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RSS2008 Vol. 20, No. 02
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2008,
20.
Abstract:
The strong electromagnetic interference generated in high power TEA CO2 laser system mainly comes from the main discharge circuit, pulse spark switch and power supply. Such strong electromagnetic interference causes some problems such as data confusion, display frame frequency rolling and damage of power module, etc. in the high power TEA CO2 laser control sub-system. The parts in the high power TEA CO2 laser system where the strong electromagnetic interference occurs and the interference means are tested and analyzed. Adjusting the parameters of the discharge circuit to reduce the electromagnetic interference strength, adopting the patent technology of the buried coaxial high-voltage electric connector to shield the main discharge return circuit, using the PLC as the control core and shie
The strong electromagnetic interference generated in high power TEA CO2 laser system mainly comes from the main discharge circuit, pulse spark switch and power supply. Such strong electromagnetic interference causes some problems such as data confusion, display frame frequency rolling and damage of power module, etc. in the high power TEA CO2 laser control sub-system. The parts in the high power TEA CO2 laser system where the strong electromagnetic interference occurs and the interference means are tested and analyzed. Adjusting the parameters of the discharge circuit to reduce the electromagnetic interference strength, adopting the patent technology of the buried coaxial high-voltage electric connector to shield the main discharge return circuit, using the PLC as the control core and shie
2008,
20.
Abstract:
The atmospheric structure constant of refractive index is an important parameter of denoting atmospheric turbulence, it was measured continuously in Hefei using QHTP-2 micro-thermal meter. The vertical profile of atmospheric structure constant of refractive index in Hefei（0～25 km）is investigated by analysis of experimental data,and the vertical atmospheric structure constant of refractive index model of atmospheric structure constant of refractive index in Hefei is gained based on Hufnagel-Valley model. It is found that the vertical profiles of atmospheric turbulence in Hefei have obvious daily and seasonal diversification. Atmospheric turbulence reduces with random fluctuation as height increases, it has obvious jumping configuration; upper air turbulence model in Hefei preferably acco
The atmospheric structure constant of refractive index is an important parameter of denoting atmospheric turbulence, it was measured continuously in Hefei using QHTP-2 micro-thermal meter. The vertical profile of atmospheric structure constant of refractive index in Hefei（0～25 km）is investigated by analysis of experimental data,and the vertical atmospheric structure constant of refractive index model of atmospheric structure constant of refractive index in Hefei is gained based on Hufnagel-Valley model. It is found that the vertical profiles of atmospheric turbulence in Hefei have obvious daily and seasonal diversification. Atmospheric turbulence reduces with random fluctuation as height increases, it has obvious jumping configuration; upper air turbulence model in Hefei preferably acco
2008,
20.
Abstract:
The efficiency of spectral beam combining based on grating-cavity mostly depends on the coupling efficiency between emitter and cavity. Based on the diffraction integral equation, the coupling efficiency model with abaxial aberration is established. Then, the effect of the system parameters on the coupling efficiency is analyzed quantitatively. The results show that the coupling efficiency decreases when abaxial distance or the order of mode increases, or when mode field radius increases, or when the grating plane or the array plane deviates farther from the focal plane. The grating’s tilt angle and the distance between the grating plane and the output coupling mirror have few influence on the coupling efficiency. For the system with bi-convex lens of 500 mm focal length and 10 mm array
The efficiency of spectral beam combining based on grating-cavity mostly depends on the coupling efficiency between emitter and cavity. Based on the diffraction integral equation, the coupling efficiency model with abaxial aberration is established. Then, the effect of the system parameters on the coupling efficiency is analyzed quantitatively. The results show that the coupling efficiency decreases when abaxial distance or the order of mode increases, or when mode field radius increases, or when the grating plane or the array plane deviates farther from the focal plane. The grating’s tilt angle and the distance between the grating plane and the output coupling mirror have few influence on the coupling efficiency. For the system with bi-convex lens of 500 mm focal length and 10 mm array
2008,
20.
Abstract:
Based on the generalized nonlinear Schrdinger equation, the propagation characteristics of a super Gaussian femtosecond pulse in photonic crystal fibers were numerically simulated by split-step Fourier method. The result shows that soliton disintegration occured in shorter distances and soliton self-frequency shift was more remarkable for super Gaussian pulse than for Gaussian pulse, and a new lower power soliton appeared on the left side of the strong soliton. Otherwise, the 3rd-dispersion would lead to the dissymmetry and the complex structure for the pulse shape and its spectrum, and that would lead to the trend to form soliton. The pulse shape was smoothed by intrapulse stimulated Raman scattering. At the same time the energy between the two solitons was redistributed by self-ste
Based on the generalized nonlinear Schrdinger equation, the propagation characteristics of a super Gaussian femtosecond pulse in photonic crystal fibers were numerically simulated by split-step Fourier method. The result shows that soliton disintegration occured in shorter distances and soliton self-frequency shift was more remarkable for super Gaussian pulse than for Gaussian pulse, and a new lower power soliton appeared on the left side of the strong soliton. Otherwise, the 3rd-dispersion would lead to the dissymmetry and the complex structure for the pulse shape and its spectrum, and that would lead to the trend to form soliton. The pulse shape was smoothed by intrapulse stimulated Raman scattering. At the same time the energy between the two solitons was redistributed by self-ste
2008,
20.
Abstract:
The model of annular beams is given based on the model of flattened multi-Gaussian beams proposed by Tovar. Using the generalized Huygens-Fresnel diffraction integral, the transformation and focusing properties of annular beams passing through an astigmatic lens are studied and analyzed. Furthermore, the effect of astigmatism on the beam quality of the annular beams passing through an astigmatic lens is also discussed. The results show that the annular beams become non-rotational symmetric after passing through an astigmatic lens. The focusing intensity decreases gradually with the increasing of the astigmatic coefficients. The azimuth angle of focusing spot is determined merely by astigmatic coefficients. For the given beam orders and the wavelength of the annular beams, the transformatio
The model of annular beams is given based on the model of flattened multi-Gaussian beams proposed by Tovar. Using the generalized Huygens-Fresnel diffraction integral, the transformation and focusing properties of annular beams passing through an astigmatic lens are studied and analyzed. Furthermore, the effect of astigmatism on the beam quality of the annular beams passing through an astigmatic lens is also discussed. The results show that the annular beams become non-rotational symmetric after passing through an astigmatic lens. The focusing intensity decreases gradually with the increasing of the astigmatic coefficients. The azimuth angle of focusing spot is determined merely by astigmatic coefficients. For the given beam orders and the wavelength of the annular beams, the transformatio
2008,
20.
Abstract:
This paper presents a detailed comparison of several typical theoretical models describing far-field intensity distributions of laser diode with the experimental results in the literature. It is found that the propagation and far-field properties of laser diode have to be described by the non-paraxial theory, and the far-field intensity distributions vary with the output power in general. Different models should be suitably chosen to simulate the far-field behavior in the fast and slow axes of heterostructure laser diode at different power levels. In addition, the Hermite-Gaussian(H-G) model is modified, where the contributions of the odd-order H-G modes are included and the coherent superposition of H-G modes is replaced by the incoherent superposition of H-G modes. The improved model is
This paper presents a detailed comparison of several typical theoretical models describing far-field intensity distributions of laser diode with the experimental results in the literature. It is found that the propagation and far-field properties of laser diode have to be described by the non-paraxial theory, and the far-field intensity distributions vary with the output power in general. Different models should be suitably chosen to simulate the far-field behavior in the fast and slow axes of heterostructure laser diode at different power levels. In addition, the Hermite-Gaussian(H-G) model is modified, where the contributions of the odd-order H-G modes are included and the coherent superposition of H-G modes is replaced by the incoherent superposition of H-G modes. The improved model is
2008,
20.
Abstract:
For the broadband laser obtained by chirped pulses stacking(CPS) method, the physical mechanism has been analyzed and the temporal shape and the spectrum distribution have been given. The effects of the intensity and bandwidth of the incident fundamental field on the third harmonic conversion efficiency of CPS laser using type Ⅰ/Ⅱ and type Ⅰ/Ⅱ/Ⅱ angle-detuning schemes have been analyzed quantitatively. The numerical calculation results have been compared with those of temporal phase modulation(TPM) broadband laser. The results indicate that the Ⅰ/Ⅱ/Ⅱ angle-detuning scheme can increase the third harmonic conversion efficiency obviously, and the third harmonic conversion efficiency of CPS laser can be increased more obviously than that of TPM laser.
For the broadband laser obtained by chirped pulses stacking(CPS) method, the physical mechanism has been analyzed and the temporal shape and the spectrum distribution have been given. The effects of the intensity and bandwidth of the incident fundamental field on the third harmonic conversion efficiency of CPS laser using type Ⅰ/Ⅱ and type Ⅰ/Ⅱ/Ⅱ angle-detuning schemes have been analyzed quantitatively. The numerical calculation results have been compared with those of temporal phase modulation(TPM) broadband laser. The results indicate that the Ⅰ/Ⅱ/Ⅱ angle-detuning scheme can increase the third harmonic conversion efficiency obviously, and the third harmonic conversion efficiency of CPS laser can be increased more obviously than that of TPM laser.
2008,
20.
Abstract:
The physical model of a two-dimensional three-temperature radiation magneto-hydrodynamics code, named MARED, is introduced. The code’s 1 D simulation results are also presented, which include results for different currents and load parameters on facilities of Saturn and Qiangguang-Ⅰ. The plasma parameters’ spatio-temporal distributions are obtained, and their self-consistent dynamic variations suggest that MARED code applies to simulations on different pulse power facilities and load conditions. By comparing results with different load materials, it is found that X-ray power of tungsten wire-array implosion is greater than that of aluminium wire-array for the same load mass. In addition, MARED simulations also show that the calculated X-ray power goes up with the load current, and goes
The physical model of a two-dimensional three-temperature radiation magneto-hydrodynamics code, named MARED, is introduced. The code’s 1 D simulation results are also presented, which include results for different currents and load parameters on facilities of Saturn and Qiangguang-Ⅰ. The plasma parameters’ spatio-temporal distributions are obtained, and their self-consistent dynamic variations suggest that MARED code applies to simulations on different pulse power facilities and load conditions. By comparing results with different load materials, it is found that X-ray power of tungsten wire-array implosion is greater than that of aluminium wire-array for the same load mass. In addition, MARED simulations also show that the calculated X-ray power goes up with the load current, and goes
2008,
20.
Abstract:
Al and MgF2 metal-dielectric multi-layer filters have been fabricated by thermal and electron beam evaporation. Influences of vacuum annealing at 100 ℃, 150 ℃, 200 ℃ and 300 ℃ respectively for 40 min on spectrum, morphology and environmental stability have been analyzed. For all samples, results show that after annealing, rms roughness reduces, maximal transmittance and half width increase. During the storage of the samples in desiccated chamber, the locations of the maximal transmittances have shifted much toward long wavelength, the maximal transmittances reduce and the restrain abilities of visible spectrum weaken for the as-deposited and 300 ℃ annealed samples. While the locations of the maximal transmittances have little shift, the maximal transmittance and the restrain ability o
Al and MgF2 metal-dielectric multi-layer filters have been fabricated by thermal and electron beam evaporation. Influences of vacuum annealing at 100 ℃, 150 ℃, 200 ℃ and 300 ℃ respectively for 40 min on spectrum, morphology and environmental stability have been analyzed. For all samples, results show that after annealing, rms roughness reduces, maximal transmittance and half width increase. During the storage of the samples in desiccated chamber, the locations of the maximal transmittances have shifted much toward long wavelength, the maximal transmittances reduce and the restrain abilities of visible spectrum weaken for the as-deposited and 300 ℃ annealed samples. While the locations of the maximal transmittances have little shift, the maximal transmittance and the restrain ability o
2008,
20.
Abstract:
Phase-shifting interference(PSI) is an important method in surface roughness measurement. In this paper, on the basis of analyzing phase distribution of micro-shell interface, the measuring principle of interior surface roughness of micro-shells is discussed. Inner surface images of PS and PAMS micro-shells were obtained with PSI method. The results are consistent with the measured results by atomic force microscope. The measurement error is analyzed by studying the influence of thickness fluctuation of micro-shell and outer surface roughness of micro-shell on measured results of SiC and crystal Si surface roughness. The experimental result shows that the measuring uncertainty is under 0.4 nm for micro-shells with 30 nm outer surface roughness and 9 μm thickness.
Phase-shifting interference(PSI) is an important method in surface roughness measurement. In this paper, on the basis of analyzing phase distribution of micro-shell interface, the measuring principle of interior surface roughness of micro-shells is discussed. Inner surface images of PS and PAMS micro-shells were obtained with PSI method. The results are consistent with the measured results by atomic force microscope. The measurement error is analyzed by studying the influence of thickness fluctuation of micro-shell and outer surface roughness of micro-shell on measured results of SiC and crystal Si surface roughness. The experimental result shows that the measuring uncertainty is under 0.4 nm for micro-shells with 30 nm outer surface roughness and 9 μm thickness.
2008,
20.
Abstract:
Temperature and thermal stress distributions in the KDP, heated by repetition frequency laser, are given by means of finite element methods. Depolarized loss, which is induced by temperature dependence of the refractive index, electro-optic coefficient, and by thermal-stress, is calculated. The simulated results indicate: variation of electro-optic coefficient as well as stress birefringence is the main factor, which induces depolarized loss of the switch. When the average power of the incident laser is 40 W, after 420 s irradiation, the highest temperature in KDP crystal is 38.43 ℃. The largest depolarized loss induced by variation of electro-optic coefficient and stress birefringence is correspondingly 2.38%, 4.04%. Depolarized loss, induced by stress birefringence, is measured. The mea
Temperature and thermal stress distributions in the KDP, heated by repetition frequency laser, are given by means of finite element methods. Depolarized loss, which is induced by temperature dependence of the refractive index, electro-optic coefficient, and by thermal-stress, is calculated. The simulated results indicate: variation of electro-optic coefficient as well as stress birefringence is the main factor, which induces depolarized loss of the switch. When the average power of the incident laser is 40 W, after 420 s irradiation, the highest temperature in KDP crystal is 38.43 ℃. The largest depolarized loss induced by variation of electro-optic coefficient and stress birefringence is correspondingly 2.38%, 4.04%. Depolarized loss, induced by stress birefringence, is measured. The mea
2008,
20.
Abstract:
It is very important and difficult to obtain accurate layer thickness of super thin films for further research of its optic and electronic properties. Three measuring methods were used to obtain the layer thickness of super thin films, which are reflectance curve fitting in soft X-ray region method, Bragg diffraction equation method and reflectance Fourier transform method. The reflectance of super thin films were measured using soft X-ray of synchrotron radiation, and X-ray diffraction were also measured at the same time. Two samples, single layer of W film based on silicon substrate and bilayer of C/W film based on silicon substrate, were used to test the accuracy of the results obtained from the three methods. The single layer W film’s the thicknesses measured by the three methods are
It is very important and difficult to obtain accurate layer thickness of super thin films for further research of its optic and electronic properties. Three measuring methods were used to obtain the layer thickness of super thin films, which are reflectance curve fitting in soft X-ray region method, Bragg diffraction equation method and reflectance Fourier transform method. The reflectance of super thin films were measured using soft X-ray of synchrotron radiation, and X-ray diffraction were also measured at the same time. Two samples, single layer of W film based on silicon substrate and bilayer of C/W film based on silicon substrate, were used to test the accuracy of the results obtained from the three methods. The single layer W film’s the thicknesses measured by the three methods are
2008,
20.
Abstract:
A one-dimension analysis model was set up to describe the thin mirror deformation process caused by discrete external forces, especially with small bending approximating. With the model, a thin mirror with a diameter of 300 mm and a ratio of 40 of diameter to thickness at discrete supports is simulated by finite element analysis method and four different deformations are calculated. The external concentrated forces can be obtained from the analysis results. During the optimization process, the location and the magnitude of external forces are determined by zero order optimization method. The optimization analysis results show that the deformation curve with optimization corresponds to the target curve. The maximum average difference decreases as much as 58%, compared with the results witho
A one-dimension analysis model was set up to describe the thin mirror deformation process caused by discrete external forces, especially with small bending approximating. With the model, a thin mirror with a diameter of 300 mm and a ratio of 40 of diameter to thickness at discrete supports is simulated by finite element analysis method and four different deformations are calculated. The external concentrated forces can be obtained from the analysis results. During the optimization process, the location and the magnitude of external forces are determined by zero order optimization method. The optimization analysis results show that the deformation curve with optimization corresponds to the target curve. The maximum average difference decreases as much as 58%, compared with the results witho
2008,
20.
Abstract:
Fe nanoparticles were prepared by flow- levitation method for physical doping of ICF target materials. The morphologies, granularities and structures of Fe particles were investigated by TEM, XRD techniques. The results show that the particles prepared by this means are spherical and the particle size can be controlled availably in 30～70 nm. In addition, it is discovered by XRD techniques that there appeared Fe3O4 oxide film generated in the air, adhering to the surface of the nanoparticles.
Fe nanoparticles were prepared by flow- levitation method for physical doping of ICF target materials. The morphologies, granularities and structures of Fe particles were investigated by TEM, XRD techniques. The results show that the particles prepared by this means are spherical and the particle size can be controlled availably in 30～70 nm. In addition, it is discovered by XRD techniques that there appeared Fe3O4 oxide film generated in the air, adhering to the surface of the nanoparticles.
2008,
20.
Abstract:
At the same temperature, constituents of a material mixture are in temperature and pressure equilibrium by density-pressure iteration algorithm. Combining the adding principle, EOS of a material mixture was calculated by program. In order to verify this procedure, the parameters of state of different deuterium-tritium(DT) and argon mixtures are analysed. For DT doped with a small quantity of argon, the computed EOS agrees well with that of pure DT. Similarly, the EOS of argon with a little DT is in accordance with that of pure argon. The results indicate that the program is feasible.
At the same temperature, constituents of a material mixture are in temperature and pressure equilibrium by density-pressure iteration algorithm. Combining the adding principle, EOS of a material mixture was calculated by program. In order to verify this procedure, the parameters of state of different deuterium-tritium(DT) and argon mixtures are analysed. For DT doped with a small quantity of argon, the computed EOS agrees well with that of pure DT. Similarly, the EOS of argon with a little DT is in accordance with that of pure argon. The results indicate that the program is feasible.
2008,
20.
Abstract:
A curved crystal X-ray spectrographs of reflection type spherical geometry was required based on the Johann scheme. Due to their high efficiency and resolution, X-ray spectrographs of focusing spectrograph spatial resolution are suitable for detecting weak X-ray spectra in spectrometers for laser fusion research. Spherically bent mica crystal with a radius of curvature of 380 mm was used in the spectrometer. The Bragg angle of the crystal analyzer was 51°.The image plate was employed to obtain high spatial resolution and a narrow spectral band width, with an effective area of 30 mm×80 mm. The designed optical path of the X-ray spectrometer beam was 980 mm long from the source to the crystal and the detector. The first experiment was carried out at the 20 J energy laser facility of Resear
A curved crystal X-ray spectrographs of reflection type spherical geometry was required based on the Johann scheme. Due to their high efficiency and resolution, X-ray spectrographs of focusing spectrograph spatial resolution are suitable for detecting weak X-ray spectra in spectrometers for laser fusion research. Spherically bent mica crystal with a radius of curvature of 380 mm was used in the spectrometer. The Bragg angle of the crystal analyzer was 51°.The image plate was employed to obtain high spatial resolution and a narrow spectral band width, with an effective area of 30 mm×80 mm. The designed optical path of the X-ray spectrometer beam was 980 mm long from the source to the crystal and the detector. The first experiment was carried out at the 20 J energy laser facility of Resear
2008,
20.
Abstract:
A Pspice subcircuit model has been proposed for PIN diode to study the PIN limiter, the electro-thermal diode model including temperature dependences of physical parameters is also described. The relationship between junction temperature and time for input pulse is calculated by FORTRAN with the output data of Pspice code. By tuning a small set of model parameters under different junction temperature, the transient response of PIN diode limiter have been simulated with Pspice, and spike leakage power varying with frequency, pulse rising time ,and temperature are obtained. Results indicate that bigger pulse amplitude causes quicker juction temperature grow and spike leakage power will be augmented by the junction temperature rise under different frequency and pulse rising time.
A Pspice subcircuit model has been proposed for PIN diode to study the PIN limiter, the electro-thermal diode model including temperature dependences of physical parameters is also described. The relationship between junction temperature and time for input pulse is calculated by FORTRAN with the output data of Pspice code. By tuning a small set of model parameters under different junction temperature, the transient response of PIN diode limiter have been simulated with Pspice, and spike leakage power varying with frequency, pulse rising time ,and temperature are obtained. Results indicate that bigger pulse amplitude causes quicker juction temperature grow and spike leakage power will be augmented by the junction temperature rise under different frequency and pulse rising time.
2008,
20.
Abstract:
An S-band tapered magnetically insulated transmission line oscillator with slowly tapered vanes and sharply tapered vanes has been studied at long-pulse operation. Under the diode voltage of 350 kV, the diode current of 25 kA and the pulse duration of 128 ns, the output microwave with the power of 500 MW and the pulse duration of 90 ns has been obtained in the experiments. Further analysis showed that the poor microwave shape attributed to the poor diode voltage waveform and better diode voltage waveform was crucial to achieving a longer microwave pulse. In addition, two kinds of load structure were used to collect the e-beams. The experimental results indicat that using the graphite load could get the better performance than the stainless steel load.
An S-band tapered magnetically insulated transmission line oscillator with slowly tapered vanes and sharply tapered vanes has been studied at long-pulse operation. Under the diode voltage of 350 kV, the diode current of 25 kA and the pulse duration of 128 ns, the output microwave with the power of 500 MW and the pulse duration of 90 ns has been obtained in the experiments. Further analysis showed that the poor microwave shape attributed to the poor diode voltage waveform and better diode voltage waveform was crucial to achieving a longer microwave pulse. In addition, two kinds of load structure were used to collect the e-beams. The experimental results indicat that using the graphite load could get the better performance than the stainless steel load.
2008,
20.
Abstract:
A two- dimensional magnetohydrodynamics arbitrary Lagrangian Eulerian(MHD ALE) code, named APMFCG, is used to simulate the dynamic behavior of helical magnetic flux compression generators(MFCG). APMFCG solves the coupled equations of electromagnetics and mechanics in the region of explosive, metal armature and coil, air or filled insulation gas in the generator. A circuit equation couples the electromagnetic fields in the generator to the external load. In this paper, the basic physical model and the main equations are introduced. APMFCG is used to simulate the series of experimental results of a simply wound helical MFCG device developed in Texas Technology University. The agreement of output current and inductance of coil between the experimental and the numerical results is quite sati
A two- dimensional magnetohydrodynamics arbitrary Lagrangian Eulerian(MHD ALE) code, named APMFCG, is used to simulate the dynamic behavior of helical magnetic flux compression generators(MFCG). APMFCG solves the coupled equations of electromagnetics and mechanics in the region of explosive, metal armature and coil, air or filled insulation gas in the generator. A circuit equation couples the electromagnetic fields in the generator to the external load. In this paper, the basic physical model and the main equations are introduced. APMFCG is used to simulate the series of experimental results of a simply wound helical MFCG device developed in Texas Technology University. The agreement of output current and inductance of coil between the experimental and the numerical results is quite sati
2008,
20.
Abstract:
This paper presents a quantitative study of the critical current above which absolute instability would be excited in gyrotron traveling wave amplifier with the distributed loss waveguide. The dispersion property of a distributed-loss waveguide is derived in detail. The numerical results show that the threshold current depends on the skin depth of the waveguide wall, the magnetic field detuning and the perpendicular-to-parallel velocity ratio of the electrons. By designing the beam-wave interaction circuit with distributed-loss waveguide, the applied magnetic field and the velocity ratio, stable operation of the gyrotron traveling amplifier with wide band width and high efficiency can be ensured.
This paper presents a quantitative study of the critical current above which absolute instability would be excited in gyrotron traveling wave amplifier with the distributed loss waveguide. The dispersion property of a distributed-loss waveguide is derived in detail. The numerical results show that the threshold current depends on the skin depth of the waveguide wall, the magnetic field detuning and the perpendicular-to-parallel velocity ratio of the electrons. By designing the beam-wave interaction circuit with distributed-loss waveguide, the applied magnetic field and the velocity ratio, stable operation of the gyrotron traveling amplifier with wide band width and high efficiency can be ensured.
2008,
20.
Abstract:
The theory of periodic permanent magnetic focusing system was studied. 2-D software UESTC_PPM was implemented. It focuses on axisymmetric models and uses finite differential method(FDM) to compute the magnetic displacement. The one magnetic ring model and the one period model were simulated. The results were compared with the results of Ansoft Maxwell 3D. The magnetic induction intensity curve at axis of symmetry and the absolute value of magnetic induction intensity displacement at axial plane of symmetry that were computed with two kind of software are consistent with each other. UESTC_PPM is useful and accurate.
The theory of periodic permanent magnetic focusing system was studied. 2-D software UESTC_PPM was implemented. It focuses on axisymmetric models and uses finite differential method(FDM) to compute the magnetic displacement. The one magnetic ring model and the one period model were simulated. The results were compared with the results of Ansoft Maxwell 3D. The magnetic induction intensity curve at axis of symmetry and the absolute value of magnetic induction intensity displacement at axial plane of symmetry that were computed with two kind of software are consistent with each other. UESTC_PPM is useful and accurate.
2008,
20.
Abstract:
In order to improve cooling capability of the collector and guarantee the multi-beam millimeter-wave traveling wave tube’s reliability and stability, thermal analysis of the collector with finite element software ANSYS is performed and simulation results are provided to obtain the main guidelines for thermal design of collector. The size, material and even structure of the collector are optimized. The results show that: (1) Thermal contact resistance is a major factor for the collector temperature rise. The temperature rise caused by thermal contact resistances is about one-third of the total; (2) Larger width of electrode contact with insulating ceramics might not correspond with stronger collector cooling capacity, there is a limit for the cooling capacity under certain work conditions;
In order to improve cooling capability of the collector and guarantee the multi-beam millimeter-wave traveling wave tube’s reliability and stability, thermal analysis of the collector with finite element software ANSYS is performed and simulation results are provided to obtain the main guidelines for thermal design of collector. The size, material and even structure of the collector are optimized. The results show that: (1) Thermal contact resistance is a major factor for the collector temperature rise. The temperature rise caused by thermal contact resistances is about one-third of the total; (2) Larger width of electrode contact with insulating ceramics might not correspond with stronger collector cooling capacity, there is a limit for the cooling capacity under certain work conditions;
2008,
20.
Abstract:
Three stripline beam position monitors and some feed-throughs were developed to measure the position of beam non-imterceptively in test beam facility. After three stripline beam position monitors were produced,calibrations of the monitors were carried out on a workbench,which has high precision and is controlled by a computer. Then two monitors were installed at the beam line and some experiments were carried out. Four 1 mm thickness stainless steel strips are main modules of the monitor,signals induced in these strips reflect the position of the beam bunch．Calibration coefficient,system characteristic impedance and port transmission coefficient of monitor are introduced in this paper.
Three stripline beam position monitors and some feed-throughs were developed to measure the position of beam non-imterceptively in test beam facility. After three stripline beam position monitors were produced,calibrations of the monitors were carried out on a workbench,which has high precision and is controlled by a computer. Then two monitors were installed at the beam line and some experiments were carried out. Four 1 mm thickness stainless steel strips are main modules of the monitor,signals induced in these strips reflect the position of the beam bunch．Calibration coefficient,system characteristic impedance and port transmission coefficient of monitor are introduced in this paper.
2008,
20.
Abstract:
According to the characteristics of flash radiographic image with low signal-to-noise ratio, a new image reconstruction algorithm is proposed for radiography. The new algorithm uses a nonlinear partial differential equation(PDE ) to constrain the noise of the reconstructed image. It can avoid amplifying the noise and preserve image edges at the same time. Numerical experimental results show that in comparison with the Landweber algorithm and preconditioned constrained conjugate(PCCG) algorithm, the new algorithm has stronger ability of noise removal and edge preserving.
According to the characteristics of flash radiographic image with low signal-to-noise ratio, a new image reconstruction algorithm is proposed for radiography. The new algorithm uses a nonlinear partial differential equation(PDE ) to constrain the noise of the reconstructed image. It can avoid amplifying the noise and preserve image edges at the same time. Numerical experimental results show that in comparison with the Landweber algorithm and preconditioned constrained conjugate(PCCG) algorithm, the new algorithm has stronger ability of noise removal and edge preserving.
2008,
20.
Abstract:
Based on the radiation transfer equation, the radiation energy density flux with higher terms was obtained using iterative method. Using the formula, the satisfied qualification of the radiative heat conduction approximation was analyzed when radiation transferred in light media. The approximation always required the quotient between varying scale of temperature and Rosseland mean free path to be far larger than some value, as called citerion h, it indicated the hardness of satisfaction of the approximation: as the criterion increased, the approximation will be hardly satisfied. The results indicated that the criterion is between 3 and 60 when the bremsstrahlung and scattering process are both concerned. And the influence of two factors, the changing scale of density in space and the radiu
Based on the radiation transfer equation, the radiation energy density flux with higher terms was obtained using iterative method. Using the formula, the satisfied qualification of the radiative heat conduction approximation was analyzed when radiation transferred in light media. The approximation always required the quotient between varying scale of temperature and Rosseland mean free path to be far larger than some value, as called citerion h, it indicated the hardness of satisfaction of the approximation: as the criterion increased, the approximation will be hardly satisfied. The results indicated that the criterion is between 3 and 60 when the bremsstrahlung and scattering process are both concerned. And the influence of two factors, the changing scale of density in space and the radiu
2008,
20.
Abstract:
Parameters of Zumbro lens are optimized to minimize the image blur. When the length of outer drift equals to the length of inner drift, the image blur is minimized or is very close to the minimum. Field of view of Zumbro lens is also investigated, which is not sensitive to parameters of Zumbro lens and is close to two thirds of the aperture of quadrupole magnet. Parameters of a Zumbro lens for 20 GeV proton radiography are presented. Geant4 simulation resluts show that the parameters are valid.
Parameters of Zumbro lens are optimized to minimize the image blur. When the length of outer drift equals to the length of inner drift, the image blur is minimized or is very close to the minimum. Field of view of Zumbro lens is also investigated, which is not sensitive to parameters of Zumbro lens and is close to two thirds of the aperture of quadrupole magnet. Parameters of a Zumbro lens for 20 GeV proton radiography are presented. Geant4 simulation resluts show that the parameters are valid.
2008,
20.
Abstract:
Focus character for double-negative dielectric volume with regular triangular,square and hexagonal structure under electric line source is analyzed using finite difference time domain method. The computation results show that “focus”does not exist in the double-negative dielectric volume, when the excitation is located on the outside extension line of angular bisector of corner angle in double-negative volume with very small permitivity and permeability. The results are compared with Arslanagic’s analytic results and their validity is proved.
Focus character for double-negative dielectric volume with regular triangular,square and hexagonal structure under electric line source is analyzed using finite difference time domain method. The computation results show that “focus”does not exist in the double-negative dielectric volume, when the excitation is located on the outside extension line of angular bisector of corner angle in double-negative volume with very small permitivity and permeability. The results are compared with Arslanagic’s analytic results and their validity is proved.
2008,
20.
Abstract:
Lanthanum hexaboride field-emitter arrays(LaB6 FEAs) with tip structures are fabricated by oxygen plasma oxidation-etching method. The field emission characteristics are studied in a conventional diode test cell in vacuum system. LaB6-FEAs exhibit a much lower turn-on field of 7 V·μm-1 due to its lower work function of 2.6 eV. The Fower-Nordheim plot obtained from the current-voltage characteristic is found to be nearly linear in accordance with the quantum mechanical tunneling phenomenon. In addition, oxygen plasma oxidation-etching method is also compared with argon-oxygen plasma etching method and electro-chemical etching method, which indicates that oxygen plasma oxidation-etching method is a very promising fabrication technique for the preparation of LaB6-FEAs.
Lanthanum hexaboride field-emitter arrays(LaB6 FEAs) with tip structures are fabricated by oxygen plasma oxidation-etching method. The field emission characteristics are studied in a conventional diode test cell in vacuum system. LaB6-FEAs exhibit a much lower turn-on field of 7 V·μm-1 due to its lower work function of 2.6 eV. The Fower-Nordheim plot obtained from the current-voltage characteristic is found to be nearly linear in accordance with the quantum mechanical tunneling phenomenon. In addition, oxygen plasma oxidation-etching method is also compared with argon-oxygen plasma etching method and electro-chemical etching method, which indicates that oxygen plasma oxidation-etching method is a very promising fabrication technique for the preparation of LaB6-FEAs.
2008,
20.
Abstract:
Defects on radiography images limit the measurement accuracy. Based on the character of multiple films of radiography, a method of defects removal was obtained. First,the original images was accurately registered, then an averaged image was obtained by these registered images, the defect image was obtained from the difference of the original image and the averaged image. The defects on the defect image was partitioned and posited by FCM. At last, the original image was restored by the averaged image, the defect images and the classification of defects. The simulative results confirm the method.
Defects on radiography images limit the measurement accuracy. Based on the character of multiple films of radiography, a method of defects removal was obtained. First,the original images was accurately registered, then an averaged image was obtained by these registered images, the defect image was obtained from the difference of the original image and the averaged image. The defects on the defect image was partitioned and posited by FCM. At last, the original image was restored by the averaged image, the defect images and the classification of defects. The simulative results confirm the method.
2008,
20.
Abstract:
Based on the scanning proton microprobe system in Shanghai Institute of Applied Physics, scanning transmission ion microscopy(STIM) experimentation were carried out and simulated by SIMNRA procedure. A paraffin-embedded slice of rat’s thighbone and a thin small ball were tested by on-axis and off-axis STIM respectively. P_STIM software dedicated to STIM analysis of thin samples using proton beams was developed, which includes the reconstruction of the median filtering energy loss image of the sample, as well as accurate calculation of sample thickness of the scanning regions. Theoretical analysis and experimental results showed that median filtering used to reduce the data acquired by on-axis detection provides quantitative areal density distribution results and energy-window filtering m
Based on the scanning proton microprobe system in Shanghai Institute of Applied Physics, scanning transmission ion microscopy(STIM) experimentation were carried out and simulated by SIMNRA procedure. A paraffin-embedded slice of rat’s thighbone and a thin small ball were tested by on-axis and off-axis STIM respectively. P_STIM software dedicated to STIM analysis of thin samples using proton beams was developed, which includes the reconstruction of the median filtering energy loss image of the sample, as well as accurate calculation of sample thickness of the scanning regions. Theoretical analysis and experimental results showed that median filtering used to reduce the data acquired by on-axis detection provides quantitative areal density distribution results and energy-window filtering m
2008,
20.
Abstract:
The main factor of laser induced field damage is the modulation of light field by the defects on the fused silica subsurface. The finite element method is used to simulate the light intensity distribution in the vicinity of defects(planar and conical cracks)on the fused silica subsurface.The results show that light intensity distribution around a crack is determined by several factors, including crack morphology, geometry dimension, azimuth and incidence angle. The enhancement effect of a crack on the output surface is stronger than that on the input surface. When total internal reflection occurs at both the ideal morphology planar crack and the surface, high light intensification can occur in area adjacent to the planar crack. The light distribution in the vicinity of a conical crack prov
The main factor of laser induced field damage is the modulation of light field by the defects on the fused silica subsurface. The finite element method is used to simulate the light intensity distribution in the vicinity of defects(planar and conical cracks)on the fused silica subsurface.The results show that light intensity distribution around a crack is determined by several factors, including crack morphology, geometry dimension, azimuth and incidence angle. The enhancement effect of a crack on the output surface is stronger than that on the input surface. When total internal reflection occurs at both the ideal morphology planar crack and the surface, high light intensification can occur in area adjacent to the planar crack. The light distribution in the vicinity of a conical crack prov
2008,
20.
Abstract:
The study of the TEA CO2 weak lines were carried out by adopting two grating cavities and lengthening the gain region of the discharge chamber. Six near 11 μm weak lines (sequence band and hot band lines) were obtained successfully with 16% CO2, 21% N2, 63% He (volume ratio) at total pressure of 57.3 kPa. The pulse width of weak lines is 400 ns around. While the center of grating is on the axis of the discharge chamber, the maximal energy output appears, which is several hundred mJ.
The study of the TEA CO2 weak lines were carried out by adopting two grating cavities and lengthening the gain region of the discharge chamber. Six near 11 μm weak lines (sequence band and hot band lines) were obtained successfully with 16% CO2, 21% N2, 63% He (volume ratio) at total pressure of 57.3 kPa. The pulse width of weak lines is 400 ns around. While the center of grating is on the axis of the discharge chamber, the maximal energy output appears, which is several hundred mJ.
2008,
20.
Abstract:
An eight-switch linear tronsformar driver(LTD) module with 100 kA output capability was designed based on a former four-switch one. The spoke-like eight bricks discharge in parallel to drive the load in the center. A 10-stage 100 GW LTD system was physically designed with the newly designed modules. Circuit simulation with Pspice and particle-in-cell (PIC) simulation were done to assess the system’s physical properties. Simulations have proved that the design is reasonable. Voltage was magnetically and inductively added, and the system can drive a 10 Ω load with 100 GW pulse, with rise time of the pulse less than 60 ns.
An eight-switch linear tronsformar driver(LTD) module with 100 kA output capability was designed based on a former four-switch one. The spoke-like eight bricks discharge in parallel to drive the load in the center. A 10-stage 100 GW LTD system was physically designed with the newly designed modules. Circuit simulation with Pspice and particle-in-cell (PIC) simulation were done to assess the system’s physical properties. Simulations have proved that the design is reasonable. Voltage was magnetically and inductively added, and the system can drive a 10 Ω load with 100 GW pulse, with rise time of the pulse less than 60 ns.
2008,
20.
Abstract:
Developing a compact flash X-ray tube with high operating voltage is necessary to high energy pulsed X-radiography. The operating principle of the field-emission cold-cathode X-ray tube is described in this paper. A novel compact flash X-ray tube with vacuum insulator stack, the voltage of the tube of 1 MV and exposure of 4.128×10-4 C/kg per pulse, is designed. The stack is composed of ten insulators and nine grading rings in alternating sequence. The length of the stack is 260 mm. Static simulation results show that the highest operating field strength of the tube is 94.8 kV/cm, which is lower than the empirical 120 kV/cm; the highest operating field strength of all the triple piont is 26 kV/cm, also lower than the empirical 30 kV/cm. The cubage of the tube is small and high vacuum will
Developing a compact flash X-ray tube with high operating voltage is necessary to high energy pulsed X-radiography. The operating principle of the field-emission cold-cathode X-ray tube is described in this paper. A novel compact flash X-ray tube with vacuum insulator stack, the voltage of the tube of 1 MV and exposure of 4.128×10-4 C/kg per pulse, is designed. The stack is composed of ten insulators and nine grading rings in alternating sequence. The length of the stack is 260 mm. Static simulation results show that the highest operating field strength of the tube is 94.8 kV/cm, which is lower than the empirical 120 kV/cm; the highest operating field strength of all the triple piont is 26 kV/cm, also lower than the empirical 30 kV/cm. The cubage of the tube is small and high vacuum will
2008,
20.
Abstract:
A high power pulse modulator is presented. It is made up of capacitors, a trigger switch, an air core transformer, a water dielectric pulse forming line（PFL）, a hydrogen switch, and a field-emission vacuum diode. The circuit simulation saftware Pspice was used to calculate the diode voltage, diode current and charging voltage of PFL. The static electric field of the PFL and switch is analyzed. When the hydrogen switch breakdown voltage was 520 kV, a 60 ns pulse width and 230 kV, 30 kA pulse was obtained on the field-emission diode. The rise times values of diode voltage with different gases such as H2, N2, SF6 in man swithch have been compared.It is concluded that hydrogen switch can reduce the rise time of diode voltage obviously. The results are in agreement with theory etical analyses
A high power pulse modulator is presented. It is made up of capacitors, a trigger switch, an air core transformer, a water dielectric pulse forming line（PFL）, a hydrogen switch, and a field-emission vacuum diode. The circuit simulation saftware Pspice was used to calculate the diode voltage, diode current and charging voltage of PFL. The static electric field of the PFL and switch is analyzed. When the hydrogen switch breakdown voltage was 520 kV, a 60 ns pulse width and 230 kV, 30 kA pulse was obtained on the field-emission diode. The rise times values of diode voltage with different gases such as H2, N2, SF6 in man swithch have been compared.It is concluded that hydrogen switch can reduce the rise time of diode voltage obviously. The results are in agreement with theory etical analyses
2008,
20.
Abstract:
A new multi-stage and multi-channel closing switch (MMCS) was designed for main switch of Flash-Ⅱ accelerator. The synchronization of three MMCS is important in operation, thus the characteristic of MMCS should be consistency. According to Bradley experiential formula, parameter setup of MMCS was acquired from the experiment in low-voltage condition on Flash-Ⅱ. In the condition of trigger pulse voltage 85 kV, closure voltage 1.0~2.0 MV, the working state of MMCS was stable and reliable in operation. At the same time, property data of MMCS were acquired, the delay time of MMCS was less than 100 ns, the jitter was 8 ns, the breakdown time among the three MMCS was less than 10 ns.
A new multi-stage and multi-channel closing switch (MMCS) was designed for main switch of Flash-Ⅱ accelerator. The synchronization of three MMCS is important in operation, thus the characteristic of MMCS should be consistency. According to Bradley experiential formula, parameter setup of MMCS was acquired from the experiment in low-voltage condition on Flash-Ⅱ. In the condition of trigger pulse voltage 85 kV, closure voltage 1.0~2.0 MV, the working state of MMCS was stable and reliable in operation. At the same time, property data of MMCS were acquired, the delay time of MMCS was less than 100 ns, the jitter was 8 ns, the breakdown time among the three MMCS was less than 10 ns.
2008,
20.
Abstract:
Based on the numerical simulation results in time domain, the characteristic of the power loss caused by the emitting electrons in the different phases of establishing the magnetic insulation is discussed in this paper.The loss is caused by the electrons losing to the anode and the movement of the electrons in the magnetic insulation. The corresponding impact factors to the loss are analyzed, which are the length and the radius ratio of the transmission line, the peak pulse voltage and the time-varying rate of the input pulsed power. By analyzing the values and the characteristics of the loss, and the corresponding electron distributions in different periods with different pulse excitations, a staged model is proposed to calculate the total transmission efficiency, which divides the entire
Based on the numerical simulation results in time domain, the characteristic of the power loss caused by the emitting electrons in the different phases of establishing the magnetic insulation is discussed in this paper.The loss is caused by the electrons losing to the anode and the movement of the electrons in the magnetic insulation. The corresponding impact factors to the loss are analyzed, which are the length and the radius ratio of the transmission line, the peak pulse voltage and the time-varying rate of the input pulsed power. By analyzing the values and the characteristics of the loss, and the corresponding electron distributions in different periods with different pulse excitations, a staged model is proposed to calculate the total transmission efficiency, which divides the entire
2008,
20.
Abstract:
Electro-optic sampling measurement of relativistic electron pulses is promising. In this paper the theory and the experiment setup of the measurement are introduced. The coulomb field of electron bunch is analyzed and simulated. The relation of this field with the electro-optic effect of ZnTe crystal is studied.The polarization change of the probe light and the relation of the electron bunch length and the detected signal are calculated by Jones calculus. The results show that the coulomb field of electron bunch should be perpendicular to the ［001］ axis of ZnTe crystal, the initial polarization of probe light should lie at an angle of 45° or 135° with y″ axis of ZnTe crystal and the fast axis of 1/4 wave plate should lie at an angle of 45° with z″ axis of ZnTe crystal. In such situa
Electro-optic sampling measurement of relativistic electron pulses is promising. In this paper the theory and the experiment setup of the measurement are introduced. The coulomb field of electron bunch is analyzed and simulated. The relation of this field with the electro-optic effect of ZnTe crystal is studied.The polarization change of the probe light and the relation of the electron bunch length and the detected signal are calculated by Jones calculus. The results show that the coulomb field of electron bunch should be perpendicular to the ［001］ axis of ZnTe crystal, the initial polarization of probe light should lie at an angle of 45° or 135° with y″ axis of ZnTe crystal and the fast axis of 1/4 wave plate should lie at an angle of 45° with z″ axis of ZnTe crystal. In such situa
