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RSS2006 Vol. 18, No. 12
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2006,
18.
Abstract:
The solid heat capacity laser needs cooling after continuous operation for a short time before the next operation, so the cooling speed directly affects its working efficiency. The Nd: GGG disk laser medium end symmetrically pumped from four directions by the diode arrays was adopted. Based on the heat transfer equation with heat depositing mode, the numerical simulations of the temperature field and the thermal stress distribution in the slab medium were performed under the condition of heat capacity operation by finite element analysis method. Four cooling methods, including cold gas, water cycle, atomization and phase cooling, were respectively used to cool the slab medium. The transient temperature history and the stress history of the medium were simulated. The simulation result indi
The solid heat capacity laser needs cooling after continuous operation for a short time before the next operation, so the cooling speed directly affects its working efficiency. The Nd: GGG disk laser medium end symmetrically pumped from four directions by the diode arrays was adopted. Based on the heat transfer equation with heat depositing mode, the numerical simulations of the temperature field and the thermal stress distribution in the slab medium were performed under the condition of heat capacity operation by finite element analysis method. Four cooling methods, including cold gas, water cycle, atomization and phase cooling, were respectively used to cool the slab medium. The transient temperature history and the stress history of the medium were simulated. The simulation result indi
2006,
18.
Abstract:
In order to explore new high power laser systems, a liquid laser pumped by diode was build up. In the experiment, diode laser was adopted to pump neodymium ion doped inorganic laser liquid on single side. By measuring the near field profile, pulse shapes and the spectrums of the output light, liquid laser output was proved. Laser wavelength is 1 053 nm. A laser pulse output energy value reached 47 mJ and optical to optical efficiency 14%. Its optical efficiency was much higher than that of flash lamp as pump light source, which shows that liquid lasers has the outlook to high power laser systems.
In order to explore new high power laser systems, a liquid laser pumped by diode was build up. In the experiment, diode laser was adopted to pump neodymium ion doped inorganic laser liquid on single side. By measuring the near field profile, pulse shapes and the spectrums of the output light, liquid laser output was proved. Laser wavelength is 1 053 nm. A laser pulse output energy value reached 47 mJ and optical to optical efficiency 14%. Its optical efficiency was much higher than that of flash lamp as pump light source, which shows that liquid lasers has the outlook to high power laser systems.
2006,
18.
Abstract:
Based on analysis for nozzle thermal ablation, reflecting and absorbing thermal protection approaches were presented to provide thermal protection for nozzles. Two types of corresponding nozzles were designed. Initial investigation was carried out on the two types of thermal protection of the two nozzle types, in which a pulsed 10 kW CO2 laser and a three-reflection laser thruster were employed. The results showed that the nozzles were ablated to different extent, depending on the relative focus position, working time etc. A reflecting thermal protection approach, in which direct absorption of the laser energy was reduced by the optical surface of the nozzle and the penetrated energy was refocused to improve energy transferring efficiency, with good circular cooling, is prospective to be d
Based on analysis for nozzle thermal ablation, reflecting and absorbing thermal protection approaches were presented to provide thermal protection for nozzles. Two types of corresponding nozzles were designed. Initial investigation was carried out on the two types of thermal protection of the two nozzle types, in which a pulsed 10 kW CO2 laser and a three-reflection laser thruster were employed. The results showed that the nozzles were ablated to different extent, depending on the relative focus position, working time etc. A reflecting thermal protection approach, in which direct absorption of the laser energy was reduced by the optical surface of the nozzle and the penetrated energy was refocused to improve energy transferring efficiency, with good circular cooling, is prospective to be d
2006,
18.
Abstract:
Researches into effects of temperature rising rate on mechanical properties of metals under rapid heating are reviewed, including those carried out by American researchers using methods of macroscopic tensile-heating experiments in 1950 or so and those by domestic researchers employing combined methods of macroscopic property measurements and microscopic constitution observations in recent years. It is mentioned that, as far as effects of temperature rising rate on mechanical properties of metals is concerned, more accurate and systematical macroscopic-microscopic experiments and theoretical modeling and numerical simulation of multi-scale thermo-mechanical-material coupling should be performed, clearer laws should be understood, and available mathematical formula in engineering should be
Researches into effects of temperature rising rate on mechanical properties of metals under rapid heating are reviewed, including those carried out by American researchers using methods of macroscopic tensile-heating experiments in 1950 or so and those by domestic researchers employing combined methods of macroscopic property measurements and microscopic constitution observations in recent years. It is mentioned that, as far as effects of temperature rising rate on mechanical properties of metals is concerned, more accurate and systematical macroscopic-microscopic experiments and theoretical modeling and numerical simulation of multi-scale thermo-mechanical-material coupling should be performed, clearer laws should be understood, and available mathematical formula in engineering should be
2006,
18.
Abstract:
An analytic formula for the mean temperature along the axial direction of a rotating cylinder shell irradiated by high energy laser beams is presented. For the laser beam with Gaussian distribution of power density, it’s very difficult to give an analytic expression, hence a fitting formula is derived. The formula is determined by only one fitting coefficient with physical meaning, which is called distribution factor. The results obtained by using the analytic fitting formula and numerical calculation agree well with each other. As an application example, a formula for rupturing time of inner-pressured rotating cylinder irradiated by laser beams is presented, and the results agree well with that of numerical calculation.
An analytic formula for the mean temperature along the axial direction of a rotating cylinder shell irradiated by high energy laser beams is presented. For the laser beam with Gaussian distribution of power density, it’s very difficult to give an analytic expression, hence a fitting formula is derived. The formula is determined by only one fitting coefficient with physical meaning, which is called distribution factor. The results obtained by using the analytic fitting formula and numerical calculation agree well with each other. As an application example, a formula for rupturing time of inner-pressured rotating cylinder irradiated by laser beams is presented, and the results agree well with that of numerical calculation.
2006,
18.
Abstract:
For restraining the temperature excursion accumulation and the anti-Stokes back-scattering intermingling with the Rayleigh back-scattering, an optical fiber sampling ring was set after an inswept death section of the sensing optical fiber. The anti-Stokes back-scattering was demodulated by Rayleigh back-scattering and the fiber's temperature was calculated by the sampling ring, which advanced the temperature precision and stability of the system. A 10 ns, 100 mW, 1.55 μm pulse laser, a 15 dB gain of EDFA, two high sensitive and low noise APD, two100M14bitA/D and two DSP chips using for 212~213 digital average form the experimental system. The spatial resolution of 1 m and temperature resolution of 0.03 ℃ were achieved using these techniques.
For restraining the temperature excursion accumulation and the anti-Stokes back-scattering intermingling with the Rayleigh back-scattering, an optical fiber sampling ring was set after an inswept death section of the sensing optical fiber. The anti-Stokes back-scattering was demodulated by Rayleigh back-scattering and the fiber's temperature was calculated by the sampling ring, which advanced the temperature precision and stability of the system. A 10 ns, 100 mW, 1.55 μm pulse laser, a 15 dB gain of EDFA, two high sensitive and low noise APD, two100M14bitA/D and two DSP chips using for 212~213 digital average form the experimental system. The spatial resolution of 1 m and temperature resolution of 0.03 ℃ were achieved using these techniques.
2006,
18.
Abstract:
In order to use the laser energy efficiently, a numerical model is presented to simulate the temperature distribution on the rotational cylindrical shell under CW and repetition frequency laser irradiation . By numerical analyzing, a conclusion is drown that the heating efficiency of laser is affected by repetition frequency and the duty ratio of pulsed laser, and the heating efficiency of pulsed laser is greater than that of CW laser. Temperature rises with the duty ratio decreasing under the same repetition frequency of pulsed laser, while the temperature periodic change is more obvious with the lower repetition frequency under the same duty ratio of pulsed laser. When the duty ratio of pulsed laser is small, repetition frequency has little effect on the heating efficiency of pulsed las
In order to use the laser energy efficiently, a numerical model is presented to simulate the temperature distribution on the rotational cylindrical shell under CW and repetition frequency laser irradiation . By numerical analyzing, a conclusion is drown that the heating efficiency of laser is affected by repetition frequency and the duty ratio of pulsed laser, and the heating efficiency of pulsed laser is greater than that of CW laser. Temperature rises with the duty ratio decreasing under the same repetition frequency of pulsed laser, while the temperature periodic change is more obvious with the lower repetition frequency under the same duty ratio of pulsed laser. When the duty ratio of pulsed laser is small, repetition frequency has little effect on the heating efficiency of pulsed las
2006,
18.
Abstract:
The dispersions resulted from practical stretcher and compressor in optical parametric chirped pulse amplify system are studied by ray-tracing method, and the pulse amplify is numerically simulated using Runge-Kutta method. The effects of misalignment of grating planes and grooves, signal intensity and pump intensity are discussed. The simulations show that misalignment of gating planes leads to pulse broadening. When the angle of grating groove is 0.8°, the pulse width is the narrowest in the case of group delay dispersion. When the angle of grating groove is 1°, the pulse width is the narrowest in the case of three-order dispersion.
The dispersions resulted from practical stretcher and compressor in optical parametric chirped pulse amplify system are studied by ray-tracing method, and the pulse amplify is numerically simulated using Runge-Kutta method. The effects of misalignment of grating planes and grooves, signal intensity and pump intensity are discussed. The simulations show that misalignment of gating planes leads to pulse broadening. When the angle of grating groove is 0.8°, the pulse width is the narrowest in the case of group delay dispersion. When the angle of grating groove is 1°, the pulse width is the narrowest in the case of three-order dispersion.
2006,
18.
Abstract:
Sodium resonance fluorescence lidar was used to detect sodium layer at Hefei. The configuration of sodium resonance fluorescence lidar was introduced. The measurement data have been retrieved and analyzed. The results show that the density of sodium varied much during Dec.2005 to Mar.2006: The column abundance of sodium layer changed from 5.4×109cm-2 to 2.4×109cm-2, reduced almost 50%; The mean RMS width also declined, and the centroid height of sodium layer had small fluctuation. The variation trend of sodium layer at Hefei is similar to those in the other mid-latitude places (such as Illinois, Tokyo) in the world.
Sodium resonance fluorescence lidar was used to detect sodium layer at Hefei. The configuration of sodium resonance fluorescence lidar was introduced. The measurement data have been retrieved and analyzed. The results show that the density of sodium varied much during Dec.2005 to Mar.2006: The column abundance of sodium layer changed from 5.4×109cm-2 to 2.4×109cm-2, reduced almost 50%; The mean RMS width also declined, and the centroid height of sodium layer had small fluctuation. The variation trend of sodium layer at Hefei is similar to those in the other mid-latitude places (such as Illinois, Tokyo) in the world.
2006,
18.
Abstract:
By analysing the performance features of laser diode array end-pumped disk laser amplifier, a finite element thermal model of laser crystal Nd:YLF was established. 3D and transient distributions of temperature and thermal stress of Nd:YLF pumped with 56 kW, 520 μs and 10 Hz LD were respactively calculated when the transverse distribution of pump energies was uniform, Gaussian and Super-Gaussian. The result shows that the thermal effect of the crystal under Super-Gaussian transverse distribution is the weakest, the maxmum temperature is 103.3 ℃, and the maxmum Mises stress is 47.6 MPa. When the effective pump energy reaches up to 10 kW/cm2, the fracture due to thermal stress will occur.
By analysing the performance features of laser diode array end-pumped disk laser amplifier, a finite element thermal model of laser crystal Nd:YLF was established. 3D and transient distributions of temperature and thermal stress of Nd:YLF pumped with 56 kW, 520 μs and 10 Hz LD were respactively calculated when the transverse distribution of pump energies was uniform, Gaussian and Super-Gaussian. The result shows that the thermal effect of the crystal under Super-Gaussian transverse distribution is the weakest, the maxmum temperature is 103.3 ℃, and the maxmum Mises stress is 47.6 MPa. When the effective pump energy reaches up to 10 kW/cm2, the fracture due to thermal stress will occur.
2006,
18.
Abstract:
The iso-pressure approximation model used in laser propagation in gas medium and its disadvantage under complex border conditions were analyzed. The weakly compressible fluid model based on the Mach uniform method introduced by Peter Wesseling was developed. Using the weakly compressible fluid model and scalar wave equation, a numerical study was carried out for the gas thermal effects on laser propagating in a closed tube full-filled with air. The far-field beam shape at different time were obtained and compared with the experimental ones. The weakly compressible fluid model could be well adapted problems with complex border conditions, which proves that it is more flexible than the compressible fluid model or the iso-pressure approximate model．
The iso-pressure approximation model used in laser propagation in gas medium and its disadvantage under complex border conditions were analyzed. The weakly compressible fluid model based on the Mach uniform method introduced by Peter Wesseling was developed. Using the weakly compressible fluid model and scalar wave equation, a numerical study was carried out for the gas thermal effects on laser propagating in a closed tube full-filled with air. The far-field beam shape at different time were obtained and compared with the experimental ones. The weakly compressible fluid model could be well adapted problems with complex border conditions, which proves that it is more flexible than the compressible fluid model or the iso-pressure approximate model．
2006,
18.
Abstract:
The principle of single frequency operation of the fiber laser with mode selected with fiber Bragg grating Fabry-Perot etalon is presented. The all-fiber single frequency Er3+-doped fiber ring laser has been designed in which two 976 nm laser dodes are used as the pump sources, the high concentration Er3+ -doped fiber as the gain medium, the travelling cavity is adopted to eliminate the spatial hole burning effect. The designed etalon can discriminate and select laser longitudinal modes efficiently and a stable single-frequency laser is obtained. The experiment using 5 m and 3 m long Er3+-doped fibers respectively is presented. When the maximum pump power is 145 mW, the output powers are 19 mW and 42 mW respectively and the optical-optical conversion efficiency are 13% and 29%, the slope e
The principle of single frequency operation of the fiber laser with mode selected with fiber Bragg grating Fabry-Perot etalon is presented. The all-fiber single frequency Er3+-doped fiber ring laser has been designed in which two 976 nm laser dodes are used as the pump sources, the high concentration Er3+ -doped fiber as the gain medium, the travelling cavity is adopted to eliminate the spatial hole burning effect. The designed etalon can discriminate and select laser longitudinal modes efficiently and a stable single-frequency laser is obtained. The experiment using 5 m and 3 m long Er3+-doped fibers respectively is presented. When the maximum pump power is 145 mW, the output powers are 19 mW and 42 mW respectively and the optical-optical conversion efficiency are 13% and 29%, the slope e
2006,
18.
Abstract:
A synthesis of carbon nanotubes(CNT) for field emission was grown speedly and vertically by microwave plasma chemical vapor deposition with a multi-layered stack as the catalyst lay. The SEM and TEM analysis results of the CNT samples showed that as-grown CNT were typical multi-layered ones with few defects, aligned and straight, and uniform in diameter and length. The growth rate of CNT was more than 5 μm/min. The field emission results showed that the as-grown CNT emission array presented excellent and stable field emission with current density more than 6 A/cm2. The work function of the as-grown CNT was 4.59 eV measured by UPS and the corresponding field factor was about 1 400.
A synthesis of carbon nanotubes(CNT) for field emission was grown speedly and vertically by microwave plasma chemical vapor deposition with a multi-layered stack as the catalyst lay. The SEM and TEM analysis results of the CNT samples showed that as-grown CNT were typical multi-layered ones with few defects, aligned and straight, and uniform in diameter and length. The growth rate of CNT was more than 5 μm/min. The field emission results showed that the as-grown CNT emission array presented excellent and stable field emission with current density more than 6 A/cm2. The work function of the as-grown CNT was 4.59 eV measured by UPS and the corresponding field factor was about 1 400.
2006,
18.
Abstract:
Environment temperature is an important factor affecting the stability of electron beam orbit . Most accelerator laboratories of the world have built environment temperature monitoring systems and air-condition systems. HLS is a light source of the second generation, the shift of the global beam orbit is required to stabilize within 100 mm in vertical plane. An environment temperature monitoring system was built recently for analyzing the environment temperature influence on beam orbit. The structure of the system and the problem of radiation interference are described. The data analysis indicates that beam orbit fluctuation is strongly correlated to temperature variation and the beam orbit in vertical plane varies 10~20 mm when the environment temperature changes 1 ℃.
Environment temperature is an important factor affecting the stability of electron beam orbit . Most accelerator laboratories of the world have built environment temperature monitoring systems and air-condition systems. HLS is a light source of the second generation, the shift of the global beam orbit is required to stabilize within 100 mm in vertical plane. An environment temperature monitoring system was built recently for analyzing the environment temperature influence on beam orbit. The structure of the system and the problem of radiation interference are described. The data analysis indicates that beam orbit fluctuation is strongly correlated to temperature variation and the beam orbit in vertical plane varies 10~20 mm when the environment temperature changes 1 ℃.
2006,
18.
Abstract:
Based on a water-dielectric helix line, a 2.2 m long accelerator with a diameter of 0.4 m was designed and tested. The influence of the impedence mismatching between the joint section in pulse forming line and the helical line on the voltage waveform of the diode was analyzed. A high impedance annulus made of macromolecule material with an inner radius of 10 cm and an outer radius of 18 cm was added to the joint section. By making the impedance of the joint section be close to that of the helical line and the electric length minish, the upshot was eliminated, the fall time was minished, and a square pulse with a risetime about 18 ns, a fall time about 40 ns and a pulse top duration about 200 ns was obtained.
Based on a water-dielectric helix line, a 2.2 m long accelerator with a diameter of 0.4 m was designed and tested. The influence of the impedence mismatching between the joint section in pulse forming line and the helical line on the voltage waveform of the diode was analyzed. A high impedance annulus made of macromolecule material with an inner radius of 10 cm and an outer radius of 18 cm was added to the joint section. By making the impedance of the joint section be close to that of the helical line and the electric length minish, the upshot was eliminated, the fall time was minished, and a square pulse with a risetime about 18 ns, a fall time about 40 ns and a pulse top duration about 200 ns was obtained.
2006,
18.
Abstract:
FDTD method of lossy left-handed material is used to simulate the focus of a parallel-sided slab illuminated by a monochromatic source on the far side. Different slab thickness structures are simulated separately. Comparison shows that the thinner LHM slab would make its image focus point closer to the slab side. However, a very narrow slab could make the image focus disappear.
FDTD method of lossy left-handed material is used to simulate the focus of a parallel-sided slab illuminated by a monochromatic source on the far side. Different slab thickness structures are simulated separately. Comparison shows that the thinner LHM slab would make its image focus point closer to the slab side. However, a very narrow slab could make the image focus disappear.
2006,
18.
Abstract:
Axial vircators driven by hollow electron beam and solid electron beam, respectively, are compared with each other and analyzed theoretically. The output power of microwave under the same structural parameters was numerically calculated for comparison. Further analysis on the radius of electron beams for the TM01, the TM02 and the TM03 modes was also carried out. PIC simulations using KARAT are accordant with the calculation. Results show that the power of TM01 mode driven by the solid electron beam is higher than the case of hollow electron beam, but in the case of the higher order TM0n modes, the hollow electron beam is probably better for the power generation of microwaves.
Axial vircators driven by hollow electron beam and solid electron beam, respectively, are compared with each other and analyzed theoretically. The output power of microwave under the same structural parameters was numerically calculated for comparison. Further analysis on the radius of electron beams for the TM01, the TM02 and the TM03 modes was also carried out. PIC simulations using KARAT are accordant with the calculation. Results show that the power of TM01 mode driven by the solid electron beam is higher than the case of hollow electron beam, but in the case of the higher order TM0n modes, the hollow electron beam is probably better for the power generation of microwaves.
2006,
18.
Abstract:
Through numerical calculation, S-band magnetically insulated line oscillator (S-MILO) is calculated. The frequencies of the π/4, π/2, 3π/4 and π mode of primary coaxial slow wave structure (SWS) cavity calculated in the simulation are 1.40, 2.21, 2.46 and 2.51 GHz, respectrively. The frequencies of corresponding modes of the S-MILO closed cavity are 1.26, 2.04, 2.42 and 2.53 GHz. The quality-factor of π mode is also calculated. The eigen-frequency of S-MILO open cavity is 2.43 GHz by calculation, the frequency from 2.25 to 3.05 GHz is cut off in the RF choke, the output frequency is from 2.2 to 2.5 GHz. The results indicate that the high frequency structure of the S-MILO is reasonable.
Through numerical calculation, S-band magnetically insulated line oscillator (S-MILO) is calculated. The frequencies of the π/4, π/2, 3π/4 and π mode of primary coaxial slow wave structure (SWS) cavity calculated in the simulation are 1.40, 2.21, 2.46 and 2.51 GHz, respectrively. The frequencies of corresponding modes of the S-MILO closed cavity are 1.26, 2.04, 2.42 and 2.53 GHz. The quality-factor of π mode is also calculated. The eigen-frequency of S-MILO open cavity is 2.43 GHz by calculation, the frequency from 2.25 to 3.05 GHz is cut off in the RF choke, the output frequency is from 2.2 to 2.5 GHz. The results indicate that the high frequency structure of the S-MILO is reasonable.
2006,
18.
Abstract:
In the summer of 2005, a comprehensive observation on triggered lightning discharges was conducted in Binzhou, Shandong. Five lightning flashes were successfully triggered with three with classical triggering method and two with altitude triggering method. The vertical electric field changes of the bidirection leader system and the dart leader-return stroke of negative triggered lightning discharges at distances of 60 m and 550 m are presented. The electric field changes produced by the bidirection leader system at 60 m and 550 m are negative 4.70~14.60 kV/m and positive 0.11~0.16 kV/m, respectively. The slope coefficient of the charge distribution along lightning channel for the bidirection leader system is estimated to be (1.2~3.8)×10-7C·m-2. The dart leader-return stroke sequences ap
In the summer of 2005, a comprehensive observation on triggered lightning discharges was conducted in Binzhou, Shandong. Five lightning flashes were successfully triggered with three with classical triggering method and two with altitude triggering method. The vertical electric field changes of the bidirection leader system and the dart leader-return stroke of negative triggered lightning discharges at distances of 60 m and 550 m are presented. The electric field changes produced by the bidirection leader system at 60 m and 550 m are negative 4.70~14.60 kV/m and positive 0.11~0.16 kV/m, respectively. The slope coefficient of the charge distribution along lightning channel for the bidirection leader system is estimated to be (1.2~3.8)×10-7C·m-2. The dart leader-return stroke sequences ap
2006,
18.
Abstract:
The Dyadic Green’s function about spherical-shell microwave windows is presented in this paper, with which the influence on radiation pattern caused by the hemispherical-shell microwave windows is analyzed. The results show that the effect on the radiation pattern is prominent with the enhanced side lobe and the narrowed main lobe when the beam waist of Gauss distribution field is large, while the effect weakens as the beam waist decreases, thus it is concluded that the hemispherical-shell microwave windows are fit for the Gauss feed with small beam waist but unfit for the feed with large beam waist.
The Dyadic Green’s function about spherical-shell microwave windows is presented in this paper, with which the influence on radiation pattern caused by the hemispherical-shell microwave windows is analyzed. The results show that the effect on the radiation pattern is prominent with the enhanced side lobe and the narrowed main lobe when the beam waist of Gauss distribution field is large, while the effect weakens as the beam waist decreases, thus it is concluded that the hemispherical-shell microwave windows are fit for the Gauss feed with small beam waist but unfit for the feed with large beam waist.
2006,
18.
Abstract:
An electron gun and a magnetic-focus system for folded waveguide millimeter-wave traveling wave tube(TWT) were designed by electron gun code(VBGUN) based on visual boundary element method and magnetic field code(MOM) based on boundary element method. A definition of relative coefficient was used to optimize parameters, and a sensitive coefficient was defined to review the effect of fabrication-errors. The design results show that this kind of gun is easily affected both by the shape of the electrodes and the fabrication-errors. The maximum magnetic field on axis is limited by the dimension of the slow wave structure. This is the main problem for the focus system design of the folded waveguide TWT, which can be solved by augmenting the working voltage or decreasing the beam current. Consequ
An electron gun and a magnetic-focus system for folded waveguide millimeter-wave traveling wave tube(TWT) were designed by electron gun code(VBGUN) based on visual boundary element method and magnetic field code(MOM) based on boundary element method. A definition of relative coefficient was used to optimize parameters, and a sensitive coefficient was defined to review the effect of fabrication-errors. The design results show that this kind of gun is easily affected both by the shape of the electrodes and the fabrication-errors. The maximum magnetic field on axis is limited by the dimension of the slow wave structure. This is the main problem for the focus system design of the folded waveguide TWT, which can be solved by augmenting the working voltage or decreasing the beam current. Consequ
2006,
18.
Abstract:
The one dimensional(1-D) USED CARS experimental system was constructed. The 1-D CARS spectra of N2 Q-branch were obtained from the air as well as premixed CH4/Air flame with the equivalence ratio phi being 1, the flux per minute of methane being 0.7 L, at the atmospheric pressure. The data were analyzed by CARS software, and temperature was calculated. The temperature distribution in small range at various height above the burner was given in four fragments. The temperature in the flame decreased with increasing height, not only in the scale of the width of laser sheet, but also in the whole flame, by the influence of the air around the burner. The uncertainty of the experimental result is less than 7%. This technology can be used to measure the temperature in stable combustion field.
The one dimensional(1-D) USED CARS experimental system was constructed. The 1-D CARS spectra of N2 Q-branch were obtained from the air as well as premixed CH4/Air flame with the equivalence ratio phi being 1, the flux per minute of methane being 0.7 L, at the atmospheric pressure. The data were analyzed by CARS software, and temperature was calculated. The temperature distribution in small range at various height above the burner was given in four fragments. The temperature in the flame decreased with increasing height, not only in the scale of the width of laser sheet, but also in the whole flame, by the influence of the air around the burner. The uncertainty of the experimental result is less than 7%. This technology can be used to measure the temperature in stable combustion field.
2006,
18.
Abstract:
The effects of bipolar flow on the performance of planar diode are analyzed and simulated by a PIC code. The effects of bipolar flow in an MILO device with radial emission are simulated. Some qualitative conclusions in this kind of microwave tube with low impedance are presented. The beam current increase caused by the bipolar flow in the tube may remove the operation point away from the optimal operation point. As a result the microwave output power and efficiency of the tube decrease. When the voltage gets higher, the work point of the tube is further away from the optimal operation point. The operation point of the tube would move below of B-H curve when the voltage is high enough. The tube is over-insulated and can not work well.
The effects of bipolar flow on the performance of planar diode are analyzed and simulated by a PIC code. The effects of bipolar flow in an MILO device with radial emission are simulated. Some qualitative conclusions in this kind of microwave tube with low impedance are presented. The beam current increase caused by the bipolar flow in the tube may remove the operation point away from the optimal operation point. As a result the microwave output power and efficiency of the tube decrease. When the voltage gets higher, the work point of the tube is further away from the optimal operation point. The operation point of the tube would move below of B-H curve when the voltage is high enough. The tube is over-insulated and can not work well.
2006,
18.
Abstract:
Three-fold helical rippled waveguide makes TE11 and TE21 coupling, the dispersion characteristic in physical mechanism make the electron the cyclotron resonance in the broad frequency band, so the dispersion equation need to be researched. The dispersion equation of the traveling wave mode and backward wave mode are put forward for the engineering application. The coupling coefficient of the dispersion equation is simplified, whose error is about 1%. The model is built and the helical rippled waveguide is simulated using VBA program in CST software. A simulation method is put forward by the coupling mode characteristic in the simulated transmission characteristic curve. The simulation result is compared with the theoretical one and the error is about 5%. The simulation method and theory in
Three-fold helical rippled waveguide makes TE11 and TE21 coupling, the dispersion characteristic in physical mechanism make the electron the cyclotron resonance in the broad frequency band, so the dispersion equation need to be researched. The dispersion equation of the traveling wave mode and backward wave mode are put forward for the engineering application. The coupling coefficient of the dispersion equation is simplified, whose error is about 1%. The model is built and the helical rippled waveguide is simulated using VBA program in CST software. A simulation method is put forward by the coupling mode characteristic in the simulated transmission characteristic curve. The simulation result is compared with the theoretical one and the error is about 5%. The simulation method and theory in
2006,
18.
Abstract:
Microwave equivalent circuit (microwave net) is adopt to study the rectangle wave-guide output window of klystron. Transfer matrix is utilized to calculate the standing wave ratio and optimal size of the window is found based on the condition of no reflection. Meanwhile, a more precise simulation is done by ISFEL3D. Compared the result by microwave equivalent circuit method to the result by ISFEL3D and experiment, the conclusion indicates that the method is feasible for the initial design, which is easy to programe and fast to compute, without much distinction to experimental result, based on its brief theory.
Microwave equivalent circuit (microwave net) is adopt to study the rectangle wave-guide output window of klystron. Transfer matrix is utilized to calculate the standing wave ratio and optimal size of the window is found based on the condition of no reflection. Meanwhile, a more precise simulation is done by ISFEL3D. Compared the result by microwave equivalent circuit method to the result by ISFEL3D and experiment, the conclusion indicates that the method is feasible for the initial design, which is easy to programe and fast to compute, without much distinction to experimental result, based on its brief theory.
2006,
18.
Abstract:
This paper presents an overmoded complex device of which the output power may approach 10 GW level without breakdown, derives self-consistently the phase lock equation of the radiation wave of the device driven by both the external electromagnetic signal and the prebunching electron beam simutaneously, and shows that when the phase is locked by the external electromagnetic signal and the prebunching electron beam simultaneously, the operation time reaching the phase lock can be shortened, the shift of the operation frequency to the locking frequency(the frequency of the external electromagnetic signal ) decreased, and the bandwidth of the phase lock operation enlarged.
This paper presents an overmoded complex device of which the output power may approach 10 GW level without breakdown, derives self-consistently the phase lock equation of the radiation wave of the device driven by both the external electromagnetic signal and the prebunching electron beam simutaneously, and shows that when the phase is locked by the external electromagnetic signal and the prebunching electron beam simultaneously, the operation time reaching the phase lock can be shortened, the shift of the operation frequency to the locking frequency(the frequency of the external electromagnetic signal ) decreased, and the bandwidth of the phase lock operation enlarged.
2006,
18.
Abstract:
The paper analyzes the characteristic of a multiple-beam klystron output circuit, π-mode double gap cavity loaded by cutoff waveguide filter, with 3D simulation method. The research is focused on the influence of the size of the coupling port, coupling line and the capacitive metal rods in cutoff waveguide on the gap impedance. The result shows that, the size of the coupling port has strong influence on the external quality factor of the output cavity, while the size of the coupling line and the capacitive metal rods mainly affect the tuning frequency of cutoff waveguide filter. Since the coupling line brings about an additive inductance in cutoff waveguide filter, which makes the quality factor bigger and resonant band narrower, π-mode double gap cavities are not more advantageous to a
The paper analyzes the characteristic of a multiple-beam klystron output circuit, π-mode double gap cavity loaded by cutoff waveguide filter, with 3D simulation method. The research is focused on the influence of the size of the coupling port, coupling line and the capacitive metal rods in cutoff waveguide on the gap impedance. The result shows that, the size of the coupling port has strong influence on the external quality factor of the output cavity, while the size of the coupling line and the capacitive metal rods mainly affect the tuning frequency of cutoff waveguide filter. Since the coupling line brings about an additive inductance in cutoff waveguide filter, which makes the quality factor bigger and resonant band narrower, π-mode double gap cavities are not more advantageous to a
2006,
18.
Abstract:
The finite-difference time-domain(FDTD) method is widely used to solve electromagnetic problems in computer simulation. Some common problems for design of excitation source in waveguide are discussed in the first instance. According to the propagation property of electromagnetic wave, a new method is presented for simulating the excitation source in waveguide simply. The formulas of this method and the special processes are also presented. Results show that FDTD method can simulate complex situation and eliminite the false reflection on the boundary of the excitation source. Comparing with comventional methods, the validity and advantage of this method are proved by computing magnetically insulated transmission line oscillator(MILO) as an example.
The finite-difference time-domain(FDTD) method is widely used to solve electromagnetic problems in computer simulation. Some common problems for design of excitation source in waveguide are discussed in the first instance. According to the propagation property of electromagnetic wave, a new method is presented for simulating the excitation source in waveguide simply. The formulas of this method and the special processes are also presented. Results show that FDTD method can simulate complex situation and eliminite the false reflection on the boundary of the excitation source. Comparing with comventional methods, the validity and advantage of this method are proved by computing magnetically insulated transmission line oscillator(MILO) as an example.
2006,
18.
Abstract:
A 70 GHz second-harmonic frequency-doubling gyroklystron with four cavities has been studied. The input cavity operates in the fundamental harmonic TE01 mode at 35 GHz and the other cavities operate in the second harmonic TE02 mode at 70 GHz. The quality factor and mode conversion of the bunching cavities were studied in detail with field matching analysis to reduce the RF crosstalk of the 70 GHz TE01 mode between cavities. And the RF circuit was designed and optimized to enhance operating bandwidth and electron efficiency. And then a 70 GHz second-harmonic frequency-doubling gyroklystron was designed. 256 kW output power, 44 dB saturation gain, 28% electron efficiency with about 160 MHz instantaneous bandwidth were obtained by PIC simulation at 70 kV, 13 A electron beam. The instantaneous
A 70 GHz second-harmonic frequency-doubling gyroklystron with four cavities has been studied. The input cavity operates in the fundamental harmonic TE01 mode at 35 GHz and the other cavities operate in the second harmonic TE02 mode at 70 GHz. The quality factor and mode conversion of the bunching cavities were studied in detail with field matching analysis to reduce the RF crosstalk of the 70 GHz TE01 mode between cavities. And the RF circuit was designed and optimized to enhance operating bandwidth and electron efficiency. And then a 70 GHz second-harmonic frequency-doubling gyroklystron was designed. 256 kW output power, 44 dB saturation gain, 28% electron efficiency with about 160 MHz instantaneous bandwidth were obtained by PIC simulation at 70 kV, 13 A electron beam. The instantaneous
2006,
18.
Abstract:
Radiation transport in matter can be supersonic when the Mach number of the heat wave front is typically over 3. In this paper, the conditions under which the supersonic radiation transport was diffusive were investigated in the case of an external radiation source with constant temperature. This model was based on the analytic theory of the radiation diffusion equation in one dimension. The ranges of parameters where supersonic diffusive transport occurs were obtained for a fixed mass density in an analytical way. Furthermore, critical values for the temperature of the external radiation source and the radiation heat wave front position were also derived analytically. They are the functions of the mass density. A calculating case for SiO2 foam is presented to show the basic physical pictu
Radiation transport in matter can be supersonic when the Mach number of the heat wave front is typically over 3. In this paper, the conditions under which the supersonic radiation transport was diffusive were investigated in the case of an external radiation source with constant temperature. This model was based on the analytic theory of the radiation diffusion equation in one dimension. The ranges of parameters where supersonic diffusive transport occurs were obtained for a fixed mass density in an analytical way. Furthermore, critical values for the temperature of the external radiation source and the radiation heat wave front position were also derived analytically. They are the functions of the mass density. A calculating case for SiO2 foam is presented to show the basic physical pictu
2006,
18.
Abstract:
A general Godunov finite difference schemes-WENO（weighted essentially non-oscillatory）Schemes which have fifth-order accuracy is used to make a numerical calculation of 2-dimensional axis symmetrical laser-supported plasma flow field under laser ablated solid target. The models of the calculation of ionization degree of plasma and the interaction between laser beam and plasma and the simplified EOS(equation of state) of plasma are considered in the simulation. Variation of plasma field parameters during and after laser interaction is also obtained. The comparison of simulation results and theoretical model shows that the results of theoretical model which has no consideration of 2-D expansion effect greater than the results of 2-D simulation, and there is no order difference in magnitude
A general Godunov finite difference schemes-WENO（weighted essentially non-oscillatory）Schemes which have fifth-order accuracy is used to make a numerical calculation of 2-dimensional axis symmetrical laser-supported plasma flow field under laser ablated solid target. The models of the calculation of ionization degree of plasma and the interaction between laser beam and plasma and the simplified EOS(equation of state) of plasma are considered in the simulation. Variation of plasma field parameters during and after laser interaction is also obtained. The comparison of simulation results and theoretical model shows that the results of theoretical model which has no consideration of 2-D expansion effect greater than the results of 2-D simulation, and there is no order difference in magnitude
2006,
18.
Abstract:
Based on the experience of adaptive optics application in high power laser systems, a deformable mirror located at cavity mirror can largely improve the dynamic range of correction aberrations. The four-pass amplifier laser facility has two features different from other facilities. The beam size has an alteration and beam rolls an angle of 90° between 1~2 pass and 3~4 pass propagation. The solution existence of deformable mirror face at this four-pass amplify facility cavity mirror is proved. How the ratio of beam alteration to affect the face solving problem of deformable mirror is analyzed by numerical simulation.
Based on the experience of adaptive optics application in high power laser systems, a deformable mirror located at cavity mirror can largely improve the dynamic range of correction aberrations. The four-pass amplifier laser facility has two features different from other facilities. The beam size has an alteration and beam rolls an angle of 90° between 1~2 pass and 3~4 pass propagation. The solution existence of deformable mirror face at this four-pass amplify facility cavity mirror is proved. How the ratio of beam alteration to affect the face solving problem of deformable mirror is analyzed by numerical simulation.
2006,
18.
Abstract:
Silver nanoclusters were prepared by flow-levitation technique. The nucleation and growth mechanism of the nanoclusters were studied theoretically, and the experiment conditions and technological parameters were studied experimentally. The morphology, granularity, structure, chemical components and electronic structure properties of the as-grown silver nanoclusters were characterized. The results indicate that the average size and dimension distribution of the nanoparticles mainly depend on the cooling efficiency, flow rate and inert gas pressure of the inert gas, and the temperature and size of the metal drop. Only He was used as the carrying gas for producing particles with an average size less than 10 nm. The optical absorption spectra of Ag nanoclusters show that the value of the surfa
Silver nanoclusters were prepared by flow-levitation technique. The nucleation and growth mechanism of the nanoclusters were studied theoretically, and the experiment conditions and technological parameters were studied experimentally. The morphology, granularity, structure, chemical components and electronic structure properties of the as-grown silver nanoclusters were characterized. The results indicate that the average size and dimension distribution of the nanoparticles mainly depend on the cooling efficiency, flow rate and inert gas pressure of the inert gas, and the temperature and size of the metal drop. Only He was used as the carrying gas for producing particles with an average size less than 10 nm. The optical absorption spectra of Ag nanoclusters show that the value of the surfa
2006,
18.
Abstract:
Discharge cell fixed on metal objects surface has great application values, so it is necessary to study its discharge features. In this paper, the discharge process is simulated. To solve the float conductor boundary condition problem, a method is proposed by using charge conservation law and Gaussian law. It is found that the potential of float conductor is between the potential of anode and that of cathode and varies as the inner field of plasma region varies. Using PIC-MCC method, a simulation of the discharge process is successfully done. The results show that the existence of float conductor boundary changes the inner field structure, which is favorable for gas discharge as well as the formation of plasma region. Moreover, the float conductor forms a float electrode that drives away a
Discharge cell fixed on metal objects surface has great application values, so it is necessary to study its discharge features. In this paper, the discharge process is simulated. To solve the float conductor boundary condition problem, a method is proposed by using charge conservation law and Gaussian law. It is found that the potential of float conductor is between the potential of anode and that of cathode and varies as the inner field of plasma region varies. Using PIC-MCC method, a simulation of the discharge process is successfully done. The results show that the existence of float conductor boundary changes the inner field structure, which is favorable for gas discharge as well as the formation of plasma region. Moreover, the float conductor forms a float electrode that drives away a
2006,
18.
Abstract:
Surface irradiation of refractory alloy DZ4 is now realized by using high intensity pulsed ion beam(HIPIB) containing Cn+ and H+, where the accelerating voltage, pulse duration and current density were fixed at 250 kV, 70 ns and 160 A/cm2 respectively, while the treating pulses were chosen as 2, 5, 10 and 15 times. The morphologies of the samples are analyzed by SEM. Craters appear on the surface of DZ4 alloy after a few radiations, and disappear when irradiated for more times. According to cross-section SEM image, there is a remelting layer with depth of 1~2 mm on the surface of the irradiated samples, and the grains of the remelting layer are refined and the grain boundaries are blurry. The results of electron probe microanalysis demonstrate that there are plenty of Cr and Mo around the
Surface irradiation of refractory alloy DZ4 is now realized by using high intensity pulsed ion beam(HIPIB) containing Cn+ and H+, where the accelerating voltage, pulse duration and current density were fixed at 250 kV, 70 ns and 160 A/cm2 respectively, while the treating pulses were chosen as 2, 5, 10 and 15 times. The morphologies of the samples are analyzed by SEM. Craters appear on the surface of DZ4 alloy after a few radiations, and disappear when irradiated for more times. According to cross-section SEM image, there is a remelting layer with depth of 1~2 mm on the surface of the irradiated samples, and the grains of the remelting layer are refined and the grain boundaries are blurry. The results of electron probe microanalysis demonstrate that there are plenty of Cr and Mo around the
2006,
18.
Abstract:
In conventional radiography, X rays which pass through an object along different paths are differentially absorbed, and the intensity pattern of the emerging beam records the distribution of absorbing materials within the sample. A non-conventional X-ray radiography-phase-contrast imaging is described, which records variations of the phase of the emerging radiation, shows dramatic contrast enhancement for low density or weakly absorbing materials with hard X-ray. A general treatment of X-ray image formation by Fresnel diffraction theory is presented. According to the optical transfer function, the distance of object-image and spatial frequency on the imaging phase-contrast is discussed. Resolution and contrast are the criteria used to specify the visibility of an image, resolution in turn
In conventional radiography, X rays which pass through an object along different paths are differentially absorbed, and the intensity pattern of the emerging beam records the distribution of absorbing materials within the sample. A non-conventional X-ray radiography-phase-contrast imaging is described, which records variations of the phase of the emerging radiation, shows dramatic contrast enhancement for low density or weakly absorbing materials with hard X-ray. A general treatment of X-ray image formation by Fresnel diffraction theory is presented. According to the optical transfer function, the distance of object-image and spatial frequency on the imaging phase-contrast is discussed. Resolution and contrast are the criteria used to specify the visibility of an image, resolution in turn
2006,
18.
Abstract:
By using the Fourier optics, a theoretical model based on the far field is put forward for the coherent addition of multi-ultrashort pulses. The impacts of all kinds of errors on the temporal and spatial properties in the far field are studied for a system with a 50 cm aperture and 1 ps ultrashort pulses. Results show that the phase-delay error must be less than 0.63 and the rotation errors must be less than 0.37 μrad and 0.34 μrad in the direction of x and y, respectively, with a criterion that the encircled energy in the 1×diffraction limit not less than 0.9 of that in the ideal case. Results also show that the residual chirp factor must be less than 1.32 and l.52 without and with 0.63 phase delay, respectively, with a criterion that the temporal stretch in the far field less than 0.2
By using the Fourier optics, a theoretical model based on the far field is put forward for the coherent addition of multi-ultrashort pulses. The impacts of all kinds of errors on the temporal and spatial properties in the far field are studied for a system with a 50 cm aperture and 1 ps ultrashort pulses. Results show that the phase-delay error must be less than 0.63 and the rotation errors must be less than 0.37 μrad and 0.34 μrad in the direction of x and y, respectively, with a criterion that the encircled energy in the 1×diffraction limit not less than 0.9 of that in the ideal case. Results also show that the residual chirp factor must be less than 1.32 and l.52 without and with 0.63 phase delay, respectively, with a criterion that the temporal stretch in the far field less than 0.2
2006,
18.
Abstract:
Tungsten wire array Z-pinch experiments performed on a 100 kA, 100 ns rise-time POS-based inductive generator were reported. The array consisted of 2 or 4 tungsten wires of 7 mm or 20 mm in diameter. Plasma luminescence pictures with 0.05 mm/ns resolution were taken by a fast streak camera. It turns out that 67%~78% of the 105 kA conduction current has been transferred from POS to the wire array loads, and the rise time of load current is 84~110 ns. The corona plasma formation, implosion and expansion after electrically exploding of tungsten wires were observed distinctly.
Tungsten wire array Z-pinch experiments performed on a 100 kA, 100 ns rise-time POS-based inductive generator were reported. The array consisted of 2 or 4 tungsten wires of 7 mm or 20 mm in diameter. Plasma luminescence pictures with 0.05 mm/ns resolution were taken by a fast streak camera. It turns out that 67%~78% of the 105 kA conduction current has been transferred from POS to the wire array loads, and the rise time of load current is 84~110 ns. The corona plasma formation, implosion and expansion after electrically exploding of tungsten wires were observed distinctly.
2006,
18.
Abstract:
In this paper the circuit modeling of parallel transmission lines by TLCODE method is introduced. The formula of interface voltage between parallel transmission lines and the series transmission line, necessary for TLCODE, is deduced, and a PSPICE circuit with four parallel transmission lines is constructed. The comparison of calculated results between TLCODE and PSPICE shows that the modeling of parallel transmission lines by TLCODE method is valid.
In this paper the circuit modeling of parallel transmission lines by TLCODE method is introduced. The formula of interface voltage between parallel transmission lines and the series transmission line, necessary for TLCODE, is deduced, and a PSPICE circuit with four parallel transmission lines is constructed. The comparison of calculated results between TLCODE and PSPICE shows that the modeling of parallel transmission lines by TLCODE method is valid.
