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RSS2005 Vol. 17, No. 11
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2005,
17.
Abstract:
A precise measurement system of high reflectivity for scanning large aperture components in high power laser system is developed. The structure and working principle of this system are introduced, and those factors that influence its metrical precision are analyzed. According to theoretic analysis, precision of this measurement system is 2×10-5. Experimental measurements for capability of this system were carried out, which show that RMS of measurement in linear cavity is better than 2.052 28×10-5. Results give that the biggest measurement error is 3.554 04×10-5, which is in good agreement with the analysis. Scanning experimental measurements for large aperture components were also carried out. Results show that distribution of reflectivity is circular symmetric about the center of mirr
A precise measurement system of high reflectivity for scanning large aperture components in high power laser system is developed. The structure and working principle of this system are introduced, and those factors that influence its metrical precision are analyzed. According to theoretic analysis, precision of this measurement system is 2×10-5. Experimental measurements for capability of this system were carried out, which show that RMS of measurement in linear cavity is better than 2.052 28×10-5. Results give that the biggest measurement error is 3.554 04×10-5, which is in good agreement with the analysis. Scanning experimental measurements for large aperture components were also carried out. Results show that distribution of reflectivity is circular symmetric about the center of mirr
2005,
17.
Abstract:
Based on the standing-wave theory, a theoretical model with high energy absorption at the surface and interfaces is employed to describe laser-induced damages to optical multilayer films. The temperature distributions in two types of reflective multilayer films are calculated, and the characteristics, modes and damage thresholds are analyzed. The results show that energy absorption is mainly determined by the distribution of the standing-wave and extinction coefficients of the material. Multi-peaks over the temperature profiles are found at the surface and interfaces, where the optical multilayer films are prone to damage. Melting and falling off are two main kinds of damage mode, while inclusion, if present, may cause spallation of the layers.
Based on the standing-wave theory, a theoretical model with high energy absorption at the surface and interfaces is employed to describe laser-induced damages to optical multilayer films. The temperature distributions in two types of reflective multilayer films are calculated, and the characteristics, modes and damage thresholds are analyzed. The results show that energy absorption is mainly determined by the distribution of the standing-wave and extinction coefficients of the material. Multi-peaks over the temperature profiles are found at the surface and interfaces, where the optical multilayer films are prone to damage. Melting and falling off are two main kinds of damage mode, while inclusion, if present, may cause spallation of the layers.
2005,
17.
Abstract:
Barium nitrate crystal was proposed as one of the perspective Raman materials due to its intense symmetrical vibrations with the frequency of 1 047 cm-1 and comparative high Raman gain. A harmonic of Nd:YAG laser (532 nm) pumped barium nitrate crystal in external resonator and excited stimulated Raman laser. Experimental setup adopted the Raman shifter consisted of external cavity and two prisms spectrometer. The external cavity was composed of diachronic mirrors with optimal reflectivity for Stokes components. Barium nitrate crystal was grown by the aqua-solution cooling method with the size of 48 mm×10 mm×10 mm. When the pump laser energy is 65 mJ, the output energy of first Stokes laser (563 nm) and that of second Stokes laser (599 nm) were measured as 21 mJ and 16 mJ respectively. Th
Barium nitrate crystal was proposed as one of the perspective Raman materials due to its intense symmetrical vibrations with the frequency of 1 047 cm-1 and comparative high Raman gain. A harmonic of Nd:YAG laser (532 nm) pumped barium nitrate crystal in external resonator and excited stimulated Raman laser. Experimental setup adopted the Raman shifter consisted of external cavity and two prisms spectrometer. The external cavity was composed of diachronic mirrors with optimal reflectivity for Stokes components. Barium nitrate crystal was grown by the aqua-solution cooling method with the size of 48 mm×10 mm×10 mm. When the pump laser energy is 65 mJ, the output energy of first Stokes laser (563 nm) and that of second Stokes laser (599 nm) were measured as 21 mJ and 16 mJ respectively. Th
2005,
17.
Abstract:
When a laser beam irradiates a cylinder shell, the irradiated area becomes softer and the cylinder shell will be destroyed. In this paper, a 3-D solid element was adopted to simulate the stresses of internally pressured static and rotational cylinder shells irradiated by laser. It was contrastively analyzed by numerical simulation that the crack initiated from the beam spot edge at both static and rotational cylinder shells. In addition, the fracture occurred simultaneously at the whole outer cycle through the beam center of the rotational cylinder shell. It is concluded that the static cylinder shell will be destroyed more probably at the condition of the same laser power.
When a laser beam irradiates a cylinder shell, the irradiated area becomes softer and the cylinder shell will be destroyed. In this paper, a 3-D solid element was adopted to simulate the stresses of internally pressured static and rotational cylinder shells irradiated by laser. It was contrastively analyzed by numerical simulation that the crack initiated from the beam spot edge at both static and rotational cylinder shells. In addition, the fracture occurred simultaneously at the whole outer cycle through the beam center of the rotational cylinder shell. It is concluded that the static cylinder shell will be destroyed more probably at the condition of the same laser power.
2005,
17.
Abstract:
This paper gives a new method of solution to fluid field in the DF chemical laser combustion chamber. The method is a numerical solution of multi-component chemical equilibrium flows with the elements distributing equations and thermodynamic calculation of chemical equilibrium. This method avoids the problem of stiff equations caused by chemical reaction source terms in the components equations, and the number of components equations is reduced. The result shows that the wall of the combustion chamber is cooled down to a certain extent by the gas helium injected.
This paper gives a new method of solution to fluid field in the DF chemical laser combustion chamber. The method is a numerical solution of multi-component chemical equilibrium flows with the elements distributing equations and thermodynamic calculation of chemical equilibrium. This method avoids the problem of stiff equations caused by chemical reaction source terms in the components equations, and the number of components equations is reduced. The result shows that the wall of the combustion chamber is cooled down to a certain extent by the gas helium injected.
2005,
17.
Abstract:
The frequency upshifting and differential cross section of the laser synchrotron source (LSS) are studied based on the Thomson backscattering of intense laser radiation from a counterstreaming relativistic electron. A counterstreaming relativistic electron interacting with an incident short pulse laser emits attosecond X-ray pulse, the frequency upshifting of the backward scattered radiation under the short pulse laser is identical with that under the long pulse laser. The pulse width of the backward scattered radiation decreases with the increase of the electron’s initial energy, and the collimation of the scattered radiation becomes better.
The frequency upshifting and differential cross section of the laser synchrotron source (LSS) are studied based on the Thomson backscattering of intense laser radiation from a counterstreaming relativistic electron. A counterstreaming relativistic electron interacting with an incident short pulse laser emits attosecond X-ray pulse, the frequency upshifting of the backward scattered radiation under the short pulse laser is identical with that under the long pulse laser. The pulse width of the backward scattered radiation decreases with the increase of the electron’s initial energy, and the collimation of the scattered radiation becomes better.
2005,
17.
Abstract:
External cavity feedback for a broad-area laser diode (BAL) with antireflection coating on the front facet was investigated experimentally. The feedback was created by a high-reflection mirror and a blazed grating, which reflected two parts of the laser emission back to the BAL, thereby forming an external resonator. When a Fabry-Perot etalon was inserted into the resonator, an output beam with a bandwidth of 0.02 nm and a power of 150 mW was obtained. The beam diffraction limited factor M2 is 1.16.
External cavity feedback for a broad-area laser diode (BAL) with antireflection coating on the front facet was investigated experimentally. The feedback was created by a high-reflection mirror and a blazed grating, which reflected two parts of the laser emission back to the BAL, thereby forming an external resonator. When a Fabry-Perot etalon was inserted into the resonator, an output beam with a bandwidth of 0.02 nm and a power of 150 mW was obtained. The beam diffraction limited factor M2 is 1.16.
2005,
17.
Abstract:
Multi-order Stokes is generated in H2 pumped by a pulsed Nd:YAG laser at 532 nm. Maximum energy conversion efficiencies as high as 66%， 60% and 19% are attained for the first，second and third Stokes respectively. Under 0.44 MPa H2, significant multi-wavelength outputs can be obtained simultaneously with quantum distribution of 19% at 1 579 nm, 30% at 954 nm, 33% at 683 nm, 14% at 532 nm, 3.7% at 436 nm, and 1.4% at 368 nm. High-pressure H2 is found to be the best for highly efficient first Stokes conversion, while low-pressure H2 is proved suitable for higher order Stokes and anti-Stokes generation.
Multi-order Stokes is generated in H2 pumped by a pulsed Nd:YAG laser at 532 nm. Maximum energy conversion efficiencies as high as 66%， 60% and 19% are attained for the first，second and third Stokes respectively. Under 0.44 MPa H2, significant multi-wavelength outputs can be obtained simultaneously with quantum distribution of 19% at 1 579 nm, 30% at 954 nm, 33% at 683 nm, 14% at 532 nm, 3.7% at 436 nm, and 1.4% at 368 nm. High-pressure H2 is found to be the best for highly efficient first Stokes conversion, while low-pressure H2 is proved suitable for higher order Stokes and anti-Stokes generation.
2005,
17.
Abstract:
In an optical system, “cat eye effect” can be modeled as a focus lens system. When a system has some opto-electrical devices and is illuminated by a laser beam, the laser beam will be reflected from the system along incident direction as a result of “cat eye effect”. The “cat eye effect” is the inherent feature of opto-electrical devices. In this paper, the pointing capability of line-of-sight (LOS) over the horizon target (OTHT) is analyzed, especially the parameters of laser power. The results show that it is feasible to point different targets over the horizon using “cat eye effect”.
In an optical system, “cat eye effect” can be modeled as a focus lens system. When a system has some opto-electrical devices and is illuminated by a laser beam, the laser beam will be reflected from the system along incident direction as a result of “cat eye effect”. The “cat eye effect” is the inherent feature of opto-electrical devices. In this paper, the pointing capability of line-of-sight (LOS) over the horizon target (OTHT) is analyzed, especially the parameters of laser power. The results show that it is feasible to point different targets over the horizon using “cat eye effect”.
2005,
17.
Abstract:
From the Helmholtz equation, the optical field analytical expression of an ultrashort pulse propagating through a small aperture lens was acquired with chromatic and spherical aberration. By numerical modulation of the analytical expression, the spatial and temporal distributions of intensity in the paraxial and marginal focal plane and on the axis were obtained, and the impact of spherical aberration on them was also summarized. Because of the interference among the pulses passing through the lens from center to edge, two pulses with apparently different peak values appeared both in the paraxial and in the marginal focal plane. The intensity distribution was basically symmetrical on the axis in the focal region. The peak value didn't appear in the paraxial or marginal focal plane, but at
From the Helmholtz equation, the optical field analytical expression of an ultrashort pulse propagating through a small aperture lens was acquired with chromatic and spherical aberration. By numerical modulation of the analytical expression, the spatial and temporal distributions of intensity in the paraxial and marginal focal plane and on the axis were obtained, and the impact of spherical aberration on them was also summarized. Because of the interference among the pulses passing through the lens from center to edge, two pulses with apparently different peak values appeared both in the paraxial and in the marginal focal plane. The intensity distribution was basically symmetrical on the axis in the focal region. The peak value didn't appear in the paraxial or marginal focal plane, but at
2005,
17.
Abstract:
We present a four-rod series resonator CW Nd:YAG laser for the requirement of industrial application in this paper. The symmetrical resonator laser has been developed and is rated at 2 105 W output power with beam parameter product of 24 mm·mrad. The system's total electro-optics efficiency of lamp pumped YAG crystal is as high as 3.5%. The main factors which affect operation of high power solid-state laser module are different positions and thermal focal lengths of crystal rods, and so on. These factors are theoretically analyzed. Conclusions are drawn that the resonator would have the biggest steady range when the rods in it are symmetrically arranged and thermal focal lengths of the rods being not matched can be compensated by adjusting input power of laser system.
We present a four-rod series resonator CW Nd:YAG laser for the requirement of industrial application in this paper. The symmetrical resonator laser has been developed and is rated at 2 105 W output power with beam parameter product of 24 mm·mrad. The system's total electro-optics efficiency of lamp pumped YAG crystal is as high as 3.5%. The main factors which affect operation of high power solid-state laser module are different positions and thermal focal lengths of crystal rods, and so on. These factors are theoretically analyzed. Conclusions are drawn that the resonator would have the biggest steady range when the rods in it are symmetrically arranged and thermal focal lengths of the rods being not matched can be compensated by adjusting input power of laser system.
2005,
17.
Abstract:
The laser heating process of flying cylinder is discussed by means of geometry analysis. The meaning of heating configuration is defined and explained, the significance of this item in describing effective heating of the flying cylinder is pointed out. The distribution of the time width of heating configuration in the space above the ground is also discussed. The rules of locating the laser setup for effective heating of the flying cylinder are summarized. Selecting certain relative time width isoline according to the ratio between the laser's effective operation time and the flying time of the cylinder, and determining an effective area on the ground using the isoline as the boundary, the laser can be set on the point closest to the trajectory in the area. The dynamic heating has a maximu
The laser heating process of flying cylinder is discussed by means of geometry analysis. The meaning of heating configuration is defined and explained, the significance of this item in describing effective heating of the flying cylinder is pointed out. The distribution of the time width of heating configuration in the space above the ground is also discussed. The rules of locating the laser setup for effective heating of the flying cylinder are summarized. Selecting certain relative time width isoline according to the ratio between the laser's effective operation time and the flying time of the cylinder, and determining an effective area on the ground using the isoline as the boundary, the laser can be set on the point closest to the trajectory in the area. The dynamic heating has a maximu
2005,
17.
Abstract:
In order to get the plasma in air for aircraft stealth, this paper calculates the breakdown threshold of atmosphere from semi-classic theory. The main subjects include the connection between the breakdown threshold and atmosphere pressure, and the connection between the breakdown threshold and laser duration. At the same time, the paper has a keen study on the breakdown time of different laser intensity. Besides, the discussion on the effect of initial electron in air is also included in all above analysis, the data indicate that under the influence of the electron, the threshold for long wavelength incident laser falls distinctly, but there is not any change for short wavelength laser (0.355 μm).
In order to get the plasma in air for aircraft stealth, this paper calculates the breakdown threshold of atmosphere from semi-classic theory. The main subjects include the connection between the breakdown threshold and atmosphere pressure, and the connection between the breakdown threshold and laser duration. At the same time, the paper has a keen study on the breakdown time of different laser intensity. Besides, the discussion on the effect of initial electron in air is also included in all above analysis, the data indicate that under the influence of the electron, the threshold for long wavelength incident laser falls distinctly, but there is not any change for short wavelength laser (0.355 μm).
2005,
17.
Abstract:
The two-step（acid-base）sol-gel process was used to prepare SiO2 aerogels, with TEOS as the precursor. The influence of catalyst, water and solvent on the sol-gel process was investigated to optimize the experimental conditions. Ultralow-density silica aerogels with densities as low as 3.4 mg/cm3, solid cylinders and shells at various densities(10～50 mg/cm3) were made. Scan electron microscope, pore size distribution techniques were used to characterize the morphology and pore structure of the silica aerogel. The results show that the ultralow-density silica aerogel has good nanostructure with average pore size of 18.9 nm and specific surface area of 898.9 m2/g.
The two-step（acid-base）sol-gel process was used to prepare SiO2 aerogels, with TEOS as the precursor. The influence of catalyst, water and solvent on the sol-gel process was investigated to optimize the experimental conditions. Ultralow-density silica aerogels with densities as low as 3.4 mg/cm3, solid cylinders and shells at various densities(10～50 mg/cm3) were made. Scan electron microscope, pore size distribution techniques were used to characterize the morphology and pore structure of the silica aerogel. The results show that the ultralow-density silica aerogel has good nanostructure with average pore size of 18.9 nm and specific surface area of 898.9 m2/g.
2005,
17.
Abstract:
The development of a Ti:sapphire CPA laser facility named SILEX-I with the peak power of hundred terawatt level is reported. SILEX-I includes the femtosecond oscillator, the Offner stretcher, the regenerative amplifier, the pre-amplifier, the main amplifier, the power amplifier, the vacuum compressor and the vacuum target chamber. SILEX-I has three output powers: 5 TW, 30 TW, and hundreds terawatt, and there are corresponding target chamber for different physical experiments. The peak power of 286 TW and the pulse width of 29.8 fs after the compressor are obtained. The focal intensity is 3.36×1020 W/cm2 with the focal spot of 5.7 μm.
The development of a Ti:sapphire CPA laser facility named SILEX-I with the peak power of hundred terawatt level is reported. SILEX-I includes the femtosecond oscillator, the Offner stretcher, the regenerative amplifier, the pre-amplifier, the main amplifier, the power amplifier, the vacuum compressor and the vacuum target chamber. SILEX-I has three output powers: 5 TW, 30 TW, and hundreds terawatt, and there are corresponding target chamber for different physical experiments. The peak power of 286 TW and the pulse width of 29.8 fs after the compressor are obtained. The focal intensity is 3.36×1020 W/cm2 with the focal spot of 5.7 μm.
2005,
17.
Abstract:
A new method was used to design diffractive optical elements (DOE) based on improved iterative algorithm. This method shortened the computing time tremendously and the aberration factor of the design was about 8.4%. A DOE with 16 steps construction and quantized phase was fabricated with ion beam moving etching technology. Test results showed that the aberration factor was about 19% which proved the feasibility of the algorithm. The machining error in DOE was analyzed.
A new method was used to design diffractive optical elements (DOE) based on improved iterative algorithm. This method shortened the computing time tremendously and the aberration factor of the design was about 8.4%. A DOE with 16 steps construction and quantized phase was fabricated with ion beam moving etching technology. Test results showed that the aberration factor was about 19% which proved the feasibility of the algorithm. The machining error in DOE was analyzed.
2005,
17.
Abstract:
Pulse shaping of KrF laser by pulse stacking was experimentally studied. Compressed pulses by stimulated Brillouin scattering, short pulses with pulse-widths of 3~5 ns were gained. Shaped pulses with pulse-widths of 10~15 ns, flat-top-widths of 5~10 ns were obtained under four laser beams stacking. Using these experimental data, pulse stacking was numerically simulated, and similar results (pulse-widths of 12.7 ns, flat-top-widths of 7.7 ns) with experiment were acquired. Ability of arbitrary pulse shaping was numerically studied, and the influence of various pulse widths on shaped pulse was discussed. When variation of pulse width was less than 5%, it had little influence on shaped pulse. The amplification of the shaped pulse was theoretically and qualitatively analyzed. The results show
Pulse shaping of KrF laser by pulse stacking was experimentally studied. Compressed pulses by stimulated Brillouin scattering, short pulses with pulse-widths of 3~5 ns were gained. Shaped pulses with pulse-widths of 10~15 ns, flat-top-widths of 5~10 ns were obtained under four laser beams stacking. Using these experimental data, pulse stacking was numerically simulated, and similar results (pulse-widths of 12.7 ns, flat-top-widths of 7.7 ns) with experiment were acquired. Ability of arbitrary pulse shaping was numerically studied, and the influence of various pulse widths on shaped pulse was discussed. When variation of pulse width was less than 5%, it had little influence on shaped pulse. The amplification of the shaped pulse was theoretically and qualitatively analyzed. The results show
2005,
17.
Abstract:
A group of amorphous CHN films were fabricated successfully by hollow cathode plasma chemical vapor deposition with ammonia, hydrogen and methane as reacting gas. The variation of deposition rate as a function of DC voltage and reactive gas flows were studied, respectively. The nitrogen content in terms of atomic percentage under different conditions was identified by X-ray photoelectron spectra (XPS).The surface roughness and surface morphology were measured and presented by atomic force microscope (AFM). The results show that the actual nitrogen content in the films can be as much as 12%, the surface morphology is smooth and dense and the surface roughness is lower than 1 nm.
A group of amorphous CHN films were fabricated successfully by hollow cathode plasma chemical vapor deposition with ammonia, hydrogen and methane as reacting gas. The variation of deposition rate as a function of DC voltage and reactive gas flows were studied, respectively. The nitrogen content in terms of atomic percentage under different conditions was identified by X-ray photoelectron spectra (XPS).The surface roughness and surface morphology were measured and presented by atomic force microscope (AFM). The results show that the actual nitrogen content in the films can be as much as 12%, the surface morphology is smooth and dense and the surface roughness is lower than 1 nm.
2005,
17.
Abstract:
In this paper, the Al target in ICF experiment was produced by single point diamond turning technology. The effect of turning process on the surface roughness of Al target was discussed. The experiment results have demonstrated that lower surface roughness of Al target can be fabricated with smaller feed speed and higher spindle rotate speed. The surface roughness was analyzed by means of Form Talysurf device. The result showed that the surface roughness of the aluminum target was less than 50 nm.
In this paper, the Al target in ICF experiment was produced by single point diamond turning technology. The effect of turning process on the surface roughness of Al target was discussed. The experiment results have demonstrated that lower surface roughness of Al target can be fabricated with smaller feed speed and higher spindle rotate speed. The surface roughness was analyzed by means of Form Talysurf device. The result showed that the surface roughness of the aluminum target was less than 50 nm.
2005,
17.
Abstract:
In the SBS (stimulated Brillouin scattering) amplifier the focused Gaussian beams of 1.064 μm and 0.532 μm were used as pump lasers and SBS characteristics in different medium were simulated. Through study of SBS amplifier of self-Stokes-seeding, it is found that CaF2 can be damaged more easily than fused silica or BK7 glass in SBS process. For focused pump laser, SBS may damage material from front surface. For engineering purpose, effect of energy reflectivity, pulse compression and fidelity in different SBS materials were compared. For lower energy, CaF2 has better pulse compression but worse energy reflectivity and fidelity than fused silica or BK7, while when pumping energy is high enough, the characteristics are reverse.
In the SBS (stimulated Brillouin scattering) amplifier the focused Gaussian beams of 1.064 μm and 0.532 μm were used as pump lasers and SBS characteristics in different medium were simulated. Through study of SBS amplifier of self-Stokes-seeding, it is found that CaF2 can be damaged more easily than fused silica or BK7 glass in SBS process. For focused pump laser, SBS may damage material from front surface. For engineering purpose, effect of energy reflectivity, pulse compression and fidelity in different SBS materials were compared. For lower energy, CaF2 has better pulse compression but worse energy reflectivity and fidelity than fused silica or BK7, while when pumping energy is high enough, the characteristics are reverse.
2005,
17.
Abstract:
The characteristics of the forward hot electrons produced by 20 TW p-polarized picosecond laser-plasma interactions are studied at laser intensities from subrelativistic to relativistic. The spatial distribution of forward hot electrons is multi-peak distribution, as laser intensity is under 107 W/cm2. When laser intensity is between 1017 and 1018 W/cm2, the peak of the hot electron beam is along the target normal direction. The peak of the hot electron beam shifts to the laser propagation direction from the target normal direction as the laser intensity reaches the relativistic. The temperature of hot electrons fit resonance absorption scaling law as the laser intensity under the relativistic. The temperature of hot electrons is much higher than that expected by the empirical scaling law
The characteristics of the forward hot electrons produced by 20 TW p-polarized picosecond laser-plasma interactions are studied at laser intensities from subrelativistic to relativistic. The spatial distribution of forward hot electrons is multi-peak distribution, as laser intensity is under 107 W/cm2. When laser intensity is between 1017 and 1018 W/cm2, the peak of the hot electron beam is along the target normal direction. The peak of the hot electron beam shifts to the laser propagation direction from the target normal direction as the laser intensity reaches the relativistic. The temperature of hot electrons fit resonance absorption scaling law as the laser intensity under the relativistic. The temperature of hot electrons is much higher than that expected by the empirical scaling law
2005,
17.
Abstract:
The method of orthogonal experiment was used to study the influences caused by pressure, pressure-holding time, annealing temperature and annealing time on properties of nanocrystalline Cu produced by flow-levitation-cold press process. XRD, microhardness and density test were used to determine some properties (grain size,density and microhardness) of the specimens. The results show that the annealing temperature, pressure and annealing time are the predominant factors to the grain size, density and microhardness respectively. At the same time, the experimental results show high heat stability in asconsolidated samples．
The method of orthogonal experiment was used to study the influences caused by pressure, pressure-holding time, annealing temperature and annealing time on properties of nanocrystalline Cu produced by flow-levitation-cold press process. XRD, microhardness and density test were used to determine some properties (grain size,density and microhardness) of the specimens. The results show that the annealing temperature, pressure and annealing time are the predominant factors to the grain size, density and microhardness respectively. At the same time, the experimental results show high heat stability in asconsolidated samples．
2005,
17.
Abstract:
A function about the magnetic force of ICF targets in the levitation magnetic field was proposed using the principle of levitation, and a theoretics model about the target levitation was established. Experimental and theoretical results show that when the targets are doped with the magnetic powder of 1%~6%, the magnetic field strength of the target increases from 0.09 mT to 0.44 mT while the levitation magnetic field decreases from 0.93 mT to 0.23 mT.
A function about the magnetic force of ICF targets in the levitation magnetic field was proposed using the principle of levitation, and a theoretics model about the target levitation was established. Experimental and theoretical results show that when the targets are doped with the magnetic powder of 1%~6%, the magnetic field strength of the target increases from 0.09 mT to 0.44 mT while the levitation magnetic field decreases from 0.93 mT to 0.23 mT.
2005,
17.
Abstract:
Hydroquinone-formaldehyde organic aerogels with high HC ratio(10~40, molar ratio of hydroquinone to catalyst) have been prepared using sol-gel process. And carbon aerogels have been prepared by pyrolyzing the aerogels. In addition, the ingredients have been tested by the IR spectra which show the probability of the nano-porous structure. SEM pictures, specific surface areas and distribution of pore diameter have been tested to study the nano-porous structures in surface and some data before and after the pyrolyzing process have been gained:the size of the organic aerogel is 30~50 nm, that of the carbon aerogel is about 10nm, the specific surface area increases from 341.77 m2/g to 452.75 m2/g, the density increases from 0.170 8 g/cm3 to 0.335 6 g/cm3 respectively.
Hydroquinone-formaldehyde organic aerogels with high HC ratio(10~40, molar ratio of hydroquinone to catalyst) have been prepared using sol-gel process. And carbon aerogels have been prepared by pyrolyzing the aerogels. In addition, the ingredients have been tested by the IR spectra which show the probability of the nano-porous structure. SEM pictures, specific surface areas and distribution of pore diameter have been tested to study the nano-porous structures in surface and some data before and after the pyrolyzing process have been gained:the size of the organic aerogel is 30~50 nm, that of the carbon aerogel is about 10nm, the specific surface area increases from 341.77 m2/g to 452.75 m2/g, the density increases from 0.170 8 g/cm3 to 0.335 6 g/cm3 respectively.
2005,
17.
Abstract:
Helical array antenna is fed from a single-layered radial waveguide to realize the directional radiation of high-power microwave. Low-profile helix is used as a radiation element. The feed wire of each helix is connected with an H-coupled probe, and excited by an outgoing wave in the TEM mode between the two parallel plates of the radial waveguide. Helices and probes are arranged on the upper plate to form a circular array. The excitation amplitude and phase of each element are adjusted by changing the insert length of H-coupled probe and rotating low-profile helix respectively. This antenna accepts directly an azimuthally symmetric output of an HPM source and radiates a high-gain pattern with a boresight peak. H-coupled probes are used to make the array antenna compatible with the intense
Helical array antenna is fed from a single-layered radial waveguide to realize the directional radiation of high-power microwave. Low-profile helix is used as a radiation element. The feed wire of each helix is connected with an H-coupled probe, and excited by an outgoing wave in the TEM mode between the two parallel plates of the radial waveguide. Helices and probes are arranged on the upper plate to form a circular array. The excitation amplitude and phase of each element are adjusted by changing the insert length of H-coupled probe and rotating low-profile helix respectively. This antenna accepts directly an azimuthally symmetric output of an HPM source and radiates a high-gain pattern with a boresight peak. H-coupled probes are used to make the array antenna compatible with the intense
2005,
17.
Abstract:
The response of a short single-wire line excited by EMP was theoretically investigated and experimentally validated by means of an EMP simulator. A modified bounded-wave EMP simulator was developed with a rise time less than 5 ns and pulse width about 200 ns for the short line validation test. Comparison of current responses at the line termination between calculation using the transmission line theory and experimental measurement were presented. The good agreement shows that this bounded-wave EMP simulator can be used for short single-wire line experiment. This method of effects experiment has the characteristics of reasonably uniform electromagnetic field distribution in the working volume, easy adjustment of EMP experiment parameters and convenience to measure electric field and current
The response of a short single-wire line excited by EMP was theoretically investigated and experimentally validated by means of an EMP simulator. A modified bounded-wave EMP simulator was developed with a rise time less than 5 ns and pulse width about 200 ns for the short line validation test. Comparison of current responses at the line termination between calculation using the transmission line theory and experimental measurement were presented. The good agreement shows that this bounded-wave EMP simulator can be used for short single-wire line experiment. This method of effects experiment has the characteristics of reasonably uniform electromagnetic field distribution in the working volume, easy adjustment of EMP experiment parameters and convenience to measure electric field and current
2005,
17.
Abstract:
The electron beams produced by the needle-shaped annular carbon fiber-coated cathode soaked with cesium iodide (CsI) salt and annular stainless steel cathode were separately used to bombard the nylon targets. There was a uniform round mark on the target bombarded by the electron beam generated by the carbon fiber cathode, but there was a nonuniform mark on the target bombarded by the annular stainless steel cathode. It was believed that the different mechanism, characteristics and configuration between the carbon fiber cathode and the stainless steel cathode caused the difference of emission uniformity. Scanning with optics microscope, it was found that only the tips of the needle-shaped steel was destroyed. With electron microscope, it was found that both the tips and flanks of the carbon
The electron beams produced by the needle-shaped annular carbon fiber-coated cathode soaked with cesium iodide (CsI) salt and annular stainless steel cathode were separately used to bombard the nylon targets. There was a uniform round mark on the target bombarded by the electron beam generated by the carbon fiber cathode, but there was a nonuniform mark on the target bombarded by the annular stainless steel cathode. It was believed that the different mechanism, characteristics and configuration between the carbon fiber cathode and the stainless steel cathode caused the difference of emission uniformity. Scanning with optics microscope, it was found that only the tips of the needle-shaped steel was destroyed. With electron microscope, it was found that both the tips and flanks of the carbon
2005,
17.
Abstract:
In order to study the voltage distribution on the pulse transformer's conical windings, according to the structure of the actual pulse transformer's taper windings, the finite element model and equivalent circuit were built based on the multi-conductor transmission line theory. Using the model and circuit, the voltage distribution between the coils on the pulse was calculated. Computational results are presented to illustrate that the model can be used to calculate the voltage distribution in taper coil efficiently, which gives some references for the design of inter-turn insulation.
In order to study the voltage distribution on the pulse transformer's conical windings, according to the structure of the actual pulse transformer's taper windings, the finite element model and equivalent circuit were built based on the multi-conductor transmission line theory. Using the model and circuit, the voltage distribution between the coils on the pulse was calculated. Computational results are presented to illustrate that the model can be used to calculate the voltage distribution in taper coil efficiently, which gives some references for the design of inter-turn insulation.
2005,
17.
Abstract:
A new idea about radial reflex klystron oscillator with a virtual cathode is brought forward to improve microwave power and efficiency. The radial reflex klystron oscillator is combined with a virtual cathode oscillator in one foldaway coaxial diode. The frequency of the virtual cathode oscillator is locked by the radial reflex klystron oscillator and the bunching of the reflex electron beam reflected by the virtual cathode is enhanced. A new type of radial reflex klystron oscillator with a virtual cathode is designed and simulated by 2.5 D PIC. The results of the simulation are presented. 2.5 GW output power is generated with 620 kV voltage, 25 kA beam current and the frequency is 1.25 GHz.
A new idea about radial reflex klystron oscillator with a virtual cathode is brought forward to improve microwave power and efficiency. The radial reflex klystron oscillator is combined with a virtual cathode oscillator in one foldaway coaxial diode. The frequency of the virtual cathode oscillator is locked by the radial reflex klystron oscillator and the bunching of the reflex electron beam reflected by the virtual cathode is enhanced. A new type of radial reflex klystron oscillator with a virtual cathode is designed and simulated by 2.5 D PIC. The results of the simulation are presented. 2.5 GW output power is generated with 620 kV voltage, 25 kA beam current and the frequency is 1.25 GHz.
2005,
17.
Abstract:
This paper presents the design of 2-cell Tesla type cavity and the properties of higher order modes (HOMs) of 2-cell cavity simulated by HFSS process, including the tuning frequency, the quality factor, the shunt impedance and the distribution of the electronic fields. The simulation results of π mode using HFSS is the same as that using Superfish. The effect of HOMs on electron acceleration is analyzed. The analysis result shows that the efficiency of acceleration is decreased and the electron beam becomes unstable because of the HOMs.
This paper presents the design of 2-cell Tesla type cavity and the properties of higher order modes (HOMs) of 2-cell cavity simulated by HFSS process, including the tuning frequency, the quality factor, the shunt impedance and the distribution of the electronic fields. The simulation results of π mode using HFSS is the same as that using Superfish. The effect of HOMs on electron acceleration is analyzed. The analysis result shows that the efficiency of acceleration is decreased and the electron beam becomes unstable because of the HOMs.
2005,
17.
Abstract:
The present condition of technique research on generation of intense pulsed super-hard X-ray via bremsstrahlung of pulsed intense-current pinched electron beam was described. The characteristics of a few main techniques to generate intense pulsed super-hard X-ray were compared, and the methods to increase the super-hard X-ray yield were analyzed. Making use of the MCNP code the relations of super-hard X- ray generation efficiency with tantalum radiating converter thickness in the electron energy range of 0.4～1.4 MeV were calculated. Moreover, the three experiment techniques for generation of intense pulsed super-hard X-ray on “QuangGuang-I” accelerator were introduced and the respective results corresponding to the three kinds of diode were: (1) the super hard X-ray energy density of 5
The present condition of technique research on generation of intense pulsed super-hard X-ray via bremsstrahlung of pulsed intense-current pinched electron beam was described. The characteristics of a few main techniques to generate intense pulsed super-hard X-ray were compared, and the methods to increase the super-hard X-ray yield were analyzed. Making use of the MCNP code the relations of super-hard X- ray generation efficiency with tantalum radiating converter thickness in the electron energy range of 0.4～1.4 MeV were calculated. Moreover, the three experiment techniques for generation of intense pulsed super-hard X-ray on “QuangGuang-I” accelerator were introduced and the respective results corresponding to the three kinds of diode were: (1) the super hard X-ray energy density of 5
2005,
17.
Abstract:
A lower prepulse high power density water dielectric self-breaking switch was investigated on FlashⅡgenerator. The switch contained two or four gaps, a prepulse shield and supporting structure. The discharge current and the input or output voltages of each gap were measured by a Rogowski coil and CuSO4 resistance dividers respectively. The test and analysis methods of the experimental waveform were presented. The amplitudes of the prepulse of the water switch were significant. It was considered that the prepulse effect time of the water switch was equal to the breaking delay time. The prepulse current or prepulse voltage could be used to provide timing data to measure the delay time, the jitter of the same gap and the first-to-last switching time difference. The dI/dt signal of a gap coul
A lower prepulse high power density water dielectric self-breaking switch was investigated on FlashⅡgenerator. The switch contained two or four gaps, a prepulse shield and supporting structure. The discharge current and the input or output voltages of each gap were measured by a Rogowski coil and CuSO4 resistance dividers respectively. The test and analysis methods of the experimental waveform were presented. The amplitudes of the prepulse of the water switch were significant. It was considered that the prepulse effect time of the water switch was equal to the breaking delay time. The prepulse current or prepulse voltage could be used to provide timing data to measure the delay time, the jitter of the same gap and the first-to-last switching time difference. The dI/dt signal of a gap coul
2005,
17.
Abstract:
The experimental setup used to synthesize metal oxide nanopowders by electrical explosion of wires (EEW) was designed. Al2O3 nanopowders were synthesized successfully. The average size of the nanoparticle was 64.9 nm. Physical conditions for producing Al2O3 nanopowders by EEW were investigated. Research results show that the conditions affect the size of powders greatly. The lower the pressure in the chamber is, the smaller the particle size is. The particle size is proportional to the diameter of the wire. The smaller the diameter of the wire is, the smaller the particle size is. The particle size has some relation with the storage energy of the capacitor, too.
The experimental setup used to synthesize metal oxide nanopowders by electrical explosion of wires (EEW) was designed. Al2O3 nanopowders were synthesized successfully. The average size of the nanoparticle was 64.9 nm. Physical conditions for producing Al2O3 nanopowders by EEW were investigated. Research results show that the conditions affect the size of powders greatly. The lower the pressure in the chamber is, the smaller the particle size is. The particle size is proportional to the diameter of the wire. The smaller the diameter of the wire is, the smaller the particle size is. The particle size has some relation with the storage energy of the capacitor, too.
2005,
17.
Abstract:
It's an essential step for the commissioning of electron-positron collider to realize the absolute collision of electron and positron beams at the interaction point. The relative transverse offset between electron and positron beams causes the beam-beam deflection, which can be utilized effectively to detect and control the offset of two beams at the interaction point. Observation and measurement of the beam-beam deflection in vertical plane have been carried out in Beijing electron positron collidor (BEPC) successfully with a digital high-sensitive oscillograph and a pair of electrostatic separators. The study results not only prove the feasibility of this adjustment method but also provide valuable experience for the commissioning of BEPCⅡ.
It's an essential step for the commissioning of electron-positron collider to realize the absolute collision of electron and positron beams at the interaction point. The relative transverse offset between electron and positron beams causes the beam-beam deflection, which can be utilized effectively to detect and control the offset of two beams at the interaction point. Observation and measurement of the beam-beam deflection in vertical plane have been carried out in Beijing electron positron collidor (BEPC) successfully with a digital high-sensitive oscillograph and a pair of electrostatic separators. The study results not only prove the feasibility of this adjustment method but also provide valuable experience for the commissioning of BEPCⅡ.
2005,
17.
Abstract:
A monitoring and control system for 4 MeV electron linear induction accelerator capable of producing beams in burst mode is presented. The system is a distributed one based on local network using DataSocket. The hardware using FP2000 distributed I/O system and Chroma programmable AC power sources is described. The software architecture based on DataSocket as a communication medium in Labwindows/CVI is also presented. As to two shortages of DataSocket caused by loss of unprocessed data and complicated relationships among lots of data items, some methods such as abstracting and synthesizing data items, describing items by data dictionary and making some compromise between rapidity and reliability are presented to fix the limitations.
A monitoring and control system for 4 MeV electron linear induction accelerator capable of producing beams in burst mode is presented. The system is a distributed one based on local network using DataSocket. The hardware using FP2000 distributed I/O system and Chroma programmable AC power sources is described. The software architecture based on DataSocket as a communication medium in Labwindows/CVI is also presented. As to two shortages of DataSocket caused by loss of unprocessed data and complicated relationships among lots of data items, some methods such as abstracting and synthesizing data items, describing items by data dictionary and making some compromise between rapidity and reliability are presented to fix the limitations.
