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RSS2012 Vol. 24, No. 10
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2012,
24: 2269-2270.
doi: 10.3788/HPLPB20122410.2269
Abstract:
A Littrow external cavity was built to narrow the spectral linewidth of a diode laser to 0.16 nm by using a 2400 line/mm plane grating, with the center wavelength of the laser tunable. The laser was used as the pump source of the rubidium vapor laser. A chopper was employed to change the continuous laser to pulsed laser with the pulse width of 1 ms and the repetition rate of 100 Hz, then the laser was focused to a Rb vapor cell with the length of 8 mm which was filled with Methane at the pressure of 79 kPa. With the maximum peak power of the pulsed laser injected into the Rb cell is 1.84 W and the temperature of the cell is controlled at about 125 ℃, the linearly polarized fundamental mode Rb laser with the peak power of 17.5 mW is obtained.
A Littrow external cavity was built to narrow the spectral linewidth of a diode laser to 0.16 nm by using a 2400 line/mm plane grating, with the center wavelength of the laser tunable. The laser was used as the pump source of the rubidium vapor laser. A chopper was employed to change the continuous laser to pulsed laser with the pulse width of 1 ms and the repetition rate of 100 Hz, then the laser was focused to a Rb vapor cell with the length of 8 mm which was filled with Methane at the pressure of 79 kPa. With the maximum peak power of the pulsed laser injected into the Rb cell is 1.84 W and the temperature of the cell is controlled at about 125 ℃, the linearly polarized fundamental mode Rb laser with the peak power of 17.5 mW is obtained.
2012,
24: 2271-2276.
doi: 10.3788/HPLPB20122410.2271
Abstract:
Based on the research internal and overseas, the principle of the excimer pumped alkali laser (XPAL) is explained, and the advantages and disadvantages of the XPAL are analyzed. Taking into consideration the difficulties that the diode pumped alkali laser (DPAL) meets on its development, the ability to solve or avoid these difficulties of XPAL is also analyzed. By summing up the achievements of the XPAL, the possible further prospect is proposed. The XPAL is of possibility to improve the performance of the DPAL.
Based on the research internal and overseas, the principle of the excimer pumped alkali laser (XPAL) is explained, and the advantages and disadvantages of the XPAL are analyzed. Taking into consideration the difficulties that the diode pumped alkali laser (DPAL) meets on its development, the ability to solve or avoid these difficulties of XPAL is also analyzed. By summing up the achievements of the XPAL, the possible further prospect is proposed. The XPAL is of possibility to improve the performance of the DPAL.
2012,
24: 2277-2283.
doi: 10.3788/HPLPB20122410.2277
Abstract:
Megajoule high-power laser drivers are necessary to achieve the ignition of laser confinement fusion. The opto-mechanical structure is an important part of the high-power solid-state laser facility. The general structures of the National Ignition Facility(NIF) and Laser Megajoule(LMJ) are summarized and the structural characteristic of SG-Ⅲ laser facility is introduced. The structure characteristic and installation of the important opto-mechanical components are analyzed, and the total integration technology and the installation of A6 are summarized.
Megajoule high-power laser drivers are necessary to achieve the ignition of laser confinement fusion. The opto-mechanical structure is an important part of the high-power solid-state laser facility. The general structures of the National Ignition Facility(NIF) and Laser Megajoule(LMJ) are summarized and the structural characteristic of SG-Ⅲ laser facility is introduced. The structure characteristic and installation of the important opto-mechanical components are analyzed, and the total integration technology and the installation of A6 are summarized.
2012,
24: 2284-2286.
doi: 10.3788/HPLPB20122410.2284
Abstract:
The transmissivity and reflectivity of polarized light through Nd-glass are analyzed based on the Fresnel formula. The influence of the off-axis light in high power solid-laser facility on the isolation performance of main-amplifier system is discussed. The attitude of crystal in the small electro-optical switch is adjusted to compensate the depolarization loss due to beam rotating error,according to the mechanism that the off-axis light through the crystal of the switch will result in depolarization loss. Experimental results indicate that the system selectivity towards polarized light is not influenced by the small angle change of Nd-glass, and the isolation rate of main-amplifier system can be improved more than three times through the attitude adjustment.
The transmissivity and reflectivity of polarized light through Nd-glass are analyzed based on the Fresnel formula. The influence of the off-axis light in high power solid-laser facility on the isolation performance of main-amplifier system is discussed. The attitude of crystal in the small electro-optical switch is adjusted to compensate the depolarization loss due to beam rotating error,according to the mechanism that the off-axis light through the crystal of the switch will result in depolarization loss. Experimental results indicate that the system selectivity towards polarized light is not influenced by the small angle change of Nd-glass, and the isolation rate of main-amplifier system can be improved more than three times through the attitude adjustment.
2012,
24: 2287-2290.
doi: 10.3788/HPLPB20122410.2287
Abstract:
In order to study the surface thermal decomposition damage of millisecond pulse lasers irradiating GaAs at 0.53 m wavelength, a two-dimensional axisymmetric heat conduction model was established. Considering the temperature dependences of the thermophysical parameters, the transient temperature fields in the material were simulated by using the finite element method. The distributions of transient temperature fields and variation law with time have been obtained, and the curve of the thermal decomposition damage thresholds on the material surface was also given. Numerical results show that, heat conduction affects the whole process of millisecond pulsed laser interaction and its damage mechanism is mainly thermal effects. The temperature of the center is the highest on the irradiated surface, where it could be damaged by thermal decomposition first. With the increasing of laser energy density, the time of thermal decomposition damages occurrence would be advancing.
In order to study the surface thermal decomposition damage of millisecond pulse lasers irradiating GaAs at 0.53 m wavelength, a two-dimensional axisymmetric heat conduction model was established. Considering the temperature dependences of the thermophysical parameters, the transient temperature fields in the material were simulated by using the finite element method. The distributions of transient temperature fields and variation law with time have been obtained, and the curve of the thermal decomposition damage thresholds on the material surface was also given. Numerical results show that, heat conduction affects the whole process of millisecond pulsed laser interaction and its damage mechanism is mainly thermal effects. The temperature of the center is the highest on the irradiated surface, where it could be damaged by thermal decomposition first. With the increasing of laser energy density, the time of thermal decomposition damages occurrence would be advancing.
2012,
24: 2291-2295.
doi: 10.3788/HPLPB20122410.2291
Abstract:
An experimental system based on digital holographic interferometry is proposed for real-time high-precision micro-vibration measurement. Vibration information can be extracted directly and instantaneously from the hologram by using fast micro-vibration testing algorithm. As the received light of the proposed system is the scattered light, the proposed system approach no assumptions on object surface feature and receiving angles. The feasibility of the proposed system is demonstrated by using a vibrating object driven by standard sinusoidal signals. The result demonstrates that the measured amplitude can be output in real time (the processed time is about 0.11 ms). It also reveals that the measured amplitude from 550 to 2700 Hz is steady, with an output difference of 1.66%. The proposed system provides an effective way to quantitatively analyze the amplitude of micro-vibration.
An experimental system based on digital holographic interferometry is proposed for real-time high-precision micro-vibration measurement. Vibration information can be extracted directly and instantaneously from the hologram by using fast micro-vibration testing algorithm. As the received light of the proposed system is the scattered light, the proposed system approach no assumptions on object surface feature and receiving angles. The feasibility of the proposed system is demonstrated by using a vibrating object driven by standard sinusoidal signals. The result demonstrates that the measured amplitude can be output in real time (the processed time is about 0.11 ms). It also reveals that the measured amplitude from 550 to 2700 Hz is steady, with an output difference of 1.66%. The proposed system provides an effective way to quantitatively analyze the amplitude of micro-vibration.
2012,
24: 2296-2300.
doi: 10.3788/HPLPB20122410.2296
Abstract:
Based on the stitching method using global least squares and the image fusion method, the sub-aperture stitching interferometry method for continuous phase plates(CPPs) is established. The residual surface error calculated by correlative matching is used to evaluate the CPPs fabrication quality. Moreover, the measurement system is built using high precision dynamic interferometer. The numerical simulation and measurement are carried into execution for a CPP with 430 mm430 mm aperture. The results show that the root mean square(RMS) of residual surface error obtained by numerical simulation is only 0.005 nm and the experimental RMS of residual surface error is less than 5 nm. So these parameters can meet the demands of surface measurement and evaluation of large-aperture continuous phase plates, and the correctness and feasibility of this method are verified.
Based on the stitching method using global least squares and the image fusion method, the sub-aperture stitching interferometry method for continuous phase plates(CPPs) is established. The residual surface error calculated by correlative matching is used to evaluate the CPPs fabrication quality. Moreover, the measurement system is built using high precision dynamic interferometer. The numerical simulation and measurement are carried into execution for a CPP with 430 mm430 mm aperture. The results show that the root mean square(RMS) of residual surface error obtained by numerical simulation is only 0.005 nm and the experimental RMS of residual surface error is less than 5 nm. So these parameters can meet the demands of surface measurement and evaluation of large-aperture continuous phase plates, and the correctness and feasibility of this method are verified.
2012,
24: 2301-2305.
doi: 10.3788/HPLPB20122410.2301
Abstract:
A model for analyzing the polarization of linearly polarized light traveling through LiNbO3 crystal(LN crystal) cut at Brewster angle is presented，with the use of Jones calculus and Fresnel formulae. The relationship between the polarization state of transmitted light and voltage applied to LN crystal is given. The transmitted intensity of p-polarized light and of s-polarized light in different applied voltages is also analyzed. The experimental setup of Ho, Tm, Cr:YAG laser is established. There are three types of Q-switched lasers which include single LN crystal，the combination of LN crystal and LN slice placed at Brewster angle, and double LN crystals, respectively. The influence of voltage applied to LN crystal on the polarization state and energy of output radiation is then measured.
A model for analyzing the polarization of linearly polarized light traveling through LiNbO3 crystal(LN crystal) cut at Brewster angle is presented，with the use of Jones calculus and Fresnel formulae. The relationship between the polarization state of transmitted light and voltage applied to LN crystal is given. The transmitted intensity of p-polarized light and of s-polarized light in different applied voltages is also analyzed. The experimental setup of Ho, Tm, Cr:YAG laser is established. There are three types of Q-switched lasers which include single LN crystal，the combination of LN crystal and LN slice placed at Brewster angle, and double LN crystals, respectively. The influence of voltage applied to LN crystal on the polarization state and energy of output radiation is then measured.
2012,
24: 2306-2310.
doi: 10.3788/HPLPB20122410.2306
Abstract:
The 4-(9, 9-diethyl-2-(pyridin-4-yl)-9H-fluoren-7-yl) pyridine (DPFP) was synthesized via a Suzuki coupling reaction. The optical spectra properties of DPFP and DPFP-DNA-CTMA thin filmswere characterized by the measurements of the UV/VIS absorption spectrum and fluorescence spectrum. The amplified spontaneous emission (ASE) of the DPFP-DNA-CTMA thin film was studied experimentally by pumping of pulse laser with a wavelength of 355 nm. The result shows that the absorption peak is located at 333 nm and the fluorescence peaks of DPFP are 370 nm, 386 nm, 408 nm. The fluorescence spectrum of DPFP has the multi-peaks which are corresponding to the vibronic transitions from an excited state of S1 level to the ground state of S0 level. The ASE peaks of DPFP-DNA-CTMA thin films are located at 390 nm and 406 nm, and the threshold energy densities are 3.24 mJ/cm2 and 3.4 mJ/cm2, respectively. By adjusting the doped proportion of DPFP in DNA-CTMA, ASE can be realized at a specific wavelength.
The 4-(9, 9-diethyl-2-(pyridin-4-yl)-9H-fluoren-7-yl) pyridine (DPFP) was synthesized via a Suzuki coupling reaction. The optical spectra properties of DPFP and DPFP-DNA-CTMA thin filmswere characterized by the measurements of the UV/VIS absorption spectrum and fluorescence spectrum. The amplified spontaneous emission (ASE) of the DPFP-DNA-CTMA thin film was studied experimentally by pumping of pulse laser with a wavelength of 355 nm. The result shows that the absorption peak is located at 333 nm and the fluorescence peaks of DPFP are 370 nm, 386 nm, 408 nm. The fluorescence spectrum of DPFP has the multi-peaks which are corresponding to the vibronic transitions from an excited state of S1 level to the ground state of S0 level. The ASE peaks of DPFP-DNA-CTMA thin films are located at 390 nm and 406 nm, and the threshold energy densities are 3.24 mJ/cm2 and 3.4 mJ/cm2, respectively. By adjusting the doped proportion of DPFP in DNA-CTMA, ASE can be realized at a specific wavelength.
2012,
24: 2311-2317.
doi: 10.3788/HPLPB20122410.2311
Abstract:
The existing phase-unwrapping algorithms are analyzed and classified, aiming at solving the problem of under-sampling in wrapped-phase map. The least-square algorithm based on lateral shearing interferometry is studied. Four common phase-unwrapping algorithms are applied to the wrapped-phase map of Lygodium japonicum cell, which is obtained by image-plane digital holography recorded with spherical reference waves. The results show that the least-square algorithm based on discrete cosine transform and the pre-condition conjugate grads algorithm result in transfer of phase-unwrapping error in the under-sampled area;the quality-guided path following algorithm results in pull phenomenon and island area because of the residual point without recognition, and its processing is slow;the least-square algorithm based on lateral shearing interferometry has the best effect for dealing with the under-sampled wrapped-phase map, and its processing is the fastest.
The existing phase-unwrapping algorithms are analyzed and classified, aiming at solving the problem of under-sampling in wrapped-phase map. The least-square algorithm based on lateral shearing interferometry is studied. Four common phase-unwrapping algorithms are applied to the wrapped-phase map of Lygodium japonicum cell, which is obtained by image-plane digital holography recorded with spherical reference waves. The results show that the least-square algorithm based on discrete cosine transform and the pre-condition conjugate grads algorithm result in transfer of phase-unwrapping error in the under-sampled area;the quality-guided path following algorithm results in pull phenomenon and island area because of the residual point without recognition, and its processing is slow;the least-square algorithm based on lateral shearing interferometry has the best effect for dealing with the under-sampled wrapped-phase map, and its processing is the fastest.
2012,
24: 2318-2325.
doi: 10.3788/HPLPB20122410.2318
Abstract:
Some methods for simulating turbulent phase screen are summarized, and their characteristics are analyzed by calculating the phase structure function, decomposing phase screens into Zernike polynomials, and simulating laser propagation in the atmosphere. Through analyzing, it is found that, the turbulent high-frequency components are well contained by those phase screens simulated by the FFT method, but the low-frequency components are little contained. The low-frequency components are well contained by screens simulated by Zernike method, but the high-frequency components are not contained enough. The high-frequency components contained will be improved by increasing the order of the Zernike polynomial, but they mainly lie in the edge-area. Compared with the two methods above, the fractal method is a better method to simulate turbulent phase screens. According to the radius of the focal spot and the variance of the focal spot jitter, there are limitations in the methods except the fractal method. Combining the FFT and Zernike method or combining the FFT method and self-similar theory to simulate turbulent phase screens is an effective and appropriate way. In general, the fractal method is probably the best way.
Some methods for simulating turbulent phase screen are summarized, and their characteristics are analyzed by calculating the phase structure function, decomposing phase screens into Zernike polynomials, and simulating laser propagation in the atmosphere. Through analyzing, it is found that, the turbulent high-frequency components are well contained by those phase screens simulated by the FFT method, but the low-frequency components are little contained. The low-frequency components are well contained by screens simulated by Zernike method, but the high-frequency components are not contained enough. The high-frequency components contained will be improved by increasing the order of the Zernike polynomial, but they mainly lie in the edge-area. Compared with the two methods above, the fractal method is a better method to simulate turbulent phase screens. According to the radius of the focal spot and the variance of the focal spot jitter, there are limitations in the methods except the fractal method. Combining the FFT and Zernike method or combining the FFT method and self-similar theory to simulate turbulent phase screens is an effective and appropriate way. In general, the fractal method is probably the best way.
2012,
24: 2324-2330.
doi: 10.3788/HPLPB20122410.2325
Abstract:
The optical crosstalk of MCT infrared focal plane arrays is studied in a systematic way. Considering detectors different structure and material parameters, including the external optical structure, temperature, pixel size, epitaxial thickness, minority carrier lifetime, and absorption coefficient, the amplitude of optical crosstalk are calculated. Results show that the thickness of substrates epitaxial layer in the internal structure and the vacuum layer in the external optical structure are the major influencing factors for the amplitude of optical crosstalk.
The optical crosstalk of MCT infrared focal plane arrays is studied in a systematic way. Considering detectors different structure and material parameters, including the external optical structure, temperature, pixel size, epitaxial thickness, minority carrier lifetime, and absorption coefficient, the amplitude of optical crosstalk are calculated. Results show that the thickness of substrates epitaxial layer in the internal structure and the vacuum layer in the external optical structure are the major influencing factors for the amplitude of optical crosstalk.
2012,
24: 2331-2334.
doi: 10.3788/HPLPB20122410.2331
Abstract:
The influence of relative parameters, such as the focal length of the convergence lens and the distance between the convergence lens and the axicon, on the propagation distance of long distance diffraction-free beam generated by two axicons is analyzed using ray-tracing method. Numerical simulation is carried out with Mathcad. The results show that, while other conditions are invariable, the propagation distance of long distance diffraction-free beam decreases as the focal length of the convergence lens increases, and rises with the increasing of the distance between the convergence lens and the axicon. The theory is verified by experiment, and the experimental results are consistent with theoretical analysis.
The influence of relative parameters, such as the focal length of the convergence lens and the distance between the convergence lens and the axicon, on the propagation distance of long distance diffraction-free beam generated by two axicons is analyzed using ray-tracing method. Numerical simulation is carried out with Mathcad. The results show that, while other conditions are invariable, the propagation distance of long distance diffraction-free beam decreases as the focal length of the convergence lens increases, and rises with the increasing of the distance between the convergence lens and the axicon. The theory is verified by experiment, and the experimental results are consistent with theoretical analysis.
2012,
24: 2335-2337.
doi: 10.3788/HPLPB20122410.2335
Abstract:
An experimental study on protons from a 7 m thick copper foil target irradiated by femtosecond laser pulses has been carried out. In the SILEX-Ⅰ femtosecond laser device, the proton energy spectra are measured at the different laser energies and laser power densities and at the same pulse width of 30 fs. Results show that the protons are emitted in the normal direction of the target back and have a certain cut-off energy. Along with the increase of the proton energy, the proton beams exponentially decay. For the same 7 m thick Cu target, the greater the laser energy is, the stronger the proton beam are. With the increase of the laser power density, the cut-off energy of protons increases.
An experimental study on protons from a 7 m thick copper foil target irradiated by femtosecond laser pulses has been carried out. In the SILEX-Ⅰ femtosecond laser device, the proton energy spectra are measured at the different laser energies and laser power densities and at the same pulse width of 30 fs. Results show that the protons are emitted in the normal direction of the target back and have a certain cut-off energy. Along with the increase of the proton energy, the proton beams exponentially decay. For the same 7 m thick Cu target, the greater the laser energy is, the stronger the proton beam are. With the increase of the laser power density, the cut-off energy of protons increases.
2012,
24: 2338-2342.
doi: 10.3788/HPLPB20122410.2338
Abstract:
Influence of cleaning process on laser-induced damage threshold of polarizers was studied. Nomarski microscope was used to inspect the cleaned substrate surface, scanning electron microscope combined with focus ion beam technologies were used to characterize the damage morphologies of polarizer. The initiators that trigger laser damage were correlated with cleaning process. Proper cleaning process resulted in fewer residual particles and nodules in the prepared polarizer, which increased the laser induced damage threshold (LIDT) for S-polarization. Moreover, absorption peak of substrates became lower and sharper when surface contaminations were removed, which improved the LIDT of P-polarization. In conclusion, cleaning is an effective way to increase LIDT of polarizers.
Influence of cleaning process on laser-induced damage threshold of polarizers was studied. Nomarski microscope was used to inspect the cleaned substrate surface, scanning electron microscope combined with focus ion beam technologies were used to characterize the damage morphologies of polarizer. The initiators that trigger laser damage were correlated with cleaning process. Proper cleaning process resulted in fewer residual particles and nodules in the prepared polarizer, which increased the laser induced damage threshold (LIDT) for S-polarization. Moreover, absorption peak of substrates became lower and sharper when surface contaminations were removed, which improved the LIDT of P-polarization. In conclusion, cleaning is an effective way to increase LIDT of polarizers.
2012,
24: 2343-2346.
doi: 10.3788/HPLPB20122410.2343
Abstract:
A self-designed micro-tube gas-filling system was used to fill cryogenic targets with deuterium gas in normal temperature. The relationships between difference of gas pressure at the two ends of gas-filling tube and tube length, gas-filling rate and gas-filling time were studied. The results show that the gas-pressure difference first increases and ultimately decreases tozero, The time required for gas pressure equilibrium tends to be shorter when gas filling tube length decreases and gas-filling rate increases. The experimental results are in good agreement with the prediction on the basis of the Hagen-Poiseuille equation.
A self-designed micro-tube gas-filling system was used to fill cryogenic targets with deuterium gas in normal temperature. The relationships between difference of gas pressure at the two ends of gas-filling tube and tube length, gas-filling rate and gas-filling time were studied. The results show that the gas-pressure difference first increases and ultimately decreases tozero, The time required for gas pressure equilibrium tends to be shorter when gas filling tube length decreases and gas-filling rate increases. The experimental results are in good agreement with the prediction on the basis of the Hagen-Poiseuille equation.
2012,
24: 2347-2350.
doi: 10.3788/HPLPB20122410.2347
Abstract:
X-ray transmission gratings with high line-density are key components of various high-resolution spectrometers. X-rays transmission gratings with 5000 l/mm are needed to diffract X-ray at 2.0-5.0 keV. To obtain the absolute efficiency of the 5000 l/mm gratings made domestically, the intensity ratio of diffraction peaks was experimentally measured for different energy X-rays radiated from the synchrotron radiation source. The duty cycle fitted by measured data was consistent with that obtained by the electron scanning microscope. Finally, the absolute diffraction efficiency was calculated via the rectangle cross-section model.
X-ray transmission gratings with high line-density are key components of various high-resolution spectrometers. X-rays transmission gratings with 5000 l/mm are needed to diffract X-ray at 2.0-5.0 keV. To obtain the absolute efficiency of the 5000 l/mm gratings made domestically, the intensity ratio of diffraction peaks was experimentally measured for different energy X-rays radiated from the synchrotron radiation source. The duty cycle fitted by measured data was consistent with that obtained by the electron scanning microscope. Finally, the absolute diffraction efficiency was calculated via the rectangle cross-section model.
2012,
24: 2351-2354.
doi: 10.3788/HPLPB20122410.2351
Abstract:
Soft-X-ray spectrometers are used in diagnosis of the equivalent radiation temperature of hohlraum in indirectly driven inertial confinement fusion experiments. Uncertainties of the soft-X-ray optical elements and electronic devices of the spectrometer, and the recovery methods are determined, which influence the measurement of the radiation temperature. The uncertainty analysis method based on Monte-Carlo sampling is implemented and uncertainty of the radiation temperature including all kinds of uncertainty factors is obtained. The alignment of signals from different detection channels of the multi-channel spectrometer is analyzed separately, which proves to be a large uncertainty source.
Soft-X-ray spectrometers are used in diagnosis of the equivalent radiation temperature of hohlraum in indirectly driven inertial confinement fusion experiments. Uncertainties of the soft-X-ray optical elements and electronic devices of the spectrometer, and the recovery methods are determined, which influence the measurement of the radiation temperature. The uncertainty analysis method based on Monte-Carlo sampling is implemented and uncertainty of the radiation temperature including all kinds of uncertainty factors is obtained. The alignment of signals from different detection channels of the multi-channel spectrometer is analyzed separately, which proves to be a large uncertainty source.
2012,
24: 2355-2359.
doi: 10.3788/HPLPB20122410.2355
Abstract:
In the hohlraum of laser indirect-drive inertial confinement fusion (ICF), hydrodynamic moving processes of radiation-ablated high-Z plasma have great influence on laser injection efficiency, radiation uniformity and measurement of the hohlraum radiation temperature at the diagnosis hole (DH). To study the plasma filling in the DH, using laser-produced X-ray to heat low-Z foam-tamped high-Z gold DH, and using laser-irradiated Ti disk to generate 2-5 keV high and narrow energy X-ray as the intense backlighter source, the plasma movement in a hole was measured by an X-ray framing camera(XFC). A quantificational measuring method for the areal density distribution and evolution of plasma in a hole was studied.
In the hohlraum of laser indirect-drive inertial confinement fusion (ICF), hydrodynamic moving processes of radiation-ablated high-Z plasma have great influence on laser injection efficiency, radiation uniformity and measurement of the hohlraum radiation temperature at the diagnosis hole (DH). To study the plasma filling in the DH, using laser-produced X-ray to heat low-Z foam-tamped high-Z gold DH, and using laser-irradiated Ti disk to generate 2-5 keV high and narrow energy X-ray as the intense backlighter source, the plasma movement in a hole was measured by an X-ray framing camera(XFC). A quantificational measuring method for the areal density distribution and evolution of plasma in a hole was studied.
2012,
24: 2360-2364.
doi: 10.3788/HPLPB20122410.2360
Abstract:
The quantitative characterization of temporal response and electric properties of mechanical shutter of optical CCD has been experimentally studied, whose results can be used as database to guide setup parameters of the CCD shutter system. A real-time checking system to monitor the status of the mechanical shutter has also been developed, which could improve the experimental reliability in the application of CCD.
The quantitative characterization of temporal response and electric properties of mechanical shutter of optical CCD has been experimentally studied, whose results can be used as database to guide setup parameters of the CCD shutter system. A real-time checking system to monitor the status of the mechanical shutter has also been developed, which could improve the experimental reliability in the application of CCD.
2012,
24: 2365-2370.
doi: 10.3788/HPLPB20122410.2365
Abstract:
To investigate the deuterium permeation properties of hollow glass microspheres (HGMs) for inertial confinement fusion (ICF) targets, HGMs with different initial glass composition were fabricated by dried gel method under different atmosphere compositions in the furnace, temperatures, and lengths of refining zone. The permeability of HGMs with different wall-thicknesses to deuterium gas under ambient condition was tested. The results show that when the refining temperature is lower than 1400 ℃, the initial glass composition has notable effects on the deuterium-gas permeability of HGMs. However, the volatilization rates of alkali oxides in liquid glass bubbles increase with the temperature and the length of the refining zone, consequently, the permeability coefficients of HGMs made with different initial glass compositions increase and gradually approach to that of silica glass. With the total gas pressure unchanged, increasing the volume ratio of helium gas to argon gas in the furnace can enhance the permeability of HGMs. The permeability coefficient of HGMs to deuterium gas decreases with the increasing of the HGMs wall thickness.
To investigate the deuterium permeation properties of hollow glass microspheres (HGMs) for inertial confinement fusion (ICF) targets, HGMs with different initial glass composition were fabricated by dried gel method under different atmosphere compositions in the furnace, temperatures, and lengths of refining zone. The permeability of HGMs with different wall-thicknesses to deuterium gas under ambient condition was tested. The results show that when the refining temperature is lower than 1400 ℃, the initial glass composition has notable effects on the deuterium-gas permeability of HGMs. However, the volatilization rates of alkali oxides in liquid glass bubbles increase with the temperature and the length of the refining zone, consequently, the permeability coefficients of HGMs made with different initial glass compositions increase and gradually approach to that of silica glass. With the total gas pressure unchanged, increasing the volume ratio of helium gas to argon gas in the furnace can enhance the permeability of HGMs. The permeability coefficient of HGMs to deuterium gas decreases with the increasing of the HGMs wall thickness.
2012,
24: 2371-2374.
doi: 10.3788/HPLPB20122410.2371
Abstract:
In order to improve the lubrication of movement mechanism in final optics assembly, the plasma immersion ion implantation (PIII) technology is used to modify mechanical properties of work pieces with complex shape. The combination of suitable parameters can largely increase the hardness and wear resistance of material surfaces. The verification test was made by modifying the mechanical properties of the bearing inner race and bearing outer ring. Furthermore, the dimensional accuracy and the surface roughness of sample work pieces modified by PIII technology can maintain consistence with those of untreated pieces. The work sufficiently certificates that the PIII technology can amend the mechanical properties of work pieces and elongate the life length of movement mechanism kinematic accuracy.
In order to improve the lubrication of movement mechanism in final optics assembly, the plasma immersion ion implantation (PIII) technology is used to modify mechanical properties of work pieces with complex shape. The combination of suitable parameters can largely increase the hardness and wear resistance of material surfaces. The verification test was made by modifying the mechanical properties of the bearing inner race and bearing outer ring. Furthermore, the dimensional accuracy and the surface roughness of sample work pieces modified by PIII technology can maintain consistence with those of untreated pieces. The work sufficiently certificates that the PIII technology can amend the mechanical properties of work pieces and elongate the life length of movement mechanism kinematic accuracy.
2012,
24: 2375-2380.
doi: 10.3788/HPLPB20122410.2375
Abstract:
A novel adjusting target mechanism of three-dimensional attitude is presented according to the characteristics of the target transport subsystem in inertial confinement fusion (ICF). The mechanism consists of a tangent mechanism adjusting rotation angle and a set of orthogonal tangent mechanism adjusting two-dimensional deflection angles. The structural parameters of the adjusting target mechanism are analyzed according to principle errors, structure errors and motion errors of following. The analysis results indicate that the system error of the adjusting target mechanism is influenced by the displacement of the linear actuators, the actuator ball radius, the working radius of the tangent mechanism, the angle error of the inclined installation hole, the centralization error of the actuators, the orthogonal error of the two tangent mechanisms, and the angle errors of the inclined target rod and inclined rotation shaft. The errors of the inclined target rod and inclined rotation shaft are the two greatest impact factors, the spherical contact error is the next. By means of precise assembly and control system compensation, the accuracy of the adjusting target mechanism can be less than 0.1 mrad.
A novel adjusting target mechanism of three-dimensional attitude is presented according to the characteristics of the target transport subsystem in inertial confinement fusion (ICF). The mechanism consists of a tangent mechanism adjusting rotation angle and a set of orthogonal tangent mechanism adjusting two-dimensional deflection angles. The structural parameters of the adjusting target mechanism are analyzed according to principle errors, structure errors and motion errors of following. The analysis results indicate that the system error of the adjusting target mechanism is influenced by the displacement of the linear actuators, the actuator ball radius, the working radius of the tangent mechanism, the angle error of the inclined installation hole, the centralization error of the actuators, the orthogonal error of the two tangent mechanisms, and the angle errors of the inclined target rod and inclined rotation shaft. The errors of the inclined target rod and inclined rotation shaft are the two greatest impact factors, the spherical contact error is the next. By means of precise assembly and control system compensation, the accuracy of the adjusting target mechanism can be less than 0.1 mrad.
2012,
24: 2381-2385.
doi: 10.3788/HPLPB20122410.2381
Abstract:
This paper studies the ablation of aluminum foil (50 m thickness) under various conditions by observing the morphology of ablation caves and by analyzing the relationship of the photodiode signal of transmitted light and the number of pulses to penetration. In order to obtain better condition of ablation, several variable quantities in the experiment are tested, which are the pulse energy, position of laser focus relative to sample surface, ambient pressure and pulse shape. Preferable results are obtained by using some specific shaped pulses to ablate samples, compared to those obtained with transform-limited pulses, which means laser pulse shaping technology can be of important usage and application in micromachining metal material.
This paper studies the ablation of aluminum foil (50 m thickness) under various conditions by observing the morphology of ablation caves and by analyzing the relationship of the photodiode signal of transmitted light and the number of pulses to penetration. In order to obtain better condition of ablation, several variable quantities in the experiment are tested, which are the pulse energy, position of laser focus relative to sample surface, ambient pressure and pulse shape. Preferable results are obtained by using some specific shaped pulses to ablate samples, compared to those obtained with transform-limited pulses, which means laser pulse shaping technology can be of important usage and application in micromachining metal material.
2012,
24: 2386-2390.
doi: 10.3788/HPLPB20122410.2386
Abstract:
An implementation method of large-format framing image tube is proposed. An electrostatic focusing image tube with large input photocathode and small output image is designed. Coupling with common small-format microchannel plate (MCP) gated framing unit, image gating and enhancement can be realized. Compared to the tube with large-format MCP, this kind of framing tube avoids the high manufacturing cost of lager-format MCP and overcomes the transmission voltage loss and gain uniformity caused by long micro strips. The framing image tube has an effective input working diameter of 100 mm, an output image diameter of 40 mm, and a magnification of 0.4. The centre spatial resolution is 14.4 lp/mm, the marginal spatial resolution is 11.2 lp/mm, and the geometric distortion is less than 15%. The framing characteristic is determined by the MCP framing unit. This method is an effective way for expanding the work area of framing image tubes.
An implementation method of large-format framing image tube is proposed. An electrostatic focusing image tube with large input photocathode and small output image is designed. Coupling with common small-format microchannel plate (MCP) gated framing unit, image gating and enhancement can be realized. Compared to the tube with large-format MCP, this kind of framing tube avoids the high manufacturing cost of lager-format MCP and overcomes the transmission voltage loss and gain uniformity caused by long micro strips. The framing image tube has an effective input working diameter of 100 mm, an output image diameter of 40 mm, and a magnification of 0.4. The centre spatial resolution is 14.4 lp/mm, the marginal spatial resolution is 11.2 lp/mm, and the geometric distortion is less than 15%. The framing characteristic is determined by the MCP framing unit. This method is an effective way for expanding the work area of framing image tubes.
2012,
24: 2391-2399.
doi: 10.3788/HPLPB20122410.2391
Abstract:
A robust design method of multilayer optical coatings based on optimal control of thin-film errors sensitivity is presented in this paper. An analytical calculation model of robust design merit function under statistic layer parameters errors is established. It can avoid the computation errors of robust design merit function caused by limited number of layer parameters errors simulation sample,and can avoid the long time consumption when large number of layer parameters errors simulation samples is used. The effectiveness of the robust design method in thin film errors tolerance control is demonstrated by application to a variety of optical coatings,such as the broadband antireflection coating,neutral beam splitter and linear ramp transmittance filter. Results show that the robust design method owns an inherent fast computation characteristic and the designed film is insensitive to the monitoring thickness errors in deposition process. This method is of practical significance to improving the mass production yields and repetitive production of high quality optical coatings.
A robust design method of multilayer optical coatings based on optimal control of thin-film errors sensitivity is presented in this paper. An analytical calculation model of robust design merit function under statistic layer parameters errors is established. It can avoid the computation errors of robust design merit function caused by limited number of layer parameters errors simulation sample,and can avoid the long time consumption when large number of layer parameters errors simulation samples is used. The effectiveness of the robust design method in thin film errors tolerance control is demonstrated by application to a variety of optical coatings,such as the broadband antireflection coating,neutral beam splitter and linear ramp transmittance filter. Results show that the robust design method owns an inherent fast computation characteristic and the designed film is insensitive to the monitoring thickness errors in deposition process. This method is of practical significance to improving the mass production yields and repetitive production of high quality optical coatings.
2012,
24: 2400-2404.
doi: 10.3788/HPLPB20122410.2400
Abstract:
Thermogravimetric analysis was performed to obtain thermal degradation kinetics of poly-alpha-methylstyrene(PAMS) at different heating rates in nitrogen. Several conclusions can be obtained from the experimental. Firstly, the degradation of PAMS is a one step reaction. Secondly, when the heating rate is 10 ℃/min , the main degradation temperature ranges from 302.79 ℃ to 343.10 ℃, and maximum thermal weight loss rate temperature is 325.85 ℃. The main degradation temperature ranges tend to higher temperature with increasing of heating rate. The kinetic parameters of thermal decomposition of PAMS were calculated using Kissinger method, Flynn-Wall-Ozawa method, and Coats-Redfern method.
Thermogravimetric analysis was performed to obtain thermal degradation kinetics of poly-alpha-methylstyrene(PAMS) at different heating rates in nitrogen. Several conclusions can be obtained from the experimental. Firstly, the degradation of PAMS is a one step reaction. Secondly, when the heating rate is 10 ℃/min , the main degradation temperature ranges from 302.79 ℃ to 343.10 ℃, and maximum thermal weight loss rate temperature is 325.85 ℃. The main degradation temperature ranges tend to higher temperature with increasing of heating rate. The kinetic parameters of thermal decomposition of PAMS were calculated using Kissinger method, Flynn-Wall-Ozawa method, and Coats-Redfern method.
2012,
24: 2405-2410.
doi: 10.3788/HPLPB20122410.2405
Abstract:
Anisotropic focus electrodes and electric quadrupole lenses have been used to make a novel streak tube, whose physical temporal dispersion and edge spatial resolution are 0.38 ps and 56 lp/mm respectively. A modular remote-controllable system has been designed to control high voltage supply, environmental monitoring, deflection voltage switch and camera work mode. The Nd:YLF 8 ps pulsed laser was used to calibrate the performance index of the streak camera. The streak static and dynamic spatial resolution are 35 lp/mm and 25 lp/mm respectively. The dynamic range more than 950∶1 and time resolution of 8 ps are reached. Furthermore, the magnifications in slit and scanning direction can be adjusted respectively. When the camera is coupled with KB microscope, it is convenient to select amplification needed.
Anisotropic focus electrodes and electric quadrupole lenses have been used to make a novel streak tube, whose physical temporal dispersion and edge spatial resolution are 0.38 ps and 56 lp/mm respectively. A modular remote-controllable system has been designed to control high voltage supply, environmental monitoring, deflection voltage switch and camera work mode. The Nd:YLF 8 ps pulsed laser was used to calibrate the performance index of the streak camera. The streak static and dynamic spatial resolution are 35 lp/mm and 25 lp/mm respectively. The dynamic range more than 950∶1 and time resolution of 8 ps are reached. Furthermore, the magnifications in slit and scanning direction can be adjusted respectively. When the camera is coupled with KB microscope, it is convenient to select amplification needed.
2012,
24: 2411-2414.
doi: 10.3788/HPLPB20122410.2411
Abstract:
A compact coplanar-waveguide-fed ultra-wideband antenna with triple band-notched characteristics is designed. The antenna uses rectangle patches as a radiation unit. By etching nested inverted U-shaped, circular arc shaped and S-shaped slots, band-notched function is achieved in the three subbands of 3.3-3.7 GHz for worldwide interoperability for microwave access(WiMAX), 5.150-5.825 GHz for wireless local area networks(WLAN) and 7.25-7.75 GHz for the downlink of X-band satellite communication systems. The result shows that the voltage standing wave ratio(VSWR) of the antenna in the band of 3.1-12.0 GHz is less than 2. The proposed antenna has a stable gain and almost omnidirectional radiation patterns.
A compact coplanar-waveguide-fed ultra-wideband antenna with triple band-notched characteristics is designed. The antenna uses rectangle patches as a radiation unit. By etching nested inverted U-shaped, circular arc shaped and S-shaped slots, band-notched function is achieved in the three subbands of 3.3-3.7 GHz for worldwide interoperability for microwave access(WiMAX), 5.150-5.825 GHz for wireless local area networks(WLAN) and 7.25-7.75 GHz for the downlink of X-band satellite communication systems. The result shows that the voltage standing wave ratio(VSWR) of the antenna in the band of 3.1-12.0 GHz is less than 2. The proposed antenna has a stable gain and almost omnidirectional radiation patterns.
2012,
24: 2415-2419.
doi: 10.3788/HPLPB20122410.2415
Abstract:
An X-band dual-frequency coaxial relativistic backward-wave oscillator with a resonant reflector is proposed in this paper. The 2.5-D fully electromagnetic particle-in-cell code simulation results indicate that, with an electron beam of 520 kV and 8.5 kA guided by an axial magnetic field of 2.35 T, an average power of 1.35 GW with power conversion efficiency of 30.5% is obtained and the two dominant frequencies are 9.41 GHz and 10.29 GHz, respectively. Furthermore, the dual-frequency spectrum and the smaller dominant frequency demonstrate a periodic-like dependence on the drift waveguide, and a frequency agility bandwidth of about 400 MHz is acquired.
An X-band dual-frequency coaxial relativistic backward-wave oscillator with a resonant reflector is proposed in this paper. The 2.5-D fully electromagnetic particle-in-cell code simulation results indicate that, with an electron beam of 520 kV and 8.5 kA guided by an axial magnetic field of 2.35 T, an average power of 1.35 GW with power conversion efficiency of 30.5% is obtained and the two dominant frequencies are 9.41 GHz and 10.29 GHz, respectively. Furthermore, the dual-frequency spectrum and the smaller dominant frequency demonstrate a periodic-like dependence on the drift waveguide, and a frequency agility bandwidth of about 400 MHz is acquired.
2012,
24: 2420-2424.
doi: 10.3788/HPLPB20122410.2420
Abstract:
The theory of the connector and the subsection modeling was propounded. For the disadvantages of the magnetically insulated line oscillator (MILO) and antenna designed separately, a kind of system simulation method was proposed, and was completed by using finite-difference time-domain and particle-in-cell algorithm and message passing interface. In the simulation, a phenomenon was found that a amount of power from the antenna reflected into MILO, and the effective method to reduce the impact of reflected power was got. Results show that metal strut rods could filter out DC power, and the maxium output power of the antenna is 6.2 GW, which also proves the validity of the method.
The theory of the connector and the subsection modeling was propounded. For the disadvantages of the magnetically insulated line oscillator (MILO) and antenna designed separately, a kind of system simulation method was proposed, and was completed by using finite-difference time-domain and particle-in-cell algorithm and message passing interface. In the simulation, a phenomenon was found that a amount of power from the antenna reflected into MILO, and the effective method to reduce the impact of reflected power was got. Results show that metal strut rods could filter out DC power, and the maxium output power of the antenna is 6.2 GW, which also proves the validity of the method.
2012,
24: 2425-2429.
doi: 10.3788/HPLPB20122410.2425
Abstract:
Negative hydrogen (H-) ion beam extraction measurement experiment was conducted in the Penning ion source developed by Institute of Fluid Physics. The single electrode, double electrode and tri-electrode extraction methods were applied for the preliminary experiment. The experimental beam intensities are much higher than the theoretical calculation result of space charge limited flow. Thus, we present a new method called beam measurement of electrical shielding box. This paper describes the basic principle of dc beam measurement of electrical shielding box method, the CST numerical simulation of the beam trajectory and the experimental results of beam measurement extraction. Employing the V3/2 law of space charge limited flow to fit curve, the beam current will reach 4 mA when the extraction voltage is loaded to 40 kV.
Negative hydrogen (H-) ion beam extraction measurement experiment was conducted in the Penning ion source developed by Institute of Fluid Physics. The single electrode, double electrode and tri-electrode extraction methods were applied for the preliminary experiment. The experimental beam intensities are much higher than the theoretical calculation result of space charge limited flow. Thus, we present a new method called beam measurement of electrical shielding box. This paper describes the basic principle of dc beam measurement of electrical shielding box method, the CST numerical simulation of the beam trajectory and the experimental results of beam measurement extraction. Employing the V3/2 law of space charge limited flow to fit curve, the beam current will reach 4 mA when the extraction voltage is loaded to 40 kV.
2012,
24: 2430-2434.
doi: 10.3788/HPLPB20122410.2430
Abstract:
The beam profile measurement of BEPCⅡ storage ring by visible synchrotron light imaging method is illustrated. The optics details and precise measurement of the magnification by the method are elaborated. Approaches for possible arbitrary error and system errors are suggested, such as dealing with the diffraction error by using point spread function (PSF) deconvolution, which are also available for other similar measurement like X-ray pinhole camera. The measurement results agree well with the spatial interferometer method data.
The beam profile measurement of BEPCⅡ storage ring by visible synchrotron light imaging method is illustrated. The optics details and precise measurement of the magnification by the method are elaborated. Approaches for possible arbitrary error and system errors are suggested, such as dealing with the diffraction error by using point spread function (PSF) deconvolution, which are also available for other similar measurement like X-ray pinhole camera. The measurement results agree well with the spatial interferometer method data.
2012,
24: 2435-2440.
doi: 10.3788/HPLPB20122410.2435
Abstract:
In order to investigate the one-dimensional beam ordering in HIRFL-CSR, the ion beam of 58Ni19+ with the energy of 6.39 MeV/u was accumulated in the main ring of HIRFL-CSR with the help of electron cooling. The maximum accumulated ion beam intensity in the 10 seconds was measured, and the lifetime of ion beams was measured. The momentum spread of the ion beam varying with the particle number was measured during the ion beam decay, the power exponent was derived from these data, in additional, the momentum spread in the case of a constant particle number was plotted with the angle between ion and electron beams and electron beam profile. The oscillation and shift of the central frequency of the ion beam were observed during the experiments when the angle was large.
In order to investigate the one-dimensional beam ordering in HIRFL-CSR, the ion beam of 58Ni19+ with the energy of 6.39 MeV/u was accumulated in the main ring of HIRFL-CSR with the help of electron cooling. The maximum accumulated ion beam intensity in the 10 seconds was measured, and the lifetime of ion beams was measured. The momentum spread of the ion beam varying with the particle number was measured during the ion beam decay, the power exponent was derived from these data, in additional, the momentum spread in the case of a constant particle number was plotted with the angle between ion and electron beams and electron beam profile. The oscillation and shift of the central frequency of the ion beam were observed during the experiments when the angle was large.
2012,
24: 2441-2446.
doi: 10.3788/HPLPB20122410.2441
Abstract:
Orientation-averaged optical properties of natural aerosol aggregates were analyzed by using discrete dipole approximation (DDA) for the effective radius in the range of 0.01 to 2 m with the corresponding size parameter from 0.1 to 23 for the wavelength of 0.55 m. Effects of the composition and morphology on the optical properties were also investigated. The composition show small influence on the extinction-efficiency factor in Mie scattering region, scattering-and backscattering-efficiency factors, and asymmetry factor, but great on the extinction efficiency factor in Rayleigh scattering region and absorption-efficiency factor. The extinction-efficiency factor with the size parameter from 9 to 23 and asymmetry factor with the size parameter below 2.3 are almost independent of the natural aerosol composition. The extinction-, absorption-, scattering-, and backscattering-efficiency factors with the size parameter below 0.7 are irrespective of the aggregate morphologly. The intrinsic symmetry and discontinuity of the normal direction of the particle surface have obvious effects on the scattering properties for the size parameter above 4.6. Furthermore, the scattering phase functions of natural aerosol aggregates are enhanced at the backscattering direction (opposition effect) for large size parameters in the range of Mie scattering.
Orientation-averaged optical properties of natural aerosol aggregates were analyzed by using discrete dipole approximation (DDA) for the effective radius in the range of 0.01 to 2 m with the corresponding size parameter from 0.1 to 23 for the wavelength of 0.55 m. Effects of the composition and morphology on the optical properties were also investigated. The composition show small influence on the extinction-efficiency factor in Mie scattering region, scattering-and backscattering-efficiency factors, and asymmetry factor, but great on the extinction efficiency factor in Rayleigh scattering region and absorption-efficiency factor. The extinction-efficiency factor with the size parameter from 9 to 23 and asymmetry factor with the size parameter below 2.3 are almost independent of the natural aerosol composition. The extinction-, absorption-, scattering-, and backscattering-efficiency factors with the size parameter below 0.7 are irrespective of the aggregate morphologly. The intrinsic symmetry and discontinuity of the normal direction of the particle surface have obvious effects on the scattering properties for the size parameter above 4.6. Furthermore, the scattering phase functions of natural aerosol aggregates are enhanced at the backscattering direction (opposition effect) for large size parameters in the range of Mie scattering.
2012,
24: 2447-2450.
doi: 10.3788/HPLPB20122410.2447
Abstract:
A method for measuring the gating time of the gated image intensifier by using a CCD to record the time delay produced by the ultra-fast laser pulse and the fiber array is presented. The feasibility of the method is analyzed, and the measurement system is built. The gating time of the gated image intensifier for the ultra-high-speed photoelectronic framing camera is measured and the experimental images corresponding to the gating time of 10, 20, 30 and 50 ns are obtained. Compared with the results corresponding to the gating time of 12.50, 18.50, 28.75 ns and 48.6 ns, obtained with the high-voltage pulses method, the proposed method greatly improves the measuring accuracy. The method has great significance in calibrating the exposure time of the gated image intensifier and the ultra-high-speed photoelectronic framing camera.
A method for measuring the gating time of the gated image intensifier by using a CCD to record the time delay produced by the ultra-fast laser pulse and the fiber array is presented. The feasibility of the method is analyzed, and the measurement system is built. The gating time of the gated image intensifier for the ultra-high-speed photoelectronic framing camera is measured and the experimental images corresponding to the gating time of 10, 20, 30 and 50 ns are obtained. Compared with the results corresponding to the gating time of 12.50, 18.50, 28.75 ns and 48.6 ns, obtained with the high-voltage pulses method, the proposed method greatly improves the measuring accuracy. The method has great significance in calibrating the exposure time of the gated image intensifier and the ultra-high-speed photoelectronic framing camera.
2012,
24: 2451-2453.
doi: 10.3788/HPLPB20122410.2451
Abstract:
By using two calibrated ST401 scintillation detectors, the neutron yield of a pulse neutron tube was measured, and by adding a Pb shield before one detector, the influence of the Pb shield on neutron flux was determined. The 1 cm thick Pb shield decreases the neutron flux by 18.20%. The influence of the Pb shield on accelerator neutron sources was determined the same way. The 0.5 cm thick Pb shield decreases the neutron flux by 2.90%. The measurements of two neutron sources were simulated by Monte Carlo. Compared with the neutron tube experiment, the accelerator experiment results agree with the simulation better. The theoretical analysis shows that neutron tubes can generate much bremsstrahlung X rays, which may have harmful impact on the measurement of neutron tube yields.
By using two calibrated ST401 scintillation detectors, the neutron yield of a pulse neutron tube was measured, and by adding a Pb shield before one detector, the influence of the Pb shield on neutron flux was determined. The 1 cm thick Pb shield decreases the neutron flux by 18.20%. The influence of the Pb shield on accelerator neutron sources was determined the same way. The 0.5 cm thick Pb shield decreases the neutron flux by 2.90%. The measurements of two neutron sources were simulated by Monte Carlo. Compared with the neutron tube experiment, the accelerator experiment results agree with the simulation better. The theoretical analysis shows that neutron tubes can generate much bremsstrahlung X rays, which may have harmful impact on the measurement of neutron tube yields.
2012,
24: 2454-2458.
doi: 10.3788/HPLPB20122410.2454
Abstract:
Hypervelocity impact experiments were conducted under four experimental conditions to investigate evolutionary characteristics of light flash radiation by using optical pyrometer measurement system established and two-stage light-gas gun loading system. One optical fiber probe was used in every experiment. Evolution of light flash intensity was obtained based on original data and calibration by Matlab programmable treatments under the given experimental condition and the optical-fiber probe scheme. Evolutionary characteristics of radiation temperature were acquired by using ratio methods. Experimental results show that impact light flash intensity and radiation temperature peak value decrease with impact angles increasing in the range of 488 to 667 nm during hypervelocity impact on LY12 Aluminum targets.
Hypervelocity impact experiments were conducted under four experimental conditions to investigate evolutionary characteristics of light flash radiation by using optical pyrometer measurement system established and two-stage light-gas gun loading system. One optical fiber probe was used in every experiment. Evolution of light flash intensity was obtained based on original data and calibration by Matlab programmable treatments under the given experimental condition and the optical-fiber probe scheme. Evolutionary characteristics of radiation temperature were acquired by using ratio methods. Experimental results show that impact light flash intensity and radiation temperature peak value decrease with impact angles increasing in the range of 488 to 667 nm during hypervelocity impact on LY12 Aluminum targets.
2012,
24: 2459-2463.
doi: 10.3788/HPLPB20122410.2459
Abstract:
CVD diamond thick films were etched by oxygen cyclotron ion beams and polished by mechanical methods and the effect was investigated. The influences of gas pressure and bias voltage of anode cylinders on the ion parameters were studied by an ion sensitive probe. The etching of CVD diamond films was accomplished under the optimized gas pressure and bias voltage of the anode cylinder. The optimized gas pressure and bias voltage of the anode cylinder for diamond etching are 0.03 Pa and 200 V, respectively. Under these conditions, the ion temperature is 7.38 eV and the ion density is 23.81010 cm-3. The diamond film was etched for 4 h by the oxygen cyclotron ion beam under temperature of the sample holder of 600 ℃ and then polished for 15 min by mechanical lapping. The results show that the diamond surface roughness decreases from 3.525 m to 2.512 m by ion beam etching, and then decreases to 0.517 m by mechanical polishing. The efficiency of mechanical polishing is dramatically improved when the diamond film is etched by oxygen cyclotron ion beams.
CVD diamond thick films were etched by oxygen cyclotron ion beams and polished by mechanical methods and the effect was investigated. The influences of gas pressure and bias voltage of anode cylinders on the ion parameters were studied by an ion sensitive probe. The etching of CVD diamond films was accomplished under the optimized gas pressure and bias voltage of the anode cylinder. The optimized gas pressure and bias voltage of the anode cylinder for diamond etching are 0.03 Pa and 200 V, respectively. Under these conditions, the ion temperature is 7.38 eV and the ion density is 23.81010 cm-3. The diamond film was etched for 4 h by the oxygen cyclotron ion beam under temperature of the sample holder of 600 ℃ and then polished for 15 min by mechanical lapping. The results show that the diamond surface roughness decreases from 3.525 m to 2.512 m by ion beam etching, and then decreases to 0.517 m by mechanical polishing. The efficiency of mechanical polishing is dramatically improved when the diamond film is etched by oxygen cyclotron ion beams.
2012,
24: 2464-2468.
doi: 10.3788/HPLPB20122410.2464
Abstract:
As a neutron detecting and imaging device used for detection of special nuclear material (SNM), the newly reported neutron scatter camera can acquire the neutron position and energy information simultaneously. In this paper, the particle transport code MCNP was used together with the program MATLAB and Fortran to simulate a five-units prototype of a neutron scatter camera, and to reconstruct the image and energy of a 252Cf neutron source. The calculation results show that the cameras energy resolution is about 9% and its angular resolution is related to the size of the scintillators; when the neutron energy equals 2 MeV, the detection efficiency reaches a maximum;the distance of the source, the size of the scintillators, the distance between the front and rear surfaces of the detectors, and the number of the events have influence on the resolution of the image to a certain extent;the scatter camera can measure the fission neutron energy spectrum, but the factors such as the cameras structure and detection threshold could result in some inaccuracy of the measurement. This simulation work lays a foundation for further experimental research, and its conclusion can be generalized to the neutron scatter camera with much units.
As a neutron detecting and imaging device used for detection of special nuclear material (SNM), the newly reported neutron scatter camera can acquire the neutron position and energy information simultaneously. In this paper, the particle transport code MCNP was used together with the program MATLAB and Fortran to simulate a five-units prototype of a neutron scatter camera, and to reconstruct the image and energy of a 252Cf neutron source. The calculation results show that the cameras energy resolution is about 9% and its angular resolution is related to the size of the scintillators; when the neutron energy equals 2 MeV, the detection efficiency reaches a maximum;the distance of the source, the size of the scintillators, the distance between the front and rear surfaces of the detectors, and the number of the events have influence on the resolution of the image to a certain extent;the scatter camera can measure the fission neutron energy spectrum, but the factors such as the cameras structure and detection threshold could result in some inaccuracy of the measurement. This simulation work lays a foundation for further experimental research, and its conclusion can be generalized to the neutron scatter camera with much units.
2012,
24: 2469-2473.
doi: 10.3788/HPLPB20122410.2469
Abstract:
This paper describes the performance of the LIPS-200 ion thruster discharge chamber which was developed by Lanzhou Institute of Physics. Based on the discharge chamber geometric configuration and magnetic field, the completely self-consistent analytical model is utilized to discuss performance optimization of the discharge chamber of the LIPS-200. The thrust is enhanced from 40 mN up to 60 mN at rated impulse and efficiency. The results show that the 188.515 W/A beam ion production cost at a propellant flow rate of 2.1671017 m-3 requires that the thruster runs at a discharge current of 6.9 A to produce 1.2 A ion beam current. Also, during the process of LIPS-200 ion thruster discharge chamber performance optimization, the sheath potential is always within 3.80~6.65 eV.
This paper describes the performance of the LIPS-200 ion thruster discharge chamber which was developed by Lanzhou Institute of Physics. Based on the discharge chamber geometric configuration and magnetic field, the completely self-consistent analytical model is utilized to discuss performance optimization of the discharge chamber of the LIPS-200. The thrust is enhanced from 40 mN up to 60 mN at rated impulse and efficiency. The results show that the 188.515 W/A beam ion production cost at a propellant flow rate of 2.1671017 m-3 requires that the thruster runs at a discharge current of 6.9 A to produce 1.2 A ion beam current. Also, during the process of LIPS-200 ion thruster discharge chamber performance optimization, the sheath potential is always within 3.80~6.65 eV.
2012,
24: 2474-2478.
doi: 10.3788/HPLPB20122410.2474
Abstract:
The effect of storage capacitors loss on the discharging characteristics of the xenon flash lamp was studied, and the xenon flash lamp discharging circuit was analyzed and improved. The capacitor can be equivalent to a series of an ideal capacitor and a loss resistance. The improved formula of the xenon lamp discharging characteristics was given when actual capacitance loss is not zero, and the xenon lamp discharging current and discharging power are calculated and analyzed in detail with the increase of the capacitor loss. The results show that the increase of loss will lead to the decrease of xenon lamp discharging current and peak power and the xenon lamp flash time, and influence laser pumping efficiency. The loss will also lead to the capacitor inverse charging in LC discharging circuit; this will influence normal working of the capacitor and decrease the life of the xenon lamp. The actual energy storage capacitor charging and discharging experiments show that the increase of capacitor loss will lead to the decrease of xenon lamp light-emitting waveform peak, shortening of the flash time and increase of the electrode sputter, thus verity, the reasonableness of theoretical analysis. In addition, the experiments show that environmental factors have very significant impact on the increase of the storage capacitor loss.
The effect of storage capacitors loss on the discharging characteristics of the xenon flash lamp was studied, and the xenon flash lamp discharging circuit was analyzed and improved. The capacitor can be equivalent to a series of an ideal capacitor and a loss resistance. The improved formula of the xenon lamp discharging characteristics was given when actual capacitance loss is not zero, and the xenon lamp discharging current and discharging power are calculated and analyzed in detail with the increase of the capacitor loss. The results show that the increase of loss will lead to the decrease of xenon lamp discharging current and peak power and the xenon lamp flash time, and influence laser pumping efficiency. The loss will also lead to the capacitor inverse charging in LC discharging circuit; this will influence normal working of the capacitor and decrease the life of the xenon lamp. The actual energy storage capacitor charging and discharging experiments show that the increase of capacitor loss will lead to the decrease of xenon lamp light-emitting waveform peak, shortening of the flash time and increase of the electrode sputter, thus verity, the reasonableness of theoretical analysis. In addition, the experiments show that environmental factors have very significant impact on the increase of the storage capacitor loss.
2012,
24: 2479-2482.
doi: 10.3788/HPLPB20122410.2479
Abstract:
A primary unit was designed for high-repetition-frequency pulsed power generators based on semiconductor opening switches at tens of kHz. The low frequency circuit in the primary unit was optimized, including that the series and parallel modules of IGBT were adopted as discharge switches, the high frequency synchronized trigger generator was used to control operation of IGBTs, and the current feedback circuit was added. The experimental results indicate that residual voltage of the discharge capacitor after discharging of the primary unit could impact the output stability of the pulse generator, and such primary unit reinforces the stability and reliability of the developed high-frequency pulsed power generator at tens of kHz. According to experimental waveforms, the operating voltage is 1 kV and current is 1.5 kA, the primary unit could operate stably at 10 kHz.
A primary unit was designed for high-repetition-frequency pulsed power generators based on semiconductor opening switches at tens of kHz. The low frequency circuit in the primary unit was optimized, including that the series and parallel modules of IGBT were adopted as discharge switches, the high frequency synchronized trigger generator was used to control operation of IGBTs, and the current feedback circuit was added. The experimental results indicate that residual voltage of the discharge capacitor after discharging of the primary unit could impact the output stability of the pulse generator, and such primary unit reinforces the stability and reliability of the developed high-frequency pulsed power generator at tens of kHz. According to experimental waveforms, the operating voltage is 1 kV and current is 1.5 kA, the primary unit could operate stably at 10 kHz.
2012,
24: 2483-2487.
doi: 10.3788/HPLPB20122410.2483
Abstract:
The switching process of thyristor has been analyzed from the aspects of transmission carrier and carrier density. The effect of high current triggering on switching characteristics of triggered thyristor is investigated. Based on fast switching characteristics and flow capacity, high current trigger circuit has been designed. The relationship of switching characteristics with different triggering current and operation voltages has been studied. The experiment results indicate that the switching time of thyristor is determined by triggering mode and operation voltage. The delay time and breakdown time can be shortened by high current mode and high operation voltage, respectively, which can improve the switching characteristics efficiently.
The switching process of thyristor has been analyzed from the aspects of transmission carrier and carrier density. The effect of high current triggering on switching characteristics of triggered thyristor is investigated. Based on fast switching characteristics and flow capacity, high current trigger circuit has been designed. The relationship of switching characteristics with different triggering current and operation voltages has been studied. The experiment results indicate that the switching time of thyristor is determined by triggering mode and operation voltage. The delay time and breakdown time can be shortened by high current mode and high operation voltage, respectively, which can improve the switching characteristics efficiently.
2012,
24: 2488-2492.
doi: 10.3788/HPLPB20122410.2488
Abstract:
Stability of high current diode under pulse voltages with 80 ns and 34 ns rise time was studied on the flash Ⅱ accelerator. Influence of rise time of diode voltage on startup time and cathode emission uniformity and repeatability of diode impedance was analyzed by comparing the experimental results with numerically simulated results, and the influence mechanism was discussed. The startup time of diode increases with the increasing of rise time of voltage, and the repeatability of diode impedance decreases. Discal plane cathode is prone to emit rays intensely in the center area, the time that plasma covers the surface of the cathode increases and the shielding effect has moreimpact on cathode emission according to the increase of rise time. Local intense emission on the cathode increases expansion speed of plasma and reduces the effective emission area. The stability of characteristic impedance of diode under a pulse voltage with slow rise time is decreased by the combined action of expansion speed of plasma and the effective emission area.
Stability of high current diode under pulse voltages with 80 ns and 34 ns rise time was studied on the flash Ⅱ accelerator. Influence of rise time of diode voltage on startup time and cathode emission uniformity and repeatability of diode impedance was analyzed by comparing the experimental results with numerically simulated results, and the influence mechanism was discussed. The startup time of diode increases with the increasing of rise time of voltage, and the repeatability of diode impedance decreases. Discal plane cathode is prone to emit rays intensely in the center area, the time that plasma covers the surface of the cathode increases and the shielding effect has moreimpact on cathode emission according to the increase of rise time. Local intense emission on the cathode increases expansion speed of plasma and reduces the effective emission area. The stability of characteristic impedance of diode under a pulse voltage with slow rise time is decreased by the combined action of expansion speed of plasma and the effective emission area.
Plasma electron temperature diagnosis in aluminum wire array Z-pinches based on soft X-ray continuum
2012,
24: 2493-2496.
doi: 10.3788/HPLPB20122410.2493
Abstract:
A curved crystal spectrometer was developed on Qiang-guang I generator to measure the electron temperature of aluminum planar wire array Z-pinches. The spectrometer is composed of an elliptically-curved TlAP crystal and a Biomax-MS film, and the spectral range is from 1.8 keV to 3.0 keV, which covers part of the H-like and He-like K shell lines and continuum. The time-integrated spectra with axial distinction for shot 10084 with a planar aluminum wire array load were recorded by the spectrometer. The slope of the continuum radiated from a hot spot indicates an electron temperature of 520(135%)eV.
A curved crystal spectrometer was developed on Qiang-guang I generator to measure the electron temperature of aluminum planar wire array Z-pinches. The spectrometer is composed of an elliptically-curved TlAP crystal and a Biomax-MS film, and the spectral range is from 1.8 keV to 3.0 keV, which covers part of the H-like and He-like K shell lines and continuum. The time-integrated spectra with axial distinction for shot 10084 with a planar aluminum wire array load were recorded by the spectrometer. The slope of the continuum radiated from a hot spot indicates an electron temperature of 520(135%)eV.
2012,
24: 2497-2501.
doi: 10.3788/HPLPB20122410.2497
Abstract:
A kind of simple-mechanism, easy-disassembly self-integrating capacitive divider used for measuring diode output voltage of intense electron beam accelerator (IEBA) is developed. The structure of the capacitive divider is described, and the capacitance value of the capacitive divider is calculated by theoretical analysis and electromagnetic simulation. The dependence of measurement voltage on electrical parameters such as stray capacitance, earth capacitance of front resistance is obtained by PSpice simulation. Measured waveforms appear overshoot phenomenon when stray capacitance of front resistance is larger, and the wavefront will be affected when earth capacitance of front resistance is larger. The diode output voltage waveforms of intense electron beam accelerator, are measured by capacitive divider and calibrated by water resistance divider, which is accordance with that measured by a resistive divider, the division ratio is about 563 007. The designed capacitive divider can be used to measure high-voltage pulse with 100 ns full width at half maximum.
A kind of simple-mechanism, easy-disassembly self-integrating capacitive divider used for measuring diode output voltage of intense electron beam accelerator (IEBA) is developed. The structure of the capacitive divider is described, and the capacitance value of the capacitive divider is calculated by theoretical analysis and electromagnetic simulation. The dependence of measurement voltage on electrical parameters such as stray capacitance, earth capacitance of front resistance is obtained by PSpice simulation. Measured waveforms appear overshoot phenomenon when stray capacitance of front resistance is larger, and the wavefront will be affected when earth capacitance of front resistance is larger. The diode output voltage waveforms of intense electron beam accelerator, are measured by capacitive divider and calibrated by water resistance divider, which is accordance with that measured by a resistive divider, the division ratio is about 563 007. The designed capacitive divider can be used to measure high-voltage pulse with 100 ns full width at half maximum.
2012,
24: 2502-2506.
doi: 10.3788/HPLPB20122410.2502
Abstract:
The factors affecting the voltage transfer efficiency of Blumlein pulse forming networks (PFNs) based on photoconductive semiconductor switch (PCSS) were preliminarily studied in experiment to get rectangle high voltage pulses on high impedance loads with high energy transfer efficiency and high repetition rate. The Blumlein-PFN is composed of the ceramic capacitor,aluminum strip and GaAs-PCSS. The Blumlein-PFNs impedance is 7.8 with an electric length of 32.6 ns. The relations of voltage transfer efficiency to PCSS electric field and laser energy were studied on a matched load. Experiment results shows that high on-resistance is the main factor affecting the voltage transfer efficiency. When the electric field is 25.1 kV/cm,the efficiency is 75.6% with an on-resistance of 2.88 at a laser energy of 3.5 mJ and 83.2% with an on-resistance of 1.89 at a laser energy of 30.4 mJ.
The factors affecting the voltage transfer efficiency of Blumlein pulse forming networks (PFNs) based on photoconductive semiconductor switch (PCSS) were preliminarily studied in experiment to get rectangle high voltage pulses on high impedance loads with high energy transfer efficiency and high repetition rate. The Blumlein-PFN is composed of the ceramic capacitor,aluminum strip and GaAs-PCSS. The Blumlein-PFNs impedance is 7.8 with an electric length of 32.6 ns. The relations of voltage transfer efficiency to PCSS electric field and laser energy were studied on a matched load. Experiment results shows that high on-resistance is the main factor affecting the voltage transfer efficiency. When the electric field is 25.1 kV/cm,the efficiency is 75.6% with an on-resistance of 2.88 at a laser energy of 3.5 mJ and 83.2% with an on-resistance of 1.89 at a laser energy of 30.4 mJ.
2012,
24: 2507-2510.
doi: 10.3788/HPLPB20122410.2507
Abstract:
Using spark preionization, a trigatron gas switch is designed in the paper. The trigger electrode is disk-ring nested structure with 10 mm spacing, The electrode of switch is made from 304 stainless for operating voltage level up to 100 kV. Experimental results show that the preionization could reduce the trigger delay and jitter of the trigatron under low working voltage obviously. The earlier the preionization is imposed, the lower the delay and jitter of trigatron is under nanosecond trigger pulses. The average delay of 40 ns and jitter of 1 ns or better is achieved when the trigatron switch works at the coefficient of 80% with the trigger pulse of 30 kV and 8 ns risetime.
Using spark preionization, a trigatron gas switch is designed in the paper. The trigger electrode is disk-ring nested structure with 10 mm spacing, The electrode of switch is made from 304 stainless for operating voltage level up to 100 kV. Experimental results show that the preionization could reduce the trigger delay and jitter of the trigatron under low working voltage obviously. The earlier the preionization is imposed, the lower the delay and jitter of trigatron is under nanosecond trigger pulses. The average delay of 40 ns and jitter of 1 ns or better is achieved when the trigatron switch works at the coefficient of 80% with the trigger pulse of 30 kV and 8 ns risetime.
2012,
24: 2511-2515.
doi: 10.3788/HPLPB20122410.2511
Abstract:
A differential B-dot used for current measure of the magnetically insulated transmission lines (MITL) has been developed. By using the commercial PSpice software, the equivalent circuit model of the B-dot monitor, the transfer-equations and the frequency responses of the B-dot were obtained. Calculation results show that signals with frequency more than 2.5 MHz can be perfectly measured by the B-dot. This B-dot monitor has been used for the 1.0 m long, 2 cm AK gap coaxial-MITL experiments on QiangGuang-Ⅰ accelerator. Experimental results show that with the shorted load, the current waveforms measured by the B-dots along the MITL are almost the same (the peak current is 1.0 MA, and the risetime is 125 ns), namely, the current loss along the line is negligible. This results perfectly accord with the theoretical transfer characteristics of the MITL with shorted load.
A differential B-dot used for current measure of the magnetically insulated transmission lines (MITL) has been developed. By using the commercial PSpice software, the equivalent circuit model of the B-dot monitor, the transfer-equations and the frequency responses of the B-dot were obtained. Calculation results show that signals with frequency more than 2.5 MHz can be perfectly measured by the B-dot. This B-dot monitor has been used for the 1.0 m long, 2 cm AK gap coaxial-MITL experiments on QiangGuang-Ⅰ accelerator. Experimental results show that with the shorted load, the current waveforms measured by the B-dots along the MITL are almost the same (the peak current is 1.0 MA, and the risetime is 125 ns), namely, the current loss along the line is negligible. This results perfectly accord with the theoretical transfer characteristics of the MITL with shorted load.
2012,
24: 2516-2520.
doi: 10.3788/HPLPB20122410.2516
Abstract:
The self-breakdown water switch with coaxial-triplate configuration is used for the pulse output switch of the pulse forming section in Primary Test Stand (PTS). The research contains two stages, the first is the 1.5 MV coaxial water switch experiment on FLASH-Ⅱand the second is the experiment of 4 MV coaxial-triplate multi-channel water switch on the prototype module of PTS. Results show that the output current is 500 kA with 100 ns rise time at 3.5 MV self-breakdown voltage, the total switch inductance is 65 nH, and the jitter of charging time is 1.3 ns.
The self-breakdown water switch with coaxial-triplate configuration is used for the pulse output switch of the pulse forming section in Primary Test Stand (PTS). The research contains two stages, the first is the 1.5 MV coaxial water switch experiment on FLASH-Ⅱand the second is the experiment of 4 MV coaxial-triplate multi-channel water switch on the prototype module of PTS. Results show that the output current is 500 kA with 100 ns rise time at 3.5 MV self-breakdown voltage, the total switch inductance is 65 nH, and the jitter of charging time is 1.3 ns.
