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RSS2009 Vol. 21, No. 07
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2009,
21.
Abstract:
Influences of the transparent liquids’ bulk modulus, dynamic-viscosity coefficient and the absorbed laser pulse energy in the breakdown region on the peak pressure, the sound energy and the dominant frequency of the laser induced expanding sound are analyzed. An experimental system is developed for producing and measuring laser induced expanding sound in three transparent liquids-distilled water, alcohol and glycerin. The parameters of laser induced expanding sound are calculated within certain ranges of bulk modulus (0.2~7.0 GPa), dynamic-viscosity coefficient (0.001~30.000 Pa·s) and absorbed laser pulse energy (10~400 mJ). The results of theoretical calculation and experiment is as follows: Firstly, the dominant frequency, the peak sound pressure and the sound energy increase as the bu
Influences of the transparent liquids’ bulk modulus, dynamic-viscosity coefficient and the absorbed laser pulse energy in the breakdown region on the peak pressure, the sound energy and the dominant frequency of the laser induced expanding sound are analyzed. An experimental system is developed for producing and measuring laser induced expanding sound in three transparent liquids-distilled water, alcohol and glycerin. The parameters of laser induced expanding sound are calculated within certain ranges of bulk modulus (0.2~7.0 GPa), dynamic-viscosity coefficient (0.001~30.000 Pa·s) and absorbed laser pulse energy (10~400 mJ). The results of theoretical calculation and experiment is as follows: Firstly, the dominant frequency, the peak sound pressure and the sound energy increase as the bu
2009,
21.
Abstract:
In order to explore the relation between N2-broadening and air-broadening coefficients of water vapor molecules in near-infrared region, a high-sensitive continuous-wave cavity ring down spectroscopy, which used a glass-ceramic as the cavity and a distributed feedback diode laser as the light source, was applied to measure the spectral lines of water vapor molecules(near 1 517 μm in the spectral region of 6 586.5~6 596.5 cm-1), and the noise (RMS) equivalent absorption sensitivity of about 3.2×10-9 cm-1 was achieved. According to those measured broadening coefficients of water vapor molecules in air and in N2, their ratio is obtained as 0.896 9±0.068 7(within 3 times the standard deviation), which is in agreement with the resul
In order to explore the relation between N2-broadening and air-broadening coefficients of water vapor molecules in near-infrared region, a high-sensitive continuous-wave cavity ring down spectroscopy, which used a glass-ceramic as the cavity and a distributed feedback diode laser as the light source, was applied to measure the spectral lines of water vapor molecules(near 1 517 μm in the spectral region of 6 586.5~6 596.5 cm-1), and the noise (RMS) equivalent absorption sensitivity of about 3.2×10-9 cm-1 was achieved. According to those measured broadening coefficients of water vapor molecules in air and in N2, their ratio is obtained as 0.896 9±0.068 7(within 3 times the standard deviation), which is in agreement with the resul
2009,
21.
Abstract:
The (1+1)D spatial optical soliton solutions in nematic liquid crystal are obtained in both weakly and strongly nonlocal limits. By an approximate calculation of the nonlocal nonlinear term in both cases, the propagation equation of beams is derived. In weakly nonlocal case, the solution can be gotten by directive integral and one hump soliton is shown. In strongly nonlocal case, the bright soliton solutions can be expressed by Bessel function, and the number of humps coincides with the number of eigenmodes, predicting the existence of multihump solitons. These results are in good agreement with numerical ones in other papers. The exact solutions are also compared with hyperbolic approximate analytic ones.
The (1+1)D spatial optical soliton solutions in nematic liquid crystal are obtained in both weakly and strongly nonlocal limits. By an approximate calculation of the nonlocal nonlinear term in both cases, the propagation equation of beams is derived. In weakly nonlocal case, the solution can be gotten by directive integral and one hump soliton is shown. In strongly nonlocal case, the bright soliton solutions can be expressed by Bessel function, and the number of humps coincides with the number of eigenmodes, predicting the existence of multihump solitons. These results are in good agreement with numerical ones in other papers. The exact solutions are also compared with hyperbolic approximate analytic ones.
2009,
21.
Abstract:
A high-average-power high-efficiency high-repetition-rate mid-infrared laser at 3.84 μm was demonstrated.The laser was based on quasi-phase-matched periodically poled LiNbO3(PPMgLN) optical parametric oscillator(OPO),pumped by elliptical 1.06 μm laser beam.The PPMgLN crystal was 5% MgO-doped.The OPO was extra-cavity and single-resonated OPO.The pump beam polarization matched e→e+e interaction in PPMgLN, thus maximal nonlinear coefficient was effective. When pump power was 73 W at acoustic-optic Q-switch repetition rate 7.5 kHz, 8.3 W average output power at 3.84 μm was obtained with slope efficiency 14.1%.The optical beam quality factors were 1.94,4.57 in horizontal and perpendicular direction,respectively.
A high-average-power high-efficiency high-repetition-rate mid-infrared laser at 3.84 μm was demonstrated.The laser was based on quasi-phase-matched periodically poled LiNbO3(PPMgLN) optical parametric oscillator(OPO),pumped by elliptical 1.06 μm laser beam.The PPMgLN crystal was 5% MgO-doped.The OPO was extra-cavity and single-resonated OPO.The pump beam polarization matched e→e+e interaction in PPMgLN, thus maximal nonlinear coefficient was effective. When pump power was 73 W at acoustic-optic Q-switch repetition rate 7.5 kHz, 8.3 W average output power at 3.84 μm was obtained with slope efficiency 14.1%.The optical beam quality factors were 1.94,4.57 in horizontal and perpendicular direction,respectively.
2009,
21.
Abstract:
Large eddy simulation has been preformed for the mixing analysis of chemical oxygen-iodine lasers. Traceable results for both flow field and scalar field show that large eddy simulation is a valid approach for the theoretical study of chemical flows. Compared with Reynolds averaging numerical simulation, large eddy simulation is accredited a high accuracy in capture transport processes, especially for the small scale mixing. According to the simulation results, a new method of I2 flow injection has been proposed for the mixing enhancement. With this method, the small signal gain coefficient has increased by 5%.
Large eddy simulation has been preformed for the mixing analysis of chemical oxygen-iodine lasers. Traceable results for both flow field and scalar field show that large eddy simulation is a valid approach for the theoretical study of chemical flows. Compared with Reynolds averaging numerical simulation, large eddy simulation is accredited a high accuracy in capture transport processes, especially for the small scale mixing. According to the simulation results, a new method of I2 flow injection has been proposed for the mixing enhancement. With this method, the small signal gain coefficient has increased by 5%.
2009,
21.
Abstract:
The thermal distortion in the conduction cooled end-pumped zig-zag slab under different cooling conditions were analyzed by numerical simulation. The results indicate that the thermal distortion could be reduced by 3 orders of magnitude in zig-zag propagation. The inversion phenomenon of wave front was observed when different zig-zag optical paths were selected. The zig-zag optical path can eliminate the influence of the non-uniform heat dissipating capacity in length and height directions, but not in width direction. When the heat dissipating capacity in slab’s width direction is non-uniform, the thermal distortion increases significantly and the propagation direction will be deviated．Therefore, when the heat dissipating capacity of the slab is non-uniform, small bounce number of zig-za
The thermal distortion in the conduction cooled end-pumped zig-zag slab under different cooling conditions were analyzed by numerical simulation. The results indicate that the thermal distortion could be reduced by 3 orders of magnitude in zig-zag propagation. The inversion phenomenon of wave front was observed when different zig-zag optical paths were selected. The zig-zag optical path can eliminate the influence of the non-uniform heat dissipating capacity in length and height directions, but not in width direction. When the heat dissipating capacity in slab’s width direction is non-uniform, the thermal distortion increases significantly and the propagation direction will be deviated．Therefore, when the heat dissipating capacity of the slab is non-uniform, small bounce number of zig-za
2009,
21.
Abstract:
An eigenvector method is used to calculate the mode distribution, misalignment and beam quality factor of a resonator with a two-dimensional misalignment angle. In the calculation model, the gain medium is regarded as a sheet inside the mirror. It is found that resonator misalignment leads to the uneven distribution of modes and the change of mode orders. And when the misalignment is in a certain range, it may bring forth new mode competition. The beam quality factor will not always get bad when disorder level increases, however, beam quality generally degrades as mode orders increases, and some degenerate modes may not be degenerate any more.
An eigenvector method is used to calculate the mode distribution, misalignment and beam quality factor of a resonator with a two-dimensional misalignment angle. In the calculation model, the gain medium is regarded as a sheet inside the mirror. It is found that resonator misalignment leads to the uneven distribution of modes and the change of mode orders. And when the misalignment is in a certain range, it may bring forth new mode competition. The beam quality factor will not always get bad when disorder level increases, however, beam quality generally degrades as mode orders increases, and some degenerate modes may not be degenerate any more.
2009,
21.
Abstract:
A novel multiple-electrode electrostatic deflector (petal-like) is introduced. It can be got by symmetrically slotting a cylindrical electrode into eight separate parts. The Fourier analysis of the potential distribution on the circumference of the electrode circle has elicited the principle for electrode potential settings to generate a nearly transversely-uniform deflecting field. Based on the rotational symmetry in its shape and the harmonicity of the solution of Laplace equation, multipole fields generated by the petal-like electrode would not affect the focusing property of the conventional electrostatic lens in the paraxial region, when the focusing potential additionally applied. Therefore, the introduced multiple-electrode petal-like defector can be combined with the commonly used
A novel multiple-electrode electrostatic deflector (petal-like) is introduced. It can be got by symmetrically slotting a cylindrical electrode into eight separate parts. The Fourier analysis of the potential distribution on the circumference of the electrode circle has elicited the principle for electrode potential settings to generate a nearly transversely-uniform deflecting field. Based on the rotational symmetry in its shape and the harmonicity of the solution of Laplace equation, multipole fields generated by the petal-like electrode would not affect the focusing property of the conventional electrostatic lens in the paraxial region, when the focusing potential additionally applied. Therefore, the introduced multiple-electrode petal-like defector can be combined with the commonly used
2009,
21.
Abstract:
Features of a practical asymmetric electrode system were studied. The anode of this system is an analytical electrode such as Chang electrode and Ernst electrode, and the cathode is a simple electrode with line-arc structure. The electric field of the system was calculated with high-precision finite element method(FEM), and was analysed and compared with that of two symmetric electrode systems. With the analysis of effects of the parameters used in construction of the asymmetric electrodes, some suggestions were made for optimal choice of the shape of simple electrodes. The results show that the asymmetric electrodes are suitable for TEA CO2 lasers, and uniform electric field with required size can be obtained by proper choices of electrode parameters.
Features of a practical asymmetric electrode system were studied. The anode of this system is an analytical electrode such as Chang electrode and Ernst electrode, and the cathode is a simple electrode with line-arc structure. The electric field of the system was calculated with high-precision finite element method(FEM), and was analysed and compared with that of two symmetric electrode systems. With the analysis of effects of the parameters used in construction of the asymmetric electrodes, some suggestions were made for optimal choice of the shape of simple electrodes. The results show that the asymmetric electrodes are suitable for TEA CO2 lasers, and uniform electric field with required size can be obtained by proper choices of electrode parameters.
2009,
21.
Abstract:
According to the steady-state heat conduction equation, the temperature distribution in the high power double-clad fiber laser(DCFL) has been analyzed. The influence of fiber size, cooling-boundary condition and pump power on temperature distribution are discussed based on the analytic solution. The theoretical maximum output power with given parameters is obtained. The maximum power of a commonly used DCFL is limited by the melting point of the material and the non-linear effect. The bottlenecks can be easily determined so as to come up with effective improved shemes, such as weakening or eliminating the linear effect, raising the heat-resistant of outer-clad and improving the cooling method.
According to the steady-state heat conduction equation, the temperature distribution in the high power double-clad fiber laser(DCFL) has been analyzed. The influence of fiber size, cooling-boundary condition and pump power on temperature distribution are discussed based on the analytic solution. The theoretical maximum output power with given parameters is obtained. The maximum power of a commonly used DCFL is limited by the melting point of the material and the non-linear effect. The bottlenecks can be easily determined so as to come up with effective improved shemes, such as weakening or eliminating the linear effect, raising the heat-resistant of outer-clad and improving the cooling method.
2009,
21.
Abstract:
A series of low energy X-ray spectral lines which have constant energy have been detected in hydrogen gas discharge source bombarding targets. Their energy are 1.7 keV, 2.3 keV, 2.6 keV, 3.3 keV and 3.7 keV, respectively. These anonymous spectral lines can not be explained by the known theories.There are still possibilities that they are produced by potential impurity elements in targets or in the discharge chamber, although the energy of the anonymous spectral lines are close to the energy of the characteristic X-ray of some elements, such as Si, Ta, S, Cl, K, Ca and Ti, etc. In this paper, the origin of impurity elements in the experimental system are analyzed, the influence of impurity elements in the discharge chamber and targets on the new spectral lines are studied, and the target s
A series of low energy X-ray spectral lines which have constant energy have been detected in hydrogen gas discharge source bombarding targets. Their energy are 1.7 keV, 2.3 keV, 2.6 keV, 3.3 keV and 3.7 keV, respectively. These anonymous spectral lines can not be explained by the known theories.There are still possibilities that they are produced by potential impurity elements in targets or in the discharge chamber, although the energy of the anonymous spectral lines are close to the energy of the characteristic X-ray of some elements, such as Si, Ta, S, Cl, K, Ca and Ti, etc. In this paper, the origin of impurity elements in the experimental system are analyzed, the influence of impurity elements in the discharge chamber and targets on the new spectral lines are studied, and the target s
2009,
21.
Abstract:
A new method for ICF fuel content measuring based on laser Raman scattering is presented, which can directly and non-destructively analyzes deuterium gas content in shells. Since the incident and scattered lights would traverse through the shell wall, therefore the material performance of the shell will greatly affect the measured results. Thus corresponding experiments have been done using a confocal laser Raman microscope, and the factors that will influence the results, such as shells florescence, laser wavelength and power, grating resolution,and system confocal performance, have been investigated, which proves the feasibility of the method.
A new method for ICF fuel content measuring based on laser Raman scattering is presented, which can directly and non-destructively analyzes deuterium gas content in shells. Since the incident and scattered lights would traverse through the shell wall, therefore the material performance of the shell will greatly affect the measured results. Thus corresponding experiments have been done using a confocal laser Raman microscope, and the factors that will influence the results, such as shells florescence, laser wavelength and power, grating resolution,and system confocal performance, have been investigated, which proves the feasibility of the method.
2009,
21.
Abstract:
According to the requirement of beam smoothing in laser systems, the continuous phase plate with Gaussian distribution is designed. The far-field distributions of such phase plate with correlation lengths of 39 mm, 30 mm, 10 mm and 3 mm are calculated. The numerical results show that while the correlation length is longer than 10 mm, far-field distribution of the phase plate is inordinate for the ergodic condition is not satisfied. While the correlation length is less than 10 mm, far-field distribution of the phase plate is very close to ideal Gaussian distribution. Using the continuous phase plate with the correlation length of 3 mm, the beam smoothing process is simulated. The results show that after propagating through a phase plate the intensity distribution of the laser beam on the f
According to the requirement of beam smoothing in laser systems, the continuous phase plate with Gaussian distribution is designed. The far-field distributions of such phase plate with correlation lengths of 39 mm, 30 mm, 10 mm and 3 mm are calculated. The numerical results show that while the correlation length is longer than 10 mm, far-field distribution of the phase plate is inordinate for the ergodic condition is not satisfied. While the correlation length is less than 10 mm, far-field distribution of the phase plate is very close to ideal Gaussian distribution. Using the continuous phase plate with the correlation length of 3 mm, the beam smoothing process is simulated. The results show that after propagating through a phase plate the intensity distribution of the laser beam on the f
2009,
21.
Abstract:
In order to systemically investigate the morphology and microstructure induced in fused silica by UV (355 nm) laser pulses at high fluence, a suite of microscopic tools have been used, such as Nomarski optics microscope,AFM and SEM. Two types of damage are observed on the input surface of fused silica, that is, micro-pits and star-like cracks with diameters of 0.8～2.5 μm and 1.0～5.5 μm, respectively. Correspondingly, there are three types of damage on the output surface, namely micro-pits,shell-like damage and craters with diameters of 0.48～1.33 μm,4～20 μm and 12～30 μm, respectively. By comparing morphology of fused silica and laser fluence, several assumptions have been given to understand the damage initiation mechanism,especially for 1 μm scale laser initialed damage.
In order to systemically investigate the morphology and microstructure induced in fused silica by UV (355 nm) laser pulses at high fluence, a suite of microscopic tools have been used, such as Nomarski optics microscope,AFM and SEM. Two types of damage are observed on the input surface of fused silica, that is, micro-pits and star-like cracks with diameters of 0.8～2.5 μm and 1.0～5.5 μm, respectively. Correspondingly, there are three types of damage on the output surface, namely micro-pits,shell-like damage and craters with diameters of 0.48～1.33 μm,4～20 μm and 12～30 μm, respectively. By comparing morphology of fused silica and laser fluence, several assumptions have been given to understand the damage initiation mechanism,especially for 1 μm scale laser initialed damage.
2009,
21.
Abstract:
Based on the light defect images against the dark background in a scattering imaging system, a digital detection system of surface defects for large aperture optical elements has been presented. In the system, the image is segmented by a multi-area self-adaptive threshold segmentation method, then a pixel labeling method based on replacing arrays is adopted to extract defect features quickly, and at last the defects are classified through back-propagation neural networks. Experiment results show that the system can achieve real-time detection and classification.
Based on the light defect images against the dark background in a scattering imaging system, a digital detection system of surface defects for large aperture optical elements has been presented. In the system, the image is segmented by a multi-area self-adaptive threshold segmentation method, then a pixel labeling method based on replacing arrays is adopted to extract defect features quickly, and at last the defects are classified through back-propagation neural networks. Experiment results show that the system can achieve real-time detection and classification.
2009,
21.
Abstract:
Plated ICF glass targets were treated under 300 ℃, 700 ℃ and 1 000 ℃ for one hour, respectively. Structure, morphology and magnetic property of the plated ICF glass targets were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and vibrating sample magnetometry(VSM). The results show that the Ni-P plating on the surface of the ICF glass targets will be crystallized after the targets are thermally treated. The diameter of the crystalline grains and the corresponding magnetic parameters of the Ni-P plating increases with increasing the thermal treatment temperature. The treated ICF glass targets could be used in research of magnetic suspension experiment.
Plated ICF glass targets were treated under 300 ℃, 700 ℃ and 1 000 ℃ for one hour, respectively. Structure, morphology and magnetic property of the plated ICF glass targets were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and vibrating sample magnetometry(VSM). The results show that the Ni-P plating on the surface of the ICF glass targets will be crystallized after the targets are thermally treated. The diameter of the crystalline grains and the corresponding magnetic parameters of the Ni-P plating increases with increasing the thermal treatment temperature. The treated ICF glass targets could be used in research of magnetic suspension experiment.
2009,
21.
Abstract:
Microwave power spatial synthesis from multi-source is an effective and widely used method to realize high power microwave radiation. In many cases, output power of high power microwave sources is with random phase shift because of their unstable property. This paper employs numerical calculations, deals with the phase shift of microwave sources which are even distribution and calculates the synthesis efficiency using the average gain of radiation antenna arrays. By numerical calculations, the impact of the coupling coefficient between antenna elements, the type and polarization of antenna arrays, and the antenna gain on the synthesis efficiency are analyzed. The analysis shows that the coupling between antenna elements may seriously reduce the synthesis efficiency; the effect of antenna t
Microwave power spatial synthesis from multi-source is an effective and widely used method to realize high power microwave radiation. In many cases, output power of high power microwave sources is with random phase shift because of their unstable property. This paper employs numerical calculations, deals with the phase shift of microwave sources which are even distribution and calculates the synthesis efficiency using the average gain of radiation antenna arrays. By numerical calculations, the impact of the coupling coefficient between antenna elements, the type and polarization of antenna arrays, and the antenna gain on the synthesis efficiency are analyzed. The analysis shows that the coupling between antenna elements may seriously reduce the synthesis efficiency; the effect of antenna t
2009,
21.
Abstract:
Waveform converting and angular filtering properties of zero-electric and zero-magnetic(ZEM) materials slab were simulated under line source, TM wave and dipole irradiation, respectively, using finite-difference time-domain(FDTD) method. Simulation results show that electromagnetic wave can tunnel through the ZEM materials when the wave impinges on the entrance face of the materials perpendicularly; the phase pattern of the transmitted wave is dependent on the exit faces of ZEM materials; when the electromagnetic waves emitted from a line source or dipole transmit through a ZEM materials slab with planar exit face, it can be transformed into perfect plane waves. Moreover, the ZEM materials can be used in the design of antenna array. The radiation intensity of the ZEM material-assisted ante
Waveform converting and angular filtering properties of zero-electric and zero-magnetic(ZEM) materials slab were simulated under line source, TM wave and dipole irradiation, respectively, using finite-difference time-domain(FDTD) method. Simulation results show that electromagnetic wave can tunnel through the ZEM materials when the wave impinges on the entrance face of the materials perpendicularly; the phase pattern of the transmitted wave is dependent on the exit faces of ZEM materials; when the electromagnetic waves emitted from a line source or dipole transmit through a ZEM materials slab with planar exit face, it can be transformed into perfect plane waves. Moreover, the ZEM materials can be used in the design of antenna array. The radiation intensity of the ZEM material-assisted ante
2009,
21.
Abstract:
To understand timedomain change characteristics of electrical field in the building, the simulation of three electromagnetic pulses propagating, reflecting and transmitting in a building was done by FDTD method. The influence of different pulse parameters on the maximum strength and distribution of electric field were generally analyzed. With the incidence of differential Gaussian pulses with varied pulse width, the maximum strength in the building changes within 3.0~5.5 dB and the range of reinforced field reduces as pulse width increases, and the required minimum pulse repetition frequency is the highest. The maximum strength and distribution area of electric field are the least in the building radiated by Gaussian pulses, of which the minimum repetition frequency is the lowest. When t
To understand timedomain change characteristics of electrical field in the building, the simulation of three electromagnetic pulses propagating, reflecting and transmitting in a building was done by FDTD method. The influence of different pulse parameters on the maximum strength and distribution of electric field were generally analyzed. With the incidence of differential Gaussian pulses with varied pulse width, the maximum strength in the building changes within 3.0~5.5 dB and the range of reinforced field reduces as pulse width increases, and the required minimum pulse repetition frequency is the highest. The maximum strength and distribution area of electric field are the least in the building radiated by Gaussian pulses, of which the minimum repetition frequency is the lowest. When t
2009,
21.
Abstract:
The super fragment separator (super-FRS) of the FAIR project (facility for antiproton and ion research) consists of two superconducting coils. The maximum magnetic field is as high as 1.6 T, which results in large magnetic force. In order to assure the mechanical stability of the superconducting magnet, we conducted a 3D finite element analysis of its mechanical behavior. For numerical simulation and analysis of the phenomena inside the structure, the ADINA and TOSCA codes were chosen. The ADINA code is commonly used for numerical simulations of the structure analysis and the TOSCA code is professional software to calculate the magnetic field and Lorentz Forces. The results show that for the coil case is made of 316LN stainless steel cast, the structure with iron core and fixers in the mid
The super fragment separator (super-FRS) of the FAIR project (facility for antiproton and ion research) consists of two superconducting coils. The maximum magnetic field is as high as 1.6 T, which results in large magnetic force. In order to assure the mechanical stability of the superconducting magnet, we conducted a 3D finite element analysis of its mechanical behavior. For numerical simulation and analysis of the phenomena inside the structure, the ADINA and TOSCA codes were chosen. The ADINA code is commonly used for numerical simulations of the structure analysis and the TOSCA code is professional software to calculate the magnetic field and Lorentz Forces. The results show that for the coil case is made of 316LN stainless steel cast, the structure with iron core and fixers in the mid
2009,
21.
Abstract:
To study the phase characteristics of solid-state amplifiers (20 kW/142.8 MHz, 10 kW/571.2 MHz) in sub-harmonic bunchers(SHBs) of the BEPC Ⅱ linear accelerator, phase shift in pulse and phase stability are measured using a digital measurement method based on field programmable gate array(FPGA ). The hardware of the measurement system includes the frequency synthesizer, digital signal processing board(FPGA) and PC, and the software includes an internal algorithm on FPGA, communication procedures and PC client interface procedures. The measurement results of phase characteristics are consistent with the actual situation, which is the basis for the further implement of phase compensation in SHBs.
To study the phase characteristics of solid-state amplifiers (20 kW/142.8 MHz, 10 kW/571.2 MHz) in sub-harmonic bunchers(SHBs) of the BEPC Ⅱ linear accelerator, phase shift in pulse and phase stability are measured using a digital measurement method based on field programmable gate array(FPGA ). The hardware of the measurement system includes the frequency synthesizer, digital signal processing board(FPGA) and PC, and the software includes an internal algorithm on FPGA, communication procedures and PC client interface procedures. The measurement results of phase characteristics are consistent with the actual situation, which is the basis for the further implement of phase compensation in SHBs.
2009,
21.
Abstract:
Recently, great attention has been paid to short electron pulses because of the requirement for free electron laser(FEL) projects. To generate a 0.2 nC, 5 ps, 2 MeV electron bunch with a normalized emittance better than 50 mm·mrad without compensation coil, a self-bunching RF gun with independently tunable cells (ITC) is employed, which consists of two independent cavities to compress short pulses. The first cell compresses the beam from a high-voltage DC gun and the second is an acceleration cell. The two cells can be power fed independently, and beams with excellent characteristics can be obtained by choosing appropriate feeding power and phase for the two cells. This paper describes the design of an external injecting ITC RF gun (DC-ITC-RF gun) and presents simulation results of beam p
Recently, great attention has been paid to short electron pulses because of the requirement for free electron laser(FEL) projects. To generate a 0.2 nC, 5 ps, 2 MeV electron bunch with a normalized emittance better than 50 mm·mrad without compensation coil, a self-bunching RF gun with independently tunable cells (ITC) is employed, which consists of two independent cavities to compress short pulses. The first cell compresses the beam from a high-voltage DC gun and the second is an acceleration cell. The two cells can be power fed independently, and beams with excellent characteristics can be obtained by choosing appropriate feeding power and phase for the two cells. This paper describes the design of an external injecting ITC RF gun (DC-ITC-RF gun) and presents simulation results of beam p
2009,
21.
Abstract:
The beam horizontal orbit at Hefei light source(HLS) was drifting all along while the storage ring was operating due to the drift of BPM chamber mainly caused by the thermal effect of synchrotron light. To monitor the BPM chamber motion for all BPMs, a BPM chamber motion measurement system is built in real-time to correct the reading of BPMs. The raster gauges are used to measure the displacement, and the displacement data are transmitted by RS485 serial network to an industrial personal computer which processes the data and sends them to HLS control system. The design of BPM chamber motion measurement system is described and the measurement results are given.
The beam horizontal orbit at Hefei light source(HLS) was drifting all along while the storage ring was operating due to the drift of BPM chamber mainly caused by the thermal effect of synchrotron light. To monitor the BPM chamber motion for all BPMs, a BPM chamber motion measurement system is built in real-time to correct the reading of BPMs. The raster gauges are used to measure the displacement, and the displacement data are transmitted by RS485 serial network to an industrial personal computer which processes the data and sends them to HLS control system. The design of BPM chamber motion measurement system is described and the measurement results are given.
2009,
21.
Abstract:
The laser shock-induced phase transformation of iron with different volume voids has been investigated by means of molecular dynamics（MD）simulations. By comparing the perfect single crystal iron and the iron with different volume voids, the effects of the void volume have been presented. Simulation results show that the void decreases the phase transformation pressure, and the bigger void induces lower pressure; the increase of void volume speed up the nucleation and the expansion of transformation; the void also changes the initial nucleation district, and makes a butterfly shaped nucleation pattern. The influence of rarefaction wave in bigger void is stronger, which affects phase transformation nucleation sites, and brings on a lot of atoms with amorphous structures. The effect of void
The laser shock-induced phase transformation of iron with different volume voids has been investigated by means of molecular dynamics（MD）simulations. By comparing the perfect single crystal iron and the iron with different volume voids, the effects of the void volume have been presented. Simulation results show that the void decreases the phase transformation pressure, and the bigger void induces lower pressure; the increase of void volume speed up the nucleation and the expansion of transformation; the void also changes the initial nucleation district, and makes a butterfly shaped nucleation pattern. The influence of rarefaction wave in bigger void is stronger, which affects phase transformation nucleation sites, and brings on a lot of atoms with amorphous structures. The effect of void
2009,
21.
Abstract:
Irregularly-shaped tungsten powders(average granular sizes of 5~12 μm) have been spheroidized by radio frequency(RF) induction plasma. The effects of feed rate, mode of material dispersion, particle size on spheroidization efficiency are investigated. Experimental results show that the spheroidization efficiency decreases rapidly when the feed rate increases to more than 95 g/min. Only 30% spheroidization efficiency is gained at the feed rate of 135.75 g/min. The spheroidization efficiency is also affected by the flow rate of carrier gas. When the flow rate of carrier gas is 0.12 m3/h, the dispersion effect is the best, and the spheroidization efficiency is almost 100%. The apparent density of tungsten powders increases a bit with the increase of spheroidization efficiency. And the partic
Irregularly-shaped tungsten powders(average granular sizes of 5~12 μm) have been spheroidized by radio frequency(RF) induction plasma. The effects of feed rate, mode of material dispersion, particle size on spheroidization efficiency are investigated. Experimental results show that the spheroidization efficiency decreases rapidly when the feed rate increases to more than 95 g/min. Only 30% spheroidization efficiency is gained at the feed rate of 135.75 g/min. The spheroidization efficiency is also affected by the flow rate of carrier gas. When the flow rate of carrier gas is 0.12 m3/h, the dispersion effect is the best, and the spheroidization efficiency is almost 100%. The apparent density of tungsten powders increases a bit with the increase of spheroidization efficiency. And the partic
2009,
21.
Abstract:
The energy spectrum of the developed sandwich chemical vapor deposition(CVD) diamond film detector to alpha-particles,has been measured by experiments at room temperature, for 241Am source with a characteristic energy of 5.485 MeV and 243Am and 244Cm source with characteristic energies of 5.275 MeV and 5.805 MeV respectively. The trend of the charge collection efficiency changing with biased voltage was obtained, and the mean efficiency under different biased voltages and that at 10% of the trailing edge of the spectrum were also calculated. Results show that the performance of the detector is steady, and the charge collection efficiency of the detector to alpha-particles increases with the biased voltage increasing and is saturated at a certain biased voltage. The saturated mean charge co
The energy spectrum of the developed sandwich chemical vapor deposition(CVD) diamond film detector to alpha-particles,has been measured by experiments at room temperature, for 241Am source with a characteristic energy of 5.485 MeV and 243Am and 244Cm source with characteristic energies of 5.275 MeV and 5.805 MeV respectively. The trend of the charge collection efficiency changing with biased voltage was obtained, and the mean efficiency under different biased voltages and that at 10% of the trailing edge of the spectrum were also calculated. Results show that the performance of the detector is steady, and the charge collection efficiency of the detector to alpha-particles increases with the biased voltage increasing and is saturated at a certain biased voltage. The saturated mean charge co
2009,
21.
Abstract:
An analytic approach to all-optical switch was present, and the two-photon absorption effect were taking into account to analyze all-optical switch, which is based on two-dimensional photonic crystal directional coupler, by means of the finite-difference time-domain method. The numerical study shows that, for short device and high intensity control beam, nonlinear two-photon absorption(TPA) can take effect on the process of coupling action in all-optical switch, and then change the transmission characteristics of input beam. Therefore, under realistic conditions, TPA should be considered in desgning all-optical switch devices based on photonic crystal directional coupler.
An analytic approach to all-optical switch was present, and the two-photon absorption effect were taking into account to analyze all-optical switch, which is based on two-dimensional photonic crystal directional coupler, by means of the finite-difference time-domain method. The numerical study shows that, for short device and high intensity control beam, nonlinear two-photon absorption(TPA) can take effect on the process of coupling action in all-optical switch, and then change the transmission characteristics of input beam. Therefore, under realistic conditions, TPA should be considered in desgning all-optical switch devices based on photonic crystal directional coupler.
2009,
21.
Abstract:
A novel approach for subwavelength imaging is proposed using a positive-refractive-index(PRI) media slab lens excited by an embedded source. Both evanescent wave and propagating voltage wave distribution are analyzed inside and outside a PRI media slab, which is surrounded by a negative-refractive-index (NRI) material. The PRI and NRI materials consist of two -dimensional unloaded transmission line(TL) and inductor, capacitor (L,C) loaded TL networks, respectively. The microwave-circuit simulation and numerical simulation results show that there is strong voltage amplitudes near the two interfaces of the slab due to the growth of evanescent field in the slab. The results confirm that evanescent waves are restored at the focus by the proposed PRI TL lens, thus enhancing the resolution of th
A novel approach for subwavelength imaging is proposed using a positive-refractive-index(PRI) media slab lens excited by an embedded source. Both evanescent wave and propagating voltage wave distribution are analyzed inside and outside a PRI media slab, which is surrounded by a negative-refractive-index (NRI) material. The PRI and NRI materials consist of two -dimensional unloaded transmission line(TL) and inductor, capacitor (L,C) loaded TL networks, respectively. The microwave-circuit simulation and numerical simulation results show that there is strong voltage amplitudes near the two interfaces of the slab due to the growth of evanescent field in the slab. The results confirm that evanescent waves are restored at the focus by the proposed PRI TL lens, thus enhancing the resolution of th
2009,
21.
Abstract:
The current automated defect recognition of industrial computerized tomography(ICT) slice images is mostly carried out in individual image. Certain false detections would exist for some isolated noises can not be wiped off without considering the information of neighbor layer images. To solve this problem, a new automated defect recognition method is presented based on a two-step analysis of consecutive slice images. First, all potential defects are segmented using a classic method in each image. Second, real defects and false defects are recognized by all potential defect matching of neighbor layer images in two steps based on the continuity of real defects characteristic and the non-continuity of false defects between the neighbor images. The method is verified by experiments and result
The current automated defect recognition of industrial computerized tomography(ICT) slice images is mostly carried out in individual image. Certain false detections would exist for some isolated noises can not be wiped off without considering the information of neighbor layer images. To solve this problem, a new automated defect recognition method is presented based on a two-step analysis of consecutive slice images. First, all potential defects are segmented using a classic method in each image. Second, real defects and false defects are recognized by all potential defect matching of neighbor layer images in two steps based on the continuity of real defects characteristic and the non-continuity of false defects between the neighbor images. The method is verified by experiments and result
2009,
21.
Abstract:
To detect the fast logic pulse sequence related to random events, an online detecting system has been realized based on a 1 GHz ultra-high-speed A/D converter and a high-speed FPAG processor.PeakTDC algorithm was designed to seek the peak position of the pulses and therefore demarcate the corresponding pulse time, and then to form the time code and peak amplitude for the pulse sequence. The practical test results of the system show a time interval error of 1 ns, a peak amplitude error of 2 quantization units, and a paired pulse resolution of 10 ns. The algorithm theory and experimental results demonstrate that the system can achieve ns-level time-digital-conversion for random pulse sequences on a limited long time-bin, and simultaneously obtain the peak value of pulses.
To detect the fast logic pulse sequence related to random events, an online detecting system has been realized based on a 1 GHz ultra-high-speed A/D converter and a high-speed FPAG processor.PeakTDC algorithm was designed to seek the peak position of the pulses and therefore demarcate the corresponding pulse time, and then to form the time code and peak amplitude for the pulse sequence. The practical test results of the system show a time interval error of 1 ns, a peak amplitude error of 2 quantization units, and a paired pulse resolution of 10 ns. The algorithm theory and experimental results demonstrate that the system can achieve ns-level time-digital-conversion for random pulse sequences on a limited long time-bin, and simultaneously obtain the peak value of pulses.
2009,
21.
Abstract:
Some research has been conducted on making compact, portable pulse forming lines. Two kinds of dielectric are used as the energy storage materials in the pulse forming lines. They are a kind of ceramic and a kind of newly developed composite polymer. The ceramic’s dielectric constant ranges from 200 to 1 000 and the composite polymer’s dielectric constant ranges from 50 to 250. The characteristics of the two dielectrics are experimentally tested,such as flashover and bulk breakdown under pulsed voltage. Using the large composite polymer bulk as the dielectric, the planar Blumlein line can generate voltage pulses up to 3 kV with a duration of about 58 ns. And using the ceramic bulk as the dielectric, the planar line can generate voltage pulses up to 60 kV with a duration of about 92 ns．
Some research has been conducted on making compact, portable pulse forming lines. Two kinds of dielectric are used as the energy storage materials in the pulse forming lines. They are a kind of ceramic and a kind of newly developed composite polymer. The ceramic’s dielectric constant ranges from 200 to 1 000 and the composite polymer’s dielectric constant ranges from 50 to 250. The characteristics of the two dielectrics are experimentally tested,such as flashover and bulk breakdown under pulsed voltage. Using the large composite polymer bulk as the dielectric, the planar Blumlein line can generate voltage pulses up to 3 kV with a duration of about 58 ns. And using the ceramic bulk as the dielectric, the planar line can generate voltage pulses up to 60 kV with a duration of about 92 ns．
2009,
21.
Abstract:
A temporally-and spatially-resolved X-ray spectrometer, with spectral range of 1 500～2 300 eV and temporal resolution about 2 ns, has been developed for diagnosing K-shell radiation of aluminum wire array Z-pinch plasma driven by Qiangguang-I generator (1.5 MA, 80～100 ns). It consisted of an elliptically-curved TAP crystal and a four-channel X-ray frame camera. Theoretical analyses were made to check out possible effects of different signal transfer and conversion processes on spectral response of the spectrometer. It recorded time-resolved and -integrated K-shell resonance lines of H-, He-like aluminum ions and satellite lines of Li-, He-like ions. Results were compared with spectral-resolved X-ray images obtained by pinhole cameras. Time-resolved K-shell spectra show many differences o
A temporally-and spatially-resolved X-ray spectrometer, with spectral range of 1 500～2 300 eV and temporal resolution about 2 ns, has been developed for diagnosing K-shell radiation of aluminum wire array Z-pinch plasma driven by Qiangguang-I generator (1.5 MA, 80～100 ns). It consisted of an elliptically-curved TAP crystal and a four-channel X-ray frame camera. Theoretical analyses were made to check out possible effects of different signal transfer and conversion processes on spectral response of the spectrometer. It recorded time-resolved and -integrated K-shell resonance lines of H-, He-like aluminum ions and satellite lines of Li-, He-like ions. Results were compared with spectral-resolved X-ray images obtained by pinhole cameras. Time-resolved K-shell spectra show many differences o
2009,
21.
Abstract:
In Z-pinch diagnostic, Dante spectrometer plays an important role in the measurement of soft X-ray spectrum and total flux. This paper reports on the structure and channel configuration of a “Dante” spectrometer designed for z-pinch experiments on Yang accelerator. Calibration of X-ray devices used in the spectrometer, such as X-ray diodes, grazing incidence mirrors and filters are described in detail and reasons accounting for the deviation from theoretical values have also been discussed. Waveforms and unfolding results which also compared with X-ray scintillator powermeter obtained in an argon gas-puff experiment are presented as well, the power of X- ray radiation is about 30～40 GW and the energy of it is about 0.8 kJ, the difference of the results of Dante spectrometer and X-ray sc
In Z-pinch diagnostic, Dante spectrometer plays an important role in the measurement of soft X-ray spectrum and total flux. This paper reports on the structure and channel configuration of a “Dante” spectrometer designed for z-pinch experiments on Yang accelerator. Calibration of X-ray devices used in the spectrometer, such as X-ray diodes, grazing incidence mirrors and filters are described in detail and reasons accounting for the deviation from theoretical values have also been discussed. Waveforms and unfolding results which also compared with X-ray scintillator powermeter obtained in an argon gas-puff experiment are presented as well, the power of X- ray radiation is about 30～40 GW and the energy of it is about 0.8 kJ, the difference of the results of Dante spectrometer and X-ray sc
