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RSS2007 Vol. 19, No. 05
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2007,
19.
Abstract:
Using the second-order-moment and entropy-based definitions of the beam width, changes of the beam parameters including beam width, far-field divergence angle and beam quality factor of flat-topped beams passing through a spherically aberrated lens are studied. It is shown that the spherical aberration affects the beam parameters in the image space. The relative errors of the beam width and far-field divergence angle introduced by the spherical aberration increase with increasing spherical aberration coefficient and decreasing beam order. The spherical aberration results in an increase of the beam quality factor of flat-topped beams. The relative errors of the waist width at the real focal plane depend on the sign of the spherical aberration coefficient, whereas the relative errors of the
Using the second-order-moment and entropy-based definitions of the beam width, changes of the beam parameters including beam width, far-field divergence angle and beam quality factor of flat-topped beams passing through a spherically aberrated lens are studied. It is shown that the spherical aberration affects the beam parameters in the image space. The relative errors of the beam width and far-field divergence angle introduced by the spherical aberration increase with increasing spherical aberration coefficient and decreasing beam order. The spherical aberration results in an increase of the beam quality factor of flat-topped beams. The relative errors of the waist width at the real focal plane depend on the sign of the spherical aberration coefficient, whereas the relative errors of the
2007,
19.
Abstract:
The influence of resonator aberration upon the laser output mode is analyzed and simulated with Fox-Li method. The aberration is expanded by Zernike polynomials, and laser self-reproducing low-order modes upon aberrations with different Fresnel number has been calculated. The mirror surface is also fitted by Zernike polynomials and the influence function of the central actuator is calculated. At the same time the control model of the mirror is established. Compensation of laser output mode was validated by experiment using the deformable mirror as an end mirror of the laser resonator, an output with mostly TEM00 mode was got by the deformable mirror compensation.
The influence of resonator aberration upon the laser output mode is analyzed and simulated with Fox-Li method. The aberration is expanded by Zernike polynomials, and laser self-reproducing low-order modes upon aberrations with different Fresnel number has been calculated. The mirror surface is also fitted by Zernike polynomials and the influence function of the central actuator is calculated. At the same time the control model of the mirror is established. Compensation of laser output mode was validated by experiment using the deformable mirror as an end mirror of the laser resonator, an output with mostly TEM00 mode was got by the deformable mirror compensation.
2007,
19.
Abstract:
The theoretical model of spectral beam combining of fiber lasers is presented. It includes a fiber laser array, a lens and a diffraction grating. Based on the conversion and diffraction theories of Gaussian beam, far-field optical intensity expression is derived, and the systemic parameters are optimized. Numerical results show that diffraction efficiency can be improved by overlapping the negative first-order interference principal maximum and the zeroth-order diffraction maximum of the central-wavelength-laser, overlapping the zeroth-order interference principal maximum and the first-order diffraction minima of the central-wavelength-laser, and overlapping the negative first-order interference principal maximums of other lasers and the zeroth-order diffraction maximum of the central-wave
The theoretical model of spectral beam combining of fiber lasers is presented. It includes a fiber laser array, a lens and a diffraction grating. Based on the conversion and diffraction theories of Gaussian beam, far-field optical intensity expression is derived, and the systemic parameters are optimized. Numerical results show that diffraction efficiency can be improved by overlapping the negative first-order interference principal maximum and the zeroth-order diffraction maximum of the central-wavelength-laser, overlapping the zeroth-order interference principal maximum and the first-order diffraction minima of the central-wavelength-laser, and overlapping the negative first-order interference principal maximums of other lasers and the zeroth-order diffraction maximum of the central-wave
2007,
19.
Abstract:
Based on the propagation theory of partially coherent beam, the axial light intensity distribution of partially coherent flattened Gaussian beam(PCFGB) focused by a lens with spherical aberration(SA) is studied. Simulation results show that, when SA changes from negative to positive, the best focal point moves towards the geometrical focus and even exceeds it. The larger order of the PCFGB, the smaller the positive SA of causing the best focal point to exceed the geometrical focus. The best focal points corresponding to positive and negative SAs always locate at the two sides of the focus for no-SA cases, respectively. Light intensity the of axial best focus decreases while SA changes from negative to positive. Light intensity of the axial best focal point changes sharply when SA approache
Based on the propagation theory of partially coherent beam, the axial light intensity distribution of partially coherent flattened Gaussian beam(PCFGB) focused by a lens with spherical aberration(SA) is studied. Simulation results show that, when SA changes from negative to positive, the best focal point moves towards the geometrical focus and even exceeds it. The larger order of the PCFGB, the smaller the positive SA of causing the best focal point to exceed the geometrical focus. The best focal points corresponding to positive and negative SAs always locate at the two sides of the focus for no-SA cases, respectively. Light intensity the of axial best focus decreases while SA changes from negative to positive. Light intensity of the axial best focal point changes sharply when SA approache
2007,
19.
Abstract:
Elementary theoretical investigation on self-organized fiber laser array was carried out in this paper. The simplest case for the fiber laser array, i.e., the phase-locking course of two fiber lasers was modeled and analyzed theoretically and numerically. The effect of detuning frequency and coupling coefficient to the phase-locking course was analyzed. For the case that there was no frequency detuning, the array was always in out-of-phase mode. Otherwise, the condition of frequency detuning for phase locking was deduced, and the method for weakening the condition was analyzed in short.
Elementary theoretical investigation on self-organized fiber laser array was carried out in this paper. The simplest case for the fiber laser array, i.e., the phase-locking course of two fiber lasers was modeled and analyzed theoretically and numerically. The effect of detuning frequency and coupling coefficient to the phase-locking course was analyzed. For the case that there was no frequency detuning, the array was always in out-of-phase mode. Otherwise, the condition of frequency detuning for phase locking was deduced, and the method for weakening the condition was analyzed in short.
2007,
19.
Abstract:
Laser pre-treatment is an efficient means to increase damagethresholds of optics. In order to validate the effect of laser pre-treatment on pickoff optics and study its value in engineering application, 1 064 nm YLF laser was used to raster scan pickoff optics with high reflection physics multilayer coating by means of power increase by degrees periodicity. The result was that zero probability damage-thresholds increased 38.8% and 50% probability damage-thresholds increased 7.6%, damage resistance of pickoff optics was evidently enhanced through pre-treatment.
Laser pre-treatment is an efficient means to increase damagethresholds of optics. In order to validate the effect of laser pre-treatment on pickoff optics and study its value in engineering application, 1 064 nm YLF laser was used to raster scan pickoff optics with high reflection physics multilayer coating by means of power increase by degrees periodicity. The result was that zero probability damage-thresholds increased 38.8% and 50% probability damage-thresholds increased 7.6%, damage resistance of pickoff optics was evidently enhanced through pre-treatment.
2007,
19.
Abstract:
The conductivity of the plasma channel are shown in detail by electrical detecting method on the conditions of different focal lengths, different laser energies and polarities of the external voltage. The experimental results show that there are long ionization channels after lens with different focal length. The equivalent resistivity of the channels change slightly, and usually the maximum value of resistivity appears near the geometric focal point. If the focal length is longer, the peak point would get closer to the geometry focal point. With voltage of different polarity, the electrostatic field force and Lorentz force as well as the ponderomotive force will together change the current of plasma channel. In front of the focal point, the variation of the current is not obvious, and the
The conductivity of the plasma channel are shown in detail by electrical detecting method on the conditions of different focal lengths, different laser energies and polarities of the external voltage. The experimental results show that there are long ionization channels after lens with different focal length. The equivalent resistivity of the channels change slightly, and usually the maximum value of resistivity appears near the geometric focal point. If the focal length is longer, the peak point would get closer to the geometry focal point. With voltage of different polarity, the electrostatic field force and Lorentz force as well as the ponderomotive force will together change the current of plasma channel. In front of the focal point, the variation of the current is not obvious, and the
2007,
19.
Abstract:
The laser energy is one of the key characteristics of Beijing Free Electron Laser(BFEL) facility. This paper calculated the gain and the laser energy of BFEL with a steady-state code and a time-dependent code. The calculation shows that by adopting suitable measures such as decreasing the emittance of the electron beam from 50 pmm·mrad to 30 pmm·mrad, the small signal gain of BFEL will grow from 16% to 28%, and the laser energy will increase approximately one order.
The laser energy is one of the key characteristics of Beijing Free Electron Laser(BFEL) facility. This paper calculated the gain and the laser energy of BFEL with a steady-state code and a time-dependent code. The calculation shows that by adopting suitable measures such as decreasing the emittance of the electron beam from 50 pmm·mrad to 30 pmm·mrad, the small signal gain of BFEL will grow from 16% to 28%, and the laser energy will increase approximately one order.
2007,
19.
Abstract:
On the Shenguang-Ⅱ high power laser facility, temporal- and spatial-resolved experimental records of light emitting from heating luminescence at the rear surface of step samples were obtained by an optical streak camera. The velocity and planarity of the shock wave were measured. The radiation temperature measured by soft X-ray spectrometer was consistent with the result by optical streak camera. The results indicated that the radiation temperature was about 160 eV in a high Z cylindrical hohlraum which was irradiated by eight laser pulses with 260 J energy each, the length of the shock wave with a better planarity was 288 mm, the velocity was 3.15×106 cm/s and the pressure of the shock wave was 1.66×1012 Pa.
On the Shenguang-Ⅱ high power laser facility, temporal- and spatial-resolved experimental records of light emitting from heating luminescence at the rear surface of step samples were obtained by an optical streak camera. The velocity and planarity of the shock wave were measured. The radiation temperature measured by soft X-ray spectrometer was consistent with the result by optical streak camera. The results indicated that the radiation temperature was about 160 eV in a high Z cylindrical hohlraum which was irradiated by eight laser pulses with 260 J energy each, the length of the shock wave with a better planarity was 288 mm, the velocity was 3.15×106 cm/s and the pressure of the shock wave was 1.66×1012 Pa.
2007,
19.
Abstract:
The spatial refractive index distribution of typical rapid-growth(RG) crystals and conventional-growth(CG) crystals were obtained with orthogonal polarization interferometry. By numerical simulation, the influence of crystal refractive-index non-uniformities on 3w conversion efficiency was also conducted for a fixed doubler detuning angle of 0 and 220 mrad respectively. The results show that the RMS refractive index uniformities error of RG crystals is about sixfold compared with that of CG crystals, and 3w conversion efficiency is insensitive to refractive-index non-uniformities when 1w irradiance was low, however, it is sensitive around the inflexion point. The refractive index variation of a doubler contributes more to the degrading of 3w conversion efficiency than that of a tripler, on
The spatial refractive index distribution of typical rapid-growth(RG) crystals and conventional-growth(CG) crystals were obtained with orthogonal polarization interferometry. By numerical simulation, the influence of crystal refractive-index non-uniformities on 3w conversion efficiency was also conducted for a fixed doubler detuning angle of 0 and 220 mrad respectively. The results show that the RMS refractive index uniformities error of RG crystals is about sixfold compared with that of CG crystals, and 3w conversion efficiency is insensitive to refractive-index non-uniformities when 1w irradiance was low, however, it is sensitive around the inflexion point. The refractive index variation of a doubler contributes more to the degrading of 3w conversion efficiency than that of a tripler, on
2007,
19.
Abstract:
Effects of sulfate doping on the growth and properties of KDP crystals were studied by “point seed”growth meth. The results show that this kind of impurity with low content sulfate anion has no obvious effect on the growth of KDP-type crystals. The structure of KDP crystals is little affected by this kind of impurity when the content of sulfate anion is 50×10－6．Optical properties comparison between the doped KDP crystal and the pure KDP crystal proves that sulfate doping has no evident effect on KDP’s transition, homogeneity but it decreases the laser damage threshold (LDT).
Effects of sulfate doping on the growth and properties of KDP crystals were studied by “point seed”growth meth. The results show that this kind of impurity with low content sulfate anion has no obvious effect on the growth of KDP-type crystals. The structure of KDP crystals is little affected by this kind of impurity when the content of sulfate anion is 50×10－6．Optical properties comparison between the doped KDP crystal and the pure KDP crystal proves that sulfate doping has no evident effect on KDP’s transition, homogeneity but it decreases the laser damage threshold (LDT).
2007,
19.
Abstract:
Magnetic ICF targets were prepared by electroless plating technology. The morphology, composition, structure and magnetic property of the magnetic ICF targets were analyzed by scanning electron microscopy, energy diffraction spectrum, X-ray diffraction and vibrating sample magnetometer. The results show that the magnetic plating is composed of Ni and P, the content of P in plating is about 7.6%, the structure of Ni-P magnetic plating is 4 μm or so, and the structure of the plated ICF targets is amorphous. The plated ICF targets can be used in magnetic suspension experiment. Furthermore, mechanism of electroless plating on ICF targets is discussed.
Magnetic ICF targets were prepared by electroless plating technology. The morphology, composition, structure and magnetic property of the magnetic ICF targets were analyzed by scanning electron microscopy, energy diffraction spectrum, X-ray diffraction and vibrating sample magnetometer. The results show that the magnetic plating is composed of Ni and P, the content of P in plating is about 7.6%, the structure of Ni-P magnetic plating is 4 μm or so, and the structure of the plated ICF targets is amorphous. The plated ICF targets can be used in magnetic suspension experiment. Furthermore, mechanism of electroless plating on ICF targets is discussed.
2007,
19.
Abstract:
The spatial distributions were explored in the laser-induced air plasmas for clearer understanding of the micromechanism. A column of plasmas were formed by focusing Nd:YAG laser beam at 1.06 μm (energy is about 500 mJ/pulse, pulse width 10 ns,and frequency 30 Hz ). The column was about 8 cm long and 5 cm in diameter. The spectra of the column in different position have been detected from vertical and parallel direction of laser beam respectively. From these data, the electron densities and the electron temperature distributions in the laser-induced air plasmas can be estimated. The experimental results indicate that the laser-induced air plasma exists in the shape of a tear drop, symmetrical in the vertical direction but not symmetrical in the horizontal direction. The largest electron d
The spatial distributions were explored in the laser-induced air plasmas for clearer understanding of the micromechanism. A column of plasmas were formed by focusing Nd:YAG laser beam at 1.06 μm (energy is about 500 mJ/pulse, pulse width 10 ns,and frequency 30 Hz ). The column was about 8 cm long and 5 cm in diameter. The spectra of the column in different position have been detected from vertical and parallel direction of laser beam respectively. From these data, the electron densities and the electron temperature distributions in the laser-induced air plasmas can be estimated. The experimental results indicate that the laser-induced air plasma exists in the shape of a tear drop, symmetrical in the vertical direction but not symmetrical in the horizontal direction. The largest electron d
2007,
19.
Abstract:
A series of Mo/Si multilayers were prepared by magnetron sputtering, with top layers being Mo layer and Si layer respectively. Periodic length of Mo/Si multilayers were determined by small angle X-ray diffraction. As fresh surfaces of Mo/Si multilayers with different period number were approximatively equal to the interface of the same multilayer, interface roughness change law of multilayers as layer number increases was studied by atomic force microscope. Soft X-ray reflectivity of Mo/Si multilayers were measured in National Synchrotron Radiation Laboratory. As the number of layers increases, interface roughness and peak reflectivity of multilayers first increase and then reduce．
A series of Mo/Si multilayers were prepared by magnetron sputtering, with top layers being Mo layer and Si layer respectively. Periodic length of Mo/Si multilayers were determined by small angle X-ray diffraction. As fresh surfaces of Mo/Si multilayers with different period number were approximatively equal to the interface of the same multilayer, interface roughness change law of multilayers as layer number increases was studied by atomic force microscope. Soft X-ray reflectivity of Mo/Si multilayers were measured in National Synchrotron Radiation Laboratory. As the number of layers increases, interface roughness and peak reflectivity of multilayers first increase and then reduce．
2007,
19.
Abstract:
Silica antireflective coatings with vacuum organic contamination resistant property were prepared by sol-gel method along with ammonia post-treatment. The peak transmittance of such a coating was approximately 100%. Exposing the coating to a vacuum of 10-3 Pa with silicone oil for one week, the transmittance showed little change. However, the peak transmittance of the coating without ammonia post-treatment decreased from 100% to 95.5% under the same condition. The properties of the coatings were analyzed by spectrophotometry, FTIR-spectroscopy, scanning probe microscope method, contact angle measurement, and spectroscopic ellipsometry.
Silica antireflective coatings with vacuum organic contamination resistant property were prepared by sol-gel method along with ammonia post-treatment. The peak transmittance of such a coating was approximately 100%. Exposing the coating to a vacuum of 10-3 Pa with silicone oil for one week, the transmittance showed little change. However, the peak transmittance of the coating without ammonia post-treatment decreased from 100% to 95.5% under the same condition. The properties of the coatings were analyzed by spectrophotometry, FTIR-spectroscopy, scanning probe microscope method, contact angle measurement, and spectroscopic ellipsometry.
2007,
19.
Abstract:
Multi-keV X-ray sources generated by irradiating thick solid target with a 2 ns-duration laser pulse are investigated on Shenguang Ⅱ laser facility. With the long laser pulse, the significant three-dimensional expansion of the plasma leads to that the longitudinal scale length of the X-ray emission region is finally determined by the laser spot size and the emission volume is proportional to the third power of the laser spot size. Theoretical analysis shows that X-ray flux can be enhanced by increasing the laser spot size because in the steady state the X-ray flux is proportional to the five-third power of the laser sopt size under the same laser power. The scaling law is in good agreement with the experimental data. It is also shown that short wavelength laser is suitable for the multi-k
Multi-keV X-ray sources generated by irradiating thick solid target with a 2 ns-duration laser pulse are investigated on Shenguang Ⅱ laser facility. With the long laser pulse, the significant three-dimensional expansion of the plasma leads to that the longitudinal scale length of the X-ray emission region is finally determined by the laser spot size and the emission volume is proportional to the third power of the laser spot size. Theoretical analysis shows that X-ray flux can be enhanced by increasing the laser spot size because in the steady state the X-ray flux is proportional to the five-third power of the laser sopt size under the same laser power. The scaling law is in good agreement with the experimental data. It is also shown that short wavelength laser is suitable for the multi-k
2007,
19.
Abstract:
In the 9th laser system of SGⅡ inertial confinement fusion(ICF) facility, tunable Fabry-Perot(F-P) filter is adopted to compensate the FM-AM(frequency modulation-amplitude modulation) effect, according to the technical requirements of compensation device, a precise displacement monitor system using the capacitive displacement sensor with nanometer scale precision to stabilize the spacing of the tunable F-P filter is proposed firstly，then the basic structure and operating principle of the monitor system are analyzed. The design scheme of the driving circuit for capacitive displacement sensor and the data processing as well as the system controlling software are discussed, and the precision of capacitive displacement sensor is calibrated. The experimental results show that the spacing stab
In the 9th laser system of SGⅡ inertial confinement fusion(ICF) facility, tunable Fabry-Perot(F-P) filter is adopted to compensate the FM-AM(frequency modulation-amplitude modulation) effect, according to the technical requirements of compensation device, a precise displacement monitor system using the capacitive displacement sensor with nanometer scale precision to stabilize the spacing of the tunable F-P filter is proposed firstly，then the basic structure and operating principle of the monitor system are analyzed. The design scheme of the driving circuit for capacitive displacement sensor and the data processing as well as the system controlling software are discussed, and the precision of capacitive displacement sensor is calibrated. The experimental results show that the spacing stab
2007,
19.
Abstract:
An accurate evaluation of the growth rate of the Rayleigh-Taylor(RT)instability is a critical issue for inertial confinement fusion. This paper uses the face-on radiography technology to investigate the Rayleigh-Taylor instability of sine modulated surface target at the Shengguang Ⅱ facility and gains vivid space and time resolution images. The experimental results are analyzed by two methods, i.e., figuring out fundamental mode Fourier coefficient and figuring out the D-value of wave crest and wave hollow. The two methods obtain the same perturbation growth factor. Moreover, this paper presents possible reasons for the little growth with a qualitative interpretation, i.e., the density gradient stabilization and ablative stabilization suppress the perturbation growth, or the perturbation
An accurate evaluation of the growth rate of the Rayleigh-Taylor(RT)instability is a critical issue for inertial confinement fusion. This paper uses the face-on radiography technology to investigate the Rayleigh-Taylor instability of sine modulated surface target at the Shengguang Ⅱ facility and gains vivid space and time resolution images. The experimental results are analyzed by two methods, i.e., figuring out fundamental mode Fourier coefficient and figuring out the D-value of wave crest and wave hollow. The two methods obtain the same perturbation growth factor. Moreover, this paper presents possible reasons for the little growth with a qualitative interpretation, i.e., the density gradient stabilization and ablative stabilization suppress the perturbation growth, or the perturbation
2007,
19.
Abstract:
The guided-mode resonance effect of the compressed grating is studied. The characteristic matrix method and the coupled-wave method are used to calculate the eigenvalues of the stack structure and the grating structure. The precondition of this effect in the dielectric compressed grating has been analyzed. The diffractive efficiency near the grating is calculated. To avoid the disadvantage of the guided-mode resonance effect, the grating periods should be 0.667 μm and the depth should be 0.6 μm.
The guided-mode resonance effect of the compressed grating is studied. The characteristic matrix method and the coupled-wave method are used to calculate the eigenvalues of the stack structure and the grating structure. The precondition of this effect in the dielectric compressed grating has been analyzed. The diffractive efficiency near the grating is calculated. To avoid the disadvantage of the guided-mode resonance effect, the grating periods should be 0.667 μm and the depth should be 0.6 μm.
2007,
19.
Abstract:
THz wave radiation induced by femtosecond pulse in periodically poled nonlinear crystal is theoretically studied based on optical rectification. Using the principle of the antenna radiation and the theory of the grating diffraction, the study focuses on the distribution of the field of the frequency domain and the field of the time domain. The center frequency, the width of the spectrum and the electronic field of the THz wave are discussed and analyzed varying with the radiation angle. The result of the study shows that the bandwidth of the THz wave is inversly proportional to the length of the crystal and the number of the grating, and that the electronic field varying with the radiation angle is quasi-harmonic.
THz wave radiation induced by femtosecond pulse in periodically poled nonlinear crystal is theoretically studied based on optical rectification. Using the principle of the antenna radiation and the theory of the grating diffraction, the study focuses on the distribution of the field of the frequency domain and the field of the time domain. The center frequency, the width of the spectrum and the electronic field of the THz wave are discussed and analyzed varying with the radiation angle. The result of the study shows that the bandwidth of the THz wave is inversly proportional to the length of the crystal and the number of the grating, and that the electronic field varying with the radiation angle is quasi-harmonic.
2007,
19.
Abstract:
Coaxial inserting fin phase shifter is a new kind of high power microwave phase shifter. Based on the fundamental working principle of coaxial inserting fin phase shifter, numerical simulation and optimization design are presented and its structure and control system are discussed. A coaxial-inserting-fin phase shifter model with a central frequency of 4.1 GHz is designed and fabricated. Experiment has been carried out with the vector network analyzer, which shows that in the range of 4.0~4.2 GHz, the phase shifter can realize a phase shift of 90°, phase shift precision realizable can be 1° and phase shift precision is ±10°, the insertion loss of this phase shifter is over 1.5 dB．
Coaxial inserting fin phase shifter is a new kind of high power microwave phase shifter. Based on the fundamental working principle of coaxial inserting fin phase shifter, numerical simulation and optimization design are presented and its structure and control system are discussed. A coaxial-inserting-fin phase shifter model with a central frequency of 4.1 GHz is designed and fabricated. Experiment has been carried out with the vector network analyzer, which shows that in the range of 4.0~4.2 GHz, the phase shifter can realize a phase shift of 90°, phase shift precision realizable can be 1° and phase shift precision is ±10°, the insertion loss of this phase shifter is over 1.5 dB．
2007,
19.
Abstract:
This paper analyzes the equivalent current method in FDTD for excitation source design. The method is based on the method for avoiding the unwanted non-physical scattering fields in computational electromagnetics. It excites electromagnetic fields by introducing equivalent electric or magnetic current into FDTD formulae. The analysis of the excitation source technology in PIC simulation and the formulae of the new method are also provided. According to the theoretical analysis, the new method has a compact form and can be easily introduced into FDTD formulae for numerical realization. According to the numerical validation, the new method needn’t set an addisional scattering field region for scattering field calculation specially, and it has more than 20% higher efficiency and obvious lowe
This paper analyzes the equivalent current method in FDTD for excitation source design. The method is based on the method for avoiding the unwanted non-physical scattering fields in computational electromagnetics. It excites electromagnetic fields by introducing equivalent electric or magnetic current into FDTD formulae. The analysis of the excitation source technology in PIC simulation and the formulae of the new method are also provided. According to the theoretical analysis, the new method has a compact form and can be easily introduced into FDTD formulae for numerical realization. According to the numerical validation, the new method needn’t set an addisional scattering field region for scattering field calculation specially, and it has more than 20% higher efficiency and obvious lowe
2007,
19.
Abstract:
Plasma filling has been widely used as an effective method to improve the performance of Cerenkov devices. In the process of designing a hard-tube MILO, we found that it might improve the output power largely without obvious pulse shortening at a low vacuum range of 0.01~2 Pa, which had not been reported on MILO previously. Experimental method associated with PIC simulation was adopted to investigate the performance of an L band ladder cathode MILO at low vacuum levels. The result tells that the MILO could work better at low vacuum levels.
Plasma filling has been widely used as an effective method to improve the performance of Cerenkov devices. In the process of designing a hard-tube MILO, we found that it might improve the output power largely without obvious pulse shortening at a low vacuum range of 0.01~2 Pa, which had not been reported on MILO previously. Experimental method associated with PIC simulation was adopted to investigate the performance of an L band ladder cathode MILO at low vacuum levels. The result tells that the MILO could work better at low vacuum levels.
2007,
19.
Abstract:
A waveguide twist for 9 GHz klystron power combining output structure has been designed in the paper, which is used to connect klystron power combiner and output cavity. The waveguide twist is composed of a rectangular resonator, two rectangular coupling slots and two waveguides. The two waveguides which serve as input and output work in rectangular TE10 and TE01 modes respectively and they offset from the center while perpendicular to each other. The rectangular resonator in the center works in the combined modes of TM110, TE101 and TE011. Optimization result shows that this waveguide twist has three reflection zeros forming a large passband. Finally, a klystron output cavity was loaded by a power combiner with the designed waveguide twist. The calculation result of its gap impedance show
A waveguide twist for 9 GHz klystron power combining output structure has been designed in the paper, which is used to connect klystron power combiner and output cavity. The waveguide twist is composed of a rectangular resonator, two rectangular coupling slots and two waveguides. The two waveguides which serve as input and output work in rectangular TE10 and TE01 modes respectively and they offset from the center while perpendicular to each other. The rectangular resonator in the center works in the combined modes of TM110, TE101 and TE011. Optimization result shows that this waveguide twist has three reflection zeros forming a large passband. Finally, a klystron output cavity was loaded by a power combiner with the designed waveguide twist. The calculation result of its gap impedance show
2007,
19.
Abstract:
A theoretical investigation of the principle of self-focusing and defocusing of narrow radio beam in lower ionosphere was presented. Nonlinear propagation equation, focusing parameter and defocusing parameter are deduced, which are used to analyze the microwave beam’s width when propagating in lower ionosphere. Finally, the influence of frequency and microwave power on the final beam width is discussed. Results show that the lower ionosphere is mainly a defocusing material that will greatly reduce the microwave energy arriving at the destination, especially when the frequency is low and the radiating energy is high. But with frequency higher than several GHz, the defocusing is so weak that it can be ignored.
A theoretical investigation of the principle of self-focusing and defocusing of narrow radio beam in lower ionosphere was presented. Nonlinear propagation equation, focusing parameter and defocusing parameter are deduced, which are used to analyze the microwave beam’s width when propagating in lower ionosphere. Finally, the influence of frequency and microwave power on the final beam width is discussed. Results show that the lower ionosphere is mainly a defocusing material that will greatly reduce the microwave energy arriving at the destination, especially when the frequency is low and the radiating energy is high. But with frequency higher than several GHz, the defocusing is so weak that it can be ignored.
2007,
19.
Abstract:
2.5 dimensional(2.5 D) particle in cell simulation code MAGIC and 3 D electromagnetic simulation code HFSS were used to investigate the helix traveling wave tube(TWT) with positively negatively tapered structure for efficiency enhancement. Some key parameters to efficiency were analyzed, including high frequency parameter, non synchronous parameter, gain parameter and electron phase. A positively negatively tapered helix TWT were designed and fabricated. The results show that the measured efficiency of the tapered TWT reaches 29%, while that of the non tapered TWT is 19%. It shows the average relative error of the simulation method is about 5%．
2.5 dimensional(2.5 D) particle in cell simulation code MAGIC and 3 D electromagnetic simulation code HFSS were used to investigate the helix traveling wave tube(TWT) with positively negatively tapered structure for efficiency enhancement. Some key parameters to efficiency were analyzed, including high frequency parameter, non synchronous parameter, gain parameter and electron phase. A positively negatively tapered helix TWT were designed and fabricated. The results show that the measured efficiency of the tapered TWT reaches 29%, while that of the non tapered TWT is 19%. It shows the average relative error of the simulation method is about 5%．
2007,
19.
Abstract:
A ladder cathode L-band MILO is experimentally investigated. The measurement methods and measurement system are introduced. The proper cathode material is selected and the cathode emission of electrons is investigated, then one of the key factors is obtained, which results in an asymmetric microwave mode generated by symmetric MILO. Additionally, other factors are also investigated, which can affect the output microwave power such as the dimension of the diode shelter, the diameter of the choke vanes, the extraction gap, and so on. After experimental investigation, employing an electron beam of about 420 kV and 33 kA, ladder cathode L-band MILO generates 1.22~1.47 GW of high power microwave with over 20 ns of pulse duration at 1.21 GHz. The conversion efficiency between electrons and micro
A ladder cathode L-band MILO is experimentally investigated. The measurement methods and measurement system are introduced. The proper cathode material is selected and the cathode emission of electrons is investigated, then one of the key factors is obtained, which results in an asymmetric microwave mode generated by symmetric MILO. Additionally, other factors are also investigated, which can affect the output microwave power such as the dimension of the diode shelter, the diameter of the choke vanes, the extraction gap, and so on. After experimental investigation, employing an electron beam of about 420 kV and 33 kA, ladder cathode L-band MILO generates 1.22~1.47 GW of high power microwave with over 20 ns of pulse duration at 1.21 GHz. The conversion efficiency between electrons and micro
2007,
19.
Abstract:
A large power matching load with a resistance of 20 W was developed. It has been applied to modulating the high current electron beam accelerator based on water-dielectric spiral pulse forming line. When the resistance of the PFL matches the load(which is fixed in a diode), fairly good voltage and current waveforms of the load are obtained: the amplitude of the voltage is 200 kV, the current is 9 kA and the FWHM is 150 ns. According to the parameter of the matching load, the inductance of 2.12×10-8 H and capacitance of 4.51×10-10 F are calculated theoretically. In addition, the process of a square voltage wave feeding the matching load is simulated by Pspice and the distribution of static electric field of the matching load is simulated by ANSYS. The theoretical analysis agrees well wit
A large power matching load with a resistance of 20 W was developed. It has been applied to modulating the high current electron beam accelerator based on water-dielectric spiral pulse forming line. When the resistance of the PFL matches the load(which is fixed in a diode), fairly good voltage and current waveforms of the load are obtained: the amplitude of the voltage is 200 kV, the current is 9 kA and the FWHM is 150 ns. According to the parameter of the matching load, the inductance of 2.12×10-8 H and capacitance of 4.51×10-10 F are calculated theoretically. In addition, the process of a square voltage wave feeding the matching load is simulated by Pspice and the distribution of static electric field of the matching load is simulated by ANSYS. The theoretical analysis agrees well wit
2007,
19.
Abstract:
A D-dot monitor was designed to measure the voltage of Yang accelerator water transmission line. A signal proportional to the time derivative of the voltage was given with capacitor from high voltage electrode to the probe and the voltage was given with the RC integrator. The parameters (inductance and capacitance) were estimated using the transient analysis of OrCAD/Pspice and the amplitude-frequency response of the monitor was analyzed. The result of measurement can be explained using the analysis. The monitor was calibrated in-situ with resistive divider while accelerator was short-circuit at lower Marx-bank charge voltages. The experimental result indicates that the designed D-dot monitor is satisfactory to the measurement requirement.
A D-dot monitor was designed to measure the voltage of Yang accelerator water transmission line. A signal proportional to the time derivative of the voltage was given with capacitor from high voltage electrode to the probe and the voltage was given with the RC integrator. The parameters (inductance and capacitance) were estimated using the transient analysis of OrCAD/Pspice and the amplitude-frequency response of the monitor was analyzed. The result of measurement can be explained using the analysis. The monitor was calibrated in-situ with resistive divider while accelerator was short-circuit at lower Marx-bank charge voltages. The experimental result indicates that the designed D-dot monitor is satisfactory to the measurement requirement.
2007,
19.
Abstract:
Equilateral-triangle configuration iron core with secondary coil divided into 40 stages, each stage is three-phase full-wave rectified and outputs 30 kV in the design of high power high voltage DC generator, which in series output 1.2 MV/A with energy efficiency of 95% and leakage impedance of 21.7%. Configuration of none-filter capacitance and starlike/trangular connection mode were applied with ripple factor less than ±4%. The whole generator was encapsulated in a steel cylinder filled with highly purified SF6 gas as insulation medium at pressure 0.8 MPa and maximum electric field less than 130 kV/cm, with special cooling system and operating temperature of SF6 controlled less than 60 ℃. Gas-filled coaxial transmission line structure was adopted for high voltage output. All the technic
Equilateral-triangle configuration iron core with secondary coil divided into 40 stages, each stage is three-phase full-wave rectified and outputs 30 kV in the design of high power high voltage DC generator, which in series output 1.2 MV/A with energy efficiency of 95% and leakage impedance of 21.7%. Configuration of none-filter capacitance and starlike/trangular connection mode were applied with ripple factor less than ±4%. The whole generator was encapsulated in a steel cylinder filled with highly purified SF6 gas as insulation medium at pressure 0.8 MPa and maximum electric field less than 130 kV/cm, with special cooling system and operating temperature of SF6 controlled less than 60 ℃. Gas-filled coaxial transmission line structure was adopted for high voltage output. All the technic
2007,
19.
Abstract:
The experiment of deuterium fiber neutron emission was carried out on Qiangguang-Ⅰ facility. The DD neutron measurement device has two scintillator detectors. The experiment shows that measurement of neutron signal could be influenced by quite strong concomitant hard X-ray during the emission of neutrons. An effective shielding system was established for eliminating disturbance and for protecting the detectors from hard X-ray in aluminum array Z-pinch experiment.The emission of DD neutrons was confirmed by time-of-flight method in shot 4172, which resulted in a neutron yield of about 109 and neutron energy of about(2.45±0.26) MeV.
The experiment of deuterium fiber neutron emission was carried out on Qiangguang-Ⅰ facility. The DD neutron measurement device has two scintillator detectors. The experiment shows that measurement of neutron signal could be influenced by quite strong concomitant hard X-ray during the emission of neutrons. An effective shielding system was established for eliminating disturbance and for protecting the detectors from hard X-ray in aluminum array Z-pinch experiment.The emission of DD neutrons was confirmed by time-of-flight method in shot 4172, which resulted in a neutron yield of about 109 and neutron energy of about(2.45±0.26) MeV.
2007,
19.
Abstract:
The surface of 316L stainless steel was treated by high-intensity pulsed ion beams(HIPIB). The influence of the HIPIB irradiation on the electrochemical corrosion resistance of 316L stainless steel in 0.5 mol/L H2SO4 was investigated. The polarization curves show that the corrosion resistance of the irradiated specimens can be improved markedly, and the free corrosion current depends more on the shot number of HIPIB than the free corrosion potential. The surface morphology and the phase structure in the near surface region of the original and the treated specimens were analyzed with scanning electron microscopy and X-ray diffraction. Electron probe microanalysis was used to study the distribution of elements on the irradiated specimens. It is found that the HIPIB irradiation can smooth the
The surface of 316L stainless steel was treated by high-intensity pulsed ion beams(HIPIB). The influence of the HIPIB irradiation on the electrochemical corrosion resistance of 316L stainless steel in 0.5 mol/L H2SO4 was investigated. The polarization curves show that the corrosion resistance of the irradiated specimens can be improved markedly, and the free corrosion current depends more on the shot number of HIPIB than the free corrosion potential. The surface morphology and the phase structure in the near surface region of the original and the treated specimens were analyzed with scanning electron microscopy and X-ray diffraction. Electron probe microanalysis was used to study the distribution of elements on the irradiated specimens. It is found that the HIPIB irradiation can smooth the
2007,
19.
Abstract:
The properties of surface waves along the single-negative slab waveguide are analyzed in this paper. According to the eigen equations, the graphical-solution technique is used to get dispersion curves profiles and energy flux distribution profiles of odd and even symmetric TM surface modes which propagate along the epsilon-negative slab. It is found that surface waves propagate along the single-negative slab more slower than that along the double-positive or double-negative slab waveguide; Field and energy are confined on the top and bottom surfaces; Energy fluxes of odd and even symmetric surface waves have opposite directions in a certain frequency range. It is proposed that a power divider and a directional coupler can be constructed by a single single-negative slab. This simplifies the
The properties of surface waves along the single-negative slab waveguide are analyzed in this paper. According to the eigen equations, the graphical-solution technique is used to get dispersion curves profiles and energy flux distribution profiles of odd and even symmetric TM surface modes which propagate along the epsilon-negative slab. It is found that surface waves propagate along the single-negative slab more slower than that along the double-positive or double-negative slab waveguide; Field and energy are confined on the top and bottom surfaces; Energy fluxes of odd and even symmetric surface waves have opposite directions in a certain frequency range. It is proposed that a power divider and a directional coupler can be constructed by a single single-negative slab. This simplifies the
2007,
19.
Abstract:
The highly stripped ions of C4+, N5+, and S6+ were produced when 1 064 nm laser with an intensity of 1011 W·cm-2 was used to irradiate the molecular beam of benzene, ammonia and sulfide hydrogen. The ratio of the produced multiply charged ions to the total ion signals decreased scarcely as the laser intensity decreased by almost two magnitudes. When 532 nm laser was used, the main ion products turned to be C2+, C3+, N2+, N3+, S4+, S3+ and S2+ with lower charge states. While when 266 nm laser was used, no multiply charged ions were detected. The highly charged ions are speculated to arise from the electron impact ionization process in the cluster. The initial electrons are produced by multiphoton ionization and then heated by inverse bremsstrahlung, where the heating rates scale with the
The highly stripped ions of C4+, N5+, and S6+ were produced when 1 064 nm laser with an intensity of 1011 W·cm-2 was used to irradiate the molecular beam of benzene, ammonia and sulfide hydrogen. The ratio of the produced multiply charged ions to the total ion signals decreased scarcely as the laser intensity decreased by almost two magnitudes. When 532 nm laser was used, the main ion products turned to be C2+, C3+, N2+, N3+, S4+, S3+ and S2+ with lower charge states. While when 266 nm laser was used, no multiply charged ions were detected. The highly charged ions are speculated to arise from the electron impact ionization process in the cluster. The initial electrons are produced by multiphoton ionization and then heated by inverse bremsstrahlung, where the heating rates scale with the
2007,
19.
Abstract:
CO is known as one of the main gas for Pd alloy membrane poisoning during hydrogen permeation.A scheme is put forward to reduce CO adsorption on Pd alloy membrane by modifying the CO molecular orientation. On this basis, two structures of different molecular orientation on Pd(111) surface at 0.75 coverage of monolayer have been calculated using density functional theory.It is found that the structure with carbon near Pd(111) surface is stable while the structure with oxygen is quite difficult, therefore, controlling the orientation of CO molecule adsorbed on Pd surface may be effective to inhibit CO adsorption on Pd surface.
CO is known as one of the main gas for Pd alloy membrane poisoning during hydrogen permeation.A scheme is put forward to reduce CO adsorption on Pd alloy membrane by modifying the CO molecular orientation. On this basis, two structures of different molecular orientation on Pd(111) surface at 0.75 coverage of monolayer have been calculated using density functional theory.It is found that the structure with carbon near Pd(111) surface is stable while the structure with oxygen is quite difficult, therefore, controlling the orientation of CO molecule adsorbed on Pd surface may be effective to inhibit CO adsorption on Pd surface.
2007,
19.
Abstract:
Based on constrained conjugate gradient algorithm, a 3D constrained conjugate gradient algorithm (3D-CCG) is proposed for the reconstruction on high-energy radiography image. Constrained with prior knowledge, the reconstruction equation of 3D-CCG based on three-dimension reconstruction theory is solved by use of the preconditioned conjugate gradient algorithm. Numerical experiment results show that compared with the filter back projection algorithm and RPCCG, 3D-CCG is more efficient in reconstruction quality.
Based on constrained conjugate gradient algorithm, a 3D constrained conjugate gradient algorithm (3D-CCG) is proposed for the reconstruction on high-energy radiography image. Constrained with prior knowledge, the reconstruction equation of 3D-CCG based on three-dimension reconstruction theory is solved by use of the preconditioned conjugate gradient algorithm. Numerical experiment results show that compared with the filter back projection algorithm and RPCCG, 3D-CCG is more efficient in reconstruction quality.
2007,
19.
Abstract:
Using the transmission line model, the response in radiation and pulsed current injection(PCI) environments of braided cable shields coupling to inner conductor is calculated by finite-difference time-domain method. The numerical results indicate that the peak value of voltage of radiation environment is larger than the near port of PCI environments, and the far port is the biggest. The peak value of voltage and the integrate value of absolute value of voltage are in direct ratio with the current amplitude of shields. And the value is independent of the rise time. The value is non-linear with the full wave at half maximum(FWHM) for small FWHM, but it is just the opposite for big FWHM. The peak value and the length of cable are changed in the same ratio for short cable, as the length change
Using the transmission line model, the response in radiation and pulsed current injection(PCI) environments of braided cable shields coupling to inner conductor is calculated by finite-difference time-domain method. The numerical results indicate that the peak value of voltage of radiation environment is larger than the near port of PCI environments, and the far port is the biggest. The peak value of voltage and the integrate value of absolute value of voltage are in direct ratio with the current amplitude of shields. And the value is independent of the rise time. The value is non-linear with the full wave at half maximum(FWHM) for small FWHM, but it is just the opposite for big FWHM. The peak value and the length of cable are changed in the same ratio for short cable, as the length change
2007,
19.
Abstract:
A flat-plate diode cathode was produced using multi-crystal lanthanum hexaboride(LaB6) material. The anode was molybdenum, and the cathode was heated by thermal conduction and radiated with a graphite heater. The pulse emission properties and the emission stabilities were investigated at different cathode temperature and under different vacuum level. When the LaB6 cathode with an emission area of 0.012 1 cm2 was operated at 1 600 ℃, 1 650 ℃, 1 700 ℃, respectively, the corresponding maximum of pulse thermionic emission current densities were 34.0 A/cm2, 44.0 A/cm2, 53.8 A/cm2, under 2×10-4 Pa, the pulse width of 40 ms, and repetition frequency of 107 Hz. The pulse thermionic emission density of LaB6 cathode was also measured under 2×10-4 Pa, 5×10-4 Pa, 2×10-3 Pa, respectively, and it
A flat-plate diode cathode was produced using multi-crystal lanthanum hexaboride(LaB6) material. The anode was molybdenum, and the cathode was heated by thermal conduction and radiated with a graphite heater. The pulse emission properties and the emission stabilities were investigated at different cathode temperature and under different vacuum level. When the LaB6 cathode with an emission area of 0.012 1 cm2 was operated at 1 600 ℃, 1 650 ℃, 1 700 ℃, respectively, the corresponding maximum of pulse thermionic emission current densities were 34.0 A/cm2, 44.0 A/cm2, 53.8 A/cm2, under 2×10-4 Pa, the pulse width of 40 ms, and repetition frequency of 107 Hz. The pulse thermionic emission density of LaB6 cathode was also measured under 2×10-4 Pa, 5×10-4 Pa, 2×10-3 Pa, respectively, and it
2007,
19.
Abstract:
A two-electrode gas spark switch is designed. It has been built for high current, large charge transfers, slight electrode erosion and long lifetime. The switch operates without a trigger electrode, reducing losses by eliminating two arc/electrode contacts. The uniform erosion of graphite minimizes pitting and roughening of the electrodes. The switch is expected to discharge a 23 kV, 1.2 MJ bank with the peak current of 300 kA and charge transfer of 110 C per pulse on a single shot. In the elementary experimental study, the switch operates at a voltage of 15 kV with reliable performance for triggering and uniform electorde erosion.
A two-electrode gas spark switch is designed. It has been built for high current, large charge transfers, slight electrode erosion and long lifetime. The switch operates without a trigger electrode, reducing losses by eliminating two arc/electrode contacts. The uniform erosion of graphite minimizes pitting and roughening of the electrodes. The switch is expected to discharge a 23 kV, 1.2 MJ bank with the peak current of 300 kA and charge transfer of 110 C per pulse on a single shot. In the elementary experimental study, the switch operates at a voltage of 15 kV with reliable performance for triggering and uniform electorde erosion.
