Email alert
RSS2011 Vol. 23, No. 09
Recommend Articles
Display Method:
2011,
23.
Abstract:
An RKA(relativistic klystron amplifier) input cavity with dual coupling holes is analyzed by means of equivalent circuit method, and the scattering matrix (S-matrix) of the coupling system is obtained. Based on the derivative of phase of S21 with respect to its angular frequency, the expression of loaded quality(Q) factor of the system is derived. The value of loaded Q factor can be obtained upon the resonant frequency and group delay, given by high frequency field analysis software. The result is validated against that derived by field decaying method, with good agreement. Moreover, the study method is fast and can realize structure optimization with parameter scanning.
An RKA(relativistic klystron amplifier) input cavity with dual coupling holes is analyzed by means of equivalent circuit method, and the scattering matrix (S-matrix) of the coupling system is obtained. Based on the derivative of phase of S21 with respect to its angular frequency, the expression of loaded quality(Q) factor of the system is derived. The value of loaded Q factor can be obtained upon the resonant frequency and group delay, given by high frequency field analysis software. The result is validated against that derived by field decaying method, with good agreement. Moreover, the study method is fast and can realize structure optimization with parameter scanning.
2011,
23.
Abstract:
The paper discusses the near field of rectangular aperture antenna under focusing of Gaussian beam by using aperture field method, and obtains the analytic expressions of the near field intensity and gain. Corresponding simulations are conducted under different focusing conditions. The results show that in near field, the nearer the focusing position is from the axis, the bigger the field intensity and gain are, and the field intensity and gain reach their maxima when the focusing position is on the axis. Therefore, the effective range of antenna can be improved by focusing due to its ability to enhance near field intensity and gain of antenna aperture.
The paper discusses the near field of rectangular aperture antenna under focusing of Gaussian beam by using aperture field method, and obtains the analytic expressions of the near field intensity and gain. Corresponding simulations are conducted under different focusing conditions. The results show that in near field, the nearer the focusing position is from the axis, the bigger the field intensity and gain are, and the field intensity and gain reach their maxima when the focusing position is on the axis. Therefore, the effective range of antenna can be improved by focusing due to its ability to enhance near field intensity and gain of antenna aperture.
2011,
23.
Abstract:
The high-order mode output of high power millimeter wave gyrotron should be converted due to its disadvantages in space transport, which can be hardly solved by waveguide mode converter. Thus the built-in quasi-optical mode converter is studied. The converter consists of Vlasov launcher, quasi-parabolic mirror and phase correcting mirros. The simulation program is developed according to scalar diffraction theory and KSA algorithm, and phase correcting mirrors are designed. The calculation analysis of field distribution at the reference plane shows that, the converter’s scalar conversion efficiency is larger than 98%, and the vector conversion efficiency is larger than 93%. The results indicate that the method can guide the design of quasi-optical mode converter efficiently.
The high-order mode output of high power millimeter wave gyrotron should be converted due to its disadvantages in space transport, which can be hardly solved by waveguide mode converter. Thus the built-in quasi-optical mode converter is studied. The converter consists of Vlasov launcher, quasi-parabolic mirror and phase correcting mirros. The simulation program is developed according to scalar diffraction theory and KSA algorithm, and phase correcting mirrors are designed. The calculation analysis of field distribution at the reference plane shows that, the converter’s scalar conversion efficiency is larger than 98%, and the vector conversion efficiency is larger than 93%. The results indicate that the method can guide the design of quasi-optical mode converter efficiently.
2011,
23.
Abstract:
A microwave rectifier is an essential part of a microwave power transmission system. In order to maintain high rectifying efficiency at a high input microwave power level, a novel microstrip microwave rectifier based on diode array is presented in this paper. The microwave input power was enhanced to 33 dBm at 2.45 GHz. The simulated and measured results show the proposed microwave rectifier presents a reasonable efficiency at given input microwave power, while the load varies within a certain range. The rectifying efficiency is higher than 60% when the input microwave power is between 27 dBm to 31.7 dBm. The maximum efficiency of 63.3% is achieved at 30 dBm input microwave power.
A microwave rectifier is an essential part of a microwave power transmission system. In order to maintain high rectifying efficiency at a high input microwave power level, a novel microstrip microwave rectifier based on diode array is presented in this paper. The microwave input power was enhanced to 33 dBm at 2.45 GHz. The simulated and measured results show the proposed microwave rectifier presents a reasonable efficiency at given input microwave power, while the load varies within a certain range. The rectifying efficiency is higher than 60% when the input microwave power is between 27 dBm to 31.7 dBm. The maximum efficiency of 63.3% is achieved at 30 dBm input microwave power.
2011,
23.
Abstract:
Based on the critical temperature difference of ceramic materials, the critical heat dissipation power of gyrotron windows of different materials has been studied. Different heating modes in the windows caused by electromagnetic wave of different modes, such as TE01, TE11 and TE02, have been analyzed respectively. The heat power dissipation capabilities have been compared among alumina window, beryllia window, boron nitride window and sapphire window. In addition, as the thickness of window changes, the variations of critical heat dissipation power of windows of different materials have been analyzed and verified. The study shows that sapphire window and beryllia window, especially the former, exhibit better heat power dissipation capability; less heat is dissipated by alumina window and b
Based on the critical temperature difference of ceramic materials, the critical heat dissipation power of gyrotron windows of different materials has been studied. Different heating modes in the windows caused by electromagnetic wave of different modes, such as TE01, TE11 and TE02, have been analyzed respectively. The heat power dissipation capabilities have been compared among alumina window, beryllia window, boron nitride window and sapphire window. In addition, as the thickness of window changes, the variations of critical heat dissipation power of windows of different materials have been analyzed and verified. The study shows that sapphire window and beryllia window, especially the former, exhibit better heat power dissipation capability; less heat is dissipated by alumina window and b
2011,
23.
Abstract:
A transient analysis in time domain of beam-wave interaction for gyroklystron is made with self-consistent field theory. A nonlinear theory for gyroklystron with multiple cavities is then established, and corresponding electron motion equations and transient electromagnetic field equations with a complex form are given. For a Ka-band gyroklystron with four cavities, some numerical results of beam-wave interaction are given and analyzed. A saturated output power of 335 kW, corresponding to efficiency of 39.6% and saturated bandwidth of 320 MHz is achieved with a 72.8 kV, 11.8 A electron beam in TE01 mode when the speed spread is 5%. The numerical results agree well with the experimental data.
A transient analysis in time domain of beam-wave interaction for gyroklystron is made with self-consistent field theory. A nonlinear theory for gyroklystron with multiple cavities is then established, and corresponding electron motion equations and transient electromagnetic field equations with a complex form are given. For a Ka-band gyroklystron with four cavities, some numerical results of beam-wave interaction are given and analyzed. A saturated output power of 335 kW, corresponding to efficiency of 39.6% and saturated bandwidth of 320 MHz is achieved with a 72.8 kV, 11.8 A electron beam in TE01 mode when the speed spread is 5%. The numerical results agree well with the experimental data.
2011,
23.
Abstract:
Thermal analysis of Faraday cup analyzer for measuring electron beams of traveling wave tubes(TWTs) using ANSYS package is presented. With beams of different power density and different pulses, temperature of the Faraday cup had been simulated. The results show that with a single pulse, only temperature of spot size on aperture plate rises quickly, whereas temperature of other part is constant. For normal operating, pulse width must be smaller than 0.5 μs, 0.1 μs and 0.2 μs are better, to measure beams of power density larger than 5×106 W/cm2. Pulse width for measuring a beam of fixed power density should be limited, and different pulses should be used for measuring different power density beams. In addition, taking heat cumulating effect into account, suitable pulse repetition frequen
Thermal analysis of Faraday cup analyzer for measuring electron beams of traveling wave tubes(TWTs) using ANSYS package is presented. With beams of different power density and different pulses, temperature of the Faraday cup had been simulated. The results show that with a single pulse, only temperature of spot size on aperture plate rises quickly, whereas temperature of other part is constant. For normal operating, pulse width must be smaller than 0.5 μs, 0.1 μs and 0.2 μs are better, to measure beams of power density larger than 5×106 W/cm2. Pulse width for measuring a beam of fixed power density should be limited, and different pulses should be used for measuring different power density beams. In addition, taking heat cumulating effect into account, suitable pulse repetition frequen
2011,
23.
Abstract:
The output section used in an S-band high average power klystron with 7.1% bandwidth is investigated. It adopts the two-gap overlapping-mode coupled cavity which uses the short slot coupled mode. The dimension of the coupled slot is obtained by formula, and the two cavities’ parameters of frequency, quality factor, and two gap centers’ distance are chosen generally. According to the above parameters, the cold-test model is processed. The slot’s resonant frequency and coupling coefficient derived by the cold test have an error of 2.5% compared with the original design values, the calculated impedance matrix curve has the same direction as the cold-test relative impedance curve, and the calculated power and the hot-test results satisfy the design requirements of more than 1.1 MW peak powe
The output section used in an S-band high average power klystron with 7.1% bandwidth is investigated. It adopts the two-gap overlapping-mode coupled cavity which uses the short slot coupled mode. The dimension of the coupled slot is obtained by formula, and the two cavities’ parameters of frequency, quality factor, and two gap centers’ distance are chosen generally. According to the above parameters, the cold-test model is processed. The slot’s resonant frequency and coupling coefficient derived by the cold test have an error of 2.5% compared with the original design values, the calculated impedance matrix curve has the same direction as the cold-test relative impedance curve, and the calculated power and the hot-test results satisfy the design requirements of more than 1.1 MW peak powe
2011,
23.
Abstract:
A theoretical analysis approach for mode stirred reverberation chambers (MSRCs) is presented. Based on the discretized probability model of ideal reverberation chambers, this approach applies Monte Carlo simulation to obtain probabilistic and statistical properties of the electromagnetic fields in MSRC and their associated physical quantities, such as the probability distribution functions of some normalized field values, the mean coupling cross-section of a uniform lossless single-wire transmission line in MSRC and the probability distribution functions of the magnitude of its terminal load current. These results are in agreement with the data published in the literature, which resulted from analytic calculations or measurements. Because of the universality of Monte Carlo method, the prop
A theoretical analysis approach for mode stirred reverberation chambers (MSRCs) is presented. Based on the discretized probability model of ideal reverberation chambers, this approach applies Monte Carlo simulation to obtain probabilistic and statistical properties of the electromagnetic fields in MSRC and their associated physical quantities, such as the probability distribution functions of some normalized field values, the mean coupling cross-section of a uniform lossless single-wire transmission line in MSRC and the probability distribution functions of the magnitude of its terminal load current. These results are in agreement with the data published in the literature, which resulted from analytic calculations or measurements. Because of the universality of Monte Carlo method, the prop
2011,
23.
Abstract:
The paper proposes and studies an experimental scheme that tests microwave gas breakdown by enhancing electric field. The electric field enhancement is realized through two metal pins placed parallel to the field polarization direction in the middle of the waveguide, and air breakdown can be gotten by adjusting the power of the microwave source and the distance between the two metal pins. The experimental principle and corresponding diagnostic method are introduced. Air breakdown experiments have been conducted under 0.1 MPa with 2.86 GHz microwave of 180 ns pulse duration. The results derived agree with theoretical design, validating the feasibility of the experimental scheme.
The paper proposes and studies an experimental scheme that tests microwave gas breakdown by enhancing electric field. The electric field enhancement is realized through two metal pins placed parallel to the field polarization direction in the middle of the waveguide, and air breakdown can be gotten by adjusting the power of the microwave source and the distance between the two metal pins. The experimental principle and corresponding diagnostic method are introduced. Air breakdown experiments have been conducted under 0.1 MPa with 2.86 GHz microwave of 180 ns pulse duration. The results derived agree with theoretical design, validating the feasibility of the experimental scheme.
2011,
23.
Abstract:
Based on sheath model, high-frequency characteristics including dispersion properties and coupling impedance of rectangular helix structure are derived by using field-matching method combining with integral boundary conditions. The numerical results, which are generally based on approximation approach, agree well with the results obtained by three-dimensional electromagnetic simulation software. Only when the aspect ratio of rectangular cross-section is larger than 4, the influence of the section width on the high-frequency characteristics can be neglected. Moreover, changing the pitch and dimensions of rectangular cross-section can improve the dispersion characteristics and the coupling impedance.
Based on sheath model, high-frequency characteristics including dispersion properties and coupling impedance of rectangular helix structure are derived by using field-matching method combining with integral boundary conditions. The numerical results, which are generally based on approximation approach, agree well with the results obtained by three-dimensional electromagnetic simulation software. Only when the aspect ratio of rectangular cross-section is larger than 4, the influence of the section width on the high-frequency characteristics can be neglected. Moreover, changing the pitch and dimensions of rectangular cross-section can improve the dispersion characteristics and the coupling impedance.
2011,
23.
Abstract:
The distributed dielectric loading technology has been successively applied in many gyrotron-travelling wave tube(gyro-TWT) experiments to suppress absolute instabilities. Based on the stability analysis of a Ka-band TE01-mode gyro-TWT with distributed-loss interaction circuit, propagation loss of operation and parasitic modes, start current of operation mode under different propagation losses are calculated. Start lengths of the three main parasitic modes under different loss-loading conditions and operation currents are given. Dielectric loss parameters including thickness of loss layer and relative permittivity are then decided. Taking advantage of the optimized parameters of loaded dielectric, a high gain scheme has been demonstrated in a 34 GHz, TE01-mode gyro-TWT, producing 160 kW sa
The distributed dielectric loading technology has been successively applied in many gyrotron-travelling wave tube(gyro-TWT) experiments to suppress absolute instabilities. Based on the stability analysis of a Ka-band TE01-mode gyro-TWT with distributed-loss interaction circuit, propagation loss of operation and parasitic modes, start current of operation mode under different propagation losses are calculated. Start lengths of the three main parasitic modes under different loss-loading conditions and operation currents are given. Dielectric loss parameters including thickness of loss layer and relative permittivity are then decided. Taking advantage of the optimized parameters of loaded dielectric, a high gain scheme has been demonstrated in a 34 GHz, TE01-mode gyro-TWT, producing 160 kW sa
2011,
23.
Abstract:
A dual-band relativistic backward-wave oscillator(RBWO) with dual annular electron beams generating C-band and X-band microwaves is investigated by particle-in-cell (PIC) simulation. Two separated beam-wave interaction regions are supplied to obtain independent generation processes of the dual-band microwaves. With the diode voltage of 650 kV, the inner beam current of 5.4 kA and the outer beam current of 6.4 kA guided by a magnetic field of about 2.2 T, the dual-band microwaves are generated with dominant frequencies of 4.625 GHz and 8.450 GHz. The powers of the dual-band microwaves are 920 MW and 600 MW with efficiencies of 21.8% and 17.1%, respectively. The influence of the guiding magnetic field, diode voltage and key structure parameters on the powers and frequencies of the dual-band
A dual-band relativistic backward-wave oscillator(RBWO) with dual annular electron beams generating C-band and X-band microwaves is investigated by particle-in-cell (PIC) simulation. Two separated beam-wave interaction regions are supplied to obtain independent generation processes of the dual-band microwaves. With the diode voltage of 650 kV, the inner beam current of 5.4 kA and the outer beam current of 6.4 kA guided by a magnetic field of about 2.2 T, the dual-band microwaves are generated with dominant frequencies of 4.625 GHz and 8.450 GHz. The powers of the dual-band microwaves are 920 MW and 600 MW with efficiencies of 21.8% and 17.1%, respectively. The influence of the guiding magnetic field, diode voltage and key structure parameters on the powers and frequencies of the dual-band
2011,
23.
Abstract:
A laterally graded multilayer was deposited on silicon substrate by using magnetron sputtering. The d-spacing gradient of 0.03 nm/mm was achieved across a 65 mm long range on the substrate’s surface, with d-spacing varying linearly from 8.41 nm to 6.57 nm, which was measured by grazing incidence X-ray reflection (GIXR). Extreme ultraviolet reflectivity was measured in National Synchrotron Radiation Laboratory(NSRL). The measured reflectivity is 60%~65% at the wavelength range of 13.3 to 15.9 nm.
A laterally graded multilayer was deposited on silicon substrate by using magnetron sputtering. The d-spacing gradient of 0.03 nm/mm was achieved across a 65 mm long range on the substrate’s surface, with d-spacing varying linearly from 8.41 nm to 6.57 nm, which was measured by grazing incidence X-ray reflection (GIXR). Extreme ultraviolet reflectivity was measured in National Synchrotron Radiation Laboratory(NSRL). The measured reflectivity is 60%~65% at the wavelength range of 13.3 to 15.9 nm.
2011,
23.
Abstract:
A laser-induced damage model has been built for fused silica surface with metal particles as absorbers, which are introduced by processing. The evolution of the temperature field around absorbers during laser irradiation was simulated, and shows that the temperature at the hottest point will soon reach the critical temperature of damage in a pulse time. Damage densities of samples with and without etching have been experimentally compared, revealing the strong correlation between metal particles amount and damage density. Moreover, both simulation and experiment show that, the metal particles in fused silica surface are important damage precursors, which decrease the material’s laser damage threshold.
A laser-induced damage model has been built for fused silica surface with metal particles as absorbers, which are introduced by processing. The evolution of the temperature field around absorbers during laser irradiation was simulated, and shows that the temperature at the hottest point will soon reach the critical temperature of damage in a pulse time. Damage densities of samples with and without etching have been experimentally compared, revealing the strong correlation between metal particles amount and damage density. Moreover, both simulation and experiment show that, the metal particles in fused silica surface are important damage precursors, which decrease the material’s laser damage threshold.
2011,
23.
Abstract:
The plastic scintillation detector is used to measure the yield of DD neutrons or DT neutrons. Fast neutrons incident on the scintillator give rise to recoil protons. Because the range of the recoil protons is usually small compared with the dimensions of the scintillator, their full energy is deposited in the scintillator. The statistic fluctuation of the protons’ number and that of the protons’ total energy are two sources of the measurement uncertainty. Based on DT neutrons, this paper presents the algorithms to compute the probability density functions of the two statistic fluctuations. The algorithms are applicable to the related computation for other fast monoenergetic neutrons in the plastic scintillator.
The plastic scintillation detector is used to measure the yield of DD neutrons or DT neutrons. Fast neutrons incident on the scintillator give rise to recoil protons. Because the range of the recoil protons is usually small compared with the dimensions of the scintillator, their full energy is deposited in the scintillator. The statistic fluctuation of the protons’ number and that of the protons’ total energy are two sources of the measurement uncertainty. Based on DT neutrons, this paper presents the algorithms to compute the probability density functions of the two statistic fluctuations. The algorithms are applicable to the related computation for other fast monoenergetic neutrons in the plastic scintillator.
2011,
23.
Abstract:
The paper discusses the effects of length-to-diameter ratio of cylindrical hohlraum on irradiation nonuniformity of capsule on Shenguang-Ⅲ facility. The parameters of laser spots on hohlraum's inner wall are calculated according to the parameters of Shenguang-Ⅲ facility. The variation of irradiation nonuniformity with the length-to-diameter ratio is analyzed with view factor method for a simplified dual-core irradiation model, and the variations of the best length-to-diameter ratio and irradiation nonuniformity with the albedo of hohlraum's inner wall, power ratio between inner and outer cones and motion of laser spots are also discussed. The calculation results show that the root-mean-square nonuniformity of irradiation is less than 1% at the best length-to-diameter ratio, which agrees
The paper discusses the effects of length-to-diameter ratio of cylindrical hohlraum on irradiation nonuniformity of capsule on Shenguang-Ⅲ facility. The parameters of laser spots on hohlraum's inner wall are calculated according to the parameters of Shenguang-Ⅲ facility. The variation of irradiation nonuniformity with the length-to-diameter ratio is analyzed with view factor method for a simplified dual-core irradiation model, and the variations of the best length-to-diameter ratio and irradiation nonuniformity with the albedo of hohlraum's inner wall, power ratio between inner and outer cones and motion of laser spots are also discussed. The calculation results show that the root-mean-square nonuniformity of irradiation is less than 1% at the best length-to-diameter ratio, which agrees
2011,
23.
Abstract:
The spatial resolution of KBA X-ray microscope is studied with ray-tracing simulation and experimental test. In the experiment, the imaging object is Au grid, backlit by X-rays produced by the 9th laser interaction with Cu target on Shenguang Ⅱ laser facility. The spatial resolution of KBA X-ray microscope is found to be asymmetric about the center of its field of view. Moreover, the experimental data show that, the variation of resolution in the reducing direction of grazing incidence angle is smaller than that in the increasing direction, and the resolution asymmetry is about 30% relative to the field center.
The spatial resolution of KBA X-ray microscope is studied with ray-tracing simulation and experimental test. In the experiment, the imaging object is Au grid, backlit by X-rays produced by the 9th laser interaction with Cu target on Shenguang Ⅱ laser facility. The spatial resolution of KBA X-ray microscope is found to be asymmetric about the center of its field of view. Moreover, the experimental data show that, the variation of resolution in the reducing direction of grazing incidence angle is smaller than that in the increasing direction, and the resolution asymmetry is about 30% relative to the field center.
2011,
23.
Abstract:
The misalignment characteristics of PPLN optical parametric oscillator(OPO) have been experimentally studied. On the basis of PPLN mid-infrared output, the effects of PPLN shift and mirror tilt on misalignment characteristics have been studied in order to provide references for optimization and practical use. The results show that the misalignment characteristics of PPLN OPO are different from those of normal laser because of the small size and parametric oscillating characteristics of PPLN. The misalignment tolerance of PPLN OPO to crystal shift along x-axis is larger than that to y-axis shift; the misalignment tolerance to mirror tilt around y-axis is larger than that to mirror tilt around x-axis. The temperature and channel of PPLN almost have no effect on misalignment tolerances of PPL
The misalignment characteristics of PPLN optical parametric oscillator(OPO) have been experimentally studied. On the basis of PPLN mid-infrared output, the effects of PPLN shift and mirror tilt on misalignment characteristics have been studied in order to provide references for optimization and practical use. The results show that the misalignment characteristics of PPLN OPO are different from those of normal laser because of the small size and parametric oscillating characteristics of PPLN. The misalignment tolerance of PPLN OPO to crystal shift along x-axis is larger than that to y-axis shift; the misalignment tolerance to mirror tilt around y-axis is larger than that to mirror tilt around x-axis. The temperature and channel of PPLN almost have no effect on misalignment tolerances of PPL
2011,
23.
Abstract:
Based on the wave coupling theory and the evolution model of the critical pump power (or Brillouin threshold) for stimulated Brillouin scattering(SBS) in double-clad fiber amplifiers, the influence of signal bandwidth, fiber-core diameter and amplifier gain on SBS threshold is simulated theoretically. And experimental measurements of SBS are presented in ytterbium-doped double-clad fiber amplifiers with single-frequency hundred nanosecond pulse amplification. Under different input signal pulses, the forward amplified pulse distortion is observed when the pulse energy is up to 660 nJ and the peak power is up to 3.3 W in the pulse amplification with pulse duration of 200 ns and repetition rate of 1 Hz. And the backward SBS narrow pulse appears. The pulse peak power equals to SBS threshold.
Based on the wave coupling theory and the evolution model of the critical pump power (or Brillouin threshold) for stimulated Brillouin scattering(SBS) in double-clad fiber amplifiers, the influence of signal bandwidth, fiber-core diameter and amplifier gain on SBS threshold is simulated theoretically. And experimental measurements of SBS are presented in ytterbium-doped double-clad fiber amplifiers with single-frequency hundred nanosecond pulse amplification. Under different input signal pulses, the forward amplified pulse distortion is observed when the pulse energy is up to 660 nJ and the peak power is up to 3.3 W in the pulse amplification with pulse duration of 200 ns and repetition rate of 1 Hz. And the backward SBS narrow pulse appears. The pulse peak power equals to SBS threshold.
2011,
23.
Abstract:
Mo films were fabricated at different sputtering powers by DC magnetron sputtering. The deposition rate, surface topography and crystal structure of Mo films were studied. The effects of sputtering power on grain size and stress of Mo films were discussed. AFM analyses show that when sputtering power increases from 20 W to 100 W, the roughness of Mo films raises. The X-ray diffraction analysis indicates that all the films are in cubic polycrystal structure. The grain size varies from 14.1 nm to 17.9 nm, and the stress in the Mo films increases firstly and then decreases as the sputtering power increases, reaching a maximum of 2.383 GPa at the sputtering power of 40 W.
Mo films were fabricated at different sputtering powers by DC magnetron sputtering. The deposition rate, surface topography and crystal structure of Mo films were studied. The effects of sputtering power on grain size and stress of Mo films were discussed. AFM analyses show that when sputtering power increases from 20 W to 100 W, the roughness of Mo films raises. The X-ray diffraction analysis indicates that all the films are in cubic polycrystal structure. The grain size varies from 14.1 nm to 17.9 nm, and the stress in the Mo films increases firstly and then decreases as the sputtering power increases, reaching a maximum of 2.383 GPa at the sputtering power of 40 W.
2011,
23.
Abstract:
Thermal annealing at high temperature is used to relieve the residual stress of fused silica induced by CO2 laser repair. The effects of annealing environment on surface contamination of fused silica as well as the effects of different annealing temperatures (600 to 900 ℃) and time (3 to 10 h) on residual stress, transmission wavefront, surface roughness, and laser induced damage threshold (LIDT) are investigated. The results show that the residual stress induced by CO2 laser repair can be effectively relieved after annealing at 800 ℃ for 10 h and there is no obvious change in the wavefront and surface roughness of optics. A silica shield box can reduce surface contamination from annealing environment but there are still some contaminations undetectable for X-ray photoelectron spectrosco
Thermal annealing at high temperature is used to relieve the residual stress of fused silica induced by CO2 laser repair. The effects of annealing environment on surface contamination of fused silica as well as the effects of different annealing temperatures (600 to 900 ℃) and time (3 to 10 h) on residual stress, transmission wavefront, surface roughness, and laser induced damage threshold (LIDT) are investigated. The results show that the residual stress induced by CO2 laser repair can be effectively relieved after annealing at 800 ℃ for 10 h and there is no obvious change in the wavefront and surface roughness of optics. A silica shield box can reduce surface contamination from annealing environment but there are still some contaminations undetectable for X-ray photoelectron spectrosco
2011,
23.
Abstract:
In order to achieve three-step pulse shaping (time proportion 1.5 ns∶1.0 ns∶0.5 ns, power proportion 1∶4∶16, total energy 500 J) required by the physical experiments on Shenguang-Ⅲ technical integration experimental line(TIL), some researches on waveform control of high power laser pulse shaping have been done on the basis of TIL system structure and the technology which can form arbitrary pulse waveform. By analyzing gain saturation effect and frequency conversion process, the paper gets the pulse change in transmission, amplification and frequency conversion processes, and builds a simple prediction model. Good experimental results are obtained by pulse waveform predicting, pulse shaping and repeated iteration of laser emission data, and used in the physical experiments. A prelimina
In order to achieve three-step pulse shaping (time proportion 1.5 ns∶1.0 ns∶0.5 ns, power proportion 1∶4∶16, total energy 500 J) required by the physical experiments on Shenguang-Ⅲ technical integration experimental line(TIL), some researches on waveform control of high power laser pulse shaping have been done on the basis of TIL system structure and the technology which can form arbitrary pulse waveform. By analyzing gain saturation effect and frequency conversion process, the paper gets the pulse change in transmission, amplification and frequency conversion processes, and builds a simple prediction model. Good experimental results are obtained by pulse waveform predicting, pulse shaping and repeated iteration of laser emission data, and used in the physical experiments. A prelimina
2011,
23.
Abstract:
A single-shot transient-grating frequency-resolved optical gating(TG-FROG) device was set up to measure UV ultrashort pulse laser with pulse duration within 10 ps. The performance of the device was demonstrated by experimental data measured on discharge-pumped KrF laser which is operated in 10 Hz repeated frequency mode, and on electron-beam-pumped KrF laser which is only operated in single-shot mode. For the former, the TG-FROG can distinguish the changes of the pulse shape, spectrum and phase when the pulse chirp is changed. For the later, the TG-FROG finds that the pulse shape has multiple peaks whose pulse duration is about 2 ps, and the spectrum is modulated whose bandwidth is about 1.3 nm, and the corresponding phases present parabolic structure.
A single-shot transient-grating frequency-resolved optical gating(TG-FROG) device was set up to measure UV ultrashort pulse laser with pulse duration within 10 ps. The performance of the device was demonstrated by experimental data measured on discharge-pumped KrF laser which is operated in 10 Hz repeated frequency mode, and on electron-beam-pumped KrF laser which is only operated in single-shot mode. For the former, the TG-FROG can distinguish the changes of the pulse shape, spectrum and phase when the pulse chirp is changed. For the later, the TG-FROG finds that the pulse shape has multiple peaks whose pulse duration is about 2 ps, and the spectrum is modulated whose bandwidth is about 1.3 nm, and the corresponding phases present parabolic structure.
2011,
23.
Abstract:
The magnetic field around a wire-array load of Z-pinch is essential to understand the wire-array ablation and ablated plasma flowing, as well as the following implosion processes. All the currents of the wire-array, return-posts, anode and cathode were divided by many small current lines or current surfaces, whose magnetic field were calculated by the formula of Biot-Savart’s law. The total magnetic field was obtained by summing all the fields contributed from all the current elements. The magnetic field contributed only by the wire-array currents deflects from the formula values of a long straight wire, while the total magnetic field is close to the formula values. The uniformity of the magnetic field in the region of the load can be improved by increasing the wire numbers, due to reduce
The magnetic field around a wire-array load of Z-pinch is essential to understand the wire-array ablation and ablated plasma flowing, as well as the following implosion processes. All the currents of the wire-array, return-posts, anode and cathode were divided by many small current lines or current surfaces, whose magnetic field were calculated by the formula of Biot-Savart’s law. The total magnetic field was obtained by summing all the fields contributed from all the current elements. The magnetic field contributed only by the wire-array currents deflects from the formula values of a long straight wire, while the total magnetic field is close to the formula values. The uniformity of the magnetic field in the region of the load can be improved by increasing the wire numbers, due to reduce
2011,
23.
Abstract:
In hydrodynamics instability experiment, the quantificational relation between amplitude fluctuation of sample and X-ray intensity is important to analysing Rayleigh-Taylor instability exactly. The signal-to-noise of the data is always low due to the complex image environment, thus improving the signal-to-noise of the image is inevitable. With the area backlighting, the X-ray intensity images were recorded by XSC in ShenguangⅡ facility. Daubechies wavelet filtering and Wiener filtering were used to de-noise the data separately. The results show that the Daubechies wavelet filtering is better than the Wiener filtering in de-noising and maintaining the detail of the signal.
In hydrodynamics instability experiment, the quantificational relation between amplitude fluctuation of sample and X-ray intensity is important to analysing Rayleigh-Taylor instability exactly. The signal-to-noise of the data is always low due to the complex image environment, thus improving the signal-to-noise of the image is inevitable. With the area backlighting, the X-ray intensity images were recorded by XSC in ShenguangⅡ facility. Daubechies wavelet filtering and Wiener filtering were used to de-noise the data separately. The results show that the Daubechies wavelet filtering is better than the Wiener filtering in de-noising and maintaining the detail of the signal.
2011,
23.
Abstract:
A novel electro-optically Q-switched laser with short cavity was demonstrated. Its optimal structure parameters were determined via the analysis of factors related to output pulse width. Quasi-continuous end-pumped Nd:YVO4 crystal with concentration of 1.0 % was cut along Brewster angle in a-axis, in order to ensure polarized oscillation. Thus, the cavity length was shortened efficiently due to the omission of quarter wave plate in voltage-decreased Q-switching structure. In condition of 20 mm physical cavity length, the narrowest output pulse width of 1.049 ns, pulse energy of 0.32 mJ and beam quality factor of 1.9 were achieved.
A novel electro-optically Q-switched laser with short cavity was demonstrated. Its optimal structure parameters were determined via the analysis of factors related to output pulse width. Quasi-continuous end-pumped Nd:YVO4 crystal with concentration of 1.0 % was cut along Brewster angle in a-axis, in order to ensure polarized oscillation. Thus, the cavity length was shortened efficiently due to the omission of quarter wave plate in voltage-decreased Q-switching structure. In condition of 20 mm physical cavity length, the narrowest output pulse width of 1.049 ns, pulse energy of 0.32 mJ and beam quality factor of 1.9 were achieved.
2011,
23.
Abstract:
The paper reports the research progress in all-solid-state high power green laser. The intracavity frequency-doubled green laser adopts the two-rod L-shaped cavity. When the pumping power is 1 174 W, the 532 nm output power is 186 W and the optical-optical efficiency is 15.8% with LBO frequency-doubling crystal. A diode pumped master oscillator power amplifier laser with output pulse energy of 1.2 J at 400 Hz repetition rate is demonstrated. With a type Ⅱ phase matched KTP crystal, 525 mJ green light pulse energy at 400 Hz repetition rate is obtained. The frequency conversion efficiency is about 43.7%. The laser energy of the double beam laser is more than 1 J with the technique of polarization synthesis. Moreover, a 90°quartz rotator is placed between the two laser modules to fulfill t
The paper reports the research progress in all-solid-state high power green laser. The intracavity frequency-doubled green laser adopts the two-rod L-shaped cavity. When the pumping power is 1 174 W, the 532 nm output power is 186 W and the optical-optical efficiency is 15.8% with LBO frequency-doubling crystal. A diode pumped master oscillator power amplifier laser with output pulse energy of 1.2 J at 400 Hz repetition rate is demonstrated. With a type Ⅱ phase matched KTP crystal, 525 mJ green light pulse energy at 400 Hz repetition rate is obtained. The frequency conversion efficiency is about 43.7%. The laser energy of the double beam laser is more than 1 J with the technique of polarization synthesis. Moreover, a 90°quartz rotator is placed between the two laser modules to fulfill t
2011,
23.
Abstract:
To suppress the influences aroused by CCD noise in measuring laser near field distribution, the paper proposes a method to correct CCD noise using a priori knowledge of CCD noise and its observed value based on contrast test model. Compared with the existing method, this method can suppress the influences caused by CCD noise effectively, thus lowering measurement uncertainty and improving measurement confidence, and the extended uncertainty reduces from 0.6% to 0.3%.
To suppress the influences aroused by CCD noise in measuring laser near field distribution, the paper proposes a method to correct CCD noise using a priori knowledge of CCD noise and its observed value based on contrast test model. Compared with the existing method, this method can suppress the influences caused by CCD noise effectively, thus lowering measurement uncertainty and improving measurement confidence, and the extended uncertainty reduces from 0.6% to 0.3%.
2011,
23.
Abstract:
Aiming at the shortcomings of laser point-to-point communication, the assumption of constructing communication networks by laser diffusion from sea surface was come up with, and the characteristics of the scattered field of laser from perfect conductor surface(PCS) was studied. First, the 3D model of incident laser beam was established with 3D scalar tapered wave. Second, the matrix equation was given and discretized with the method of moments. Finally, the 3D bistatic scattering coefficient was obtained with forward-backward method to accurately express the 3D scalar characteristics of laser diffusion from PCS.
Aiming at the shortcomings of laser point-to-point communication, the assumption of constructing communication networks by laser diffusion from sea surface was come up with, and the characteristics of the scattered field of laser from perfect conductor surface(PCS) was studied. First, the 3D model of incident laser beam was established with 3D scalar tapered wave. Second, the matrix equation was given and discretized with the method of moments. Finally, the 3D bistatic scattering coefficient was obtained with forward-backward method to accurately express the 3D scalar characteristics of laser diffusion from PCS.
2011,
23.
Abstract:
Using water as coolant, a closed loop spray cooling system with a builtin condenser is established and the variation of startup time is measured dynamically. The optimized startup sequence for different modules is condenser, pump and heater. Under the optimized startup sequence, experimental investigation of the effect of operation parameters, such as cooling water flow rate, heating power, pump height and spray flow rate, on startup characteristics is made. The startup time decreases with the increase of the cooling water flow rate and spray flow rate. The descending order of influence of the factors is as follows: spray flow rate, cooling water flow rate, heating power, and relative height of pump. The startup time reduces by about 5 000 s when the spray flow rate increases from 10 mL/
Using water as coolant, a closed loop spray cooling system with a builtin condenser is established and the variation of startup time is measured dynamically. The optimized startup sequence for different modules is condenser, pump and heater. Under the optimized startup sequence, experimental investigation of the effect of operation parameters, such as cooling water flow rate, heating power, pump height and spray flow rate, on startup characteristics is made. The startup time decreases with the increase of the cooling water flow rate and spray flow rate. The descending order of influence of the factors is as follows: spray flow rate, cooling water flow rate, heating power, and relative height of pump. The startup time reduces by about 5 000 s when the spray flow rate increases from 10 mL/
2011,
23.
Abstract:
Laser thrusters with single nozzle of parabolic or conic profile fail to constrict the high-pressured flow efficiently, resulting in poor propulsion performance. Under air-breathing mode and different single-pulse laser energy, the laser thruster with elongate cylindrical nozzle which features a parabolic nozzle tailed by a cylindrical nozzle is studied numerically for different shape parameters by building physical computation model. Readily, its impulse coupling coefficient is tested to be more than 600 N/MW with a good accordance with the foreign experiments. Meanwhile, the results show that, the impulse coupling coefficient increases along with cylindrical nozzle length and approaches a constant value, and the proposed cylindrical nozzle saturation length increases linearly with laser
Laser thrusters with single nozzle of parabolic or conic profile fail to constrict the high-pressured flow efficiently, resulting in poor propulsion performance. Under air-breathing mode and different single-pulse laser energy, the laser thruster with elongate cylindrical nozzle which features a parabolic nozzle tailed by a cylindrical nozzle is studied numerically for different shape parameters by building physical computation model. Readily, its impulse coupling coefficient is tested to be more than 600 N/MW with a good accordance with the foreign experiments. Meanwhile, the results show that, the impulse coupling coefficient increases along with cylindrical nozzle length and approaches a constant value, and the proposed cylindrical nozzle saturation length increases linearly with laser
2011,
23.
Abstract:
The spectrum of a series of low concentration carbon monoxide and mixed gas (carbon monoxide, methane and nitrogen) was obtained around 2.33 μm using a tunable distributed feedback semiconductor laser with an astigmatic mirror multi-pass absorption cell (optical path length 100 m) at room temperature through direct absorption technique. The absorption lines of carbon monoxide at 4 288.289 8 cm-1 and methane at 4 287.650 15 cm-1 were chosen for trace detection. At the total pressure of 40 698 Pa, the detection limits of carbon monoxide and methane were gotten respectively, i.e. 8.15×10-6 for carbon monoxide (signal-to-noise ratio is about 216) and 18.48×10-6 for methane (signal-to-noise ratio is about 147).
The spectrum of a series of low concentration carbon monoxide and mixed gas (carbon monoxide, methane and nitrogen) was obtained around 2.33 μm using a tunable distributed feedback semiconductor laser with an astigmatic mirror multi-pass absorption cell (optical path length 100 m) at room temperature through direct absorption technique. The absorption lines of carbon monoxide at 4 288.289 8 cm-1 and methane at 4 287.650 15 cm-1 were chosen for trace detection. At the total pressure of 40 698 Pa, the detection limits of carbon monoxide and methane were gotten respectively, i.e. 8.15×10-6 for carbon monoxide (signal-to-noise ratio is about 216) and 18.48×10-6 for methane (signal-to-noise ratio is about 147).
2011,
23.
Abstract:
Based on the analysis of the working principle of automatic gain control (AGC) circuit, the mechanism of laser jamming on AGC circuit is discussed, and the experiment of laser jamming on the AGC circuit of an infrared thermal imaging device is carried out. An analysis method which uses the change of regional gray scale to test the gain of AGC circuit is then proposed. Finally, a quantitative analysis is conducted on the experiment data, and the result indicates that, the persistent effective interference of laser on AGC circuit of infrared thermal imaging device can be realized, on condition that the pulse period of interference laser is less than the adjustment time of automatic gain.
Based on the analysis of the working principle of automatic gain control (AGC) circuit, the mechanism of laser jamming on AGC circuit is discussed, and the experiment of laser jamming on the AGC circuit of an infrared thermal imaging device is carried out. An analysis method which uses the change of regional gray scale to test the gain of AGC circuit is then proposed. Finally, a quantitative analysis is conducted on the experiment data, and the result indicates that, the persistent effective interference of laser on AGC circuit of infrared thermal imaging device can be realized, on condition that the pulse period of interference laser is less than the adjustment time of automatic gain.
2011,
23.
Abstract:
According to the definition of fluorescence lifetime and the gain equation of optical parametric amplification, optical parametric fluorescence lifetime(OPFL) distribution characteristics are studied in a novel nonlinear crystal BaAlBO3F2 under three different phase matching modes. The calculation results indicate that for homochromatic signal injection, OPFL distribution changes from an ellipsoid to a torus with the increasing of pump phase matching angle. When a broadband signal is injected, OPFL shows firstly a scattered distribution and then a concentrated distribution. If a broadband pump is injected into the optical parametric amplifier, the range of OPFL distribution expands greatly for the increasing phase matching range.
According to the definition of fluorescence lifetime and the gain equation of optical parametric amplification, optical parametric fluorescence lifetime(OPFL) distribution characteristics are studied in a novel nonlinear crystal BaAlBO3F2 under three different phase matching modes. The calculation results indicate that for homochromatic signal injection, OPFL distribution changes from an ellipsoid to a torus with the increasing of pump phase matching angle. When a broadband signal is injected, OPFL shows firstly a scattered distribution and then a concentrated distribution. If a broadband pump is injected into the optical parametric amplifier, the range of OPFL distribution expands greatly for the increasing phase matching range.
2011,
23.
Abstract:
An ultralow-repetition-rate, all-normal-dispersion fiber laser is proposed which is passively mode-locked by an SESAM (semiconductor saturable absorber mirror) with ultra long cavity length and high concentration single mode ytterbium-doped fiber. The central wavelength, repetition rate, average power and energy of a single output pulse are 1 064 nm, 281.5 kHz, 11 mW and 39 nJ, respectively. A band-pass filter is employed in the cavity to stabilize the central wavelength and realize self-start operation. The laser operates stably and has no Q-switching instabilities, which greatly reduces the damage probability of the SESAM.
An ultralow-repetition-rate, all-normal-dispersion fiber laser is proposed which is passively mode-locked by an SESAM (semiconductor saturable absorber mirror) with ultra long cavity length and high concentration single mode ytterbium-doped fiber. The central wavelength, repetition rate, average power and energy of a single output pulse are 1 064 nm, 281.5 kHz, 11 mW and 39 nJ, respectively. A band-pass filter is employed in the cavity to stabilize the central wavelength and realize self-start operation. The laser operates stably and has no Q-switching instabilities, which greatly reduces the damage probability of the SESAM.
2011,
23.
Abstract:
A quantity of atmospheric moderate resolution radiation results at Chaohu Lake basin(water site and vegetation site) in summer are obtained, including transmittance along observation path, atmospheric radiance, atmospheric profiles, etc., using MODIS(moderate resolution imaging spectroradiometer) data and radiative transfer model MODTRAN(moderate resolution transmission). The results show that, influenced by visibility, the transmittance at water site is slightly higher. Spectral distributions of path radiance at the entrance pupil of satellite at the two sites are similar. In visible and near infrared bands, the path radiation is very similar to the scattered solar radiation, and they both decrease gradually with the increase of wavelength; the atmospheric thermal radiance is very small.
A quantity of atmospheric moderate resolution radiation results at Chaohu Lake basin(water site and vegetation site) in summer are obtained, including transmittance along observation path, atmospheric radiance, atmospheric profiles, etc., using MODIS(moderate resolution imaging spectroradiometer) data and radiative transfer model MODTRAN(moderate resolution transmission). The results show that, influenced by visibility, the transmittance at water site is slightly higher. Spectral distributions of path radiance at the entrance pupil of satellite at the two sites are similar. In visible and near infrared bands, the path radiation is very similar to the scattered solar radiation, and they both decrease gradually with the increase of wavelength; the atmospheric thermal radiance is very small.
2011,
23.
Abstract:
Radiation forces and trapping stability of focused flat-topped beam and flat-topped vortex beam on metallic (i.e. gold) Rayleigh particle are analyzed, where the dependence of radiation forces on topological charge and beam order are stressed and illustrated by numerical examples. The results show that the maximum intensity and radiation forces (absolute value) decrease with increasing topological charge or beam order, and the trapping stiffness and range decrease with increasing the beam order of the flat-topped beam. The flat-topped beam can be used to trap gold Rayleigh particles at the geometrical focal plane, while the flat-topped vortex beam cannot trap the particles owing to the gradient force which could not act as restoring force. Finally, necessary conditions of complex dielectri
Radiation forces and trapping stability of focused flat-topped beam and flat-topped vortex beam on metallic (i.e. gold) Rayleigh particle are analyzed, where the dependence of radiation forces on topological charge and beam order are stressed and illustrated by numerical examples. The results show that the maximum intensity and radiation forces (absolute value) decrease with increasing topological charge or beam order, and the trapping stiffness and range decrease with increasing the beam order of the flat-topped beam. The flat-topped beam can be used to trap gold Rayleigh particles at the geometrical focal plane, while the flat-topped vortex beam cannot trap the particles owing to the gradient force which could not act as restoring force. Finally, necessary conditions of complex dielectri
2011,
23.
Abstract:
The low threshold of compression gratings determines the maximum output energy of high-energy PW laser systems. For the compressor in the Xingguang-Ⅲ facility which is under development, this paper designed a 2-D photonic-crystal grating of fused silica which utilizes photonic crystal technology and the grating’s micro-structure. The results show that the diffraction efficiency of the minus first order of the grating exceeds 92% for incident angle from 57° to 77° when the incident wavelength is 1 053 nm, and for wavelength from 1 040 nm to 1 090 nm when the incident angle is 71°. The grating meets the requirements of wide spectral range (50 nm) and wide range of angle of incidence (18°).
The low threshold of compression gratings determines the maximum output energy of high-energy PW laser systems. For the compressor in the Xingguang-Ⅲ facility which is under development, this paper designed a 2-D photonic-crystal grating of fused silica which utilizes photonic crystal technology and the grating’s micro-structure. The results show that the diffraction efficiency of the minus first order of the grating exceeds 92% for incident angle from 57° to 77° when the incident wavelength is 1 053 nm, and for wavelength from 1 040 nm to 1 090 nm when the incident angle is 71°. The grating meets the requirements of wide spectral range (50 nm) and wide range of angle of incidence (18°).
2011,
23.
Abstract:
To avoid the smile effect, which seriously restricts the linewidth narrowing of high power diode laser for alkali vapor laser, a 780 nm single-broad-area high power diode laser was studied. An output beam with 11.5 W power, 61% external cavity efficiency was obtained with the optimized Littman configuration, when the laser run freely at 19 W. When the beam transmitted through a 25 cm long, 110 ℃ Rb vapor cell with 80 kPa ethane, 96.7% power was absorbed. The theory calculation supports the 0.03 nm linewidth (15 GHz spectral width) derived from experimental results.
To avoid the smile effect, which seriously restricts the linewidth narrowing of high power diode laser for alkali vapor laser, a 780 nm single-broad-area high power diode laser was studied. An output beam with 11.5 W power, 61% external cavity efficiency was obtained with the optimized Littman configuration, when the laser run freely at 19 W. When the beam transmitted through a 25 cm long, 110 ℃ Rb vapor cell with 80 kPa ethane, 96.7% power was absorbed. The theory calculation supports the 0.03 nm linewidth (15 GHz spectral width) derived from experimental results.
2011,
23.
Abstract:
An arbitrary length nozzle design method(ALN method) is applied to the nozzle design of a gasdynamic laser. For comparison, four ALN nozzles and one MLN nozzle (designed by minimum length nozzle design method) are designed with the same Mach number on nozzle exit plane, the same height of nozzle throat and the same length of nozzle. Two-dimensional small signal gain(SSG) field simulation is carried out for the five nozzles and the simulation results indicate that the ALN method can control the SSG field distribution of nozzle effectively. ALN nozzles with proper design parameters can obtain shorter nozzle length and bigger SSG than MLN nozzles.
An arbitrary length nozzle design method(ALN method) is applied to the nozzle design of a gasdynamic laser. For comparison, four ALN nozzles and one MLN nozzle (designed by minimum length nozzle design method) are designed with the same Mach number on nozzle exit plane, the same height of nozzle throat and the same length of nozzle. Two-dimensional small signal gain(SSG) field simulation is carried out for the five nozzles and the simulation results indicate that the ALN method can control the SSG field distribution of nozzle effectively. ALN nozzles with proper design parameters can obtain shorter nozzle length and bigger SSG than MLN nozzles.
2011,
23.
Abstract:
In order to meet the requirement of high-energy laser output from a vacuum resonator to atmosphere and reduce the effect of windows thermal deformation on laser beam performance, the paper introduces a technical solution which can reduce laser irradiation on solid window. In the solution, solid window is driven by high torque hollow DC motor and rotates uniformly. The isolation between vacuum resonator and environmental atmosphere is fulfilled by high-precision dynamic seals. And thus the irradiation on window is more uniform, i.e. the window temperature and stress gradient are decreased greatly, the laser beam quality is improved, and cracks in window can be avoided in long-time running. The results show that the solution is of several advantages, such as small volume, light weight, compa
In order to meet the requirement of high-energy laser output from a vacuum resonator to atmosphere and reduce the effect of windows thermal deformation on laser beam performance, the paper introduces a technical solution which can reduce laser irradiation on solid window. In the solution, solid window is driven by high torque hollow DC motor and rotates uniformly. The isolation between vacuum resonator and environmental atmosphere is fulfilled by high-precision dynamic seals. And thus the irradiation on window is more uniform, i.e. the window temperature and stress gradient are decreased greatly, the laser beam quality is improved, and cracks in window can be avoided in long-time running. The results show that the solution is of several advantages, such as small volume, light weight, compa
2011,
23.
Abstract:
Based on the research results at home and abroad, this paper provides a brief summarization and comments on the heat transfer characteristics, mechanisms, strengthening way and affecting parameters of spray cooling. Some theoretical models for critical heat flux are presented. And the development direction of spray cooling is proposed according to the cooling requirements of high power lasers.
Based on the research results at home and abroad, this paper provides a brief summarization and comments on the heat transfer characteristics, mechanisms, strengthening way and affecting parameters of spray cooling. Some theoretical models for critical heat flux are presented. And the development direction of spray cooling is proposed according to the cooling requirements of high power lasers.
2011,
23.
Abstract:
Based on the mechanism of quasi-stationary wave (QSW) formed by optical pulsed discharge (OPD), which is generated by high frequency pulsed laser, a self-compiled computational fluid dynamics program is validated. The results indicate that this program can be used to study air-breathing high frequency pulsed laser propulsion numerically. Impulse coupling coefficients of QSW fluid field based on moving igniting point mode and jet flow mode are both up to about 600 N/MW, which are higher than that of traditional low frequency pulsed laser propulsion (250 N/MW). Advantages and disadvantages of the two modes are compared, and their applicable situation is listed. Moreover, the jet flow mode is easier to realize for mechanism study.
Based on the mechanism of quasi-stationary wave (QSW) formed by optical pulsed discharge (OPD), which is generated by high frequency pulsed laser, a self-compiled computational fluid dynamics program is validated. The results indicate that this program can be used to study air-breathing high frequency pulsed laser propulsion numerically. Impulse coupling coefficients of QSW fluid field based on moving igniting point mode and jet flow mode are both up to about 600 N/MW, which are higher than that of traditional low frequency pulsed laser propulsion (250 N/MW). Advantages and disadvantages of the two modes are compared, and their applicable situation is listed. Moreover, the jet flow mode is easier to realize for mechanism study.
2011,
23.
Abstract:
For it is hard to remove clutters, especially the clutter edge, with conventional high-pass filters in spatial or temporal domain, a dim moving target detection method based on the time-frequency characters of target, noise and clutter is presented. Theoretical analysis shows that the magnitude at the target location in time-frequency domain is a small wave packet, whose magnitude is consistent with the target amplitude, and width is inversely proportional to target speed; the magnitude at clutter edge in time-frequency domain is an uphill or downhill. This target detection method uses two-stage filtering to detect dim target. At first, a threshold based on false alarm ratio criteria in time-frequency domain is adopted to remove noise, and then the energy ratio between main lobe and side l
For it is hard to remove clutters, especially the clutter edge, with conventional high-pass filters in spatial or temporal domain, a dim moving target detection method based on the time-frequency characters of target, noise and clutter is presented. Theoretical analysis shows that the magnitude at the target location in time-frequency domain is a small wave packet, whose magnitude is consistent with the target amplitude, and width is inversely proportional to target speed; the magnitude at clutter edge in time-frequency domain is an uphill or downhill. This target detection method uses two-stage filtering to detect dim target. At first, a threshold based on false alarm ratio criteria in time-frequency domain is adopted to remove noise, and then the energy ratio between main lobe and side l
2011,
23.
Abstract:
By incorporating a commercial diode-laser-bar into a volume Bragg grating(VBG) based external cavity, we obtained 80 W CW output power with 0.1 nm linewidth centered at 780.2 nm. To reduce the thermal effect, a chopper was used to convert the CW pump light into pulsed mode, with pulse duration of 440 μs and duty ratio of 1∶5. The 5 mm long gain medium was filled with metallic Rb and buffer gases of 33 kPa ethane and 47 kPa helium at room temperature. At peak pump power of 35.4 W and gain medium temperature of 120 ℃, we obtained 600 mW peak power output of the 795 nm Rb laser with slope efficiency of 1.7%.
By incorporating a commercial diode-laser-bar into a volume Bragg grating(VBG) based external cavity, we obtained 80 W CW output power with 0.1 nm linewidth centered at 780.2 nm. To reduce the thermal effect, a chopper was used to convert the CW pump light into pulsed mode, with pulse duration of 440 μs and duty ratio of 1∶5. The 5 mm long gain medium was filled with metallic Rb and buffer gases of 33 kPa ethane and 47 kPa helium at room temperature. At peak pump power of 35.4 W and gain medium temperature of 120 ℃, we obtained 600 mW peak power output of the 795 nm Rb laser with slope efficiency of 1.7%.
2011,
23.
Abstract:
An X-ray backlight imaging system using spherically bent crystal has been set up based on the X-ray Bragg diffraction theory. The primary component of the system is a spherically bent α-quartz crystal whose curvature radius is 143 mm. The monochromatic X-ray backlight imaging experiment using the imaging system has been carried out on the anode accelerator of Institute of Fluid Physics, China Academy of Engineering Physics(CAEP). In the experiment, the backlighter is a laser-produced plasma X-ray source created using Al wire arrays implosion; the test object is stainless steel wires of diameter of 100 μm and period of 500 μm; the X-ray film is used to obtain the two-dimensional monochromatic X-ray backlight images. The imaging system provides a spatial resolution of approximately 75 μm
An X-ray backlight imaging system using spherically bent crystal has been set up based on the X-ray Bragg diffraction theory. The primary component of the system is a spherically bent α-quartz crystal whose curvature radius is 143 mm. The monochromatic X-ray backlight imaging experiment using the imaging system has been carried out on the anode accelerator of Institute of Fluid Physics, China Academy of Engineering Physics(CAEP). In the experiment, the backlighter is a laser-produced plasma X-ray source created using Al wire arrays implosion; the test object is stainless steel wires of diameter of 100 μm and period of 500 μm; the X-ray film is used to obtain the two-dimensional monochromatic X-ray backlight images. The imaging system provides a spatial resolution of approximately 75 μm
2011,
23.
Abstract:
A technical scheme of super-cavity with two parabolic mirrors is presented. The total photon density at the collision point of parabolic super-cavity is computed. By using the Compton scattering theory, the high brightness laser synchrotron source based on the parabolic super-cavity, including photon yield are discussed and calculated. The results show that when the reflectivity of parabolic mirror is equal to 99.99%, the total photon density at the collision point after infinite reflection is about 5 000 times higher than the photon density of the input laser beam at the collision point, and the photon yield of corresponding Compton vertical scattering is about 5 000 times higher than the photon yield of Compton vertical scattering between electron beam and input laser beam at the collisi
A technical scheme of super-cavity with two parabolic mirrors is presented. The total photon density at the collision point of parabolic super-cavity is computed. By using the Compton scattering theory, the high brightness laser synchrotron source based on the parabolic super-cavity, including photon yield are discussed and calculated. The results show that when the reflectivity of parabolic mirror is equal to 99.99%, the total photon density at the collision point after infinite reflection is about 5 000 times higher than the photon density of the input laser beam at the collision point, and the photon yield of corresponding Compton vertical scattering is about 5 000 times higher than the photon yield of Compton vertical scattering between electron beam and input laser beam at the collisi
2011,
23.
Abstract:
To realize high-sensitive and rapid analysis of trace cadmium in water, an unpolluted thin wood slice was chosen as substrate to absorb water sample and then analyzed with laser-induced breakdown spectroscopy(LIBS) after being dried, which overcomes the drawbacks of low sensitivity and reproducibility existing in the process of direct analysis of water sample with LIBS. The 214.44 nm ionic line of cadmium was chosen as analytical line. A calibration curve was established for the purpose of quantitative analysis. The limit of detection of cadmium in water was determined to be 55 μg/L and the relative standard deviation of signal in different measurements was less than 5%. The time needed for each measurement was less than 5 min.
To realize high-sensitive and rapid analysis of trace cadmium in water, an unpolluted thin wood slice was chosen as substrate to absorb water sample and then analyzed with laser-induced breakdown spectroscopy(LIBS) after being dried, which overcomes the drawbacks of low sensitivity and reproducibility existing in the process of direct analysis of water sample with LIBS. The 214.44 nm ionic line of cadmium was chosen as analytical line. A calibration curve was established for the purpose of quantitative analysis. The limit of detection of cadmium in water was determined to be 55 μg/L and the relative standard deviation of signal in different measurements was less than 5%. The time needed for each measurement was less than 5 min.
2011,
23.
Abstract:
The parameters of laser have impact on the process of producing quasimonoenergetic proton beams which use a high power laser interacting with plasmas. The duration of the laser is an important parameter of them. A one dimension particle-in cell code LPIC++ is used to simulate the P-polarized laser interacting with the cold dense target. In the simulation, the ponderomotive force pushing the plasma layer and launching a shock wave are observed. The moving shock wave in the target traps ions and reflect them to as much as two times of the ion-acoustic velocity. It is also observed that if suitable laser duration is utilized, just as the duration matches the thickness of the target, the energy spread of the proton’s beam is about 30%. The quasimonoenergetic protons beam’s energy also can be
The parameters of laser have impact on the process of producing quasimonoenergetic proton beams which use a high power laser interacting with plasmas. The duration of the laser is an important parameter of them. A one dimension particle-in cell code LPIC++ is used to simulate the P-polarized laser interacting with the cold dense target. In the simulation, the ponderomotive force pushing the plasma layer and launching a shock wave are observed. The moving shock wave in the target traps ions and reflect them to as much as two times of the ion-acoustic velocity. It is also observed that if suitable laser duration is utilized, just as the duration matches the thickness of the target, the energy spread of the proton’s beam is about 30%. The quasimonoenergetic protons beam’s energy also can be
2011,
23.
Abstract:
Parameters of the laser-induced aluminum alloy E414d plasma are studied. The Local Thermodynamic Equilibrium (LTE) is proved valid for the electron number density (1.9×1018 cm-3), inferred from the Lorentz fit of Mg (Ⅰ) 285.21 nm, is lager than the lower limit (9.8×1015 cm-3) for LTE exists. The electron temperatures at different height are determined using the Blotzmann plot method with Al (Ⅰ) 256.80 nm, Al (Ⅰ) 308.21 nm and Al (Ⅰ) 396.15 nm. The electron temperature is maximum at the distance of 1.5 mm above the target surface and it decreases both at the plasma edge and close to the target surface. The physical explanations for this spatial distribution are presented.
Parameters of the laser-induced aluminum alloy E414d plasma are studied. The Local Thermodynamic Equilibrium (LTE) is proved valid for the electron number density (1.9×1018 cm-3), inferred from the Lorentz fit of Mg (Ⅰ) 285.21 nm, is lager than the lower limit (9.8×1015 cm-3) for LTE exists. The electron temperatures at different height are determined using the Blotzmann plot method with Al (Ⅰ) 256.80 nm, Al (Ⅰ) 308.21 nm and Al (Ⅰ) 396.15 nm. The electron temperature is maximum at the distance of 1.5 mm above the target surface and it decreases both at the plasma edge and close to the target surface. The physical explanations for this spatial distribution are presented.
2011,
23.
Abstract:
Much attention has been paid to seeking efficient methods for the controlled release of nuclear energy in appropriate isomer systems, which is an interdisciplinary subject. Utilizing atomic processes for releasing is a relatively feasible scheme, where atomic data play very important roles. A high-efficient atomic database is introduced. Such database has the energy structure information of elements with atomic number smaller than 96 (including their ions with all ionization degrees), which allows a fast searching. Therefore some possible isomer systems which can be triggered by atomic processes can be found out. The applications of the database in the processes of nuclear excitation by electronic transition(NEET) of 197Au and nuclear excitation by electron capture(NEEC) of 178Hf are prese
Much attention has been paid to seeking efficient methods for the controlled release of nuclear energy in appropriate isomer systems, which is an interdisciplinary subject. Utilizing atomic processes for releasing is a relatively feasible scheme, where atomic data play very important roles. A high-efficient atomic database is introduced. Such database has the energy structure information of elements with atomic number smaller than 96 (including their ions with all ionization degrees), which allows a fast searching. Therefore some possible isomer systems which can be triggered by atomic processes can be found out. The applications of the database in the processes of nuclear excitation by electronic transition(NEET) of 197Au and nuclear excitation by electron capture(NEEC) of 178Hf are prese
2011,
23.
Abstract:
By introducing photonic crystal (or PBG) structure to the traditional disk-loaded accelerating tube, wakefields in the accelerating structure can be effectively damped. Machining methods of a 2D metallic PBG cavity were investigated and X-band PBG cavities with high quality factor were successfully fabricated. Suppression brought by the absorbers placed at the periphery of these PBG accelerating cavities is significant to the high order modes, but has very little effect on the accelerating mode TM01-like. Design and fabrication of a 4-cell traveling wave accelerating structure operating at the frequency of 11.42 GHz were accomplished and the cold test results were in agreement with the numerical simulations.
By introducing photonic crystal (or PBG) structure to the traditional disk-loaded accelerating tube, wakefields in the accelerating structure can be effectively damped. Machining methods of a 2D metallic PBG cavity were investigated and X-band PBG cavities with high quality factor were successfully fabricated. Suppression brought by the absorbers placed at the periphery of these PBG accelerating cavities is significant to the high order modes, but has very little effect on the accelerating mode TM01-like. Design and fabrication of a 4-cell traveling wave accelerating structure operating at the frequency of 11.42 GHz were accomplished and the cold test results were in agreement with the numerical simulations.
2011,
23.
Abstract:
A reconstruction algorithm is proposed for flash radiographic image with low signal-to-noise ratio. The algorithm is based on Bayesian principle, and uses smoothness constraint to handle the blurring effects caused by the X-ray source of radiography and imaging device. It is implemented with regularization schemes for performing tomographic image reconstruction from a single noisy projection. Numerical experimental results show that, in comparison with the conventional algebraic reconstruction technique, the algorithm has stronger ability of noise removal and edge preservation.
A reconstruction algorithm is proposed for flash radiographic image with low signal-to-noise ratio. The algorithm is based on Bayesian principle, and uses smoothness constraint to handle the blurring effects caused by the X-ray source of radiography and imaging device. It is implemented with regularization schemes for performing tomographic image reconstruction from a single noisy projection. Numerical experimental results show that, in comparison with the conventional algebraic reconstruction technique, the algorithm has stronger ability of noise removal and edge preservation.
2011,
23.
Abstract:
The vertical beam size of BEPCⅡstorage ring was measured by using visible synchrotron light spatial interference method, and the measured size is 155 μm. The measurement results fit well with the calculation predication. This method can avoid the measurement error caused by synchrotron light diffraction and makes the measurement results more accurate. In addition, the method is applicable to other small size incoherent light source.
The vertical beam size of BEPCⅡstorage ring was measured by using visible synchrotron light spatial interference method, and the measured size is 155 μm. The measurement results fit well with the calculation predication. This method can avoid the measurement error caused by synchrotron light diffraction and makes the measurement results more accurate. In addition, the method is applicable to other small size incoherent light source.
2011,
23.
Abstract:
An embedded synchronization system based on FPGA for high energy industry CT is introduced. FPGA is the main unit of the system, including UART, decoding module, LCD module, reading/writing EEPROM module, synchronization timing module, and so on. Decoding module is designed with finite state machine, and has good expansibility. Look-up table is adopted in the counter of frequency module to increase processing speed and decrease resource consumption. The control software is designed by VC++, and high quality images have been acquired through experiments.
An embedded synchronization system based on FPGA for high energy industry CT is introduced. FPGA is the main unit of the system, including UART, decoding module, LCD module, reading/writing EEPROM module, synchronization timing module, and so on. Decoding module is designed with finite state machine, and has good expansibility. Look-up table is adopted in the counter of frequency module to increase processing speed and decrease resource consumption. The control software is designed by VC++, and high quality images have been acquired through experiments.
2011,
23.
Abstract:
A Penning-type negative hydrogen ion source was diagnosed by emission spectrometry, and the source arc power was measured under different conditions in the meantime. The ion source was designed to offer negative hydrogen to a small medical cyclotron. The relative intensities of the first three lines in hydrogen Balmer series of the ion source and the source arc power were measured under different hydrogen flows, source arc currents and magnetic fields, and then the ion source’s working status was analyzed under these conditions. The result indicates that, the working status of the ion source is not sensitive to the variations in arc current and magnetic field, and mainly affected by hydrogen flow.
A Penning-type negative hydrogen ion source was diagnosed by emission spectrometry, and the source arc power was measured under different conditions in the meantime. The ion source was designed to offer negative hydrogen to a small medical cyclotron. The relative intensities of the first three lines in hydrogen Balmer series of the ion source and the source arc power were measured under different hydrogen flows, source arc currents and magnetic fields, and then the ion source’s working status was analyzed under these conditions. The result indicates that, the working status of the ion source is not sensitive to the variations in arc current and magnetic field, and mainly affected by hydrogen flow.
2011,
23.
Abstract:
Due to the limited number of views in high-energy X-ray radiography, the density reconstruction for asymmetric objects from a single radiograph is studied. The approach proposed can make explicit use of model-based information concerning the symmetric and asymmetric information from the radiograph to compose the other rotational views in a more exact fashion. The three dimension program for the density reconstruction is developed based on total variation and algebraic reconstruction techniques. Numerical simulations show the impact on the accuracy of density reconstruction by varying the number of the radiographic views.
Due to the limited number of views in high-energy X-ray radiography, the density reconstruction for asymmetric objects from a single radiograph is studied. The approach proposed can make explicit use of model-based information concerning the symmetric and asymmetric information from the radiograph to compose the other rotational views in a more exact fashion. The three dimension program for the density reconstruction is developed based on total variation and algebraic reconstruction techniques. Numerical simulations show the impact on the accuracy of density reconstruction by varying the number of the radiographic views.
2011,
23.
Abstract:
A magnetically-insulated transmission line(MITL) with inductive spring is designed according to PSpice calculation to study the energy transmission influence of the spring. A system for its calibration and diagnosis is then designed. In one shot, when the input cathode current is 90.08 kA, the output cathode current is 93.88 kA and the transmission efficiency is 95.96%. The average transmission efficiency of the experiments conducted is 92.8%. The experimental results are consistent with the theoretical analysis, validating the feasibility of the MITL.
A magnetically-insulated transmission line(MITL) with inductive spring is designed according to PSpice calculation to study the energy transmission influence of the spring. A system for its calibration and diagnosis is then designed. In one shot, when the input cathode current is 90.08 kA, the output cathode current is 93.88 kA and the transmission efficiency is 95.96%. The average transmission efficiency of the experiments conducted is 92.8%. The experimental results are consistent with the theoretical analysis, validating the feasibility of the MITL.
2011,
23.
Abstract:
Based on the current element model for magnetic ring, the magnetic field distribution along central axis was analyzed for permanent magnetic ring. Theoretical calculation and measured results show that the whole magnetic ring only exhibits an axial magnetic field without radial component. For the open magnetic ring with a gap, the axial magnetic field decreases and the radial magnetic field increases, producing a non-axis-symmetrical magnetic field along central axis. Therefore, the application of the open magnetic ring in periodic permanent magnet(PPM) focusing system is limited. The structure of the PPM focusing system with open magnetic rings was proposed and optimized, according to the distribution characteristic of the axial magnetic field and radial magnetic field, and the periodic m
Based on the current element model for magnetic ring, the magnetic field distribution along central axis was analyzed for permanent magnetic ring. Theoretical calculation and measured results show that the whole magnetic ring only exhibits an axial magnetic field without radial component. For the open magnetic ring with a gap, the axial magnetic field decreases and the radial magnetic field increases, producing a non-axis-symmetrical magnetic field along central axis. Therefore, the application of the open magnetic ring in periodic permanent magnet(PPM) focusing system is limited. The structure of the PPM focusing system with open magnetic rings was proposed and optimized, according to the distribution characteristic of the axial magnetic field and radial magnetic field, and the periodic m
2011,
23.
Abstract:
The flashover probability of vacuum insulator stack (VIS) is calculated based on statistical model. The calculation results show that the probability reduces with lower peak voltage of VIS, shorter effective pulse duration, smaller material constant and smaller stack radius in a certain range of VIS voltage. The flashover probability is also calculated with the consideration of magnetic flashover inhibition (MFI) under different critical ratios. The critical ratio is defined as the ratio of electric field strength to magnetic induction strength when MFI begins to be effective, and is changed according to different angles between insulator and electrode considering the relation of the three-phase point electric field strength of cathode and the average electric field strength of VIS. The si
The flashover probability of vacuum insulator stack (VIS) is calculated based on statistical model. The calculation results show that the probability reduces with lower peak voltage of VIS, shorter effective pulse duration, smaller material constant and smaller stack radius in a certain range of VIS voltage. The flashover probability is also calculated with the consideration of magnetic flashover inhibition (MFI) under different critical ratios. The critical ratio is defined as the ratio of electric field strength to magnetic induction strength when MFI begins to be effective, and is changed according to different angles between insulator and electrode considering the relation of the three-phase point electric field strength of cathode and the average electric field strength of VIS. The si
2011,
23.
Abstract:
A new method of piezoelectric detection is presented for diagnosing ignition thresholds of LSCW and LSDW by measuring strain and stress, which generated on surface of target due to interaction between Nd:YAG laser operating at 1 064 nm and aluminum target. Changes of piezoelectric signal observed in experimental results might be divided into three stages, which can be explained as photothermal elastic strain, plasma enhanced coupling and LSDW pressure on the target surface in theory. Ignition thresholds of LSCW and LSDW can be determined by analyzing the shift of piezoelectric signal. Experimental results obtained are largely in accord with those from other methods.
A new method of piezoelectric detection is presented for diagnosing ignition thresholds of LSCW and LSDW by measuring strain and stress, which generated on surface of target due to interaction between Nd:YAG laser operating at 1 064 nm and aluminum target. Changes of piezoelectric signal observed in experimental results might be divided into three stages, which can be explained as photothermal elastic strain, plasma enhanced coupling and LSDW pressure on the target surface in theory. Ignition thresholds of LSCW and LSDW can be determined by analyzing the shift of piezoelectric signal. Experimental results obtained are largely in accord with those from other methods.
