Email alert
RSS2010 Vol. 22, No. 10
Recommend Articles
Display Method:
2010,
22.
Abstract:
The influence of applied magnetic field on the process of vacuum flashover, especially on electric field-induced secondary electron emission and electron avalanche, has been investigated by a Monte-Carlo code based on single particle model. It is found that, the presence of applied magnetic field alters the motion of surface electrons, and then affects the distribution of surface charge, which finally influences the flashover voltage. Proper magnetic field applied on vacuum surface can inhibit the secondary electron avalanche, and thus enhances the flashover voltage. The effect of applied magnetic field on flashover depends on the field’s spatial distribution, and the near-cathode field is more favorable than the near-anode one.
The influence of applied magnetic field on the process of vacuum flashover, especially on electric field-induced secondary electron emission and electron avalanche, has been investigated by a Monte-Carlo code based on single particle model. It is found that, the presence of applied magnetic field alters the motion of surface electrons, and then affects the distribution of surface charge, which finally influences the flashover voltage. Proper magnetic field applied on vacuum surface can inhibit the secondary electron avalanche, and thus enhances the flashover voltage. The effect of applied magnetic field on flashover depends on the field’s spatial distribution, and the near-cathode field is more favorable than the near-anode one.
2010,
22.
Abstract:
The parameters of miniature MA-level helical explosively-driven magnetic flux compression generator(HEMCG) are calculated by method of equivalent circuit，and the result indicates that the main loss of HEMCG is non-Ohmic loss．The entire outer diameter of HEMCG with initial inductance of 128.7 μH is about 140 mm，and the length is less than 550 mm．When the initial current injected is 3.6 kA in the experiment, a pulse current with 75.2 μs risetime and 1.87 MA peak value is obtained on the 100 nH load while the seed current is amplified by 519.4 times，which means that the energy amplification coefficient is 209.6，and the conversion efficiency from chemical energy of explosive to electromagnetic energy is 6%．The HEMCG is modulated by cable transformer with about 440 nH primary inductanc
The parameters of miniature MA-level helical explosively-driven magnetic flux compression generator(HEMCG) are calculated by method of equivalent circuit，and the result indicates that the main loss of HEMCG is non-Ohmic loss．The entire outer diameter of HEMCG with initial inductance of 128.7 μH is about 140 mm，and the length is less than 550 mm．When the initial current injected is 3.6 kA in the experiment, a pulse current with 75.2 μs risetime and 1.87 MA peak value is obtained on the 100 nH load while the seed current is amplified by 519.4 times，which means that the energy amplification coefficient is 209.6，and the conversion efficiency from chemical energy of explosive to electromagnetic energy is 6%．The HEMCG is modulated by cable transformer with about 440 nH primary inductanc
2010,
22.
Abstract:
The realization technique of modularization on the long pulse high power generator was expounded. The energy efficiency was analyzed. The main influence factors on the wave distortion from the primary pulse to the system output waveforms were discussed. In engineering experiments, a long pulse power electron beam of up to several GW with repetition frequency of 25 Hz and rise time of about 40 ns were obtained. It is proved that the technique of fast linear transformer driver is successful in developing compact and high efficient pulse generator.
The realization technique of modularization on the long pulse high power generator was expounded. The energy efficiency was analyzed. The main influence factors on the wave distortion from the primary pulse to the system output waveforms were discussed. In engineering experiments, a long pulse power electron beam of up to several GW with repetition frequency of 25 Hz and rise time of about 40 ns were obtained. It is proved that the technique of fast linear transformer driver is successful in developing compact and high efficient pulse generator.
2010,
22.
Abstract:
This paper analyzes the factors influencing the failures of high power linear xenon-filled flash lamps in NOVA, NIF and Shenguang-Ⅲ. The factors include the correlations between the stress and flash lamp explosion, the correlation between lifetime and lamp size, microdefects of lamp wall, electrode sputtering, insulation, xenon purity, sealing reliability and the increase in energy deposition into flash lamp quartz envelopes caused by the absorption of radiation from neighboring flash lamps. Given the same input energy, the lifetime is longer for the lamp with longer arc length and bigger bore diameter. Direct causes of flash lamp explosion are the surface static tensile stress on the flash lamp quartz envelopes, the microdefects on the inner surface and the increase in energy deposition
This paper analyzes the factors influencing the failures of high power linear xenon-filled flash lamps in NOVA, NIF and Shenguang-Ⅲ. The factors include the correlations between the stress and flash lamp explosion, the correlation between lifetime and lamp size, microdefects of lamp wall, electrode sputtering, insulation, xenon purity, sealing reliability and the increase in energy deposition into flash lamp quartz envelopes caused by the absorption of radiation from neighboring flash lamps. Given the same input energy, the lifetime is longer for the lamp with longer arc length and bigger bore diameter. Direct causes of flash lamp explosion are the surface static tensile stress on the flash lamp quartz envelopes, the microdefects on the inner surface and the increase in energy deposition
2010,
22.
Abstract:
A spiral pulse forming line was presented, which consisted of inner cylinder and outer cylinder, and was densely wound by thin lines with multiple origins. Combining it with Tesla transformer, a compact long pulse generator was constructed, which had high energy efficiency, compact structure, and could work at repetitive rate. On the design principle of maximizing charging voltage, the impedance value of the forming line would be 12.6 times the slow wave coefficient, and high coupling coefficient 0.95 of Tesla transformer would be obtained when the aspect ratio of the line was greater than 3.1. On the design principle of maximizing stored energy, the impedance value of the line would be 7.5 times the slow wave coefficient, and high coupling coefficient 0.95 of Tesla transformer would be ob
A spiral pulse forming line was presented, which consisted of inner cylinder and outer cylinder, and was densely wound by thin lines with multiple origins. Combining it with Tesla transformer, a compact long pulse generator was constructed, which had high energy efficiency, compact structure, and could work at repetitive rate. On the design principle of maximizing charging voltage, the impedance value of the forming line would be 12.6 times the slow wave coefficient, and high coupling coefficient 0.95 of Tesla transformer would be obtained when the aspect ratio of the line was greater than 3.1. On the design principle of maximizing stored energy, the impedance value of the line would be 7.5 times the slow wave coefficient, and high coupling coefficient 0.95 of Tesla transformer would be ob
2010,
22.
Abstract:
A linear transformer driver (LTD) module with 150 kV output capability was designed based on a former 125 kV LTD module, which used Blumlein line as the pulse forming line. A 600 kV LTD system was contrived with four newly designed modules connected in series. Calculation and simulation were done, respectively, to decide the dimensions of the secondary coil of the LTD equipment which also sufficed the requirement about insulation, and to analyze the influence of input mode on output pulse. The results show that the output pulse waveform of the left input type is better than the right input type, and compared with the unilateral input mode, the rising time of the symmetrical input mode is shorter. The result of circuit simulation proves that the LTD system can drive a 40 Ω load with a 600
A linear transformer driver (LTD) module with 150 kV output capability was designed based on a former 125 kV LTD module, which used Blumlein line as the pulse forming line. A 600 kV LTD system was contrived with four newly designed modules connected in series. Calculation and simulation were done, respectively, to decide the dimensions of the secondary coil of the LTD equipment which also sufficed the requirement about insulation, and to analyze the influence of input mode on output pulse. The results show that the output pulse waveform of the left input type is better than the right input type, and compared with the unilateral input mode, the rising time of the symmetrical input mode is shorter. The result of circuit simulation proves that the LTD system can drive a 40 Ω load with a 600
2010,
22.
Abstract:
The experiments of unstable resonator were performed for compressing divergence angle through modifying a high-power stable resonator TEA CO2 laser. The virtual confocal positive branch was adopted to study the influences of structure parameters and mode volume on output energy and optical beam divergence for the unstable resonator. Twenty sets of mirrors with four magnifications and five mode volumes were designed and manufactured. In the same experimental conditions, the maximum pulsed energy of the unstable resonator is 14 J, which is 70% of that of the plano-concave stable resonator, but the divergence angle is just a quarter of the latter’s.
The experiments of unstable resonator were performed for compressing divergence angle through modifying a high-power stable resonator TEA CO2 laser. The virtual confocal positive branch was adopted to study the influences of structure parameters and mode volume on output energy and optical beam divergence for the unstable resonator. Twenty sets of mirrors with four magnifications and five mode volumes were designed and manufactured. In the same experimental conditions, the maximum pulsed energy of the unstable resonator is 14 J, which is 70% of that of the plano-concave stable resonator, but the divergence angle is just a quarter of the latter’s.
2010,
22.
Abstract:
A calibrating method of high voltage and current probe for fast pulse measurements is presented based on pulse formation principle. A voltage and current generator which used the output line and diode of Flash Ⅱ accelerator as pulse formation line was built with a self-developed low inductance gas switch and load. A quasi-square waveform, with a rise time of about 3 ns and a half width of 20 ns, was measured when the voltage and current on the load are 0.75 kA and 13.5 kV, respectively. The voltage and current probes of diode of flash Ⅱ accelerator were then calibrated, and their time responses were less than 4 ns. The calibrating method can generate a fast pulse for high voltage and current probe calibration in practical circumstance, it can also calibrate the probes of transmission-lin
A calibrating method of high voltage and current probe for fast pulse measurements is presented based on pulse formation principle. A voltage and current generator which used the output line and diode of Flash Ⅱ accelerator as pulse formation line was built with a self-developed low inductance gas switch and load. A quasi-square waveform, with a rise time of about 3 ns and a half width of 20 ns, was measured when the voltage and current on the load are 0.75 kA and 13.5 kV, respectively. The voltage and current probes of diode of flash Ⅱ accelerator were then calibrated, and their time responses were less than 4 ns. The calibrating method can generate a fast pulse for high voltage and current probe calibration in practical circumstance, it can also calibrate the probes of transmission-lin
2010,
22.
Abstract:
The band gap structure of 3-element 1-D photonics crystal with defective mode was studied by transfer matrix method，and the influence of the variation of the defect thickness on band gap structure was analyzed through numerical simulation. The simulation indicates that， for 3-element 1-D photonic crystal with symmetrically distributed defects，the defect thickness has little influence on the width of band gap；in the broader band gap，there is a sharp transmission peak, which will take red shift with increase of the defect thickness. Within a given range，the nonlinear relationship between wave length of the transmission peaks and defect thickness was presented，on which，FWHM of the transmission peak in band gap was calculated， furthermore， the relation graph between wave length FWHM
The band gap structure of 3-element 1-D photonics crystal with defective mode was studied by transfer matrix method，and the influence of the variation of the defect thickness on band gap structure was analyzed through numerical simulation. The simulation indicates that， for 3-element 1-D photonic crystal with symmetrically distributed defects，the defect thickness has little influence on the width of band gap；in the broader band gap，there is a sharp transmission peak, which will take red shift with increase of the defect thickness. Within a given range，the nonlinear relationship between wave length of the transmission peaks and defect thickness was presented，on which，FWHM of the transmission peak in band gap was calculated， furthermore， the relation graph between wave length FWHM
2010,
22.
Abstract:
The hydroxyl radical(OH) and oxygen atom(O) play important roles in atmospheric chemistry, surface treatment and chemical decontamination. The present work reports the measurement of OH and O in atmospheric pressure plasma jet by optical emission spectroscopy. The OH and O are observed in discharges of the H2O/O2/Ar mixture. The effects of discharge power and O2 addition in discharge system on the emission intensity of OH and O are studied. By comparing the measured emission spectrum of OH with that simulated from Lifbase data, the rotational temperature is evaluated for OH.It is shown that the rotational temperature of OH increase with the increase of discharge power,and decrease with the increase of discharge gas flow rate.
The hydroxyl radical(OH) and oxygen atom(O) play important roles in atmospheric chemistry, surface treatment and chemical decontamination. The present work reports the measurement of OH and O in atmospheric pressure plasma jet by optical emission spectroscopy. The OH and O are observed in discharges of the H2O/O2/Ar mixture. The effects of discharge power and O2 addition in discharge system on the emission intensity of OH and O are studied. By comparing the measured emission spectrum of OH with that simulated from Lifbase data, the rotational temperature is evaluated for OH.It is shown that the rotational temperature of OH increase with the increase of discharge power,and decrease with the increase of discharge gas flow rate.
2010,
22.
Abstract:
To solve the problem of dead time loss, a novel method for measuring and correcting dead-time is proposed with the use of autocorrelation function based on a 252Cf -source-driven spectrum analyzing system. The experiment shows that the dead-time of the analyzing system is 40 ns. The dead-time can be obtained directly from the spectrum of autocorrelation with high measuring precision of nanosecond level.
To solve the problem of dead time loss, a novel method for measuring and correcting dead-time is proposed with the use of autocorrelation function based on a 252Cf -source-driven spectrum analyzing system. The experiment shows that the dead-time of the analyzing system is 40 ns. The dead-time can be obtained directly from the spectrum of autocorrelation with high measuring precision of nanosecond level.
2010,
22.
Abstract:
For further understanding of the interactions between different materials in the electromagnetic metamaterials, the change characteristics of the effective permittivity of wire array embedded in a single negative permeability medium were analyzed theoretically. The interactions between the single negative permittivity and single negative permeability were investigated using both numerical calculation and electromagnetic simulation methods. The strategy of reducing such interactions was also proposed. The simulation results indicate that the wire array embedded directly in the single negative permeability medium exhibits only transmission forbidden band in the whole frequency band. While the wires are cladded with dielectric insulation materials, the above forbidden band turns into transmis
For further understanding of the interactions between different materials in the electromagnetic metamaterials, the change characteristics of the effective permittivity of wire array embedded in a single negative permeability medium were analyzed theoretically. The interactions between the single negative permittivity and single negative permeability were investigated using both numerical calculation and electromagnetic simulation methods. The strategy of reducing such interactions was also proposed. The simulation results indicate that the wire array embedded directly in the single negative permeability medium exhibits only transmission forbidden band in the whole frequency band. While the wires are cladded with dielectric insulation materials, the above forbidden band turns into transmis
2010,
22.
Abstract:
Based on the interdependent relationship between fission neutrons(252Cf)) and fission chain((235U system), the paper presents the time-frequency feature analysis and recognition in fission neutron signal based on support vector machine(SVM) through the analysis on signal characteristics and the measuring principle of the 252 fission neutron signal. The time-frequency characteristics and energy features of the fission neutron signal are extracted by using wavelet decomposition and de-noising wavelet packet decomposition, and then applied to training and classification by means of support vector machine based on statistical learning theory. The results show that, it is effective to obtain features of nuclear signal via wavelet decomposition and de-noising wav
Based on the interdependent relationship between fission neutrons(252Cf)) and fission chain((235U system), the paper presents the time-frequency feature analysis and recognition in fission neutron signal based on support vector machine(SVM) through the analysis on signal characteristics and the measuring principle of the 252 fission neutron signal. The time-frequency characteristics and energy features of the fission neutron signal are extracted by using wavelet decomposition and de-noising wavelet packet decomposition, and then applied to training and classification by means of support vector machine based on statistical learning theory. The results show that, it is effective to obtain features of nuclear signal via wavelet decomposition and de-noising wav
2010,
22.
Abstract:
Based on a new room-temperature CdZnTe detector, the energy spectrum of each pixel and the image of the 662 keV 137Cs source have been obtained with a thick pinhole system. According to penetration and scattering effect of the high energy photons in pinhole, the degradation of system spatial resolution was analyzed, and the images derived at different bias voltage were analyzed and compared. The experiments indicate that, the equivalent diameter, caused by penetration and scattering effect of the high energy photons, is the main reason for the degradation of system spatial resolution when the magnification is smaller than 3, and the influence of the pixel size is subtle. The quality of image would be improved when the bias voltage increases. However, extremely high voltage (high
Based on a new room-temperature CdZnTe detector, the energy spectrum of each pixel and the image of the 662 keV 137Cs source have been obtained with a thick pinhole system. According to penetration and scattering effect of the high energy photons in pinhole, the degradation of system spatial resolution was analyzed, and the images derived at different bias voltage were analyzed and compared. The experiments indicate that, the equivalent diameter, caused by penetration and scattering effect of the high energy photons, is the main reason for the degradation of system spatial resolution when the magnification is smaller than 3, and the influence of the pixel size is subtle. The quality of image would be improved when the bias voltage increases. However, extremely high voltage (high
2010,
22.
Abstract:
The resolution of time spectrum is an important factor to obtain the excellent prompt gamma spectrum in the explosive detection. In this paper, we consider the scattering of α particle in the D-T reaction chamber wall is the main reason to the resolution of time spectrum. A measured device of time spectra based on associated α particle technique was built. A cone-shaped α particle collimator was designed to restrain the gamma induced by the neutron which is correlated to the scattering α particle. Thus, the resolution of the time spectrum was improved. Measurements show that with and without the collimator, the resolutions of the time spectrum are 1.8 ns and 6.4 ns, respectively.
The resolution of time spectrum is an important factor to obtain the excellent prompt gamma spectrum in the explosive detection. In this paper, we consider the scattering of α particle in the D-T reaction chamber wall is the main reason to the resolution of time spectrum. A measured device of time spectra based on associated α particle technique was built. A cone-shaped α particle collimator was designed to restrain the gamma induced by the neutron which is correlated to the scattering α particle. Thus, the resolution of the time spectrum was improved. Measurements show that with and without the collimator, the resolutions of the time spectrum are 1.8 ns and 6.4 ns, respectively.
2010,
22.
Abstract:
Compression limit of low-Z fluid is the most important criterion of theoretical and experimental study of equations-of-state at high pressure. Virial theorem and Hugoniot equation show that the shock compression ratio is decided by the excitation degree of internal degree-of-freedom, average potential energy, average kinetic energy and the scaling exponent of the potential in inverse-power law. If the scaling exponent exceeds two, the interaction effects make the fluid less compressible than an ideal gas, otherwise the interaction effects make the fluid more compressible. The excitation of internal degree-of-freedom makes the fluid easier to compress. Accordingly, the low-Z fluid has different compression limits at different pressure ranges where different effects work. A simple function f
Compression limit of low-Z fluid is the most important criterion of theoretical and experimental study of equations-of-state at high pressure. Virial theorem and Hugoniot equation show that the shock compression ratio is decided by the excitation degree of internal degree-of-freedom, average potential energy, average kinetic energy and the scaling exponent of the potential in inverse-power law. If the scaling exponent exceeds two, the interaction effects make the fluid less compressible than an ideal gas, otherwise the interaction effects make the fluid more compressible. The excitation of internal degree-of-freedom makes the fluid easier to compress. Accordingly, the low-Z fluid has different compression limits at different pressure ranges where different effects work. A simple function f
2010,
22.
Abstract:
A 40 kW, 204 MHz solid state RF amplifier is being developed for the 800 MeV electron storage ring at Hefei Light Source. The solid state amplifier is composed of 130 amplifier units combined by three-stage combiners in two towers. Some prototypes of key components have been manufactured and tested, which include a 2.5 kW 8-way combiner, a 20 kW 8-way combiner, a 40 kW 2-way combiner and 10 amplifier units. The output port’s VSWR of all combiners is not over 1.05. The amplifier unit's gain reaches 26 dB. Unbalance of gain and phase is less than 0.1 dB and 5°, respectively, satisfying the design requirements.
A 40 kW, 204 MHz solid state RF amplifier is being developed for the 800 MeV electron storage ring at Hefei Light Source. The solid state amplifier is composed of 130 amplifier units combined by three-stage combiners in two towers. Some prototypes of key components have been manufactured and tested, which include a 2.5 kW 8-way combiner, a 20 kW 8-way combiner, a 40 kW 2-way combiner and 10 amplifier units. The output port’s VSWR of all combiners is not over 1.05. The amplifier unit's gain reaches 26 dB. Unbalance of gain and phase is less than 0.1 dB and 5°, respectively, satisfying the design requirements.
2010,
22.
Abstract:
The theory and the devices of the pulsed wire magnetic measurement system are described. The effects on the measurement accuracy of wire gravity, noise and reflected signal are theoretically analyzed. Some methods such as symmetric wire mounting, night measuring and lownoise circuit design are proposed for optimizing various components of the device to reduce the effects. The results of magnetic measurement of the pulsed wire system are compared with that of Hall probe method. It is applied to measure the practical electromagnetic undulator to be put to use in National Synchrotron Radiation Laboratory and verify the current relationship between the correction coils and main coils．
The theory and the devices of the pulsed wire magnetic measurement system are described. The effects on the measurement accuracy of wire gravity, noise and reflected signal are theoretically analyzed. Some methods such as symmetric wire mounting, night measuring and lownoise circuit design are proposed for optimizing various components of the device to reduce the effects. The results of magnetic measurement of the pulsed wire system are compared with that of Hall probe method. It is applied to measure the practical electromagnetic undulator to be put to use in National Synchrotron Radiation Laboratory and verify the current relationship between the correction coils and main coils．
2010,
22.
Abstract:
The propagation of a relativistic (300 keV) sheet electron beam carrying high current (3 kA) through the offset-pole periodic cusped magnetic fields with low amplitude (0.173 T) and short period (20 mm) has been investigated theoretically and numerically. The expressions of the space-charge fields with finite width of the waveguide are given, followed by the expressions of the transverse focusing forces acting on the sheet electron beam with finite thickness. The amplitude and the period of the offset-pole periodic cusped magnetic fields, as well as the width and height of the beam channel, are obtained through beam matching. The 3D-PIC simulations according to the theoretical results show that, the intense relativistic sheet electron beam could be well focused in the horizontal direction,
The propagation of a relativistic (300 keV) sheet electron beam carrying high current (3 kA) through the offset-pole periodic cusped magnetic fields with low amplitude (0.173 T) and short period (20 mm) has been investigated theoretically and numerically. The expressions of the space-charge fields with finite width of the waveguide are given, followed by the expressions of the transverse focusing forces acting on the sheet electron beam with finite thickness. The amplitude and the period of the offset-pole periodic cusped magnetic fields, as well as the width and height of the beam channel, are obtained through beam matching. The 3D-PIC simulations according to the theoretical results show that, the intense relativistic sheet electron beam could be well focused in the horizontal direction,
2010,
22.
Abstract:
This paper presents the status of various tune measurement techniques, and describes the beam spectra analysis method based on turn-by-turn beam position data. The physical requirements, hardware layout and key modules of the betatron tune monitor system is introduced for the Shanghai Synchrotron Radiation Facility (SSRF) storage ring. A series of beam experiments have been carried out in order to optimize system configuration, and to evaluate systematic measurement error and resolution. The comparison of various running modes of the tune monitor are made, and suitable running modes are analyzed for different accelerator operation phases. The experimental data show the resolution of SSRF storage ring tune monitor is better than 0.000 05 and the systematic measurement error is smaller than
This paper presents the status of various tune measurement techniques, and describes the beam spectra analysis method based on turn-by-turn beam position data. The physical requirements, hardware layout and key modules of the betatron tune monitor system is introduced for the Shanghai Synchrotron Radiation Facility (SSRF) storage ring. A series of beam experiments have been carried out in order to optimize system configuration, and to evaluate systematic measurement error and resolution. The comparison of various running modes of the tune monitor are made, and suitable running modes are analyzed for different accelerator operation phases. The experimental data show the resolution of SSRF storage ring tune monitor is better than 0.000 05 and the systematic measurement error is smaller than
2010,
22.
Abstract:
An artificial transmission line as a right-handed transmission line is edge-coupled with a CRLH-TL to realize coupling between the left-handed and the right-handed transmission line. The directional coupler is a compact planar structure with characteristics of backward and tight coupling. Experimental results show that a 10 dB coupling coefficient is achieved from 1.3 GHz to 1.8 GHz. The corresponding fractional bandwidth is about 32%, and the isolation is greater than 25 dB. Simulation results agree well with measured results. The directional coupler covers a wider coefficient range than the conventional one.
An artificial transmission line as a right-handed transmission line is edge-coupled with a CRLH-TL to realize coupling between the left-handed and the right-handed transmission line. The directional coupler is a compact planar structure with characteristics of backward and tight coupling. Experimental results show that a 10 dB coupling coefficient is achieved from 1.3 GHz to 1.8 GHz. The corresponding fractional bandwidth is about 32%, and the isolation is greater than 25 dB. Simulation results agree well with measured results. The directional coupler covers a wider coefficient range than the conventional one.
2010,
22.
Abstract:
The spatial power-combination, adopting parabolic antennas as the array cells, has been studied, considering the relation between the spatial power-combination efficiency and the amplitude error and phase error of antenna cells. The results of numerical theoretical analyses and show that the efficiency of spatial power-combination is only related with the amplitude error and phase error of antenna cells only. The simulation on the antenna units and the antenna array shows a spatial power-combination efficiency about 92%.The influencing factors and the improvement methods of the efficiency have been presented．
The spatial power-combination, adopting parabolic antennas as the array cells, has been studied, considering the relation between the spatial power-combination efficiency and the amplitude error and phase error of antenna cells. The results of numerical theoretical analyses and show that the efficiency of spatial power-combination is only related with the amplitude error and phase error of antenna cells only. The simulation on the antenna units and the antenna array shows a spatial power-combination efficiency about 92%.The influencing factors and the improvement methods of the efficiency have been presented．
2010,
22.
Abstract:
The comparative studies by using a tri-cathode accelerator are presented on the cathode emission capability, relative emission delay and emission-time jitter of several common cathode materials, that is, stainless-steel, brass, aluminum, velvet and graphite. The stainless-steel has better quality than other metal cathode materials. At 300~450 kV diode voltage and 30 mm anode-cathode gap, the stainless-steel cathode emission current density is 0.78 ~1.50 kA/cm2 accordingly. With a constant diode voltage, the emission-time jitter of the stainless-steel is less than 8 ns, and both the velvet and graphite emission-time jitters are less than 4 ns. The cathode emission starting time of all those materials shortens when cathodes work shot by shot frequently.
The comparative studies by using a tri-cathode accelerator are presented on the cathode emission capability, relative emission delay and emission-time jitter of several common cathode materials, that is, stainless-steel, brass, aluminum, velvet and graphite. The stainless-steel has better quality than other metal cathode materials. At 300~450 kV diode voltage and 30 mm anode-cathode gap, the stainless-steel cathode emission current density is 0.78 ~1.50 kA/cm2 accordingly. With a constant diode voltage, the emission-time jitter of the stainless-steel is less than 8 ns, and both the velvet and graphite emission-time jitters are less than 4 ns. The cathode emission starting time of all those materials shortens when cathodes work shot by shot frequently.
2010,
22.
Abstract:
A C-band resonant relativistic backward-wave oscillator(RBWO) is designed, and its structure feature and operation mechanism are analyzed. Operation characteristics of the designed device were investigated by particle-in-cell(PIC) simulation. Simulation results indicate that both the length of the insert and the radius of the reflector influence the power efficiency of the device. With the diode voltage ranging from 500 kV to 1 MV, the efficiency of designed device remains 20%~25%, while the generated microwave frequency keeps around 4.25 GHz. Furthermore, according to the analysis on the electrodynamics characteristics of the device, the longitudinal resonant modes and corresponding quality factors are studied with emphasis, which reveals that the device has a high efficiency with operati
A C-band resonant relativistic backward-wave oscillator(RBWO) is designed, and its structure feature and operation mechanism are analyzed. Operation characteristics of the designed device were investigated by particle-in-cell(PIC) simulation. Simulation results indicate that both the length of the insert and the radius of the reflector influence the power efficiency of the device. With the diode voltage ranging from 500 kV to 1 MV, the efficiency of designed device remains 20%~25%, while the generated microwave frequency keeps around 4.25 GHz. Furthermore, according to the analysis on the electrodynamics characteristics of the device, the longitudinal resonant modes and corresponding quality factors are studied with emphasis, which reveals that the device has a high efficiency with operati
2010,
22.
Abstract:
A uniform mushroom-like electromagnetic band-gap (EBG) structure can realize only one surface-wave suppression bandgap. Hence, two kinds of units with different parameters mushroom-like EBG structures are cascaded to realize the dual-band or broadband surface-wave suppression bandgap. This paper presents a dual-band EBG structure using cascaded mushroom-like structures with different patch sizes. Two kinds of uniform EBG structures are used to produce two suppression surface-wave bandgaps covering the two operating frequency respectively. The cascaded structure is integrated between slotted microstrip antennas. Simulation and experimental results show that the cascaded structure can suppress the surface-wave effectively and decrease the mutual coupling of the two operating frequencies at t
A uniform mushroom-like electromagnetic band-gap (EBG) structure can realize only one surface-wave suppression bandgap. Hence, two kinds of units with different parameters mushroom-like EBG structures are cascaded to realize the dual-band or broadband surface-wave suppression bandgap. This paper presents a dual-band EBG structure using cascaded mushroom-like structures with different patch sizes. Two kinds of uniform EBG structures are used to produce two suppression surface-wave bandgaps covering the two operating frequency respectively. The cascaded structure is integrated between slotted microstrip antennas. Simulation and experimental results show that the cascaded structure can suppress the surface-wave effectively and decrease the mutual coupling of the two operating frequencies at t
2010,
22.
Abstract:
A 300 MHz-center frequency wideband patch antenna has been developed for high power wideband electromagnetic (EM) pulse radiation, small signal test and high power experiments were performed. The two-layer-patch antenna structure was optimized by Taguchi global optimization method associated with EM simulation software, 60.2% impedance bandwidth (VSWR<3) and 8.1 dB maximum gain were obtained in the simulation, and then insulation design was performed to enhance the antenna’s power capability. The measured S11 in the small signal experiment matches well with the simulated result, and the measured impedance bandwidth reaches 64.2%. Fed by the 3 ns-long bipolar pulse with -89 kV/+81 kV peaks in high power experiments, the radiation factor reaches 75.2 kV with 46% percent bandwidth of the rad
A 300 MHz-center frequency wideband patch antenna has been developed for high power wideband electromagnetic (EM) pulse radiation, small signal test and high power experiments were performed. The two-layer-patch antenna structure was optimized by Taguchi global optimization method associated with EM simulation software, 60.2% impedance bandwidth (VSWR<3) and 8.1 dB maximum gain were obtained in the simulation, and then insulation design was performed to enhance the antenna’s power capability. The measured S11 in the small signal experiment matches well with the simulated result, and the measured impedance bandwidth reaches 64.2%. Fed by the 3 ns-long bipolar pulse with -89 kV/+81 kV peaks in high power experiments, the radiation factor reaches 75.2 kV with 46% percent bandwidth of the rad
2010,
22.
Abstract:
The experiments have been conducted about lightning electromagnetic pulse (LEMP) coupling to buried cables in the depth of 0.5 m. The test system and the measurement method are both introduced, and the lightning induced overvoltages at the end of the buried cables are analyzed. The cables are used in automatic weather stations, i.e. the power cable without shielding layer, the signal cable with a braided copper shield and the control cable with a steel shield. Relative to the peak voltage induced on the power cable, the peak voltages induced on the control cable and the signal cable are 65% and 26% respectively. The peak induced overvoltage of the three cables has a similar trend in the initial stage of the LEMP. The steel belt shielding layer can effectively reduce 400 kHz～1 MHz componen
The experiments have been conducted about lightning electromagnetic pulse (LEMP) coupling to buried cables in the depth of 0.5 m. The test system and the measurement method are both introduced, and the lightning induced overvoltages at the end of the buried cables are analyzed. The cables are used in automatic weather stations, i.e. the power cable without shielding layer, the signal cable with a braided copper shield and the control cable with a steel shield. Relative to the peak voltage induced on the power cable, the peak voltages induced on the control cable and the signal cable are 65% and 26% respectively. The peak induced overvoltage of the three cables has a similar trend in the initial stage of the LEMP. The steel belt shielding layer can effectively reduce 400 kHz～1 MHz componen
2010,
22.
Abstract:
The voltage conversion ratio of the photoconductive semiconductor switch (PCSS) is measured in the microstrip test circuit. The analytical equation of the ratio is deduced according to transmission line theory with the consideration of reflection from the source end and non-zero on-state resistances of PCSS. Calculations show that, when the PCSS is operated in linear mode, the voltage conversion ratio is always less than 50%; when the PCSS is operated in lock-on nonlinear mode, the ratio can be more than 50%, and reach 100% in ideal case; the output electrical pulse includes two peak voltages when the PCSS is operated in the critical case between the above two modes. The theoretical computation is in good agreement with the measured data within the error limitation. It is found that the mi
The voltage conversion ratio of the photoconductive semiconductor switch (PCSS) is measured in the microstrip test circuit. The analytical equation of the ratio is deduced according to transmission line theory with the consideration of reflection from the source end and non-zero on-state resistances of PCSS. Calculations show that, when the PCSS is operated in linear mode, the voltage conversion ratio is always less than 50%; when the PCSS is operated in lock-on nonlinear mode, the ratio can be more than 50%, and reach 100% in ideal case; the output electrical pulse includes two peak voltages when the PCSS is operated in the critical case between the above two modes. The theoretical computation is in good agreement with the measured data within the error limitation. It is found that the mi
2010,
22.
Abstract:
This paper presents the electrostatic particle-in-cell (PIC) Monte Carlo collisions (MCC) method for simulating the breakdown on dielectric surface illuminated by high-power microwaves, and the dielectric surface breakdown at different pressures in argon is simulated by the PIC-MCC code. The temporal evolution of the number of particles and the mean kinetic energy of electrons, and the breakdown delay time are obtained. The simulation results show that, in the case of low pressure, the influence of multipactor is visible, while the number of electrons increases slowly after saturation and the breakdown delay is long. As the pressure increases, the influence of multipactor becomes smaller with gas ionization starting to dominate the breakdown process, and the breakdown delay gradually becom
This paper presents the electrostatic particle-in-cell (PIC) Monte Carlo collisions (MCC) method for simulating the breakdown on dielectric surface illuminated by high-power microwaves, and the dielectric surface breakdown at different pressures in argon is simulated by the PIC-MCC code. The temporal evolution of the number of particles and the mean kinetic energy of electrons, and the breakdown delay time are obtained. The simulation results show that, in the case of low pressure, the influence of multipactor is visible, while the number of electrons increases slowly after saturation and the breakdown delay is long. As the pressure increases, the influence of multipactor becomes smaller with gas ionization starting to dominate the breakdown process, and the breakdown delay gradually becom
2010,
22.
Abstract:
A novel power combiner applied to high power microwave is described and analyzed. It consists of two overmoded rectangular waveguides which are connected vertically, and several metal plates are inserted vertically with the polarization direction of the transmitted modes, respectively. Thus the two modes with different polarization directions, such as TE10 and TE01 rectangular waveguide mode, can be transmitted separately to realize power combining. A power combiner at 9.55 GHz is designed and optimized based on this scheme. The calculated results show that it has high power handling capacity, and the transmission efficiency for each channel is about 98% and 99% at center frequency, respectively. The return loss and coupling loss located at the joint are less than -21 dB, which can be
A novel power combiner applied to high power microwave is described and analyzed. It consists of two overmoded rectangular waveguides which are connected vertically, and several metal plates are inserted vertically with the polarization direction of the transmitted modes, respectively. Thus the two modes with different polarization directions, such as TE10 and TE01 rectangular waveguide mode, can be transmitted separately to realize power combining. A power combiner at 9.55 GHz is designed and optimized based on this scheme. The calculated results show that it has high power handling capacity, and the transmission efficiency for each channel is about 98% and 99% at center frequency, respectively. The return loss and coupling loss located at the joint are less than -21 dB, which can be
2010,
22.
Abstract:
Typical spatial distribution of the discharge plasma fluorescence and temporal evolutions of the discharge current and voltage in SF6/C2H6 mixture have been measured, which serves as the working gas of the discharge-pumped pulsed HF laser. Discharge stability, residual voltage and energy deposition efficiency were systematically analyzed by changing the initial conditions. It is shown that the process of discharge in the gas mixture has three phases: main discharge, voltage plateau and arc discharge, each of which has different discharge characters. Deposited energy in the gas mixture increases with the increase of charge voltage, but the duration of voltage plateau would be shortened. The raise in C2H6 concentration will postpone the
Typical spatial distribution of the discharge plasma fluorescence and temporal evolutions of the discharge current and voltage in SF6/C2H6 mixture have been measured, which serves as the working gas of the discharge-pumped pulsed HF laser. Discharge stability, residual voltage and energy deposition efficiency were systematically analyzed by changing the initial conditions. It is shown that the process of discharge in the gas mixture has three phases: main discharge, voltage plateau and arc discharge, each of which has different discharge characters. Deposited energy in the gas mixture increases with the increase of charge voltage, but the duration of voltage plateau would be shortened. The raise in C2H6 concentration will postpone the
2010,
22.
Abstract:
In inertial confinement fusion (ICF) system, manual way has been used to collimate the pellet traditionally, which is time-consuming and low-level automated. A new method based on Binocular Vision is proposed, which can place the prospecting apparatus on the public diagnosis platform to reach relevant engineering target and uses the high precision two dimension calibration board. Iterative method is adopted to satisfy 0.1 pixel for corner extraction precision. Furthermore, SVD decomposition is used to remove the singularity corners and advanced Zhang’s calibration method is applied to promote camera calibration precision. Experiments indicate that the RMS of three dimension coordinate measurement precision is 25 μm, and the max system RMS of distance measurement is better than 100 μm, s
In inertial confinement fusion (ICF) system, manual way has been used to collimate the pellet traditionally, which is time-consuming and low-level automated. A new method based on Binocular Vision is proposed, which can place the prospecting apparatus on the public diagnosis platform to reach relevant engineering target and uses the high precision two dimension calibration board. Iterative method is adopted to satisfy 0.1 pixel for corner extraction precision. Furthermore, SVD decomposition is used to remove the singularity corners and advanced Zhang’s calibration method is applied to promote camera calibration precision. Experiments indicate that the RMS of three dimension coordinate measurement precision is 25 μm, and the max system RMS of distance measurement is better than 100 μm, s
2010,
22.
Abstract:
In order to diagnose X-ray emitted from the plasma, a spherically bent crystals spectrometer was developed based on the X-ray Bragg diffraction theory. In the experiment, the dispersive element of crystal analyzer was quartz, the bent radius was 250 mm and the range of Bragg angle of the crystal was 30° to 67.5°. The X-ray film, as its principal detector, obtained spectra information which had an effective area of 10 mm×50 mm. The experiment was carried out at the anode accelerator. The detector obtained the X-ray spectra information of the K-shell Ti spectra. By the analysis of spectra information, the spectral resolution of spherically bent quartz crystals can be achieved for more than 1 000, and the spectral passband is 0.43 eV.
In order to diagnose X-ray emitted from the plasma, a spherically bent crystals spectrometer was developed based on the X-ray Bragg diffraction theory. In the experiment, the dispersive element of crystal analyzer was quartz, the bent radius was 250 mm and the range of Bragg angle of the crystal was 30° to 67.5°. The X-ray film, as its principal detector, obtained spectra information which had an effective area of 10 mm×50 mm. The experiment was carried out at the anode accelerator. The detector obtained the X-ray spectra information of the K-shell Ti spectra. By the analysis of spectra information, the spectral resolution of spherically bent quartz crystals can be achieved for more than 1 000, and the spectral passband is 0.43 eV.
2010,
22.
Abstract:
A nanosecond pulsed high voltage power based on semiconductor opening switch was employed to generate atmospheric pressure glow air plasma between a high voltage needle-array electrode and a grounded plate electrode. The discharge volume was 1 600 mm×100 mm×25 mm. In the plasma generator, conical glow discharges were generated simultaneously at all the needle tips and large area glow discharges were formed at the grounded plate electrode at the same time. The diameter and length of each needle, the space between adjacent needles and the distance from the needle tip to the grounded plate electrode surface were 1, 20, 20 and 25 mm, respectively. The electrical property of the discharge was studied by measuring the voltage across the discharge with a high voltage probe. The result shows tha
A nanosecond pulsed high voltage power based on semiconductor opening switch was employed to generate atmospheric pressure glow air plasma between a high voltage needle-array electrode and a grounded plate electrode. The discharge volume was 1 600 mm×100 mm×25 mm. In the plasma generator, conical glow discharges were generated simultaneously at all the needle tips and large area glow discharges were formed at the grounded plate electrode at the same time. The diameter and length of each needle, the space between adjacent needles and the distance from the needle tip to the grounded plate electrode surface were 1, 20, 20 and 25 mm, respectively. The electrical property of the discharge was studied by measuring the voltage across the discharge with a high voltage probe. The result shows tha
2010,
22.
Abstract:
To fabricate high quality hollow glass microsphere (HGM) for inertial confinement fusion targets by dried gel method, effects of gel particle diameter, specific heat, blowing agent concentration and thermal radiation absorption coefficient on the transformation process from gel particle to HGMs and the resulting quality of HGMs were investigated by numerical simulation and experiments. The results show that with the increase of diameter and/or specific heat of dried-gel particles, heating-up rate of gel particle in heating and encapsulating stages is significantly reduced, and the residence time in various stages of the transformation process is sharply shortened, especially for the residence time in refining stage. The velocity of particle/microsphere increases remarkably with decreasing
To fabricate high quality hollow glass microsphere (HGM) for inertial confinement fusion targets by dried gel method, effects of gel particle diameter, specific heat, blowing agent concentration and thermal radiation absorption coefficient on the transformation process from gel particle to HGMs and the resulting quality of HGMs were investigated by numerical simulation and experiments. The results show that with the increase of diameter and/or specific heat of dried-gel particles, heating-up rate of gel particle in heating and encapsulating stages is significantly reduced, and the residence time in various stages of the transformation process is sharply shortened, especially for the residence time in refining stage. The velocity of particle/microsphere increases remarkably with decreasing
2010,
22.
Abstract:
Some thermodynamic functions, mechanics and spectroscopic properties for LiX(X=H,D,T) were calculated with ab initio method. The vibration energy and vibration entropy for solid Li were calculated based on the quasi-harmonic Debye’s theory. The changes of thermodynamic functions were calculated and discussed, which are the enthalpy, reaction entropy, Gibbs free energy and equilibrium pressures of hydrogen gases for Li absorbing hydrogen isotopes processes. Results show that all the calculations are feasible. In the reaction of Li absorbing hydrogen gases, the enthalpy and reaction entropy are negative and their absolute values increase with the elevation of temperature, while Gibbs free energy increases toward the positive values. At the same temperature and pressure, the substitutions of
Some thermodynamic functions, mechanics and spectroscopic properties for LiX(X=H,D,T) were calculated with ab initio method. The vibration energy and vibration entropy for solid Li were calculated based on the quasi-harmonic Debye’s theory. The changes of thermodynamic functions were calculated and discussed, which are the enthalpy, reaction entropy, Gibbs free energy and equilibrium pressures of hydrogen gases for Li absorbing hydrogen isotopes processes. Results show that all the calculations are feasible. In the reaction of Li absorbing hydrogen gases, the enthalpy and reaction entropy are negative and their absolute values increase with the elevation of temperature, while Gibbs free energy increases toward the positive values. At the same temperature and pressure, the substitutions of
2010,
22.
Abstract:
This paper researches the influence of different molecular weight polyvinylpyrrolidone on silver nanoconfiguration in polyol process. The silver nanoparticles are characterized by scanning electron microscopy and X-ray diffraction. Their optical properties are studied by UV-Vis spectrophotometer. The results indicate that under of silver nanoparticles different morphology will be made by different molecular weight polyvinylpyrrolidone under the same experimental conditions; the yield of silver nanowires is the largest when the molecular weight of polyvinylpyrrolidone is 1.0×104, and silver nanowires will reduce and silver nanocubes will increase when the molecular weight of polyvinylpyrrolidone increases.
This paper researches the influence of different molecular weight polyvinylpyrrolidone on silver nanoconfiguration in polyol process. The silver nanoparticles are characterized by scanning electron microscopy and X-ray diffraction. Their optical properties are studied by UV-Vis spectrophotometer. The results indicate that under of silver nanoparticles different morphology will be made by different molecular weight polyvinylpyrrolidone under the same experimental conditions; the yield of silver nanowires is the largest when the molecular weight of polyvinylpyrrolidone is 1.0×104, and silver nanowires will reduce and silver nanocubes will increase when the molecular weight of polyvinylpyrrolidone increases.
2010,
22.
Abstract:
Characteristics of laser-induced damage of some optical thin films deposited by e-beam evaporation were investigated in vacuum and atmosphere environments，and the differences of laser-induced damage in two conditions were analyzed and discussed. The results show that compared to normal atmospheric conditions, optical thin films have a decreasing laser induced damage thresholds under vacuum environments. The morphologies of the damages under two conditions are quite different. Gas heat conduction has little influence on the difference of damage thresholds under two conditions. The hydrolysis-induced tension increase and the laser-irradiated nonstoichiometric defects of films in vacuum environments probably result in different laser-induced damages in vacuum and atmosphere environments．
Characteristics of laser-induced damage of some optical thin films deposited by e-beam evaporation were investigated in vacuum and atmosphere environments，and the differences of laser-induced damage in two conditions were analyzed and discussed. The results show that compared to normal atmospheric conditions, optical thin films have a decreasing laser induced damage thresholds under vacuum environments. The morphologies of the damages under two conditions are quite different. Gas heat conduction has little influence on the difference of damage thresholds under two conditions. The hydrolysis-induced tension increase and the laser-irradiated nonstoichiometric defects of films in vacuum environments probably result in different laser-induced damages in vacuum and atmosphere environments．
2010,
22.
Abstract:
The experiment of filamentary dielectric barrier discharge (DBD) in nitrogen at atmospheric pressure has been studied, in which the needle-plate reactor was employed. The temporal evolution of vibrational temperature of the N2 (C3Πu→B3Πg) molecules was successfully recorded by optical emission spectrometry. And the N2 vibrational temperature was calculated at the different discharge voltage and pressure．The experiment results show that the molecular vibrational temperature of N2 ranges from 2 000 K to 3 500 K. It reduces with increasing time in both positive and negative semi-cycles of discharge, and it is always higher in the negative semi-cycle. The vibrational temperature rises with increasing discharge vol
The experiment of filamentary dielectric barrier discharge (DBD) in nitrogen at atmospheric pressure has been studied, in which the needle-plate reactor was employed. The temporal evolution of vibrational temperature of the N2 (C3Πu→B3Πg) molecules was successfully recorded by optical emission spectrometry. And the N2 vibrational temperature was calculated at the different discharge voltage and pressure．The experiment results show that the molecular vibrational temperature of N2 ranges from 2 000 K to 3 500 K. It reduces with increasing time in both positive and negative semi-cycles of discharge, and it is always higher in the negative semi-cycle. The vibrational temperature rises with increasing discharge vol
2010,
22.
Abstract:
This paper analyzes the principle and method of X-ray phase contrast imaging technique used to characterize the microstructure of polymer foam. The analytical result shows that the image contrast of low Z polymer foam can be considerably improved with X-ray phase contrast tomography. The three dimensional microstructure of polymer foam is observing combined phase contrast tomography with computed tomography, and the characterization method of foam density distribution is introduced by calculating the centroid of framework “particle”. The experimental result indicates that, the three dimensional density distribution of foams can be completely characterized through phase contrast computed tomography technique and the statistical method of framework “particle” centroid.
This paper analyzes the principle and method of X-ray phase contrast imaging technique used to characterize the microstructure of polymer foam. The analytical result shows that the image contrast of low Z polymer foam can be considerably improved with X-ray phase contrast tomography. The three dimensional microstructure of polymer foam is observing combined phase contrast tomography with computed tomography, and the characterization method of foam density distribution is introduced by calculating the centroid of framework “particle”. The experimental result indicates that, the three dimensional density distribution of foams can be completely characterized through phase contrast computed tomography technique and the statistical method of framework “particle” centroid.
2010,
22.
Abstract:
Monodisperse polystyrene(PS) microspheres with average sizes of 1.2 to 1.5 μm were obtained by emulsion polymerization. Using PS microspheres as the cores, some PS/Ag core shell particles were prepared after ultrasonic sensitization, deoxidization and electroless process. Their morphology, component, structure and optical properties were characterized and investigated by transmission electron microscopy, X-ray diffraction, infrared ray, and UV-Vis adsorption spectra. The results indicate that the size distribution of the composite particles is narrow and the shell thickness of silver can be controlled by multiple sensitization and adjusting the second concentration of ［Ag(NH4)2］+, from 0.002 to 0.006 mol/L. In addition, while the silver nanoparticles coated on the polystyrene grows, the
Monodisperse polystyrene(PS) microspheres with average sizes of 1.2 to 1.5 μm were obtained by emulsion polymerization. Using PS microspheres as the cores, some PS/Ag core shell particles were prepared after ultrasonic sensitization, deoxidization and electroless process. Their morphology, component, structure and optical properties were characterized and investigated by transmission electron microscopy, X-ray diffraction, infrared ray, and UV-Vis adsorption spectra. The results indicate that the size distribution of the composite particles is narrow and the shell thickness of silver can be controlled by multiple sensitization and adjusting the second concentration of ［Ag(NH4)2］+, from 0.002 to 0.006 mol/L. In addition, while the silver nanoparticles coated on the polystyrene grows, the
2010,
22.
Abstract:
The two-dimensional(2D) three-temperature radiation hydrodynamics code, LARED-H(laser radiation electron dynamic hohlraum), is improved to simulate the 2D radiation-driven implosion process. In order to solve the linear-algebraic equations discretized from the two-dimensional and three-temperature energy equations by a nine point scheme, the efficient solver of Krylov method is used for improving the iterative capability. The numerical result comparison with 1D CFJ code shows the accuracy of the LARED-H code. Finally, the compressed shapes of the capsule driven by a radiation field in cylindrical gold hohlraums with different length are simulated by the LARED-H code. The shape of the fuel becomes sausage-like, ball-like or cake-like, respectively with the different hohlraum length, which a
The two-dimensional(2D) three-temperature radiation hydrodynamics code, LARED-H(laser radiation electron dynamic hohlraum), is improved to simulate the 2D radiation-driven implosion process. In order to solve the linear-algebraic equations discretized from the two-dimensional and three-temperature energy equations by a nine point scheme, the efficient solver of Krylov method is used for improving the iterative capability. The numerical result comparison with 1D CFJ code shows the accuracy of the LARED-H code. Finally, the compressed shapes of the capsule driven by a radiation field in cylindrical gold hohlraums with different length are simulated by the LARED-H code. The shape of the fuel becomes sausage-like, ball-like or cake-like, respectively with the different hohlraum length, which a
2010,
22.
Abstract:
The principles and characteristics of point-projection radiography were studied through static imaging experiments, using laser-driven about 4.8 keV Ti plasma X-ray source. The application of point-projection to dynamic diagnosis was then developed, and an experimental platform was accomplished with about 4.8 keV photon energy, about 100 ps time resolution and about 10 μm spatial resolution. A series of experimental results from this platform were introduced, including those on hydrodynamic instability, laser-accelerated plasma jet and compression characters of materials.
The principles and characteristics of point-projection radiography were studied through static imaging experiments, using laser-driven about 4.8 keV Ti plasma X-ray source. The application of point-projection to dynamic diagnosis was then developed, and an experimental platform was accomplished with about 4.8 keV photon energy, about 100 ps time resolution and about 10 μm spatial resolution. A series of experimental results from this platform were introduced, including those on hydrodynamic instability, laser-accelerated plasma jet and compression characters of materials.
2010,
22.
Abstract:
The sol-gel process and structure of monolithic TiO2 aerogels were experimentally studied. It has been shown that, the increasing of the catalyst and precursor amounts can both lead to shorter gelation time and the hardness improvement of the wet gel, while they lead to a decrease and few change in the wet gel transparency, respectively. The gelation time, the transparency and hardness of the wet gel vary in the parabolic manner. The aerogels of different densities prepared with different catalyst amount were characterized by scanning electron microscopy. The reaction degree of polycondensation is found to increase with the increase of the catalyst and precursor amounts, the degree of cross linking of the aerogel colloid particles also increases, and no ≡C—O bond exists in the aerogels b
The sol-gel process and structure of monolithic TiO2 aerogels were experimentally studied. It has been shown that, the increasing of the catalyst and precursor amounts can both lead to shorter gelation time and the hardness improvement of the wet gel, while they lead to a decrease and few change in the wet gel transparency, respectively. The gelation time, the transparency and hardness of the wet gel vary in the parabolic manner. The aerogels of different densities prepared with different catalyst amount were characterized by scanning electron microscopy. The reaction degree of polycondensation is found to increase with the increase of the catalyst and precursor amounts, the degree of cross linking of the aerogel colloid particles also increases, and no ≡C—O bond exists in the aerogels b
2010,
22.
Abstract:
Using the spectral width from the Airda16000 low stratospheric wind profiler radar, removing the non-turbulent contaminations, then obtaining the spectral width contributed by turbulence, the turbulent dissipation rate could be estimated. The height profiler, diurnal and seasonal variability of turbulent dissipation rate in the troposphere were studied. Results show that: First, the turbulent dissipation rate distributed between 10-6~10-2 m2·s-3 on clear air days, and decreased with the increase of height. Second, it had remarkable diurnal variability below 3 km, which increased in the midday and decreased in the evening and morning, also, there was a delay of diurnal variability with time, the dissipation rate did not display the tendency of di
Using the spectral width from the Airda16000 low stratospheric wind profiler radar, removing the non-turbulent contaminations, then obtaining the spectral width contributed by turbulence, the turbulent dissipation rate could be estimated. The height profiler, diurnal and seasonal variability of turbulent dissipation rate in the troposphere were studied. Results show that: First, the turbulent dissipation rate distributed between 10-6~10-2 m2·s-3 on clear air days, and decreased with the increase of height. Second, it had remarkable diurnal variability below 3 km, which increased in the midday and decreased in the evening and morning, also, there was a delay of diurnal variability with time, the dissipation rate did not display the tendency of di
2010,
22.
Abstract:
A coupling method is put forward for laser-diode array (LDA) end-pumped amplifiers. The LDA is inscribed on a cylindrical surface and then a duct is connected to it. That means the laser diodes are arranged in the shape of an arch. The center of the arch is at the geometrical center of the gain medium. A three dimensional ray-tracing program is made to simulate the coupling of the cylindrical LDAs. Simulating results show that the cylindrical laser diode array can be arranged flexibly. When laser diode are arranged as 1×12, 2×6 and 3×4 arrays, high coupling coefficient and uniform coupling intensity distribution can be obtained simultaneously when the radius of the arch changes in a wide range; when the gain media is close to the output end of the duct, top-hat deposited pumping intensi
A coupling method is put forward for laser-diode array (LDA) end-pumped amplifiers. The LDA is inscribed on a cylindrical surface and then a duct is connected to it. That means the laser diodes are arranged in the shape of an arch. The center of the arch is at the geometrical center of the gain medium. A three dimensional ray-tracing program is made to simulate the coupling of the cylindrical LDAs. Simulating results show that the cylindrical laser diode array can be arranged flexibly. When laser diode are arranged as 1×12, 2×6 and 3×4 arrays, high coupling coefficient and uniform coupling intensity distribution can be obtained simultaneously when the radius of the arch changes in a wide range; when the gain media is close to the output end of the duct, top-hat deposited pumping intensi
2010,
22.
Abstract:
A dimensionless factor of conical nozzle is defined combined with incident laser energy, energy deposit efficiency, ambient air pressure, generatrix length and semi-apex angle of nozzle, and it is extended to the study of parabolic nozzle. Effects on impulse coupling coefficients of conical and parabolic nozzles under four semi-apex angles are calculated by radiation gas-dynamics computational code. Results indicate that, there are the maximum impulse coupling coefficients of the two nozzles, and the corresponding dimensionless factor is about 0.4. Impulse coupling coefficient increases with the decrease of semi-apex angle at same dimensionless factor, and the impulse coupling coefficient of parabolic nozzle is greater than that of conical nozzle under the same conditions.
A dimensionless factor of conical nozzle is defined combined with incident laser energy, energy deposit efficiency, ambient air pressure, generatrix length and semi-apex angle of nozzle, and it is extended to the study of parabolic nozzle. Effects on impulse coupling coefficients of conical and parabolic nozzles under four semi-apex angles are calculated by radiation gas-dynamics computational code. Results indicate that, there are the maximum impulse coupling coefficients of the two nozzles, and the corresponding dimensionless factor is about 0.4. Impulse coupling coefficient increases with the decrease of semi-apex angle at same dimensionless factor, and the impulse coupling coefficient of parabolic nozzle is greater than that of conical nozzle under the same conditions.
2010,
22.
Abstract:
A parameter optimization system is established for X-ray in-line phase contrast imaging of the object of two dimensional Gaussian distribution based on the theoretical analysis of the imaging technology. The dependence of the evaluation parameters including contrast, signal-to-noise ratio, resolution and sampling on the systematic parameters including X-ray energy, source size, detector resolution, imaging geometry and sample properties is clarified. The systematic parameters of the imaging systems under the irradiation of sub-micron focus X-ray source, laser-driven micro-focus X-ray source and synchrotron radiation X-ray source are optimized, respectively, by the means of numerical simulation. The outcome shows that the optimization system completes the optimization task very well.
A parameter optimization system is established for X-ray in-line phase contrast imaging of the object of two dimensional Gaussian distribution based on the theoretical analysis of the imaging technology. The dependence of the evaluation parameters including contrast, signal-to-noise ratio, resolution and sampling on the systematic parameters including X-ray energy, source size, detector resolution, imaging geometry and sample properties is clarified. The systematic parameters of the imaging systems under the irradiation of sub-micron focus X-ray source, laser-driven micro-focus X-ray source and synchrotron radiation X-ray source are optimized, respectively, by the means of numerical simulation. The outcome shows that the optimization system completes the optimization task very well.
2010,
22.
Abstract:
The influence of spectrum characteristics on diode pumped alkali laser has been studied based on the rate equations. The result shows that, there exists an optimal operation temperature for alkali lasers, and the influences of temperature and gain medium length are equivalent, thus an efficiency, independent of temperature and length, can be introduced to describe the optimal efficiency when other parameters are fixed. The influence of pump linewidth on threshold pump intensity is linear, and a high efficiency may be achieved even when the pump linewidth is much broader than the atomic absorption linewidth because of the large absorption cross section in the far wings of alkali atoms. The influence of atomic absorption linewidth on threshold pump intensity is nonlinear, and as the absorpti
The influence of spectrum characteristics on diode pumped alkali laser has been studied based on the rate equations. The result shows that, there exists an optimal operation temperature for alkali lasers, and the influences of temperature and gain medium length are equivalent, thus an efficiency, independent of temperature and length, can be introduced to describe the optimal efficiency when other parameters are fixed. The influence of pump linewidth on threshold pump intensity is linear, and a high efficiency may be achieved even when the pump linewidth is much broader than the atomic absorption linewidth because of the large absorption cross section in the far wings of alkali atoms. The influence of atomic absorption linewidth on threshold pump intensity is nonlinear, and as the absorpti
2010,
22.
Abstract:
The reconstruction method of digital holographic phase information based on lateral shearing interferometer was studied and a method to obtain the coefficients of the linear phase aberration was proposed. It is pointed out that one-dimensional phase unwrapping for original phase map is the precondition of the lateral shearing method. The numerical reconstruction for digital holograms with and without noise was conducted. The results show that the proposed process is very effective for a weak noisy hologram, but for a strong noisy hologram, median filter should be applied to the original phase map and then applied to the reconstructed phase map to obtain a high quality image. Only if the maximum of the phase difference between the two proximate pixels is smaller than 2π, which can be achie
The reconstruction method of digital holographic phase information based on lateral shearing interferometer was studied and a method to obtain the coefficients of the linear phase aberration was proposed. It is pointed out that one-dimensional phase unwrapping for original phase map is the precondition of the lateral shearing method. The numerical reconstruction for digital holograms with and without noise was conducted. The results show that the proposed process is very effective for a weak noisy hologram, but for a strong noisy hologram, median filter should be applied to the original phase map and then applied to the reconstructed phase map to obtain a high quality image. Only if the maximum of the phase difference between the two proximate pixels is smaller than 2π, which can be achie
2010,
22.
Abstract:
Nonlinear refraction and absorption properties in carbon disulfide(CS2) have been investigated by Z-scan technique under femtosecond pulse lasers at 800 nm in a broad intensity range. It is found that the Z-scan transmittance curve has a large displacement on the axis with the increase of intensity. At low intensity, it is mainly due to two-photon absorption effect, while the fifth-order processes and two-photon absorption are at present simultaneously at high intensity. The critical intensity which determines the existence of the fifth-order nonlinear process is presented, along with the relationship between the axial displacement and some parameters of the transmittance curves.
Nonlinear refraction and absorption properties in carbon disulfide(CS2) have been investigated by Z-scan technique under femtosecond pulse lasers at 800 nm in a broad intensity range. It is found that the Z-scan transmittance curve has a large displacement on the axis with the increase of intensity. At low intensity, it is mainly due to two-photon absorption effect, while the fifth-order processes and two-photon absorption are at present simultaneously at high intensity. The critical intensity which determines the existence of the fifth-order nonlinear process is presented, along with the relationship between the axial displacement and some parameters of the transmittance curves.
2010,
22.
Abstract:
A line-imaging velocity interferometer was developed and implemented, which is used for laser-driven-flyer velocity measurement with high temporal and spatial resolution. Based on VISAR and ORVIS, this system reshapes the probe laser to line light on the target, collects scattered reflection by imaging lens, uses a wide angle Michelson interferometer to produce a comb fringe as velocity information carrier and records the image using streak camera. The velocimeter is capable of 50 ps temporal resolution and 20 μm spatial resolution. Velocity measurement for Al flyer driven by laser was implemented to test this system. Very intuitive image records and data processing results provided a large number of valuable information, confirming that the velocimeter is adequate for laser driven flyer
A line-imaging velocity interferometer was developed and implemented, which is used for laser-driven-flyer velocity measurement with high temporal and spatial resolution. Based on VISAR and ORVIS, this system reshapes the probe laser to line light on the target, collects scattered reflection by imaging lens, uses a wide angle Michelson interferometer to produce a comb fringe as velocity information carrier and records the image using streak camera. The velocimeter is capable of 50 ps temporal resolution and 20 μm spatial resolution. Velocity measurement for Al flyer driven by laser was implemented to test this system. Very intuitive image records and data processing results provided a large number of valuable information, confirming that the velocimeter is adequate for laser driven flyer
2010,
22.
Abstract:
The temporal spectra of scintillation and angle-of-arrival fluctuations have been studied experimentally for light-waves traveling in turbulence of different inner scales. Because of the complexity and uncontrollability of the real atmosphere, the experiment was performed with an atmospheric turbulence chamber. The scintillation and angle-of-arrival fluctuations of the propagating light-wave were simultaneously measured by a position sensitive detector, and the turbulence inner scale along the optical propagation path was derived through inversion. Experimental results show that the high frequency region of both kinds of temporal spectra obey the same power law, and the absolute value of the power exponent and the turbulence inner scale are in linear relation. With the increase of the inn
The temporal spectra of scintillation and angle-of-arrival fluctuations have been studied experimentally for light-waves traveling in turbulence of different inner scales. Because of the complexity and uncontrollability of the real atmosphere, the experiment was performed with an atmospheric turbulence chamber. The scintillation and angle-of-arrival fluctuations of the propagating light-wave were simultaneously measured by a position sensitive detector, and the turbulence inner scale along the optical propagation path was derived through inversion. Experimental results show that the high frequency region of both kinds of temporal spectra obey the same power law, and the absolute value of the power exponent and the turbulence inner scale are in linear relation. With the increase of the inn
2010,
22.
Abstract:
An off-axis external cavity with double feedback is designed to simultaneously reduce spectral bandwidth and improve the beam quality of the laser diode bar. The external cavity is made up of a high-reflection mirror and a blazed grating, where the selected spatial mode can be amplified. The grating can also provide a spectral-sensitive feedback to the laser diode bar. In addition, a half-wave plate is inserted into the grating-feedback branch to control the feedback light amount, and the output laser is taken from the grating-feedback branch. The bandwidth and the beam parameter product are respectively reduced to 0.15 nm and 283 mm·mrad for laser diode bar with the external cavity at a drive current of 16 A. The center wavelength is almost unchanged as the temperature varies, the laser
An off-axis external cavity with double feedback is designed to simultaneously reduce spectral bandwidth and improve the beam quality of the laser diode bar. The external cavity is made up of a high-reflection mirror and a blazed grating, where the selected spatial mode can be amplified. The grating can also provide a spectral-sensitive feedback to the laser diode bar. In addition, a half-wave plate is inserted into the grating-feedback branch to control the feedback light amount, and the output laser is taken from the grating-feedback branch. The bandwidth and the beam parameter product are respectively reduced to 0.15 nm and 283 mm·mrad for laser diode bar with the external cavity at a drive current of 16 A. The center wavelength is almost unchanged as the temperature varies, the laser
2010,
22.
Abstract:
Taking the partially coherent Hermite-Gaussian(H-G) beam as a typical example, this paper studies the distribution of diffraction intensity and the visibility of interference fringes in Young’s two-slit set-up illuminated by the multi-mode partially coherent beam, where the Young’s interference experiment is regarded as a two-slit diffraction phenomenon. Numerical calculations show that, the spatial coherence parameter and mode orders of partially coherent beams, and the obstruction ratio of the two-slit set-up all have some effect on the distribution of the diffraction intensity (i.e. interference pattern) and the visibility of the interference fringes. With the coherence of the partially coherent beams increasing, destructive interference may appear on the axis when the mode orders of
Taking the partially coherent Hermite-Gaussian(H-G) beam as a typical example, this paper studies the distribution of diffraction intensity and the visibility of interference fringes in Young’s two-slit set-up illuminated by the multi-mode partially coherent beam, where the Young’s interference experiment is regarded as a two-slit diffraction phenomenon. Numerical calculations show that, the spatial coherence parameter and mode orders of partially coherent beams, and the obstruction ratio of the two-slit set-up all have some effect on the distribution of the diffraction intensity (i.e. interference pattern) and the visibility of the interference fringes. With the coherence of the partially coherent beams increasing, destructive interference may appear on the axis when the mode orders of
2010,
22.
Abstract:
A deployable umbrella-shaped keel concentrator has been proposed for the solar thermal thruster (STP) system. The improved concentrator overcomes the shortcomings of traditional inflatable concentrators and rigid fixed concentrators. A deployable solar paraboloid concentrator has been designed. It adopts the collapsible umbrella-shaped keel with a concentration power of 100 kW and an aperture radius of this 4.9 m. The performance of the STP system equipped with this concentrator has been investigated with the software Fluent. The results reveal that the thrust and specific impulse can reach 10.23 N and 701.4 s respectively, indicating this system is applicable to attitude control and orbit transfer for micro- and nano-satellites.
A deployable umbrella-shaped keel concentrator has been proposed for the solar thermal thruster (STP) system. The improved concentrator overcomes the shortcomings of traditional inflatable concentrators and rigid fixed concentrators. A deployable solar paraboloid concentrator has been designed. It adopts the collapsible umbrella-shaped keel with a concentration power of 100 kW and an aperture radius of this 4.9 m. The performance of the STP system equipped with this concentrator has been investigated with the software Fluent. The results reveal that the thrust and specific impulse can reach 10.23 N and 701.4 s respectively, indicating this system is applicable to attitude control and orbit transfer for micro- and nano-satellites.
2010,
22.
Abstract:
The mechanism of laser induced damage on optical films, and the methods to improve the laser-induced damage threshold (LIDT) were reviewed in two respects including theory and experiment. We summarized the existing theory models and their applicable scope, and also discussed the problems about defects from various aspects. The characteristics of different coating technics and after-treatment ways were compared in detail. By gathering the achievements of our own and peer institutions at home and abroad, we generalized the sol-gel technics which could be used to improve the LIDT. We also pointed out the direction of future work considering some newly emerging problems such as contamination in vacuum and the subsurface damage.
The mechanism of laser induced damage on optical films, and the methods to improve the laser-induced damage threshold (LIDT) were reviewed in two respects including theory and experiment. We summarized the existing theory models and their applicable scope, and also discussed the problems about defects from various aspects. The characteristics of different coating technics and after-treatment ways were compared in detail. By gathering the achievements of our own and peer institutions at home and abroad, we generalized the sol-gel technics which could be used to improve the LIDT. We also pointed out the direction of future work considering some newly emerging problems such as contamination in vacuum and the subsurface damage.
