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RSS2005 Vol. 17, No. 02
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2005,
17: 161- .
Abstract:
With the continuous increase of COIL output power, the conventional HR film stack gradually can't satisfy the practical requirements. In this paper, on the base of multiple frequency film stack, a -200 mm HR phase retardance mirror at 45° incidence is designed and fabricated by ebeam evaporation equipment. The substrate is fused silica, and the high and low refractive index materials are ZrO２ and SiO２ respectively. The measured results show that the reflectivity at 632.8 nm is no less than 95.0%, the reflectivity at 1 315 nm is no less than 99.8%， and phase retardance at 1 315 nm is 90.235°～95.586°．
With the continuous increase of COIL output power, the conventional HR film stack gradually can't satisfy the practical requirements. In this paper, on the base of multiple frequency film stack, a -200 mm HR phase retardance mirror at 45° incidence is designed and fabricated by ebeam evaporation equipment. The substrate is fused silica, and the high and low refractive index materials are ZrO２ and SiO２ respectively. The measured results show that the reflectivity at 632.8 nm is no less than 95.0%, the reflectivity at 1 315 nm is no less than 99.8%， and phase retardance at 1 315 nm is 90.235°～95.586°．
2005,
17: 164- .
Abstract:
A beam-gas-interaction model was developed by combining the scalar diffraction theory with the N-S equations. With this model, the high power density beam propagating through a Zshape tube with blowing non-absorbing gas in at different velocities was calculated and the emitting beam qualities at far field were analyzed. The results show that, the thermal effects on beam propagation will be efficiently restrained and the beam quality at receiving section at far field could be improved. Especially, the blowing process itself may bring an other greater influence which caused place of peak intensity and centroid of intensity distribution to be deviated from the ideal ones, and the higher the blowing velocity is, the greater the deviations are, the bigger the spead of beam spot is. So the ado
A beam-gas-interaction model was developed by combining the scalar diffraction theory with the N-S equations. With this model, the high power density beam propagating through a Zshape tube with blowing non-absorbing gas in at different velocities was calculated and the emitting beam qualities at far field were analyzed. The results show that, the thermal effects on beam propagation will be efficiently restrained and the beam quality at receiving section at far field could be improved. Especially, the blowing process itself may bring an other greater influence which caused place of peak intensity and centroid of intensity distribution to be deviated from the ideal ones, and the higher the blowing velocity is, the greater the deviations are, the bigger the spead of beam spot is. So the ado
2005,
17: 169- .
Abstract:
The effect of different parameters on the thermal blooming for laser channel transmission is described. The numerical results suggest that the effect of thermal blooming on the beam quality for laser channel transmission must be considered, when the initial beam quality factor is 1, the beam power is 10 kW, the propagation length is 25 m and the absorption coefficient is greater than 0.013 km-1. When the absorption coefficient, the propagation length and the beam power are increased , the thermal blooming becomes gradually strong and some methods should be used in order to decrease it.
The effect of different parameters on the thermal blooming for laser channel transmission is described. The numerical results suggest that the effect of thermal blooming on the beam quality for laser channel transmission must be considered, when the initial beam quality factor is 1, the beam power is 10 kW, the propagation length is 25 m and the absorption coefficient is greater than 0.013 km-1. When the absorption coefficient, the propagation length and the beam power are increased , the thermal blooming becomes gradually strong and some methods should be used in order to decrease it.
2005,
17: 173- .
Abstract:
In this paper, the principle and experimental setup of PLIF is discussed. Through the proper choice of OH excited lines and improving the beam quality of the laser by spatial filter, the two-dimensional temperature field in a methane-air flame can be quntitatively measured. Veriation relationships of flam temperature with high above and distance from the centre of a furnace face were given and discussed. Compared to the results of CARS, the uncertainty of the temperature field in the measurement is less than 5%.
In this paper, the principle and experimental setup of PLIF is discussed. Through the proper choice of OH excited lines and improving the beam quality of the laser by spatial filter, the two-dimensional temperature field in a methane-air flame can be quntitatively measured. Veriation relationships of flam temperature with high above and distance from the centre of a furnace face were given and discussed. Compared to the results of CARS, the uncertainty of the temperature field in the measurement is less than 5%.
2005,
17: 177- .
Abstract:
The framing photographs of XeF2 photodissociation wave (PDW) under different experimental conditions have been taken, showing the forming process of the PDW. The variations of the radius, thickness and developing velocity of the PDW with time were obtained under different primary XeF2 concentrations. The temporal and spatial characteristics of the PDW were analyzed. Results show the maximum travelling distance of PDW is about 3 cm, and the maximum developing velocity of the PDW is about 28 km/s. As the primary XeF2 concentration is lower, the radius will be larger, the developing velocity higher and the PDW thicher.
The framing photographs of XeF2 photodissociation wave (PDW) under different experimental conditions have been taken, showing the forming process of the PDW. The variations of the radius, thickness and developing velocity of the PDW with time were obtained under different primary XeF2 concentrations. The temporal and spatial characteristics of the PDW were analyzed. Results show the maximum travelling distance of PDW is about 3 cm, and the maximum developing velocity of the PDW is about 28 km/s. As the primary XeF2 concentration is lower, the radius will be larger, the developing velocity higher and the PDW thicher.
2005,
17: 181- .
Abstract:
The computational simulations of the mixing flowfield of supersonic chemical oxygeniodine laser (COIL) using FLUENT (CFD) computation of fluid dynamics commercial software have been performed. The distribution of the averaged small signal gain along the downstream for nozzle profiles, orifices locations, pressure of secondary flow, O2(1Δ) yields, content of water vapor and dilute gases was caculated. The numerical simulation for two experimental conditions of Dalian Institute of Chemical Physics show that the trend of the computational averaged small signal gain coincides with the measured output mole power．
The computational simulations of the mixing flowfield of supersonic chemical oxygeniodine laser (COIL) using FLUENT (CFD) computation of fluid dynamics commercial software have been performed. The distribution of the averaged small signal gain along the downstream for nozzle profiles, orifices locations, pressure of secondary flow, O2(1Δ) yields, content of water vapor and dilute gases was caculated. The numerical simulation for two experimental conditions of Dalian Institute of Chemical Physics show that the trend of the computational averaged small signal gain coincides with the measured output mole power．
2005,
17: 186- .
Abstract:
The deformation of two contacting plates irradiated by laser can influence heat transfer by contact obviously. The effect of atmospheric pressure on heat transfer by contact are analyzed by some experiments and numerical simulations. It is shown that: the effect of pressure on heat transfer by contact is prominent, when atmospheric pressure is up to some degree, the interface of two plates always contact each other closely, and the rear temperature raise curve is protruding toward up; when atmospheric pressure is in some scope, the interface of two plates contact ever and again, and the rear temperature raise curve is analogous to linearity; when atmospheric pressure is under some degree, the rear temperature would transit up at some time. Three kinds of temperature curve would be observed
The deformation of two contacting plates irradiated by laser can influence heat transfer by contact obviously. The effect of atmospheric pressure on heat transfer by contact are analyzed by some experiments and numerical simulations. It is shown that: the effect of pressure on heat transfer by contact is prominent, when atmospheric pressure is up to some degree, the interface of two plates always contact each other closely, and the rear temperature raise curve is protruding toward up; when atmospheric pressure is in some scope, the interface of two plates contact ever and again, and the rear temperature raise curve is analogous to linearity; when atmospheric pressure is under some degree, the rear temperature would transit up at some time. Three kinds of temperature curve would be observed
2005,
17: 191- .
Abstract:
The laser-induced damage threshold(LIDT) and damage morphology of Ta2O5/SiO2 narrow-band interference filters under single-pulse laser and free-running laser were investigated. The weak absorptance and the standing-wave fields of the filters have also been measured and analyzed. It was shown that narrow-band interference filters had unique laser-induced damage behaviors. All the filters exhibited a pass-band center dependent LIDT and absorptance behavior: LIDT of the samples decreased, as the sample’s pass-band center was closer to laser wavelength 1 064 nm; Absorptances of the samples increased as the sample’s pass-band center was closer to laser wavelength 1 064 nm. Under single-pulse laser irradiation, the damage morphologies of the filters depended greatly on the irradiation waveleng
The laser-induced damage threshold(LIDT) and damage morphology of Ta2O5/SiO2 narrow-band interference filters under single-pulse laser and free-running laser were investigated. The weak absorptance and the standing-wave fields of the filters have also been measured and analyzed. It was shown that narrow-band interference filters had unique laser-induced damage behaviors. All the filters exhibited a pass-band center dependent LIDT and absorptance behavior: LIDT of the samples decreased, as the sample’s pass-band center was closer to laser wavelength 1 064 nm; Absorptances of the samples increased as the sample’s pass-band center was closer to laser wavelength 1 064 nm. Under single-pulse laser irradiation, the damage morphologies of the filters depended greatly on the irradiation waveleng
2005,
17: 197- .
Abstract:
Propagation of laser beam through turbulent atmosphere was numerically studied using phase screen approximation. And partially coherent flat-topped Gaussian beam was expanded as a superposition of independent Hermite-Gaussian modes. In order to fit the results of numerical simulation, two expressions were deduced. One describes the dependence of the rms width of the beam on the order number, the spreading distance and the intensity of turbulence. The other describes the dependence of the coherent length of the beam on that of it’s initial time and that of turbulence. At the same, it is concluded that the coherente of laser beams are worse, the effects of them by turbulence are less; And that on the propagation of laser beams through trubulence, the effects of the initial coherent characte
Propagation of laser beam through turbulent atmosphere was numerically studied using phase screen approximation. And partially coherent flat-topped Gaussian beam was expanded as a superposition of independent Hermite-Gaussian modes. In order to fit the results of numerical simulation, two expressions were deduced. One describes the dependence of the rms width of the beam on the order number, the spreading distance and the intensity of turbulence. The other describes the dependence of the coherent length of the beam on that of it’s initial time and that of turbulence. At the same, it is concluded that the coherente of laser beams are worse, the effects of them by turbulence are less; And that on the propagation of laser beams through trubulence, the effects of the initial coherent characte
2005,
17: 203- .
Abstract:
The X-ray conversion material in radiophotography system plays a very important role. Its efficiency is a crucial factor to improve the system QDE(quantum detection efficiency). The luminescent efficiency of CsI∶Tl crystal excited by Xray is analyzed in detail and the efficiency formula of the system adopting CCD camera,CsI∶Tl crystal is derived. The formula shows that the output of such a radiophotography system is proportional to the irradiation flux of incident X-ray. The QDE of such a system can be easily improved by changing the CsI∶Tl crystal thickness. Some experimental data obtained from a 30MeV electron linear accelerator are given to prove the linear relationship．
The X-ray conversion material in radiophotography system plays a very important role. Its efficiency is a crucial factor to improve the system QDE(quantum detection efficiency). The luminescent efficiency of CsI∶Tl crystal excited by Xray is analyzed in detail and the efficiency formula of the system adopting CCD camera,CsI∶Tl crystal is derived. The formula shows that the output of such a radiophotography system is proportional to the irradiation flux of incident X-ray. The QDE of such a system can be easily improved by changing the CsI∶Tl crystal thickness. Some experimental data obtained from a 30MeV electron linear accelerator are given to prove the linear relationship．
2005,
17: 206- .
Abstract:
The density and drift velocity of the low-temperature plasma produced by a cable plasma gun array are measured with charge collectors under positive(135 V) and negative bias(-117 V) and low-pressure air-embedment(0.5 Pa) without bias. The drift velocities under different collecting conditions are close to each other, which are 2.5,2.4,2.0 cm·μs-1 respectively. At the same place, the measured plasma densities are 8.3×1014,1.2×1015,4.8×1014 cm-3 respectively. The density is the greatest with negative bias and the smallest with low-pressure air-embedment.
The density and drift velocity of the low-temperature plasma produced by a cable plasma gun array are measured with charge collectors under positive(135 V) and negative bias(-117 V) and low-pressure air-embedment(0.5 Pa) without bias. The drift velocities under different collecting conditions are close to each other, which are 2.5,2.4,2.0 cm·μs-1 respectively. At the same place, the measured plasma densities are 8.3×1014,1.2×1015,4.8×1014 cm-3 respectively. The density is the greatest with negative bias and the smallest with low-pressure air-embedment.
2005,
17: 209- .
Abstract:
Filling gas on the spot is widely used to fabricate the hohlraum gas-filled target. This paper focuses on the synthesis of the polypyromellitamic acid, preparation of polyimide film by the method of spin coating and gas-filled targets assemblage. Two key issues here are the preparation of synthetic polypyromellitamic acid and the examination of leakage in vacuum. The gas pressure can be read by transducer connected with the target through the gas tube. Under suitable condition the polyimide film can be made with thickness of 0.2~1.0 μm. The film finish is about 0.3~0.4 nm and the pressure error inside the target is less than 0.1%.
Filling gas on the spot is widely used to fabricate the hohlraum gas-filled target. This paper focuses on the synthesis of the polypyromellitamic acid, preparation of polyimide film by the method of spin coating and gas-filled targets assemblage. Two key issues here are the preparation of synthetic polypyromellitamic acid and the examination of leakage in vacuum. The gas pressure can be read by transducer connected with the target through the gas tube. Under suitable condition the polyimide film can be made with thickness of 0.2~1.0 μm. The film finish is about 0.3~0.4 nm and the pressure error inside the target is less than 0.1%.
2005,
17: 213- .
Abstract:
ZrO2 thin films were deposited on K9 glass substrates by e-beam evaporation method and some samples were treated with low energy O+2 after deposition. Surface weak absorption was measured using surface thermal lens technique, and micro-defect density was measured using optical microscope. The experimental results indicate that the absorption of the samples decreases from 1.147×10-4 to 9.56×10-5 after post-treatment, and the micro-defect density reduces from 18.6/mm2 to 6.2/mm2 compared with the un-treated samples. Anti-laser-irradiation test indicates that the laser-induced damage threshold are improved from 15.9 J/cm2 to 23.1 J/cm2 comparing the ion-post treatment samples with the untreated samples. By analysis of the defect density, weak absorption, and damage morphologies of the sampl
ZrO2 thin films were deposited on K9 glass substrates by e-beam evaporation method and some samples were treated with low energy O+2 after deposition. Surface weak absorption was measured using surface thermal lens technique, and micro-defect density was measured using optical microscope. The experimental results indicate that the absorption of the samples decreases from 1.147×10-4 to 9.56×10-5 after post-treatment, and the micro-defect density reduces from 18.6/mm2 to 6.2/mm2 compared with the un-treated samples. Anti-laser-irradiation test indicates that the laser-induced damage threshold are improved from 15.9 J/cm2 to 23.1 J/cm2 comparing the ion-post treatment samples with the untreated samples. By analysis of the defect density, weak absorption, and damage morphologies of the sampl
2005,
17: 217- .
Abstract:
ZrO2 coatings were deposited on different substrates of Yb∶YAG and fused silica by electron beam evaporation. After annealed for 12 hours at 673 K and 1 073 K respectively, weak absorption of coatings was measured by surface thermal lensing, and then laser-induced damage threshold was determined. The crystalline phase of ZrO2 coatings and the size of the crystal grain were investigated by X-ray diffraction. It is found that microstructure of ZrO2 coatings is dependent on both annealing temperature and substrate structure, anneal at high temperature helps to produce monoclinic phases, and coatings containing monoclinic phases have higher damage threshold than others. Due to the strong absorption of Yb∶YAG, damage threshold of coatings on Yb∶YAG is much less than that on fused silica.
ZrO2 coatings were deposited on different substrates of Yb∶YAG and fused silica by electron beam evaporation. After annealed for 12 hours at 673 K and 1 073 K respectively, weak absorption of coatings was measured by surface thermal lensing, and then laser-induced damage threshold was determined. The crystalline phase of ZrO2 coatings and the size of the crystal grain were investigated by X-ray diffraction. It is found that microstructure of ZrO2 coatings is dependent on both annealing temperature and substrate structure, anneal at high temperature helps to produce monoclinic phases, and coatings containing monoclinic phases have higher damage threshold than others. Due to the strong absorption of Yb∶YAG, damage threshold of coatings on Yb∶YAG is much less than that on fused silica.
2005,
17: 222- .
Abstract:
Zirconium oxide films were deposited on SiO2 substrates using high vacuum electron beam evaporation at room temperature．The films' transmittance and surface structure were investigated by means of ultraviolet spectrophotometer，AFM and XRD．The main effect of annealing at different temperatures on the physical properties of the films were studied as well．The AFM images differ little for ZrO２ films annealed at 700,900,and 1 050 ℃,showing crystal grains about 25 nm in diameter. However, the diameter of grains tends to grow with the temperature increase and it is about 400 nm at 1 150 ℃.The leakage current obviously increases and decreases the hot stability of zirconium oxide film while the temperature increases to about 1 150 ℃.
Zirconium oxide films were deposited on SiO2 substrates using high vacuum electron beam evaporation at room temperature．The films' transmittance and surface structure were investigated by means of ultraviolet spectrophotometer，AFM and XRD．The main effect of annealing at different temperatures on the physical properties of the films were studied as well．The AFM images differ little for ZrO２ films annealed at 700,900,and 1 050 ℃,showing crystal grains about 25 nm in diameter. However, the diameter of grains tends to grow with the temperature increase and it is about 400 nm at 1 150 ℃.The leakage current obviously increases and decreases the hot stability of zirconium oxide film while the temperature increases to about 1 150 ℃.
2005,
17: 225- .
Abstract:
The effects of electron number density and its profile on the microwave propagation characteristics in a plasma slab are discussed. The incident wave travels vertically on the plasma slab. The plasma layer is modeled as adjacent, homogeneous sub-slaps, whose approximate distributions are linear or parabolic. The theoretical method to analyze the propagation of the wave is based on the stratified layer model and invariant imbedding principle. Multiple reflections between sub-slab interfaces are analyzed with the model. The numerical result shows that absorption with parabolic distribution plasma is better than the linear one, but the reflection is higher for the linear profile plasma. The power coefficient of reflection increases and the absorption coefficient decreases after an early peak
The effects of electron number density and its profile on the microwave propagation characteristics in a plasma slab are discussed. The incident wave travels vertically on the plasma slab. The plasma layer is modeled as adjacent, homogeneous sub-slaps, whose approximate distributions are linear or parabolic. The theoretical method to analyze the propagation of the wave is based on the stratified layer model and invariant imbedding principle. Multiple reflections between sub-slab interfaces are analyzed with the model. The numerical result shows that absorption with parabolic distribution plasma is better than the linear one, but the reflection is higher for the linear profile plasma. The power coefficient of reflection increases and the absorption coefficient decreases after an early peak
2005,
17: 229- .
Abstract:
In light of poloidal motion velocity changed by electric drift, the paper derives the equation for safety factor when negative radial electric field existed, analyzes the influence of safety factor upon the drift displacement and motion orbit of charged particles, and established mathematical models for charged particles moving in the gradient and curvature magnetic fields. Through numerical simulation, the paper concludes new features and rules about drift displacement and motion orbits of both transit and banana particles: Negative radial electric field changes the maximum drift displacement of charged particles. When the poloidal velocity of charged particles increases, the maximum drift displaccment decrcases and contrarily it increases; Change the orbit of charged particles, the obit
In light of poloidal motion velocity changed by electric drift, the paper derives the equation for safety factor when negative radial electric field existed, analyzes the influence of safety factor upon the drift displacement and motion orbit of charged particles, and established mathematical models for charged particles moving in the gradient and curvature magnetic fields. Through numerical simulation, the paper concludes new features and rules about drift displacement and motion orbits of both transit and banana particles: Negative radial electric field changes the maximum drift displacement of charged particles. When the poloidal velocity of charged particles increases, the maximum drift displaccment decrcases and contrarily it increases; Change the orbit of charged particles, the obit
2005,
17: 233- .
Abstract:
In this paper, a novel way that can be combined with FDTD methods to deal with the EMP response on thin wire with resistance load is developed, in which the thin wire is divided into three parts and described by different partial differential equations,respectively. This method can be used to calculate some coupling problems involving thin wires, which usually connected with circuit input or output ports. The dissipated energy and power on the equivalent resistance can be obtained. The results gotten from this new method are compared with the results from references,some typical results are given and analyzed as an example. Modified partly this algorithm can also be used to solve the nonresistance load cases．
In this paper, a novel way that can be combined with FDTD methods to deal with the EMP response on thin wire with resistance load is developed, in which the thin wire is divided into three parts and described by different partial differential equations,respectively. This method can be used to calculate some coupling problems involving thin wires, which usually connected with circuit input or output ports. The dissipated energy and power on the equivalent resistance can be obtained. The results gotten from this new method are compared with the results from references,some typical results are given and analyzed as an example. Modified partly this algorithm can also be used to solve the nonresistance load cases．
2005,
17: 237- .
Abstract:
This paper presents the coaxial interlaced disc-loaded slow-wave system of the relativistic traveling wave tube(TWT). The dispersion function of the slow-wave structure is deduced by variation method and Bessel function orthogonatity without regard for thickness of disc. The paper puts much emphasis on discussing the changing of the dispersion curves following several different parameters' variety, comparing three different structures' influence upon the dispersion characteristics. The results show that this coaxial interlaced structure could make the bandwidth wider than other non-coaxial structures.
This paper presents the coaxial interlaced disc-loaded slow-wave system of the relativistic traveling wave tube(TWT). The dispersion function of the slow-wave structure is deduced by variation method and Bessel function orthogonatity without regard for thickness of disc. The paper puts much emphasis on discussing the changing of the dispersion curves following several different parameters' variety, comparing three different structures' influence upon the dispersion characteristics. The results show that this coaxial interlaced structure could make the bandwidth wider than other non-coaxial structures.
2005,
17: 241- .
Abstract:
A novel resonator of quasi-periodic structure is put out in the paper. The interaction between the beam and the microwave field in the cavity is theoretically investigated with 2.5 dimensional particle simulation code. With this type of structures, theoretically beam-microwave interaction efficiency can reach 52%. An X-band quasi-periodic structure cavity is designed, its working frequency is 9.4 GHz. With the voltage 700 kV, current 6.6 kA and magnet field 4.4 T in the simulation, the output power is 1.67 GW, the frequency 9.4 GHz and interaction efficiency about 36%. Driven by Sinus-700 accelerator in the experiment, microwave power is 1.3 GW, the frequency is 9.4 GHz, pulse duration is about 26 ns, and the efficiency is 26%.
A novel resonator of quasi-periodic structure is put out in the paper. The interaction between the beam and the microwave field in the cavity is theoretically investigated with 2.5 dimensional particle simulation code. With this type of structures, theoretically beam-microwave interaction efficiency can reach 52%. An X-band quasi-periodic structure cavity is designed, its working frequency is 9.4 GHz. With the voltage 700 kV, current 6.6 kA and magnet field 4.4 T in the simulation, the output power is 1.67 GW, the frequency 9.4 GHz and interaction efficiency about 36%. Driven by Sinus-700 accelerator in the experiment, microwave power is 1.3 GW, the frequency is 9.4 GHz, pulse duration is about 26 ns, and the efficiency is 26%.
2005,
17: 245- .
Abstract:
In this paper, the experimental method of HPM breakdown of coaxialcable and connector is introduced. It is given by experimentaly that the microwave breakdown thresholds of several kinds of coaxial-cables and connectors vary with microwave frequency, pulse width, repetitive frequency and burst duration. Breakdown power threshold increases as pulse width (30 ns~1 μs) decreases, and an inflexion appear at about 100 ns. In low repetitive frequency region, i.e, from single pulse to 1 kHz, the repetitive rate of microwave pulse literally has no effect on breakdown power. Microwave frequency tuned from 2.856 GHz to 937 GHz, no significant change of breakdown power level is observed. When the pulse width becomes as narrow as tens of nanoseconds, the breakdown power varies little even though
In this paper, the experimental method of HPM breakdown of coaxialcable and connector is introduced. It is given by experimentaly that the microwave breakdown thresholds of several kinds of coaxial-cables and connectors vary with microwave frequency, pulse width, repetitive frequency and burst duration. Breakdown power threshold increases as pulse width (30 ns~1 μs) decreases, and an inflexion appear at about 100 ns. In low repetitive frequency region, i.e, from single pulse to 1 kHz, the repetitive rate of microwave pulse literally has no effect on breakdown power. Microwave frequency tuned from 2.856 GHz to 937 GHz, no significant change of breakdown power level is observed. When the pulse width becomes as narrow as tens of nanoseconds, the breakdown power varies little even though
2005,
17: 249- .
Abstract:
Variation relation between the effective emitting area of field induced explosive ementting graphite cathode and time has been acquired experimentally under different externally applied electric field corresponding to different anode cathode gaps. It is illustrated that the effective emitting area increase over time at the beginning of emission.The time for the effective emitting area to reach 1.0 decreases with increasing mean electric field in the gap. Under approximate 100 kV/cm mean electric field between anode and cathode, about 20 ns is needed for the effective emitting area to reach 1.0. The relative delay time of effective emitting area reaching 0.5 to 50 % voltage pulse with the electric field behaves as a decaying exponential curve．
Variation relation between the effective emitting area of field induced explosive ementting graphite cathode and time has been acquired experimentally under different externally applied electric field corresponding to different anode cathode gaps. It is illustrated that the effective emitting area increase over time at the beginning of emission.The time for the effective emitting area to reach 1.0 decreases with increasing mean electric field in the gap. Under approximate 100 kV/cm mean electric field between anode and cathode, about 20 ns is needed for the effective emitting area to reach 1.0. The relative delay time of effective emitting area reaching 0.5 to 50 % voltage pulse with the electric field behaves as a decaying exponential curve．
2005,
17: 253- .
Abstract:
It requires knowledge of stochastic features of lightning electromagnetic pulse (LEMP) to study effect evaluation of the potentially harmful coupling of LEMP to the electronic systems. Based on statistical characters of lightning currents, LEMP under a general probabilistic framework were discussed, the probability distribution and density functions of peak amplitude of LEMF were deduced. The probability distributions, cumulative probability distributions, means and standard deviations of peak electric field intensity and peak magnetic field intensity at different positions were calculated using multiple-integral method, and the results agree well with the ones obtained by Monte Carlo simulation．
It requires knowledge of stochastic features of lightning electromagnetic pulse (LEMP) to study effect evaluation of the potentially harmful coupling of LEMP to the electronic systems. Based on statistical characters of lightning currents, LEMP under a general probabilistic framework were discussed, the probability distribution and density functions of peak amplitude of LEMF were deduced. The probability distributions, cumulative probability distributions, means and standard deviations of peak electric field intensity and peak magnetic field intensity at different positions were calculated using multiple-integral method, and the results agree well with the ones obtained by Monte Carlo simulation．
2005,
17: 262- .
Abstract:
To control the BEPCⅡ-linac beam performance within the upgrading goals, the error effects such as the initial beam offset and the accelerator misalignment effects on the beam performance have been systematically studied with beam modeling. The most important operating jitter effects including the phasing drift jitter and the modulator's jitter effects have also been studied. The tolerances of the errors and jitters have been decided and the effective beam orbit correction scheme is further confirmed. By controlling the initial beam offset from the electron gun within ±0.3 mm, the tolerance of the accelerating structures and quadruple misalignment within ±0.2 mm, the phase drift error within ±2°, and the modulator's voltage jitter within ±0.1%, and by employing the phase control syste
To control the BEPCⅡ-linac beam performance within the upgrading goals, the error effects such as the initial beam offset and the accelerator misalignment effects on the beam performance have been systematically studied with beam modeling. The most important operating jitter effects including the phasing drift jitter and the modulator's jitter effects have also been studied. The tolerances of the errors and jitters have been decided and the effective beam orbit correction scheme is further confirmed. By controlling the initial beam offset from the electron gun within ±0.3 mm, the tolerance of the accelerating structures and quadruple misalignment within ±0.2 mm, the phase drift error within ±2°, and the modulator's voltage jitter within ±0.1%, and by employing the phase control syste
2005,
17: 263- .
Abstract:
A 3.5 MeV injector for linear induction accelerator has been built up at Institute of Fluid Physics, China Academy of Engineering Physics. The injector is based on the principle of inductive adder. It consists of 12 induction cells. Seven induction cells are on the cathode stem side, which are connected in series, and provide about 2 MV on the cathode of the diode. The other five are connected in series on the anode stem side and provide about 1.5 MV on the anode of the diode. A 3.5 MV pulsed power system to provide energy for the injector has been designed, which consists of two Marx generators,12 water insulated Blumleins, and trigger system. Charge voltage of each water insulated Blumlein is 200 kV. A 300 kV/90 ns high voltage pulse is fed into one induction cell since load impedance is
A 3.5 MeV injector for linear induction accelerator has been built up at Institute of Fluid Physics, China Academy of Engineering Physics. The injector is based on the principle of inductive adder. It consists of 12 induction cells. Seven induction cells are on the cathode stem side, which are connected in series, and provide about 2 MV on the cathode of the diode. The other five are connected in series on the anode stem side and provide about 1.5 MV on the anode of the diode. A 3.5 MV pulsed power system to provide energy for the injector has been designed, which consists of two Marx generators,12 water insulated Blumleins, and trigger system. Charge voltage of each water insulated Blumlein is 200 kV. A 300 kV/90 ns high voltage pulse is fed into one induction cell since load impedance is
2005,
17: 268- .
Abstract:
In this paper, the results of repetitive nanosecond breakdown in transformer oil are introduced. The breakdown characteristics of 25# transformer oil under repetitive nanosecond pulses ranged from 1 Hz to 1 000 Hz and the gap distances range from 0.3~1.5 mm have been investigated. The breakdown waveforms of voltage, current and breakdown time have been measured. The results indicate that ns level high voltage pulse breakdown field is much higher than breakdown in DC and AC. The breakdown field value decreases with the repetitive rate increases. From 10 Hz to 100 Hz, the breakdown field falls quickly. When repetitive rates exceed 100 Hz, the field value fall down speed is slow. The experimental results show that the lowering of the breakdown elactric field under repetitive pulses conditions
In this paper, the results of repetitive nanosecond breakdown in transformer oil are introduced. The breakdown characteristics of 25# transformer oil under repetitive nanosecond pulses ranged from 1 Hz to 1 000 Hz and the gap distances range from 0.3~1.5 mm have been investigated. The breakdown waveforms of voltage, current and breakdown time have been measured. The results indicate that ns level high voltage pulse breakdown field is much higher than breakdown in DC and AC. The breakdown field value decreases with the repetitive rate increases. From 10 Hz to 100 Hz, the breakdown field falls quickly. When repetitive rates exceed 100 Hz, the field value fall down speed is slow. The experimental results show that the lowering of the breakdown elactric field under repetitive pulses conditions
2005,
17: 271- .
Abstract:
This paper describes the aberration and distortion of e-beam deflection magnetic field in which the parameters keep close to in the normal solution. The relationship between the principal trajectory of e-beam and aberrations has been investigated in combined round magnetic lenses and deflection system of SDS-3 e-beam machine．Formulae for the first-order chromatic and third-order geometrical aberration coefficients of superimposed magnetic focus and deflection field of both electric and magnetic type in the case of a point source on the Z-axis are obtained．The aberration of superimposed focus-deflection system is so small that the dynamic correction is unnecessary.
This paper describes the aberration and distortion of e-beam deflection magnetic field in which the parameters keep close to in the normal solution. The relationship between the principal trajectory of e-beam and aberrations has been investigated in combined round magnetic lenses and deflection system of SDS-3 e-beam machine．Formulae for the first-order chromatic and third-order geometrical aberration coefficients of superimposed magnetic focus and deflection field of both electric and magnetic type in the case of a point source on the Z-axis are obtained．The aberration of superimposed focus-deflection system is so small that the dynamic correction is unnecessary.
2005,
17: 275- .
Abstract:
The slow extraction of beam from CSR main ring(CSRm) is designed and simply simulated by Winagile program in this paper. The amplitude-momentum selection scheme is used, and both fast and slow extraction will be arranged in the same extraction passage. The third integer resonant scheme is adopted in slow extraction to obtain extracted beam with a horizontal emittance less than 1 πmm·mrad in about 1 second.
The slow extraction of beam from CSR main ring(CSRm) is designed and simply simulated by Winagile program in this paper. The amplitude-momentum selection scheme is used, and both fast and slow extraction will be arranged in the same extraction passage. The third integer resonant scheme is adopted in slow extraction to obtain extracted beam with a horizontal emittance less than 1 πmm·mrad in about 1 second.
2005,
17: 279- .
Abstract:
The design of lengthening the diffusion lengths of negative electron affinity emitter GaAs was introduced; the secondary electron emission coefficients of normal GaAs was compared with that of specially designed GaAs.The conclusion shows that the deviation of the two kinds of secondary electron emission coefficient is smaller if primary electron incident energy is lower （less than 10 keV）and that the deviation of the two kinds of secondary electron emission coefficient is larger if primary electron incident energy is higher（more than 20 keV）.With the primary electron incident energy becoming higher, the deviation of the two kinds of secondary electron emission coefficient becomes larger．
The design of lengthening the diffusion lengths of negative electron affinity emitter GaAs was introduced; the secondary electron emission coefficients of normal GaAs was compared with that of specially designed GaAs.The conclusion shows that the deviation of the two kinds of secondary electron emission coefficient is smaller if primary electron incident energy is lower （less than 10 keV）and that the deviation of the two kinds of secondary electron emission coefficient is larger if primary electron incident energy is higher（more than 20 keV）.With the primary electron incident energy becoming higher, the deviation of the two kinds of secondary electron emission coefficient becomes larger．
2005,
17: 283- .
Abstract:
A numerical method in time domain on skin current of ground laying shielded cable excited by electromagnetic pulse is studied. The method overcomes the ambiguity of the transmission line theory in studying such a problem. The finite difference time domain (FDTD) method based on the scattering of thin wire which can solve the problem effectively is derived. An extensional Gedney perfectly matched layer is developed. It can be used to truncate FDTD lattices of lossy media.The method is used to simulate the distribution of a skin current and characteristics of waveform on a ground laying shielded cable excited by the electromagnetic pulse. The problems are studied experimentally in the radiated EMP simulator.Compared with experimental data, the numerical results proved to be reliable．
A numerical method in time domain on skin current of ground laying shielded cable excited by electromagnetic pulse is studied. The method overcomes the ambiguity of the transmission line theory in studying such a problem. The finite difference time domain (FDTD) method based on the scattering of thin wire which can solve the problem effectively is derived. An extensional Gedney perfectly matched layer is developed. It can be used to truncate FDTD lattices of lossy media.The method is used to simulate the distribution of a skin current and characteristics of waveform on a ground laying shielded cable excited by the electromagnetic pulse. The problems are studied experimentally in the radiated EMP simulator.Compared with experimental data, the numerical results proved to be reliable．
2005,
17: 287- .
Abstract:
Proton irradiation at temperatures of 310 and 350 ℃ has been researched using 2 MeV proton to a atom displacement damage level of 5 dpa at a dose rate of 8.5×1013 cm－２·s－１. Amorphization and Fe loss of Zr(Cr,Fe)2 and ZrFe2 precipitates are observed. No amorphization appears in ZrFe2 precipitates at 310 and 350 ℃. Proton irradiation at 350 ℃ does not lead to measurable amorphization or elemental redistribution. An amorphous rim is observed on the surface of Zr(Fe,Cr)2 precipitates, the thickness of which is 5～10 nm, in both a conventional and high-resolution TEM micrograph at 310 ℃. A bright rim is observed in the Fe map, less than 10 nm wide, indicating Fe segregation. Energy-filtered images indicate Fe accumulation in the matrix near the precipitate．
Proton irradiation at temperatures of 310 and 350 ℃ has been researched using 2 MeV proton to a atom displacement damage level of 5 dpa at a dose rate of 8.5×1013 cm－２·s－１. Amorphization and Fe loss of Zr(Cr,Fe)2 and ZrFe2 precipitates are observed. No amorphization appears in ZrFe2 precipitates at 310 and 350 ℃. Proton irradiation at 350 ℃ does not lead to measurable amorphization or elemental redistribution. An amorphous rim is observed on the surface of Zr(Fe,Cr)2 precipitates, the thickness of which is 5～10 nm, in both a conventional and high-resolution TEM micrograph at 310 ℃. A bright rim is observed in the Fe map, less than 10 nm wide, indicating Fe segregation. Energy-filtered images indicate Fe accumulation in the matrix near the precipitate．
2005,
17: 291- .
Abstract:
A new radiochromic film is developed by using a polymer as the base and doping an organic dye and an organic halide. It is a clear transparent solid film, but it becomes blue after irradiated by γ-ray. As shown in the UV-VIS spectrum of irradiated films, the peak in visual region locates about 624 nm, and there is a linear relationship between the net optical density and absorbed dose in dose range from 10 kGy to 90 kGy. The chemical reaction mechanism of the radiation effect on the radiochromic film has also been researched.
A new radiochromic film is developed by using a polymer as the base and doping an organic dye and an organic halide. It is a clear transparent solid film, but it becomes blue after irradiated by γ-ray. As shown in the UV-VIS spectrum of irradiated films, the peak in visual region locates about 624 nm, and there is a linear relationship between the net optical density and absorbed dose in dose range from 10 kGy to 90 kGy. The chemical reaction mechanism of the radiation effect on the radiochromic film has also been researched.
2005,
17: 295- .
Abstract:
The gas puff is one of the main loads used in Z pinch research. In this paper the basic physics process of the Laval nozzle on Qiangguang I generator is analyzed using one dimension isentropic gas dynamics equation.The Mach number 4.6 of the gas flow is calculated and corrected as 3.5 considering the effect of boundary. Combining the data of gas puff Z pinch experiments on Qiangguang I generator, the expression of the line mass is obtained using the implosion time expression which is deduced from snowplow model. In the end of the paper the distribution of the gas density is given by the BollisticTransport (B-T) model and the gas density is between 10１６/cm３ and １０１７／cm３. Along the axis within 2 cm, a hollow gas shell structure is formed．
The gas puff is one of the main loads used in Z pinch research. In this paper the basic physics process of the Laval nozzle on Qiangguang I generator is analyzed using one dimension isentropic gas dynamics equation.The Mach number 4.6 of the gas flow is calculated and corrected as 3.5 considering the effect of boundary. Combining the data of gas puff Z pinch experiments on Qiangguang I generator, the expression of the line mass is obtained using the implosion time expression which is deduced from snowplow model. In the end of the paper the distribution of the gas density is given by the BollisticTransport (B-T) model and the gas density is between 10１６/cm３ and １０１７／cm３. Along the axis within 2 cm, a hollow gas shell structure is formed．
2005,
17: 303- .
Abstract:
The parameters of an upgraded optical klystron (OK) were given by 3-dimensional finite element electromagnetic computation for free electron laser (FEL) research in Hefei electron storage ring. The Hefei Light Source (HLS) is routinely operated at 800 MeV by ramping up the injected 200 MeV electron beam. In order to match the routine operated energy of HLS and get more FEL photos, the symmetry OK is being upgraded to asymmetry structure for harmonic generation (HG) FEL experiments. Several HG FEL experimental groups of matched parameters of the upgraded OK were listed at the HLS injected energy as well as the maximum experimental energy. Primary computation shows that the energy spread of HLS in FEL experiments is below 2.05×10-4, the correction factor due to it for FEL radiation is over
The parameters of an upgraded optical klystron (OK) were given by 3-dimensional finite element electromagnetic computation for free electron laser (FEL) research in Hefei electron storage ring. The Hefei Light Source (HLS) is routinely operated at 800 MeV by ramping up the injected 200 MeV electron beam. In order to match the routine operated energy of HLS and get more FEL photos, the symmetry OK is being upgraded to asymmetry structure for harmonic generation (HG) FEL experiments. Several HG FEL experimental groups of matched parameters of the upgraded OK were listed at the HLS injected energy as well as the maximum experimental energy. Primary computation shows that the energy spread of HLS in FEL experiments is below 2.05×10-4, the correction factor due to it for FEL radiation is over
2005,
17: 304- .
Abstract:
Power flow characteristics between a plasma opening switch (POS) and an inductive load were investigated via particle-in-cell simulations based on the experimental parameters. A dynamic switch model was adopted to simulate the POS. The switch voltage and load current from the simulations agree well with the experiments, and electron flow along the anode and the propagation of the low density plasma (about 1012·cm－3) at 1cm/ns from the POS to the load were observed in the simulations. It was shown that larger POS impedance would increase the power transferred to the load. It was inferred that large current loss exists in the discontinuity of the geometrical impedance, which should be avoided in the design．
Power flow characteristics between a plasma opening switch (POS) and an inductive load were investigated via particle-in-cell simulations based on the experimental parameters. A dynamic switch model was adopted to simulate the POS. The switch voltage and load current from the simulations agree well with the experiments, and electron flow along the anode and the propagation of the low density plasma (about 1012·cm－3) at 1cm/ns from the POS to the load were observed in the simulations. It was shown that larger POS impedance would increase the power transferred to the load. It was inferred that large current loss exists in the discontinuity of the geometrical impedance, which should be avoided in the design．
2005,
17: 309- .
Abstract:
Power MOSFET IRF540N and IRF9530 were irradiated by X-ray and gamma ray, and the relationship of their threshold voltage and absorbed dose was studied. It is found that the change of threshold voltage value fits in exponential law with absorbed dose,which is caused by the effect of space charge and interface charge.The space charges affect threshold voltage of MOSFET varying linearly with absorbed dose,and the interface charges have a compensational role to space charges,it affects threshold voltage varying linearly with square of absorbed dose．
Power MOSFET IRF540N and IRF9530 were irradiated by X-ray and gamma ray, and the relationship of their threshold voltage and absorbed dose was studied. It is found that the change of threshold voltage value fits in exponential law with absorbed dose,which is caused by the effect of space charge and interface charge.The space charges affect threshold voltage of MOSFET varying linearly with absorbed dose,and the interface charges have a compensational role to space charges,it affects threshold voltage varying linearly with square of absorbed dose．
2005,
17: 313- .
Abstract:
The paper introduces the principle of pulse form network (PFN), the PSpice simulation result of Marx-PFN and the design process of 200 kV long pulse power generator. A 200 kV long pulsed power generator based on five-stage Marx-PFN has been built, with network impedance of 14 Ω. The results indicate that the FWHM of the output pulse with 3 μs flat-top is 43 μs，the ripples of the top of the pulse are less than 1%,the risetime of the pulse is less than 500 ns, and the voltage of the pulse is about 200 kV. The effect of earthing resistance and induction on waveform is analyzed too．
The paper introduces the principle of pulse form network (PFN), the PSpice simulation result of Marx-PFN and the design process of 200 kV long pulse power generator. A 200 kV long pulsed power generator based on five-stage Marx-PFN has been built, with network impedance of 14 Ω. The results indicate that the FWHM of the output pulse with 3 μs flat-top is 43 μs，the ripples of the top of the pulse are less than 1%,the risetime of the pulse is less than 500 ns, and the voltage of the pulse is about 200 kV. The effect of earthing resistance and induction on waveform is analyzed too．
2005,
17: 317- .
Abstract:
This paper summarizes an experimental study of the delayed breakdown performance of silicon PIN diode. Single PIN diode, double series PIN diodes and stacked PIN diodes in parallel and series were tested,the results shown that the pulsefronts of input voltage became steep obviously.Single PIN diode operates at a hold- off voltage exceeding 2.2 kV, and the time rate of voltage(d V /dt) is promoted from 0.95 kV/ns to 1.37 kV/ns. Double series PIN diodes operates at a hold- off voltage of 4.2 kV, and the d V /d t is promoted from 1.7 kV/ns to 2.3 kV/ns. Stacked PIN diodes in parallel and series operate at a hold- off voltage of 8.0 kV,and the d V /d t is promoted from 2.4 kV/ns to 3.2 kV/ns．
This paper summarizes an experimental study of the delayed breakdown performance of silicon PIN diode. Single PIN diode, double series PIN diodes and stacked PIN diodes in parallel and series were tested,the results shown that the pulsefronts of input voltage became steep obviously.Single PIN diode operates at a hold- off voltage exceeding 2.2 kV, and the time rate of voltage(d V /dt) is promoted from 0.95 kV/ns to 1.37 kV/ns. Double series PIN diodes operates at a hold- off voltage of 4.2 kV, and the d V /d t is promoted from 1.7 kV/ns to 2.3 kV/ns. Stacked PIN diodes in parallel and series operate at a hold- off voltage of 8.0 kV,and the d V /d t is promoted from 2.4 kV/ns to 3.2 kV/ns．
