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RSS2012 Vol. 24, No. 01
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2012,
24: 1-2.
Abstract:
A contamination control plan was introduced to improve the cleanliness of slab amplifiers for Shenguang-Ⅲ laser driver, including laser structure optimization and precision cleaning methods, and the non-volatile-residue amount on the surface of mechanical structures was lower than 1 mg/m2 after precision cleaning. The illuminating cleaning experiment by flashlamp light was introduced to further improve the facilitys cleanliness. The results indicate that the cleanliness of Shenguang-Ⅲ laser driver is close to that of NIF, but better than other similar devices in the world. The aerosol concentration in Shenguang-Ⅲ amplifier cavity-during-flashlamp shots maintained among 5 000 to 10 000 particles (larger than 0.5 m) per cubic foot, and most of the surface organic residue was released at the first few shots and a clean amplifier was obtained finally. The significant improvements in cleanliness have provided a strong guarantee for the safe operation of Shenguang-Ⅲ laser driver.
A contamination control plan was introduced to improve the cleanliness of slab amplifiers for Shenguang-Ⅲ laser driver, including laser structure optimization and precision cleaning methods, and the non-volatile-residue amount on the surface of mechanical structures was lower than 1 mg/m2 after precision cleaning. The illuminating cleaning experiment by flashlamp light was introduced to further improve the facilitys cleanliness. The results indicate that the cleanliness of Shenguang-Ⅲ laser driver is close to that of NIF, but better than other similar devices in the world. The aerosol concentration in Shenguang-Ⅲ amplifier cavity-during-flashlamp shots maintained among 5 000 to 10 000 particles (larger than 0.5 m) per cubic foot, and most of the surface organic residue was released at the first few shots and a clean amplifier was obtained finally. The significant improvements in cleanliness have provided a strong guarantee for the safe operation of Shenguang-Ⅲ laser driver.
2012,
24: 3-4.
Abstract:
A simple and effective method based on boundary element method, is proposed for computer determination of the resonant frequency and field distribution of the waveguide-loaded cavity in klystron output system. This paper calculates a common rectangular-waveguide-loaded rectangular cavity. The TE10 mode wave is used as the input wave, and the Robin-type boundary condition is used in the output waveport. The maximum of the electric field is searched, which corresponds to the eigenfrequency. The obtained eigenfrequency is lower than that of the cavity of the same size and loaded with no waveguide, and the field distribution is under the influence of coupling hole. It is shown that this method needs less computing time and resources in solving the half-open system like a waveguide-loaded cavity with high precision.
A simple and effective method based on boundary element method, is proposed for computer determination of the resonant frequency and field distribution of the waveguide-loaded cavity in klystron output system. This paper calculates a common rectangular-waveguide-loaded rectangular cavity. The TE10 mode wave is used as the input wave, and the Robin-type boundary condition is used in the output waveport. The maximum of the electric field is searched, which corresponds to the eigenfrequency. The obtained eigenfrequency is lower than that of the cavity of the same size and loaded with no waveguide, and the field distribution is under the influence of coupling hole. It is shown that this method needs less computing time and resources in solving the half-open system like a waveguide-loaded cavity with high precision.
2012,
24: 5-6.
doi: 10.3788/HPLPB20122401.0005
Abstract:
A 650 GHz watt-class backward wave oscillator has been proposed by using a sine waveguide slow-wave structure which possesses low loss and low reflection. In this letter, the three-dimensional particle-in-cell method is applied to predict the output performance of the backward wave oscillator. The investigation results show that, the backward wave oscillator can produce 1.55 W peak power output at 645.9 GHz under 20 kV operating voltage and 5 mA beam current. Its output mode is the TE10 mode. By tuning the operating voltage from 15 kV to 25 kV, the backward wave oscillator has over 1 W peak power output with a tuning bandwidth of 80 GHz.
A 650 GHz watt-class backward wave oscillator has been proposed by using a sine waveguide slow-wave structure which possesses low loss and low reflection. In this letter, the three-dimensional particle-in-cell method is applied to predict the output performance of the backward wave oscillator. The investigation results show that, the backward wave oscillator can produce 1.55 W peak power output at 645.9 GHz under 20 kV operating voltage and 5 mA beam current. Its output mode is the TE10 mode. By tuning the operating voltage from 15 kV to 25 kV, the backward wave oscillator has over 1 W peak power output with a tuning bandwidth of 80 GHz.
2012,
24: 7-9.
Abstract:
The design and realization of a terahertz(THz) radar system with 0.14 THz carrier frequency and 5 GHz bandwidth have been presented. The Ka band signal was frequency-doubled to be used as the local oscillator signal for sub-harmonic mixer in the systems transceiver chain. For the transmitted signal was a linearly frequency-modulated continuous-wave(LFM-CW), the dechirp technique was used in the THz radar receiver front end. By using this THz radar system, 3 cm high resolution range profiles were obtained as well as inverse synthetic aperture radar(ISAR) images, which exactly represent the subtle features of targets.
The design and realization of a terahertz(THz) radar system with 0.14 THz carrier frequency and 5 GHz bandwidth have been presented. The Ka band signal was frequency-doubled to be used as the local oscillator signal for sub-harmonic mixer in the systems transceiver chain. For the transmitted signal was a linearly frequency-modulated continuous-wave(LFM-CW), the dechirp technique was used in the THz radar receiver front end. By using this THz radar system, 3 cm high resolution range profiles were obtained as well as inverse synthetic aperture radar(ISAR) images, which exactly represent the subtle features of targets.
2012,
24: 10-15.
Abstract:
This is the first of a series of review papers on repetitive pulsed power technology. It gives general description about the technological characteristics such as high number of working-cycles, short time interval, and high average power. Typical applications in excimer laser, atmospheric gas discharge, and high-energy accelerator are introduced in order to highlight the significance of the technology. Repetitive pulsed power technology will be further developed mainly in the direction of short pulse and waveform control, while operation parameters of practical generators for specific applications will be pushed to the component limit. Future development of repetitive pulsed power and related technologies will bring more benefits into industrial and civil areas.
This is the first of a series of review papers on repetitive pulsed power technology. It gives general description about the technological characteristics such as high number of working-cycles, short time interval, and high average power. Typical applications in excimer laser, atmospheric gas discharge, and high-energy accelerator are introduced in order to highlight the significance of the technology. Repetitive pulsed power technology will be further developed mainly in the direction of short pulse and waveform control, while operation parameters of practical generators for specific applications will be pushed to the component limit. Future development of repetitive pulsed power and related technologies will bring more benefits into industrial and civil areas.
2012,
24: 16-23.
Abstract:
The paper reviews the worldwide research status and progress of dielectric window (DW) breakdown in vacuum under high power microwave (HPM). With respect to experimental studies, representative research results aboard are introduced, and the laws of breakdown development on the DW surface and inside the DW and the corresponding theoretical model are presented according to the results introduced combined with our research. With respect to theory and simulation studies, the progress aboard in understanding the mechanism of DW surface multipactor discharge under HPM is discussed, which is achieved with Monte Carlo and particle-in-cell simulations. Then along with our research, motion laws of DW surface electrons with diffe-rent emission angles and microwave electromagnetic parameters are introduced, and another theoretical model is proposed, which can essentially explain why the multipactor electron number and the surface electrostatic field oscillate at a frequency twice that of the HPM. Finally, several effective DW breakdown suppression technologies are summarized.
The paper reviews the worldwide research status and progress of dielectric window (DW) breakdown in vacuum under high power microwave (HPM). With respect to experimental studies, representative research results aboard are introduced, and the laws of breakdown development on the DW surface and inside the DW and the corresponding theoretical model are presented according to the results introduced combined with our research. With respect to theory and simulation studies, the progress aboard in understanding the mechanism of DW surface multipactor discharge under HPM is discussed, which is achieved with Monte Carlo and particle-in-cell simulations. Then along with our research, motion laws of DW surface electrons with diffe-rent emission angles and microwave electromagnetic parameters are introduced, and another theoretical model is proposed, which can essentially explain why the multipactor electron number and the surface electrostatic field oscillate at a frequency twice that of the HPM. Finally, several effective DW breakdown suppression technologies are summarized.
2012,
24: 24-28.
Abstract:
This work is devoted to the study of thermal-induced dephasing in mid-infrared continuous-wave singly resonant optical parametric oscillator(CW-SRO). The thermal-induced dephasing in crystal output section versus pump power and output coupling of signal is calculated. The simulation results indicate that the crystal thermal effect of CW-SRO with 3.3 m idler output is mainly affected by the absorption of the circulating signal power. Under the same input conditions, the CW-SROs thermal-induced dephasing with pump power above 30 W will greatly reduce the pump depletion. The thermal-induced dephasing will reduce with increasing the signal output coupling, while the threshold of CW-SRO will increase.
This work is devoted to the study of thermal-induced dephasing in mid-infrared continuous-wave singly resonant optical parametric oscillator(CW-SRO). The thermal-induced dephasing in crystal output section versus pump power and output coupling of signal is calculated. The simulation results indicate that the crystal thermal effect of CW-SRO with 3.3 m idler output is mainly affected by the absorption of the circulating signal power. Under the same input conditions, the CW-SROs thermal-induced dephasing with pump power above 30 W will greatly reduce the pump depletion. The thermal-induced dephasing will reduce with increasing the signal output coupling, while the threshold of CW-SRO will increase.
2012,
24: 29-33.
Abstract:
An optical pumping source by segmented surface discharge on Al2O3 ceramic substrate is developed to realize stable operation of XeF(C-A) laser with pulse repetition mode. The discharge jitter and the deviation of radiation intensity are investigated under gas-flow condition. Photographs of discharge plasma are obtained by high-speed camera, and the stability of discharge plasma is investigated. The experimental results show that the discharge jitter and stability of discharge plasma mainly depend on charging voltage and gas-flow rate, but less depend on pulse repetition rate in the range of 1 to 5 Hz. The deviation of radiation intensity correlates with charging voltage mainly and is hardly unaffected by pulse repetition rate and gas-flow rate. When the charging voltage is added to 26.8 kV, the stable discharge with discharge jitter less than 45 ns, the deviation of radiation intensity below 2%, and spatially stable discharge plasma can be obtained.
An optical pumping source by segmented surface discharge on Al2O3 ceramic substrate is developed to realize stable operation of XeF(C-A) laser with pulse repetition mode. The discharge jitter and the deviation of radiation intensity are investigated under gas-flow condition. Photographs of discharge plasma are obtained by high-speed camera, and the stability of discharge plasma is investigated. The experimental results show that the discharge jitter and stability of discharge plasma mainly depend on charging voltage and gas-flow rate, but less depend on pulse repetition rate in the range of 1 to 5 Hz. The deviation of radiation intensity correlates with charging voltage mainly and is hardly unaffected by pulse repetition rate and gas-flow rate. When the charging voltage is added to 26.8 kV, the stable discharge with discharge jitter less than 45 ns, the deviation of radiation intensity below 2%, and spatially stable discharge plasma can be obtained.
2012,
24: 33-38.
Abstract:
The paper studies the influence of frequency components on coherent combining efficiency by using frequency components with different central spectral lines and spectral widths. Experiment results show that closer central spectral lines lead to higher coherent combining efficiency; the coherent combining efficiency is higher when the spectral width is wider and the spectral shapes are similar, which can be close to the ideal value of 100%. The coherent combination of two Er-doped fiber lasers by using frequency components with the same central spectral line and width is achieved, of which the output power is 375 mW, and the coherent combining efficiency is as high as 99.3%.
The paper studies the influence of frequency components on coherent combining efficiency by using frequency components with different central spectral lines and spectral widths. Experiment results show that closer central spectral lines lead to higher coherent combining efficiency; the coherent combining efficiency is higher when the spectral width is wider and the spectral shapes are similar, which can be close to the ideal value of 100%. The coherent combination of two Er-doped fiber lasers by using frequency components with the same central spectral line and width is achieved, of which the output power is 375 mW, and the coherent combining efficiency is as high as 99.3%.
2012,
24: 39-42.
Abstract:
The refractive index structure constant (RISC) near the ground in Gobi region from April to December in 2010 was measured by using micro-thermal meter. The logarithmic average of measured data was calculated by the month, and then its daily variation characteristics were analyzed. Thus the times when the atmospheric turbulence was strong or weak in a day were given. In Gobi region, the atmospheric turbulence at sunset is weaker than at sunrise. At sunrise conversion time, the averaged RISC is below 10-15 m-2/3. At sunset conversion time, the averaged RISC is about 10-16 m-2/3. The atmospheric turbulence is stronger in April, June, August, and September, and weaker in November and December.
The refractive index structure constant (RISC) near the ground in Gobi region from April to December in 2010 was measured by using micro-thermal meter. The logarithmic average of measured data was calculated by the month, and then its daily variation characteristics were analyzed. Thus the times when the atmospheric turbulence was strong or weak in a day were given. In Gobi region, the atmospheric turbulence at sunset is weaker than at sunrise. At sunrise conversion time, the averaged RISC is below 10-15 m-2/3. At sunset conversion time, the averaged RISC is about 10-16 m-2/3. The atmospheric turbulence is stronger in April, June, August, and September, and weaker in November and December.
2012,
24: 43-46.
Abstract:
The paper studies the cooling system of a diode laser stack, and presents a phase transition cooling system using R134a as coolant and a heat sink based on throttle microchannel phase transition cooling. The packaging of the quasi-continuous wave (pulsed) 3 kW laser diode stack is finished. The influence of the temperature difference of coolant at inlet and outlet on the output wavelength of the stack is analyzed. Experimental results showthat the stack achieves a 3 030 W peak light-output power with a duty cycle of 20% at a current of 197 A. The wall plug efficiency is 39% and the vaporization rate of R134a in the cooler is 50%. The half width at full maximum of spectrum is smaller than 3.8 nm. The flow rate of the coolant R134a is 0.60 L/min, which is about 20% that of water. Therefore, the coolant flow becomes smaller and the volume of the thermal management unit diminishes significantly.
The paper studies the cooling system of a diode laser stack, and presents a phase transition cooling system using R134a as coolant and a heat sink based on throttle microchannel phase transition cooling. The packaging of the quasi-continuous wave (pulsed) 3 kW laser diode stack is finished. The influence of the temperature difference of coolant at inlet and outlet on the output wavelength of the stack is analyzed. Experimental results showthat the stack achieves a 3 030 W peak light-output power with a duty cycle of 20% at a current of 197 A. The wall plug efficiency is 39% and the vaporization rate of R134a in the cooler is 50%. The half width at full maximum of spectrum is smaller than 3.8 nm. The flow rate of the coolant R134a is 0.60 L/min, which is about 20% that of water. Therefore, the coolant flow becomes smaller and the volume of the thermal management unit diminishes significantly.
2012,
24: 47-50.
Abstract:
In order to improve the concentration efficiency and eliminate the optical aberration, the umbrella-shaped keel structure has been introduced into the deployable concentrator. The concentration performance of deployable solar paraboloid concentrator with concentration power of 100 kW working in the space environment has been investigated with the software ANSYS and ZEMAX. Under the influence of film tension and solar wind, the maximum stress of umbrella fabric is 1.66 MPa, which is much smaller than the threshold intensity of Kevlar and Ti-6Al-4V keel materials. The maximum deformation of umbrella fabric is 0.941 mm, the radius of the spot size is 6.37 cm, and the geometric concentration ratio can achieve 5 917, only 1.25% lower than the ratio of the standard parabolic concentrator. The results reveal that the influence of film tension and solar wind on the working shape of concentrator can be offset to a large extent by the introduction of the umbrella-shaped keel structure, which could eliminate wrinkles and enhance the deployability and stability of umbrella-shaped keel concentrator. The selected umbrella-shaped keel structure and Kevlar materials are proved to be appropriate.
In order to improve the concentration efficiency and eliminate the optical aberration, the umbrella-shaped keel structure has been introduced into the deployable concentrator. The concentration performance of deployable solar paraboloid concentrator with concentration power of 100 kW working in the space environment has been investigated with the software ANSYS and ZEMAX. Under the influence of film tension and solar wind, the maximum stress of umbrella fabric is 1.66 MPa, which is much smaller than the threshold intensity of Kevlar and Ti-6Al-4V keel materials. The maximum deformation of umbrella fabric is 0.941 mm, the radius of the spot size is 6.37 cm, and the geometric concentration ratio can achieve 5 917, only 1.25% lower than the ratio of the standard parabolic concentrator. The results reveal that the influence of film tension and solar wind on the working shape of concentrator can be offset to a large extent by the introduction of the umbrella-shaped keel structure, which could eliminate wrinkles and enhance the deployability and stability of umbrella-shaped keel concentrator. The selected umbrella-shaped keel structure and Kevlar materials are proved to be appropriate.
2012,
24: 51-55.
Abstract:
The test model of water jet cooled copper mirror was made and temperature measurement of the mirror was carried out. The temperature uniformity of the water jet cooled copper mirror was proved by the measurements of infrared camera and experimental results of thermocouples agree well with the results of numerical simulation, which verified the reliability of the numerical model. The deformation characteristics of the water jet cooled mirror and the linear-channel water cooled mirror were analyzed in the scenario of high power chemical lasers. The results show that the water jet cooled mirror can be well used in high power chemical lasers and the mirror must be processed under certain pressure. In addition,the diameter and number of cooling holes were further analyzed to explore their effects on the deformation of water jet cooled mirror in high power chemical lasers. More holes with larger diameter lead to better cooling effects.
The test model of water jet cooled copper mirror was made and temperature measurement of the mirror was carried out. The temperature uniformity of the water jet cooled copper mirror was proved by the measurements of infrared camera and experimental results of thermocouples agree well with the results of numerical simulation, which verified the reliability of the numerical model. The deformation characteristics of the water jet cooled mirror and the linear-channel water cooled mirror were analyzed in the scenario of high power chemical lasers. The results show that the water jet cooled mirror can be well used in high power chemical lasers and the mirror must be processed under certain pressure. In addition,the diameter and number of cooling holes were further analyzed to explore their effects on the deformation of water jet cooled mirror in high power chemical lasers. More holes with larger diameter lead to better cooling effects.
2012,
24: 56-60.
Abstract:
The propagation properties of (1+1) D Gaussian double light beams in strongly nonlocal nonlinear media with low losses are studied. By simplifying the nonlocal nonlinear Schrdinger equation which the light propagation in strongly nonlocal nonlinear media with low losses obeys, the propagation model of (1+1) D Gaussian double light beams in the media is obtained. With analysis method, the evolution laws of double light beams propagation are studied, the quasi double solitons solution is obtained. Further studies point out that the trajectories of the two light beams centers in propagation are Airy functions; the two light beams will collide and separate; with the increase of propagation distance, the maximal distance between the two light beams centers will become larger. When the losses increase, the collision spatial period will become smaller, and the maximal distance between the two light beams centers will become larger.
The propagation properties of (1+1) D Gaussian double light beams in strongly nonlocal nonlinear media with low losses are studied. By simplifying the nonlocal nonlinear Schrdinger equation which the light propagation in strongly nonlocal nonlinear media with low losses obeys, the propagation model of (1+1) D Gaussian double light beams in the media is obtained. With analysis method, the evolution laws of double light beams propagation are studied, the quasi double solitons solution is obtained. Further studies point out that the trajectories of the two light beams centers in propagation are Airy functions; the two light beams will collide and separate; with the increase of propagation distance, the maximal distance between the two light beams centers will become larger. When the losses increase, the collision spatial period will become smaller, and the maximal distance between the two light beams centers will become larger.
2012,
24: 61-64.
Abstract:
To study the forward-scattering effect on underwater laser imaging, a forward-scattering model of underwater laser imaging system based on radiative transfer theory was established. The forward-scattering influence coefficient was proposed, and the analytical expression of the coefficient and the forward-scattering power was given. The variation of the forward-scattering power and influence coefficient with exploration depth and water attenuation coefficient was attained using Matlab, which proved that the effect of asymmetry factor on underwater imaging quality was large.
To study the forward-scattering effect on underwater laser imaging, a forward-scattering model of underwater laser imaging system based on radiative transfer theory was established. The forward-scattering influence coefficient was proposed, and the analytical expression of the coefficient and the forward-scattering power was given. The variation of the forward-scattering power and influence coefficient with exploration depth and water attenuation coefficient was attained using Matlab, which proved that the effect of asymmetry factor on underwater imaging quality was large.
2012,
24: 65-68.
Abstract:
The effects of Kerr nonlinearity on Airy beams are investigated using the nonlinear Schrdinger equation. Based on the method of moments, the evolution of effective beam width is analytically obtained as well as the collapse power for Airy beams propagating in Kerr medium. Numerical simulations indicate that central parts of the major lobe of Airy beams give rise to initially radial compression during propagation even though the root-mean-square beam width broadens. Partial collapse of the central parts will appear for input power below the threshold for a global collapse. The field distributions of Airy beams are different during propagation in different media while the profiles and trajectories of the beams still remain invariant. In focused Kerr medium, the field of Airy beams is focused on center. In disfocused Kerr medium, it is dispersed.
The effects of Kerr nonlinearity on Airy beams are investigated using the nonlinear Schrdinger equation. Based on the method of moments, the evolution of effective beam width is analytically obtained as well as the collapse power for Airy beams propagating in Kerr medium. Numerical simulations indicate that central parts of the major lobe of Airy beams give rise to initially radial compression during propagation even though the root-mean-square beam width broadens. Partial collapse of the central parts will appear for input power below the threshold for a global collapse. The field distributions of Airy beams are different during propagation in different media while the profiles and trajectories of the beams still remain invariant. In focused Kerr medium, the field of Airy beams is focused on center. In disfocused Kerr medium, it is dispersed.
2012,
24: 69-74.
Abstract:
Conventional numerical methods of diffractive calculation are usually for the plane, and they are infeasible when the diffraction field applied in ICF is curved surface. In this paper, a method based on the idea of layering calculation, combining the algorithm of fast Fourier transform(FFT) with the technology of numerical fitting, has been proposed to calculate the light intensity distribution on the curved observation surface. This method can be applied to the surface with arbitrary shape, and it has comparatively high accuracy at fast calculation speed. The computation results show that the accuracy is improved as the layer number increases, and thus the method can effectively realize the light intensity distribution calculation of curved surface diffraction patterns applied in ICF.
Conventional numerical methods of diffractive calculation are usually for the plane, and they are infeasible when the diffraction field applied in ICF is curved surface. In this paper, a method based on the idea of layering calculation, combining the algorithm of fast Fourier transform(FFT) with the technology of numerical fitting, has been proposed to calculate the light intensity distribution on the curved observation surface. This method can be applied to the surface with arbitrary shape, and it has comparatively high accuracy at fast calculation speed. The computation results show that the accuracy is improved as the layer number increases, and thus the method can effectively realize the light intensity distribution calculation of curved surface diffraction patterns applied in ICF.
2012,
24: 76-78.
Abstract:
An approach based on sequential likelihood ratio test is presented to rapidly initiate track for dim moving target using the target amplitude acquired by the infrared tracking system. The two-dimensional dynamic assignment algorithm is adopted firstly to associate measurement with track, and the sequential likelihood ratio test is then taken to evaluate the quality of track. The target track is confirmed immediately once the likelihood ratio is greater than the threshold. This approach can take different scans to initiate target track according to the signal-to-noise ratio(SNR) of target, and the bigger the SNR of target is, the less frame it needs to achieve a given track detection probability. Some experiments are included and the results show that this approach can improve the speed of track initiation and enhance the detection probability of target track, without the limitation of the M/N logical method that the number of scans must be fixed to initiate target track with different SNRs.
An approach based on sequential likelihood ratio test is presented to rapidly initiate track for dim moving target using the target amplitude acquired by the infrared tracking system. The two-dimensional dynamic assignment algorithm is adopted firstly to associate measurement with track, and the sequential likelihood ratio test is then taken to evaluate the quality of track. The target track is confirmed immediately once the likelihood ratio is greater than the threshold. This approach can take different scans to initiate target track according to the signal-to-noise ratio(SNR) of target, and the bigger the SNR of target is, the less frame it needs to achieve a given track detection probability. Some experiments are included and the results show that this approach can improve the speed of track initiation and enhance the detection probability of target track, without the limitation of the M/N logical method that the number of scans must be fixed to initiate target track with different SNRs.
2012,
24: 79-83.
Abstract:
A digital holographic method is proposed to detect the surface quanlity of optic-components with spherical surface. It can obtain the surface curvature radius and defects simultaneously, and uses the least square parameter calculation to avoid the effects of tilt compensation. The defects are extracted by subtracting a simulated spherical surface generated by the calculated parameters from reconstruction data. Validity of the method is demonstrated by experiments. The difference is less than 1.5% between the results of the proposed method and white light interferometer, and less than 1% among the results obtained with different tilt compensation factors.
A digital holographic method is proposed to detect the surface quanlity of optic-components with spherical surface. It can obtain the surface curvature radius and defects simultaneously, and uses the least square parameter calculation to avoid the effects of tilt compensation. The defects are extracted by subtracting a simulated spherical surface generated by the calculated parameters from reconstruction data. Validity of the method is demonstrated by experiments. The difference is less than 1.5% between the results of the proposed method and white light interferometer, and less than 1% among the results obtained with different tilt compensation factors.
2012,
24: 84-88.
Abstract:
A good understanding of Z-pinch wire array ablation is of critical importance to the study of the dynamics of the wire array Z-pinch. To model the ablation process, a two-dimensional(2D) magnetohydrodynamics(MHD) program called FOI has been developed. The ablation is approximated in an adiabatic single-fluid single-phase MHD framework. Eulerian computation is adopted with a monotonic advection scheme. The numerical results obtained from FOI successfully qualitatively demonstrate the primary aspects of the ablation process, such as the core-corona structure, radial plasma streams, the formation of an on-axis precursor plasma column, longevity of the stationary wire cores and the extended ablation phase, though some discrepancies are observed.
A good understanding of Z-pinch wire array ablation is of critical importance to the study of the dynamics of the wire array Z-pinch. To model the ablation process, a two-dimensional(2D) magnetohydrodynamics(MHD) program called FOI has been developed. The ablation is approximated in an adiabatic single-fluid single-phase MHD framework. Eulerian computation is adopted with a monotonic advection scheme. The numerical results obtained from FOI successfully qualitatively demonstrate the primary aspects of the ablation process, such as the core-corona structure, radial plasma streams, the formation of an on-axis precursor plasma column, longevity of the stationary wire cores and the extended ablation phase, though some discrepancies are observed.
2012,
24: 89-92.
Abstract:
Poly-(-methylstyrene) (PAMS) microspheres were fabricated with W1/O/W2 double emulsion microencapsulation method,and the effects of polyvinylalcohol (PVA) and CaCl2 weight concentrations and the O/W2 phase ratio on the percentages of defected PAMS microspheres were studied. The weight concentrations of PVA and CaCl2 and the O/W2 phase ratio in the fabrication process of PAMS microspheres were optimized. The results show that, for the three parameters being 1.0%, 1.5%, and 0.01, respectively, the percentage of the defect-free PAMS microspheres without vacuoles in the shell wall can be up to 60%.
Poly-(-methylstyrene) (PAMS) microspheres were fabricated with W1/O/W2 double emulsion microencapsulation method,and the effects of polyvinylalcohol (PVA) and CaCl2 weight concentrations and the O/W2 phase ratio on the percentages of defected PAMS microspheres were studied. The weight concentrations of PVA and CaCl2 and the O/W2 phase ratio in the fabrication process of PAMS microspheres were optimized. The results show that, for the three parameters being 1.0%, 1.5%, and 0.01, respectively, the percentage of the defect-free PAMS microspheres without vacuoles in the shell wall can be up to 60%.
2012,
24: 93-96.
Abstract:
To study the effect of hohlraum gas on both laser-plasma interaction and implosion symmetry, the paper presents the design, material selection and fabrication of gas bag target, the filling gas technology and the implementation of the target on the Shenguang Ⅱ facility. The gas bag target is made by gluing two 400 nm thick polyimide films to a 400 m thick aluminum (Al) washer. The target is inflated with gas through a small filling tube mounted into the aluminum washer and the polyimide is stretched to a near-spherical shape.
To study the effect of hohlraum gas on both laser-plasma interaction and implosion symmetry, the paper presents the design, material selection and fabrication of gas bag target, the filling gas technology and the implementation of the target on the Shenguang Ⅱ facility. The gas bag target is made by gluing two 400 nm thick polyimide films to a 400 m thick aluminum (Al) washer. The target is inflated with gas through a small filling tube mounted into the aluminum washer and the polyimide is stretched to a near-spherical shape.
2012,
24: 97-99.
Abstract:
A new precision coupling technology of image plate and X-ray streak camera is developed to obtain the images of target in inertial confinement fusion experiments. Combining the characteristics of image plate and X-ray streak camera, one-dimensional dynamic image and two-dimensional static integral image of peripheral area of the cathode slit can be obtained at the same time, with precision coupling of an image plate in front of the slit. The technology can be used in the comparison of two-dimensional static and one-dimensional dynamic images. It can also be used in the precision positioning of image system. With this technology and Kirkpatrick-Baez microscope, implosion streamlines and Rayleigh-Taylor instability images have been acquired on Shenguang-Ⅱ laser facility.
A new precision coupling technology of image plate and X-ray streak camera is developed to obtain the images of target in inertial confinement fusion experiments. Combining the characteristics of image plate and X-ray streak camera, one-dimensional dynamic image and two-dimensional static integral image of peripheral area of the cathode slit can be obtained at the same time, with precision coupling of an image plate in front of the slit. The technology can be used in the comparison of two-dimensional static and one-dimensional dynamic images. It can also be used in the precision positioning of image system. With this technology and Kirkpatrick-Baez microscope, implosion streamlines and Rayleigh-Taylor instability images have been acquired on Shenguang-Ⅱ laser facility.
2012,
24: 100-104.
Abstract:
Ag2Al intermetallic compound nanoparticles were synthesized by the flow-levitation method. The morphologies, granularity and phase structure were investigated by transmission electron microscope, X-ray diffractometer, and energy dispersive spectrometer. The results indicate that the prepared nanoparticles are regular spheres, with the grain size ranging from 20 to 110 nm. The nanoparticles are mainly composed of Ag2Al, including a little Al. The data of chemistry elementary analysis indicate that the atomic ratio of Ag to Al in the nanoparticles is about 66.5∶33.5. The grain size of Ag2Al in the prepared nanoparticles is about 33 nm, and that of Al is about 21 nm.
Ag2Al intermetallic compound nanoparticles were synthesized by the flow-levitation method. The morphologies, granularity and phase structure were investigated by transmission electron microscope, X-ray diffractometer, and energy dispersive spectrometer. The results indicate that the prepared nanoparticles are regular spheres, with the grain size ranging from 20 to 110 nm. The nanoparticles are mainly composed of Ag2Al, including a little Al. The data of chemistry elementary analysis indicate that the atomic ratio of Ag to Al in the nanoparticles is about 66.5∶33.5. The grain size of Ag2Al in the prepared nanoparticles is about 33 nm, and that of Al is about 21 nm.
2012,
24: 105-109.
Abstract:
A kind of bismuth ball, i.e. a plastic ball coated with bismuth, has been designed to replace the conventional implosion target. The X-ray framing camera was utilized to obtain the 2D image of the reemission X-ray emitted by the bismuth ball driven by radiation. In the experiment, a branch of light was divided from the lasers, to yield the trigger signal of the camera by photoelectric conversion. The camera time scale was established by gold ball directly driven by the laser beams. According to the time scale, the time relationship of each frame of image relative to the laser beams is obtained. Analyzing the X-ray images of the bismuth ball, the ablation time of the CH film which was holding the bismuth ball and the variation of the bismuth sphere radius can be defined. The diagnostic holes size, and the symmetry of the supporting CH film can also be inferred by the X-ray images.
A kind of bismuth ball, i.e. a plastic ball coated with bismuth, has been designed to replace the conventional implosion target. The X-ray framing camera was utilized to obtain the 2D image of the reemission X-ray emitted by the bismuth ball driven by radiation. In the experiment, a branch of light was divided from the lasers, to yield the trigger signal of the camera by photoelectric conversion. The camera time scale was established by gold ball directly driven by the laser beams. According to the time scale, the time relationship of each frame of image relative to the laser beams is obtained. Analyzing the X-ray images of the bismuth ball, the ablation time of the CH film which was holding the bismuth ball and the variation of the bismuth sphere radius can be defined. The diagnostic holes size, and the symmetry of the supporting CH film can also be inferred by the X-ray images.
2012,
24: 110-114.
Abstract:
The paper studies Weibel instabilities in ultra intense laser-plasma interactions and its mechanism by using relativistic particle-in-cell method, and gives linear dispersion relations, saturated magnetic fields and anisotropy parameters of Weibel instabilities. It is found that the presence of Weibel instabilities in ultraintense laser-plasma interactions makes the self-generated magnetic field saturate, and then the saturated magnetic field causes the anisotropy of particle velocity distribution along the laser propagation direction. The linear and non-linear saturation processes of Weibel instabilities are also discussed. These results may be important for understanding the static magnetic field generation and fast electron propagation in the fast ignition physics.
The paper studies Weibel instabilities in ultra intense laser-plasma interactions and its mechanism by using relativistic particle-in-cell method, and gives linear dispersion relations, saturated magnetic fields and anisotropy parameters of Weibel instabilities. It is found that the presence of Weibel instabilities in ultraintense laser-plasma interactions makes the self-generated magnetic field saturate, and then the saturated magnetic field causes the anisotropy of particle velocity distribution along the laser propagation direction. The linear and non-linear saturation processes of Weibel instabilities are also discussed. These results may be important for understanding the static magnetic field generation and fast electron propagation in the fast ignition physics.
2012,
24: 115-118.
Abstract:
A multi-purpose microgripper for ICF targets has been developed based on the characteristic of ICF targets and target-assembly. The microgripper, whose fingers can be changed for different ICF targets, works with flexure hinge and piezoceramics actuator. The flexure hinges of the microgripper are designed and optimized based on the finite element analysis, and the best simulation results are presented. By measuring the strains of the different flexure hinges, the displacement and holding force of the microgripper can be detected independently and they are calibrated precisely. The displacement reaches 1 320 m and its detection resolution is 5 m. The holding force is 365.0 mN and its detection resolution is 1.3 mN.
A multi-purpose microgripper for ICF targets has been developed based on the characteristic of ICF targets and target-assembly. The microgripper, whose fingers can be changed for different ICF targets, works with flexure hinge and piezoceramics actuator. The flexure hinges of the microgripper are designed and optimized based on the finite element analysis, and the best simulation results are presented. By measuring the strains of the different flexure hinges, the displacement and holding force of the microgripper can be detected independently and they are calibrated precisely. The displacement reaches 1 320 m and its detection resolution is 5 m. The holding force is 365.0 mN and its detection resolution is 1.3 mN.
2012,
24: 119-122.
Abstract:
In ICF experiments, high dynamic range, high temporal and spatial resolution X-ray streak camera is a necessary diagnosis tool. To meet this requirement, a streak tube which uses bilamellar electrode lens and quadrupolar lens to focus electrons has been designed. This tube uses different ways to focus electrons in temporal axis and spatial axis. In temporal axis, it uses two bilamellar electrode lenses to focus electrons and in spatial axis it uses quadrupolar lens which can reduce image aberration effectively. The spatial resolution of this tube reaches 40 lp/mm even at the edge of photocathode, the temporal resolution is about 10 ps and the effective length of photocathode is 20 mm. Using different focusing ways in temporal and spatial directions, the tube will not focus electronsto a small spot, compared with conventional rotary and symmetric tubes, and thus its space charge effect is much weaker, and dynamic range is much larger.
In ICF experiments, high dynamic range, high temporal and spatial resolution X-ray streak camera is a necessary diagnosis tool. To meet this requirement, a streak tube which uses bilamellar electrode lens and quadrupolar lens to focus electrons has been designed. This tube uses different ways to focus electrons in temporal axis and spatial axis. In temporal axis, it uses two bilamellar electrode lenses to focus electrons and in spatial axis it uses quadrupolar lens which can reduce image aberration effectively. The spatial resolution of this tube reaches 40 lp/mm even at the edge of photocathode, the temporal resolution is about 10 ps and the effective length of photocathode is 20 mm. Using different focusing ways in temporal and spatial directions, the tube will not focus electronsto a small spot, compared with conventional rotary and symmetric tubes, and thus its space charge effect is much weaker, and dynamic range is much larger.
2012,
24: 123-128.
Abstract:
The interaction physics between energetic particle and plasma are introduced. The energy loss, range and pass-through time of energetic electron, proton, D, T or He in pure D plasma of 500 g/cm3 in density and 50 m in diameter at room temperature or 10 keV were calculated by Monte-Carlo method. The results show that, for electron, proton, D, T or He beam, the lowest beam intensity needed for edge(center) igniting is 363(458), 187(355), 13.1(24.8), 10.9(20.9) or 9.34(17.0) MA, respectively; the longest time for single particle to pass through plasma is 0.036(0.078), 0.219(0.569), 0.241(0.651), 0.320(0.854) or 0.228(0.592) ps, respectively. All the time above is below the fuel confinement time. Because of the Bragg peak of energy loss curve or higher energy loss, the end of particle range should be located in the heating zone to improve the heating efficiency and lower the bunch intensity needed for ignition. The lowest energy for ignition should be realized by increasing bunch intensity.
The interaction physics between energetic particle and plasma are introduced. The energy loss, range and pass-through time of energetic electron, proton, D, T or He in pure D plasma of 500 g/cm3 in density and 50 m in diameter at room temperature or 10 keV were calculated by Monte-Carlo method. The results show that, for electron, proton, D, T or He beam, the lowest beam intensity needed for edge(center) igniting is 363(458), 187(355), 13.1(24.8), 10.9(20.9) or 9.34(17.0) MA, respectively; the longest time for single particle to pass through plasma is 0.036(0.078), 0.219(0.569), 0.241(0.651), 0.320(0.854) or 0.228(0.592) ps, respectively. All the time above is below the fuel confinement time. Because of the Bragg peak of energy loss curve or higher energy loss, the end of particle range should be located in the heating zone to improve the heating efficiency and lower the bunch intensity needed for ignition. The lowest energy for ignition should be realized by increasing bunch intensity.
2012,
24: 129-132.
Abstract:
The paper presents the particle simulation of peer-to-peer locking for mutually coupled relativistic backward-wave oscillators(BWOs). In the simulation, a pair of relativistic BWOs with identical physical structures are driven by different accelerating voltages, which will work at different states with different oscillatory frequencies and output powers. The results indicate that, the relativistic BWOs connected in parallel with a special coupling slot will lock phase mutually. Their oscillatory frequencies are locked to a common frequency, and their energy conversion efficiencies are improved with an increase in the total output power of no less than 10%. Both their output powers become more stable.
The paper presents the particle simulation of peer-to-peer locking for mutually coupled relativistic backward-wave oscillators(BWOs). In the simulation, a pair of relativistic BWOs with identical physical structures are driven by different accelerating voltages, which will work at different states with different oscillatory frequencies and output powers. The results indicate that, the relativistic BWOs connected in parallel with a special coupling slot will lock phase mutually. Their oscillatory frequencies are locked to a common frequency, and their energy conversion efficiencies are improved with an increase in the total output power of no less than 10%. Both their output powers become more stable.
2012,
24: 133-138.
Abstract:
Based on the space-charge wave small signal theory, an electron conductance model of each gap in the multi-gap coupled cavity, a model for mode stability analysis, was presented. The formulas of each gaps electron conductance in a three-gap coupled cavity were derived as an example. Through the theoretical and simulative method, the beam-loading of different cavity electric field modes was studied, and the beam-wave interaction and mode stability in the coupled cavity were analyzed. The calculation and analysis show that the electron conductances in different cavity gaps and gap field modes are clearly distinct. Compared with the electron conductances in the first and second gaps, the electron conductance in the third gap greatly depends on the beam voltage and gap distance, and therefore it has a principal effect on the beam-wave interaction in the cavity gap and the mode stability. In addition, the model can be used in the beam-wave interaction simulation of extended interaction klystron.
Based on the space-charge wave small signal theory, an electron conductance model of each gap in the multi-gap coupled cavity, a model for mode stability analysis, was presented. The formulas of each gaps electron conductance in a three-gap coupled cavity were derived as an example. Through the theoretical and simulative method, the beam-loading of different cavity electric field modes was studied, and the beam-wave interaction and mode stability in the coupled cavity were analyzed. The calculation and analysis show that the electron conductances in different cavity gaps and gap field modes are clearly distinct. Compared with the electron conductances in the first and second gaps, the electron conductance in the third gap greatly depends on the beam voltage and gap distance, and therefore it has a principal effect on the beam-wave interaction in the cavity gap and the mode stability. In addition, the model can be used in the beam-wave interaction simulation of extended interaction klystron.
2012,
24: 139-141.
Abstract:
A rhombus-shaped microstrip meander-line slow-wave structure is proposed for use in a low voltage, wide bandwidth, moderate power and high efficiency millimeter-wave traveling-wave tube. The structure is evolved from the original V-shaped microstrip meander-line slow-wave structure. Compared with the conventional slow-wave structure, it is a kind of planar structure, whose fabrication can be easily realized by utilizing the technology of 2-D micro-fabrication. Whats more, the structure can realize beam-wave interaction with sheet electron beam, and no additional electron beam channel is needed. The electromagnetic characteristics and the interaction between the sheet electron beam and slow wave in the structure are obtained by utilizing the electromagnetic simulation software HFSS and the particle-in-cell code in CST Particle Studio, respectively. Our calculations indicate that, at a beam voltage of 7 kV and a beam current of 90 mA, the traveling wave tube based on the structure is capable of delivering several tens of watts output power with an interaction efficiency of 14.3％ and a transient 3 dB bandwidth of 18 GHz(ranging from 132 GHz to 150 GHz)
A rhombus-shaped microstrip meander-line slow-wave structure is proposed for use in a low voltage, wide bandwidth, moderate power and high efficiency millimeter-wave traveling-wave tube. The structure is evolved from the original V-shaped microstrip meander-line slow-wave structure. Compared with the conventional slow-wave structure, it is a kind of planar structure, whose fabrication can be easily realized by utilizing the technology of 2-D micro-fabrication. Whats more, the structure can realize beam-wave interaction with sheet electron beam, and no additional electron beam channel is needed. The electromagnetic characteristics and the interaction between the sheet electron beam and slow wave in the structure are obtained by utilizing the electromagnetic simulation software HFSS and the particle-in-cell code in CST Particle Studio, respectively. Our calculations indicate that, at a beam voltage of 7 kV and a beam current of 90 mA, the traveling wave tube based on the structure is capable of delivering several tens of watts output power with an interaction efficiency of 14.3％ and a transient 3 dB bandwidth of 18 GHz(ranging from 132 GHz to 150 GHz)
2012,
24: 142-146.
Abstract:
By means of changing the effective aperture of horn antenna, the experiment of air and SF6 microwave breakdown is carried out for L-band microwave with pulse duration being 30 ns. The microwave breakdown waveforms are derived, and the effect of air and SF6 breakdown on the transmission of high power microwave is analyzed. The experiment shows that, air breakdown mainly shortens the pulse width of high power microwave, while SF6 breakdown mainly reduces the peak power of high power microwave.
By means of changing the effective aperture of horn antenna, the experiment of air and SF6 microwave breakdown is carried out for L-band microwave with pulse duration being 30 ns. The microwave breakdown waveforms are derived, and the effect of air and SF6 breakdown on the transmission of high power microwave is analyzed. The experiment shows that, air breakdown mainly shortens the pulse width of high power microwave, while SF6 breakdown mainly reduces the peak power of high power microwave.
2012,
24: 147-151.
Abstract:
The effects of electromagnetic interference with increasing frequencies from 1 MHz to 20 GHz on CMOS inverter have been studied using our two dimensional mixed-level circuit and semiconductor device simulator. The simulation results show that the channel of MOS devices could be formed or cutoff deliberately by electromagnetic interference at the lower frequency range. As a result, the normal operation of CMOS inverter is disturbed. Electromagnetic interference at the higher frequency range could couple to the output through the small intrinsic capacitances in MOS devices to upset the operation of CMOS inverter. Moreover, electromagnetic interference at the lower frequency range causes greater upsets than that at the higher frequency range.
The effects of electromagnetic interference with increasing frequencies from 1 MHz to 20 GHz on CMOS inverter have been studied using our two dimensional mixed-level circuit and semiconductor device simulator. The simulation results show that the channel of MOS devices could be formed or cutoff deliberately by electromagnetic interference at the lower frequency range. As a result, the normal operation of CMOS inverter is disturbed. Electromagnetic interference at the higher frequency range could couple to the output through the small intrinsic capacitances in MOS devices to upset the operation of CMOS inverter. Moreover, electromagnetic interference at the lower frequency range causes greater upsets than that at the higher frequency range.
2012,
24: 152-156.
Abstract:
The gap impedance and the group delay time of the output cavity for a klystron loaded with a filter are deduced using the microwave transmission line theory and the equivalent circuit theory. A method that analyzes the gap impedance of the output cavity through its group delay time is proposed. Two typical examples of the output cavity at X band and Ku band are calculated by the software CST, and the calculated results are consistent with those evaluated by other methods. The proposed method is proved to be reasonable, with more simple calculation and more explicit outcome based on the powerful post-processing capability of the calculation software.
The gap impedance and the group delay time of the output cavity for a klystron loaded with a filter are deduced using the microwave transmission line theory and the equivalent circuit theory. A method that analyzes the gap impedance of the output cavity through its group delay time is proposed. Two typical examples of the output cavity at X band and Ku band are calculated by the software CST, and the calculated results are consistent with those evaluated by other methods. The proposed method is proved to be reasonable, with more simple calculation and more explicit outcome based on the powerful post-processing capability of the calculation software.
2012,
24: 157-161.
Abstract:
This paper presents the experimental results of a 95 GHz quasi-optical mode converter. The test system is a near-field scanning system based on millimeter wave antenna. The mode converter includes a Vlasov launcher, a quasi-elliptical mirror and two phase correcting mirrors. It converts the TE62 mode in a circular waveguide of 5.62 mm radiusinto a Gaussian mode of 22.4 mm waist. The scalar correlation coefficient is 97.43%, and the vector correlation coefficient is 88.65%.
This paper presents the experimental results of a 95 GHz quasi-optical mode converter. The test system is a near-field scanning system based on millimeter wave antenna. The mode converter includes a Vlasov launcher, a quasi-elliptical mirror and two phase correcting mirrors. It converts the TE62 mode in a circular waveguide of 5.62 mm radiusinto a Gaussian mode of 22.4 mm waist. The scalar correlation coefficient is 97.43%, and the vector correlation coefficient is 88.65%.
2012,
24: 162-166.
Abstract:
The development and experiment of a small bounded wave simulator are introduced, including the development of the double exponential repetitive frequency pulse source based on the hydrogen thyratron inductive-adder, the design of output coaxial shielding structure, the calculation of the field distribution of the output transformer, the development of the small flat-plate radiator, and the calculation and simulation about the working space E-field of the radiator. The preliminary measurement results of the working space E-field of the radiator are also presented. The experiment results show that the E-field in the working space of the radiator space accords with the linear superposition principle, even if there are differences between the parameters of thyratrons and between the parameters of grid trigger clocks.
The development and experiment of a small bounded wave simulator are introduced, including the development of the double exponential repetitive frequency pulse source based on the hydrogen thyratron inductive-adder, the design of output coaxial shielding structure, the calculation of the field distribution of the output transformer, the development of the small flat-plate radiator, and the calculation and simulation about the working space E-field of the radiator. The preliminary measurement results of the working space E-field of the radiator are also presented. The experiment results show that the E-field in the working space of the radiator space accords with the linear superposition principle, even if there are differences between the parameters of thyratrons and between the parameters of grid trigger clocks.
2012,
24: 167-170.
Abstract:
The paper presents a compact ultra-wideband coplanar-waveguide-fed monopole antenna with dual band-notched function. Two types of simple slots, L-shaped and semicircular, are cut in the radiating patch to realize the dual band-notched function in the frequency ranges of3.3 to 3.7 GHz for world interoperability for microwave access(WiMAX) applications and 5.150 to 5.825 GHz for wireless local area network(WLAN) applications. Experimental results show that the voltage standing wave ratio (VSWR) in the working band of 3 to 14 GHz is less than 2 except in the two band notches (VSWR more than 4). The proposed antenna has an almost omnidirectional radiation pattern and a good stable gain over the whole working band except the two band notches. The antenna has a small size and can be easily processed, which can greatly simplify the circuit design of a communication system.
The paper presents a compact ultra-wideband coplanar-waveguide-fed monopole antenna with dual band-notched function. Two types of simple slots, L-shaped and semicircular, are cut in the radiating patch to realize the dual band-notched function in the frequency ranges of3.3 to 3.7 GHz for world interoperability for microwave access(WiMAX) applications and 5.150 to 5.825 GHz for wireless local area network(WLAN) applications. Experimental results show that the voltage standing wave ratio (VSWR) in the working band of 3 to 14 GHz is less than 2 except in the two band notches (VSWR more than 4). The proposed antenna has an almost omnidirectional radiation pattern and a good stable gain over the whole working band except the two band notches. The antenna has a small size and can be easily processed, which can greatly simplify the circuit design of a communication system.
2012,
24: 171-174.
Abstract:
This paper studies the smooth cusp magnetic field for an axis-encircling large-orbit electron gun, which is realized by three different coils. Theoretical analysis and computer simulation of the field distribution agree well with each other. The Lagrangian for the electron is used to deduce the electrons equations of motion. The trajectories of electrons are then numerically calculated with the equations and the result is consistent with that of the three-dimensional particle-in-cell simulation. Through optimization of the ampere turns of the three coils, the velocity ratio from 1.4 to 2.5 and the axial velocity spread below 8% (at the velocity ratio equal to 1.9) are obtained with a 40 kV, 1 A electron beam.
This paper studies the smooth cusp magnetic field for an axis-encircling large-orbit electron gun, which is realized by three different coils. Theoretical analysis and computer simulation of the field distribution agree well with each other. The Lagrangian for the electron is used to deduce the electrons equations of motion. The trajectories of electrons are then numerically calculated with the equations and the result is consistent with that of the three-dimensional particle-in-cell simulation. Through optimization of the ampere turns of the three coils, the velocity ratio from 1.4 to 2.5 and the axial velocity spread below 8% (at the velocity ratio equal to 1.9) are obtained with a 40 kV, 1 A electron beam.
2012,
24: 175-180.
Abstract:
The physical model is established according to the characteristics of coaxial relativistic backward wave oscillator(CRBWO) to study the wave-beam interaction in CRBWO employing the finite-difference time-domain method. The research indicates that the output efficiency of the wave-beam interaction in CRBWO is sensitively dependent on the reflections on both ends of the wave-beam interaction region. And the distribution of the field in CRBWO is beneficial for the promotion of the output efficiency. In the case of electron beam of 500 keV and 4.0 kA, the calculated output efficiency more than 38% through optimizing and the starting time 7 ns agree with those obtained from previous numerical simulation and experiment results very well. The space charge effect can be considered as a small influence on the wave-beam interaction in CRBWO compared with that in hollow relativistic backward wave oscillator.
The physical model is established according to the characteristics of coaxial relativistic backward wave oscillator(CRBWO) to study the wave-beam interaction in CRBWO employing the finite-difference time-domain method. The research indicates that the output efficiency of the wave-beam interaction in CRBWO is sensitively dependent on the reflections on both ends of the wave-beam interaction region. And the distribution of the field in CRBWO is beneficial for the promotion of the output efficiency. In the case of electron beam of 500 keV and 4.0 kA, the calculated output efficiency more than 38% through optimizing and the starting time 7 ns agree with those obtained from previous numerical simulation and experiment results very well. The space charge effect can be considered as a small influence on the wave-beam interaction in CRBWO compared with that in hollow relativistic backward wave oscillator.
2012,
24: 181-183.
Abstract:
A C-band 2 MeV standing wave accelerator is under development for engineering research on accelerator miniatu-rization. At present, significant progress has been achieved. The accelerating tube has been fully sealed, and the hot test platform for the accelerator has been built. At the repetition rate of 50 Hz, preliminary power test has been performed. It used the ionization chamber dose monitor to test the dose rate of X-rays at 1 m before the target, and the steel absorption method to test the energy of the electron beam. The preliminary test results show that, the beam energy is about 2.5 MeV, and the dose rate can be over 330 mGy/(minm).
A C-band 2 MeV standing wave accelerator is under development for engineering research on accelerator miniatu-rization. At present, significant progress has been achieved. The accelerating tube has been fully sealed, and the hot test platform for the accelerator has been built. At the repetition rate of 50 Hz, preliminary power test has been performed. It used the ionization chamber dose monitor to test the dose rate of X-rays at 1 m before the target, and the steel absorption method to test the energy of the electron beam. The preliminary test results show that, the beam energy is about 2.5 MeV, and the dose rate can be over 330 mGy/(minm).
2012,
24: 184-188.
Abstract:
A two-ring ferrite test system for ferrite-loaded cavities of rapid cycling synchrotron(RCS) of China spallation neutron source(CSNS) has been developed. The measurement of ferrite ring provides very important information for designing the cavities and the whole RF system. Even more, all the ferrite rings used in the RCS will be sorted based on the measurements with the test system. The cavity structure in the test system ensures the measurement reliability and repeatability with good field uniformity. A control system including LLRF control, bias current control and data acquisition has also been developed for increasing the efficiency of the test system, and it is also necessary for measurements in the frequency-sweeping mode. The preliminary cold-mode test and high-power test results in the static state are presented.
A two-ring ferrite test system for ferrite-loaded cavities of rapid cycling synchrotron(RCS) of China spallation neutron source(CSNS) has been developed. The measurement of ferrite ring provides very important information for designing the cavities and the whole RF system. Even more, all the ferrite rings used in the RCS will be sorted based on the measurements with the test system. The cavity structure in the test system ensures the measurement reliability and repeatability with good field uniformity. A control system including LLRF control, bias current control and data acquisition has also been developed for increasing the efficiency of the test system, and it is also necessary for measurements in the frequency-sweeping mode. The preliminary cold-mode test and high-power test results in the static state are presented.
2012,
24: 189-192.
Abstract:
The output signal of beam position monitor (BPM) carries not only position information but also charge information. It can reflect the changes of the beam charge and be used for beam lifetime measurement. In this paper, the feasibility of beam lifetime measurement using BPM was investigated through theoretical analysis. Some experiments were conducted on the storage ring of Shanghai Synchrotron Radiation Facility(SSRF) to evaluate the performance. Compared with the DC current transformer(DCCT) system, the lifetime measured by BPM has higher data rate and resolution. It is useful for the beam lifetime evaluation of different time scales and the measurement accuracy can be further improved by averaging the results of multiple BPMs.
The output signal of beam position monitor (BPM) carries not only position information but also charge information. It can reflect the changes of the beam charge and be used for beam lifetime measurement. In this paper, the feasibility of beam lifetime measurement using BPM was investigated through theoretical analysis. Some experiments were conducted on the storage ring of Shanghai Synchrotron Radiation Facility(SSRF) to evaluate the performance. Compared with the DC current transformer(DCCT) system, the lifetime measured by BPM has higher data rate and resolution. It is useful for the beam lifetime evaluation of different time scales and the measurement accuracy can be further improved by averaging the results of multiple BPMs.
2012,
24: 193-196.
Abstract:
The paper investigates the layout optimization for flash radiography with scatter using CCD to improve the imaging quality. The best layout is gained with the best factor of merit. The best magnification of the radiography system is 2 with the experimentally measured blur and Gaussian style assumption. The distance from the object to back windows is 50 cm. The best system length is related to the noise, and more noise leads to shorter system. The range of the best length is 3 to 5 m. The test has verified the above results.
The paper investigates the layout optimization for flash radiography with scatter using CCD to improve the imaging quality. The best layout is gained with the best factor of merit. The best magnification of the radiography system is 2 with the experimentally measured blur and Gaussian style assumption. The distance from the object to back windows is 50 cm. The best system length is related to the noise, and more noise leads to shorter system. The range of the best length is 3 to 5 m. The test has verified the above results.
2012,
24: 197-201.
Abstract:
To obtain the micro-pulse bunch with the order of hundred femtoseconds length and high repetition rate, the paper proposes the independently tunable cells (ITC) RF gun, which has a double-cell structure with the cells being power fed independently. By choosing appropriate feeding power and phase of the two cells, this ITC-RF gun can achieve bunches of excellent characteristics. Additionally, the application of -magnet and laser system can be avoided, which leads to more compact layout. An external injecting ITC-RF gun (DC-ITC-RF gun) structure is designed accordingly. The external injecting structure can increase beam current, decrease energy spread, and cancel the back-bombardment effect almost completely. By means of 1-D and 3-D beam dynamics calculation with different structure parameters, a group of RF parameters are obtained for better beam characteristics. Then the paper designs a pre-injector so that particles can be accelerated to 10 MeV. By choosing appropriate feeding power and incident particle phase for the pre-injector, the bunch length can be further compressed.
To obtain the micro-pulse bunch with the order of hundred femtoseconds length and high repetition rate, the paper proposes the independently tunable cells (ITC) RF gun, which has a double-cell structure with the cells being power fed independently. By choosing appropriate feeding power and phase of the two cells, this ITC-RF gun can achieve bunches of excellent characteristics. Additionally, the application of -magnet and laser system can be avoided, which leads to more compact layout. An external injecting ITC-RF gun (DC-ITC-RF gun) structure is designed accordingly. The external injecting structure can increase beam current, decrease energy spread, and cancel the back-bombardment effect almost completely. By means of 1-D and 3-D beam dynamics calculation with different structure parameters, a group of RF parameters are obtained for better beam characteristics. Then the paper designs a pre-injector so that particles can be accelerated to 10 MeV. By choosing appropriate feeding power and incident particle phase for the pre-injector, the bunch length can be further compressed.
2012,
24: 202-206.
Abstract:
A GEANT4 based Monte-Carlo simulation on collimation processes of single-particle microbeam at Fudan University by capillary collimator was performed with regard to the incident beam parameters, including the divergent angle of incident beam, the incident beam energy, the misalignment angle of beam collimation and the length of collimator. As a result,a proton beam with 2.2 MeV peak energy and 130 keV FWHM which was 2.4 m in radius, was acquired by the collimator which was 1 m in diameter,and 1 mm in length, meeting the requirements of design. The simulation shows the possibility of acquiring microbeams in micron scale, and reveals the relationship of system design parameters and incident beam parameters with capillary-based microbeam, which determines the quality of microbeam and as it irradiates the cells.
A GEANT4 based Monte-Carlo simulation on collimation processes of single-particle microbeam at Fudan University by capillary collimator was performed with regard to the incident beam parameters, including the divergent angle of incident beam, the incident beam energy, the misalignment angle of beam collimation and the length of collimator. As a result,a proton beam with 2.2 MeV peak energy and 130 keV FWHM which was 2.4 m in radius, was acquired by the collimator which was 1 m in diameter,and 1 mm in length, meeting the requirements of design. The simulation shows the possibility of acquiring microbeams in micron scale, and reveals the relationship of system design parameters and incident beam parameters with capillary-based microbeam, which determines the quality of microbeam and as it irradiates the cells.
2012,
24: 207-209.
Abstract:
Diamond-like carbon(DLC) films were deposited by un-balanced magnetron sputtering(UBMS) technology and a comparison of their damage morphologies with and without external electric field was then made. With the applied electric field, a large amount of filiform films appeared and the damaged area decreased as well. Thus the external electric field influences the damage morphology of DLC films. Under the influence of the electric field, the photoelectrons excited by laser in the films will perform a speedy movement, which indirectly reduces the energy density in some parts of the laser-irradiated area and slows down the graphitizing process of the films. As a result, the films are more difficult to be damaged by laser.
Diamond-like carbon(DLC) films were deposited by un-balanced magnetron sputtering(UBMS) technology and a comparison of their damage morphologies with and without external electric field was then made. With the applied electric field, a large amount of filiform films appeared and the damaged area decreased as well. Thus the external electric field influences the damage morphology of DLC films. Under the influence of the electric field, the photoelectrons excited by laser in the films will perform a speedy movement, which indirectly reduces the energy density in some parts of the laser-irradiated area and slows down the graphitizing process of the films. As a result, the films are more difficult to be damaged by laser.
2012,
24: 210-214.
Abstract:
Studying on sensitivity of detector has most guiding significance for the selecting of X-ray Energy, the designing of detector and matching between X-ray source and detector. Several major factors of sensitivity and their quantitative relation were studied. First, factors such as energy deposition rate, absolute scintillation efficiency, light collection efficiency and photoelectrical conversion efficiency were analyzed. Then, a simulation for energy deposition rate of scintillation crystal and light collection efficiency was carried out by Monte Carlo method. The fluorescence conversion efficiency of the CsI(Tl) scintillator and the photoelectric conversion efficiency of the photoelectric diode were computed. The concept of matching between the scintillator and the photoelectric diode was defined. Finally, the sensitivity expression with universal meaning of the detector was obtained. The maximum error between theoretical value and practical measurement result is less than 20.4%. The experiments show the validity and the accuracy of the computing method of the sensitivity.
Studying on sensitivity of detector has most guiding significance for the selecting of X-ray Energy, the designing of detector and matching between X-ray source and detector. Several major factors of sensitivity and their quantitative relation were studied. First, factors such as energy deposition rate, absolute scintillation efficiency, light collection efficiency and photoelectrical conversion efficiency were analyzed. Then, a simulation for energy deposition rate of scintillation crystal and light collection efficiency was carried out by Monte Carlo method. The fluorescence conversion efficiency of the CsI(Tl) scintillator and the photoelectric conversion efficiency of the photoelectric diode were computed. The concept of matching between the scintillator and the photoelectric diode was defined. Finally, the sensitivity expression with universal meaning of the detector was obtained. The maximum error between theoretical value and practical measurement result is less than 20.4%. The experiments show the validity and the accuracy of the computing method of the sensitivity.
2012,
24: 215-219.
Abstract:
The principle of 252Cf-source-driven power spectrum density measurement method is introduced. A measurement system and platform is realized accordingly, which is a combination of hardware and software, for measuring nuclear parameters. The detection method of neutron pulses based on an ultra-high-speed data acquisition card (three channels, 1 GHz sampling rate, 1 ns synchronization) is described, and the data processing process and the power spectrum density algorithm on PC are designed. This 252Cf-source-driven power spectrum density measurement system can effectively obtain the nuclear tag parameters of nuclear random processes, such as correlation function and power spectrum density.
The principle of 252Cf-source-driven power spectrum density measurement method is introduced. A measurement system and platform is realized accordingly, which is a combination of hardware and software, for measuring nuclear parameters. The detection method of neutron pulses based on an ultra-high-speed data acquisition card (three channels, 1 GHz sampling rate, 1 ns synchronization) is described, and the data processing process and the power spectrum density algorithm on PC are designed. This 252Cf-source-driven power spectrum density measurement system can effectively obtain the nuclear tag parameters of nuclear random processes, such as correlation function and power spectrum density.
2012,
24: 220-224.
Abstract:
The dispersive negative index metamaterial possesses a negative refractive index in the microwave region(1 to 10 GHz), whose effective permittivity and permeability determine different refractive indexes in different frequency regions. The dispersive negative index metamaterial is introduced into one-dimensional photonic crystal to form two structures: positive index media photonic crystal with negative index metamaterial defect, and positive and negative index media photonic crystal with positive index medium defect. By numerical simulation, transmission spectra are shown for the two structures under homogeneous plane electromagnetic wave (TE wave) normal incidence and oblique incidence, in which single- and dual-defect modes appear in different forbidden bands when both effective permittivity and permeability are negative. These defect modes can be used to realize single- and dual-channel filtering, respectively.
The dispersive negative index metamaterial possesses a negative refractive index in the microwave region(1 to 10 GHz), whose effective permittivity and permeability determine different refractive indexes in different frequency regions. The dispersive negative index metamaterial is introduced into one-dimensional photonic crystal to form two structures: positive index media photonic crystal with negative index metamaterial defect, and positive and negative index media photonic crystal with positive index medium defect. By numerical simulation, transmission spectra are shown for the two structures under homogeneous plane electromagnetic wave (TE wave) normal incidence and oblique incidence, in which single- and dual-defect modes appear in different forbidden bands when both effective permittivity and permeability are negative. These defect modes can be used to realize single- and dual-channel filtering, respectively.
2012,
24: 225-228.
Abstract:
The Lagrangian formula is used to analyze the velocity spread and beam ripple of electrons in smooth cusp magnetic field. The characteristics of the cusp electron gun including cusp magnets are calculated by co-simulation employing softwares Matlab and Magic. A Matlab code is written to simulate the motion of single electron in a given electric field, and a given magnetic field, which shows the relationship between the electrons radial velocity and velocity spread. The cusp magnetic field optimized accordingly can reduce the radial velocity at the anode region, which is the key to achieve small beam velocity spread. When the cusp electron gun is designed to generate a 1 A, 30 keV beam, an optimized velocity spread less than 2.5% can be obtained with an axial velocity spread less than 8.5% and a velocity ratio about 2.
The Lagrangian formula is used to analyze the velocity spread and beam ripple of electrons in smooth cusp magnetic field. The characteristics of the cusp electron gun including cusp magnets are calculated by co-simulation employing softwares Matlab and Magic. A Matlab code is written to simulate the motion of single electron in a given electric field, and a given magnetic field, which shows the relationship between the electrons radial velocity and velocity spread. The cusp magnetic field optimized accordingly can reduce the radial velocity at the anode region, which is the key to achieve small beam velocity spread. When the cusp electron gun is designed to generate a 1 A, 30 keV beam, an optimized velocity spread less than 2.5% can be obtained with an axial velocity spread less than 8.5% and a velocity ratio about 2.
2012,
24: 229-233.
Abstract:
Ni-Nd-B samples were prepared by arc-type melt-spinning/suction casting techniques, and then were analyzed by X-ray diffraction, scanning electron microscopy and differential thermal analyses and with static magnetic tester. The results show that 6 mm-diameter bulk amorphous samples have been prepared, which conform with the depth eutectic theory and show relatively ideal glass forming ability. The undercooling temperatures of Ni4NdB and Ni13Nd3B2 are 79.13 ℃ and 69.37 ℃, respectively. The trace changes of Ni, Nd compositions cause evident crystallization of materials, and they also lead to the decrease in material coercivity and saturation magnetization.
Ni-Nd-B samples were prepared by arc-type melt-spinning/suction casting techniques, and then were analyzed by X-ray diffraction, scanning electron microscopy and differential thermal analyses and with static magnetic tester. The results show that 6 mm-diameter bulk amorphous samples have been prepared, which conform with the depth eutectic theory and show relatively ideal glass forming ability. The undercooling temperatures of Ni4NdB and Ni13Nd3B2 are 79.13 ℃ and 69.37 ℃, respectively. The trace changes of Ni, Nd compositions cause evident crystallization of materials, and they also lead to the decrease in material coercivity and saturation magnetization.
2012,
24: 234-238.
Abstract:
The time-integrated two-dimensional distribution of aluminum wire array Z-pinch plasma K-shell radiation which is characterized by Ly line was measured in a 1.3 MA generator, with spherically bent mica crystal in a specific layout of appropriate design parameters. The employment of spherically bent crystal instead of filter can realize accurate setting of measurement energy region and thus effectively improve the measurement accuracy of K-shell radiation distribution. The results presentedprovide more accurate calibration parameters for the radiation transport codes of Z-pinch plasma.
The time-integrated two-dimensional distribution of aluminum wire array Z-pinch plasma K-shell radiation which is characterized by Ly line was measured in a 1.3 MA generator, with spherically bent mica crystal in a specific layout of appropriate design parameters. The employment of spherically bent crystal instead of filter can realize accurate setting of measurement energy region and thus effectively improve the measurement accuracy of K-shell radiation distribution. The results presentedprovide more accurate calibration parameters for the radiation transport codes of Z-pinch plasma.
2012,
24: 239-242.
Abstract:
A resistor divider has been designed for voltage measurement of diode load for 1 MV/100 kA fast linear transformer driver(LTD). The divider is designed with two stages. The primary stage is a column of alternating annular metal grading rings and tapered insulators enclosing a resistive solution of sodium thiosulfate. A middle electrode is connected to the secondary voltage dividing stage. There is a 4 k resistor in series with the 50 input impedance of the attenuator or oscilloscope. The equivalent circuit of the divider which includes distributed capacitance and inductance has been calculated. It indicates that the high frequency limit of the divider is about 200 MHz. The divider has been calibrated in-situ using a P6015A probe and a high voltage pulser. The calibration ratio is 5 400∶1. The voltage of diode load reaches 1.08 MV when the charging voltage of LTD stage is 85 kV respectively, according with the simulation of LTD.
A resistor divider has been designed for voltage measurement of diode load for 1 MV/100 kA fast linear transformer driver(LTD). The divider is designed with two stages. The primary stage is a column of alternating annular metal grading rings and tapered insulators enclosing a resistive solution of sodium thiosulfate. A middle electrode is connected to the secondary voltage dividing stage. There is a 4 k resistor in series with the 50 input impedance of the attenuator or oscilloscope. The equivalent circuit of the divider which includes distributed capacitance and inductance has been calculated. It indicates that the high frequency limit of the divider is about 200 MHz. The divider has been calibrated in-situ using a P6015A probe and a high voltage pulser. The calibration ratio is 5 400∶1. The voltage of diode load reaches 1.08 MV when the charging voltage of LTD stage is 85 kV respectively, according with the simulation of LTD.
2012,
24: 243-247.
Abstract:
To keep good interfacial contact between the sliding armature and the two electrodes of electromagnetic rail thruster, the electrode spacing should fluctuate within an allowable range under the impulse force generated by pulse current. A transient coupled model of the electrodes and their bracing structures is built by time-varying field theory and transient dynamics equation. The distributions of parameters of transient electromagnetic field are analyzed, and the dynamic response parameters of the electrodes and their bracing structures are obtained. The simulated results show that the epoxy bracing structures have good cushioning capacity to resist the impulse force generated by pulse current; the bracing material with low elastic modulus is more easily vibrated at the rising and peak phases of pulse current, and the vibrated deformation has little effect on the electrode spacing.
To keep good interfacial contact between the sliding armature and the two electrodes of electromagnetic rail thruster, the electrode spacing should fluctuate within an allowable range under the impulse force generated by pulse current. A transient coupled model of the electrodes and their bracing structures is built by time-varying field theory and transient dynamics equation. The distributions of parameters of transient electromagnetic field are analyzed, and the dynamic response parameters of the electrodes and their bracing structures are obtained. The simulated results show that the epoxy bracing structures have good cushioning capacity to resist the impulse force generated by pulse current; the bracing material with low elastic modulus is more easily vibrated at the rising and peak phases of pulse current, and the vibrated deformation has little effect on the electrode spacing.
2012,
24: 248-252.
Abstract:
The work studies the evolution characteristics of the plasma channel in high power pulsed xenonflashlamps. Various influence factors are analyzed, including the charging voltage, the main pulse width, and the time interval between the pre-ionization pulse and the main pulse. Distinct branching phenomena are observed near the grounding terminal of the flashlamps. It is found that the electric field distribution in the flashlamps working environment has the most significant influence on the evolution process of the plasma channel. Moreover, the electric field distribution determines the shape of the plasma channel, while other factors influence its brightness and uniformity.
The work studies the evolution characteristics of the plasma channel in high power pulsed xenonflashlamps. Various influence factors are analyzed, including the charging voltage, the main pulse width, and the time interval between the pre-ionization pulse and the main pulse. Distinct branching phenomena are observed near the grounding terminal of the flashlamps. It is found that the electric field distribution in the flashlamps working environment has the most significant influence on the evolution process of the plasma channel. Moreover, the electric field distribution determines the shape of the plasma channel, while other factors influence its brightness and uniformity.
