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RSS2008 Vol. 20, No. 07
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2008,
20.
Abstract:
With an external cavity containing a wavelength-chirped volume Bragg grating, multi-wavelength beam combining is realized with a standard bar of 49 emitters. The width of the emitter is 100 μm, and the fill factor is 0.5. Beam quality factor of 6 for both the fast axis and the slow axis is achieved at CW operating, and a nearly round output spot of high intensity with a peak power of 11.2 W is gotten. The efficiency at the maximum operating current is about 30%. An efficiency of 64% at maximum working current is proven in a more detailed experimental study. The technical advantages and possible applications are discussed.
With an external cavity containing a wavelength-chirped volume Bragg grating, multi-wavelength beam combining is realized with a standard bar of 49 emitters. The width of the emitter is 100 μm, and the fill factor is 0.5. Beam quality factor of 6 for both the fast axis and the slow axis is achieved at CW operating, and a nearly round output spot of high intensity with a peak power of 11.2 W is gotten. The efficiency at the maximum operating current is about 30%. An efficiency of 64% at maximum working current is proven in a more detailed experimental study. The technical advantages and possible applications are discussed.
2008,
20.
Abstract:
By means of analyzing the point source transmittance of the laser receiver with optical structure of cylindric cavity, the feasibility and relative light power demand to jam laser rangefinder with the stray light is investigated. According to the increasing incident angle of jamming light, three major mechanisms of stray light jamming, i.e., diffuse reflection-specular reflection jamming, double diffuse reflection jamming and single diffuse reflection jamming are presented. The corresponding PST function is also derived. Furthermore, the digital simulation using Tracepro software is adopted to verify the functions. The results show that under typical condition to jam the laser range finder reliably within 30°, the jamming light power should be 5×106 times than that of jamming at 0°, and
By means of analyzing the point source transmittance of the laser receiver with optical structure of cylindric cavity, the feasibility and relative light power demand to jam laser rangefinder with the stray light is investigated. According to the increasing incident angle of jamming light, three major mechanisms of stray light jamming, i.e., diffuse reflection-specular reflection jamming, double diffuse reflection jamming and single diffuse reflection jamming are presented. The corresponding PST function is also derived. Furthermore, the digital simulation using Tracepro software is adopted to verify the functions. The results show that under typical condition to jam the laser range finder reliably within 30°, the jamming light power should be 5×106 times than that of jamming at 0°, and
2008,
20.
Abstract:
The damage processes of fused silica under the fundamental frequency and third harmonic of Nd:YAG laser were studied with instantaneous scattering pulses measurements via fast photodiodes and high bandwidth oscilloscope. The optical micrographs of ablated craters on fused silica surface were also analyzed. The sharp increase of scattered light of pump pulse was assumed to be the damage precursor, therefore, the damage started nearly at the peak of the pump pulse. Fundamental frequency laser induced-damage of fused silica began before that of the third harmonic laser. The plasmas flash due to ion-electron recombination occurred about 21 ns after the peak of pump pulses. Based on Keldysh theory, the photoionization rate of fused silica vs laser intensity under 355 and 1 064 nm laser was calc
The damage processes of fused silica under the fundamental frequency and third harmonic of Nd:YAG laser were studied with instantaneous scattering pulses measurements via fast photodiodes and high bandwidth oscilloscope. The optical micrographs of ablated craters on fused silica surface were also analyzed. The sharp increase of scattered light of pump pulse was assumed to be the damage precursor, therefore, the damage started nearly at the peak of the pump pulse. Fundamental frequency laser induced-damage of fused silica began before that of the third harmonic laser. The plasmas flash due to ion-electron recombination occurred about 21 ns after the peak of pump pulses. Based on Keldysh theory, the photoionization rate of fused silica vs laser intensity under 355 and 1 064 nm laser was calc
2008,
20.
Abstract:
A theory based on energy-band is used to study the free electron density in material conductive band and to investigate the interaction of laser and optical material. The relationship between the damage threshold and the laser-wave length, the pulse duration and the band gap is discussed. The influnces of laser wavelength and pulse duration on damage threshold are numerically analyzed. The conclusion shows that, when the pulse duration is shorter than 1 ps, the damage threshold decreases with the increas of pulse duration, while the pulse duration is longer than 1 ps, the damage threshold increases with the increasement of pulse duration, and laser-induced damage threshold in SiO2 decreases with the decreasement of laser wave length in range of 10 fs to 10 ns.
A theory based on energy-band is used to study the free electron density in material conductive band and to investigate the interaction of laser and optical material. The relationship between the damage threshold and the laser-wave length, the pulse duration and the band gap is discussed. The influnces of laser wavelength and pulse duration on damage threshold are numerically analyzed. The conclusion shows that, when the pulse duration is shorter than 1 ps, the damage threshold decreases with the increas of pulse duration, while the pulse duration is longer than 1 ps, the damage threshold increases with the increasement of pulse duration, and laser-induced damage threshold in SiO2 decreases with the decreasement of laser wave length in range of 10 fs to 10 ns.
2008,
20.
Abstract:
The definition and measuring principle of laser beam quality foctor are introduced.The uncertainty sources of beam quality are analyzed. The standard uncertainty and combined standard uncertainty are calculated based on some experimental data.Specific methods are put forward for reducing standard uncertainty of beam quality measurement. The definition method of beam diameter must be uniformed.Invariant measurement condition and high accuracy of laser beam quality measurement system are important for reducing standard uncertainty of beam quality measurement.
The definition and measuring principle of laser beam quality foctor are introduced.The uncertainty sources of beam quality are analyzed. The standard uncertainty and combined standard uncertainty are calculated based on some experimental data.Specific methods are put forward for reducing standard uncertainty of beam quality measurement. The definition method of beam diameter must be uniformed.Invariant measurement condition and high accuracy of laser beam quality measurement system are important for reducing standard uncertainty of beam quality measurement.
2008,
20.
Abstract:
Microtemperature method is used to measure the turbulence strength of different positions near the telescopic dome which is an isolated building. From analyzing the refractive index structure parameter near the dome and the same parameter at tower, the parameter of turbulence at altitude of 8.2 m, 8.5 m, 9.0 m are stronger than that of same altitude of general atmosphere. The refractive index structure parameters of equidistance between sensors and dome in different directions are different. The vertical turbulence intensity is stronger than the horizontal turbulence intensity. It is unreliable to consider the range near dome as near ground. The spectrum of temperature fluctuations near the dome follows the －5/3 law．
Microtemperature method is used to measure the turbulence strength of different positions near the telescopic dome which is an isolated building. From analyzing the refractive index structure parameter near the dome and the same parameter at tower, the parameter of turbulence at altitude of 8.2 m, 8.5 m, 9.0 m are stronger than that of same altitude of general atmosphere. The refractive index structure parameters of equidistance between sensors and dome in different directions are different. The vertical turbulence intensity is stronger than the horizontal turbulence intensity. It is unreliable to consider the range near dome as near ground. The spectrum of temperature fluctuations near the dome follows the －5/3 law．
2008,
20.
Abstract:
The kinetics and microscopic mechanisms of ultrashort laser melting of a copper film is studied by modified molecular dynamics method. A model considering the thermal conductivity of free electrons and the consumption of latent heat of melting is used to make the simulation more realistic. The mechanism responsible for the melting of copper under picosecond laser pulse irradiation can be attributed to the homogeneous nucleation of the liquid phase inside the solid region. The melting is a overheated melting caused by homogeneous nucleation, and the velocity of propagation of “melt front” is found up to be 5.8 nm/ps. Picosecond laser pulse induced melting occurring under the condition of thermal confinement results in a less complicate temperature distribution and a weaker effect of unloa
The kinetics and microscopic mechanisms of ultrashort laser melting of a copper film is studied by modified molecular dynamics method. A model considering the thermal conductivity of free electrons and the consumption of latent heat of melting is used to make the simulation more realistic. The mechanism responsible for the melting of copper under picosecond laser pulse irradiation can be attributed to the homogeneous nucleation of the liquid phase inside the solid region. The melting is a overheated melting caused by homogeneous nucleation, and the velocity of propagation of “melt front” is found up to be 5.8 nm/ps. Picosecond laser pulse induced melting occurring under the condition of thermal confinement results in a less complicate temperature distribution and a weaker effect of unloa
2008,
20.
Abstract:
Samples were excited by pulse laser and plasma was formed at atmospheric pressure. The technique of laser induced breakdown spectroscopy(LIBS) was applied to analyzing the carbon content in the samples. The matrix element Si was selected as internal standard, calibration curves were drawn respectively using the peak intensity of carbon line and the intensity ratio of carbon line and silica line. The fitting degree of two different calibration curves, signal reproducibility and the accuracy of calibrated values were analyzed. The results of the analysis show that the intensity ratio method seems more adequate than the peak intensity method for establishing the calibration cures.
Samples were excited by pulse laser and plasma was formed at atmospheric pressure. The technique of laser induced breakdown spectroscopy(LIBS) was applied to analyzing the carbon content in the samples. The matrix element Si was selected as internal standard, calibration curves were drawn respectively using the peak intensity of carbon line and the intensity ratio of carbon line and silica line. The fitting degree of two different calibration curves, signal reproducibility and the accuracy of calibrated values were analyzed. The results of the analysis show that the intensity ratio method seems more adequate than the peak intensity method for establishing the calibration cures.
2008,
20.
Abstract:
Using trimethylol propane triacrylate(TMPTA) as the initial material, low density TMPTA foam columns were successfully prepared by UV irradiation technique and freezing-drying process. These foam columns have the density range of 4 mg/cm3 to 20 mg/cm3 and they can sustain themselves. The shrinkage of the foams results in d, which is defined as the ratio of the factual density to the theoretic density, is larger than 1, and d decreases with the theoretic density increasing. It is found that the TPMTA foams are thermally stable up to 290 ℃ by TGA analysis. The foams have uniform and open network structure as demonstrated by SEM. Hg porosimetry tests show that the pore size of these foams mainly distributes in the range of 3.0 mm to 7.5 mm and the average pore size is 7.37 mm.
Using trimethylol propane triacrylate(TMPTA) as the initial material, low density TMPTA foam columns were successfully prepared by UV irradiation technique and freezing-drying process. These foam columns have the density range of 4 mg/cm3 to 20 mg/cm3 and they can sustain themselves. The shrinkage of the foams results in d, which is defined as the ratio of the factual density to the theoretic density, is larger than 1, and d decreases with the theoretic density increasing. It is found that the TPMTA foams are thermally stable up to 290 ℃ by TGA analysis. The foams have uniform and open network structure as demonstrated by SEM. Hg porosimetry tests show that the pore size of these foams mainly distributes in the range of 3.0 mm to 7.5 mm and the average pore size is 7.37 mm.
2008,
20.
Abstract:
The breakdown time delay and jitter are very important for the plasma-electrode Pockels cells(PEPC) electro-optic switch driven by one-pulse process. Their reduction is the key to improve the performance large aperture electro-optic switches. A method is proposed in this paper: the cathode is illuminated by ultraviolet ray, so that the secondary electron can be excited and come into a steady initialized electron flow on the surface of the cathode. Under the high voltage pulse, the initial electron flow avalanches quickly in the cell, and the helium gas breaks down and discharge happened. Experimental results have demonstrated that the method did reduce the switching time and the time jitter. And the average time jitter and the average breakdown time delay were cut down by 88% and 36%, resp
The breakdown time delay and jitter are very important for the plasma-electrode Pockels cells(PEPC) electro-optic switch driven by one-pulse process. Their reduction is the key to improve the performance large aperture electro-optic switches. A method is proposed in this paper: the cathode is illuminated by ultraviolet ray, so that the secondary electron can be excited and come into a steady initialized electron flow on the surface of the cathode. Under the high voltage pulse, the initial electron flow avalanches quickly in the cell, and the helium gas breaks down and discharge happened. Experimental results have demonstrated that the method did reduce the switching time and the time jitter. And the average time jitter and the average breakdown time delay were cut down by 88% and 36%, resp
2008,
20.
Abstract:
Based on the heat conductivity principles, a mathematic model about pulsed laser induced crystallization of a-Si thin film had been developed. With the finite difference method, the effect of varied parameters, such as wavelength and energy density of laser, on the temperature distribution and phase change of the thin film during crystallization was analyzed. The melt threshold energy densities for 500 nm a-Si irradiated with different lasers were calculated. The results show that the crystallization with excimer lasers requires the lowest threshold energy densities. However, it does not create the deepest melt depth, compared with green or red lasers. The effect of different substrate temperatures on the crystallization speed and grain size was analyzed, and the calculated results accord
Based on the heat conductivity principles, a mathematic model about pulsed laser induced crystallization of a-Si thin film had been developed. With the finite difference method, the effect of varied parameters, such as wavelength and energy density of laser, on the temperature distribution and phase change of the thin film during crystallization was analyzed. The melt threshold energy densities for 500 nm a-Si irradiated with different lasers were calculated. The results show that the crystallization with excimer lasers requires the lowest threshold energy densities. However, it does not create the deepest melt depth, compared with green or red lasers. The effect of different substrate temperatures on the crystallization speed and grain size was analyzed, and the calculated results accord
2008,
20.
Abstract:
Based on the technique of micro fluid injection molding, RF hollow microspheres were synthesized by using dibutyl phthalate as oil phase, RF solution as water phase, and by sol-gel, solvent exchanging and supercritical drying. The components, morphology, aperture, and diameter distribution of RF hollow microspheres were characterized by infrared spectrum, X-ray micro analysis, TEM, and nitrogen adsorption-desorption respectively.The results show that RF hollow microsphere is monolayered and has a typical structure of the porous aerogel. The pores are consisting of nearly uniform nano-particles about 10 nm in diameter, and their average aperture is about 20 nm. The sphericity and concentricity of the monolayer hollow microsphere is higher than 95%, the diameter distribution of RF hollow mic
Based on the technique of micro fluid injection molding, RF hollow microspheres were synthesized by using dibutyl phthalate as oil phase, RF solution as water phase, and by sol-gel, solvent exchanging and supercritical drying. The components, morphology, aperture, and diameter distribution of RF hollow microspheres were characterized by infrared spectrum, X-ray micro analysis, TEM, and nitrogen adsorption-desorption respectively.The results show that RF hollow microsphere is monolayered and has a typical structure of the porous aerogel. The pores are consisting of nearly uniform nano-particles about 10 nm in diameter, and their average aperture is about 20 nm. The sphericity and concentricity of the monolayer hollow microsphere is higher than 95%, the diameter distribution of RF hollow mic
2008,
20.
Abstract:
The CH coating on microshells was fabricated by low-pressure plasma chemical vapor deposition (LPPCVD) with a bounce pan system. The influence of bounce modes on the surface topography of the CH coating was discussed. The surface topography was probed by optical microscopy and scanning electron microscopy(SEM). Roughness and sphericity were measured with an atomic force microscopy(AFM). X-radiography was used to obtain the concentricity. The results show that the surface topography of the coating is improved significantly by the intermittent bounce mode, and the roughness of medium high mode is reduced. The surface finish is improved ulteriorly by the intermittent bounce mode as the duty ratio is reduced. The RMS roughness of 30 mm CH coating is less than 30 nm. The spericity and concentri
The CH coating on microshells was fabricated by low-pressure plasma chemical vapor deposition (LPPCVD) with a bounce pan system. The influence of bounce modes on the surface topography of the CH coating was discussed. The surface topography was probed by optical microscopy and scanning electron microscopy(SEM). Roughness and sphericity were measured with an atomic force microscopy(AFM). X-radiography was used to obtain the concentricity. The results show that the surface topography of the coating is improved significantly by the intermittent bounce mode, and the roughness of medium high mode is reduced. The surface finish is improved ulteriorly by the intermittent bounce mode as the duty ratio is reduced. The RMS roughness of 30 mm CH coating is less than 30 nm. The spericity and concentri
2008,
20.
Abstract:
A method of designing continuous phase plates(CPP) for beam smoothing has been studied. The new CPP was obtained through adding some procedures into the traditional GerchbergSaxton(G-S) algorithm that was giving a new way of initial phase, adding steps of unwrapping and filtering in iterative procedure and aiming at controlling the spatial spectrum of focal spot. The surface of CPP was continuous and controllable, and compared to the traditional design, it could reduce the GRMS of CPP, get better focal spot shape, and depress the special frequency region’s modulation.Combined with SSD, the new CPP have the better effect for controlling focal spot than the CPP designed by “standard” method.
A method of designing continuous phase plates(CPP) for beam smoothing has been studied. The new CPP was obtained through adding some procedures into the traditional GerchbergSaxton(G-S) algorithm that was giving a new way of initial phase, adding steps of unwrapping and filtering in iterative procedure and aiming at controlling the spatial spectrum of focal spot. The surface of CPP was continuous and controllable, and compared to the traditional design, it could reduce the GRMS of CPP, get better focal spot shape, and depress the special frequency region’s modulation.Combined with SSD, the new CPP have the better effect for controlling focal spot than the CPP designed by “standard” method.
2008,
20.
Abstract:
This article describes the laser Thomson scattering principle and the developed system on HL-2A device. The high power Q-switch Nd:YAG laser, with a wavelength of 1 064 nm, can sufficiently satisfy the measurement requirement. The polycromator consisting of avalanche photo-diodes(APD) and narrow band interference filters, can effectively improve the measurement of scattering light. The electron temperature is deduced by error-weighted lookup table method, which improves the data-processing speed or efficiency. Finally, the experiment results of the one-point electron temperature during different discharges of plasma are presented.
This article describes the laser Thomson scattering principle and the developed system on HL-2A device. The high power Q-switch Nd:YAG laser, with a wavelength of 1 064 nm, can sufficiently satisfy the measurement requirement. The polycromator consisting of avalanche photo-diodes(APD) and narrow band interference filters, can effectively improve the measurement of scattering light. The electron temperature is deduced by error-weighted lookup table method, which improves the data-processing speed or efficiency. Finally, the experiment results of the one-point electron temperature during different discharges of plasma are presented.
2008,
20.
Abstract:
In this paper, mesh pans for coating poly-olphe-methycstyrene(PAMS) microspheres with polymer are designed. The difference between bounces on a mesh pan and a glass pan is evaluated. The capability of mesh pans for bouncing PAMS microspheres is examined. The effect of the related parameters of the mesh pans on the surface roughness of the microshells has been explored. The experimental results show that the mesh pans improve significantly the bounce of PAMS microspheres in comparison with glass pans. In order to improve the surface roughness of microspheres, an intermittent vibration mode must be applied on the mesh pans for bouncing the microsphere．
In this paper, mesh pans for coating poly-olphe-methycstyrene(PAMS) microspheres with polymer are designed. The difference between bounces on a mesh pan and a glass pan is evaluated. The capability of mesh pans for bouncing PAMS microspheres is examined. The effect of the related parameters of the mesh pans on the surface roughness of the microshells has been explored. The experimental results show that the mesh pans improve significantly the bounce of PAMS microspheres in comparison with glass pans. In order to improve the surface roughness of microspheres, an intermittent vibration mode must be applied on the mesh pans for bouncing the microsphere．
2008,
20.
Abstract:
Structure stability is an important design index of ICF driver. Based on laser prototype facility(TIL) design characteristic of multi-pass amplifier and frame structure, the optical matrix is used to analyze the single optical element influence on the beam drift and get the mathematic model. Considering all the optical elements influence on the beam drift, the mathematic model of the optical element stability index allocation is built, the parameter relation of the mathematic model is defined according to the structure characteristic of TIL, the stability index of each optical element is got as the support structure design index. Charge-coupled device(CCD) detect technology is used to measure the general beam stability of TIL. The root mean square beam drift in x and y direction are 2.78
Structure stability is an important design index of ICF driver. Based on laser prototype facility(TIL) design characteristic of multi-pass amplifier and frame structure, the optical matrix is used to analyze the single optical element influence on the beam drift and get the mathematic model. Considering all the optical elements influence on the beam drift, the mathematic model of the optical element stability index allocation is built, the parameter relation of the mathematic model is defined according to the structure characteristic of TIL, the stability index of each optical element is got as the support structure design index. Charge-coupled device(CCD) detect technology is used to measure the general beam stability of TIL. The root mean square beam drift in x and y direction are 2.78
2008,
20.
Abstract:
A novel UWB horn antenna based on TEM horn structure with wedge-shaped dielectric-filling is investigated. For the wedge-shape dielectric-filling horn antenna, it is found that the radiation energy converged in the dielectric-filling region, thus the radiation field in the direction of the horn axis is improved. Moreover, the appropriate filling of insulating dielectric could prevent the antenna from electric breakdown. The finite difference time domain(FDTD) numerical analysis approach has been adopted to simulate the proposed antenna and the results indicate that it is well suited to high power UWB applications.
A novel UWB horn antenna based on TEM horn structure with wedge-shaped dielectric-filling is investigated. For the wedge-shape dielectric-filling horn antenna, it is found that the radiation energy converged in the dielectric-filling region, thus the radiation field in the direction of the horn axis is improved. Moreover, the appropriate filling of insulating dielectric could prevent the antenna from electric breakdown. The finite difference time domain(FDTD) numerical analysis approach has been adopted to simulate the proposed antenna and the results indicate that it is well suited to high power UWB applications.
2008,
20.
Abstract:
A system of high power centimeter wave(HPCW) was built up. The temperature change of tenebrio molitor and lawn was sampled during HPCW irradiation . It is shown that the relationship between the temperature increase of tenebrio molitor and irradiation time is approximately linear, and the relationship between the temperature increase of lawn and irradiation time is nonlinear. It is also considered that the temperature of lawn increases faster than that of tenebrio molitor does during the earlier stage of irradiation. The death percentage of tenebrio molitor and injury rate of lawn irradiated by HPCW could be fitted by normal distribution. The fitting curves of relations between death rate and irradiation time and between death rate and temperature are presented.
A system of high power centimeter wave(HPCW) was built up. The temperature change of tenebrio molitor and lawn was sampled during HPCW irradiation . It is shown that the relationship between the temperature increase of tenebrio molitor and irradiation time is approximately linear, and the relationship between the temperature increase of lawn and irradiation time is nonlinear. It is also considered that the temperature of lawn increases faster than that of tenebrio molitor does during the earlier stage of irradiation. The death percentage of tenebrio molitor and injury rate of lawn irradiated by HPCW could be fitted by normal distribution. The fitting curves of relations between death rate and irradiation time and between death rate and temperature are presented.
2008,
20.
Abstract:
A cylindrical waveguide filled with thin annular plasma is studied in a strong longitudinal magnetic field. The beam and the annular plasma have been considered as anisotropic dielectric. So the hot cavity dispersion equation can be derived on the basis of the matched boundary conditions and the wave growth rate is obtained by means of equipotential line method. The dispersion equation and the growth rate with different parameters are numerically calculated. The numerical results show the Cherenkov radiation can be produced through the interaction between the former two low frequency plasma modes and the slow space charge wave, and with the increase of the in plasma density, the maser have several merits, such as enhanced output frequency , higher growth rate and significantly broader band
A cylindrical waveguide filled with thin annular plasma is studied in a strong longitudinal magnetic field. The beam and the annular plasma have been considered as anisotropic dielectric. So the hot cavity dispersion equation can be derived on the basis of the matched boundary conditions and the wave growth rate is obtained by means of equipotential line method. The dispersion equation and the growth rate with different parameters are numerically calculated. The numerical results show the Cherenkov radiation can be produced through the interaction between the former two low frequency plasma modes and the slow space charge wave, and with the increase of the in plasma density, the maser have several merits, such as enhanced output frequency , higher growth rate and significantly broader band
2008,
20.
Abstract:
A great equal range microstrip power equalizer was studied and a kind of circuit topology was proposed. In the circuit, the parallel stub resonator was used to get bandstop effect, and the resistor was used to modify the attenuation character. Furthermore, a compact structure was employed. Using the above circuit topology, an attenuation curve of equal range up to 20 dB was fulfilled to satisfy a traveling wave tube(TWT) covering X and Ku frequency band. The simulation and its implementation have been carried out. The measured results of the equalizer agree with the simulation results very well. The equalizer has the characteristic of wide bandwidth, great equal range and compact size．
A great equal range microstrip power equalizer was studied and a kind of circuit topology was proposed. In the circuit, the parallel stub resonator was used to get bandstop effect, and the resistor was used to modify the attenuation character. Furthermore, a compact structure was employed. Using the above circuit topology, an attenuation curve of equal range up to 20 dB was fulfilled to satisfy a traveling wave tube(TWT) covering X and Ku frequency band. The simulation and its implementation have been carried out. The measured results of the equalizer agree with the simulation results very well. The equalizer has the characteristic of wide bandwidth, great equal range and compact size．
2008,
20.
Abstract:
The ADI-BOR-FDTD method can reduce a three-dimensional problem to a two-dimensional one, resulting in an efficient saving of CPU running time and memory requirement. By incorporating the plane wave expanding technique and total-field/scattered-field boundary into ADI-BOR-FDTD method, the non-nuclear EMP coupling to thin wire in free space was simulated. The relation between the peak value of induced current and the length of wire was analyzed. Numerical results indicate that the ADI-BOR-FDTD method runs several times faster than conventional three-dimensional FDTD method and saves a great deal of computational memory.
The ADI-BOR-FDTD method can reduce a three-dimensional problem to a two-dimensional one, resulting in an efficient saving of CPU running time and memory requirement. By incorporating the plane wave expanding technique and total-field/scattered-field boundary into ADI-BOR-FDTD method, the non-nuclear EMP coupling to thin wire in free space was simulated. The relation between the peak value of induced current and the length of wire was analyzed. Numerical results indicate that the ADI-BOR-FDTD method runs several times faster than conventional three-dimensional FDTD method and saves a great deal of computational memory.
2008,
20.
Abstract:
The connecting face of small loop probe is optimized with slope cutting, so that the probe can exactly measure weak coupling electromagnetic field in the cavities. Under the irradiation of electromagnetic pulse, the change of voltage in loop probe is simulated by FDTD. The receiving characteristics of three loop probes with different slopes are calculated. The high frequency receiving capability of loop probe with 15° slope is improved by 2~5 dB. The receiving experiments of 40 mm diameter loop probe with 15° slope are conducted. Measurement result is compared with calculation result, whose change trends coincide well in the main, which proves credibility of numerical analysis．
The connecting face of small loop probe is optimized with slope cutting, so that the probe can exactly measure weak coupling electromagnetic field in the cavities. Under the irradiation of electromagnetic pulse, the change of voltage in loop probe is simulated by FDTD. The receiving characteristics of three loop probes with different slopes are calculated. The high frequency receiving capability of loop probe with 15° slope is improved by 2~5 dB. The receiving experiments of 40 mm diameter loop probe with 15° slope are conducted. Measurement result is compared with calculation result, whose change trends coincide well in the main, which proves credibility of numerical analysis．
2008,
20.
Abstract:
This paper presents the criteria to judge the quality of electron-beam in designing the TWT’s electron gun by numerical simulation: uniform current density of cathode surface emission, good laminar flow property of the electron beam, uniform radial distribution of the beam near the beam waist and smooth of envelope which contain certain percent electrons. Designing the electron gun of a TWT by the code we have compiled code, judging and comparing the quality of beams of different structures, the better e-gun structure can be obtained.
This paper presents the criteria to judge the quality of electron-beam in designing the TWT’s electron gun by numerical simulation: uniform current density of cathode surface emission, good laminar flow property of the electron beam, uniform radial distribution of the beam near the beam waist and smooth of envelope which contain certain percent electrons. Designing the electron gun of a TWT by the code we have compiled code, judging and comparing the quality of beams of different structures, the better e-gun structure can be obtained.
2008,
20.
Abstract:
Based on a series of electromagnetic field equations which are in line with the boundary conditions, the eigenequation of coaxial waveguide with outer slotted structure is derived using the fields matching method. When the radius of the inner conductor equals zero, the outer slotted coaxial waveguide is equivalent to an outer slotted cylindrical waveguide, and its eigenequation is derived as well. Numerical results reveal the propagation characteristics of both the coaxial waveguide and cylindrical waveguide with outer slotted structure. The deeper the slots are and the smaller the half angle of the slot gap is, the small the latent roots are.
Based on a series of electromagnetic field equations which are in line with the boundary conditions, the eigenequation of coaxial waveguide with outer slotted structure is derived using the fields matching method. When the radius of the inner conductor equals zero, the outer slotted coaxial waveguide is equivalent to an outer slotted cylindrical waveguide, and its eigenequation is derived as well. Numerical results reveal the propagation characteristics of both the coaxial waveguide and cylindrical waveguide with outer slotted structure. The deeper the slots are and the smaller the half angle of the slot gap is, the small the latent roots are.
2008,
20.
Abstract:
The nonlinear consistent equations were put forward which could describe the beam-wave interaction in relativistic-backward-wave-oscillator(RBWO). The effects of different parameters on the peak superradiant-power of RBWO, such as accelerating voltage, beam current and coupling impedance, were studied and analyzed by solving the beam-wave interaction nonlinear consistent equations numerically. The PIC simulation results indicate that in superradiant regime, the peak superradiant-power increases markedly by linear-modulating diode voltage and current and adopting non-uniform slow-wave structure, because of correspondingly extended resonating-voltage range and improved energy-exchange efficiency of beam and wave.
The nonlinear consistent equations were put forward which could describe the beam-wave interaction in relativistic-backward-wave-oscillator(RBWO). The effects of different parameters on the peak superradiant-power of RBWO, such as accelerating voltage, beam current and coupling impedance, were studied and analyzed by solving the beam-wave interaction nonlinear consistent equations numerically. The PIC simulation results indicate that in superradiant regime, the peak superradiant-power increases markedly by linear-modulating diode voltage and current and adopting non-uniform slow-wave structure, because of correspondingly extended resonating-voltage range and improved energy-exchange efficiency of beam and wave.
2008,
20.
Abstract:
The structure of tri-bend circular waveguides was studied by theoretical calculation, theoretical design and numerical simulation. The TM01-TE11 conversion efficiency formula were derived and the condition for the highest conversion efficiency was obtained. Two mode converters of this kind with an inner radius of 3.0 cm and 3.5 cm were analyzed. The conversion efficiency exceeded 99.64% and 98.62% at 4.25 GHz and its bandwidth of power conversion efficiency exceeding 90% reached 9.88% and 12.71%, respectively. The simulation verified the theoretical design.
The structure of tri-bend circular waveguides was studied by theoretical calculation, theoretical design and numerical simulation. The TM01-TE11 conversion efficiency formula were derived and the condition for the highest conversion efficiency was obtained. Two mode converters of this kind with an inner radius of 3.0 cm and 3.5 cm were analyzed. The conversion efficiency exceeded 99.64% and 98.62% at 4.25 GHz and its bandwidth of power conversion efficiency exceeding 90% reached 9.88% and 12.71%, respectively. The simulation verified the theoretical design.
2008,
20.
Abstract:
The transient response of the high power PIN diode limiter to the step electromagnetic pulse descending edge is calculated by PSpice. Pulse-inversion is observed in the output of the high power PIN diode limiter while the limiter is affected by the step pulse descending edge. The magnitude of the pulse-inversion is equivalent to or in some conditions even larger than spike leakage. Besides the spike leakage, the pulse-inversion may be another potential safety hazard to the high power limiter. The magnitude of the pulse-inversion increases with the augment of the duration and magnitude of the input pulse, and decreases of the input pulse’s fall time and value of the RF impedance inductor.
The transient response of the high power PIN diode limiter to the step electromagnetic pulse descending edge is calculated by PSpice. Pulse-inversion is observed in the output of the high power PIN diode limiter while the limiter is affected by the step pulse descending edge. The magnitude of the pulse-inversion is equivalent to or in some conditions even larger than spike leakage. Besides the spike leakage, the pulse-inversion may be another potential safety hazard to the high power limiter. The magnitude of the pulse-inversion increases with the augment of the duration and magnitude of the input pulse, and decreases of the input pulse’s fall time and value of the RF impedance inductor.
2008,
20.
Abstract:
Based on theory of temperature field and thermal stress field around inclusions in KDP crystals, the distribution of crystal temperature field and thermal stress field is analyzed under the influence of micro-nano machined superficial layer’s inclusions. It is found that ions of inclusions absorbing mucl injected laser lead to crystal damages. Inclusions’ sfrong absorbing of laser influenc KDP crystals laser damage threshold. The radius of adverse inclusion is obtained, with which the also inclusion absorbs the maximumenergy and reaches the wighest temperature. In addition, different kinds and different contents of inclusions have different effect on the crystal laser damage threshold．
Based on theory of temperature field and thermal stress field around inclusions in KDP crystals, the distribution of crystal temperature field and thermal stress field is analyzed under the influence of micro-nano machined superficial layer’s inclusions. It is found that ions of inclusions absorbing mucl injected laser lead to crystal damages. Inclusions’ sfrong absorbing of laser influenc KDP crystals laser damage threshold. The radius of adverse inclusion is obtained, with which the also inclusion absorbs the maximumenergy and reaches the wighest temperature. In addition, different kinds and different contents of inclusions have different effect on the crystal laser damage threshold．
2008,
20.
Abstract:
Through Geant4 simulation, the characteristics of recoil proton in plastic scintillating fibers irradiated by high-energy neutrons have been presented. The energy and angular distributions of recoil proton have been analyzed with incident neutron energy of 2, 4, 6, 8 MeV. The results show that the energy of the recoil proton ranges from zero to incident neutron energy. The recoil proton energies vary inversely as angles, that is, the protons along the direction of incident neutrons have the biggest energy and those along the fiber radius have relative smaller energy.
Through Geant4 simulation, the characteristics of recoil proton in plastic scintillating fibers irradiated by high-energy neutrons have been presented. The energy and angular distributions of recoil proton have been analyzed with incident neutron energy of 2, 4, 6, 8 MeV. The results show that the energy of the recoil proton ranges from zero to incident neutron energy. The recoil proton energies vary inversely as angles, that is, the protons along the direction of incident neutrons have the biggest energy and those along the fiber radius have relative smaller energy.
2008,
20.
Abstract:
The metal particles of different elements, concentrations and diameters are doped in PVC and the targets are tested by using a high-power pulsed TEA-CO2 laser. The results show that: the coupling coefficient changes slightly with elements and diameters of metal particles doped in PVC, but the specific impulse is significantly improved for different laser power densities. The doped nano-Fe powder PVC shows the best performance; the maximum specific impulse appears at 50% nano-Fe power concentration for the energy density of 5×106 W/cm2. At the atmospheric environment, the coupling coefficient for PVC target containing 20% nano-zinc powder increases first and then decreases with the increase of laser power density, and the specific impulse is not even better than that for PVC targets doped
The metal particles of different elements, concentrations and diameters are doped in PVC and the targets are tested by using a high-power pulsed TEA-CO2 laser. The results show that: the coupling coefficient changes slightly with elements and diameters of metal particles doped in PVC, but the specific impulse is significantly improved for different laser power densities. The doped nano-Fe powder PVC shows the best performance; the maximum specific impulse appears at 50% nano-Fe power concentration for the energy density of 5×106 W/cm2. At the atmospheric environment, the coupling coefficient for PVC target containing 20% nano-zinc powder increases first and then decreases with the increase of laser power density, and the specific impulse is not even better than that for PVC targets doped
2008,
20.
Abstract:
The fabrication of LaB6 field emission arrays is the key technology for manufacturing LaB6 field emission cathodes. Silicon nitride film was deposited as mask layer on the (111) single crystal LaB6 substrate by plasma-enhanced chemical vapor deposition method, and then patterned to form an array of 4 μm diameter silicon nitride disks by reactive ion etching method. Using these Si3N4 disks as hard masks, the underlying LaB6 was etched to form tip field emission arrays by electro-chemical etching method. The etching mechanism was discussed, and the sample morphologies were investigated by SEM as the etching conditions changed. The experimental results indicated that H3PO4 could overcome the anisotropic phenomenon usually occurred in previous electro-chemical etching experiments. The emitter
The fabrication of LaB6 field emission arrays is the key technology for manufacturing LaB6 field emission cathodes. Silicon nitride film was deposited as mask layer on the (111) single crystal LaB6 substrate by plasma-enhanced chemical vapor deposition method, and then patterned to form an array of 4 μm diameter silicon nitride disks by reactive ion etching method. Using these Si3N4 disks as hard masks, the underlying LaB6 was etched to form tip field emission arrays by electro-chemical etching method. The etching mechanism was discussed, and the sample morphologies were investigated by SEM as the etching conditions changed. The experimental results indicated that H3PO4 could overcome the anisotropic phenomenon usually occurred in previous electro-chemical etching experiments. The emitter
2008,
20.
Abstract:
In order to investigate the blur caused by the container in proton radiography, the expression of blurring FWHM of the container was deduced on the base of the multiple Coulomb scattering and the characteristic of the lens imaging system. The results show that the blurring FWHM is proportional to the distance between the object and the container and root mean square of container’s thickness, and inverse proportional to the proton momentum. The front wall and back wall of container will cause the blur. And on the same situation, the container made of aluminum has smaller blur than that of the iron one. The blurring FWHM of aluminum container (radius 200 cm , thickness 5 cm) is 1.30 mm, larger than the object’s. The analytic results agree with the simulation one by MC program.
In order to investigate the blur caused by the container in proton radiography, the expression of blurring FWHM of the container was deduced on the base of the multiple Coulomb scattering and the characteristic of the lens imaging system. The results show that the blurring FWHM is proportional to the distance between the object and the container and root mean square of container’s thickness, and inverse proportional to the proton momentum. The front wall and back wall of container will cause the blur. And on the same situation, the container made of aluminum has smaller blur than that of the iron one. The blurring FWHM of aluminum container (radius 200 cm , thickness 5 cm) is 1.30 mm, larger than the object’s. The analytic results agree with the simulation one by MC program.
2008,
20.
Abstract:
Semi-analytical method , a new solution to calculate electromagnetic field, is applied to analyze three kinds of quadrupole field of shape-varied electrodes in electron optics. Positions of polar points can be determined precisely, simply and efficiently by equivalent source filling according to the different shape of electrodes. Since the general solution of this method is analytic series of scalar potential, electric field intensity could be obtained by first derivation. Calculation relative errors are almost 10-3 for quadrupole fields of curved cylindrical electrodes and plat plate electrodes, while 0.001% for field of prominence cylindrical electrodes.
Semi-analytical method , a new solution to calculate electromagnetic field, is applied to analyze three kinds of quadrupole field of shape-varied electrodes in electron optics. Positions of polar points can be determined precisely, simply and efficiently by equivalent source filling according to the different shape of electrodes. Since the general solution of this method is analytic series of scalar potential, electric field intensity could be obtained by first derivation. Calculation relative errors are almost 10-3 for quadrupole fields of curved cylindrical electrodes and plat plate electrodes, while 0.001% for field of prominence cylindrical electrodes.
2008,
20.
Abstract:
Ice cylinders are common in middle-latitude cirrostratus. Using wave theory for infinitely long cylinder irradiated by linearly polarized light, the intensity and polarization of scattering light by single ice cylinder are studied at different incident angles, size parameters and polarizations of incident light: (1) With increase of incident angle, intensity and polarization tend to be symmetrical and their numeric oscillation frequencies decrease. Intensity of scattering light totally weaken and changing degree of polarization increas; (2) With increase of size parameter, numeric oscillation frequencies of intensity and polarization increase, but amplitude of scattering intensity oscillation totally decrease; the number, intensity and location change when electric vector is parallel to in
Ice cylinders are common in middle-latitude cirrostratus. Using wave theory for infinitely long cylinder irradiated by linearly polarized light, the intensity and polarization of scattering light by single ice cylinder are studied at different incident angles, size parameters and polarizations of incident light: (1) With increase of incident angle, intensity and polarization tend to be symmetrical and their numeric oscillation frequencies decrease. Intensity of scattering light totally weaken and changing degree of polarization increas; (2) With increase of size parameter, numeric oscillation frequencies of intensity and polarization increase, but amplitude of scattering intensity oscillation totally decrease; the number, intensity and location change when electric vector is parallel to in
2008,
20.
Abstract:
The change in optical properties and the damage mechanism of ZnO/silicone white paint caused by low energy protons were investigated in terms of ground-based simulation testing. The results show that the solar absorptance ratio increases with the increase of irradiation fluence of proton as well as the proton energy. Under proton exposure, the degradation in optical properties of ZnO/silicone white paint mainly occurs in the visible radiation region of the solar spectrum. The damage mechanism was studied by Fourier transform infrared spectrum. The amount of free oxygen increases under proton exposure. Free oxygen would oxidate the radicals in the silicone binder and form active hydroxide radical (—OH), which could accelerate the break of Si—O—Si bond. Meanwhile, the no-bonding lone-pair
The change in optical properties and the damage mechanism of ZnO/silicone white paint caused by low energy protons were investigated in terms of ground-based simulation testing. The results show that the solar absorptance ratio increases with the increase of irradiation fluence of proton as well as the proton energy. Under proton exposure, the degradation in optical properties of ZnO/silicone white paint mainly occurs in the visible radiation region of the solar spectrum. The damage mechanism was studied by Fourier transform infrared spectrum. The amount of free oxygen increases under proton exposure. Free oxygen would oxidate the radicals in the silicone binder and form active hydroxide radical (—OH), which could accelerate the break of Si—O—Si bond. Meanwhile, the no-bonding lone-pair
2008,
20.
Abstract:
Two bracing type MV gas switches are designed, the cantilever switch has a cantilevered HV electrode sealed in the brace insulating cylinder, the section-brace switch has an HV electrode spreading out of the brace insulating cylinder. Through self-breakdown experiment and electrostatic field simulation, the optimization of insulator envelop is discussed. The result indicates that the section-brace switch is safer and stabler than the cantilever switch. The reason of puncture in insulator cylinder of cantilever switch is that the stream formed in switch is accelerated by the electric field and then strikes the surface of outer cylinder. Bradley formula with field enhancement factor is given and it accords well with experimental data.
Two bracing type MV gas switches are designed, the cantilever switch has a cantilevered HV electrode sealed in the brace insulating cylinder, the section-brace switch has an HV electrode spreading out of the brace insulating cylinder. Through self-breakdown experiment and electrostatic field simulation, the optimization of insulator envelop is discussed. The result indicates that the section-brace switch is safer and stabler than the cantilever switch. The reason of puncture in insulator cylinder of cantilever switch is that the stream formed in switch is accelerated by the electric field and then strikes the surface of outer cylinder. Bradley formula with field enhancement factor is given and it accords well with experimental data.
2008,
20.
Abstract:
Two D-dot monitors have been designed to measure the voltage pulse on a high-power triplate transmission line. One has been installed in the entrance and the other in the exit. A signal proportional to the time derivative of voltage is given from the D-dot monitor, and the voltage can be got by a passive RC integrator. Insulation of probe is achieved by epoxy, and dispersed capacitance between the probe and the ground can reduce by the designed waterproof configuration. Two-dimensional electrostatic simulations show that the amplitude of electric field at water-insulator-metal triple-point is low. These monitors are calibrated in-situ using a calibrated resistive divider and a pulser which produces high voltage with an HV cable as a forming line. The generated signal with steps and rise ti
Two D-dot monitors have been designed to measure the voltage pulse on a high-power triplate transmission line. One has been installed in the entrance and the other in the exit. A signal proportional to the time derivative of voltage is given from the D-dot monitor, and the voltage can be got by a passive RC integrator. Insulation of probe is achieved by epoxy, and dispersed capacitance between the probe and the ground can reduce by the designed waterproof configuration. Two-dimensional electrostatic simulations show that the amplitude of electric field at water-insulator-metal triple-point is low. These monitors are calibrated in-situ using a calibrated resistive divider and a pulser which produces high voltage with an HV cable as a forming line. The generated signal with steps and rise ti
2008,
20.
Abstract:
A high voltage pulse generator with fast rise-time and adjustable output waveform was developed. The new generator is mainly composed of five separate modules including Marx generator, pulse forming assembly, main switch, matching load and test cavity. The Marx is the primary energy storage of the generator. An alterable shunt resistor and a tunable inductor are placed in the output terminal of the Marx. By adjusting the assembly of shunt resistor, tunable inductor and the separate modules, multiple output waveforms (four exponential waveforms and a rectangular waveform) could be produced. The pulse width of the output waveform could be varied from 20 ns to 1 μs, and the amplitude of the output voltage could be regulated from 200 kV to 600 kV. The minimum rise-time of the output waveform
A high voltage pulse generator with fast rise-time and adjustable output waveform was developed. The new generator is mainly composed of five separate modules including Marx generator, pulse forming assembly, main switch, matching load and test cavity. The Marx is the primary energy storage of the generator. An alterable shunt resistor and a tunable inductor are placed in the output terminal of the Marx. By adjusting the assembly of shunt resistor, tunable inductor and the separate modules, multiple output waveforms (four exponential waveforms and a rectangular waveform) could be produced. The pulse width of the output waveform could be varied from 20 ns to 1 μs, and the amplitude of the output voltage could be regulated from 200 kV to 600 kV. The minimum rise-time of the output waveform
