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RSS2010 Vol. 22, No. 09
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2010,
22.
Abstract:
Intensity fluctuation in linearly chirped Gaussian pulse stacking(LCGPS) is studied systematically based on spectral analysis. Two-pulse LCGPS and multi-pulse LCGPS are analyzed with simulations based on Fourier transform. The variation of fluctuation frequencies with the number, chirp factor, time delay and pulse width of the Gaussian pulses is discussed in the case of multi-pulse LCGPS with inital pulses of the same amplitude and the same time delay. Finally a brief discussion is presented on the general case of multi-pulse LCGPS with initial pulses of different amplitude attenuation and different time delay. The results show that there are several separated frequency sidebands in the intensity spectrum of the stacked pulse, responsible for the intensity fluctuation. The higher frequency
Intensity fluctuation in linearly chirped Gaussian pulse stacking(LCGPS) is studied systematically based on spectral analysis. Two-pulse LCGPS and multi-pulse LCGPS are analyzed with simulations based on Fourier transform. The variation of fluctuation frequencies with the number, chirp factor, time delay and pulse width of the Gaussian pulses is discussed in the case of multi-pulse LCGPS with inital pulses of the same amplitude and the same time delay. Finally a brief discussion is presented on the general case of multi-pulse LCGPS with initial pulses of different amplitude attenuation and different time delay. The results show that there are several separated frequency sidebands in the intensity spectrum of the stacked pulse, responsible for the intensity fluctuation. The higher frequency
2010,
22.
Abstract:
The thermal analysis of glass-fiber/epoxy composite has been carried out with a thermogravimetric analyzer in air and in nitrogen, respectively. The heat of ablation in air is 3 125 to 3 440 J/g, while no obvious oxidation exothermal peak appears in nitrogen. Thermal decomposition kinetic parameters of glass-fiber/epoxy composite are calculated based on the multi-step decomposing model of Arrhenius relation and the direct solution method. Analysis results indicate that, the multi-step decomposing model can reflect the process of thermal decomposition and the direct solution method is suitable for calculating thermal decomposition kinetic parameters of the composite. The obtained thermal decomposition kinetic parameters are valid.
The thermal analysis of glass-fiber/epoxy composite has been carried out with a thermogravimetric analyzer in air and in nitrogen, respectively. The heat of ablation in air is 3 125 to 3 440 J/g, while no obvious oxidation exothermal peak appears in nitrogen. Thermal decomposition kinetic parameters of glass-fiber/epoxy composite are calculated based on the multi-step decomposing model of Arrhenius relation and the direct solution method. Analysis results indicate that, the multi-step decomposing model can reflect the process of thermal decomposition and the direct solution method is suitable for calculating thermal decomposition kinetic parameters of the composite. The obtained thermal decomposition kinetic parameters are valid.
2010,
22.
Abstract:
The maximum range of a laser range finder has been tested by measuring the extinction ratio outdoors and the time-sequence gain coefficient ratio indoors. Other major parameters, such as ranging accuracy, gating range, gating accuracy, range resolution, were tested using an indoor system composed of an electronic delayer, two laser source simulators, a variable optic attenuator, and a computer. The principle of the measuring methods is discussed and the measured results are analyzed. The experimental results prove the validity of these measuring methods.
The maximum range of a laser range finder has been tested by measuring the extinction ratio outdoors and the time-sequence gain coefficient ratio indoors. Other major parameters, such as ranging accuracy, gating range, gating accuracy, range resolution, were tested using an indoor system composed of an electronic delayer, two laser source simulators, a variable optic attenuator, and a computer. The principle of the measuring methods is discussed and the measured results are analyzed. The experimental results prove the validity of these measuring methods.
2010,
22.
Abstract:
Three-dimension heat transfer finite-element model in electro-optic crystal, which is orthotropic and actively heated by resistance wire, is established. Based on the model, thermo-effects are analyzed in the plasma electrodes Pockels cell. A thermo-management idea is put forward and the optical switch performance is studied in the average power Pockels cell. The results are as follows: for 50 J/10 Hz laser system with 50 mm×30 mm light beam aperture, the maximum depolarization is 3.58%, the average depolarization is 0.90 %, and PV is 1.59λ; With 500 W/m2 resistance wire heating the edge of the electro-optic crystal, the maximum depolarization of the Pockels cell reduces to 0.17%, the average depolarization is 0.05%, and PV decreases to 0.26λ. The performance of the Pockels cell is impr
Three-dimension heat transfer finite-element model in electro-optic crystal, which is orthotropic and actively heated by resistance wire, is established. Based on the model, thermo-effects are analyzed in the plasma electrodes Pockels cell. A thermo-management idea is put forward and the optical switch performance is studied in the average power Pockels cell. The results are as follows: for 50 J/10 Hz laser system with 50 mm×30 mm light beam aperture, the maximum depolarization is 3.58%, the average depolarization is 0.90 %, and PV is 1.59λ; With 500 W/m2 resistance wire heating the edge of the electro-optic crystal, the maximum depolarization of the Pockels cell reduces to 0.17%, the average depolarization is 0.05%, and PV decreases to 0.26λ. The performance of the Pockels cell is impr
2010,
22.
Abstract:
Using a high resolution continuous-wave mid-infrared difference frequency generation spectrometer and a long adjustable optical path White cell, water vapor pressure broadening coefficients for 22 transitions in the R branch and last 4 transitions in the P branch of the 10011←10002 band of CO2 has been detected at room temperature. The recorded lineshapes were fitted with Voigt line profile in order to determine the water vapor collisional broadening coefficients of 26 CO2 transitions from 2 422 cm-1 to 2 457 cm-1，the result shows that the water vapor collisional broadening coefficients are about 52% bigger than the dry air collisional broadening coefficients. The transmission of CO2 perturbed by dry and wet air(2.0 kPa water vapor) at the pressure of 0.1
Using a high resolution continuous-wave mid-infrared difference frequency generation spectrometer and a long adjustable optical path White cell, water vapor pressure broadening coefficients for 22 transitions in the R branch and last 4 transitions in the P branch of the 10011←10002 band of CO2 has been detected at room temperature. The recorded lineshapes were fitted with Voigt line profile in order to determine the water vapor collisional broadening coefficients of 26 CO2 transitions from 2 422 cm-1 to 2 457 cm-1，the result shows that the water vapor collisional broadening coefficients are about 52% bigger than the dry air collisional broadening coefficients. The transmission of CO2 perturbed by dry and wet air(2.0 kPa water vapor) at the pressure of 0.1
2010,
22.
Abstract:
The paper studies the optical performance of a new sub-wavelength nanostructure which consists of non-close-packed polycrystalline colloidal crystals fabricated by dip-coating. Effective medium theory (EMT) is used to analyze the optical property of the as prepared structure. The structure exhibits excellent transmission performance. It can turn the maximum transmission wavelength from visible light to infrared wave by different withdrawal speed. The structure can be used for antireflection coating, and the measured effective refractive index is 1.22, and the maximum transmission of a glass substrate is increased to 99.8%.
The paper studies the optical performance of a new sub-wavelength nanostructure which consists of non-close-packed polycrystalline colloidal crystals fabricated by dip-coating. Effective medium theory (EMT) is used to analyze the optical property of the as prepared structure. The structure exhibits excellent transmission performance. It can turn the maximum transmission wavelength from visible light to infrared wave by different withdrawal speed. The structure can be used for antireflection coating, and the measured effective refractive index is 1.22, and the maximum transmission of a glass substrate is increased to 99.8%.
2010,
22.
Abstract:
An efficient laser -diode(LD) pumped Nd:YAG extracavity frequency conversion all -solid -state quasi -continuous -wave(QCW) ultraviolet laser at 266nm was reported. The laser adopted LBO and BBO as the second and fourth harmonic generation crystals, and was pumped by three LD configurations (high polarization LD， low polarization LD and low polarization LD with a Brewster plate) in the experiment. When the pump power was 25 W and the modulation frequency was 10 kHz， 266 nm UV lasers were obtained with the output power of 0.85， 0.61 and 0.72 W, respectively. A high power UV laser was obtained by using high polarization ratio LD with a single pulse energy of 85 μJ， and a pulse width of 5 ns. The corresponding peak power was as high as 17 kW， and the optical -to -optical conversion effi
An efficient laser -diode(LD) pumped Nd:YAG extracavity frequency conversion all -solid -state quasi -continuous -wave(QCW) ultraviolet laser at 266nm was reported. The laser adopted LBO and BBO as the second and fourth harmonic generation crystals, and was pumped by three LD configurations (high polarization LD， low polarization LD and low polarization LD with a Brewster plate) in the experiment. When the pump power was 25 W and the modulation frequency was 10 kHz， 266 nm UV lasers were obtained with the output power of 0.85， 0.61 and 0.72 W, respectively. A high power UV laser was obtained by using high polarization ratio LD with a single pulse energy of 85 μJ， and a pulse width of 5 ns. The corresponding peak power was as high as 17 kW， and the optical -to -optical conversion effi
2010,
22.
Abstract:
To improve the fiber-coupling efficiency of free space optical communication systems, an adaptive optics system based on blind optimization is suggested to correct wavefront aberrations caused by atmospheric turbulences. The system adopts no wavefront sensor. The aberrated signal is splitted into a photoelectric detector to calculate the coupling efficiency before it enters the receiver. The stochastic parallel gradient descent algorithm (SPGDA) is then used to adapt the micromachined deformable mirror to optimize the optical power coupled into the fiber, with the Strehl ratio, the estimation formula of coupling efficiency, as the objective function. Numerical results demonstrate that the coupling efficiency is improved from 6% to about 60%.
To improve the fiber-coupling efficiency of free space optical communication systems, an adaptive optics system based on blind optimization is suggested to correct wavefront aberrations caused by atmospheric turbulences. The system adopts no wavefront sensor. The aberrated signal is splitted into a photoelectric detector to calculate the coupling efficiency before it enters the receiver. The stochastic parallel gradient descent algorithm (SPGDA) is then used to adapt the micromachined deformable mirror to optimize the optical power coupled into the fiber, with the Strehl ratio, the estimation formula of coupling efficiency, as the objective function. Numerical results demonstrate that the coupling efficiency is improved from 6% to about 60%.
2010,
22.
Abstract:
连续波DF/HF化学激光器气膜冷却式喷管流场数值分析 李 兰， 袁圣付， 华卫红， 姜宗福 (国防科学技术大学 光电科学与工程学院, 长沙 410073) 摘要：在连续波DF/HF化学激光器主喷管收缩段采用气膜冷却方式，从3维离散小孔注入氦气射流以隔离壁面和主气流。通过对3种气膜孔排布方式下喷管内主气流状态进行数值模拟研究，分析氦气与主气流之间的相互作用，比较了不同方式下主气流氟原子冻结效率及壁面冷却效果。考虑到DF/HF化学激光器主喷管结构尺寸较小，采用适当间隔的单排圆孔注入是现实可行的,并有望达到较好的冷却保护效果，从而提高激光器运转效率。 关键词： 连续波DF/HF化学激光器； 喷管； 气膜冷却； 数值模拟 Numerical analysis of nozzle flow field with gaseous film cooling in CW DF/HF chemical laser Li Lan, Yuan Shengfu, Hua Weihong, Jiang Zongfu (College of Opto-Electronic Science and Engineering, National Un
连续波DF/HF化学激光器气膜冷却式喷管流场数值分析 李 兰， 袁圣付， 华卫红， 姜宗福 (国防科学技术大学 光电科学与工程学院, 长沙 410073) 摘要：在连续波DF/HF化学激光器主喷管收缩段采用气膜冷却方式，从3维离散小孔注入氦气射流以隔离壁面和主气流。通过对3种气膜孔排布方式下喷管内主气流状态进行数值模拟研究，分析氦气与主气流之间的相互作用，比较了不同方式下主气流氟原子冻结效率及壁面冷却效果。考虑到DF/HF化学激光器主喷管结构尺寸较小，采用适当间隔的单排圆孔注入是现实可行的,并有望达到较好的冷却保护效果，从而提高激光器运转效率。 关键词： 连续波DF/HF化学激光器； 喷管； 气膜冷却； 数值模拟 Numerical analysis of nozzle flow field with gaseous film cooling in CW DF/HF chemical laser Li Lan, Yuan Shengfu, Hua Weihong, Jiang Zongfu (College of Opto-Electronic Science and Engineering, National Un
2010,
22.
Abstract:
Considering the changes of the background refractive index and the period of the volume Bragg grating (VBG) induced by surface thermal distortion, which further lead to the change of the dielectric constant of the VBG, the propagation properties of Gaussian laser beams propagating in the VBG have been studied. The scalar wave equation for Gaussian beam propagation in the VBG with deformation has been solved numerically and iteratively by finite-different and sparse matrix methods. The changes of the power reflection coefficient, beam waist width, far-field divergence angle and M2-factor of laser beams through the VBG with deformation have been analyzed quantitatively. The result shows that the power reflection coefficient decreases obviously with the increasing of the grating deformation,
Considering the changes of the background refractive index and the period of the volume Bragg grating (VBG) induced by surface thermal distortion, which further lead to the change of the dielectric constant of the VBG, the propagation properties of Gaussian laser beams propagating in the VBG have been studied. The scalar wave equation for Gaussian beam propagation in the VBG with deformation has been solved numerically and iteratively by finite-different and sparse matrix methods. The changes of the power reflection coefficient, beam waist width, far-field divergence angle and M2-factor of laser beams through the VBG with deformation have been analyzed quantitatively. The result shows that the power reflection coefficient decreases obviously with the increasing of the grating deformation,
2010,
22.
Abstract:
The temperature distribution inside KTP crystal was calculated by finite element analysis accurately. The phase matching angles, walk-off angles, tolerance angles and effective nonlinear coefficient of type Ⅱ KTP crystal were calculated according to the conservation of mass and phase matched for parametric process and the thermo-optic dispersion of KTP crystal. The results showed that the distribution of temperature inside the crystal was non-uniform. Along the direction of light, temperature distributions of crystal sections were different. Strengthening the cooling effect of crystal can effectively reduce the temperature influences on the phase matching angles, walk-off angles, tolerance angles and effective nonlinear coefficient of crystal．
The temperature distribution inside KTP crystal was calculated by finite element analysis accurately. The phase matching angles, walk-off angles, tolerance angles and effective nonlinear coefficient of type Ⅱ KTP crystal were calculated according to the conservation of mass and phase matched for parametric process and the thermo-optic dispersion of KTP crystal. The results showed that the distribution of temperature inside the crystal was non-uniform. Along the direction of light, temperature distributions of crystal sections were different. Strengthening the cooling effect of crystal can effectively reduce the temperature influences on the phase matching angles, walk-off angles, tolerance angles and effective nonlinear coefficient of crystal．
2010,
22.
Abstract:
The frequency-domain interferometry has been used to study the properties of shock waves driven by the femtosecond laser. The observation results of shock waves driven by a 0.7 mJ, 35 fs pulse laser with the intensity of 1014W/cm2 level in a 200 nm-thick aluminum film were presented. From the transit time varying with the thickness of aluminium film, the shock velocity was measured to be about 6 km/s. The measured frequency-domain interferograms showed that the rear surface velocity was 1 km/s, and according to the relation of planar shock waves, the shock pressure was calculated to be 9 GPa．
The frequency-domain interferometry has been used to study the properties of shock waves driven by the femtosecond laser. The observation results of shock waves driven by a 0.7 mJ, 35 fs pulse laser with the intensity of 1014W/cm2 level in a 200 nm-thick aluminum film were presented. From the transit time varying with the thickness of aluminium film, the shock velocity was measured to be about 6 km/s. The measured frequency-domain interferograms showed that the rear surface velocity was 1 km/s, and according to the relation of planar shock waves, the shock pressure was calculated to be 9 GPa．
2010,
22.
Abstract:
In order to research the hard damage effect on visible light CCD imaging system of off-band laser irradiation, one type of visible light imaging camera was irradiated by a continuous-wave chemical oxygen-iodine laser. Experiments with different camera aperture sizes were carried out. It was found that if aperture size became smaller, the hard damage would be more unlikely to happen, and the reason for this phenomenon was described. The hard damage threshold of the CCD was 5.5×104 W/cm2. Based on the CCD microscopic images, a preliminary discussion on the mechanism of hard damage was made.
In order to research the hard damage effect on visible light CCD imaging system of off-band laser irradiation, one type of visible light imaging camera was irradiated by a continuous-wave chemical oxygen-iodine laser. Experiments with different camera aperture sizes were carried out. It was found that if aperture size became smaller, the hard damage would be more unlikely to happen, and the reason for this phenomenon was described. The hard damage threshold of the CCD was 5.5×104 W/cm2. Based on the CCD microscopic images, a preliminary discussion on the mechanism of hard damage was made.
2010,
22.
Abstract:
The H Balmer emission lines have been measured on a high-pressure microwave plasma apparatus with pure hydrogen at 2.45 GHz. The broadening caused by Stark effect was obtained by separating (deconvolution) the Doppler broadening and instrumental broadening, which were supposed to be Gaussian profiles, from the total broadened profile. The electron density and the electric field were simultaneously obtained by the derived Stark broadening of spectral lines. The results indicate that both the electron density and the electric field strength increase with the increase of microwave power, and they increase initially and then decrease with the increase of the pressure. Their peaks are respectively 3.55×12 cm-3 and 4.01 kV/cm at the gas pressure of 25 kPa when the microwa
The H Balmer emission lines have been measured on a high-pressure microwave plasma apparatus with pure hydrogen at 2.45 GHz. The broadening caused by Stark effect was obtained by separating (deconvolution) the Doppler broadening and instrumental broadening, which were supposed to be Gaussian profiles, from the total broadened profile. The electron density and the electric field were simultaneously obtained by the derived Stark broadening of spectral lines. The results indicate that both the electron density and the electric field strength increase with the increase of microwave power, and they increase initially and then decrease with the increase of the pressure. Their peaks are respectively 3.55×12 cm-3 and 4.01 kV/cm at the gas pressure of 25 kPa when the microwa
2010,
22.
Abstract:
The atmospheric electron-beam produced air plasma attracts intensive attentions recently. Based on a Monte Carlo toolkit named Geant4, a model including complete physics processes is established to simulate the passage of the electron beam in air in nonuniform magnetic field. By using the model, the characteristics of the electron-beam produced air plasma are simulated. The results indicate that, the nonuniform magnetic field is effective controlling the trajectories of electron beams and can reduce the beam divergence obviously. The energy spectrum becomes wider with the increase of beam penetration depth and secondary electrons play a significant role in low energy range. Moreover, the magnitude of energy deposition at the outlet of the transportation section is two orders higher than th
The atmospheric electron-beam produced air plasma attracts intensive attentions recently. Based on a Monte Carlo toolkit named Geant4, a model including complete physics processes is established to simulate the passage of the electron beam in air in nonuniform magnetic field. By using the model, the characteristics of the electron-beam produced air plasma are simulated. The results indicate that, the nonuniform magnetic field is effective controlling the trajectories of electron beams and can reduce the beam divergence obviously. The energy spectrum becomes wider with the increase of beam penetration depth and secondary electrons play a significant role in low energy range. Moreover, the magnitude of energy deposition at the outlet of the transportation section is two orders higher than th
2010,
22.
Abstract:
Elliptical crystal spectrometers are key instruments to detect the line spectra of soft X-rays in Z-pinch diagnostics. This paper deals with the data processing for an elliptical crystal spectrometer. Taking the diagnostic results obtained in a neon gas-puff Z-pinch experiment as an example, the detailed processes, such as changing the optical density to X-ray intensity according a calibrated film response curve, determining the X-ray energy of the measured spectrum using the energy and the order number of scanned point of identified spectral lines, and correcting the intensity of spectrum using the formula given by Henke are discussed. In the Henke’s formula, the effect of nonuniform dispersion, integrated reflectivity of crystals and transmission of X-ray filters are considered. The fin
Elliptical crystal spectrometers are key instruments to detect the line spectra of soft X-rays in Z-pinch diagnostics. This paper deals with the data processing for an elliptical crystal spectrometer. Taking the diagnostic results obtained in a neon gas-puff Z-pinch experiment as an example, the detailed processes, such as changing the optical density to X-ray intensity according a calibrated film response curve, determining the X-ray energy of the measured spectrum using the energy and the order number of scanned point of identified spectral lines, and correcting the intensity of spectrum using the formula given by Henke are discussed. In the Henke’s formula, the effect of nonuniform dispersion, integrated reflectivity of crystals and transmission of X-ray filters are considered. The fin
2010,
22.
Abstract:
Virtual confocal unstable resonator has high beam quality, and corner cube resonator has the advantage of free-of-adjustment. To obtain resonators with these advantages, the scheme of virtual confocal unstable resonator with sphere corner cube prism as the end-mirror was demonstrated. A sphere corner cube prism(SCCP) unstable resonator Nd:glass laser was got by replacing the end-mirror of the virtual confocal unstable resonator Nd:glass laser with a sphere corner cube prism. The output mode distributions of the two lasers are simulated. The performance of the two lasers was compared through experiments. The results show that the mode distributions agree with the simulation. The maximal output energy is 2 176.9 J and 2 340.6 J for the SCCP resonator laser and virtual confocal unstable reson
Virtual confocal unstable resonator has high beam quality, and corner cube resonator has the advantage of free-of-adjustment. To obtain resonators with these advantages, the scheme of virtual confocal unstable resonator with sphere corner cube prism as the end-mirror was demonstrated. A sphere corner cube prism(SCCP) unstable resonator Nd:glass laser was got by replacing the end-mirror of the virtual confocal unstable resonator Nd:glass laser with a sphere corner cube prism. The output mode distributions of the two lasers are simulated. The performance of the two lasers was compared through experiments. The results show that the mode distributions agree with the simulation. The maximal output energy is 2 176.9 J and 2 340.6 J for the SCCP resonator laser and virtual confocal unstable reson
2010,
22.
Abstract:
The research on in-line phase-contrast imaging with laser-based hard X-ray source was carried out on Shanghai “Shenguang Ⅱ” laser facility, in which the X-rays emitted from laser-produced plasma Ti targets passed through the pinhole with diameter 10 μm, and the X-ray film was used to record the result. Multi-layer capsule structure was obtained in this experiment with the spatial resolution better than 10 μm. The research indicates that the phase contrast imaging have advantages in low-Z material diagnosis and can be used in ICF experiment．
The research on in-line phase-contrast imaging with laser-based hard X-ray source was carried out on Shanghai “Shenguang Ⅱ” laser facility, in which the X-rays emitted from laser-produced plasma Ti targets passed through the pinhole with diameter 10 μm, and the X-ray film was used to record the result. Multi-layer capsule structure was obtained in this experiment with the spatial resolution better than 10 μm. The research indicates that the phase contrast imaging have advantages in low-Z material diagnosis and can be used in ICF experiment．
2010,
22.
Abstract:
A diagnostic of time-resolved spectra of scattered light has been developed using optical multichannel analyzer coupled with optical scanning camera. The time-resolved spectra could achieve a goal of SRS temporal response with 10 ps resolution and dimensional response with 0.5 nm resolution. An experiment of laser-plasma interaction in hohlraum plasmas produced by laser beams with 351 nm wavelength, 1 ns pulse duration at SGⅡ laser facility is reported. The time-resolved spectra of scattered light by stimulated Raman scattering(SRS) were measured. There existed a delay-time for the Raman scattering corresponding to the entering laser. When laser entered into a smaller hohlraum, the delay-time was minished. Electron density was obtained by cut-off wavelength analysis.
A diagnostic of time-resolved spectra of scattered light has been developed using optical multichannel analyzer coupled with optical scanning camera. The time-resolved spectra could achieve a goal of SRS temporal response with 10 ps resolution and dimensional response with 0.5 nm resolution. An experiment of laser-plasma interaction in hohlraum plasmas produced by laser beams with 351 nm wavelength, 1 ns pulse duration at SGⅡ laser facility is reported. The time-resolved spectra of scattered light by stimulated Raman scattering(SRS) were measured. There existed a delay-time for the Raman scattering corresponding to the entering laser. When laser entered into a smaller hohlraum, the delay-time was minished. Electron density was obtained by cut-off wavelength analysis.
2010,
22.
Abstract:
It is a new concept to reduce the wave drag of hypersonic vehicles by laser plasma, where the ignition location is an important research parameter. A second-order accurate scheme based on finite volume method and domain decomposition of structural grid is used to compute the influence of ignition location on drag reduction at Mach number of 6.5 and flight height of 30 km. The results show that laser plasma can effectively reduce hypersonic blunt body vehicle’s drag. When the ratio of the distance between ignition location and stagnation point to vehicle diameter is 2, the reduction effect is the best, and the results of numerical simulation and theory are consistent．
It is a new concept to reduce the wave drag of hypersonic vehicles by laser plasma, where the ignition location is an important research parameter. A second-order accurate scheme based on finite volume method and domain decomposition of structural grid is used to compute the influence of ignition location on drag reduction at Mach number of 6.5 and flight height of 30 km. The results show that laser plasma can effectively reduce hypersonic blunt body vehicle’s drag. When the ratio of the distance between ignition location and stagnation point to vehicle diameter is 2, the reduction effect is the best, and the results of numerical simulation and theory are consistent．
2010,
22.
Abstract:
The design principle of magnetic probe for current measurement through plasmas is introduced. A micro magnetic probe device is manufactured to diagnose the load current in Z-pinch experiments on pulsed power facilities, according to the actual structure of wire-array load and the experimental layout. The sensitivity of the probe is calibrated through a load simulator that has the same size as the load used in experiments. Experimental results show that, when the pulsed power facility works at 1.2 MA peak current with 60 ns rise-time, the load current measured by this probe has 12% difference in magnitude and 5 ns difference in peak current time from that measured by accelerator current monitor.
The design principle of magnetic probe for current measurement through plasmas is introduced. A micro magnetic probe device is manufactured to diagnose the load current in Z-pinch experiments on pulsed power facilities, according to the actual structure of wire-array load and the experimental layout. The sensitivity of the probe is calibrated through a load simulator that has the same size as the load used in experiments. Experimental results show that, when the pulsed power facility works at 1.2 MA peak current with 60 ns rise-time, the load current measured by this probe has 12% difference in magnitude and 5 ns difference in peak current time from that measured by accelerator current monitor.
2010,
22.
Abstract:
A theoretical model of signal-to-noise ratio(SNR) in interferometric imaging system is proposed by means of statistical optics. According to the theoretical model, relations between system’s SNR and parameters are analyzed numerically and some conclusions are drawn. To obtain high SNR, the ratio of signal intensity to noise intensity should be improved, the intensities of reference and test beams should be matched, the number and roughness of optical elements in imaging system should be decreased, and the coherent length of optical field should be about 2 to 5 times the optical path difference between reference and test beams. In order to make SNR higher than 10, the standard deviation of fabrication error of all optical elements in system must be less than one-fourth of wavelength. The t
A theoretical model of signal-to-noise ratio(SNR) in interferometric imaging system is proposed by means of statistical optics. According to the theoretical model, relations between system’s SNR and parameters are analyzed numerically and some conclusions are drawn. To obtain high SNR, the ratio of signal intensity to noise intensity should be improved, the intensities of reference and test beams should be matched, the number and roughness of optical elements in imaging system should be decreased, and the coherent length of optical field should be about 2 to 5 times the optical path difference between reference and test beams. In order to make SNR higher than 10, the standard deviation of fabrication error of all optical elements in system must be less than one-fourth of wavelength. The t
2010,
22.
Abstract:
Time-resolved X-ray spectroscopy has been used to study the implosion physics of indirectly driven inertial confinement fusion experiments on the SG Ⅱ laser facility. Through the use of high-Z dopants (Ar) in D2 gas, K-shell emissions, which provide information on core conditions, were recorded by streaked X-ray crystal spectrometer. Evolution of core electron temperatures was then deduced by comparing the line intensity ratio of the Heα to Lyα resonance lines inferred from experiments with that obtained by theoretical calculations, and self-absorption effects are corrected by the escape factor. The results show that this method for electron temperature diagnosis is not sensitive to the variation of electron density, and the Heα and Lyα lines are optically thin in current experiments.
Time-resolved X-ray spectroscopy has been used to study the implosion physics of indirectly driven inertial confinement fusion experiments on the SG Ⅱ laser facility. Through the use of high-Z dopants (Ar) in D2 gas, K-shell emissions, which provide information on core conditions, were recorded by streaked X-ray crystal spectrometer. Evolution of core electron temperatures was then deduced by comparing the line intensity ratio of the Heα to Lyα resonance lines inferred from experiments with that obtained by theoretical calculations, and self-absorption effects are corrected by the escape factor. The results show that this method for electron temperature diagnosis is not sensitive to the variation of electron density, and the Heα and Lyα lines are optically thin in current experiments.
2010,
22.
Abstract:
The lower hybrid current drive experiment has been performed on the HT-7 tokamak. The wave power varied from 100 kW to 700 kW with a frequency of 2.45 GHz. The relation between the power of lower hybrid wave and the average effective charge number and electron temperature was studied. It is shown that the current drive efficiency is proportional to the electron temperature, and inversely proportional to the effective charge number. The dynamic control of the impurity of plasma is a key to improve the current drive efficiency.
The lower hybrid current drive experiment has been performed on the HT-7 tokamak. The wave power varied from 100 kW to 700 kW with a frequency of 2.45 GHz. The relation between the power of lower hybrid wave and the average effective charge number and electron temperature was studied. It is shown that the current drive efficiency is proportional to the electron temperature, and inversely proportional to the effective charge number. The dynamic control of the impurity of plasma is a key to improve the current drive efficiency.
2010,
22.
Abstract:
This paper studies the edge enhancement imaging using a spiral zone plate(SZP), which can improve imaging quality of the border areas inside the plasma. An SZP was fabricated for the visible light imaging with the outmost width of 3 μm. Edge-enhanced imaging of amplitude objects were carried out using the SZP. High quality images of edges in the amplitude objects were obtained in our experiments and the intensity of edges areas in the images was improved greatly. Experimental analysis shows that high quality edge-enhanced imaging can also be obtained using SZP even when the separation between the objects and optics is in the Fresnel diffraction ranges. This means that the spiral zone plate can provide a wide field of view and can be used for large-size object imaging.
This paper studies the edge enhancement imaging using a spiral zone plate(SZP), which can improve imaging quality of the border areas inside the plasma. An SZP was fabricated for the visible light imaging with the outmost width of 3 μm. Edge-enhanced imaging of amplitude objects were carried out using the SZP. High quality images of edges in the amplitude objects were obtained in our experiments and the intensity of edges areas in the images was improved greatly. Experimental analysis shows that high quality edge-enhanced imaging can also be obtained using SZP even when the separation between the objects and optics is in the Fresnel diffraction ranges. This means that the spiral zone plate can provide a wide field of view and can be used for large-size object imaging.
2010,
22.
Abstract:
Thermal gravity analysis was applied to obtain the thermal pyrolysis behaviour of four kinds of poly (alpha-methylstyrene) of different average relative molecular mass. Experiments indicated that the pyrolysis temperature of poly (alpha-methylstyrene) covered 220 ℃ to 340 ℃, and that of glow discharge polymer covered 350 ℃ to 450 ℃. Degradation temperature kept fixed at the rate of 20 ℃/min and 30 ℃/min, and the temperature increased when the rate was no more than 20 ℃/min.
Thermal gravity analysis was applied to obtain the thermal pyrolysis behaviour of four kinds of poly (alpha-methylstyrene) of different average relative molecular mass. Experiments indicated that the pyrolysis temperature of poly (alpha-methylstyrene) covered 220 ℃ to 340 ℃, and that of glow discharge polymer covered 350 ℃ to 450 ℃. Degradation temperature kept fixed at the rate of 20 ℃/min and 30 ℃/min, and the temperature increased when the rate was no more than 20 ℃/min.
2010,
22.
Abstract:
Based on the microliquid technique, a T-microchannel droplet generator was designed and developed for the continuous fabrication of hollow foam micro-shells of controlled size. Solutions of an internal water phase, an oil phase (divinylbenzene(DVB) monomer, dibutylphthalate solvent, and azodiisobutyronitrile initiator), and an external water phase were used in the fabrication of micro-shells. DVB hollow foam micro-shells of 700 to 1 200 μm in diameter and 60 to 100 μm in thickness were finally prepared in the density of 90 to 120 mg·cm-3 by level-rotation-heating, solvent exchanging and supercritical drying. Their morphology and diameter dispersivity were characterized by optical microscope, X-ray diffraction microscope and scanning electron microscope, etc. The results show that, the m
Based on the microliquid technique, a T-microchannel droplet generator was designed and developed for the continuous fabrication of hollow foam micro-shells of controlled size. Solutions of an internal water phase, an oil phase (divinylbenzene(DVB) monomer, dibutylphthalate solvent, and azodiisobutyronitrile initiator), and an external water phase were used in the fabrication of micro-shells. DVB hollow foam micro-shells of 700 to 1 200 μm in diameter and 60 to 100 μm in thickness were finally prepared in the density of 90 to 120 mg·cm-3 by level-rotation-heating, solvent exchanging and supercritical drying. Their morphology and diameter dispersivity were characterized by optical microscope, X-ray diffraction microscope and scanning electron microscope, etc. The results show that, the m
2010,
22.
Abstract:
According to the requirements of the Shenguang Ⅱ high power laser facility, a novel piezoelectric stepper actuator was designed using piezoelectric stack as actuator element. Utilizing lever mechanism, the moving part is clamped alternatively by clamp mechanism and feed mechanism, and large stroke is created by accumulating the relatively small displacements produced by piezoelectric elements. The characteristics of the system are simple control, large stroke, high resolution and power-off hold. The experiment of the prototype shows that, the actuator has a resolution of 50 nm, travel of 21 mm．
According to the requirements of the Shenguang Ⅱ high power laser facility, a novel piezoelectric stepper actuator was designed using piezoelectric stack as actuator element. Utilizing lever mechanism, the moving part is clamped alternatively by clamp mechanism and feed mechanism, and large stroke is created by accumulating the relatively small displacements produced by piezoelectric elements. The characteristics of the system are simple control, large stroke, high resolution and power-off hold. The experiment of the prototype shows that, the actuator has a resolution of 50 nm, travel of 21 mm．
2010,
22.
Abstract:
High power microwave (HPM) subaerial propagation is simulated with finite difference time domain (FDTD) method. In the simulation, a mixed absorbing boundary is presented by combining perfectly matched layer (PML) with generalized perfectly matched layer (GPML). The correctness of the model is verified by contrasting the numerical value with the analytic value at level ground, and the scattering properties of HPM is analyzed by the numerical values at rough ground. Theoretical analyses and simulation results show that, diffraction phenomena arising from the edge can be restrained by using this method. The scattering coefficient curve of rough surface is similar to that at level ground in overall trend, however, it has no Brewster angle.
High power microwave (HPM) subaerial propagation is simulated with finite difference time domain (FDTD) method. In the simulation, a mixed absorbing boundary is presented by combining perfectly matched layer (PML) with generalized perfectly matched layer (GPML). The correctness of the model is verified by contrasting the numerical value with the analytic value at level ground, and the scattering properties of HPM is analyzed by the numerical values at rough ground. Theoretical analyses and simulation results show that, diffraction phenomena arising from the edge can be restrained by using this method. The scattering coefficient curve of rough surface is similar to that at level ground in overall trend, however, it has no Brewster angle.
2010,
22.
Abstract:
A rational physical model of anode grid, used to describe the electron scattering process in anode grid, was established based on the 3D Yee grid model and the time-discrete frog-leap model. According to the classical collision theory, the formulas of scattering angle and momentum were deduced. The anode grid scattering process of Gaussian electron beams in a radial vircator was simulated by Monte-Carlo method. The simulation results demonstrate an evident virtual cathode phenomenon. The average power is up to 0.60 GW, the efficiency of virtual cathode is 4.5%, the microwave frequency is 4.7 GHz, and the main mode is TM01. The results accord with the simulation data derived in previous papers.
A rational physical model of anode grid, used to describe the electron scattering process in anode grid, was established based on the 3D Yee grid model and the time-discrete frog-leap model. According to the classical collision theory, the formulas of scattering angle and momentum were deduced. The anode grid scattering process of Gaussian electron beams in a radial vircator was simulated by Monte-Carlo method. The simulation results demonstrate an evident virtual cathode phenomenon. The average power is up to 0.60 GW, the efficiency of virtual cathode is 4.5%, the microwave frequency is 4.7 GHz, and the main mode is TM01. The results accord with the simulation data derived in previous papers.
2010,
22.
Abstract:
This paper introduces a self-developed, three-dimensional parallelized fully-electromagnetic particle simulation code UNIPIC-3D. In the code, the electromagnetic fields are updated using the second-order, finite-difference time-domain (FDTD) method, and the particles are moved using the relativistic Newton-Lorentz force equation. The code can be used to simulate the high-power microwave (HPM) devices, such as the relativistic backward wave oscillator, coaxial vircator, and magnetically insulated line oscillator (MILO), etc. Users can use the graphical user’s interface to create complex geometric structures of the simulated HPM devices, which can be automatically meshed by UNIPIC-3D code. The code has a powerful post-processor which can display the electric field, magnetic field, current,
This paper introduces a self-developed, three-dimensional parallelized fully-electromagnetic particle simulation code UNIPIC-3D. In the code, the electromagnetic fields are updated using the second-order, finite-difference time-domain (FDTD) method, and the particles are moved using the relativistic Newton-Lorentz force equation. The code can be used to simulate the high-power microwave (HPM) devices, such as the relativistic backward wave oscillator, coaxial vircator, and magnetically insulated line oscillator (MILO), etc. Users can use the graphical user’s interface to create complex geometric structures of the simulated HPM devices, which can be automatically meshed by UNIPIC-3D code. The code has a powerful post-processor which can display the electric field, magnetic field, current,
2010,
22.
Abstract:
A code used to analyze beam-wave interaction in complex cavity is written based on the self-consistent nonlinear beam-wave interaction theory. The code is used to optimize cavity and electromagnetic parameters of a gradual transition complex cavity with second-harmonic waves of TE021-TE031 mode group. Simulations using the software Magic show a good agreement with calculations. Based on the calculations and simulations, a second-harmonics complex-cavity gyrotron is developed. Experiments show that the gyrotron delivers steadily peak power of 156 kW with an efficiency of 27.1% and output of TE01 mode at frequency 94 GHz, voltage 57.5 kV and current 10 A. Data of calculations and simulations are consistent with those from the experiments.
A code used to analyze beam-wave interaction in complex cavity is written based on the self-consistent nonlinear beam-wave interaction theory. The code is used to optimize cavity and electromagnetic parameters of a gradual transition complex cavity with second-harmonic waves of TE021-TE031 mode group. Simulations using the software Magic show a good agreement with calculations. Based on the calculations and simulations, a second-harmonics complex-cavity gyrotron is developed. Experiments show that the gyrotron delivers steadily peak power of 156 kW with an efficiency of 27.1% and output of TE01 mode at frequency 94 GHz, voltage 57.5 kV and current 10 A. Data of calculations and simulations are consistent with those from the experiments.
2010,
22.
Abstract:
Based on the possible application of low power, large area, inhomogeneous plasma to radar stealth, many standard commercial fluorescent lamps placed directly against each other were used to produce a inhomogeneous plasma layer (area 60 cm×52 cm, power 400 W). The reflection and transmission of E-waves (electric field of the waves was parallel to tube axis ) in the frequency range of 1 to 8 GHz were investigated both experimentally and numerically. The strong absorption and weak reflection of E-waves were observed near 1 to 4 GHz, and the one-way attenuation trended to a peak of 8 dB. The two-dimensional piecewise linear current density (JE) recursive convolution finite-difference time-domain (PLJERC-FDTD) algorithm was applied to simulate the transient progress of E-waves traveling throug
Based on the possible application of low power, large area, inhomogeneous plasma to radar stealth, many standard commercial fluorescent lamps placed directly against each other were used to produce a inhomogeneous plasma layer (area 60 cm×52 cm, power 400 W). The reflection and transmission of E-waves (electric field of the waves was parallel to tube axis ) in the frequency range of 1 to 8 GHz were investigated both experimentally and numerically. The strong absorption and weak reflection of E-waves were observed near 1 to 4 GHz, and the one-way attenuation trended to a peak of 8 dB. The two-dimensional piecewise linear current density (JE) recursive convolution finite-difference time-domain (PLJERC-FDTD) algorithm was applied to simulate the transient progress of E-waves traveling throug
2010,
22.
Abstract:
Based on the 2D band-limited Weierstrass function, the model of the rough sea surface is developed, and the effects of the fractal dimension, the frequency and amplitude factor are discussed. Considering the simulated fractal surface, the analytic expression of scattering coefficient is deduced based on Helmholtz integral and Kirchhoff approximation. The shadow function is used to amend the scattering coefficient at low grazing angle when microwaves are shaded by the rough sea surface. The effects of the fractal dimension, the frequency and amplitude factor and the incidence angle on the electromagnetic scattering are discussed. The peaks of scattering coefficient are more uniformly distributed with the increasing of the fractal dimension or the frequency and amplitude factor. The back sca
Based on the 2D band-limited Weierstrass function, the model of the rough sea surface is developed, and the effects of the fractal dimension, the frequency and amplitude factor are discussed. Considering the simulated fractal surface, the analytic expression of scattering coefficient is deduced based on Helmholtz integral and Kirchhoff approximation. The shadow function is used to amend the scattering coefficient at low grazing angle when microwaves are shaded by the rough sea surface. The effects of the fractal dimension, the frequency and amplitude factor and the incidence angle on the electromagnetic scattering are discussed. The peaks of scattering coefficient are more uniformly distributed with the increasing of the fractal dimension or the frequency and amplitude factor. The back sca
2010,
22.
Abstract:
Titanium-zirconium-vanadium(TiZrV) non-evaporable getter (NEG), which can be fully activated after 24 hours heating at 180 ℃, has been applied in some particle accelerators owing to its outstanding vacuum performance. In our experiments, TiZrV films were deposited onto the inner wall of stainless steel pipes via DC sputtering using argon gas as the sputtering gas. Witness samples were investigated by scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The average composition of TiZrV samples deposited under various conditions was Ti 30%, Zr 30%, and V 40%, which is in the “low activation temperature zone”. XRD results show that TiZrV films are amorphous and composed of nanocrystalline grains.
Titanium-zirconium-vanadium(TiZrV) non-evaporable getter (NEG), which can be fully activated after 24 hours heating at 180 ℃, has been applied in some particle accelerators owing to its outstanding vacuum performance. In our experiments, TiZrV films were deposited onto the inner wall of stainless steel pipes via DC sputtering using argon gas as the sputtering gas. Witness samples were investigated by scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The average composition of TiZrV samples deposited under various conditions was Ti 30%, Zr 30%, and V 40%, which is in the “low activation temperature zone”. XRD results show that TiZrV films are amorphous and composed of nanocrystalline grains.
2010,
22.
Abstract:
For deuterium clusters and methane clusters produced by specific jet nozzle, Rayleigh scattering has been employed to investigate the cluster formation process and to measure the cluster size at different gas back pressure. The comparison between Hegena’s theory and our experiment shows that, experimental sizes of deuterium and methane clusters are larger than their respective theoretical ones; the methane clusters derived at 298 K is smaller than the deuterium clusters derived at 80 K, but hydrogen atoms in methane clusters are at least 1.98 times the number of deuterium atoms in deuterium clusters under the same back pressure.
For deuterium clusters and methane clusters produced by specific jet nozzle, Rayleigh scattering has been employed to investigate the cluster formation process and to measure the cluster size at different gas back pressure. The comparison between Hegena’s theory and our experiment shows that, experimental sizes of deuterium and methane clusters are larger than their respective theoretical ones; the methane clusters derived at 298 K is smaller than the deuterium clusters derived at 80 K, but hydrogen atoms in methane clusters are at least 1.98 times the number of deuterium atoms in deuterium clusters under the same back pressure.
2010,
22.
Abstract:
The injection, acceleration and extraction of sector-separated cyclotron(SSC) are analyzed and simulated to get the transverse and longitudinal acceptance, using two typical ions 238U36+ and 70Zn10+ with the energy of 9.7 MeV/u and 5.62 MeV/u respectively. In order to study the actual acceptance of SSC, the isochronous magnetic field model in coincidence with the real field is established by Kr-Kb and Lagrange methods on the basis of the actual measurement. The transverse and longitudinal acceptance is calculated under the above isochronous magnetic field model, and the main reason for the low efficiency and acceptance of SSC is the defaults in the design of MSI3 in the injection system and MSE3 in the extraction system. The results show that the
The injection, acceleration and extraction of sector-separated cyclotron(SSC) are analyzed and simulated to get the transverse and longitudinal acceptance, using two typical ions 238U36+ and 70Zn10+ with the energy of 9.7 MeV/u and 5.62 MeV/u respectively. In order to study the actual acceptance of SSC, the isochronous magnetic field model in coincidence with the real field is established by Kr-Kb and Lagrange methods on the basis of the actual measurement. The transverse and longitudinal acceptance is calculated under the above isochronous magnetic field model, and the main reason for the low efficiency and acceptance of SSC is the defaults in the design of MSI3 in the injection system and MSE3 in the extraction system. The results show that the
2010,
22.
Abstract:
The main dipole power supply is the pivotal device of the Heavy Ion Research Facility in Lanzhou-Cooling Storage Ring (HIRFL-CSR) project and is the most technically demanding source. A special topology and control method has been used in the power supply. This paper firstly introduces the main circuit topology, which includes a silicon controlled rectifier and a parallel switching-mode rectifier. The topology is adopted to realize the peak output power of 3.15 MW (3 kA, 1.45 kV) and pulse-mode working state. Then it presents and discusses the control method and double reference setting system of the power supply, which are used to fulfill the strict requirements especially for the tracking error (less than ±2×10-4). Finally, it introduces the process of commissioning and the upgrading o
The main dipole power supply is the pivotal device of the Heavy Ion Research Facility in Lanzhou-Cooling Storage Ring (HIRFL-CSR) project and is the most technically demanding source. A special topology and control method has been used in the power supply. This paper firstly introduces the main circuit topology, which includes a silicon controlled rectifier and a parallel switching-mode rectifier. The topology is adopted to realize the peak output power of 3.15 MW (3 kA, 1.45 kV) and pulse-mode working state. Then it presents and discusses the control method and double reference setting system of the power supply, which are used to fulfill the strict requirements especially for the tracking error (less than ±2×10-4). Finally, it introduces the process of commissioning and the upgrading o
2010,
22.
Abstract:
This paper introduces the digital lock-in detection theory and discusses its feasibility to obtain the damping rate in turn-by-turn measurement systems. Numerical simulations of this method were carried out with Matlab. Then principle presenting beam experiments were conducted on the Heifei Light Source(HLS) storage ring. The measured beta oscillation growth time is about 0.26 ms and the damping time is about 1.2 ms. Simulation and experimental results show that, the digital lock-in detection method is effective in damping rate measurement in turn-by-turn measurement systems.
This paper introduces the digital lock-in detection theory and discusses its feasibility to obtain the damping rate in turn-by-turn measurement systems. Numerical simulations of this method were carried out with Matlab. Then principle presenting beam experiments were conducted on the Heifei Light Source(HLS) storage ring. The measured beta oscillation growth time is about 0.26 ms and the damping time is about 1.2 ms. Simulation and experimental results show that, the digital lock-in detection method is effective in damping rate measurement in turn-by-turn measurement systems.
2010,
22.
Abstract:
An optical transition radiation (OTR)-based measurement system has been designed to obtain the instantaneous beam divergence and spot size of Dragon-Ⅰ linear induction accelerator (LIA) simultaneously. It can achieve instantaneous measurement within about 10 ns, and provides an on-line instantaneous beam diagnostic method for a 18.5 MeV, 2 kA, 90 ns electron pulse. The typical results of beam spot and beam divergence are about 9 mm and 10.5 mrad. This system lays a foundation for the study of time-resolved beam diagnostic technique which will be adopted in Dragon-Ⅰ LIA.
An optical transition radiation (OTR)-based measurement system has been designed to obtain the instantaneous beam divergence and spot size of Dragon-Ⅰ linear induction accelerator (LIA) simultaneously. It can achieve instantaneous measurement within about 10 ns, and provides an on-line instantaneous beam diagnostic method for a 18.5 MeV, 2 kA, 90 ns electron pulse. The typical results of beam spot and beam divergence are about 9 mm and 10.5 mrad. This system lays a foundation for the study of time-resolved beam diagnostic technique which will be adopted in Dragon-Ⅰ LIA.
2010,
22.
Abstract:
To meet the increasing demand for domestic industrial electron accelerators, a new type of compact continuous wave (CW) electron accelerator which works at 180 MHz is proposed. It accelerates the electron beam within the cavity and performs successive acceleration by several bending magnets located outside the cavity. The resonant cavity design is optimized by CST and the particle dynamics is simulated by Parmela. The longitudinal stability and the transverse focusing of electron beams are also analyzed and verified by beam simulation. The result shows that this accelerator can accelerate continuous beams at the output power of 100 kW with a beam energy of 9 MeV．
To meet the increasing demand for domestic industrial electron accelerators, a new type of compact continuous wave (CW) electron accelerator which works at 180 MHz is proposed. It accelerates the electron beam within the cavity and performs successive acceleration by several bending magnets located outside the cavity. The resonant cavity design is optimized by CST and the particle dynamics is simulated by Parmela. The longitudinal stability and the transverse focusing of electron beams are also analyzed and verified by beam simulation. The result shows that this accelerator can accelerate continuous beams at the output power of 100 kW with a beam energy of 9 MeV．
2010,
22.
Abstract:
In order to enhance the beam transmission efficiency, intensity and stability of SFC (Sector Focusing Cyclotron), the power supply must be stabilized with long-term variations at a magnitude of 10-4. A high-precision and stable power control system was designed and optimized adopting the ATmega128 as the microcontroller, based on CPLD logic programming to communicate between ATmega128 MCU and peripheral devices, and the device RTL8019AS was used to realize remote control. The system has been successfully used in injector SFC of heavy ion research facility in Lanzhou. The result shows that it works stably and reliably and it can be flexibly remote-controlled.
In order to enhance the beam transmission efficiency, intensity and stability of SFC (Sector Focusing Cyclotron), the power supply must be stabilized with long-term variations at a magnitude of 10-4. A high-precision and stable power control system was designed and optimized adopting the ATmega128 as the microcontroller, based on CPLD logic programming to communicate between ATmega128 MCU and peripheral devices, and the device RTL8019AS was used to realize remote control. The system has been successfully used in injector SFC of heavy ion research facility in Lanzhou. The result shows that it works stably and reliably and it can be flexibly remote-controlled.
2010,
22.
Abstract:
A novel photonic crystal 1×2 splitter is designed based on the self-imaging of multimode interferences in the two-dimensional square photonic crystal waveguides. The transmission characteristics of the splitter is analyzed numerically by the finite-difference time-domain method. In the design process of the photonic crystal waveguide splitter with two out ports, the positions of output waveguides are decided by the positions of the twofold image formed by the self-imaging effect of multimode interferences. The reflective losses are obviously decreased by inserting the dielectric rods, which can vary and match the mode field of the coupling zone, lying at the junctions between the multimode waveguide and single-mode waveguide. The results show that the transmittance of this splitter can be
A novel photonic crystal 1×2 splitter is designed based on the self-imaging of multimode interferences in the two-dimensional square photonic crystal waveguides. The transmission characteristics of the splitter is analyzed numerically by the finite-difference time-domain method. In the design process of the photonic crystal waveguide splitter with two out ports, the positions of output waveguides are decided by the positions of the twofold image formed by the self-imaging effect of multimode interferences. The reflective losses are obviously decreased by inserting the dielectric rods, which can vary and match the mode field of the coupling zone, lying at the junctions between the multimode waveguide and single-mode waveguide. The results show that the transmittance of this splitter can be
2010,
22.
Abstract:
A gamma source pinhole imaging system with direct imaging mode pixellated CdZnTe detector has been constructed based on the principle of pinhole imaging. The energy resolution and peak efficiency of CdZnTe pixellated detector were tested and analyzed. During the preliminary experiments, modulation transfer function (MTF) and additional noise characteristic of pinhole imaging system were investigated and discussed. This paper presents and evaluates the test images of a 0.5 mm diameter 137Cs gamma source. The measured pinhole images are restored with the Lucy-Richardson algorithm. The energy resolution of the CdZnTe pixellated detector system for 662 keV 137Cs are 6.25%～7.50% and photon peak efficiency are 65.0%～72.5%. There is lateral spread information in the source
A gamma source pinhole imaging system with direct imaging mode pixellated CdZnTe detector has been constructed based on the principle of pinhole imaging. The energy resolution and peak efficiency of CdZnTe pixellated detector were tested and analyzed. During the preliminary experiments, modulation transfer function (MTF) and additional noise characteristic of pinhole imaging system were investigated and discussed. This paper presents and evaluates the test images of a 0.5 mm diameter 137Cs gamma source. The measured pinhole images are restored with the Lucy-Richardson algorithm. The energy resolution of the CdZnTe pixellated detector system for 662 keV 137Cs are 6.25%～7.50% and photon peak efficiency are 65.0%～72.5%. There is lateral spread information in the source
2010,
22.
Abstract:
Two rectangular resonant cavities with different anisotropic parameters are designed and investigated, which are filled partially with right-handed semiconductor metamaterial (RHSM) and left-handed semiconductor metamaterial (LHSM). The resonant mode solutions of the general case of the 3-D rectangular resonator cavities filled with non-dispersive RHSM and dispersive LHSM are explored by graphical method. It is demonstrated that the resonant modes in such resonant cavities are closely dependent on the spatial dispersion relation of the semiconductor metamaterial. Each resonant cavity including six subcases of different combinations of real and imaginary propagation constants of the two regions is discussed, and requirements of the geometry parameters to construct a resonant cavity of no ph
Two rectangular resonant cavities with different anisotropic parameters are designed and investigated, which are filled partially with right-handed semiconductor metamaterial (RHSM) and left-handed semiconductor metamaterial (LHSM). The resonant mode solutions of the general case of the 3-D rectangular resonator cavities filled with non-dispersive RHSM and dispersive LHSM are explored by graphical method. It is demonstrated that the resonant modes in such resonant cavities are closely dependent on the spatial dispersion relation of the semiconductor metamaterial. Each resonant cavity including six subcases of different combinations of real and imaginary propagation constants of the two regions is discussed, and requirements of the geometry parameters to construct a resonant cavity of no ph
2010,
22.
Abstract:
In experiments of hydrogen discharge ,4 invariable-energy unknown X-ray lines were detected when TiT radioactive source bombarded background target. The unknown X-ray disappeared when TiT radioactive source bombarded heat treated background target, which proved that unknown X-ray lines were not emissions from impurities in the target. Two background targets of homogeneity material were made, one of which was heated, and then both were bombarded by the hydrogen discharge source to form the irradiated targets. TiT radioactive source bombarded the irradiated targets, and 4 unknown X-ray lines of the heat treated target were evident, which proves that heat treatment enhances adsorption capability of target.
In experiments of hydrogen discharge ,4 invariable-energy unknown X-ray lines were detected when TiT radioactive source bombarded background target. The unknown X-ray disappeared when TiT radioactive source bombarded heat treated background target, which proved that unknown X-ray lines were not emissions from impurities in the target. Two background targets of homogeneity material were made, one of which was heated, and then both were bombarded by the hydrogen discharge source to form the irradiated targets. TiT radioactive source bombarded the irradiated targets, and 4 unknown X-ray lines of the heat treated target were evident, which proves that heat treatment enhances adsorption capability of target.
2010,
22.
Abstract:
The supersmooth optical substrate with extremely low subsurface damage is essential to obtain high laser damage threshold films. In view of the difference in subsurface morphology, the laser confocal microscope technique combined with light scattering method is firstly used to detect the subsurface defects of fused silica substrates ground by brand W10 and W5 SiC abrasive particles, and the relation between the defects size and the scattering intensity are discussed. Then chemical etching method is introduced to expose the inner features at arbitrary depth for the polished sample, the influences of chemical resultant and redeposition layer on etching rate are analyzed, and the distribution and depth of damage layer are estimated. Furthermore, the relation between RMS roughness and etching
The supersmooth optical substrate with extremely low subsurface damage is essential to obtain high laser damage threshold films. In view of the difference in subsurface morphology, the laser confocal microscope technique combined with light scattering method is firstly used to detect the subsurface defects of fused silica substrates ground by brand W10 and W5 SiC abrasive particles, and the relation between the defects size and the scattering intensity are discussed. Then chemical etching method is introduced to expose the inner features at arbitrary depth for the polished sample, the influences of chemical resultant and redeposition layer on etching rate are analyzed, and the distribution and depth of damage layer are estimated. Furthermore, the relation between RMS roughness and etching
2010,
22.
Abstract:
This paper presents the experiment results of the combined irradiation by neutron and gamma ray on SDA9760, a 10-bit CMOS digital-to-analog converter. The electrical and functional tests were conducted in four types of irradiation: neutron, gamma ray, combined irradiation of neutron and gamma ray, and gamma ray after neutron irradiation. The experiment results show that the mixed neutron and gamma irradiation can induce a synergistic effect on the sample, i.e. the increase of total ionizing dose effect. Compared with neutron or gamma ray radiation, the device exhibits considerably severer degradation under neutron and gamma synergistic irradiation.
This paper presents the experiment results of the combined irradiation by neutron and gamma ray on SDA9760, a 10-bit CMOS digital-to-analog converter. The electrical and functional tests were conducted in four types of irradiation: neutron, gamma ray, combined irradiation of neutron and gamma ray, and gamma ray after neutron irradiation. The experiment results show that the mixed neutron and gamma irradiation can induce a synergistic effect on the sample, i.e. the increase of total ionizing dose effect. Compared with neutron or gamma ray radiation, the device exhibits considerably severer degradation under neutron and gamma synergistic irradiation.
2010,
22.
Abstract:
Auger rates for Au were calculated by quasi-relativistic configuration-averaged method, with the wave functions obtained by Cowan’s codes. Firstly, “configuration-to-configuration Auger rates” for He-like to Dy-like gold were calculated. Then “Auger rates for single electron” for average atom model (AAM) with and without l-splitting were both obtained by averaging the configuration-to-configuration rates. Our data were evaluated through the comparison with other results calculated from more detailed codes, including Cowan’s codes, flexible atomic code and fully relativistic codes. The evaluation shows that most of our data are reliable except those with high orbital quantum number l, which were replaced with valid data obtained by other codes.
Auger rates for Au were calculated by quasi-relativistic configuration-averaged method, with the wave functions obtained by Cowan’s codes. Firstly, “configuration-to-configuration Auger rates” for He-like to Dy-like gold were calculated. Then “Auger rates for single electron” for average atom model (AAM) with and without l-splitting were both obtained by averaging the configuration-to-configuration rates. Our data were evaluated through the comparison with other results calculated from more detailed codes, including Cowan’s codes, flexible atomic code and fully relativistic codes. The evaluation shows that most of our data are reliable except those with high orbital quantum number l, which were replaced with valid data obtained by other codes.
2010,
22.
Abstract:
The difference between two images obtained from two flash radiographic imaging experiments under the same conditions reflects the repeatability of imaging. The optical density curves with equal optical path obtained from the images are measured and linearly fitted to evaluate the imaging repeatability of an imaging system. The experiments are conducted to measure the repeatability of the radiographic system with and without back cone respectively, and the imaging repeatability of the film in the system is measured. The results show that the imaging repeatability of the system is about 5%, and the back cone shows no obvious influence on the repeatability. The repeatability error introduced by the film is about 1.6%.
The difference between two images obtained from two flash radiographic imaging experiments under the same conditions reflects the repeatability of imaging. The optical density curves with equal optical path obtained from the images are measured and linearly fitted to evaluate the imaging repeatability of an imaging system. The experiments are conducted to measure the repeatability of the radiographic system with and without back cone respectively, and the imaging repeatability of the film in the system is measured. The results show that the imaging repeatability of the system is about 5%, and the back cone shows no obvious influence on the repeatability. The repeatability error introduced by the film is about 1.6%.
2010,
22.
Abstract:
A new method for controlling the size distribution of Si nanoparticles during the process of pulsed laser ablation is proposed. The nanocrystalline silicon films were prepared by pulsed laser ablating a high resistivity single crystalline Si target in argon gas of 10 Pa. A bunch of argon gas flow was introduced at 2.0 cm above the ablation point within the axial range from 03 cm to 3.0 cm, and the as-prepared Si nanoparticles were deposited on single crystalline Si substrates located at 2.0 cm under the ablation point. Surface morphology of films was observed by scanning electron microscopy (SEM). It is found that the size of grain, without introducing gas flow, increases initially and then decreases with increasing distance between target and substrate, and the peak appears at the dista
A new method for controlling the size distribution of Si nanoparticles during the process of pulsed laser ablation is proposed. The nanocrystalline silicon films were prepared by pulsed laser ablating a high resistivity single crystalline Si target in argon gas of 10 Pa. A bunch of argon gas flow was introduced at 2.0 cm above the ablation point within the axial range from 03 cm to 3.0 cm, and the as-prepared Si nanoparticles were deposited on single crystalline Si substrates located at 2.0 cm under the ablation point. Surface morphology of films was observed by scanning electron microscopy (SEM). It is found that the size of grain, without introducing gas flow, increases initially and then decreases with increasing distance between target and substrate, and the peak appears at the dista
2010,
22.
Abstract:
This paper analyzes several pivotal factors that influence the obtaining of wave-control data for liquid crystal phased array. On the basis of the analysis, the phase difference between the desired phase profile and the actual phase profile is computed, and an iterative method is proposed to obtain the wave-control data by changing the reference voltage or the reference phase profile of liquid crystal phased array. The selection of key parameters in the method is discussed, and the effects of the characteristic curve range and initial Gaussian phase are studied by simulations. As the simulation results shown, the method can accurately acquire wave-control data, and the characteristic curve range of liquid crystal is a very important factor in obtaining wave-control data. When the character
This paper analyzes several pivotal factors that influence the obtaining of wave-control data for liquid crystal phased array. On the basis of the analysis, the phase difference between the desired phase profile and the actual phase profile is computed, and an iterative method is proposed to obtain the wave-control data by changing the reference voltage or the reference phase profile of liquid crystal phased array. The selection of key parameters in the method is discussed, and the effects of the characteristic curve range and initial Gaussian phase are studied by simulations. As the simulation results shown, the method can accurately acquire wave-control data, and the characteristic curve range of liquid crystal is a very important factor in obtaining wave-control data. When the character
2010,
22.
Abstract:
CO2 laser with 10.6 μm wavelength is used to irradiate damage of different types. Testing with 351 nm wavelength ultra-violet laser, it is found that for damage pits with size below 80 μm and scratchs with size below 40 μm, the larger damage size is, the less threshold enhancement of damage is. Mitigation is not distinct when the size of scratch is wider than 40 μm. During laser conditioning, heat stress results from short interaction time and asymmetrical temperature distribution, thus radial crack appears after damage and could expand if exposed to ultraviolet laser. After annealed in an oven for 3 hours, crack would not occur on the sample with damage.
CO2 laser with 10.6 μm wavelength is used to irradiate damage of different types. Testing with 351 nm wavelength ultra-violet laser, it is found that for damage pits with size below 80 μm and scratchs with size below 40 μm, the larger damage size is, the less threshold enhancement of damage is. Mitigation is not distinct when the size of scratch is wider than 40 μm. During laser conditioning, heat stress results from short interaction time and asymmetrical temperature distribution, thus radial crack appears after damage and could expand if exposed to ultraviolet laser. After annealed in an oven for 3 hours, crack would not occur on the sample with damage.
2010,
22.
Abstract:
To resolve transient response of the pole coupling parameter extraction problems from strong electromagnetic pulse, the traditional matrix pencil algorithm has been improved. Preprocessing the noisy transient response with inter-related processing method can effectively improve the extraction accuracy under low signal-to-noise ratio(SNR). The data are constructed as Hankle matrix after discretization, combined with singular value decomposition, for solving the generalized eigenvalue. Then, the signal poles parameter information can be extracted. It is verified that the improved algorithm has strong anti-noise ability and high fit through simulation analysis and reconstruction of the waveform.
To resolve transient response of the pole coupling parameter extraction problems from strong electromagnetic pulse, the traditional matrix pencil algorithm has been improved. Preprocessing the noisy transient response with inter-related processing method can effectively improve the extraction accuracy under low signal-to-noise ratio(SNR). The data are constructed as Hankle matrix after discretization, combined with singular value decomposition, for solving the generalized eigenvalue. Then, the signal poles parameter information can be extracted. It is verified that the improved algorithm has strong anti-noise ability and high fit through simulation analysis and reconstruction of the waveform.
2010,
22.
Abstract:
This paper introdues two estimating methods of equivalent stray capacitance to ground of Marx generator, i.e., step accumulation method and energy conservation method. In step accumulation method, every step stray capacitance is approximately calculated, then accumulated as the equivalent stray capacitance of Marx generator. Energy conservation method derives the equivalent stray capacitance, based on the assumption that the energy stored in each step capacitance is the same as that in equivalent stray capacitance under the voltage of output point of Marx generator. Comparison of equivalent stray capacitances calculated by the two methods and the experimental result was made for the Marx generator of Flash-Ⅱ accelerator. The theoretically calculated results are both 114 pF, and the experi
This paper introdues two estimating methods of equivalent stray capacitance to ground of Marx generator, i.e., step accumulation method and energy conservation method. In step accumulation method, every step stray capacitance is approximately calculated, then accumulated as the equivalent stray capacitance of Marx generator. Energy conservation method derives the equivalent stray capacitance, based on the assumption that the energy stored in each step capacitance is the same as that in equivalent stray capacitance under the voltage of output point of Marx generator. Comparison of equivalent stray capacitances calculated by the two methods and the experimental result was made for the Marx generator of Flash-Ⅱ accelerator. The theoretically calculated results are both 114 pF, and the experi
2010,
22.
Abstract:
A self-integrated Rogowski coil has been designed to measure the current of the capacitive pulse power supply module. The waveform of the primary Rogowski coil output will distort because of the saturation of the ferromagnetic core in the coil under large current. The way to solve the problem is to use ferromagnetic materials of large saturated magnetic field strength, and to add inverse magnetic field on the Rogowski coil or reduce the excitated current equivalently. The measurement range can be enhanced with increasing the diameter and cross section area of the core for given ferromagnetic material. To increase the ratio of the self-inductance to the resistance of the coil is another way which can be achieved by winding the insulated wire in multiple layers. The current for core saturati
A self-integrated Rogowski coil has been designed to measure the current of the capacitive pulse power supply module. The waveform of the primary Rogowski coil output will distort because of the saturation of the ferromagnetic core in the coil under large current. The way to solve the problem is to use ferromagnetic materials of large saturated magnetic field strength, and to add inverse magnetic field on the Rogowski coil or reduce the excitated current equivalently. The measurement range can be enhanced with increasing the diameter and cross section area of the core for given ferromagnetic material. To increase the ratio of the self-inductance to the resistance of the coil is another way which can be achieved by winding the insulated wire in multiple layers. The current for core saturati
2010,
22.
Abstract:
A pulse generator featured with long pulse, ultra-low impedance, and compact structure is designed based on a rolled strip pulse forming line (PFL) and a magnetic switch. This generator was designed to generate a pulse with voltage of 20 kV, current of 40 kA, and duration of 230 ns. It comprises primary energy system, pulse transformer, magnetic switch, rolled strip PFL, rail gap switch, and load. The magnetic switch operates in about 40 kV, which compresses the pulse duration from 10 μs to 2 μs. The all solid-state, rolled strip PFL is rolled up by copper plate and Mylar film separately, whose characteristic impedance and electrical length are respectively 0.5 Ω and about 115 ns. Experiment results gave a 17.8 kV, 270 ns (FWHM) voltage pulse which was a quasi-square wave on the water l
A pulse generator featured with long pulse, ultra-low impedance, and compact structure is designed based on a rolled strip pulse forming line (PFL) and a magnetic switch. This generator was designed to generate a pulse with voltage of 20 kV, current of 40 kA, and duration of 230 ns. It comprises primary energy system, pulse transformer, magnetic switch, rolled strip PFL, rail gap switch, and load. The magnetic switch operates in about 40 kV, which compresses the pulse duration from 10 μs to 2 μs. The all solid-state, rolled strip PFL is rolled up by copper plate and Mylar film separately, whose characteristic impedance and electrical length are respectively 0.5 Ω and about 115 ns. Experiment results gave a 17.8 kV, 270 ns (FWHM) voltage pulse which was a quasi-square wave on the water l
2010,
22.
Abstract:
A high power water dielectric double-pulse compact modulator has been designed using the folded coaxial transmission line method combined with the spiral line method. With two spiral transmission lines, an air core transformer and two trigger switches, double long pulses could be obtained at each end of the pulse forming line(PFL). The wave process of the pulse modulator was analyzed. The influences of the transition part of the modulator on the load voltage were also discussed. Pspice circuit was used to calculate the voltage and current at the dummy loads, and the charging voltage of the PFL. Experiments were done using high power coaxial line at 20 kV, and the results are in good agreement with the theoretical analysis and simulation results.
A high power water dielectric double-pulse compact modulator has been designed using the folded coaxial transmission line method combined with the spiral line method. With two spiral transmission lines, an air core transformer and two trigger switches, double long pulses could be obtained at each end of the pulse forming line(PFL). The wave process of the pulse modulator was analyzed. The influences of the transition part of the modulator on the load voltage were also discussed. Pspice circuit was used to calculate the voltage and current at the dummy loads, and the charging voltage of the PFL. Experiments were done using high power coaxial line at 20 kV, and the results are in good agreement with the theoretical analysis and simulation results.
