyze the radius changing circular waveguide. Using the MATLAB code and software HFSS, we analyze the transmission, the reflection coefficient and the coupling coefficient to TE02 mode and TE03 mode. When the length is 80 mm and the diameter changes from 14 mm to 32 mm, the results indicates its transmission coefficient more than -0.000 52 dB, reflection coefficient less than -65 dB, mode purity more than 0.995, the coupling coefficient to TE02 mode and TE03 mode less than -40 dB. Compared with Dolph-Chebyshev output taper, when the length and diameter are the same, the new output tapers transmission, reflection coefficient and mode purity are superior than those in 30 GHz to 33 GHz. The results of cold test for the test-sample show that S11＜-30 dB and S21＞-0.3 dB.
2013,
25: 2061-2066.
doi: 10.3788/HPLPB20132508.2061
Abstract:
To study the effect of PIN diode limiter under electromagnetic pulse (EMP), the response of PIN diode is numerically simulated by using self-developed 2D semiconductor device simulation software. Current overshoot phenomena of PIN diode during the rise time of EMP are analyzed. Overshoot current is validated to be due to the capacitive performance of PIN diode under high frequency. Shorter rise time of EMP causes higher peak of current. Overshoot current is affected by doping concentration of PIN diode. The higher doping concentration of the P layer and N layer causes higher peak of current and sooner attenuation of overshoot current. The doping concentration of the I layer also affects the overshoot current, but not as the salient as concentration of the P and N layers.
To study the effect of PIN diode limiter under electromagnetic pulse (EMP), the response of PIN diode is numerically simulated by using self-developed 2D semiconductor device simulation software. Current overshoot phenomena of PIN diode during the rise time of EMP are analyzed. Overshoot current is validated to be due to the capacitive performance of PIN diode under high frequency. Shorter rise time of EMP causes higher peak of current. Overshoot current is affected by doping concentration of PIN diode. The higher doping concentration of the P layer and N layer causes higher peak of current and sooner attenuation of overshoot current. The doping concentration of the I layer also affects the overshoot current, but not as the salient as concentration of the P and N layers.
2013,
25: 2067-2070.
doi: 10.3788/HPLPB20132508.2067
Abstract:
A pepper pot-imaging plate system has been developed and used to measure the 4-D transverse emittance of a vacuum arc ion source. Single beam pulses of tens to hundreds milliamperes were extracted from the plasma with 64 kV high voltage. An imaging plate was laid after the pepper pot to visualize the ion beamlets passing though the holes on the pepper pot. An application program was developed to show the phase-space distribution and calculate the ellipse and RMS emittances. The normalized RMS emittances are about 6.41 mmmrad in x-direction and 4.61 mmmrad in y-direction. It is shown that the emittance of the vacuum arc ion source is much larger than that of other types of ion sources, which is mainly attributed to the high current and the convex meniscus of this source.
A pepper pot-imaging plate system has been developed and used to measure the 4-D transverse emittance of a vacuum arc ion source. Single beam pulses of tens to hundreds milliamperes were extracted from the plasma with 64 kV high voltage. An imaging plate was laid after the pepper pot to visualize the ion beamlets passing though the holes on the pepper pot. An application program was developed to show the phase-space distribution and calculate the ellipse and RMS emittances. The normalized RMS emittances are about 6.41 mmmrad in x-direction and 4.61 mmmrad in y-direction. It is shown that the emittance of the vacuum arc ion source is much larger than that of other types of ion sources, which is mainly attributed to the high current and the convex meniscus of this source.
2013,
25: 2071-2074.
doi: 10.3788/HPLPB20132508.2071
Abstract:
In order to measure beam energy in Hefei Light Source accurately, a new set of precise and sensitive beam loss measurement system is built, and a kind of plastic scintillator detector which has high detection efficiency for low energy photons is adopted. According to the measured signal of beam loss, a set of digital signal processing circuit is developed. The experimental results show that the beam loss measurement system meets the requirements of the spin resonant depolarization method and can obtain the change of the beam loss accurately and sensitively. The measuring principle and theoretical basis of spin resonant depolarization is also introduced.
In order to measure beam energy in Hefei Light Source accurately, a new set of precise and sensitive beam loss measurement system is built, and a kind of plastic scintillator detector which has high detection efficiency for low energy photons is adopted. According to the measured signal of beam loss, a set of digital signal processing circuit is developed. The experimental results show that the beam loss measurement system meets the requirements of the spin resonant depolarization method and can obtain the change of the beam loss accurately and sensitively. The measuring principle and theoretical basis of spin resonant depolarization is also introduced.
2013,
25: 2075-2079.
doi: 10.3788/HPLPB20132508.2075
Abstract:
The prototype of superferric dipoles for Super-FRS of Facility for Antiprotons and Ion Research (FAIR) project was designed, fabricated, and tested in China. To investigate the performance of the superconducting coil, a so-called test coil was fabricated and tested in advance. A 3D model based on ANSYS and OPERA 3D was developed in parallel, not only to check if the design matches the numerical simulation, but also to study more details of quench phenomena. The model simplifies the epoxy impregnated coil into an anisotropic continuum medium. The simulation combines ANSYS solver routines for nonlinear transient thermal analysis, the OPERA 3D for magnetic field evaluation and the ANSYS script language for calculations of Joule heat and differential equations of the protection circuits. The time changes of temperature, voltage and current decay, and quench propagation during quench process were analyzed and illustrated. Finally, the test results of the test coil were demonstrated and compared with the results of simulation.
The prototype of superferric dipoles for Super-FRS of Facility for Antiprotons and Ion Research (FAIR) project was designed, fabricated, and tested in China. To investigate the performance of the superconducting coil, a so-called test coil was fabricated and tested in advance. A 3D model based on ANSYS and OPERA 3D was developed in parallel, not only to check if the design matches the numerical simulation, but also to study more details of quench phenomena. The model simplifies the epoxy impregnated coil into an anisotropic continuum medium. The simulation combines ANSYS solver routines for nonlinear transient thermal analysis, the OPERA 3D for magnetic field evaluation and the ANSYS script language for calculations of Joule heat and differential equations of the protection circuits. The time changes of temperature, voltage and current decay, and quench propagation during quench process were analyzed and illustrated. Finally, the test results of the test coil were demonstrated and compared with the results of simulation.
2013,
25: 2080-2084.
doi: 10.3788/HPLPB20132508.2080
Abstract:
The fault current and voltage waveforms are required to be monitored by oscilloscopes when shorting occurs in developing ITER 1 MV ion source accelerators. Therefore, it is necessary to design an automatic digital oscilloscope compatible with strong electromagnetic interference environments. Its hardware is based on FPGA and MCU, while its software is based on LABVIEW. Compared with the traditional method of using the Tektronix oscilloscope, it is cheap, small, of anti-electromagnetic interference, and can automatically store waveforms with remote monitoring.
The fault current and voltage waveforms are required to be monitored by oscilloscopes when shorting occurs in developing ITER 1 MV ion source accelerators. Therefore, it is necessary to design an automatic digital oscilloscope compatible with strong electromagnetic interference environments. Its hardware is based on FPGA and MCU, while its software is based on LABVIEW. Compared with the traditional method of using the Tektronix oscilloscope, it is cheap, small, of anti-electromagnetic interference, and can automatically store waveforms with remote monitoring.
2013,
25: 2085-2090.
doi: 10.3788/HPLPB20132508.2085
Abstract:
Ion source is the key part of an Accelerator Mass Spectrometry (AMS) in view of analytical sensitivity, stability and accuracy. SO-110 Cs+ sputtering ion source developed by High Voltage Engineering Europe, is dedicated to AMS for both solid and gas target sources, which has been successfully applied to AMS instruments including one installed in Xian AMS center. By investigation of the effect of various parameters, such as the target preparation, holder characteristics, matrix selection and the ratio between AgI and matrix on AMS measurement of 129I using SO-110 ion source, Cu is the suitable holder material, and Nb powder is the best matrix, and the optimal ratio of AgI∶Nb is 1∶3. A machine background of 1.5210-14 for 129I/127I was obtained using a NaI sample directly mixed with Nb powder and pressed in Cu target holder.
Ion source is the key part of an Accelerator Mass Spectrometry (AMS) in view of analytical sensitivity, stability and accuracy. SO-110 Cs+ sputtering ion source developed by High Voltage Engineering Europe, is dedicated to AMS for both solid and gas target sources, which has been successfully applied to AMS instruments including one installed in Xian AMS center. By investigation of the effect of various parameters, such as the target preparation, holder characteristics, matrix selection and the ratio between AgI and matrix on AMS measurement of 129I using SO-110 ion source, Cu is the suitable holder material, and Nb powder is the best matrix, and the optimal ratio of AgI∶Nb is 1∶3. A machine background of 1.5210-14 for 129I/127I was obtained using a NaI sample directly mixed with Nb powder and pressed in Cu target holder.
2013,
25: 2091-2095.
doi: 10.3788/HPLPB20132508.2091
Abstract:
Changing laser fluence, Si nano-crystal films were prepared by the pulsed laser ablation in direct current electric field that paralleled to target surface in Ar gas of 10 Pa at room temperature. The substrates were fixed on the position with different angles to plume axis. The morphology and composition of samples were characterized by scanning electron microscopy and Raman scattering spectrums. The results indicated that the average size and the area density of nanoparticles increase with the addition of laser fluence at the same angle. The average size and the area density of nanoparticles at direction of plume axis are the biggest when the laser fluence keeps invariable, furthermore, the values of them near grounded board are bigger than those near the positive board symmetrical. The results were analyzed on the base of diagnosis of changes of silicon ions density through Langmuir probe and dynamics of nucleation and growth process of nanoparticles in the nucleation region.
Changing laser fluence, Si nano-crystal films were prepared by the pulsed laser ablation in direct current electric field that paralleled to target surface in Ar gas of 10 Pa at room temperature. The substrates were fixed on the position with different angles to plume axis. The morphology and composition of samples were characterized by scanning electron microscopy and Raman scattering spectrums. The results indicated that the average size and the area density of nanoparticles increase with the addition of laser fluence at the same angle. The average size and the area density of nanoparticles at direction of plume axis are the biggest when the laser fluence keeps invariable, furthermore, the values of them near grounded board are bigger than those near the positive board symmetrical. The results were analyzed on the base of diagnosis of changes of silicon ions density through Langmuir probe and dynamics of nucleation and growth process of nanoparticles in the nucleation region.
2013,
25: 2096-2100.
doi: 10.3788/HPLPB20132508.2096
Abstract:
In order to verify the measurement accuracy of Industrial Computed Tomography (ICT), an evaluation method was designed and the standard measuring parts were made for the 9 MeV high-energy industrial CT system and 450 kV industrial CT system which were produced by National X-ray Digital Imaging Instrument Centre. The liner dimensions, the sphere diameters, the angle values, the apertures and the positioning dimensions were measured by CMM and CT system .Then comparing the results, after data analysis, different errors for these dimensions were acquired. For different materials of aluminum, nylon and stainless steel, higher density material with higher density has less measure error without considering the effect of the dimension type. These results validate the ability of industrial CT system as a high dimensional measuring machine for nondestructive examination.
In order to verify the measurement accuracy of Industrial Computed Tomography (ICT), an evaluation method was designed and the standard measuring parts were made for the 9 MeV high-energy industrial CT system and 450 kV industrial CT system which were produced by National X-ray Digital Imaging Instrument Centre. The liner dimensions, the sphere diameters, the angle values, the apertures and the positioning dimensions were measured by CMM and CT system .Then comparing the results, after data analysis, different errors for these dimensions were acquired. For different materials of aluminum, nylon and stainless steel, higher density material with higher density has less measure error without considering the effect of the dimension type. These results validate the ability of industrial CT system as a high dimensional measuring machine for nondestructive examination.
2013,
25: 2101-2105.
doi: 10.3788/HPLPB20132508.2101
Abstract:
This study describes the development and relevant issues of a new cloud droplet probe based on Mie scattering and laser technology. A small pin-hole orifice is used to simulate the light scattered to determine the sensing area for the system. Calibration is precisely done by adopting standard spherical samples with different diameters as the replacements of different size cloud droplets to obtain the system response curve, so the droplet size and concentration of cloud particles can be determined. After a series of experiments were finished in laboratory, put the probe on the airborne to do the cloud experiment, and the airborne experiments demonstrate that the new cloud droplet probe works reliably and stably, and it can show the droplet size and concentration of cloud particles in sensitive areas immediately. Analysing the stored data, calculating the number of the particles, and comparing with the droplet size in cloud, the results showed that the data is effective and reliable, the system has good capacity to probe the cloud.
This study describes the development and relevant issues of a new cloud droplet probe based on Mie scattering and laser technology. A small pin-hole orifice is used to simulate the light scattered to determine the sensing area for the system. Calibration is precisely done by adopting standard spherical samples with different diameters as the replacements of different size cloud droplets to obtain the system response curve, so the droplet size and concentration of cloud particles can be determined. After a series of experiments were finished in laboratory, put the probe on the airborne to do the cloud experiment, and the airborne experiments demonstrate that the new cloud droplet probe works reliably and stably, and it can show the droplet size and concentration of cloud particles in sensitive areas immediately. Analysing the stored data, calculating the number of the particles, and comparing with the droplet size in cloud, the results showed that the data is effective and reliable, the system has good capacity to probe the cloud.
2013,
25: 2106-2110.
doi: 10.3788/HPLPB20132508.2106
Abstract:
For the high-precision demand of electro-optical tracking system, the control technique based on on-axis tracking of rough tracking process was studied. Firstly, the principle of on-axis tracking was introduced. Secondly, methods of non-linear Kalman filters in common use were analyzed. Especially, the accuracies of predicted displacement and velocity were compared in unscented Kalman filter (UKF) and cubature Kalman filter (CKF) by simulation test. Finally, based on the advantages of UKF and CKF, two-parallel filter which was used to deal with delayed signal of compound position was designed to establish the on-axis tracking control of electro-optical tracking system. As the input signal of data measured, the simulation results show that control system of on-axis tracking improves the system tracking precision.
For the high-precision demand of electro-optical tracking system, the control technique based on on-axis tracking of rough tracking process was studied. Firstly, the principle of on-axis tracking was introduced. Secondly, methods of non-linear Kalman filters in common use were analyzed. Especially, the accuracies of predicted displacement and velocity were compared in unscented Kalman filter (UKF) and cubature Kalman filter (CKF) by simulation test. Finally, based on the advantages of UKF and CKF, two-parallel filter which was used to deal with delayed signal of compound position was designed to establish the on-axis tracking control of electro-optical tracking system. As the input signal of data measured, the simulation results show that control system of on-axis tracking improves the system tracking precision.
2013,
25: 2111-2116.
doi: 10.3788/HPLPB20132508.2111
Abstract:
Vacuum discharge plasma is generated using a single-pulse power supply with 13 s pulse width and 100~300 A discharging current. Two types of co-axial electrodes, namely the tubular electrode and the trumpet electrode, are employed as anodes. The electric field distribution with two electrodes is simulated by MAXWELL 3D simulation software. The parameters of vacuum discharge plasmas, such as electron density, electron temperature, space potential and ion kinetic energy, are measured by the Langmuir probe method to investigate the impact of co-axial electrode configurations on the plasma generation characteristics. Moreover, the effects of cathode materials on the ion velocity and kinetic energy are discussed, as lead, aluminum, and copper are used as the cathode material, respectively, with the trumpet electrode configuration. Experimental and simulation results show that the plasma generated with the trumpet electrode exhibits higher discharge current, greater plasma density, and lower breakdown voltage compared to the tubular one. The aluminum cathode can generate plasma with the highest diffusion velocity, while the lead cathode yields the maximum ion kinetic energy of plasma.
Vacuum discharge plasma is generated using a single-pulse power supply with 13 s pulse width and 100~300 A discharging current. Two types of co-axial electrodes, namely the tubular electrode and the trumpet electrode, are employed as anodes. The electric field distribution with two electrodes is simulated by MAXWELL 3D simulation software. The parameters of vacuum discharge plasmas, such as electron density, electron temperature, space potential and ion kinetic energy, are measured by the Langmuir probe method to investigate the impact of co-axial electrode configurations on the plasma generation characteristics. Moreover, the effects of cathode materials on the ion velocity and kinetic energy are discussed, as lead, aluminum, and copper are used as the cathode material, respectively, with the trumpet electrode configuration. Experimental and simulation results show that the plasma generated with the trumpet electrode exhibits higher discharge current, greater plasma density, and lower breakdown voltage compared to the tubular one. The aluminum cathode can generate plasma with the highest diffusion velocity, while the lead cathode yields the maximum ion kinetic energy of plasma.
2013,
25: 2117-2120.
doi: 10.3788/HPLPB20132508.2117
Abstract:
A computational model of the neutron multiplication coefficient ( value) of a critical power assembly is built, which is measured by current-mode detectors formed by scintillators and photomultiplier tubes (PMTs). Through producing ideal functions and setting up various kinds of fluctuation errors, we numerical simulate the effects of statistical fluctuations in measurements of the values. The results indicate that precision of measuring the values will be influenced by statistical fluctuations of the measured signals. Considering the influence of statistical fluctuations, the number of the incident particles to the detectors surface must reach a certain value in order to make the value satisfy the measurement requirements. Thus the initial intensity of the incident particles must meet different requirements for different measuring time intervals, which can be increased while the initial intensity cannot meet the requirement. When the exponential signal carries random fluctuations with it, a larger time interval for maintaining the values will effectively attenuate the influence of statistical fluctuations.
A computational model of the neutron multiplication coefficient ( value) of a critical power assembly is built, which is measured by current-mode detectors formed by scintillators and photomultiplier tubes (PMTs). Through producing ideal functions and setting up various kinds of fluctuation errors, we numerical simulate the effects of statistical fluctuations in measurements of the values. The results indicate that precision of measuring the values will be influenced by statistical fluctuations of the measured signals. Considering the influence of statistical fluctuations, the number of the incident particles to the detectors surface must reach a certain value in order to make the value satisfy the measurement requirements. Thus the initial intensity of the incident particles must meet different requirements for different measuring time intervals, which can be increased while the initial intensity cannot meet the requirement. When the exponential signal carries random fluctuations with it, a larger time interval for maintaining the values will effectively attenuate the influence of statistical fluctuations.
2013,
25: 2121-2124.
doi: 10.3788/HPLPB20132508.2121
Abstract:
The principle of an ion beam profiler based on SEE（secondary electron emission） is introduced. For ion beams with energy of several tens of keV, an ion beam profiler prototypewith sensitive area of 16 mm16 mm is constructed. The prototype only consists of an HV plane made of a metal mesh and a signal plane made of a printed circuit board (PCB). By test with an ECR source, the system shows very good linearity between the output signal and the intensity of the ion beam, and can obtain a one dimensional beam profile with a position resolution of 2 mm.
The principle of an ion beam profiler based on SEE（secondary electron emission） is introduced. For ion beams with energy of several tens of keV, an ion beam profiler prototypewith sensitive area of 16 mm16 mm is constructed. The prototype only consists of an HV plane made of a metal mesh and a signal plane made of a printed circuit board (PCB). By test with an ECR source, the system shows very good linearity between the output signal and the intensity of the ion beam, and can obtain a one dimensional beam profile with a position resolution of 2 mm.
2013,
25: 2125-2129.
doi: 10.3788/HPLPB20132508.2125
Abstract:
The bremsstrahlung and energy deposition of multi-pulse high intensity relativistic electron beam injecting into multi-layer tantalum-graphite target are investigated. The energy deposition is calculated by Geant4 code, and the bremsstrahlung by fundamental radiation theory and Monte-Carlo method. The calculated results show the energy deposition in the hotspot of each layer decreases. The emittance and the radial distribution of the bremsstrahlung and electron beam are mostly affected by the tantalum layers. The low energy deposition rate and high heat capacity of graphite layers can improve the thermodynamic properties of the target. For a single pulse, at the tantalum-graphite thickness ratio 1∶1, the graphite can absorb all heat deposition of the neighboring tantalum layers, and the bremsstrahlung efficiency is 35.4%. With 4 pulses, the ratio should be 1∶13, and the total bremsstrahlung efficiency decreases to 19.9%. Considering the requirement of bremsstrahlung X-ray quantity and quality, the total thickness of tantalum should be 1.2 mm if the Ta-C thickness ratio is 1∶5, and 0.7 mm if the ratio is 1∶10.
The bremsstrahlung and energy deposition of multi-pulse high intensity relativistic electron beam injecting into multi-layer tantalum-graphite target are investigated. The energy deposition is calculated by Geant4 code, and the bremsstrahlung by fundamental radiation theory and Monte-Carlo method. The calculated results show the energy deposition in the hotspot of each layer decreases. The emittance and the radial distribution of the bremsstrahlung and electron beam are mostly affected by the tantalum layers. The low energy deposition rate and high heat capacity of graphite layers can improve the thermodynamic properties of the target. For a single pulse, at the tantalum-graphite thickness ratio 1∶1, the graphite can absorb all heat deposition of the neighboring tantalum layers, and the bremsstrahlung efficiency is 35.4%. With 4 pulses, the ratio should be 1∶13, and the total bremsstrahlung efficiency decreases to 19.9%. Considering the requirement of bremsstrahlung X-ray quantity and quality, the total thickness of tantalum should be 1.2 mm if the Ta-C thickness ratio is 1∶5, and 0.7 mm if the ratio is 1∶10.
2013,
25: 2130-2136.
doi: 10.3788/HPLPB20132508.2130
Abstract:
Several diagnostic systems used in implosion physics research were modeled by Geant4 toolkit, including the neutron imaging system, the filter-fluorescer spectrometer for hard X-ray diagnostic, the wedged-range filter spectrometer for proton diagnostic, the CVD diamond detector for neutron diagnostics, etc. The Geant4 simulation results were used to establish proper spectrum and images reconstructed algorithm, to optimize system design, and to estimate diagnostic system performance. Besides, based on the simulation, an experiment scheme was designed and calibration methods for the diagnostics were established.
Several diagnostic systems used in implosion physics research were modeled by Geant4 toolkit, including the neutron imaging system, the filter-fluorescer spectrometer for hard X-ray diagnostic, the wedged-range filter spectrometer for proton diagnostic, the CVD diamond detector for neutron diagnostics, etc. The Geant4 simulation results were used to establish proper spectrum and images reconstructed algorithm, to optimize system design, and to estimate diagnostic system performance. Besides, based on the simulation, an experiment scheme was designed and calibration methods for the diagnostics were established.
2013,
25: 2137-2141.
doi: 10.3788/HPLPB20132508.2137
Abstract:
A two-dimensional magneto-hydrodynamic model is solved numerically by a time-split algorithm. The physical processes which are time-split are thermal and equilibrium radiation diffusion, resistive diffusion, and Lagrangian hydrodynamics. A magneto-hydrodynamic model is proposed to numerically calculate the experiment carried out on the Z machine at Sandia National Laboratories. The computed free surface velocities of the flyer plates agree well with the experimental records by velocity interferometry system for any reflector (VISAR). The obtained velocity, pressure history curves are helpful to understand the physical mechanism of magnetically accelerated plane flyers.
A two-dimensional magneto-hydrodynamic model is solved numerically by a time-split algorithm. The physical processes which are time-split are thermal and equilibrium radiation diffusion, resistive diffusion, and Lagrangian hydrodynamics. A magneto-hydrodynamic model is proposed to numerically calculate the experiment carried out on the Z machine at Sandia National Laboratories. The computed free surface velocities of the flyer plates agree well with the experimental records by velocity interferometry system for any reflector (VISAR). The obtained velocity, pressure history curves are helpful to understand the physical mechanism of magnetically accelerated plane flyers.
2013,
25: 2142-2146.
doi: 10.3788/HPLPB20132508.2142
Abstract:
The resistive bolometer is an accurate, robust, spectrally broadband technique for measuring total soft X-ray yield. By replacing the pulsed voltage driver with a pulsed current driver and removing the series-wound resistance, the change of resistance between the ends of Ni-film can be measured directly, thus the measurement precision can be promoted effectively. The applicability of this improved resistive bolometer is expanded to all typical Z-pinch loads on Qiangguang-Ⅰ facility. Data analysis shows that the uncertainty decreases from 49.0% to 19.6% in measuring X-ray yield generated by Al wire array Z-pinches. X-ray yield data from the resistive bolometer were compared with the ones from the X-ray power measure system. The ratios between them were between 0.87 and 1.04.
The resistive bolometer is an accurate, robust, spectrally broadband technique for measuring total soft X-ray yield. By replacing the pulsed voltage driver with a pulsed current driver and removing the series-wound resistance, the change of resistance between the ends of Ni-film can be measured directly, thus the measurement precision can be promoted effectively. The applicability of this improved resistive bolometer is expanded to all typical Z-pinch loads on Qiangguang-Ⅰ facility. Data analysis shows that the uncertainty decreases from 49.0% to 19.6% in measuring X-ray yield generated by Al wire array Z-pinches. X-ray yield data from the resistive bolometer were compared with the ones from the X-ray power measure system. The ratios between them were between 0.87 and 1.04.
2013,
25: 2147-2151.
doi: 10.3788/HPLPB20132508.2147
Abstract:
A high-voltage soft coaxial feeder is developed in order to meet the research needs of high-power microwave power technology, as well as high power pulse technology. According to the actual application of the feeder, and under the conditions of low voltage, high voltage, time and frequency domains, we test the pulse power attenuation and transmission characteristics of the high-voltage feeder respectively at different voltages and air pressures. The test results are analyzed and compared with each other, which show that the pulse signal power attenuation is 0.03 dB/m, meeting the technical requirement of 0.05 dB/m.
A high-voltage soft coaxial feeder is developed in order to meet the research needs of high-power microwave power technology, as well as high power pulse technology. According to the actual application of the feeder, and under the conditions of low voltage, high voltage, time and frequency domains, we test the pulse power attenuation and transmission characteristics of the high-voltage feeder respectively at different voltages and air pressures. The test results are analyzed and compared with each other, which show that the pulse signal power attenuation is 0.03 dB/m, meeting the technical requirement of 0.05 dB/m.
2013,
25: 2152-2156.
doi: 10.3788/HPLPB20132508.2152
Abstract:
The applications of the magnetic field are favored by a majority of researchers. In this paper, based on theoretical analysis and numerical simulation, a quasi-static magnetic field generator for magnetically applied pressure-shear loading to generate pure shear stress is developed and established. This device consists of four 0.5 mF/15 kV storage capacitors in parallel, which are discharged to a pair magnet coil placed upper and down magnetically driven loading electrode via a 15 kV/30 kA semiconductor silicon stack switch. When the charging voltage is 9 kV, a 10 T quasi-static magnetic field with a rise time of 1.34 ms is obtained in the sample area. The experimental testing and simulation results show that the uniformity distribution of the magnetic field is less than 2% across 7mm radius, which can meet the requirements of the technique of magnetically applied pressure-shear.
The applications of the magnetic field are favored by a majority of researchers. In this paper, based on theoretical analysis and numerical simulation, a quasi-static magnetic field generator for magnetically applied pressure-shear loading to generate pure shear stress is developed and established. This device consists of four 0.5 mF/15 kV storage capacitors in parallel, which are discharged to a pair magnet coil placed upper and down magnetically driven loading electrode via a 15 kV/30 kA semiconductor silicon stack switch. When the charging voltage is 9 kV, a 10 T quasi-static magnetic field with a rise time of 1.34 ms is obtained in the sample area. The experimental testing and simulation results show that the uniformity distribution of the magnetic field is less than 2% across 7mm radius, which can meet the requirements of the technique of magnetically applied pressure-shear.
2013,
25: 2157-2160.
doi: 10.3788/HPLPB20132508.2157
Abstract:
A modified formula for SCL current was established, based on particle-in-cell(PIC) simulation results and formulas for conventional space-charge-limited(SCL) current and critical magnetic insulation current. And a fast interpolation model for loss current in magnetically insulated transmission line(MITL) was presented, which refrains from solving generalized Poisson equation and can be used in equivalent circuit modeling. As verification, a long coaxial MITL was simulated with both the equivalent circuit method and the PIC method. It was found that the time histories of the load voltage agreed well with each other, which were obtained by the two methods separately. The interpolation model repeated the dynamic process of current loss and the computation efficiency of the equivalent circuit simulation was more than 3000 times higher than that of the PIC simulation.
A modified formula for SCL current was established, based on particle-in-cell(PIC) simulation results and formulas for conventional space-charge-limited(SCL) current and critical magnetic insulation current. And a fast interpolation model for loss current in magnetically insulated transmission line(MITL) was presented, which refrains from solving generalized Poisson equation and can be used in equivalent circuit modeling. As verification, a long coaxial MITL was simulated with both the equivalent circuit method and the PIC method. It was found that the time histories of the load voltage agreed well with each other, which were obtained by the two methods separately. The interpolation model repeated the dynamic process of current loss and the computation efficiency of the equivalent circuit simulation was more than 3000 times higher than that of the PIC simulation.
2013,
25: 2161-2166.
doi: 10.3788/HPLPB20132508.2161
Abstract:
The theories of secondary electron emission avalanche and anode-initiated flashover model are applied to optimizing the insulator stack grading rings. All results are calculated through the finite element method. Two methods are taken into account, one is to fit numerical results with analytic results, and the other is to refine those elements. Through comparing the results from the two methods, reasonable values of electric field intensity are confirmed. As for cathode, the value is the electric field at a distance of (0.005)(21/2d) from the junction (d is the thickness of the insulator), and for anode, it is the electric field at a distance of (0.008 5)(21/2d) from the junction. After the optimization, 5 bumps are selected for 10 grading rings. The largest electric field in the cathode triple junction reduces to 2.55 kV/mm, while that in the anode triple junction reduces to 23 kV/mm.
The theories of secondary electron emission avalanche and anode-initiated flashover model are applied to optimizing the insulator stack grading rings. All results are calculated through the finite element method. Two methods are taken into account, one is to fit numerical results with analytic results, and the other is to refine those elements. Through comparing the results from the two methods, reasonable values of electric field intensity are confirmed. As for cathode, the value is the electric field at a distance of (0.005)(21/2d) from the junction (d is the thickness of the insulator), and for anode, it is the electric field at a distance of (0.008 5)(21/2d) from the junction. After the optimization, 5 bumps are selected for 10 grading rings. The largest electric field in the cathode triple junction reduces to 2.55 kV/mm, while that in the anode triple junction reduces to 23 kV/mm.
2013,
25: 2167-2172.
doi: 10.3788/HPLPB20132508.2167
Abstract:
A suit of optical diagnostics, including a fiber array detector, a solar-blinded fiber detector and a framing camera, was used to investigate the discharging process on multi-gap gas switch. Experiments were carried out to study the relationship between the delay time and various switch parameters. The ratio of the statistical delay to all delay time was 42% while the formative delay was 58%, and the delay time of third gap and fourth gap were principal part of trigger delay. The evolution of channel arcs were acquired with a framing camera. The characteristic of discharge channel image and the change of discharge channel numbers with different trigger voltage and gas pressure were analyzed. The trigger voltage had a considerable influence on the channel numbers of trigger gap, while no obvious influence on other gaps. More channel numbers with higher trigger voltage were observed. There were not combination and extinguishment of channel arcs and new channel arcs might emerge.
A suit of optical diagnostics, including a fiber array detector, a solar-blinded fiber detector and a framing camera, was used to investigate the discharging process on multi-gap gas switch. Experiments were carried out to study the relationship between the delay time and various switch parameters. The ratio of the statistical delay to all delay time was 42% while the formative delay was 58%, and the delay time of third gap and fourth gap were principal part of trigger delay. The evolution of channel arcs were acquired with a framing camera. The characteristic of discharge channel image and the change of discharge channel numbers with different trigger voltage and gas pressure were analyzed. The trigger voltage had a considerable influence on the channel numbers of trigger gap, while no obvious influence on other gaps. More channel numbers with higher trigger voltage were observed. There were not combination and extinguishment of channel arcs and new channel arcs might emerge.
2013,
25: 2173-2176.
doi: 10.3788/HPLPB20132508.2173
Abstract:
The effective electromagnetic pulse protection is studied in this paper, first the interference of electromagnetic pulse simulator path is analyzed, including the digital signal processor (DSP) and the discharge circuit of coupling interference and net electricity coupling interference. Using the structure optimization design, the hardware block reinforcement measurement and the setting of open software trap, and the watchdog anti-jamming measures, the interference test is completed such as the central processor core voltage of DSP, input/output (I/O) ports of DSP and the display screen. The experimental results show that the combination of hardware and software protection reinforcement technology is effective, and the interference pulse amplitude of DSP board I/O port and the kernel work voltage are reduced, and the interference duration is reduced from 2 s to 400 ns. The interference pulse is effectively restrained.
The effective electromagnetic pulse protection is studied in this paper, first the interference of electromagnetic pulse simulator path is analyzed, including the digital signal processor (DSP) and the discharge circuit of coupling interference and net electricity coupling interference. Using the structure optimization design, the hardware block reinforcement measurement and the setting of open software trap, and the watchdog anti-jamming measures, the interference test is completed such as the central processor core voltage of DSP, input/output (I/O) ports of DSP and the display screen. The experimental results show that the combination of hardware and software protection reinforcement technology is effective, and the interference pulse amplitude of DSP board I/O port and the kernel work voltage are reduced, and the interference duration is reduced from 2 s to 400 ns. The interference pulse is effectively restrained.
