Email alert
RSS2013 Vol. 25, No. 09
Recommend Articles
Display Method:
2013,
25: 2177-2178.
doi: 10.3788/HPLPB20132509.2177
Abstract:
It is the first time that the W-band, third harmonic gyrotron radiation is observed in China. The operation mode of the third harmonic gyrotron is TE61. The magnetic field is 1.2 T and the frequency is 94.86 GHz. When beam current changes from 1.6 A to 4.4 A, keeping the anode voltage 45 kV, the third harmonic radiation can be observed. The largest output power is 4.9 kW, and the efficiency is about 3%.
It is the first time that the W-band, third harmonic gyrotron radiation is observed in China. The operation mode of the third harmonic gyrotron is TE61. The magnetic field is 1.2 T and the frequency is 94.86 GHz. When beam current changes from 1.6 A to 4.4 A, keeping the anode voltage 45 kV, the third harmonic radiation can be observed. The largest output power is 4.9 kW, and the efficiency is about 3%.
2013,
25: 2179-2180.
doi: 10.3788/HPLPB20132509.2179
Abstract:
The laser peening technology is a recently-developed surface treatment method. Using an oscillation eight-stage amplified system structure and the modular design method, a short pulse and high power Nd:YAG laser system for laser peening has been developed and tested. At ambient temperature which changes less than 2 ℃, after 20 min of warm-up, the maximum pulse energy is 25 J, the energy instability is less than 3%, the pulse width is adjustable between 16 ns and 20 ns, the pulse width instability is less than 1 ns, the beam divergence is less than 2.5 mrad, and the maximum frequency is 5 Hz. A TC4 titanium alloy work-piece is processed with the laser system, the compressive residual stress is greatly improved. The results show that the performance of the laser system is very excellent.
The laser peening technology is a recently-developed surface treatment method. Using an oscillation eight-stage amplified system structure and the modular design method, a short pulse and high power Nd:YAG laser system for laser peening has been developed and tested. At ambient temperature which changes less than 2 ℃, after 20 min of warm-up, the maximum pulse energy is 25 J, the energy instability is less than 3%, the pulse width is adjustable between 16 ns and 20 ns, the pulse width instability is less than 1 ns, the beam divergence is less than 2.5 mrad, and the maximum frequency is 5 Hz. A TC4 titanium alloy work-piece is processed with the laser system, the compressive residual stress is greatly improved. The results show that the performance of the laser system is very excellent.
2013,
25: 2181-2187.
doi: 10.3788/HPLPB20132509.2181
Abstract:
Research on electrode erosion of switches in high pressure and high current discharges was reviewed. The factors, including electrode materials of switches, discharge condition, which affect electrode erosion of switches were concluded. The characteristics of electrode erosion of switches and surface structure of electrodes after discharges were analyzed. The mechanisms of electrode heating and electrode material removal were also summarized. To extend the lifetime of switches, several measures of decreasing electrode erosion were put forward, such as choosing excellent anti-erosion performance materials, appropriate structure of switches, and optimized discharge condition.
Research on electrode erosion of switches in high pressure and high current discharges was reviewed. The factors, including electrode materials of switches, discharge condition, which affect electrode erosion of switches were concluded. The characteristics of electrode erosion of switches and surface structure of electrodes after discharges were analyzed. The mechanisms of electrode heating and electrode material removal were also summarized. To extend the lifetime of switches, several measures of decreasing electrode erosion were put forward, such as choosing excellent anti-erosion performance materials, appropriate structure of switches, and optimized discharge condition.
2013,
25: 2188-2192.
doi: 10.3788/HPLPB20132509.2188
Abstract:
The traditional monocular vision system has certain limitations when space azimuth is measured. It is not feasible for the condition under which the object is without the scope of the CCD field. Therefore, a kind of rotation matrix method to measure the objects space azimuth under CCD non-vision area is proposed. According to the principle of Zhang Zhengyou calibration method, the rotation matrix method, through processing with feature points on the cooperative target, works out rotation axiss space azimuth of the cooperative target. Then the objects space azimuth under CCD non-visual area is indirectly obtained. Experiments indicate that the rotation matrix method has certain feasibility and stability, and the root mean square error of the objects space azimuth calculated by this method is lower than 0.06.
The traditional monocular vision system has certain limitations when space azimuth is measured. It is not feasible for the condition under which the object is without the scope of the CCD field. Therefore, a kind of rotation matrix method to measure the objects space azimuth under CCD non-vision area is proposed. According to the principle of Zhang Zhengyou calibration method, the rotation matrix method, through processing with feature points on the cooperative target, works out rotation axiss space azimuth of the cooperative target. Then the objects space azimuth under CCD non-visual area is indirectly obtained. Experiments indicate that the rotation matrix method has certain feasibility and stability, and the root mean square error of the objects space azimuth calculated by this method is lower than 0.06.
2013,
25: 2193-2197.
doi: 10.3788/HPLPB20132509.2193
Abstract:
The signals received by Fourier telescopy are analyzed and demonstrated to contain not only image information but also two-dimensional velocity information of the measured target. The velocities on each component can be calculated by the periodic signal frequencies that can be extracted from received signals. Then the two-dimension velocity is composited. The frequency of the signal is extracted by fast Fourier transform analysis for coarse frequency estimate, and by ratio frequency correction algorithms using Hanning window for precise frequency correction. Simulation is made to measure the flight velocity of the missile by Fourier telescopy. The result shows that the target velocity acquired by this method has almost no error without noise, while it has relatively high precision with noise when SNR is higher than 5 dB. The velocity acquisition method from receiving signal of Fourier telescopy is demonstrated to have high precision, a good anti-noise property and to be theoretically feasible.
The signals received by Fourier telescopy are analyzed and demonstrated to contain not only image information but also two-dimensional velocity information of the measured target. The velocities on each component can be calculated by the periodic signal frequencies that can be extracted from received signals. Then the two-dimension velocity is composited. The frequency of the signal is extracted by fast Fourier transform analysis for coarse frequency estimate, and by ratio frequency correction algorithms using Hanning window for precise frequency correction. Simulation is made to measure the flight velocity of the missile by Fourier telescopy. The result shows that the target velocity acquired by this method has almost no error without noise, while it has relatively high precision with noise when SNR is higher than 5 dB. The velocity acquisition method from receiving signal of Fourier telescopy is demonstrated to have high precision, a good anti-noise property and to be theoretically feasible.
2013,
25: 2198-2202.
doi: 10.3788/HPLPB20132509.2198
Abstract:
The holographic modal wavefront sensor is a novel sensor, which directly detects the aberration modes included in the distorted wavefront by employing a multiplexed computer-generated holographic element (MCGHE). This element can be designed and generated by pre-coding multiple Zernike aberration modes. We propose an efficient approach of designing the MCGHE, which is generated through superposing several amplitude gratings distorted by specific aberration modes. The analytical formulas are derived to characterize the relationship between the sensor output signal and the coefficient of particular Zernike aberration mode，given the condition of small aberration approximation. The MCGHE is designed and simulated in detecting single Zernike aberration mode or multiple ones. The demonstration experiment is carried out by utilizing a liquid crystal light valve. The experimental results are consistent with the numerical ones to some extent.
The holographic modal wavefront sensor is a novel sensor, which directly detects the aberration modes included in the distorted wavefront by employing a multiplexed computer-generated holographic element (MCGHE). This element can be designed and generated by pre-coding multiple Zernike aberration modes. We propose an efficient approach of designing the MCGHE, which is generated through superposing several amplitude gratings distorted by specific aberration modes. The analytical formulas are derived to characterize the relationship between the sensor output signal and the coefficient of particular Zernike aberration mode，given the condition of small aberration approximation. The MCGHE is designed and simulated in detecting single Zernike aberration mode or multiple ones. The demonstration experiment is carried out by utilizing a liquid crystal light valve. The experimental results are consistent with the numerical ones to some extent.
2013,
25: 2203-2207.
doi: 10.3788/HPLPB20132509.2203
Abstract:
To meet the requirements for high accuracy and real time performance of high power laser driver beam automatic alignment, a fast and precise center location method for target of high power laser driver beam automatic alignment is proposed. The specific characteristics of the target edge are fully extracted by using multiple structuring elements-based generalized morphological edge detection, while the influences of the noises on images are diminished. Then, the edge is quickly located in sub-pixel precision by adopting the Lagrange polynomial interpolation method, at last the center position of the spot target in image is accurately acquired by using circle fitting method based on least square fitting method and geometric centroid. This algorithm is verified in the ShenguangⅡ upgrade device, the alignment time of eight prelight roads is less than 3 min, and the alignment time of the main light path is less than 7 min. The main output of the near-field beam collimation accuracy is better than 0.2%, and the far field accuracy is better than 0.2(RMS).
To meet the requirements for high accuracy and real time performance of high power laser driver beam automatic alignment, a fast and precise center location method for target of high power laser driver beam automatic alignment is proposed. The specific characteristics of the target edge are fully extracted by using multiple structuring elements-based generalized morphological edge detection, while the influences of the noises on images are diminished. Then, the edge is quickly located in sub-pixel precision by adopting the Lagrange polynomial interpolation method, at last the center position of the spot target in image is accurately acquired by using circle fitting method based on least square fitting method and geometric centroid. This algorithm is verified in the ShenguangⅡ upgrade device, the alignment time of eight prelight roads is less than 3 min, and the alignment time of the main light path is less than 7 min. The main output of the near-field beam collimation accuracy is better than 0.2%, and the far field accuracy is better than 0.2(RMS).
2013,
25: 2208-2212.
doi: 10.3788/HPLPB20132509.2208
Abstract:
The SUSAN filtering operator can not self-adaptively modulate filter coefficients due to the use of an axisymmetric Gaussian filter. In order to solve this problem, this article presents an anisotropic SUSAN filter using an anisotropic Gaussian filter instead of a Gaussian filter in the SUSAN filtering operator. The variances of long axis and short axis are determined by the variance and the pixel neighborhood smoothness of the partial image. The long axis direction is determined by the gradient direction of the point. The SUSAN filter threshold is determined by the first order norm of the difference of the gray value and the mean value. For the infrared dim target detection, experimental results show that the anisotropic SUSAN filter could preserve the image edge information, the signal-to-noise ratio gain and signal-to-clutter ratio gain greatly improved in the residual image, the size of the target got a better retention, and the false alarm decreased.
The SUSAN filtering operator can not self-adaptively modulate filter coefficients due to the use of an axisymmetric Gaussian filter. In order to solve this problem, this article presents an anisotropic SUSAN filter using an anisotropic Gaussian filter instead of a Gaussian filter in the SUSAN filtering operator. The variances of long axis and short axis are determined by the variance and the pixel neighborhood smoothness of the partial image. The long axis direction is determined by the gradient direction of the point. The SUSAN filter threshold is determined by the first order norm of the difference of the gray value and the mean value. For the infrared dim target detection, experimental results show that the anisotropic SUSAN filter could preserve the image edge information, the signal-to-noise ratio gain and signal-to-clutter ratio gain greatly improved in the residual image, the size of the target got a better retention, and the false alarm decreased.
2013,
25: 2213-2218.
doi: 10.3788/HPLPB20132509.2213
Abstract:
For more precise measurements of the temporal evolution of plasma in the study of inertial confinement fusion (ICF), we analyzed a novel optical streak camera with ultrahigh time resolution. Based on the photo-generated carrier effect, waveguide transmission and prism dispersion principles, this all-optical device can avoid the influence of the space charge effect. The feasibility for the all-optical streak camera was confirmed with the experimental result. The module with prism structure to deflect the light in the waveguide was designed and fabricated. The deflection experiment was completed with the laser pulse of 8 ps (FWHM) under the condition of the signal laser wavelength of 1053 nm and the pump laser wavelength of 527 nm.
For more precise measurements of the temporal evolution of plasma in the study of inertial confinement fusion (ICF), we analyzed a novel optical streak camera with ultrahigh time resolution. Based on the photo-generated carrier effect, waveguide transmission and prism dispersion principles, this all-optical device can avoid the influence of the space charge effect. The feasibility for the all-optical streak camera was confirmed with the experimental result. The module with prism structure to deflect the light in the waveguide was designed and fabricated. The deflection experiment was completed with the laser pulse of 8 ps (FWHM) under the condition of the signal laser wavelength of 1053 nm and the pump laser wavelength of 527 nm.
2013,
25: 2219-2222.
doi: 10.3788/HPLPB20132509.2219
Abstract:
A pair of fiber lasers with high output power and low quantum-defect at 1018 nm was demonstrated. These two 1018 nm fiber lasers were used as the source of Michelson cavity to show experimentally that a coherent beam combination of two Yb-doped double-cladding fiber lasers using all-fiber Michelson cavity technique was achieved. We obtained an output power of 55 W with a coherent combination efficiency of 90.2%, which is the highest output power that single-mode 1018 nm fiber lasers have obtained so far. Moreover, we proved that coherent beam combination by using Michelson cavity can achieve high power single-mode output of fiber laser.
A pair of fiber lasers with high output power and low quantum-defect at 1018 nm was demonstrated. These two 1018 nm fiber lasers were used as the source of Michelson cavity to show experimentally that a coherent beam combination of two Yb-doped double-cladding fiber lasers using all-fiber Michelson cavity technique was achieved. We obtained an output power of 55 W with a coherent combination efficiency of 90.2%, which is the highest output power that single-mode 1018 nm fiber lasers have obtained so far. Moreover, we proved that coherent beam combination by using Michelson cavity can achieve high power single-mode output of fiber laser.
2013,
25: 2223-2228.
doi: 10.3788/HPLPB20132509.2223
Abstract:
Due to the contrast difference of infrared and visible images, the common registration methods based on gradient magnitude are difficult to match correctly. A novel algorithm based on the phase congruency edge detection and Hough transform was proposed by analyzing the imaging mechanism. The Gauss filter and platform histogram equalization method was applied to enhance infrared image contrast. The phase congruency algorithm with image contrast invariance was used to extract the edge of the two images. And the longest line was selected by Hough transform as the similar characteristics. Then the modified phase correlation method was used as the similarity measurement to compute geometric deformation parameters of two images under the log-polar domain. The experimental results indicated that the algorithm could achieve higher precision and robustness for infrared and visible image automatic registration.
Due to the contrast difference of infrared and visible images, the common registration methods based on gradient magnitude are difficult to match correctly. A novel algorithm based on the phase congruency edge detection and Hough transform was proposed by analyzing the imaging mechanism. The Gauss filter and platform histogram equalization method was applied to enhance infrared image contrast. The phase congruency algorithm with image contrast invariance was used to extract the edge of the two images. And the longest line was selected by Hough transform as the similar characteristics. Then the modified phase correlation method was used as the similarity measurement to compute geometric deformation parameters of two images under the log-polar domain. The experimental results indicated that the algorithm could achieve higher precision and robustness for infrared and visible image automatic registration.
2013,
25: 2229-2234.
doi: 10.3788/HPLPB20132509.2229
Abstract:
A preliminary coupled thermal-fluid-structure numerical method which reflects interaction of laser, airflow and target is presented, in order to investigate failure behavior of the target irradiated by high-power laser subjected to supersonic airflow (at Mach number 1.2-4.0). The influences of different coupling methods on the target temperature are investigated. Also, the influences of laser power density and airflow velocity on the failure behavior of the irradiated target are investigated, where irradiation times to reach the yield failure and melting failure are the main concern. Results show that, laser power density significantly affects the failure behavior; there is a critical Mach number at which irradiation times to reach yield failure and melting failure are the longest. By quantitatively evaluating the aerodynamic heating, aerodynamic cooling and energy distribution for different Mach numbers, we explain the mechanism for the critical Mach number.
A preliminary coupled thermal-fluid-structure numerical method which reflects interaction of laser, airflow and target is presented, in order to investigate failure behavior of the target irradiated by high-power laser subjected to supersonic airflow (at Mach number 1.2-4.0). The influences of different coupling methods on the target temperature are investigated. Also, the influences of laser power density and airflow velocity on the failure behavior of the irradiated target are investigated, where irradiation times to reach the yield failure and melting failure are the main concern. Results show that, laser power density significantly affects the failure behavior; there is a critical Mach number at which irradiation times to reach yield failure and melting failure are the longest. By quantitatively evaluating the aerodynamic heating, aerodynamic cooling and energy distribution for different Mach numbers, we explain the mechanism for the critical Mach number.
2013,
25: 2235-2240.
doi: 10.3788/HPLPB20132509.2235
Abstract:
The correction method of three-channel polarization imaging system based on calibration is very complex in the process of calibrating non-uniformity of channels responsiveness, and this method cannot correct the non-uniformity when the physical environment changes. It affects the practicality of the polarization of the three-channel imaging system. To solve this problem, a scene-based correction method of the three-channel imaging system is proposed. The method is based on the statistics of polarization information in the scene. It separates non-polarized scenes from complex scenes, and fixes the differences of gray response among the three channels simply and quickly. As is shown in the experimental results, this method overcomes the impact of non-uniformity of channels responsiveness, gives prominence to the differences between the polarization of the different materials, makes the imaging effect of the three-channel polarization imaging system close to that of a single-channel polarization imaging system, and improves the practicality of the system perfectly.
The correction method of three-channel polarization imaging system based on calibration is very complex in the process of calibrating non-uniformity of channels responsiveness, and this method cannot correct the non-uniformity when the physical environment changes. It affects the practicality of the polarization of the three-channel imaging system. To solve this problem, a scene-based correction method of the three-channel imaging system is proposed. The method is based on the statistics of polarization information in the scene. It separates non-polarized scenes from complex scenes, and fixes the differences of gray response among the three channels simply and quickly. As is shown in the experimental results, this method overcomes the impact of non-uniformity of channels responsiveness, gives prominence to the differences between the polarization of the different materials, makes the imaging effect of the three-channel polarization imaging system close to that of a single-channel polarization imaging system, and improves the practicality of the system perfectly.
2013,
25: 2241-2246.
doi: 10.3788/HPLPB20132509.2241
Abstract:
Based on the method of vector angular spectrum representation and the method of stationary phase, the analytical expressions for the electromagnetic fields of the vectorial structure, namely the transverse electric (TE) and the transverse magnetic (TM) terms of a vortex Lorentz-Gauss beam, are derived in the far-field. Moreover, the analytical expressions of the energy flux of the TE and TM terms are also presented in the far-field. The influence of the topological charge on the energy flux distributions of the vortex Lorentz-Gauss beam and its vectorial structure are analyzed by numerical examples. The TE term is composed of two or three lobes which are located at the y-axis. The TM term can be viewed as the TE term rotating 90 degrees. When the topological charge is small, the vortex Lorentz-Gauss beam takes on dark hollow shape, and the brightly outer ring is uniform. With increasing the topological charge, the energy flux in the brightly outer ring of the vortex Lorentz-Gauss beam fluctuates, and the change in the central region is relative complicated. With increasing the topological charge, the beam sizes of the vortex Lorentz-Gauss beam and its vectorial structure also augment. However, the beam sizes of the vortex Lorentz-Gauss beam and its vectorial structure will saturate. In the practical application of the vortex Lorentz-Gauss beam, therefore, the topological charge should not be too large.
Based on the method of vector angular spectrum representation and the method of stationary phase, the analytical expressions for the electromagnetic fields of the vectorial structure, namely the transverse electric (TE) and the transverse magnetic (TM) terms of a vortex Lorentz-Gauss beam, are derived in the far-field. Moreover, the analytical expressions of the energy flux of the TE and TM terms are also presented in the far-field. The influence of the topological charge on the energy flux distributions of the vortex Lorentz-Gauss beam and its vectorial structure are analyzed by numerical examples. The TE term is composed of two or three lobes which are located at the y-axis. The TM term can be viewed as the TE term rotating 90 degrees. When the topological charge is small, the vortex Lorentz-Gauss beam takes on dark hollow shape, and the brightly outer ring is uniform. With increasing the topological charge, the energy flux in the brightly outer ring of the vortex Lorentz-Gauss beam fluctuates, and the change in the central region is relative complicated. With increasing the topological charge, the beam sizes of the vortex Lorentz-Gauss beam and its vectorial structure also augment. However, the beam sizes of the vortex Lorentz-Gauss beam and its vectorial structure will saturate. In the practical application of the vortex Lorentz-Gauss beam, therefore, the topological charge should not be too large.
2013,
25: 2247-2251.
doi: 10.3788/HPLPB20132509.2247
Abstract:
This paper studies the initiated damage threshold, the damage morphology and the subsequent damage growth on fused silicas input-surface and exit-surface under picosecond laser irradiation at 355 nm. Defects induced fluorescence on surface of the optical component is observed. The results demonstrate a significant dependence of the initiated damage on pulse duration and surface defects, and that of the damage growth on self-focusing, sub-surface defects. The damage-threshold is 3.98 J/cm2 of input surface and 2.91 J/cm2 of exit surface. The damage morphologies are quite different between input surface and exit surface. Slow growth behavior appears for the diameter of exit-surface and linear growth one for the depth of exit-surface in the lateral side of damage site with the increase of shot number. Defects have changed obviously compared with nanosecond laser damage in the damage area. Several main reasons such as electric intensification and self-focusing for the observed initiated damage and damage growth behavior are discussed.
This paper studies the initiated damage threshold, the damage morphology and the subsequent damage growth on fused silicas input-surface and exit-surface under picosecond laser irradiation at 355 nm. Defects induced fluorescence on surface of the optical component is observed. The results demonstrate a significant dependence of the initiated damage on pulse duration and surface defects, and that of the damage growth on self-focusing, sub-surface defects. The damage-threshold is 3.98 J/cm2 of input surface and 2.91 J/cm2 of exit surface. The damage morphologies are quite different between input surface and exit surface. Slow growth behavior appears for the diameter of exit-surface and linear growth one for the depth of exit-surface in the lateral side of damage site with the increase of shot number. Defects have changed obviously compared with nanosecond laser damage in the damage area. Several main reasons such as electric intensification and self-focusing for the observed initiated damage and damage growth behavior are discussed.
2013,
25: 2252-2256.
doi: 10.3788/HPLPB20132509.2252
Abstract:
Based on the extended Huygens-Fresnel principle, the analytical expressions for the root mean square width and angular spread of partially coherent Hermite-Gaussian (H-G) beams propagating through slant atmospheric turbulence are derived, and are used to study the influence of propagation path and beam orders on the propagation of partially coherent H-G beams in atmospheric turbulence along a slant path. The relative width and relative angular spread are introduced to quantitatively describe the resistance of a beam to atmospheric turbulence. It is shown that under the same conditions the influence of atmospheric turbulence along a slant path on the partially coherent H-G beam propagation is smaller than that along a horizontal path. Therefore, the slant path is more beneficial to the beam propagation through atmospheric turbulence in comparison with the horizontal propagation. The larger the beam orders m, n are, the less the partially coherent H-G beams are affected by turbulence.
Based on the extended Huygens-Fresnel principle, the analytical expressions for the root mean square width and angular spread of partially coherent Hermite-Gaussian (H-G) beams propagating through slant atmospheric turbulence are derived, and are used to study the influence of propagation path and beam orders on the propagation of partially coherent H-G beams in atmospheric turbulence along a slant path. The relative width and relative angular spread are introduced to quantitatively describe the resistance of a beam to atmospheric turbulence. It is shown that under the same conditions the influence of atmospheric turbulence along a slant path on the partially coherent H-G beam propagation is smaller than that along a horizontal path. Therefore, the slant path is more beneficial to the beam propagation through atmospheric turbulence in comparison with the horizontal propagation. The larger the beam orders m, n are, the less the partially coherent H-G beams are affected by turbulence.
2013,
25: 2257-2261.
doi: 10.3788/HPLPB20132509.2257
Abstract:
Based on the extended Huygens-Fresnel principle, analytical expressions are derived for the cross-spectral density matrix of chirped pulsed Gaussian beams propagating in turbulent atmosphere, which are then numerically simulated. It is shown that there are blue shifts in the spectra of axis point when the spectral width of chirped pulsed Gaussian beams is more than a certain value of 0.336. The turbulence induces the decrease of relative frequency shift of on-axis spectra; the relative frequency shift of on-axis spectra increases nonlinearly with the increasing light source spectral width. Increasing the beam waist radius can inhibit the relative frequency shift and the beam broadening.
Based on the extended Huygens-Fresnel principle, analytical expressions are derived for the cross-spectral density matrix of chirped pulsed Gaussian beams propagating in turbulent atmosphere, which are then numerically simulated. It is shown that there are blue shifts in the spectra of axis point when the spectral width of chirped pulsed Gaussian beams is more than a certain value of 0.336. The turbulence induces the decrease of relative frequency shift of on-axis spectra; the relative frequency shift of on-axis spectra increases nonlinearly with the increasing light source spectral width. Increasing the beam waist radius can inhibit the relative frequency shift and the beam broadening.
2013,
25: 2262-2266.
doi: 10.3788/HPLPB20132509.2262
Abstract:
Based on the theory of optical wave propagation in the slant path and the ITU-R atmospheric refractive index structure constant model which depends on the altitude, and considering the influence of inner scale, we studies the scintillation index from the transmitter to the target and that from the target to the receiver by using the modified Hill spectrum. The relationship of the scintillation index of the echo wave and the Fresnel rate is derived. The influences of inner scale, transmission distance, the beams wavelength and the target height on the echo wave scintillation index are analyzed. The results show that the inner scales and the target heights have more significant effect on the scintillation index than the wavelengths and the transmission distances.
Based on the theory of optical wave propagation in the slant path and the ITU-R atmospheric refractive index structure constant model which depends on the altitude, and considering the influence of inner scale, we studies the scintillation index from the transmitter to the target and that from the target to the receiver by using the modified Hill spectrum. The relationship of the scintillation index of the echo wave and the Fresnel rate is derived. The influences of inner scale, transmission distance, the beams wavelength and the target height on the echo wave scintillation index are analyzed. The results show that the inner scales and the target heights have more significant effect on the scintillation index than the wavelengths and the transmission distances.
Development and application of high-resolution spherically bent crystal monochromatic imaging system
2013,
25: 2267-2269.
doi: 10.3788/HPLPB20132509.2267
Abstract:
A high-resolution spherically bent crystal imaging system has been development by using quartz 1010 crystal as X ray imaging component, and it has been applied in Shengguan laser facilties. Using the imaging system, the image of four cycle grid has been acquired by using Mg as backlight material. The meridian magnification is 13.95 and the sagittal magnification is 11.61. The central energy is 1.472 keV, and the spectral resolution is 1.210-4. The resolution of the image is 4 micrometers. This imaging system is an important diagnostic tool for monochromatic X-ray image in implosion and fluid instability experiments.
A high-resolution spherically bent crystal imaging system has been development by using quartz 1010 crystal as X ray imaging component, and it has been applied in Shengguan laser facilties. Using the imaging system, the image of four cycle grid has been acquired by using Mg as backlight material. The meridian magnification is 13.95 and the sagittal magnification is 11.61. The central energy is 1.472 keV, and the spectral resolution is 1.210-4. The resolution of the image is 4 micrometers. This imaging system is an important diagnostic tool for monochromatic X-ray image in implosion and fluid instability experiments.
2013,
25: 2270-2274.
doi: 10.3788/HPLPB20132509.2270
Abstract:
The controllability of stiffness of bonnet tool polishing large aspheric lenses was studied, aiming to ensure the high stability and uniform removal rate of bonnet tool in polishing process. After analyzing the force situation of bonnet tool when polishing large aspheric lenses, the stiffness of the bonnet tool was calculated, and then influencing factors of stiffness of bonnet tool and the effects brought by stiffness of bonnet in polishing process were discussed. After that, control algorithm of bonnet tool was designed and simulated experiments were carried out, the results revealed that the controllability of stiffness of bonnet tool in polishing process could be achieved, which verified the correctness of the control algorithm.
The controllability of stiffness of bonnet tool polishing large aspheric lenses was studied, aiming to ensure the high stability and uniform removal rate of bonnet tool in polishing process. After analyzing the force situation of bonnet tool when polishing large aspheric lenses, the stiffness of the bonnet tool was calculated, and then influencing factors of stiffness of bonnet tool and the effects brought by stiffness of bonnet in polishing process were discussed. After that, control algorithm of bonnet tool was designed and simulated experiments were carried out, the results revealed that the controllability of stiffness of bonnet tool in polishing process could be achieved, which verified the correctness of the control algorithm.
2013,
25: 2275-2280.
doi: 10.3788/HPLPB20132509.2275
Abstract:
The high reflection films will be damaged when irradiated by high power laser. With the increasing of the laser energy and the numbers of irradiation, the sizes of the initial damaged structure will grow, which has a serious effect on the application of the optics. In this paper, the varying rules, the damage feature and the damage growth threshold of the HfO2/SiO2 high reflection films under 1064 nm laser irradiation have been investigated. The results indicate that the lateral dimension of the delamination initial damage structure increases almost multi-linearly with the rise of laser fluence. The damaged growth threshold along the vertical expanding is more than twice as it along the horizontal expanding. In addition, the growth rate of the initial damaged structure grows with the rise of the laser fluence exponentially in the horizontal direction while the damage growth threshold decreases obviously with the rise of the shots.
The high reflection films will be damaged when irradiated by high power laser. With the increasing of the laser energy and the numbers of irradiation, the sizes of the initial damaged structure will grow, which has a serious effect on the application of the optics. In this paper, the varying rules, the damage feature and the damage growth threshold of the HfO2/SiO2 high reflection films under 1064 nm laser irradiation have been investigated. The results indicate that the lateral dimension of the delamination initial damage structure increases almost multi-linearly with the rise of laser fluence. The damaged growth threshold along the vertical expanding is more than twice as it along the horizontal expanding. In addition, the growth rate of the initial damaged structure grows with the rise of the laser fluence exponentially in the horizontal direction while the damage growth threshold decreases obviously with the rise of the shots.
2013,
25: 2281-2286.
doi: 10.3788/HPLPB20132509.2281
Abstract:
The magnetorheological finishing (MRF) is a newly developed technique in precision optical manufacturing which can produce optical components precisely with high efficiency and has been widely used. In order to fully grasp the influence law of polishing result by magnetic field intensity, immersion depth, polishing wheel speed and moisture content, we analyzed the removal mathematical model of magnetorheological finishing and then designed a series of experiments upon these process parameters by using PKC100-P1 equipment. Then we summarized the inner link between the final quality of optical component and the polishing parameters and finally drew a corresponding impact curve. The curve indicates that these process parameters have evident effects on the removal of material and component surface quality. Mastering the effects well, we can optimize the processing accuracy. Simultaneously the experimental results verified the correctness of the magnetorheological finishing material removal theory.
The magnetorheological finishing (MRF) is a newly developed technique in precision optical manufacturing which can produce optical components precisely with high efficiency and has been widely used. In order to fully grasp the influence law of polishing result by magnetic field intensity, immersion depth, polishing wheel speed and moisture content, we analyzed the removal mathematical model of magnetorheological finishing and then designed a series of experiments upon these process parameters by using PKC100-P1 equipment. Then we summarized the inner link between the final quality of optical component and the polishing parameters and finally drew a corresponding impact curve. The curve indicates that these process parameters have evident effects on the removal of material and component surface quality. Mastering the effects well, we can optimize the processing accuracy. Simultaneously the experimental results verified the correctness of the magnetorheological finishing material removal theory.
2013,
25: 2287-2291.
doi: 10.3788/HPLPB20132509.2287
Abstract:
A two-frame laser differential interferometer system has been developed, with which two high-definition interferograms with an interval of 3 ns-12 ns can be obtained in one shot. The system generates two probe pulses with certain intersection angle and time interval via a beam splitting and delaying device. A special off-axis four-focus imaging system is used to image the object on two different areas on a single CCD ship. The system is applied to aluminum wires Z-pinch experiments. Interferograms of Z-pinch plasma evolution are obtained, including wires expanding and ablation, generation and evolution of corona plasma and precursory plasma, etc. Electron density distributions of early-stage Z-pinch plasma are calculated from the interferograms.
A two-frame laser differential interferometer system has been developed, with which two high-definition interferograms with an interval of 3 ns-12 ns can be obtained in one shot. The system generates two probe pulses with certain intersection angle and time interval via a beam splitting and delaying device. A special off-axis four-focus imaging system is used to image the object on two different areas on a single CCD ship. The system is applied to aluminum wires Z-pinch experiments. Interferograms of Z-pinch plasma evolution are obtained, including wires expanding and ablation, generation and evolution of corona plasma and precursory plasma, etc. Electron density distributions of early-stage Z-pinch plasma are calculated from the interferograms.
2013,
25: 2292-2296.
doi: 10.3788/HPLPB20132509.2292
Abstract:
The high resolving measurement of hard X-ray spectra generated in laser-produced plasma is usually performed using a cylindrically curved crystal spectrometer. In this paper, theoretical analysis and numerical simulation are performed to investigate the dependence of the energy range and resolving power on various design parameters, including crystal bending radius, source to crystal standoff distance, source size, location of the detector, etc. The investigation provides a means to design and develop cylindrically transmission curved crystal spectrometer which is used in hard X-ray diagnostics. The results show that crystal bending radius has a great influence on energy range of spectra and resolving power, and the separation between the spectral lines increases with the distance behind the focal circle faster than the line width, resulting in increased resolving power with distance.
The high resolving measurement of hard X-ray spectra generated in laser-produced plasma is usually performed using a cylindrically curved crystal spectrometer. In this paper, theoretical analysis and numerical simulation are performed to investigate the dependence of the energy range and resolving power on various design parameters, including crystal bending radius, source to crystal standoff distance, source size, location of the detector, etc. The investigation provides a means to design and develop cylindrically transmission curved crystal spectrometer which is used in hard X-ray diagnostics. The results show that crystal bending radius has a great influence on energy range of spectra and resolving power, and the separation between the spectral lines increases with the distance behind the focal circle faster than the line width, resulting in increased resolving power with distance.
2013,
25: 2297-2302.
doi: 10.3788/HPLPB20132509.2297
Abstract:
A two-dimensional hybrid model is used to study the two-dimensional characters of the plasma parameter such as the ion flux, the ion energy and angular distributions in radial and axial directions. It shows that the electric field and the sheath character at the center of the electrode are different from those at the area between the electrode and the side wall. At the area between the electrode and the side wall, the influence of the electrode is relatively small, and the sheath structure is determined by the ambipolar diffusion. Therefore, the axial electric field is small, the radial electric field is relatively stronger, and the sheath near the side wall is much thinner than that in the center of the RF electrode. The ion flux and the ion energy distributions on the electrode remain the same at the center area of the discharge chamber, however, the electric field in axial direction decreases between the side wall and the edge of electrode, which leads to a decrease of the ion flux in this region. The ion angular distributions also have little change at the center area of the discharge chamber. However, the radial electric field becomes stronger than the axial field between the side wall of the chamber and the edge of the electrode. This makes the ions in that area strike the lower electrode with a much larger angle.
A two-dimensional hybrid model is used to study the two-dimensional characters of the plasma parameter such as the ion flux, the ion energy and angular distributions in radial and axial directions. It shows that the electric field and the sheath character at the center of the electrode are different from those at the area between the electrode and the side wall. At the area between the electrode and the side wall, the influence of the electrode is relatively small, and the sheath structure is determined by the ambipolar diffusion. Therefore, the axial electric field is small, the radial electric field is relatively stronger, and the sheath near the side wall is much thinner than that in the center of the RF electrode. The ion flux and the ion energy distributions on the electrode remain the same at the center area of the discharge chamber, however, the electric field in axial direction decreases between the side wall and the edge of electrode, which leads to a decrease of the ion flux in this region. The ion angular distributions also have little change at the center area of the discharge chamber. However, the radial electric field becomes stronger than the axial field between the side wall of the chamber and the edge of the electrode. This makes the ions in that area strike the lower electrode with a much larger angle.
2013,
25: 2303-2306.
doi: 10.3788/HPLPB20132509.2303
Abstract:
An experiment of direct-drive cylindrical target compression is carried out using the eight laser beams of Shenguang-Ⅱ laser facility with the spots defocused to 200 m. A clear flow diagram of cylindrical target implosion is obtained with Mo backlight driven by the 9th laser beam and Kirkpatrick-Baez microscopy. Experimental result shows that, for the cylindrical target with an outer diameter of 260 m, a compressed density of up to 120 times the initial density is obtained, which is between the densities of electron production area and energy deposition area. Experiments of electron beam transport and energy deposition in this compressed cylindrical target could be carried out once the Shenguang-Ⅱ ps laser beam is available.
An experiment of direct-drive cylindrical target compression is carried out using the eight laser beams of Shenguang-Ⅱ laser facility with the spots defocused to 200 m. A clear flow diagram of cylindrical target implosion is obtained with Mo backlight driven by the 9th laser beam and Kirkpatrick-Baez microscopy. Experimental result shows that, for the cylindrical target with an outer diameter of 260 m, a compressed density of up to 120 times the initial density is obtained, which is between the densities of electron production area and energy deposition area. Experiments of electron beam transport and energy deposition in this compressed cylindrical target could be carried out once the Shenguang-Ⅱ ps laser beam is available.
2013,
25: 2307-2312.
doi: 10.3788/HPLPB20132509.2307
Abstract:
The oxide layer grown on the A15 Nb3Ge surface after exposure to air is found to be mainly Nb2O5 from the observation of X-ray photoelectron spectroscopy, and no germanium oxide is detected. In order to investigate the initial oxidation mechanism of Nb3Ge, the adsorption of O atoms on Nb3Ge surface is performed within density functional theory (DFT). O atom prefers to bonding with Nb atom, and the bond is both ionic and covalent, which is consistent with the experiment. As the outer Nb oxidizes gradually, the inner Nb atoms begin to exchange with outer Ge atoms with the motivation of the contact potential, therefore niobium oxide congregates on the surface, also there is Ge accumulation under this oxide layer.
The oxide layer grown on the A15 Nb3Ge surface after exposure to air is found to be mainly Nb2O5 from the observation of X-ray photoelectron spectroscopy, and no germanium oxide is detected. In order to investigate the initial oxidation mechanism of Nb3Ge, the adsorption of O atoms on Nb3Ge surface is performed within density functional theory (DFT). O atom prefers to bonding with Nb atom, and the bond is both ionic and covalent, which is consistent with the experiment. As the outer Nb oxidizes gradually, the inner Nb atoms begin to exchange with outer Ge atoms with the motivation of the contact potential, therefore niobium oxide congregates on the surface, also there is Ge accumulation under this oxide layer.
2013,
25: 2313-2316.
doi: 10.3788/HPLPB20132509.2313
Abstract:
The pinhole camera is an important device for inspecting of laser focal spot and target pointing in inertial confinement fusion experiments. In this paper, the X-ray pinhole camera has been developed for ShengguangⅡ-up equipment. This study focuses on parameter and configuration optimization. And the devices have been designed, manufactured, assembled and tested. The results of test experiments show that the energy range is 1.0-5.5 keV, the spatial resolution is better than 20 m, and the magnification ratio is 5.13-9.99. That proves that the pinhole camera can be applied on ShengguangⅡ-up equipment.
The pinhole camera is an important device for inspecting of laser focal spot and target pointing in inertial confinement fusion experiments. In this paper, the X-ray pinhole camera has been developed for ShengguangⅡ-up equipment. This study focuses on parameter and configuration optimization. And the devices have been designed, manufactured, assembled and tested. The results of test experiments show that the energy range is 1.0-5.5 keV, the spatial resolution is better than 20 m, and the magnification ratio is 5.13-9.99. That proves that the pinhole camera can be applied on ShengguangⅡ-up equipment.
2013,
25: 2317-2323.
doi: 10.3788/HPLPB20132509.2317
Abstract:
Boron carbide films were fabricated by radio frequency magnetron sputtering at different sputtering powers. The structure and components of the boron carbide films were characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Using MTS Nano Indenter XP with CSM method, the hardness and modulus of the boron carbide films were analyzed. The results show that B prefers to combining with C to form BC bond as the RF power increases. When the sputtering power reaches 250 W, the number of BC bonds is the most, and the atomic concentration ratio between B and C reaches to the maximum of 5.66. Both the hardness and modulus of the boron carbide films increase firstly and then decrease with the sputtering powers increasing. Both of them reach to the maximum of 28.22 GPa and 314.62 GPa, respectively.
Boron carbide films were fabricated by radio frequency magnetron sputtering at different sputtering powers. The structure and components of the boron carbide films were characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Using MTS Nano Indenter XP with CSM method, the hardness and modulus of the boron carbide films were analyzed. The results show that B prefers to combining with C to form BC bond as the RF power increases. When the sputtering power reaches 250 W, the number of BC bonds is the most, and the atomic concentration ratio between B and C reaches to the maximum of 5.66. Both the hardness and modulus of the boron carbide films increase firstly and then decrease with the sputtering powers increasing. Both of them reach to the maximum of 28.22 GPa and 314.62 GPa, respectively.
2013,
25: 2324-2328.
doi: 10.3788/HPLPB20132509.2324
Abstract:
An optically tunable split-ring resonator (SRR) has been designed on silicon substrate. In the terahertz regime, the samples tunable dual-resonant properties have been obtained through modulation of the conductivity of silicon substrate. We put gallium arsenide (GaAs) into the gap of SRR, and find that the resonant structure of SRR can be changed by adjusting the conductivity of GaAs. Along with the increase of the conductivity of GaAs, the SRR switches the resonance frequency from dual-band LC and dipolar resonance mode to single-band closed-ring mode. Without destroying the SRRs physical structure, the method of changing the conductivity of semiconductor can switch resonant mode and can be implemented in terahertz devices to achieve additional functionalities.
An optically tunable split-ring resonator (SRR) has been designed on silicon substrate. In the terahertz regime, the samples tunable dual-resonant properties have been obtained through modulation of the conductivity of silicon substrate. We put gallium arsenide (GaAs) into the gap of SRR, and find that the resonant structure of SRR can be changed by adjusting the conductivity of GaAs. Along with the increase of the conductivity of GaAs, the SRR switches the resonance frequency from dual-band LC and dipolar resonance mode to single-band closed-ring mode. Without destroying the SRRs physical structure, the method of changing the conductivity of semiconductor can switch resonant mode and can be implemented in terahertz devices to achieve additional functionalities.
2013,
25: 2329-2333.
doi: 10.3788/HPLPB20132509.2329
Abstract:
For a high power microwave source composed of ceramic vacuum interface, velvet cathode and stainless steel shell, which is sealed with knife-edge oxygen free copper gasket seals, the outgassing rates of the major materials and pumping down curves are simulated by the vacuum design software VacTran. The adsorption behavior of non-evaporable getter (NEG) is simulated by using a simple model in the high vacuum maintenance process. Pumping down times to 10-4 Pa in normal temperature and baked state are compared in experiments. NEG is adopted as inspiration pump when the vacuum reaches to the work pressure. The experimental results show that the pressure is still kept at 210-4 Pa after 30-day high vacuum maintenance. The accelerated life test of the high power microwave tube is done under the temperature of 80 ℃ for more than 140 hours, the pressure in the high power microwave tube is still lower than 110-2 Pa. Accordingly, the vacuum holding life lower than 110-2 Pa at room temperature is estimated more than one year.
For a high power microwave source composed of ceramic vacuum interface, velvet cathode and stainless steel shell, which is sealed with knife-edge oxygen free copper gasket seals, the outgassing rates of the major materials and pumping down curves are simulated by the vacuum design software VacTran. The adsorption behavior of non-evaporable getter (NEG) is simulated by using a simple model in the high vacuum maintenance process. Pumping down times to 10-4 Pa in normal temperature and baked state are compared in experiments. NEG is adopted as inspiration pump when the vacuum reaches to the work pressure. The experimental results show that the pressure is still kept at 210-4 Pa after 30-day high vacuum maintenance. The accelerated life test of the high power microwave tube is done under the temperature of 80 ℃ for more than 140 hours, the pressure in the high power microwave tube is still lower than 110-2 Pa. Accordingly, the vacuum holding life lower than 110-2 Pa at room temperature is estimated more than one year.
2013,
25: 2334-2340.
doi: 10.3788/HPLPB20132509.2334
Abstract:
A parallelized finite-difference time-domain(FDTD) method for simulating the bounded wave electromagnetic pulse (EMP) simulator with lumped terminator and parallel plate is presented. The effects of several model-parameters on the simulator to the fields in the working volume are simulated and analyzed. The results show that if the width of the lower PEC plate is(or is bigger than)1.5 times that of the upper plate of working volume, the projection length of front transitional section does not have a significant effect on the rise-times of electric fields at the points near the front transitional section, and the rise-times of electric fields at the points near the working volume center decrease as the projection length increases, but the decreasement of rise-time decreases. The rise-times of Ez at all points also decrease as the lower PEC plates width increases, but the decreasement of rise-time decreases. If the projection length of the front transitional section is fixed, the good results can not be obtained by increasing or decreasing the height of the simulator only, however, which has an optimal value.
A parallelized finite-difference time-domain(FDTD) method for simulating the bounded wave electromagnetic pulse (EMP) simulator with lumped terminator and parallel plate is presented. The effects of several model-parameters on the simulator to the fields in the working volume are simulated and analyzed. The results show that if the width of the lower PEC plate is(or is bigger than)1.5 times that of the upper plate of working volume, the projection length of front transitional section does not have a significant effect on the rise-times of electric fields at the points near the front transitional section, and the rise-times of electric fields at the points near the working volume center decrease as the projection length increases, but the decreasement of rise-time decreases. The rise-times of Ez at all points also decrease as the lower PEC plates width increases, but the decreasement of rise-time decreases. If the projection length of the front transitional section is fixed, the good results can not be obtained by increasing or decreasing the height of the simulator only, however, which has an optimal value.
2013,
25: 2341-2345.
doi: 10.3788/HPLPB20132509.2341
Abstract:
A scaled model is presented to simulate the opening process of semiconductor opening switches (SOSs), which can be used in Silvaco ATALAS code. The model scales all external circuit components with the same proportion and keeps physics in SOSs well. Using various equivalent SOSs with different scales of cross section to represent the original 100 SOSs in series, the simulations get the same output pulses for each diode in all cases. It is verified that the model can not only simulate the opening process of the SOS correctly, but also speed up the computation by almost one hundred times. From the evolution of carrier density distribution and electric field distribution, it can be found that the opening process starts in the n-n+ area.
A scaled model is presented to simulate the opening process of semiconductor opening switches (SOSs), which can be used in Silvaco ATALAS code. The model scales all external circuit components with the same proportion and keeps physics in SOSs well. Using various equivalent SOSs with different scales of cross section to represent the original 100 SOSs in series, the simulations get the same output pulses for each diode in all cases. It is verified that the model can not only simulate the opening process of the SOS correctly, but also speed up the computation by almost one hundred times. From the evolution of carrier density distribution and electric field distribution, it can be found that the opening process starts in the n-n+ area.
2013,
25: 2346-2350.
doi: 10.3788/HPLPB20132509.2346
Abstract:
The basic working process and special requirements for traveling wave tube filament for power supply are introduced and the characteristics of filament are also analyzed. The particularity and difficulty of filament power supply design are thoroughly analyzed. Based on the Topswitch series control chip performance and characteristics, the main circuit of the flyback converter of the filament power supply is designed. According to the start-up characteristics of the filament and the basic requirements of stability, a high precision feedback circuit and a current limiting circuit are designed. The feasibility of the hardware implementation is verified through experimental works with a prototype. The simulation experiment, laboratory and harsh environment test results show that the main circuit, feedback circuit and current limiting circuit can well meet the traveling wave tube filament requirements.
The basic working process and special requirements for traveling wave tube filament for power supply are introduced and the characteristics of filament are also analyzed. The particularity and difficulty of filament power supply design are thoroughly analyzed. Based on the Topswitch series control chip performance and characteristics, the main circuit of the flyback converter of the filament power supply is designed. According to the start-up characteristics of the filament and the basic requirements of stability, a high precision feedback circuit and a current limiting circuit are designed. The feasibility of the hardware implementation is verified through experimental works with a prototype. The simulation experiment, laboratory and harsh environment test results show that the main circuit, feedback circuit and current limiting circuit can well meet the traveling wave tube filament requirements.
2013,
25: 2351-2354.
doi: 10.3788/HPLPB20132509.2351
Abstract:
The interval censored data(ICD) are often acquired by HPM effect experiment. These data must be processed to reasonably analyze microwave effect. Based on interpolation concept, two processing methods are established by using interval censored data information and the failure mechanism and experimental phenomenon of HPM effect. By theory analysis, the second order method is better than the first order method in interval. Based on given ICD, the processed data of those methods are not significantly different in statistics, and can be applied to studying the HPM effect.
The interval censored data(ICD) are often acquired by HPM effect experiment. These data must be processed to reasonably analyze microwave effect. Based on interpolation concept, two processing methods are established by using interval censored data information and the failure mechanism and experimental phenomenon of HPM effect. By theory analysis, the second order method is better than the first order method in interval. Based on given ICD, the processed data of those methods are not significantly different in statistics, and can be applied to studying the HPM effect.
2013,
25: 2355-2362.
doi: 10.3788/HPLPB20132509.2355
Abstract:
In order to study the influences of the incident electromagnetic wave and seam parameter on the rectangular cavity of shielding effectiveness (SE), SE analysis of cavity based on the transmission law combined with equivalent transmission line method was performed. The transmission into cavity of electric field was derived in detail, we took the transmission electric field as equivalent voltage source and revised the traditional transmission line model, and the calculation formula of this method was extended, it could analyze different shapes, hole array, hole spacing and loss, etc. Research shows that hole located in the center of the body wall of SE was worse than that near the body wall edge area. Compared with incident angle and azimuth angle, polarization angle has greater impact on the cavity SE. When keeping hole array area unchanged, decreasing aperture diameter, which increases the number of holes and hole spacing, can improve the cavity SE. Greater loss factor of cavity can induce better resonant frequency suppression effect. By analysis of cavity resonance frequency with theoretical and numerical methods, the result obtained by modification and expansion of the analysis method is credible.
In order to study the influences of the incident electromagnetic wave and seam parameter on the rectangular cavity of shielding effectiveness (SE), SE analysis of cavity based on the transmission law combined with equivalent transmission line method was performed. The transmission into cavity of electric field was derived in detail, we took the transmission electric field as equivalent voltage source and revised the traditional transmission line model, and the calculation formula of this method was extended, it could analyze different shapes, hole array, hole spacing and loss, etc. Research shows that hole located in the center of the body wall of SE was worse than that near the body wall edge area. Compared with incident angle and azimuth angle, polarization angle has greater impact on the cavity SE. When keeping hole array area unchanged, decreasing aperture diameter, which increases the number of holes and hole spacing, can improve the cavity SE. Greater loss factor of cavity can induce better resonant frequency suppression effect. By analysis of cavity resonance frequency with theoretical and numerical methods, the result obtained by modification and expansion of the analysis method is credible.
2013,
25: 2363-2367.
doi: 10.3788/HPLPB20132509.2363
Abstract:
The switched /4 coaxial oscillator is used to generate high power mesoband electromagnetic pulse, the frequency response character of a coupled-output mesoband oscillator was analyzed using impulse response method. Firstly we derived the response function of the oscillator analytically, the percent bandwidth of the output pulse against the couple coefficient of the coupler was obtained as well. A coupler with nearly constant couple coefficient of 0.6 at 200-500 MHz was optimized by Taguchi method, then simulation of the oscillator working processing was performed using axial symmetric 2-D FDTD method, and the simulated frequency spectrum and bandwidth matched well with the theoretical results.
The switched /4 coaxial oscillator is used to generate high power mesoband electromagnetic pulse, the frequency response character of a coupled-output mesoband oscillator was analyzed using impulse response method. Firstly we derived the response function of the oscillator analytically, the percent bandwidth of the output pulse against the couple coefficient of the coupler was obtained as well. A coupler with nearly constant couple coefficient of 0.6 at 200-500 MHz was optimized by Taguchi method, then simulation of the oscillator working processing was performed using axial symmetric 2-D FDTD method, and the simulated frequency spectrum and bandwidth matched well with the theoretical results.
2013,
25: 2368-2372.
doi: 10.3788/HPLPB20132509.2368
Abstract:
The radiation mechanism of a TEM horn antenna both in time and frequency domain is researched. The TEM horn fed by the high-frequency signal behaves as an aperture antenna with favorable directional radiation capability and the TEM horn fed by the low-frequency signal behaves as a dipole antenna with omnidirectional radiation field. In time domain, the radiation field of TEM-horn antenna fed by a short impulse consists of four sub-waves. The waveform and comparative time sequence of every sub-wave is different in every direction, and that leads to dissimilar radiation waveform to every direction of antenna. Based on the research result, we propose an end-loading optimizing method for TEM-horn-antenna design. In this way, the radiation performance on boresight and the efficiency of the TEM horn are observably improved.
The radiation mechanism of a TEM horn antenna both in time and frequency domain is researched. The TEM horn fed by the high-frequency signal behaves as an aperture antenna with favorable directional radiation capability and the TEM horn fed by the low-frequency signal behaves as a dipole antenna with omnidirectional radiation field. In time domain, the radiation field of TEM-horn antenna fed by a short impulse consists of four sub-waves. The waveform and comparative time sequence of every sub-wave is different in every direction, and that leads to dissimilar radiation waveform to every direction of antenna. Based on the research result, we propose an end-loading optimizing method for TEM-horn-antenna design. In this way, the radiation performance on boresight and the efficiency of the TEM horn are observably improved.
2013,
25: 2373-2377.
doi: 10.3788/HPLPB20132509.2373
Abstract:
The attenuation characteristics of electromagnetic wave penetrating brick wall with multilayer periodic structure are analyzed by the modal transmission-line method. The relation curves among the transmission and reflection coefficients, the incidence angle and frequency in electromagnetic wave penetrating the brick wall are obtained by calculation. The numerical calculation result is consistent with the simulation result. The attenuation of electromagnetic wave penetrating brick wall versus frequency (2-8 GHz) is measured by the electromagnetic wave measuring system. In comprehensive consideration of both the numerical calculation result and experimental measurement result, the attenuation of electromagnetic wave penetrating brick wall is about 15-25 dB when the frequency is between 2 and 8 GHz.
The attenuation characteristics of electromagnetic wave penetrating brick wall with multilayer periodic structure are analyzed by the modal transmission-line method. The relation curves among the transmission and reflection coefficients, the incidence angle and frequency in electromagnetic wave penetrating the brick wall are obtained by calculation. The numerical calculation result is consistent with the simulation result. The attenuation of electromagnetic wave penetrating brick wall versus frequency (2-8 GHz) is measured by the electromagnetic wave measuring system. In comprehensive consideration of both the numerical calculation result and experimental measurement result, the attenuation of electromagnetic wave penetrating brick wall is about 15-25 dB when the frequency is between 2 and 8 GHz.
2013,
25: 2378-2384.
doi: 10.3788/HPLPB20132509.2378
Abstract:
A series of experiments were carried out to research the X-ray radiation characteristics of tungsten wire arrays on Yang accelerator. In those experiments, we charged the Marx generator of 60 kV, and the load current of 0.85-1.00 MA, the rise time of 75-90 ns (10%-90%). A soft X-ray scintillator powermeter which responsed flatly to 50-1800 eV X-rays was used to measure the power of soft X-ray emitted from implosion plasma. In this paper, we present the measuring results of time-resolved soft X-ray radiation power, and discuss the radiation characteristics of implosion plasma by analyzing the correlations of soft X-ray radiant power and the diameter, length, wire number of the tungsten wire arrays. The optimizing wire array configuration parameters on Yang are as follows: 8 mm array diameter, 15 mm wire length, and 24 wire number. We also present the radiant power difference in radial and axial directions of the wire arrays.
A series of experiments were carried out to research the X-ray radiation characteristics of tungsten wire arrays on Yang accelerator. In those experiments, we charged the Marx generator of 60 kV, and the load current of 0.85-1.00 MA, the rise time of 75-90 ns (10%-90%). A soft X-ray scintillator powermeter which responsed flatly to 50-1800 eV X-rays was used to measure the power of soft X-ray emitted from implosion plasma. In this paper, we present the measuring results of time-resolved soft X-ray radiation power, and discuss the radiation characteristics of implosion plasma by analyzing the correlations of soft X-ray radiant power and the diameter, length, wire number of the tungsten wire arrays. The optimizing wire array configuration parameters on Yang are as follows: 8 mm array diameter, 15 mm wire length, and 24 wire number. We also present the radiant power difference in radial and axial directions of the wire arrays.
2013,
25: 2385-2388.
doi: 10.3788/HPLPB20132509.2385
Abstract:
A time-resolved crystal spectrometer has been fabricated for the study of X-ray radiations from Z-pinch plasma on Yang accelerator. In the spectrometer, an elliptical crystal is used as light splitting element, a ten-channel PIN array is employed to record time-resolved spectral images, and at the same time imaging plate(IP) is used to record time-integral results. The spectrometer has been used in Z-pinch experiments performed on Yang accelerator. The spectra of K-shell lines are observed, when using Al wire arrays as Z-pinch loads. Computer program ZSPEC based on the collisional-radiative model has been used to analyze the experimental data. According to the line ratios of H/He and I.C./He, the averaged space and time electron density, and time-resolved electron temperature are obtained.
A time-resolved crystal spectrometer has been fabricated for the study of X-ray radiations from Z-pinch plasma on Yang accelerator. In the spectrometer, an elliptical crystal is used as light splitting element, a ten-channel PIN array is employed to record time-resolved spectral images, and at the same time imaging plate(IP) is used to record time-integral results. The spectrometer has been used in Z-pinch experiments performed on Yang accelerator. The spectra of K-shell lines are observed, when using Al wire arrays as Z-pinch loads. Computer program ZSPEC based on the collisional-radiative model has been used to analyze the experimental data. According to the line ratios of H/He and I.C./He, the averaged space and time electron density, and time-resolved electron temperature are obtained.
2013,
25: 2389-2392.
doi: 10.3788/HPLPB20132509.2389
Abstract:
A compensating method for the coaxial line drift due to the temperature change using an additional measuring coaxial line is proposed for the low-level radio frequency(RF) control system of Heavy Ion Research Facility in Lanzhou (HIRFL). We measured the temperature effects on the RF phase and RF loss at the SYV50-2-41 cable with and without using the additional measuring coaxial line, respectively. The measured results show that, the long-term phase instability with compensation can be reduced to 1/50 of the one without compensation; the long-term amplitude drift can be reduced to 1/10 at least.
A compensating method for the coaxial line drift due to the temperature change using an additional measuring coaxial line is proposed for the low-level radio frequency(RF) control system of Heavy Ion Research Facility in Lanzhou (HIRFL). We measured the temperature effects on the RF phase and RF loss at the SYV50-2-41 cable with and without using the additional measuring coaxial line, respectively. The measured results show that, the long-term phase instability with compensation can be reduced to 1/50 of the one without compensation; the long-term amplitude drift can be reduced to 1/10 at least.
2013,
25: 2393-2396.
doi: 10.3788/HPLPB20132509.2393
Abstract:
The design of an X-ray converter for the BF-5 electron linear accelerator is described. First, the thickness of the converter is optimized by Monte Carlo simulations and the water-cooling structure of the converter is designed. Then, the water cooling process is simulated by finite element analysis and the temperature distribution of the converter is computed. Finally, the dose distribution of the converter as well as the energy spectrum of the generated X-ray is calculated. The results show that the maximal temperature of the converter is below 40 ℃, thus the converter could operate consistently and stably. The mean energy of the generated X-ray is 0.65 MeV, and the absorbed dose of the X-ray for the point 1 meter ahead from the center of the converter could reach 6 Gy/min.
The design of an X-ray converter for the BF-5 electron linear accelerator is described. First, the thickness of the converter is optimized by Monte Carlo simulations and the water-cooling structure of the converter is designed. Then, the water cooling process is simulated by finite element analysis and the temperature distribution of the converter is computed. Finally, the dose distribution of the converter as well as the energy spectrum of the generated X-ray is calculated. The results show that the maximal temperature of the converter is below 40 ℃, thus the converter could operate consistently and stably. The mean energy of the generated X-ray is 0.65 MeV, and the absorbed dose of the X-ray for the point 1 meter ahead from the center of the converter could reach 6 Gy/min.
2013,
25: 2397-2402.
doi: 10.3788/HPLPB20132509.2397
Abstract:
A 325 MHz low beta half wave resonator (HWR) for proton accelerator was designed. The study on the principle of designing a superconducting cavity was described. The modeling on a new HWR was performed on different parts, then the electromagnetic analysis of the HWR was implemented. In the process of cavity design, parametric modeling was used to construct the cavity shape, then curved tetrahedral mesh cells were used to fulfill the EM calculation, and parameters sweeping was used to optimize the RF parameters of HWR superconducting cavity. The HWR cavity shape was also analyzed by means of multipacting calculation using TRACK3P code. Satisfied RF parameters were achieved on the new designed 325 MHz low beta HWR cavity. The new HWR cavity will be fabricated after more analysis and it may be applied to the linac for proton accelerator in the future.
A 325 MHz low beta half wave resonator (HWR) for proton accelerator was designed. The study on the principle of designing a superconducting cavity was described. The modeling on a new HWR was performed on different parts, then the electromagnetic analysis of the HWR was implemented. In the process of cavity design, parametric modeling was used to construct the cavity shape, then curved tetrahedral mesh cells were used to fulfill the EM calculation, and parameters sweeping was used to optimize the RF parameters of HWR superconducting cavity. The HWR cavity shape was also analyzed by means of multipacting calculation using TRACK3P code. Satisfied RF parameters were achieved on the new designed 325 MHz low beta HWR cavity. The new HWR cavity will be fabricated after more analysis and it may be applied to the linac for proton accelerator in the future.
2013,
25: 2403-2407.
doi: 10.3788/HPLPB20132509.2403
Abstract:
The magnetic-axis tilt, which is the most critical indicator of the focusing solenoid, is always the focus of researchers in related research fields. In this paper, many aspects, such as optimization of field-homogenizer design, the choice of material specifications, exploration of winding technology, design of super large size dipole steering coils, and magnetic-axis measurement technique are studied using new alignment method. The technical bottleneck of tilt less than 1.0 mrad is broken through and a large size focus solenoid whose magnetic-axis tilt is less than 0.5 mrad is successfully developed.
The magnetic-axis tilt, which is the most critical indicator of the focusing solenoid, is always the focus of researchers in related research fields. In this paper, many aspects, such as optimization of field-homogenizer design, the choice of material specifications, exploration of winding technology, design of super large size dipole steering coils, and magnetic-axis measurement technique are studied using new alignment method. The technical bottleneck of tilt less than 1.0 mrad is broken through and a large size focus solenoid whose magnetic-axis tilt is less than 0.5 mrad is successfully developed.
2013,
25: 2408-2412.
doi: 10.3788/HPLPB20132509.2408
Abstract:
The electric explosive method has the advantages of simple operation and mass production to make nano metal particles. The changes of the copper wore in the electrical explosion process are analyzed, and the changes can be divided into the states of solid, liquid, gas and plasma. The relationships between the size, size distribution and composition of nano copper particle, and the explosion energy, copper wire diameter and the length of copper wire are studied. The particle size uniformity is defined, and the distribution of the nanoparticle size is analyzed based on the comparing analysis in the average diameter size and the particle size uniformity. The corresponding experimental researches are carried out, and the analysis and the test of the produced nanometer copper powder are completed by the X-ray diffraction (XRD) and transmission electron microscopy (TEM).
The electric explosive method has the advantages of simple operation and mass production to make nano metal particles. The changes of the copper wore in the electrical explosion process are analyzed, and the changes can be divided into the states of solid, liquid, gas and plasma. The relationships between the size, size distribution and composition of nano copper particle, and the explosion energy, copper wire diameter and the length of copper wire are studied. The particle size uniformity is defined, and the distribution of the nanoparticle size is analyzed based on the comparing analysis in the average diameter size and the particle size uniformity. The corresponding experimental researches are carried out, and the analysis and the test of the produced nanometer copper powder are completed by the X-ray diffraction (XRD) and transmission electron microscopy (TEM).
2013,
25: 2413-2417.
doi: 10.3788/HPLPB20132509.2413
Abstract:
A problem about the optimal extinction diameters of fine water sprays for thermal radiation shielding is researched. Considering the optics and dynamics properties of the sprays droplets, the index of thermal shielding is defined as a criterion to measure the extinction capability of dynamical droplets. The polydisperse sprays are equal to monodispersion with Sauter diameter in the model construction. The Planck meaning method is used to obtain the radiative property parameters of sprays taken as grey body. The massive sums of repeat calculating of Mie efficiency factors are avoided by adopting the method of data invoking which are calculated and saved in an array in advance and linear interpolation. According to the evaluation method defined in this paper, the optimal extinction diameters obtained based on thermal shielding index are far greater than that obtained based on the optics properties.
A problem about the optimal extinction diameters of fine water sprays for thermal radiation shielding is researched. Considering the optics and dynamics properties of the sprays droplets, the index of thermal shielding is defined as a criterion to measure the extinction capability of dynamical droplets. The polydisperse sprays are equal to monodispersion with Sauter diameter in the model construction. The Planck meaning method is used to obtain the radiative property parameters of sprays taken as grey body. The massive sums of repeat calculating of Mie efficiency factors are avoided by adopting the method of data invoking which are calculated and saved in an array in advance and linear interpolation. According to the evaluation method defined in this paper, the optimal extinction diameters obtained based on thermal shielding index are far greater than that obtained based on the optics properties.
2013,
25: 2418-2422.
doi: 10.3788/HPLPB20132509.2418
Abstract:
In order to solve the problem that the simultaneous algebraic reconstruction technique is very time-consuming, this paper proposes a multi-GPU parallel acceleration method on the basis of single-GPU-accelerated reconstruction. The experimental result shows that compared with the CPU reconstruction speed, the muti-GPU reconstruction speed improves significantly, while the precision of reconstructed images keeps the same, and the reconstruction speed can be further improved by increasing the number of GPUs. This method is of a higher value in engineering.
In order to solve the problem that the simultaneous algebraic reconstruction technique is very time-consuming, this paper proposes a multi-GPU parallel acceleration method on the basis of single-GPU-accelerated reconstruction. The experimental result shows that compared with the CPU reconstruction speed, the muti-GPU reconstruction speed improves significantly, while the precision of reconstructed images keeps the same, and the reconstruction speed can be further improved by increasing the number of GPUs. This method is of a higher value in engineering.
2013,
25: 2423-2428.
doi: 10.3788/HPLPB20132509.2423
Abstract:
According to the common engineering workpiece with dramatic axial contour changes, a high-accuracy inter slice contour rotating integral volume measuring algorithm of Zernike moment sub-pixel edge detection is presented. Firstly, a sub-pixel level contour is detected by Zernike moment method. Secondly, using the polynomial fitting method the contour is fitted, and then the fitted contour is sampled by the same angle interval. Each edge point at the same phase angle of each slice is used to fit the contour, and then the apex of work-piece is calculated through extrapolation method. Finally, each fitted contour is rotated through one phase angle interval to calculate the integral as a rotation volume, the volume of each rotation is accumulated to be the total volume of the workpiece. Volumetric measurement experiments are carried out towards three volume-equal testing workpieces. The results indicate that the measurement errors are less than 0.7% using the proposed method. An actual work-piece with internal cavity is measured. The result indicates that the measurement accuracy of the proposed method is 1.5 times than the one of the Canny-frustum method.
According to the common engineering workpiece with dramatic axial contour changes, a high-accuracy inter slice contour rotating integral volume measuring algorithm of Zernike moment sub-pixel edge detection is presented. Firstly, a sub-pixel level contour is detected by Zernike moment method. Secondly, using the polynomial fitting method the contour is fitted, and then the fitted contour is sampled by the same angle interval. Each edge point at the same phase angle of each slice is used to fit the contour, and then the apex of work-piece is calculated through extrapolation method. Finally, each fitted contour is rotated through one phase angle interval to calculate the integral as a rotation volume, the volume of each rotation is accumulated to be the total volume of the workpiece. Volumetric measurement experiments are carried out towards three volume-equal testing workpieces. The results indicate that the measurement errors are less than 0.7% using the proposed method. An actual work-piece with internal cavity is measured. The result indicates that the measurement accuracy of the proposed method is 1.5 times than the one of the Canny-frustum method.
2013,
25: 2429-2432.
doi: 10.3788/HPLPB20132509.2429
Abstract:
In research of explosive detection by neutron probe, the gamma rays was produced by 14 MeV neutron bombardment on the sample nucleus with atom numbers bigger than 5. The gamma spectra of typical elements, such as C, N, O and simulated explosive, were measured by associated particle technique (APT) and time of flight (TOF). The large NaI(Tl) detector with the dimension of 12.5 cm20 cm was used. The measured gamma spectra were compared with those of European Union (EU). The results show that both of the experiments were at the same level.
In research of explosive detection by neutron probe, the gamma rays was produced by 14 MeV neutron bombardment on the sample nucleus with atom numbers bigger than 5. The gamma spectra of typical elements, such as C, N, O and simulated explosive, were measured by associated particle technique (APT) and time of flight (TOF). The large NaI(Tl) detector with the dimension of 12.5 cm20 cm was used. The measured gamma spectra were compared with those of European Union (EU). The results show that both of the experiments were at the same level.
2013,
25: 2433-2438.
doi: 10.3788/HPLPB20132509.2433
Abstract:
This paper discusses single-event effect (SEE) on SiGe heterojunction bipolar transistors (SiGe HBTs) using laser microbeam irradiation test. Our work observes the sensitive volume in SiGe HBTs, and measures the transient current and charge collection of the collector for different voltage and different laser energy. Then, the experimental phenomena are analyzed according to the device structure. The results show that SiGe HBTs are susceptible to SEE, the 1064 nm laser of about 1.5 nJ energy causes SEE by transient current. The region within collector/substrate (C/S) junction is the sensitive volume of the domestic SiGe HBTs. As the incident laser energy enhances, the current pulse increases, and the amount of charge collection rises. The crest of the current pulse increases when the applied voltage is increased. SiGe HBT single-event effect is affected by both voltage and laser energy. Applied voltage mainly affects the peak of transient current; however, charge collection is strongly dependent on the energy of incident laser.
This paper discusses single-event effect (SEE) on SiGe heterojunction bipolar transistors (SiGe HBTs) using laser microbeam irradiation test. Our work observes the sensitive volume in SiGe HBTs, and measures the transient current and charge collection of the collector for different voltage and different laser energy. Then, the experimental phenomena are analyzed according to the device structure. The results show that SiGe HBTs are susceptible to SEE, the 1064 nm laser of about 1.5 nJ energy causes SEE by transient current. The region within collector/substrate (C/S) junction is the sensitive volume of the domestic SiGe HBTs. As the incident laser energy enhances, the current pulse increases, and the amount of charge collection rises. The crest of the current pulse increases when the applied voltage is increased. SiGe HBT single-event effect is affected by both voltage and laser energy. Applied voltage mainly affects the peak of transient current; however, charge collection is strongly dependent on the energy of incident laser.
2013,
25: 2439-2442.
doi: 10.3788/HPLPB20132509.2439
Abstract:
Silicon macropore arrays were prepared by electrochemical etching in the solution of HF+IPA (isopropanol) and HF+IPA+CATC (cetyltrimethylammonium chloride). The effects of HF concentration, CTAC, etching current, etching time on the array morphologies were discussed. The optimized macropore array was obtained when the volume ratio of 40%HF, H2O,IPA is 7∶4∶29. The pore wall is decreased with increasing the etching current and the initial etching expands in the direction of pore diameter until the pore diameter of about 10 m. Regular arrays are not formed on the silicon with etching windows of 8 m and spacing of 5 m. Small pores are formed on macropore walls when CTAC is added in the solution. The small pores become smaller and the number of them is increased with increasing CTAC.
Silicon macropore arrays were prepared by electrochemical etching in the solution of HF+IPA (isopropanol) and HF+IPA+CATC (cetyltrimethylammonium chloride). The effects of HF concentration, CTAC, etching current, etching time on the array morphologies were discussed. The optimized macropore array was obtained when the volume ratio of 40%HF, H2O,IPA is 7∶4∶29. The pore wall is decreased with increasing the etching current and the initial etching expands in the direction of pore diameter until the pore diameter of about 10 m. Regular arrays are not formed on the silicon with etching windows of 8 m and spacing of 5 m. Small pores are formed on macropore walls when CTAC is added in the solution. The small pores become smaller and the number of them is increased with increasing CTAC.
2013,
25: 2443-2447.
doi: 10.3788/HPLPB20132509.2443
Abstract:
In multi-pulse X ray photography, plasma created by earlier pulses will affect the up-coming later ones, and cause concerns on the stability of the beams. Based on the basic theory of plasma, we simulate the beam-plasma interaction and address the instability problems in different plasma density scenarios. In external magnetic field free situation, simulation shows the beam (20 MeV, 2.5 kA, 1.3 mm) exhibits different instability properties as the density of the plasma changes. For the density ratio of beam-plasma being less than 1, sausage instability appears, but the beam is generally undisturbed and the hotspot is good. For the density ratio of beam-plasma being between 10 and 100, the pinch effect of the plasma improves the focusing. Filamentation instabilities become prominent as the density ratio of beam-plasma is greater than 1000, the beam emittance grows rapidly, and the target hotspot is dispersed.
In multi-pulse X ray photography, plasma created by earlier pulses will affect the up-coming later ones, and cause concerns on the stability of the beams. Based on the basic theory of plasma, we simulate the beam-plasma interaction and address the instability problems in different plasma density scenarios. In external magnetic field free situation, simulation shows the beam (20 MeV, 2.5 kA, 1.3 mm) exhibits different instability properties as the density of the plasma changes. For the density ratio of beam-plasma being less than 1, sausage instability appears, but the beam is generally undisturbed and the hotspot is good. For the density ratio of beam-plasma being between 10 and 100, the pinch effect of the plasma improves the focusing. Filamentation instabilities become prominent as the density ratio of beam-plasma is greater than 1000, the beam emittance grows rapidly, and the target hotspot is dispersed.
2013,
25: 2448-2452.
doi: 10.3788/HPLPB20132509.2448
Abstract:
The principle of charging low impedance forming line with ultra-wide-spectrum pulser based on Blumlein line to compress pulse is analysed in this paper. The voltage of the output pulse, the gain of the power and the energy efficiency have been figured out. A circuit model has been created with analyzing software, the simulation has verified the analysis. An experiment upon CKP-1000 has been made with complete pulse compression system. The results show that when the input pulse width is 4.5 ns, the output pulse can be compressed to be 1 ns in half-width and the front edge is only 940 ps. The power gain is up to 2.2.
The principle of charging low impedance forming line with ultra-wide-spectrum pulser based on Blumlein line to compress pulse is analysed in this paper. The voltage of the output pulse, the gain of the power and the energy efficiency have been figured out. A circuit model has been created with analyzing software, the simulation has verified the analysis. An experiment upon CKP-1000 has been made with complete pulse compression system. The results show that when the input pulse width is 4.5 ns, the output pulse can be compressed to be 1 ns in half-width and the front edge is only 940 ps. The power gain is up to 2.2.
2013,
25: 2453-2456.
doi: 10.3788/HPLPB20132509.2453
Abstract:
A single pulse breakdown experiment was performed on polymethylmethacrylate(PMMA) using a uniform field geometry, and the breakdown strength and breakdown time delay were obtained. The applied pulse amplitude was about 230 kV, rise time 760-960 ps, pulse width 2.3-4.0 ns(FWHM), and the specimen mean thickness was 1.1 mm. The experimental result shows that as the pulse width increases from 2.3 ns to 4.0 ns，the average breakdown strength of PMMA reduces from 301 kV/mm to 276 kV/mm, the average breakdown time delay approximately has a fixed value, but the standard deviation rises under the pulse with rise time 760 ps, pulse width 2.3 ns. Finally, based on the breakdown phenomena observed by stereomicroscope, the breakdown process was analyzed.
A single pulse breakdown experiment was performed on polymethylmethacrylate(PMMA) using a uniform field geometry, and the breakdown strength and breakdown time delay were obtained. The applied pulse amplitude was about 230 kV, rise time 760-960 ps, pulse width 2.3-4.0 ns(FWHM), and the specimen mean thickness was 1.1 mm. The experimental result shows that as the pulse width increases from 2.3 ns to 4.0 ns，the average breakdown strength of PMMA reduces from 301 kV/mm to 276 kV/mm, the average breakdown time delay approximately has a fixed value, but the standard deviation rises under the pulse with rise time 760 ps, pulse width 2.3 ns. Finally, based on the breakdown phenomena observed by stereomicroscope, the breakdown process was analyzed.
2013,
25: 2457-2460.
doi: 10.3788/HPLPB20132509.2457
Abstract:
Some groups of parameters for simulation device of flux compression generator(FCG) were optimized by Pspice. The comparability of the current output property curve of the simulation device and FCG with different groups of parameters were respectively analyzed with the gray relation grade analysis method. An appropriate group of parameters was confirmed at last. The simulated result proved the feasibility of the project for simulation device of FCG.
Some groups of parameters for simulation device of flux compression generator(FCG) were optimized by Pspice. The comparability of the current output property curve of the simulation device and FCG with different groups of parameters were respectively analyzed with the gray relation grade analysis method. An appropriate group of parameters was confirmed at last. The simulated result proved the feasibility of the project for simulation device of FCG.
2013,
25: 2461-2465.
doi: 10.3788/HPLPB20132509.2461
Abstract:
The influence of the pulse forming network (PFN) with L-structure on the output waveform has been studied. The three-dimensional model of the pulsed forming network with L-structure has been established and simulated via finite integration software. The simulation results of the PFNs with two different structures have been compared. The pulse rise time of the PFN with the L-structure is about 40 ns, basically consistent with linear structure; the pulse half-high width is 168 ns, which is 7 ns smaller than that of the PFN with the linear structure; the flat-top of the output waveform fluctuates in comparison with the linear structure, which features the flat-top rise at the back part of the waveform. The simulation results have been verified by the high voltage experiment of the PFNs with the two different structures. For the compact engineering applications of the pulse driver source system, the output waveform of the PFN with L-structure could meet the requirements substantially.
The influence of the pulse forming network (PFN) with L-structure on the output waveform has been studied. The three-dimensional model of the pulsed forming network with L-structure has been established and simulated via finite integration software. The simulation results of the PFNs with two different structures have been compared. The pulse rise time of the PFN with the L-structure is about 40 ns, basically consistent with linear structure; the pulse half-high width is 168 ns, which is 7 ns smaller than that of the PFN with the linear structure; the flat-top of the output waveform fluctuates in comparison with the linear structure, which features the flat-top rise at the back part of the waveform. The simulation results have been verified by the high voltage experiment of the PFNs with the two different structures. For the compact engineering applications of the pulse driver source system, the output waveform of the PFN with L-structure could meet the requirements substantially.
2013,
25: 2466-2470.
doi: 10.3788/HPLPB20132509.2466
Abstract:
The switch used in FLTD primary energy-storing system is chosen as the study object. A self-breakdown experiment of the switches with different gap length has been done at the same breakdown voltage by changing the gap pressure. The influence of the gap length on the switch performance has been researched by observing the change of the breakdown voltage distribution. The experiment result shows that, the self-breakdown voltage dispersion at 6 mm gap is the least. Breakdown voltage distribution with the gap length equal to or less than 6 mm is similar to Gauss distribution function and it is similar to extreme distribution function with the gap length larger than 6 mm. The switch with a long gap whose breakdown voltage distribution loses the symmetry has better static performance at low working ratio. According to the electrode structure used in this paper, the gap length should be chosen between 6 mm and 9 mm to get the best static performance. The reason for the change of breakdown voltage distribution is the alteration of the electric field influencing the electron emission on cathode.
The switch used in FLTD primary energy-storing system is chosen as the study object. A self-breakdown experiment of the switches with different gap length has been done at the same breakdown voltage by changing the gap pressure. The influence of the gap length on the switch performance has been researched by observing the change of the breakdown voltage distribution. The experiment result shows that, the self-breakdown voltage dispersion at 6 mm gap is the least. Breakdown voltage distribution with the gap length equal to or less than 6 mm is similar to Gauss distribution function and it is similar to extreme distribution function with the gap length larger than 6 mm. The switch with a long gap whose breakdown voltage distribution loses the symmetry has better static performance at low working ratio. According to the electrode structure used in this paper, the gap length should be chosen between 6 mm and 9 mm to get the best static performance. The reason for the change of breakdown voltage distribution is the alteration of the electric field influencing the electron emission on cathode.
2013,
25: 2471-2476.
doi: 10.3788/HPLPB20132509.2471
Abstract:
Compact vertical geometry photoconductive semiconductor switches (PCSS) made from SiC are promising candidates for high power switching. Silvaco TCAD is used to simulate the time-resolved electric field current distribution and volt-ampere characteristics of different light power in vertical geometry V-doped semi-insulated 6H-SiC photoconductive switches excited by 532 nm laser. The simulation shows that the carriers drift velocity with increasing field saturates at a constant velocity, and the time-resolved electric field current is uniformly distributed along the major electric field current direction that is perpendicular to laser incidence direction. With the simplification of semiconductor equations based on the Silvaco TCAD simulations, a SiC-PCSS circuit model has been developed in consideration of carrier field dependent mobility. With the help of the validation in reported experiment, the influence of exterior electric parameters is discussed by using the SiC-PCSS circuit model.
Compact vertical geometry photoconductive semiconductor switches (PCSS) made from SiC are promising candidates for high power switching. Silvaco TCAD is used to simulate the time-resolved electric field current distribution and volt-ampere characteristics of different light power in vertical geometry V-doped semi-insulated 6H-SiC photoconductive switches excited by 532 nm laser. The simulation shows that the carriers drift velocity with increasing field saturates at a constant velocity, and the time-resolved electric field current is uniformly distributed along the major electric field current direction that is perpendicular to laser incidence direction. With the simplification of semiconductor equations based on the Silvaco TCAD simulations, a SiC-PCSS circuit model has been developed in consideration of carrier field dependent mobility. With the help of the validation in reported experiment, the influence of exterior electric parameters is discussed by using the SiC-PCSS circuit model.
