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RSS2013 Vol. 25, No. 07
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2013,
25: 1609-1610.
doi: 10.3788/HPLPB20132507.1609
Abstract:
As one element of final assembly in high-power laser systems, beam sampling grating (BSG) is a fused silica grating with shallow depths. In order to improve the uniformity of diffraction efficiency of a BSG, a classical chemical mechanical polishing technique of fused silica, with CeO2 as the polishing material, is proposed for BSG to modify its profile and efficiency. With this method, the efficiency root mean square of a BSG with an aperture of 430 mm430 mm can be reduced from nearly 30% to less than 5%, which shows that the CeO2 polishing is a feasible and effective method to improve the efficiency uniformity of BSG.
As one element of final assembly in high-power laser systems, beam sampling grating (BSG) is a fused silica grating with shallow depths. In order to improve the uniformity of diffraction efficiency of a BSG, a classical chemical mechanical polishing technique of fused silica, with CeO2 as the polishing material, is proposed for BSG to modify its profile and efficiency. With this method, the efficiency root mean square of a BSG with an aperture of 430 mm430 mm can be reduced from nearly 30% to less than 5%, which shows that the CeO2 polishing is a feasible and effective method to improve the efficiency uniformity of BSG.
2013,
25: 1611-1612.
doi: 10.3788/HPLPB20132507.1611
Abstract:
A stable high energy all-fiber based pulsed thulium-doped fiber laser at 2 m is obtained based on gain-switched techniques. The pulse repetition rate can be tuned between 10 kHz and 50 kHz, and the central wavelength of the laser is 1958 nm. With the rise of injected pump power, the output pulse width decreases and is in a range of 1.2-1.7 s. By using two-stage thulium-doped fiber amplifiers the average output power is scaled up to 5.18 W at 10 kHz, the output pulse width is 1.6 s, and the corresponding single pulse energy after amplification is 0.518 mJ.
A stable high energy all-fiber based pulsed thulium-doped fiber laser at 2 m is obtained based on gain-switched techniques. The pulse repetition rate can be tuned between 10 kHz and 50 kHz, and the central wavelength of the laser is 1958 nm. With the rise of injected pump power, the output pulse width decreases and is in a range of 1.2-1.7 s. By using two-stage thulium-doped fiber amplifiers the average output power is scaled up to 5.18 W at 10 kHz, the output pulse width is 1.6 s, and the corresponding single pulse energy after amplification is 0.518 mJ.
2013,
25: 1613-1614.
doi: 10.3788/HPLPB20132507.1613
Abstract:
A slow-wave structure (SWS) named micro-strip angular log-periodic meander-line is proposed for a low operating voltage vacuum amplifier. It evolves from the logarithmic spiral by cutting off a fan-shaped part and connecting the ends alternately. This letter reports the electromagnetic characteristics of this kind of SWS, and the beam-wave interaction is calculated by means of the particle-in-cell (PIC) method. From our calculation, this kind of traveling-wave tube can give 26 W output power with the 3 dB frequency range of 27-46 GHz, while the operating voltage is 809 V only. Moreover, the maximum gain and interaction efficiency are about 26.5 dB and 21.7%, respectively. Through power combination of SWSs of this kind, power of hundreds of watts can be output.
A slow-wave structure (SWS) named micro-strip angular log-periodic meander-line is proposed for a low operating voltage vacuum amplifier. It evolves from the logarithmic spiral by cutting off a fan-shaped part and connecting the ends alternately. This letter reports the electromagnetic characteristics of this kind of SWS, and the beam-wave interaction is calculated by means of the particle-in-cell (PIC) method. From our calculation, this kind of traveling-wave tube can give 26 W output power with the 3 dB frequency range of 27-46 GHz, while the operating voltage is 809 V only. Moreover, the maximum gain and interaction efficiency are about 26.5 dB and 21.7%, respectively. Through power combination of SWSs of this kind, power of hundreds of watts can be output.
2013,
25: 1615-1619.
doi: 10.3788/HPLPB20132507.1615
Abstract:
Measuring the temporal-spatial distribution of far-field laser beam profile is an effective way to analyze the atmospheric transmission effects of high power laser and evaluate the characteristics of laser system. Several methods for measuring the laser far-field beam profile and their respective features are summarized, and the measuring technology based on array detector is mainly described. Finally, two laser beam profile measuring systems with photo-electric detector array are developed, which are respectively applied to measuring the far-field beam profile of high energy laser and repetitively pulsed laser. These measuring systems are compact and very suitable for moving test targets.
Measuring the temporal-spatial distribution of far-field laser beam profile is an effective way to analyze the atmospheric transmission effects of high power laser and evaluate the characteristics of laser system. Several methods for measuring the laser far-field beam profile and their respective features are summarized, and the measuring technology based on array detector is mainly described. Finally, two laser beam profile measuring systems with photo-electric detector array are developed, which are respectively applied to measuring the far-field beam profile of high energy laser and repetitively pulsed laser. These measuring systems are compact and very suitable for moving test targets.
2013,
25: 1620-1624.
doi: 10.3788/HPLPB20132507.1620
Abstract:
The basic principle and basic steps of reverse engineering technology based on industrial CT are described. The recent research progresses and situation at home and abroad of reverse engineering technology based on industrial CT image are respectively described, analyzed and summarized from two routes which are surface segmentation and volume segmentation. An example of conch is used to exhibit the results from the two routes in reverse engineering technology based on industrial CT image. Finally, some difficulties in application and the future developments of reverse engineering technology based on industrial CT are prospected.
The basic principle and basic steps of reverse engineering technology based on industrial CT are described. The recent research progresses and situation at home and abroad of reverse engineering technology based on industrial CT image are respectively described, analyzed and summarized from two routes which are surface segmentation and volume segmentation. An example of conch is used to exhibit the results from the two routes in reverse engineering technology based on industrial CT image. Finally, some difficulties in application and the future developments of reverse engineering technology based on industrial CT are prospected.
2013,
25: 1625-1629.
doi: 10.3788/HPLPB20132507.1625
Abstract:
The existence of pores is one of the most important factors affecting the performance of transparent laser ceramics. In order to analyze the influence of pore size and porosity on laser performance of transparent ceramics, zeroth-order lognormal distributions (ZOLDs) have been used to describe the pore size distributions, and Mie scattering theories combined with related solid-state laser theories have been used to illustrate the effect of pore scattering on transmittance, laser slope efficiency and laser threshold of transparent ceramics. The results show that transmittance and laser slope efficiency are significantly influenced by porosity, i.e., larger porosity leads to lower transmittance and slope efficiency at given pore size distribution; transmittance and slope efficiency decrease with increasing central pore size, and slope efficiency drops sharply when pore radii are between 0.1 and 0.3 m. Moreover, the larger the pore sizes are, the sharper the laser threshold rises. In practical applications, improving fabrication technology to control pore size is of great importance to improve the laser performance of transparent ceramics.
The existence of pores is one of the most important factors affecting the performance of transparent laser ceramics. In order to analyze the influence of pore size and porosity on laser performance of transparent ceramics, zeroth-order lognormal distributions (ZOLDs) have been used to describe the pore size distributions, and Mie scattering theories combined with related solid-state laser theories have been used to illustrate the effect of pore scattering on transmittance, laser slope efficiency and laser threshold of transparent ceramics. The results show that transmittance and laser slope efficiency are significantly influenced by porosity, i.e., larger porosity leads to lower transmittance and slope efficiency at given pore size distribution; transmittance and slope efficiency decrease with increasing central pore size, and slope efficiency drops sharply when pore radii are between 0.1 and 0.3 m. Moreover, the larger the pore sizes are, the sharper the laser threshold rises. In practical applications, improving fabrication technology to control pore size is of great importance to improve the laser performance of transparent ceramics.
2013,
25: 1630-1634.
doi: 10.3788/HPLPB20132507.1630
Abstract:
An ultrafast electron diffraction system with both ultrafast temporal resolution and ultrahigh spatial resolution was established. The temporal resolution of the system is 300 fs and spatial resolution 160 lp/mm in theory. Investigation and optimization on spatial resolution of the system was performed. The experimental results demonstrate that the system can provide an electron beam diameter less than 300 m and an incidence angle less than 0.09. The x-y deflection plates and stability of the electron beam were quantitatively analyzed. The diffraction pattern of Al was obtained by this system and it demonstrates that the system can distinguish diffraction peak position changes of 0.36%.
An ultrafast electron diffraction system with both ultrafast temporal resolution and ultrahigh spatial resolution was established. The temporal resolution of the system is 300 fs and spatial resolution 160 lp/mm in theory. Investigation and optimization on spatial resolution of the system was performed. The experimental results demonstrate that the system can provide an electron beam diameter less than 300 m and an incidence angle less than 0.09. The x-y deflection plates and stability of the electron beam were quantitatively analyzed. The diffraction pattern of Al was obtained by this system and it demonstrates that the system can distinguish diffraction peak position changes of 0.36%.
2013,
25: 1635-1638.
doi: 10.3788/HPLPB20132507.1635
Abstract:
The SWOSC-V spring steel wires manufactured by different treatment processes were treated by laser shock processing (LSP) with high power Nd：YAG laser. Residual stresses on inner surface, outer surface and lateral surface were measured by X-ray diffraction (XRD) and principal stresses were calculated. The generation model of laser shock waves in springs was established, and reasons of residual stress generation on spring surface were explained. Residual compressive stresses on each surface of springs were obtained. The changes of residual stress are different between LSP on the annealed spring and the shot blasted spring, and the material hardening by shot peening(SP) is the reason for the different changes of residual stress by LSP.
The SWOSC-V spring steel wires manufactured by different treatment processes were treated by laser shock processing (LSP) with high power Nd：YAG laser. Residual stresses on inner surface, outer surface and lateral surface were measured by X-ray diffraction (XRD) and principal stresses were calculated. The generation model of laser shock waves in springs was established, and reasons of residual stress generation on spring surface were explained. Residual compressive stresses on each surface of springs were obtained. The changes of residual stress are different between LSP on the annealed spring and the shot blasted spring, and the material hardening by shot peening(SP) is the reason for the different changes of residual stress by LSP.
2013,
25: 1639-1642.
doi: 10.3788/HPLPB20132507.1639
Abstract:
The experimental system for laser-induced acoustic signals has been built. Acoustic signals are induced by pulsed laser focusing into water. A hydrophone is used to convert the acoustic signals into electric signals. The mathematic model for laser-induced acoustic signals in time and frequency domain has been analyzed. The energy distribution of the laser-induced acoustic signals in frequency domain has been studied. Characteristics of spectrums of acoustic signals produced by lasers in different repetition rates have been analyzed through experiments. The results are as follows: the laser-induced acoustic signals have most of their energy concentrated before 200 kHz, where half of that is between 100 kHz and 200 kHz. The maxima of laser-induced acoustic signals in frequency domain can be controlled by repetition rates of lasers.
The experimental system for laser-induced acoustic signals has been built. Acoustic signals are induced by pulsed laser focusing into water. A hydrophone is used to convert the acoustic signals into electric signals. The mathematic model for laser-induced acoustic signals in time and frequency domain has been analyzed. The energy distribution of the laser-induced acoustic signals in frequency domain has been studied. Characteristics of spectrums of acoustic signals produced by lasers in different repetition rates have been analyzed through experiments. The results are as follows: the laser-induced acoustic signals have most of their energy concentrated before 200 kHz, where half of that is between 100 kHz and 200 kHz. The maxima of laser-induced acoustic signals in frequency domain can be controlled by repetition rates of lasers.
2013,
25: 1643-1647.
doi: 10.3788/HPLPB20132507.1643
Abstract:
Assuming the incident light was a plane wave, the feedback characteristics of double volume Bragg gratings (VBGs) were studied based on Kogelniks theory. According to the analysis, with the structure of the double VBGs, the bandwidth could be broadened and the diffraction efficiency could be improved through choosing the wavelength differences between the two VBGs. For a system consisting of two VBGs whose bandwidth and diffraction efficiency were 100 pm and 20% respectively, the diffraction efficiency was 33.3% when their central wavelengths had the same value, and the bandwidth could be tuned to 1.8 times (180 pm) of a single VBGs bandwidth. Since there was a thermal shift in VBGs central wavelength, changes in diffraction efficiency and bandwidth could be realized by adjusting the VBGs temperature. External cavities with double VBGs offers an efficient method for optimizing pumping source.
Assuming the incident light was a plane wave, the feedback characteristics of double volume Bragg gratings (VBGs) were studied based on Kogelniks theory. According to the analysis, with the structure of the double VBGs, the bandwidth could be broadened and the diffraction efficiency could be improved through choosing the wavelength differences between the two VBGs. For a system consisting of two VBGs whose bandwidth and diffraction efficiency were 100 pm and 20% respectively, the diffraction efficiency was 33.3% when their central wavelengths had the same value, and the bandwidth could be tuned to 1.8 times (180 pm) of a single VBGs bandwidth. Since there was a thermal shift in VBGs central wavelength, changes in diffraction efficiency and bandwidth could be realized by adjusting the VBGs temperature. External cavities with double VBGs offers an efficient method for optimizing pumping source.
2013,
25: 1648-1650.
doi: 10.3788/HPLPB20132507.1648
Abstract:
To improve the performances of chemical oxygen iodine laser (COIL), experiments were conducted for the removal of water vapor in singlet oxygen gas flows by using phosphorous pentoxide (P2O5) and sulphuric acid (H2SO4) jets. Experimental results show that P2O5 and H2SO4 jets reduce water vapor content to about 1/5 and 1/16 of its initial value respectively, for oleum even to about 1/90, in the gas flow state of the pressure of about 4 kPa, velocity of 20 m/s and resident time of 5 ms; moreover, their quenching effects on singlet oxygen are rather small. Both P2O5 and H2SO4are excellent ambient-temperature-jet dehydrating agents.
To improve the performances of chemical oxygen iodine laser (COIL), experiments were conducted for the removal of water vapor in singlet oxygen gas flows by using phosphorous pentoxide (P2O5) and sulphuric acid (H2SO4) jets. Experimental results show that P2O5 and H2SO4 jets reduce water vapor content to about 1/5 and 1/16 of its initial value respectively, for oleum even to about 1/90, in the gas flow state of the pressure of about 4 kPa, velocity of 20 m/s and resident time of 5 ms; moreover, their quenching effects on singlet oxygen are rather small. Both P2O5 and H2SO4are excellent ambient-temperature-jet dehydrating agents.
2013,
25: 1651-1656.
doi: 10.3788/HPLPB20132507.1651
Abstract:
A thermal coupling model between a medium gas and glasses in a vertical closed tube is established to study thermal effects on laser propagation. Using the thermal coupling method of gas and solid, the gas temperature distributions are simulated, which decide laser wavefront phase distributions in near field and laser beam quality in far field. It is shown that under gravity, gas temperature increase results in its flow in the tube, and the thermal coupling effects between gas and two glasses, one in the top and the other in the bottom, are important for gas temperature distribution,especially the bottom glass. Thus, laser wavefront phase distributions and beam quality change all along during laser propagation. Compared with not considering thermal coupling effects, the gas temperature distribution and beam quality in far field change much.
A thermal coupling model between a medium gas and glasses in a vertical closed tube is established to study thermal effects on laser propagation. Using the thermal coupling method of gas and solid, the gas temperature distributions are simulated, which decide laser wavefront phase distributions in near field and laser beam quality in far field. It is shown that under gravity, gas temperature increase results in its flow in the tube, and the thermal coupling effects between gas and two glasses, one in the top and the other in the bottom, are important for gas temperature distribution,especially the bottom glass. Thus, laser wavefront phase distributions and beam quality change all along during laser propagation. Compared with not considering thermal coupling effects, the gas temperature distribution and beam quality in far field change much.
2013,
25: 1657-1660.
doi: 10.3788/HPLPB20132507.1657
Abstract:
A chopper was used to change a diode bar with a center wavelength of 780 nm from continuous laser to pulsed laser, and a Littrow external cavity was build with a 2400 l/mm plane grating to narrow the linewidth of the diode laser to less than 0.2 nm. Then the diode laser was shaped by a lens group. After the linewidth narrowing and beam shaping, the laser was focused to a Rb vapor cell with a length of 8 mm. In that diode pumped alkali vapor laser system, a linearly polarized fundamental mode Rb laser with a peak power of 17.5 mW was obtained. In the latest experiment, we obtained a 2.8 W Rb laser in the improved diode pumped rubidium vapor laser system.
A chopper was used to change a diode bar with a center wavelength of 780 nm from continuous laser to pulsed laser, and a Littrow external cavity was build with a 2400 l/mm plane grating to narrow the linewidth of the diode laser to less than 0.2 nm. Then the diode laser was shaped by a lens group. After the linewidth narrowing and beam shaping, the laser was focused to a Rb vapor cell with a length of 8 mm. In that diode pumped alkali vapor laser system, a linearly polarized fundamental mode Rb laser with a peak power of 17.5 mW was obtained. In the latest experiment, we obtained a 2.8 W Rb laser in the improved diode pumped rubidium vapor laser system.
2013,
25: 1661-1665.
doi: 10.3788/HPLPB20132507.1661
Abstract:
In order to reconstruct the image using sparse emitter array, a process based on spatial non-uniform Fourier transform (NDFT) method was proposed. According to the relationship between the extracted spatial frequency of target and the position of Fourier telescope emitters and considering the MATLAB program characteristics, we completed the inverse Fourier transform of non-uniform airspace and reconstructed the image of target. Sparse emitter array configuration is as follows: 11 launch telescopes are placed on the T-array single arm, eight low-frequency components are continuously extracted and then followed by three high-frequency components. We selected four satellites with different shape and gray distribution as the imaging target. Comparing our reconstructed images with those by fast Fourier transform with zero-padding, we found that in the presence of noise (100 dB signal-to-noise ratio), the Strehl ratios of the images reconstructed with NDFT method are improved and the highest one is enhanced by 0.159 8.
In order to reconstruct the image using sparse emitter array, a process based on spatial non-uniform Fourier transform (NDFT) method was proposed. According to the relationship between the extracted spatial frequency of target and the position of Fourier telescope emitters and considering the MATLAB program characteristics, we completed the inverse Fourier transform of non-uniform airspace and reconstructed the image of target. Sparse emitter array configuration is as follows: 11 launch telescopes are placed on the T-array single arm, eight low-frequency components are continuously extracted and then followed by three high-frequency components. We selected four satellites with different shape and gray distribution as the imaging target. Comparing our reconstructed images with those by fast Fourier transform with zero-padding, we found that in the presence of noise (100 dB signal-to-noise ratio), the Strehl ratios of the images reconstructed with NDFT method are improved and the highest one is enhanced by 0.159 8.
2013,
25: 1666-1670.
doi: 10.3788/HPLPB20132507.1666
Abstract:
A set of underwater range-gated imaging system based on laser illumination was developed for the detection of underwater targets. This system used 532 nm Nd:YAG laser as illumination source whose maximum pulse power was 400 mJ, and used 10242024 ICCD as range-gated and imaging device. The minimal gate length of the system was 3 ns. A digital pulse producer DG535 was used as an accurate time-lapse device to synchronize the laser with ICCD range gate to realize the systems range-gated function. An underwater target detection experiment was carried out in a reservoir with this system. The result of the experiment indicated that the largest target recognition depth is 6.5 times the attenuation length of water for this system and the target in 8 times the attenuation length of water could be found with this system.
A set of underwater range-gated imaging system based on laser illumination was developed for the detection of underwater targets. This system used 532 nm Nd:YAG laser as illumination source whose maximum pulse power was 400 mJ, and used 10242024 ICCD as range-gated and imaging device. The minimal gate length of the system was 3 ns. A digital pulse producer DG535 was used as an accurate time-lapse device to synchronize the laser with ICCD range gate to realize the systems range-gated function. An underwater target detection experiment was carried out in a reservoir with this system. The result of the experiment indicated that the largest target recognition depth is 6.5 times the attenuation length of water for this system and the target in 8 times the attenuation length of water could be found with this system.
2013,
25: 1671-1674.
doi: 10.3788/HPLPB20132507.1671
Abstract:
Based on the target reflection section defined by the bidirectional reflectance distribution function, a method of approximate calculation and analysis of the cones and plates reflection section in laser-illuminated condition put forward. With the method, the reflection section of cone was calculated and analyzed. An experimental platform was established with Nd:YAG laser and CMOS camera, through which the experimental research is carried out on the target characteristics under the condition of laser lighting. The experimental result of the reflection section and its theoretically calculated result were in agreement with each other. The results show that, among different targets of the same shape with no paint, white paint and gray paint layer, if the incidence angle is less than 45, the reflection section gradually decreases, otherwise, the reflection cross section of the target with white paint layer is greater than others. Among plate, cylinder and cone shaped targets with the same paint layer, the reflection cross section diminishes by turns.
Based on the target reflection section defined by the bidirectional reflectance distribution function, a method of approximate calculation and analysis of the cones and plates reflection section in laser-illuminated condition put forward. With the method, the reflection section of cone was calculated and analyzed. An experimental platform was established with Nd:YAG laser and CMOS camera, through which the experimental research is carried out on the target characteristics under the condition of laser lighting. The experimental result of the reflection section and its theoretically calculated result were in agreement with each other. The results show that, among different targets of the same shape with no paint, white paint and gray paint layer, if the incidence angle is less than 45, the reflection section gradually decreases, otherwise, the reflection cross section of the target with white paint layer is greater than others. Among plate, cylinder and cone shaped targets with the same paint layer, the reflection cross section diminishes by turns.
2013,
25: 1675-1679.
doi: 10.3788/HPLPB20132507.1675
Abstract:
Scattering phase functions and lidar ratios of natural aerosol aggregates at different ratios of dust and sea-salt were carried out based on discrete dipole approximation (DDA) for the size parameters from 0.1 to 25. Curves of scattering phase function and lidar ratio for natural aerosol aggregates as a function of scattering angle were almost the same. Scattering phase functions had distinct opposition effect for the size parameters from 13 to 24, which was most evident around the size parameter of 18. The effect of increasing dust on scattering phase function of natural aerosol aggregates were greater than that of increasing sea-salt, and the main influence range of the size parameter was from 15 to 25. These effects were distinct at different scattering angle except for the backscattering with the scattering angles around 180. The lidar ratios of natural aerosol aggregates had the maximum value of about 180 around the size parameter of 3. Influences of composition variations on lidar ratios were not large for the size parameters from 0.2 to 25, especially for the size parameters from 0.5 to 2 with the differences less than 1%.
Scattering phase functions and lidar ratios of natural aerosol aggregates at different ratios of dust and sea-salt were carried out based on discrete dipole approximation (DDA) for the size parameters from 0.1 to 25. Curves of scattering phase function and lidar ratio for natural aerosol aggregates as a function of scattering angle were almost the same. Scattering phase functions had distinct opposition effect for the size parameters from 13 to 24, which was most evident around the size parameter of 18. The effect of increasing dust on scattering phase function of natural aerosol aggregates were greater than that of increasing sea-salt, and the main influence range of the size parameter was from 15 to 25. These effects were distinct at different scattering angle except for the backscattering with the scattering angles around 180. The lidar ratios of natural aerosol aggregates had the maximum value of about 180 around the size parameter of 3. Influences of composition variations on lidar ratios were not large for the size parameters from 0.2 to 25, especially for the size parameters from 0.5 to 2 with the differences less than 1%.
2013,
25: 1680-1684.
doi: 10.3788/HPLPB20132507.1680
Abstract:
The vertical smear correction of a high frame rate camera has been carried out, which takes a series of images and CCD vertical binning into consideration. Compared with the traditional arithmetic for static images, such as reversely stepwise correcting method, the arithmetic presented in this paper is fit for continuous images, particularly for the images acquired with binning. The method has been applied to a newly developed high frame rate camera based on asynchronous CCD drive which is capable of operating up to 40 000 frames per second, and the processed images proved the effectivity of this method.
The vertical smear correction of a high frame rate camera has been carried out, which takes a series of images and CCD vertical binning into consideration. Compared with the traditional arithmetic for static images, such as reversely stepwise correcting method, the arithmetic presented in this paper is fit for continuous images, particularly for the images acquired with binning. The method has been applied to a newly developed high frame rate camera based on asynchronous CCD drive which is capable of operating up to 40 000 frames per second, and the processed images proved the effectivity of this method.
2013,
25: 1685-1689.
doi: 10.3788/HPLPB20132507.1685
Abstract:
Based on the Rayleigh-Sommerfeld diffraction integrals, the closed-form expression of truncated nonparaxial cosh-Gaussian (ChG) beams in free space is derived, and some special cases are discussed. The power in the bucket (PIB) of nonparaxial regime is introduced to characterize the beam quality of truncated nonparaxial beams in the far field. It is found that the intensity and the PIB of truncated nonparaxial ChG beams depend on the waist-width-to-wavelength ratio, decentered parameter, truncation parameter and the PIB additionally depends on the bucket size. For a given bucket size, the larger waist-width-to-wavelength ratio, truncation parameter and smaller decentered parameter result in the better power focus ability in the far field and the better beam quality.
Based on the Rayleigh-Sommerfeld diffraction integrals, the closed-form expression of truncated nonparaxial cosh-Gaussian (ChG) beams in free space is derived, and some special cases are discussed. The power in the bucket (PIB) of nonparaxial regime is introduced to characterize the beam quality of truncated nonparaxial beams in the far field. It is found that the intensity and the PIB of truncated nonparaxial ChG beams depend on the waist-width-to-wavelength ratio, decentered parameter, truncation parameter and the PIB additionally depends on the bucket size. For a given bucket size, the larger waist-width-to-wavelength ratio, truncation parameter and smaller decentered parameter result in the better power focus ability in the far field and the better beam quality.
2013,
25: 1690-1696.
doi: 10.3788/HPLPB20132507.1690
Abstract:
A 1064 nm pulsed Nd:YAG laser is used for the ablation of an iron bar sample in air at atmospheric pressure and the laser-induced plasma characteristics are examined. The electron number density of 8.71017 cm-3 in the iron plasma is inferred from the Stark broadened profile of Fe I 376.553 nm averaged with 10 single spectra. In order to minimize relative errors in calculation of the electron temperature, an improved iterative Boltzmann plot method is used. Experimental results show that the electron temperature is 8058 K with a regression coefficient of 0.981 38. Based on the experimental results, the plasma is verified to be in local thermodynamic equilibrium (LTE) and free from self-absorption. Considering the laser photon frequency (2.821014 Hz) is larger than the plasma frequency (8.31012 Hz), the loss of energy due to reflection of the laser beam from the plasma can be assumed to be insignificant. Experiments also demonstrate that the inverse Bremsstrahlung (IB) absorption is the dominant photon absorption process during the laser-plasma interaction, and the corresponding IB absorption coefficient is 0.14 cm-1.
A 1064 nm pulsed Nd:YAG laser is used for the ablation of an iron bar sample in air at atmospheric pressure and the laser-induced plasma characteristics are examined. The electron number density of 8.71017 cm-3 in the iron plasma is inferred from the Stark broadened profile of Fe I 376.553 nm averaged with 10 single spectra. In order to minimize relative errors in calculation of the electron temperature, an improved iterative Boltzmann plot method is used. Experimental results show that the electron temperature is 8058 K with a regression coefficient of 0.981 38. Based on the experimental results, the plasma is verified to be in local thermodynamic equilibrium (LTE) and free from self-absorption. Considering the laser photon frequency (2.821014 Hz) is larger than the plasma frequency (8.31012 Hz), the loss of energy due to reflection of the laser beam from the plasma can be assumed to be insignificant. Experiments also demonstrate that the inverse Bremsstrahlung (IB) absorption is the dominant photon absorption process during the laser-plasma interaction, and the corresponding IB absorption coefficient is 0.14 cm-1.
2013,
25: 1697-1700.
doi: 10.3788/HPLPB20132507.1697
Abstract:
Images progressing technology of optics damage pictures which were taken in total internal reflection edge illumination was studied in this paper. Signal intensity of defects is stronger than backgrounds intensity in the edge lit images. Based on this property, local signal intensity ratio image was produced by Gaussian filter to locate the defects with high accuracy. A calibration equation between the size of the defects and the gray value was built. The size of the defects could be precisely calculated using the calibration equation. A comparison test was carried out, the results indicate that the proposed algorithm is superior to the traditional ones on the precision.
Images progressing technology of optics damage pictures which were taken in total internal reflection edge illumination was studied in this paper. Signal intensity of defects is stronger than backgrounds intensity in the edge lit images. Based on this property, local signal intensity ratio image was produced by Gaussian filter to locate the defects with high accuracy. A calibration equation between the size of the defects and the gray value was built. The size of the defects could be precisely calculated using the calibration equation. A comparison test was carried out, the results indicate that the proposed algorithm is superior to the traditional ones on the precision.
2013,
25: 1701-1704.
doi: 10.3788/HPLPB20132507.1701
Abstract:
In fabrication of high conversion efficiency hohlraums, one of the most important steps is using sodium hydroxide solution to etch away the aluminum mandrel. In order to grip the corrosion action of aluminum in sodium hydroxide solution, we use weight loss method to investigate the corrosion action of aluminum in 1-5 mol/L sodium hydroxide solution at 30 ℃ and that in 3 mol/L sodium hydroxide solution in the condition of 30-50 ℃. Through disposing the experiment data by experience formula, we obtain the kinetic parameters, i.e. reaction rate constant, order of reaction, apparent activation energy, and pre-exponential factor. Moreover, the reaction products are analyzed by means of X-ray diffraction.
In fabrication of high conversion efficiency hohlraums, one of the most important steps is using sodium hydroxide solution to etch away the aluminum mandrel. In order to grip the corrosion action of aluminum in sodium hydroxide solution, we use weight loss method to investigate the corrosion action of aluminum in 1-5 mol/L sodium hydroxide solution at 30 ℃ and that in 3 mol/L sodium hydroxide solution in the condition of 30-50 ℃. Through disposing the experiment data by experience formula, we obtain the kinetic parameters, i.e. reaction rate constant, order of reaction, apparent activation energy, and pre-exponential factor. Moreover, the reaction products are analyzed by means of X-ray diffraction.
2013,
25: 1705-1708.
doi: 10.3788/HPLPB20132507.1705
Abstract:
A laser ray-tracing method with consideration of diffractive effect is developed. The Wigner distribution function defined by laser scalar wave field is introduced along with the Liouville kinetic equation it satisfies. This function can describe the laser energy of any ray along arbitrary direction at any spatial position. The laser energy retains fixed in vacuum or attenuates in plasmas along ray trace. Compared with the conventional ray-tracing method, the Wigner distribution function method can give laser energy attached to ray theoretically and the phase information at boundary can be included in the definition of Wigner distribution function. Also, this method can describe the propagation of laser beams as well as the analytical model and the Fresnel diffraction method.
A laser ray-tracing method with consideration of diffractive effect is developed. The Wigner distribution function defined by laser scalar wave field is introduced along with the Liouville kinetic equation it satisfies. This function can describe the laser energy of any ray along arbitrary direction at any spatial position. The laser energy retains fixed in vacuum or attenuates in plasmas along ray trace. Compared with the conventional ray-tracing method, the Wigner distribution function method can give laser energy attached to ray theoretically and the phase information at boundary can be included in the definition of Wigner distribution function. Also, this method can describe the propagation of laser beams as well as the analytical model and the Fresnel diffraction method.
2013,
25: 1709-1710.
doi: 10.3788/HPLPB20132507.1709
Abstract:
To understand the self-generated magnetic field induced from the non-parallel property of temperature gradient and density gradient in the ultra-intense laser-plasma interaction, we apply the theoretical analysis and numerical simulation to studying the self-generated magnetic field in consideration of relativistic effects and its generation mechanism, then derive the analytical expressions of self-generated magnetic field, and obtain the time evolution of the spatial distribution of self-generated magnetic field. The simulation results show that once the ultra-intense laser pulse with an intensity of 1019 W/cm2 irradiates the circular concave target, one can observe the self-generated magnetic field with the maximum magnitude at the order of 51102 T on the surface of the plasma, which are consistent with the experimental measurement.
To understand the self-generated magnetic field induced from the non-parallel property of temperature gradient and density gradient in the ultra-intense laser-plasma interaction, we apply the theoretical analysis and numerical simulation to studying the self-generated magnetic field in consideration of relativistic effects and its generation mechanism, then derive the analytical expressions of self-generated magnetic field, and obtain the time evolution of the spatial distribution of self-generated magnetic field. The simulation results show that once the ultra-intense laser pulse with an intensity of 1019 W/cm2 irradiates the circular concave target, one can observe the self-generated magnetic field with the maximum magnitude at the order of 51102 T on the surface of the plasma, which are consistent with the experimental measurement.
2013,
25: 1715-1718.
doi: 10.3788/HPLPB20132507.1715
Abstract:
The mass flow ratio(MFR) of air breathing ramjet inlet would be decreased, when the Mach number is lower than the designed value. High frequency pulsed laser energy was deposited upstream of the cowl lip to reflect the stream so as to increase the MFR. When the Mach number of the flow was 5.0, and the static pressure and temperature of the flow were 2 551.6 Pa and 116.7 K, respectively, two-dimensional non-stationary compressible RANS equations were solved with upwind format to study the mechanisms of increasing MFR by high frequency pulsed laser energy deposition. The laser deposition frequency was 100 kHz and the average power was 500 W. The crossing point of the first forebody oblique shock and extension line of cowl lip was selected as the expected point. Then the deposition position was optimized by searching near the expected point. The results indicate that with the optimization of laser energy deposition position, the MFR would be increased from 63% to 97%. The potential value of increasing MFR by high frequency pulsed laser energy deposition was proved. The method for selection of the energy deposition position was also presented.
The mass flow ratio(MFR) of air breathing ramjet inlet would be decreased, when the Mach number is lower than the designed value. High frequency pulsed laser energy was deposited upstream of the cowl lip to reflect the stream so as to increase the MFR. When the Mach number of the flow was 5.0, and the static pressure and temperature of the flow were 2 551.6 Pa and 116.7 K, respectively, two-dimensional non-stationary compressible RANS equations were solved with upwind format to study the mechanisms of increasing MFR by high frequency pulsed laser energy deposition. The laser deposition frequency was 100 kHz and the average power was 500 W. The crossing point of the first forebody oblique shock and extension line of cowl lip was selected as the expected point. Then the deposition position was optimized by searching near the expected point. The results indicate that with the optimization of laser energy deposition position, the MFR would be increased from 63% to 97%. The potential value of increasing MFR by high frequency pulsed laser energy deposition was proved. The method for selection of the energy deposition position was also presented.
2013,
25: 1719-1722.
doi: 10.3788/HPLPB20132507.1719
Abstract:
A five-channel, in-chamber, X-ray imager employing five pinholes and five logarithmic spiral crystals is developed to obtain five monochromatic K-shell line images of the Al wire array Z-pinch plasmas on the Yang accelerator in one shot. This imager is compact, and easy to install and align. It has high energy resolution (less than 1.3 eV), and thus can easily distinguish the images of the He-like resonance line (1 598.4 eV) and its inter-combination line (1 588.3 eV), and the H-like resonance line (1 727.7 eV) and its inter-combination line (1729 eV) of Al from each other. Limited by the drive capability of the Yang accelerator, these images are constructed by several discrete hot-spots distributed around the axial line of the plasmas with cylindrical shape, where the temperature and density of electrons are higher than other regions. In addition, the intensity is higher and the area of hot-spots is wider for the He-like line images than for the H-like line images, which indicates that the electron temperature is not high enough so that the number of H-like ions is far less than that of He-like ions.
A five-channel, in-chamber, X-ray imager employing five pinholes and five logarithmic spiral crystals is developed to obtain five monochromatic K-shell line images of the Al wire array Z-pinch plasmas on the Yang accelerator in one shot. This imager is compact, and easy to install and align. It has high energy resolution (less than 1.3 eV), and thus can easily distinguish the images of the He-like resonance line (1 598.4 eV) and its inter-combination line (1 588.3 eV), and the H-like resonance line (1 727.7 eV) and its inter-combination line (1729 eV) of Al from each other. Limited by the drive capability of the Yang accelerator, these images are constructed by several discrete hot-spots distributed around the axial line of the plasmas with cylindrical shape, where the temperature and density of electrons are higher than other regions. In addition, the intensity is higher and the area of hot-spots is wider for the He-like line images than for the H-like line images, which indicates that the electron temperature is not high enough so that the number of H-like ions is far less than that of He-like ions.
2013,
25: 1723-1726.
doi: 10.3788/HPLPB20132507.1723
Abstract:
Self-supporting diamond-like-carbon (DLC) films have been manufactured successfully using the filtered cathodic vacuum arc system, which are ideal targets for laser phase-stable acceleration regime. The film is deposited at room temperature with a -32 V substrate bias voltage. The deposition rate is about 0.002 nm per pulse. Practically, the NaCl is deposited first as a sacrificial layer before carbon deposition. A holder with round holes is used to support the DLC film after the NaCl layer is dissolved in the water. Films with thickness 5-50 nm can mount over the apertures with a diameter up to 1 mm and the success rate is about 70%. The structure and roughness of the film have been measured by the Raman spectrum and atomic force microscope.
Self-supporting diamond-like-carbon (DLC) films have been manufactured successfully using the filtered cathodic vacuum arc system, which are ideal targets for laser phase-stable acceleration regime. The film is deposited at room temperature with a -32 V substrate bias voltage. The deposition rate is about 0.002 nm per pulse. Practically, the NaCl is deposited first as a sacrificial layer before carbon deposition. A holder with round holes is used to support the DLC film after the NaCl layer is dissolved in the water. Films with thickness 5-50 nm can mount over the apertures with a diameter up to 1 mm and the success rate is about 70%. The structure and roughness of the film have been measured by the Raman spectrum and atomic force microscope.
2013,
25: 1727-1730.
doi: 10.3788/HPLPB20132507.1727
Abstract:
The YAG precursor powder was synthesized through forward co-precipitation method. The raw material was a mixture of aluminum nitrate and yttrium nitrate, the precipitant was ammonium hydrogen carbonate, and the dispersant agents were PEG400, PEG800 and PEG1000. The samples were identified with X-ray diffractometer, laser particle size analyzer and SEM. It is shown that the dispersant agents can decrease reunion phenomenon of powders, and pure YAG powder is obtained with PEG400 and PEG800 after being calcined at 1200 ℃ for 60 min. On the other hand, the particle size of the powder obtained by PEG1000 is smaller than those by PEG400 and PEG800. The specific surface area of the former is 1 748.78 m2/kg and the average particle size is 1.42 m, those of the latter are 29.39 and 128.60 m2/kg, 196.14 and 20.55 m respectively.
The YAG precursor powder was synthesized through forward co-precipitation method. The raw material was a mixture of aluminum nitrate and yttrium nitrate, the precipitant was ammonium hydrogen carbonate, and the dispersant agents were PEG400, PEG800 and PEG1000. The samples were identified with X-ray diffractometer, laser particle size analyzer and SEM. It is shown that the dispersant agents can decrease reunion phenomenon of powders, and pure YAG powder is obtained with PEG400 and PEG800 after being calcined at 1200 ℃ for 60 min. On the other hand, the particle size of the powder obtained by PEG1000 is smaller than those by PEG400 and PEG800. The specific surface area of the former is 1 748.78 m2/kg and the average particle size is 1.42 m, those of the latter are 29.39 and 128.60 m2/kg, 196.14 and 20.55 m respectively.
2013,
25: 1731-1735.
doi: 10.3788/HPLPB20132507.1731
Abstract:
Experimental results offered by an entire suite of diagnostics are analyzed and presented to provide a detailed picture of the overall implosion process and resulting radiation output of aluminum wire array Z-pinches, including precursor radiation during ablation, bubble-spike structure, and local bright spots at stagnation. The precursor is stable after its formation. The bubble-spike structure pays a large influence on the formation of the bright spots, which can be seen at an axial position lack of trailing mass. The comparison between a fraction of spectra with spatial resolution and frame images shows that the formation of bright spots might be influenced by the high temperature and high density condition of local imploded plasma. The X-ray streak images filtered with 50 m Be show that the spatial size of hot spots is 0.8 mm and their life time is shorter than 10 ns.
Experimental results offered by an entire suite of diagnostics are analyzed and presented to provide a detailed picture of the overall implosion process and resulting radiation output of aluminum wire array Z-pinches, including precursor radiation during ablation, bubble-spike structure, and local bright spots at stagnation. The precursor is stable after its formation. The bubble-spike structure pays a large influence on the formation of the bright spots, which can be seen at an axial position lack of trailing mass. The comparison between a fraction of spectra with spatial resolution and frame images shows that the formation of bright spots might be influenced by the high temperature and high density condition of local imploded plasma. The X-ray streak images filtered with 50 m Be show that the spatial size of hot spots is 0.8 mm and their life time is shorter than 10 ns.
Influences of impedance characteristics of radiating antenna on output pulse of switched oscillators
2013,
25: 1736-1740.
doi: 10.3788/HPLPB20132507.1736
Abstract:
The oscillating voltage signal on the antenna terminal and the electric field at far-field district are analyzed by equivalent circuit and commercial electromagnetic software, respectively, taking monocone and helical antennas for examples. It is demonstrated that the center frequencies of the generated electromagnetic pulses coincide with the characteristic frequency of the switched oscillator adopting either element antenna with the same electrical length as the switched oscillator (electrical length matched) or traveling wave antenna. However, there are some differences between them. For an element antenna (electrical length matched), the duration of the output pulse is relatively short with low Q value and the energy disperses in a relatively wide band in frequency domain. On the contrary, the duration of the output pulse is relatively long with high Q value and the energy concentrates on a relatively narrow band in frequency domain for element antenna. This result helps to understand the generation of high power electromagnetic pulse utilizing switched oscillator and has practical significance to the antenna choice in different application occasions.
The oscillating voltage signal on the antenna terminal and the electric field at far-field district are analyzed by equivalent circuit and commercial electromagnetic software, respectively, taking monocone and helical antennas for examples. It is demonstrated that the center frequencies of the generated electromagnetic pulses coincide with the characteristic frequency of the switched oscillator adopting either element antenna with the same electrical length as the switched oscillator (electrical length matched) or traveling wave antenna. However, there are some differences between them. For an element antenna (electrical length matched), the duration of the output pulse is relatively short with low Q value and the energy disperses in a relatively wide band in frequency domain. On the contrary, the duration of the output pulse is relatively long with high Q value and the energy concentrates on a relatively narrow band in frequency domain for element antenna. This result helps to understand the generation of high power electromagnetic pulse utilizing switched oscillator and has practical significance to the antenna choice in different application occasions.
2013,
25: 1741-1746.
doi: 10.3788/HPLPB20132507.1741
Abstract:
The thermal damage mechanism of PIN limiter caused by microwaves was analyzed. Based on physical simulation analysis，the devices thermal damage physical model was established with software Sentaurus-TCAD. Transient temperature change and distribution of temperature in the process of PIN diode under injections of 5.3, 7.5 and 9.4 GHz microwave signals were studied. Simulation and experimental results show that the temperature increases rapidly in the spike leakage stage and near burnout stage, and increases slowly in the flat leakage stage. The peak temperature most likely appears in the I layer or on the edge between I layer and P layer.
The thermal damage mechanism of PIN limiter caused by microwaves was analyzed. Based on physical simulation analysis，the devices thermal damage physical model was established with software Sentaurus-TCAD. Transient temperature change and distribution of temperature in the process of PIN diode under injections of 5.3, 7.5 and 9.4 GHz microwave signals were studied. Simulation and experimental results show that the temperature increases rapidly in the spike leakage stage and near burnout stage, and increases slowly in the flat leakage stage. The peak temperature most likely appears in the I layer or on the edge between I layer and P layer.
2013,
25: 1747-1750.
doi: 10.3788/HPLPB20132507.1747
Abstract:
The development of high power microwave(HPM) technology now trends toward higher power and longer pulse, and overmoded devices are employed to increase the power handling capacity of HPM sources. In order to discriminate the dominant TM01 mode of an X-band long-pulse overmoded HPM source, a mode-selective directional coupler with stable coupling coefficient, high directivity and high power handling capacity in wide band is numerically investigated. At the central frequency range of 9.2-9.6 GHz, the simulation results show that the coupling coefficient is -54 dB, the directivity of TM01 mode is more than 35 dB, the suppression of TM02 mode is about 15 dB, and the power handling capacity is 3 GW.
The development of high power microwave(HPM) technology now trends toward higher power and longer pulse, and overmoded devices are employed to increase the power handling capacity of HPM sources. In order to discriminate the dominant TM01 mode of an X-band long-pulse overmoded HPM source, a mode-selective directional coupler with stable coupling coefficient, high directivity and high power handling capacity in wide band is numerically investigated. At the central frequency range of 9.2-9.6 GHz, the simulation results show that the coupling coefficient is -54 dB, the directivity of TM01 mode is more than 35 dB, the suppression of TM02 mode is about 15 dB, and the power handling capacity is 3 GW.
2013,
25: 1751-1754.
doi: 10.3788/HPLPB20132507.1751
Abstract:
In order to realize the miniaturization of the 25 GW level dual-output ultra-wide spectrum HPM pulse generator, a Tesla transformer with open circuit magnetic core as the primary power source is developed, which is fixed in the Blumlein pulse forming line. Theoretical analysis of the Tesla transformer is carried out, and the method to estimate the electric parameters such as inductances of the primary and secondary windings by using a simplified magnetic circuit model is presented. The approach to calculating the sectional area of the magnetic core and a fabricating technique of the magnetic core are also described. The Tesla transformer can generate the maximum output voltage of 880 kV, and its charge time and coupling coefficient are 20 s and 0.95, respectively. The experimental result is in good agreement with the theoretical design.
In order to realize the miniaturization of the 25 GW level dual-output ultra-wide spectrum HPM pulse generator, a Tesla transformer with open circuit magnetic core as the primary power source is developed, which is fixed in the Blumlein pulse forming line. Theoretical analysis of the Tesla transformer is carried out, and the method to estimate the electric parameters such as inductances of the primary and secondary windings by using a simplified magnetic circuit model is presented. The approach to calculating the sectional area of the magnetic core and a fabricating technique of the magnetic core are also described. The Tesla transformer can generate the maximum output voltage of 880 kV, and its charge time and coupling coefficient are 20 s and 0.95, respectively. The experimental result is in good agreement with the theoretical design.
2013,
25: 1755-1758.
doi: 10.3788/HPLPB20132507.1755
Abstract:
The finite-integration time-domain (FIT) method is adopted to calculate the radiaton fields on the boresight of TEM horn with various lengths, and the results are compared with the radiation field of infinitely long TEM horns. By analysing radiation field difference between finitely and infinitely long TEM horns, we derive the relation between horn length and pulse risetime. Based on the research in references, a optimized design method for parameters of TEM horn is presented.
The finite-integration time-domain (FIT) method is adopted to calculate the radiaton fields on the boresight of TEM horn with various lengths, and the results are compared with the radiation field of infinitely long TEM horns. By analysing radiation field difference between finitely and infinitely long TEM horns, we derive the relation between horn length and pulse risetime. Based on the research in references, a optimized design method for parameters of TEM horn is presented.
2013,
25: 1759-1762.
doi: 10.3788/HPLPB20132507.1759
Abstract:
The borehole radar is a new method in borehole geophysical detection. In order to reduce the antenna structure size and increase the bandwidth, we designed a new resistive loading omni-directional antenna according to borehole radar requirements. Through theoretical analysis and numerical optimization, we selected the better structure, the antenna had good radiation pattern and bandwidth. The outside diameter of the antenna was 65 mm. The outer diameter was 85 mm, using a 10 mm tube encapsulated. S11 of the antenna was less than -10 dB in the frequency band 70~260 MHz, with 190 MHz bandwidth. The center frequency gain was greater than -3 dB, and the radiation electric field pulse waveform tailing was less than 1/5 of the main peak amplitude, the pattern in the H-plane was omnidirectional. The measurement results of antenna characteristics using the vector network analyzer agree well with the numerical results. The results show that the design of the antenna can meet the requirements of the small size of broad borehole radar system.
The borehole radar is a new method in borehole geophysical detection. In order to reduce the antenna structure size and increase the bandwidth, we designed a new resistive loading omni-directional antenna according to borehole radar requirements. Through theoretical analysis and numerical optimization, we selected the better structure, the antenna had good radiation pattern and bandwidth. The outside diameter of the antenna was 65 mm. The outer diameter was 85 mm, using a 10 mm tube encapsulated. S11 of the antenna was less than -10 dB in the frequency band 70~260 MHz, with 190 MHz bandwidth. The center frequency gain was greater than -3 dB, and the radiation electric field pulse waveform tailing was less than 1/5 of the main peak amplitude, the pattern in the H-plane was omnidirectional. The measurement results of antenna characteristics using the vector network analyzer agree well with the numerical results. The results show that the design of the antenna can meet the requirements of the small size of broad borehole radar system.
2013,
25: 1763-1769.
doi: 10.3788/HPLPB20132507.1763
Abstract:
An electron beam was regarded as a plasma column, and the eigen frequency equations of the TM0m0 mode of a cylindrical cavity filled with a plasma column in the center are deduced based on the analytic method in this paper. It is studied in detail that the resonant frequency and the electromagnetic field distribution of the TM010 mode and the TM020 mode changes with the plasma frequency of the electron beam. The research results show that the resonant frequency of the TM010 mode and the TM020 mode will increase with the increasing of the plasma frequency of the electron beam, and the distribution of the electromagnetic fields also changes. When the electron beams plasma frequency exceeds the resonant frequency of the cavity, the electromagnetic field distribution of the TM010 mode and the TM020 mode in the cylindrical cavity will change greatly, and some peculiar phenomena will appear, such as the electric field inside the electron beam will be in the opposite direction of the electric field outside the electron beam, the electromagnetic field will be converged on the brim of the electron beam, and so on.
An electron beam was regarded as a plasma column, and the eigen frequency equations of the TM0m0 mode of a cylindrical cavity filled with a plasma column in the center are deduced based on the analytic method in this paper. It is studied in detail that the resonant frequency and the electromagnetic field distribution of the TM010 mode and the TM020 mode changes with the plasma frequency of the electron beam. The research results show that the resonant frequency of the TM010 mode and the TM020 mode will increase with the increasing of the plasma frequency of the electron beam, and the distribution of the electromagnetic fields also changes. When the electron beams plasma frequency exceeds the resonant frequency of the cavity, the electromagnetic field distribution of the TM010 mode and the TM020 mode in the cylindrical cavity will change greatly, and some peculiar phenomena will appear, such as the electric field inside the electron beam will be in the opposite direction of the electric field outside the electron beam, the electromagnetic field will be converged on the brim of the electron beam, and so on.
2013,
25: 1770-1774.
doi: 10.3788/HPLPB20132507.1770
Abstract:
Several factors causing electrons to return, e. g. the voltage and current of electron beam, the injected power of microwave are studied in relativistic klystron amplifier (RKA). In PIC simulation, we find that high injected power, high beam current and low beam voltage all can cause the return of electrons. Moreover the effect of returning electrons on the stability of RKA is studied, which shows that returning electrons will lead to self-excited oscillation of RKA and to the fail of locking of phase and frequency, and thus the device can not work stably.
Several factors causing electrons to return, e. g. the voltage and current of electron beam, the injected power of microwave are studied in relativistic klystron amplifier (RKA). In PIC simulation, we find that high injected power, high beam current and low beam voltage all can cause the return of electrons. Moreover the effect of returning electrons on the stability of RKA is studied, which shows that returning electrons will lead to self-excited oscillation of RKA and to the fail of locking of phase and frequency, and thus the device can not work stably.
2013,
25: 1775-1778.
doi: 10.3788/HPLPB20132507.1775
Abstract:
We proposed a coherent diffraction radiation (CDR) THz source with megahertz repetition rate, which is based on ultra-short electron beams of the free electron laser THz (FEL-THz) facility at CAEP. With theoretical analysis, numerical calculation and particle-in-cell (PIC) simulation, the pulse duration of this THz source is proved to be several picoseconds. The center frequency is tunable from 100 GHz to 400 GHz and the cut-off frequency is from 1 THz to 2 THz. The peak power is in 10 kW region and the average power can be a few watts. Furthermore, the THz power is proportional to the square of the electron beam current.
We proposed a coherent diffraction radiation (CDR) THz source with megahertz repetition rate, which is based on ultra-short electron beams of the free electron laser THz (FEL-THz) facility at CAEP. With theoretical analysis, numerical calculation and particle-in-cell (PIC) simulation, the pulse duration of this THz source is proved to be several picoseconds. The center frequency is tunable from 100 GHz to 400 GHz and the cut-off frequency is from 1 THz to 2 THz. The peak power is in 10 kW region and the average power can be a few watts. Furthermore, the THz power is proportional to the square of the electron beam current.
2013,
25: 1779-1782.
doi: 10.3788/HPLPB20132507.1779
Abstract:
When the conventional beam deposition method is applied to the internal beam parameters measurement in cyclotron, the induced radioactive contamination generated in the measuring probe will lead to unnecessary radiation hazards to the accelerator beam tuning staff. The AGM-6 gamma monitor was applied to on-line measurement of the induced radioactivity. By measuring the air kerma rate of the probe irradiated at different radii, the strength and the hazards of induced radioactivity were reflected indirectly. The results show that the high-frequency duty cycle should be reduced, and the probe should be cooled for 2-3 h before being removed in the beam tuning experiment. Otherwise, one should consider hazards of the residual induced radioactivity after the measuring probe being irradiated.
When the conventional beam deposition method is applied to the internal beam parameters measurement in cyclotron, the induced radioactive contamination generated in the measuring probe will lead to unnecessary radiation hazards to the accelerator beam tuning staff. The AGM-6 gamma monitor was applied to on-line measurement of the induced radioactivity. By measuring the air kerma rate of the probe irradiated at different radii, the strength and the hazards of induced radioactivity were reflected indirectly. The results show that the high-frequency duty cycle should be reduced, and the probe should be cooled for 2-3 h before being removed in the beam tuning experiment. Otherwise, one should consider hazards of the residual induced radioactivity after the measuring probe being irradiated.
2013,
25: 1783-1787.
doi: 10.3788/HPLPB20132507.1783
Abstract:
The China Accelerator Driven Sub-critical System, C-ADS, will use a linear accelerator delivering continuous-wave protons with an average current of 10 mA and a beam power of 15 MW to the sub-critical reactor. The main linac is an important part of the driver linac which is required to accelerate the beam from 10 MeV to 1.5 GeV. All the cavities in this part are superconducting structures. To avoid the frequently repeated beam interruptions causing damage to the reactor, the driver linac is requested to have a very limited number of beam interruptions during operation, thus fault tolerance strategy is implemented to the maximum possible extent and every possible solution is tried to ensure the highly required reliability and stability. In this paper, the baseline design of the main linac is introduced. The total length of the main linac is 306.4 m. The normalized root-mean-square emittance growth is controlled below 5%. The details of the design strategy together with the multiparticle simulation results are presented.
The China Accelerator Driven Sub-critical System, C-ADS, will use a linear accelerator delivering continuous-wave protons with an average current of 10 mA and a beam power of 15 MW to the sub-critical reactor. The main linac is an important part of the driver linac which is required to accelerate the beam from 10 MeV to 1.5 GeV. All the cavities in this part are superconducting structures. To avoid the frequently repeated beam interruptions causing damage to the reactor, the driver linac is requested to have a very limited number of beam interruptions during operation, thus fault tolerance strategy is implemented to the maximum possible extent and every possible solution is tried to ensure the highly required reliability and stability. In this paper, the baseline design of the main linac is introduced. The total length of the main linac is 306.4 m. The normalized root-mean-square emittance growth is controlled below 5%. The details of the design strategy together with the multiparticle simulation results are presented.
2013,
25: 1788-1792.
doi: 10.3788/HPLPB20132507.1788
Abstract:
The electric field of the transmission mode in an optical fiber waveguide is analyzed theoretically. The discipline describing the influence of optical fiber refractive index changes on waveguide electromagnetic field distribution is obtained. A real time experimental measurement system of refractive index changes has been built by using bulk fused silica material and fiber Bragg grating under 60Co -ray radiation. The refractive index changes of two candidates with given radiation doses and mode field of fiber are measured in the experiments respectively. The results show that the refractive index of the optical fiber increases with the radiation dose; the refractive index changes cause the variations of the field intensity distribution in the transmission mode, which results in radiation-induced waveguide losses; within a certain dose range of 0-2000 Gy, the optical fiber meets the weakly guiding boundary conditions and maintains the confining ability on the transmission mode.
The electric field of the transmission mode in an optical fiber waveguide is analyzed theoretically. The discipline describing the influence of optical fiber refractive index changes on waveguide electromagnetic field distribution is obtained. A real time experimental measurement system of refractive index changes has been built by using bulk fused silica material and fiber Bragg grating under 60Co -ray radiation. The refractive index changes of two candidates with given radiation doses and mode field of fiber are measured in the experiments respectively. The results show that the refractive index of the optical fiber increases with the radiation dose; the refractive index changes cause the variations of the field intensity distribution in the transmission mode, which results in radiation-induced waveguide losses; within a certain dose range of 0-2000 Gy, the optical fiber meets the weakly guiding boundary conditions and maintains the confining ability on the transmission mode.
2013,
25: 1793-1797.
doi: 10.3788/HPLPB20132507.1793
Abstract:
A Schottky barrier diode was made using 4H-SiC wide band gap material, both radiation resistance and temperature resistance of which are excellent due to its intrinsic properties. The charge collection properties of the 4H-SiC Schottky barrier diode were investigated by irradiating the diode with alpha particles from 241Am source. The net dopant concentration, 1.991015/cm3, are inferred from the capacitane-voltage curve. From the current-voltage curve, the barrier height and the ideality factor are found to be 1.66 eV and 1.07, respectively, indicating the main current transportation process of the diode is thermal electron emission. Under the reverse bias at 700 V, the diode has a leakage current of 21 nA, exhibiting a relatively high breakdown voltage. The charge collection properties of the diode to 3.5 MeV alpha particles were investigated at the reverse bias in the range of 0-350 V. The values of charge collection efficiency at 0 V and 150 V are 48.7% and 99.4%, respectively, indicating excellent charge collection properties of 4H-SiC Schottky diode.
A Schottky barrier diode was made using 4H-SiC wide band gap material, both radiation resistance and temperature resistance of which are excellent due to its intrinsic properties. The charge collection properties of the 4H-SiC Schottky barrier diode were investigated by irradiating the diode with alpha particles from 241Am source. The net dopant concentration, 1.991015/cm3, are inferred from the capacitane-voltage curve. From the current-voltage curve, the barrier height and the ideality factor are found to be 1.66 eV and 1.07, respectively, indicating the main current transportation process of the diode is thermal electron emission. Under the reverse bias at 700 V, the diode has a leakage current of 21 nA, exhibiting a relatively high breakdown voltage. The charge collection properties of the diode to 3.5 MeV alpha particles were investigated at the reverse bias in the range of 0-350 V. The values of charge collection efficiency at 0 V and 150 V are 48.7% and 99.4%, respectively, indicating excellent charge collection properties of 4H-SiC Schottky diode.
2013,
25: 1798-1802.
doi: 10.3788/HPLPB20132507.1798
Abstract:
For the property and application of dye random laser, the relations among the random laser emission threshold, luminescent properties, number density change and particle size of fluorescence particles and additional scattering particles in disorder media were discussed. Using the finite difference time domain (FDTD) method to solve Maxwells equations and rate equations directly, the curves of number density and emission line changing with laser emission threshold were simulated. When the mass fraction of Rh6G-SiO2 was 4% and the threshold was 8.5 J/pulse, the influence of additional TiO2 particles on random lasing was small enough to be neglected. Furthermore, we also simulated the threshold characteristics of random lasing in variety of conditions and background media.
For the property and application of dye random laser, the relations among the random laser emission threshold, luminescent properties, number density change and particle size of fluorescence particles and additional scattering particles in disorder media were discussed. Using the finite difference time domain (FDTD) method to solve Maxwells equations and rate equations directly, the curves of number density and emission line changing with laser emission threshold were simulated. When the mass fraction of Rh6G-SiO2 was 4% and the threshold was 8.5 J/pulse, the influence of additional TiO2 particles on random lasing was small enough to be neglected. Furthermore, we also simulated the threshold characteristics of random lasing in variety of conditions and background media.
2013,
25: 1803-1806.
doi: 10.3788/HPLPB20132507.1803
Abstract:
Based on the Monte Carlo software Geant4, we investigate the Coulomb scattering of protons by silicon and nuclear reactions induced by protons and neutrons in silicon, and the generation of recoil atoms depositing non-ionizing energy. The methodfor calculating non-ionizing energy stopping power of the protons and neutrons in silicon is established. This method describes the Coulomb scattering among atoms, and the screened Coulomb scattering between charged particles and lattice atoms. The non-ionizing energy stopping power of different energy neutrons and protons in silicon due to nuclear reaction and direct Coulomb scattering and its equivalence are calculated. The calculation results agree with the neutron ASTM standard and the proton data calculated by the reference.
Based on the Monte Carlo software Geant4, we investigate the Coulomb scattering of protons by silicon and nuclear reactions induced by protons and neutrons in silicon, and the generation of recoil atoms depositing non-ionizing energy. The methodfor calculating non-ionizing energy stopping power of the protons and neutrons in silicon is established. This method describes the Coulomb scattering among atoms, and the screened Coulomb scattering between charged particles and lattice atoms. The non-ionizing energy stopping power of different energy neutrons and protons in silicon due to nuclear reaction and direct Coulomb scattering and its equivalence are calculated. The calculation results agree with the neutron ASTM standard and the proton data calculated by the reference.
2013,
25: 1807-1811.
doi: 10.3788/HPLPB20132507.1807
Abstract:
A new helium scintillation fission neutron detector was designed to detect the neutrons in the mixed pulse fission radiation field. The time response of the detector was investigated through theoretical and experimental methods. The flying time of the fragments and recoiled helium nucleus in helium scintillator were calculated based on the experimental formulae and method of Monte Carlo. The formula of detectors time response was deduced from the convolution method. The result of the calculating detectors wave indicated that the risetime was about 19.5 ns and FWHM was about 31.0 ns. The time response was measured on the dense plasma focus device(DPF) neutron generator. The theoretical results of time response were consistent with experimental results.
A new helium scintillation fission neutron detector was designed to detect the neutrons in the mixed pulse fission radiation field. The time response of the detector was investigated through theoretical and experimental methods. The flying time of the fragments and recoiled helium nucleus in helium scintillator were calculated based on the experimental formulae and method of Monte Carlo. The formula of detectors time response was deduced from the convolution method. The result of the calculating detectors wave indicated that the risetime was about 19.5 ns and FWHM was about 31.0 ns. The time response was measured on the dense plasma focus device(DPF) neutron generator. The theoretical results of time response were consistent with experimental results.
2013,
25: 1812-1816.
doi: 10.3788/HPLPB20132507.1812
Abstract:
The elastic and thermodynamic properties of UO2 under extreme physical condition are studied by using the density functional theory and quasi-harmonic Debye model. Results show that UO2 is still stable ionic crystal under high temperatures, and pressures. Tetragonal shear constant is steady under high pressures and temperatures, while elastic constant C44 is stable under high temperatures, but rises with pressure sharply. Bulk modulus, shear modulus and Youngs modulus increase with pressure rapidly, but temperature would not cause evident debasement of the moduli, all of which indicate that UO2 has excellent mechanical properties. Heat capacity of different pressures increases with temperature and is close to the Dulong-Petit limit near 1000 K. Debye temperature decreases with temperature, and increases with pressure. Under low pressure, thermal expansion coefficient raises with temperature rapidly, and then gets slow at higher pressure and temperature. Besides, the thermal expansion coefficient of UO2 is much lower than that of other nuclear materials.
The elastic and thermodynamic properties of UO2 under extreme physical condition are studied by using the density functional theory and quasi-harmonic Debye model. Results show that UO2 is still stable ionic crystal under high temperatures, and pressures. Tetragonal shear constant is steady under high pressures and temperatures, while elastic constant C44 is stable under high temperatures, but rises with pressure sharply. Bulk modulus, shear modulus and Youngs modulus increase with pressure rapidly, but temperature would not cause evident debasement of the moduli, all of which indicate that UO2 has excellent mechanical properties. Heat capacity of different pressures increases with temperature and is close to the Dulong-Petit limit near 1000 K. Debye temperature decreases with temperature, and increases with pressure. Under low pressure, thermal expansion coefficient raises with temperature rapidly, and then gets slow at higher pressure and temperature. Besides, the thermal expansion coefficient of UO2 is much lower than that of other nuclear materials.
2013,
25: 1817-1820.
doi: 10.3788/HPLPB20132507.1817
Abstract:
The shielding is a key way to lower the measuring background and keep workers safe for residual stress neutron diffractometer (RSND) building on reactor. The shield plan was optimized with Monte Carlo codes. In view of its complexity, two programs, McStas and MCNP5, were used, with some good techniques to improve the computation efficiency. The calculation of radiating field in RSND was accomplished with three parts: the transmission of thermal neutron in guide was simulated with McStas, the radiating leakage was estimated with MCNP due to slits between shield blocks, and the whole shield plan for RSND was modeled in MCNP. Corrected with influencing factors, the simulated results were compared with data measured by dosimeter, and it was found that they fitted well and was within the permitted error.
The shielding is a key way to lower the measuring background and keep workers safe for residual stress neutron diffractometer (RSND) building on reactor. The shield plan was optimized with Monte Carlo codes. In view of its complexity, two programs, McStas and MCNP5, were used, with some good techniques to improve the computation efficiency. The calculation of radiating field in RSND was accomplished with three parts: the transmission of thermal neutron in guide was simulated with McStas, the radiating leakage was estimated with MCNP due to slits between shield blocks, and the whole shield plan for RSND was modeled in MCNP. Corrected with influencing factors, the simulated results were compared with data measured by dosimeter, and it was found that they fitted well and was within the permitted error.
2013,
25: 1821-1825.
doi: 10.3788/HPLPB20132507.1821
Abstract:
An analytic expression of the secondary capacitance of a compact Tesla pulse transformer is derived. Calculated result by the expression shows that two parts contribute to the secondary capacitance, namely the capacitance between inner and outer magnetic cores and the attached capacitance caused by the secondary winding. The attached capacitance equals to the capacitance of a coaxial line which is as long as the secondary coil, and whose outer and inner diameters are as large as the inner diameter of the outer magnetic and the outer diameter of the inner magnetic core respectively. A circuital model for analyzing compact Tesla transformer is built, and numeric calculation shows that the expression of the secondary capacitance is correct. Besides, a small compact Tesla transformer is developed, and related test is carried out. Test result confirms the calculated results by the expression derived.
An analytic expression of the secondary capacitance of a compact Tesla pulse transformer is derived. Calculated result by the expression shows that two parts contribute to the secondary capacitance, namely the capacitance between inner and outer magnetic cores and the attached capacitance caused by the secondary winding. The attached capacitance equals to the capacitance of a coaxial line which is as long as the secondary coil, and whose outer and inner diameters are as large as the inner diameter of the outer magnetic and the outer diameter of the inner magnetic core respectively. A circuital model for analyzing compact Tesla transformer is built, and numeric calculation shows that the expression of the secondary capacitance is correct. Besides, a small compact Tesla transformer is developed, and related test is carried out. Test result confirms the calculated results by the expression derived.
2013,
25: 1826-1830.
doi: 10.3788/HPLPB20132507.1826
Abstract:
Using the FR-4 as the dielectric materials, a pulse forming line (PFL) module was developed by attaching five PCB PFLs in parallel. In order to optimize electric field distribution, a shielded electrode was inserted in the dielectric materials, and the theoretical analysis shows the shielded electron has no effect on the parameter and transmission characteristics of the PFL. The PFL can withstand more than 200 kV with a insulating layer thickness of 4 mm. According to the lifetime calculation equation, it is found that the PFL has a long lifetime when the charging voltage is 50-80 kV. The size of PFL module is 700 mm550 mm40 mm, and the characteristic impedance of it is 5.35 . When the PFL module is used in a Blumlein manner and charged to 50 kV, the output voltage on the match-load of 45 kV, full width at half magnitude (FWHM) of 140 ns, flat top of 75 ns and time rise of about 65 ns are obtained.
Using the FR-4 as the dielectric materials, a pulse forming line (PFL) module was developed by attaching five PCB PFLs in parallel. In order to optimize electric field distribution, a shielded electrode was inserted in the dielectric materials, and the theoretical analysis shows the shielded electron has no effect on the parameter and transmission characteristics of the PFL. The PFL can withstand more than 200 kV with a insulating layer thickness of 4 mm. According to the lifetime calculation equation, it is found that the PFL has a long lifetime when the charging voltage is 50-80 kV. The size of PFL module is 700 mm550 mm40 mm, and the characteristic impedance of it is 5.35 . When the PFL module is used in a Blumlein manner and charged to 50 kV, the output voltage on the match-load of 45 kV, full width at half magnitude (FWHM) of 140 ns, flat top of 75 ns and time rise of about 65 ns are obtained.
2013,
25: 1831-1834.
doi: 10.3788/HPLPB20132507.1831
Abstract:
Gaussian and Weibull functions which are used to analyze self-breakdown probabilities of a gas switch are compared. Following an experiment, the self-breakdown voltages of a multi-stage switch are verified to apply a Gaussian distribution as well as a Weibull distribution, and then these two distributions are determined by using a parameter estimation method. The self-breakdown probability analysis shows that the results of these two models are in good agreement. For the same voltage, the difference of the self-breakdown probabilities given by these two methods is normally 1%, and the difference is no more than 2% for the probability greater than 90%. For the same self-breakdown probability, the calculated voltages using these two models have a difference of not more than 0.3%.
Gaussian and Weibull functions which are used to analyze self-breakdown probabilities of a gas switch are compared. Following an experiment, the self-breakdown voltages of a multi-stage switch are verified to apply a Gaussian distribution as well as a Weibull distribution, and then these two distributions are determined by using a parameter estimation method. The self-breakdown probability analysis shows that the results of these two models are in good agreement. For the same voltage, the difference of the self-breakdown probabilities given by these two methods is normally 1%, and the difference is no more than 2% for the probability greater than 90%. For the same self-breakdown probability, the calculated voltages using these two models have a difference of not more than 0.3%.
2013,
25: 1835-1838.
doi: 10.3788/HPLPB20132507.1835
Abstract:
A kind of rectangular cross-section, ferromagnetics magnetic core is selected to fabricate a magnetic switch used as the discharge switch of the solid-state accelerator. B-H curves at different locations on the magnetic core are measured with the pulsed capacitor method. Results illustrate that the properties of these cores are good enough for the utilization of the magnetic pulse compression and the shapes of the B-H curves on different sides of cores are similar. PSpice is employed to analyze the circuit of the system including the magnetic switch used as the discharge switch. Results show reasonable agreement with the theoretical prediction. Experimental research was carried out on the discharge switch driven by a rolled strip pulse forming line. A quasi-square pulse with the peak voltage of 9 kV, and pulse duration (FWHM) of 230 ns was obtained on low resistance load. The rise-time of the pulse was less than 80 ns.
A kind of rectangular cross-section, ferromagnetics magnetic core is selected to fabricate a magnetic switch used as the discharge switch of the solid-state accelerator. B-H curves at different locations on the magnetic core are measured with the pulsed capacitor method. Results illustrate that the properties of these cores are good enough for the utilization of the magnetic pulse compression and the shapes of the B-H curves on different sides of cores are similar. PSpice is employed to analyze the circuit of the system including the magnetic switch used as the discharge switch. Results show reasonable agreement with the theoretical prediction. Experimental research was carried out on the discharge switch driven by a rolled strip pulse forming line. A quasi-square pulse with the peak voltage of 9 kV, and pulse duration (FWHM) of 230 ns was obtained on low resistance load. The rise-time of the pulse was less than 80 ns.
2013,
25: 1839-1844.
doi: 10.3788/HPLPB20132507.1839
Abstract:
A self-integral capacitance divider used for voltage measurement along the magnetically insulated transmission line was developed. By using the commercial PSpice software, the equivalent circuit model, transfer-equations and frequency responses of the divider were obtained. The calculation results show that signals with frequency more than 5 MHz can be perfectly measured by the divider. Based on the test stand of the Qiangguang-Ⅰ coaxial magnetically insulated transmission line (MITL) with 1 m length and 2 cm AK gap, the working characteristics of the divider was tested. Experimental results show that with little electron reached the anode surface, the divider developed above can be perfectly used for the measurement of the voltage pulse along the MITL (with peak voltage 600 kV, risetime 80 ns).
A self-integral capacitance divider used for voltage measurement along the magnetically insulated transmission line was developed. By using the commercial PSpice software, the equivalent circuit model, transfer-equations and frequency responses of the divider were obtained. The calculation results show that signals with frequency more than 5 MHz can be perfectly measured by the divider. Based on the test stand of the Qiangguang-Ⅰ coaxial magnetically insulated transmission line (MITL) with 1 m length and 2 cm AK gap, the working characteristics of the divider was tested. Experimental results show that with little electron reached the anode surface, the divider developed above can be perfectly used for the measurement of the voltage pulse along the MITL (with peak voltage 600 kV, risetime 80 ns).
2013,
25: 1845-1850.
doi: 10.3788/HPLPB20132507.1845
Abstract:
A method based on the telegraph equation to simulate the vacuum power flow in magnetically insulated transmission line was introduced. Shot 4600 at Angara-5-1 facility was computed, and the simulation results agree well with the experiment results. The loss current of the elements at joints of different MITL structures was analyzed. Also, the difference between this method and other circuit simulation methods such as TLCODE and Bertha was discussed. The method is a new way of estimating the vacuum power flow in magnetically insulated transmission line. It can not only enhance numerical convergence of solution, but also ensure the numerical precision and self-consistency in loss current calculation.
A method based on the telegraph equation to simulate the vacuum power flow in magnetically insulated transmission line was introduced. Shot 4600 at Angara-5-1 facility was computed, and the simulation results agree well with the experiment results. The loss current of the elements at joints of different MITL structures was analyzed. Also, the difference between this method and other circuit simulation methods such as TLCODE and Bertha was discussed. The method is a new way of estimating the vacuum power flow in magnetically insulated transmission line. It can not only enhance numerical convergence of solution, but also ensure the numerical precision and self-consistency in loss current calculation.
2013,
25: 1851-1855.
doi: 10.3788/HPLPB20132507.1851
Abstract:
A stacked Blumlein pulse forming network(B-PFN) was designed to drive repetitive high-Z X-ray diode. Numerical simulation was adopted to optimize the system parameters, through which inductance design principle was aquired. B-PFN performance was analyzed from several aspects: consistency of charging voltage, distortion of output wave, efficiency of stacked voltage and amplitude of load pre-pulse. Experiments showed that the single B-PFN voltage efficiency was 0.71, the two-stage stacked voltage efficiency was 0.96, when PCSS electric field was 23.2 kV/cm and trigger laser energy was 3.5 mJ.
A stacked Blumlein pulse forming network(B-PFN) was designed to drive repetitive high-Z X-ray diode. Numerical simulation was adopted to optimize the system parameters, through which inductance design principle was aquired. B-PFN performance was analyzed from several aspects: consistency of charging voltage, distortion of output wave, efficiency of stacked voltage and amplitude of load pre-pulse. Experiments showed that the single B-PFN voltage efficiency was 0.71, the two-stage stacked voltage efficiency was 0.96, when PCSS electric field was 23.2 kV/cm and trigger laser energy was 3.5 mJ.
2013,
25: 1856-1860.
doi: 10.3788/HPLPB20132507.1856
Abstract:
An experiment in view of repetitive frequency electromagnetic pulse (EMP) interference, take the hydrogen thyratron trigger as research object, is carried out to study the interference of the hydrogen thyratron first grid and second grid under the condition of suspension and mutual ground. The results show that the two grids have intense electromagnetic interference (EMI), and the interference is mainly caused by space electromagnetic radiation and coupling of mutual ground. The experiments are separately carried out under the EMP environment with different repetitive frequency quantity and time interval. The results show that the two cases have impact on tube trigger, increasing repetitive frequency EMP quantity and reducing EMP interval both increase the probabilities of false trigger. Comparing with the theoretical analysis and the experiment results, it is concluded that this phenomenon is caused by repetitive frequency accumulation effect and high frequency component strengthen which leads to enhanced coupling.
An experiment in view of repetitive frequency electromagnetic pulse (EMP) interference, take the hydrogen thyratron trigger as research object, is carried out to study the interference of the hydrogen thyratron first grid and second grid under the condition of suspension and mutual ground. The results show that the two grids have intense electromagnetic interference (EMI), and the interference is mainly caused by space electromagnetic radiation and coupling of mutual ground. The experiments are separately carried out under the EMP environment with different repetitive frequency quantity and time interval. The results show that the two cases have impact on tube trigger, increasing repetitive frequency EMP quantity and reducing EMP interval both increase the probabilities of false trigger. Comparing with the theoretical analysis and the experiment results, it is concluded that this phenomenon is caused by repetitive frequency accumulation effect and high frequency component strengthen which leads to enhanced coupling.
2013,
25: 1861-1866.
doi: 10.3788/HPLPB20132507.1861
Abstract:
According to the field expression of arbitrary wire antennas obtained through the tensor method, this paper uses the mirror image method to give an analytical expression of the radiation field of impulse radiating antenna in time domain. The expression is then used to calculate the radiation fields of impulse radiating antenna applied to electromagnetic pulse simulator in time domain and the theoretical results are further compared with numerical ones. The results show that, the field waveforms calculated analytically are in good agreement with the numerical results; the effects of antenna parameters on antenna waveform can be easily observed by using analytical expressions, which can help to select appropriate values for parameters to achieve radiated field waveforms satisfying the standard requirements.
According to the field expression of arbitrary wire antennas obtained through the tensor method, this paper uses the mirror image method to give an analytical expression of the radiation field of impulse radiating antenna in time domain. The expression is then used to calculate the radiation fields of impulse radiating antenna applied to electromagnetic pulse simulator in time domain and the theoretical results are further compared with numerical ones. The results show that, the field waveforms calculated analytically are in good agreement with the numerical results; the effects of antenna parameters on antenna waveform can be easily observed by using analytical expressions, which can help to select appropriate values for parameters to achieve radiated field waveforms satisfying the standard requirements.
2013,
25: 1867-1872.
doi: 10.3788/HPLPB20132507.1867
Abstract:
Micro-electrodes with gaps of 5-40 micrometers were prepared by depositing 400-nm thick Al film on insulator using the micro-electro-mechanical system(MEMS) manufacturing process. Breakdown voltages of different electrode gaps under different pulse polarity and nanosecond pulse widths were measured on test samples. Moreover, the breakdown mechanism was discussed through comparing the observed results of samples after breakdown by use of scanning electron microscope(SEM) and the results of the same samples under DC. In conclusion, the breakdown voltage increases with the gap distance under nanosecond pulse, but the breakdown electric field descends sharply while the gap distance increases. Compared to the breakdown voltage under DC, pulse breakdown voltage is not too much higher, which is different from the results in the case of macro distances. Analyses show that the mechanism of the breakdown is the streamer theory, and the anode is melted layer by layer, while the cathode is sputtered with metal material.
Micro-electrodes with gaps of 5-40 micrometers were prepared by depositing 400-nm thick Al film on insulator using the micro-electro-mechanical system(MEMS) manufacturing process. Breakdown voltages of different electrode gaps under different pulse polarity and nanosecond pulse widths were measured on test samples. Moreover, the breakdown mechanism was discussed through comparing the observed results of samples after breakdown by use of scanning electron microscope(SEM) and the results of the same samples under DC. In conclusion, the breakdown voltage increases with the gap distance under nanosecond pulse, but the breakdown electric field descends sharply while the gap distance increases. Compared to the breakdown voltage under DC, pulse breakdown voltage is not too much higher, which is different from the results in the case of macro distances. Analyses show that the mechanism of the breakdown is the streamer theory, and the anode is melted layer by layer, while the cathode is sputtered with metal material.
2013,
25: 1873-1876.
doi: 10.3788/HPLPB20132507.1873
Abstract:
The pulsed power switching circuit is the basic guarantee of a reliable laser power supply. Parameters selection of the switching circuit directly influences the operating condition of thyristors and diodes, which is the basic condition to guarantee the long-term operating reliability of the laser power supply system. Simulation analysis of the switching circuit is carried out in this paper based on PSCAD software, and operating conditions of thyristors and diodes are focused on. This paper points out that the resistance-capacitance circuit parameters, the current-limiting resistance and synchronization performance of triggers have significant impact on the operating condition of thyristors and diodes. It can be determined by the simulation results that excess high current-rising-rate has caused the damage of thyristor gate and large reverse voltage has resulted in the edge breakdown of diode. Finally, an optimization scheme of circuit parameters is put forward.
The pulsed power switching circuit is the basic guarantee of a reliable laser power supply. Parameters selection of the switching circuit directly influences the operating condition of thyristors and diodes, which is the basic condition to guarantee the long-term operating reliability of the laser power supply system. Simulation analysis of the switching circuit is carried out in this paper based on PSCAD software, and operating conditions of thyristors and diodes are focused on. This paper points out that the resistance-capacitance circuit parameters, the current-limiting resistance and synchronization performance of triggers have significant impact on the operating condition of thyristors and diodes. It can be determined by the simulation results that excess high current-rising-rate has caused the damage of thyristor gate and large reverse voltage has resulted in the edge breakdown of diode. Finally, an optimization scheme of circuit parameters is put forward.
