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RSS2012 Vol. 24, No. 08
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2012,
24: 1765-1769.
doi: 10.3788/HPLPB20122408.1765
Abstract:
The electromagnetic solitons generated by laser-plasma interaction is one of the main non-linear phenomena in plasmas. The paper introduces the investigation on the electromagnetic solitons in plasmas and some important numerical simulation results. The experimental evolution recently for the electromagnetic solitons study at the Rutherford Appleton Laboratory is expatiated. The history and development about the study of electromagnetic solitons in plasma are reviewed and summarized.
The electromagnetic solitons generated by laser-plasma interaction is one of the main non-linear phenomena in plasmas. The paper introduces the investigation on the electromagnetic solitons in plasmas and some important numerical simulation results. The experimental evolution recently for the electromagnetic solitons study at the Rutherford Appleton Laboratory is expatiated. The history and development about the study of electromagnetic solitons in plasma are reviewed and summarized.
2012,
24: 1770-1774.
doi: 10.3788/HPLPB20122408.1770
Abstract:
A 2.5 keV multilayer Kirkpatrick-Baez microscope was developed and its imaging characteristics were studied from aspects of optical design and experimental calibration. The optical parameters were determined by analyzing the influences of grazing incidence angle, magnification, and radius of curvature on modulation transfer function(MTF). The multilayer, simultaneously working at 2.5 keV and 8 keV, was designed and coated to complete the system alignment. The imaging result at ShenguangⅡ laser facility shows that the MTF over the object field of 100 m is above 0.6 for 20 m wavelength, significantly better than those of the existing pinhole camera and point-projection X-ray radiography. The microscope, coupled with the streak camera, can be used for dynamic diagnostics of target ablation with small spatial perturbation mode.
A 2.5 keV multilayer Kirkpatrick-Baez microscope was developed and its imaging characteristics were studied from aspects of optical design and experimental calibration. The optical parameters were determined by analyzing the influences of grazing incidence angle, magnification, and radius of curvature on modulation transfer function(MTF). The multilayer, simultaneously working at 2.5 keV and 8 keV, was designed and coated to complete the system alignment. The imaging result at ShenguangⅡ laser facility shows that the MTF over the object field of 100 m is above 0.6 for 20 m wavelength, significantly better than those of the existing pinhole camera and point-projection X-ray radiography. The microscope, coupled with the streak camera, can be used for dynamic diagnostics of target ablation with small spatial perturbation mode.
2012,
24: 1775-1779.
doi: 10.3788/HPLPB20122408.1775
Abstract:
The Kirks stray light simulation model is adopted to study the variation of stray light on different line structures, and the effects of stray light on imaging of different line structures are analyzed according to be image contrast. The simulation based on in-house image processing software written in Matlab indicates that, imaging of a sparser line structure has a lower image contrast and is more susceptible to stray light when the critical dimension is fixed. When the ratio of line width and space is fixed, a smaller critical dimension will lead to a lower image contrast and stronger effect of stray light on image pattern. Therefore, the stray light has great influence on the image pattern of narrow and sparse line structure.
The Kirks stray light simulation model is adopted to study the variation of stray light on different line structures, and the effects of stray light on imaging of different line structures are analyzed according to be image contrast. The simulation based on in-house image processing software written in Matlab indicates that, imaging of a sparser line structure has a lower image contrast and is more susceptible to stray light when the critical dimension is fixed. When the ratio of line width and space is fixed, a smaller critical dimension will lead to a lower image contrast and stronger effect of stray light on image pattern. Therefore, the stray light has great influence on the image pattern of narrow and sparse line structure.
2012,
24: 1780-1784.
doi: 10.3788/HPLPB20122408.1780
Abstract:
On the basis of the Lamberts cosine law, the light intensity of a point on the receiving screen behind the diffuse transmission glass screen was theoretically deduced. Combining the application of the diffuse transmission glass screen in the power monitor, the influence of both single-layer glass and multi-layer glasses on the intensity distribution of the incident laser was summarized through numerical simulation. The numerical results show that when the ratio of the radius of the incident laser to the distance from the diffuse transmission screen to the receiving screen is no more than 0.3, the intensity distribution and the caliber of the incident laser couldnt influence the normalized light intensity distribution on the receiving screen. And the normalized light intensity distribution on the receiving screen mainly depends on the distance, which indicates that the arrangement of the glasses or the number of the layers almost have nothing to do with the distribution. This conclusion was proved by the experiment.
On the basis of the Lamberts cosine law, the light intensity of a point on the receiving screen behind the diffuse transmission glass screen was theoretically deduced. Combining the application of the diffuse transmission glass screen in the power monitor, the influence of both single-layer glass and multi-layer glasses on the intensity distribution of the incident laser was summarized through numerical simulation. The numerical results show that when the ratio of the radius of the incident laser to the distance from the diffuse transmission screen to the receiving screen is no more than 0.3, the intensity distribution and the caliber of the incident laser couldnt influence the normalized light intensity distribution on the receiving screen. And the normalized light intensity distribution on the receiving screen mainly depends on the distance, which indicates that the arrangement of the glasses or the number of the layers almost have nothing to do with the distribution. This conclusion was proved by the experiment.
2012,
24: 1785-1788.
doi: 10.3788/HPLPB20122408.1785
Abstract:
Mo/Si multilayer are normally used in the early extreme ultraviolet (EUV) astronomical observation. In recent years people want to get observations in higher spectral resolution. Multilayer with low=Z materials have been studied. Four kinds of multilayer, Mg/SiC, Si/SiC, Si/B4C and Si/C multilayer were designed at the wavelength of 30.4 nm and compared with the normal Mo/Si multilayer. All the multilayer were prepared with DC magnetron sputtering, and their reflectivities were measured by synchrotron radiation. The results show that the bandwidth of Mg/SiC multilayer is 1.44 nm, which is the smallest, and the reflectivity is 44%, which is the highest. While the reflectivity of Mo/Si multilayer is only 24% and the bandwidth is 3.11 nm. The bandwidths of multilayer of low=Z materials are narrower than that of the normal multilayer. Therefore, multilayer of low=Z materials can be used in the EUV high spectral resolution field.
Mo/Si multilayer are normally used in the early extreme ultraviolet (EUV) astronomical observation. In recent years people want to get observations in higher spectral resolution. Multilayer with low=Z materials have been studied. Four kinds of multilayer, Mg/SiC, Si/SiC, Si/B4C and Si/C multilayer were designed at the wavelength of 30.4 nm and compared with the normal Mo/Si multilayer. All the multilayer were prepared with DC magnetron sputtering, and their reflectivities were measured by synchrotron radiation. The results show that the bandwidth of Mg/SiC multilayer is 1.44 nm, which is the smallest, and the reflectivity is 44%, which is the highest. While the reflectivity of Mo/Si multilayer is only 24% and the bandwidth is 3.11 nm. The bandwidths of multilayer of low=Z materials are narrower than that of the normal multilayer. Therefore, multilayer of low=Z materials can be used in the EUV high spectral resolution field.
2012,
24: 1789-1792.
doi: 10.3788/HPLPB20122408.1789
Abstract:
A hybrid refractive/diffractive Petzval lens has been designed. Its working wavelength range is 3.2-4.5 m, full field of view is 8.42, efficient focal length is 95 mm and back focal length is 60.5 mm. The Petzval lens consists of four lenses, including two aspheric surfaces and a diffractive surface, which make the Petzval lens compact and light. Its modulation transfer function is above 0.7 in the temperature range from -80 to 160 ℃. The Petzval lens is compatible with the uncooled staring focal plane array which has a format of 320240 and the pixel pitch of 35 m.
A hybrid refractive/diffractive Petzval lens has been designed. Its working wavelength range is 3.2-4.5 m, full field of view is 8.42, efficient focal length is 95 mm and back focal length is 60.5 mm. The Petzval lens consists of four lenses, including two aspheric surfaces and a diffractive surface, which make the Petzval lens compact and light. Its modulation transfer function is above 0.7 in the temperature range from -80 to 160 ℃. The Petzval lens is compatible with the uncooled staring focal plane array which has a format of 320240 and the pixel pitch of 35 m.
2012,
24: 1793-1796.
doi: 10.3788/HPLPB20122408.1793
Abstract:
The residual stress of shock spot and its boundary points, before and after laser shock processing(LSP), was measured by X-ray diffractometer at three different directions. According to the calculation formulae of principal stress and its direction angle, the value and direction angle of the principal stress of test points before and after LSP are calculated, and then their distribution characteristics are analyzed. The results indicate that LSP can not only adjust the value of the surface principal residual stress of 5B05 aluminum alloy but can also adjust its direction as well. The test point where the maximum principal stress gained the most is not the point where the minimum principal stress gained the most. After the effect of laser shock wave, the surface stress state of 5B05 aluminum alloy was improved. The stress distribution became scattered and the stress field was enlarged.
The residual stress of shock spot and its boundary points, before and after laser shock processing(LSP), was measured by X-ray diffractometer at three different directions. According to the calculation formulae of principal stress and its direction angle, the value and direction angle of the principal stress of test points before and after LSP are calculated, and then their distribution characteristics are analyzed. The results indicate that LSP can not only adjust the value of the surface principal residual stress of 5B05 aluminum alloy but can also adjust its direction as well. The test point where the maximum principal stress gained the most is not the point where the minimum principal stress gained the most. After the effect of laser shock wave, the surface stress state of 5B05 aluminum alloy was improved. The stress distribution became scattered and the stress field was enlarged.
2012,
24: 1797-1800.
doi: 10.3788/HPLPB20122408.1797
Abstract:
To meet the requirements for far-field laser beam irradiation strength, and reduce the impact of thermal effect on the output beam performance, this paper introduces a lower order aberration correction method based on beam shaping. According to the beam wavefront distortion, the method dynamically adjusts the space between shaping mirrors to produce opposite aberrations to correct the aberrations of the first four orders, through the rapid action of the high-precision translation stage and the fast steering mirror, and then the output beam recovers and emits parallelly. The method significantly reduces the thermal drift and thermal distortion of the laser beam, and avoid the long-time continuous beam radiation while running. It features large correction range, control convenience and compact structure, and can greatly improve the quality of the laser output beam and the effect of the laser beam far-field.
To meet the requirements for far-field laser beam irradiation strength, and reduce the impact of thermal effect on the output beam performance, this paper introduces a lower order aberration correction method based on beam shaping. According to the beam wavefront distortion, the method dynamically adjusts the space between shaping mirrors to produce opposite aberrations to correct the aberrations of the first four orders, through the rapid action of the high-precision translation stage and the fast steering mirror, and then the output beam recovers and emits parallelly. The method significantly reduces the thermal drift and thermal distortion of the laser beam, and avoid the long-time continuous beam radiation while running. It features large correction range, control convenience and compact structure, and can greatly improve the quality of the laser output beam and the effect of the laser beam far-field.
2012,
24: 1801-1805.
doi: 10.3788/HPLPB20122408.1801
Abstract:
This paper studies the diffraction characteristics of a serrated circular aperture with random radius, and puts forward and proves that the aperture can further improve the near-field distribution of the beam and reduce the diffraction modulation in the beam center. The simulation results of the axial diffraction and the intensity distribution in the cross section are given, which shows the diffraction light after this aperture has higher filling factor and lower modulation rate compared with that after the amplitude modulation serrated aperture. The intensity modulation of Fresnel diffraction on the axis is suppressed by using the random radius serrated aperture in larger space. The farthest range of suppression can reach 0.15 m.
This paper studies the diffraction characteristics of a serrated circular aperture with random radius, and puts forward and proves that the aperture can further improve the near-field distribution of the beam and reduce the diffraction modulation in the beam center. The simulation results of the axial diffraction and the intensity distribution in the cross section are given, which shows the diffraction light after this aperture has higher filling factor and lower modulation rate compared with that after the amplitude modulation serrated aperture. The intensity modulation of Fresnel diffraction on the axis is suppressed by using the random radius serrated aperture in larger space. The farthest range of suppression can reach 0.15 m.
2012,
24: 1806-1810.
doi: 10.3788/HPLPB20122408.1806
Abstract:
The effect of the repaired subsurface defect with Gaussian profile in fused silica on incident laser is studied according to the scalar diffraction theory. The Matlab simulation results agree with the experiment results. It is shown that modulation on incident laser is produced by the repaired site and varies with the light propagation distance. The modulation may cause damage of the downstream optical components. However, the damage risk can be reduced by installing the downstream optical components at appropriate positions.
The effect of the repaired subsurface defect with Gaussian profile in fused silica on incident laser is studied according to the scalar diffraction theory. The Matlab simulation results agree with the experiment results. It is shown that modulation on incident laser is produced by the repaired site and varies with the light propagation distance. The modulation may cause damage of the downstream optical components. However, the damage risk can be reduced by installing the downstream optical components at appropriate positions.
2012,
24: 1811-1815.
doi: 10.3788/HPLPB20122408.1811
Abstract:
The performance of phase imaging in interferometric imaging system is well characterized by the system transfer function (STF). The STF of the interferometric imaging system is analyzed numerically by assuming that the system is linear and shift-invariant for the complex field. Two standard phase objects, sinusoidal phase grating and phase step, are employed and simulated to determine the STF. Numerical simulation results show that the STF decreases as the wavefront aberration of interferometric imaging system increases. It also shows that the interferometric imaging system is approximately linear for small phase (far less than 1 rad) but explicitly nonlinear for large phase (larger than 0.5 rad). The STF has a visible drop at one half or one third of the cut-off frequency of the imaging system when the amplitude of sinusoidal phase is 1 rad. For a phase step with a height of /2 rad, the STF has no visible drop but decreases slowly with the increasing of spatial frequency. The results provide a useful guidance to the design of interferometer and the measurement of STF and power spectrum density in experiment.
The performance of phase imaging in interferometric imaging system is well characterized by the system transfer function (STF). The STF of the interferometric imaging system is analyzed numerically by assuming that the system is linear and shift-invariant for the complex field. Two standard phase objects, sinusoidal phase grating and phase step, are employed and simulated to determine the STF. Numerical simulation results show that the STF decreases as the wavefront aberration of interferometric imaging system increases. It also shows that the interferometric imaging system is approximately linear for small phase (far less than 1 rad) but explicitly nonlinear for large phase (larger than 0.5 rad). The STF has a visible drop at one half or one third of the cut-off frequency of the imaging system when the amplitude of sinusoidal phase is 1 rad. For a phase step with a height of /2 rad, the STF has no visible drop but decreases slowly with the increasing of spatial frequency. The results provide a useful guidance to the design of interferometer and the measurement of STF and power spectrum density in experiment.
2012,
24: 1816-1820.
doi: 10.3788/HPLPB20122408.1816
Abstract:
Aiming at eliminating the cat-eye effect of electro-optical devices and decreasing the probability that optics windows are detected by active laser reconnaissance systems, reflection properties of the cat-eye optical system with misaligned reticles are investigated. Based on the geometrical optics and the theory of angular spectrum diffraction, the characteristics of diffraction light field distribution that plane waves pass through a cat-eye optical system are deduced and then simulated. The reflection properties of the cat-eye optical system are validated by experimental methods. It is found that the misalign of reticles leads to elliptical deformation of echo spots on output reference planes, and oblique incidence of laser beams makes this phenomenon more obvious. Making use of the reflection properties may increase the difficulty of distinguishing shape-changed targets and diffused background, so as to improve the viability of electro-optical devices on the warfare.
Aiming at eliminating the cat-eye effect of electro-optical devices and decreasing the probability that optics windows are detected by active laser reconnaissance systems, reflection properties of the cat-eye optical system with misaligned reticles are investigated. Based on the geometrical optics and the theory of angular spectrum diffraction, the characteristics of diffraction light field distribution that plane waves pass through a cat-eye optical system are deduced and then simulated. The reflection properties of the cat-eye optical system are validated by experimental methods. It is found that the misalign of reticles leads to elliptical deformation of echo spots on output reference planes, and oblique incidence of laser beams makes this phenomenon more obvious. Making use of the reflection properties may increase the difficulty of distinguishing shape-changed targets and diffused background, so as to improve the viability of electro-optical devices on the warfare.
2012,
24: 1821-1825.
doi: 10.3788/HPLPB20122408.1821
Abstract:
The paper investigates fiber coupling based on mini-bar. The mini-bar we packaged can deliver 60 W output power when the operating current is 60 A, and its central wavelength is 973.7 nm with the FWHM of 4.16 nm. The smile of this mini-bar is 0.57 m. Analysis on the characteristic of slow axis collimation shows the principle of how to choose the appropriate slow axis collimator. The divergence of the mini-bar after slow axis collimation is 47.6 mrad. The computation of beam parameter product reveals that the output laser can be directly coupled into a fiber with the core diameter of 600 m. Fiber coupling experiments based on the mini-bar have been performed. The transmission efficiency of collimator and fiber coupler is 83%-85%, the fiber coupling efficiency is 80%-93%, and the system optical-optical efficiency is over 72%.
The paper investigates fiber coupling based on mini-bar. The mini-bar we packaged can deliver 60 W output power when the operating current is 60 A, and its central wavelength is 973.7 nm with the FWHM of 4.16 nm. The smile of this mini-bar is 0.57 m. Analysis on the characteristic of slow axis collimation shows the principle of how to choose the appropriate slow axis collimator. The divergence of the mini-bar after slow axis collimation is 47.6 mrad. The computation of beam parameter product reveals that the output laser can be directly coupled into a fiber with the core diameter of 600 m. Fiber coupling experiments based on the mini-bar have been performed. The transmission efficiency of collimator and fiber coupler is 83%-85%, the fiber coupling efficiency is 80%-93%, and the system optical-optical efficiency is over 72%.
2012,
24: 1826-1830.
doi: 10.3788/HPLPB20122408.1826
Abstract:
In order to compare three kinds of scintillation detectors，the Monte Carlo method is introduced to calculate the spatial resolution and energy deposition of scintillator arrays with different fiber diameters. According to simulation results， the resolution of standard liquid scintillator array is better than that of plastic scintillator array， and the resolution of deuterated liquid scintillator array is almost half that of standard liquid scintillator array. The energy deposition of hydrogen-rich scintillator is higher than that of deuterated scintillator. Moreover, smaller fiber diameter leads to better spatial resolution, and thicker scintillator leads to higher energy deposition.
In order to compare three kinds of scintillation detectors，the Monte Carlo method is introduced to calculate the spatial resolution and energy deposition of scintillator arrays with different fiber diameters. According to simulation results， the resolution of standard liquid scintillator array is better than that of plastic scintillator array， and the resolution of deuterated liquid scintillator array is almost half that of standard liquid scintillator array. The energy deposition of hydrogen-rich scintillator is higher than that of deuterated scintillator. Moreover, smaller fiber diameter leads to better spatial resolution, and thicker scintillator leads to higher energy deposition.
2012,
24: 1831-1835.
doi: 10.3788/HPLPB20122408.1831
Abstract:
The dynamics of polystyrene(PS) micro-spheres in thin layers of continuous convective self-assembly of 2D colloidal crystals was studied systemically. The mechanisms of void and stripe patterns were analyzed, based on the model of assembly. To explain the film-formation trend, a mathematical model including the coverage percentage of colloidal crystals, the substrate withdrawing velocity and the colloidal suspension concentration was derived. The result shows that higher particle volume fraction and lower substrate withdrawing velocity lead to larger coverage percentage of colloidal crystals. Void and multilayer flaws always appear in the self-assembled 2D colloidal crystals, and the monolayer coverage percentage can be 95%.
The dynamics of polystyrene(PS) micro-spheres in thin layers of continuous convective self-assembly of 2D colloidal crystals was studied systemically. The mechanisms of void and stripe patterns were analyzed, based on the model of assembly. To explain the film-formation trend, a mathematical model including the coverage percentage of colloidal crystals, the substrate withdrawing velocity and the colloidal suspension concentration was derived. The result shows that higher particle volume fraction and lower substrate withdrawing velocity lead to larger coverage percentage of colloidal crystals. Void and multilayer flaws always appear in the self-assembled 2D colloidal crystals, and the monolayer coverage percentage can be 95%.
2012,
24: 1836-1840.
doi: 10.3788/HPLPB20122408.1836
Abstract:
The sweep time performance of the optic streak camera(OSC) is of critical importance to its application. The systematic analysis of full-screen sweep velocity shows that the traditional method based on the averaged velocity and its nonlinearity would increase the uncertainty of sweep time and can not reflect the influence of the spatial distortion of OSC. A elaborate method for sweep time has been developed with the aid of full-screen sweep velocity and its uncertainty. It is proved by the theoretical analysis and experimental study that the method would decrease the uncertainty of sweep time within 1%, which would improve the accuracy of sweep time and the reliability of OSC application.
The sweep time performance of the optic streak camera(OSC) is of critical importance to its application. The systematic analysis of full-screen sweep velocity shows that the traditional method based on the averaged velocity and its nonlinearity would increase the uncertainty of sweep time and can not reflect the influence of the spatial distortion of OSC. A elaborate method for sweep time has been developed with the aid of full-screen sweep velocity and its uncertainty. It is proved by the theoretical analysis and experimental study that the method would decrease the uncertainty of sweep time within 1%, which would improve the accuracy of sweep time and the reliability of OSC application.
2012,
24: 1841-1845.
doi: 10.3788/HPLPB20122408.1841
Abstract:
The outfield-induced resistance properties of Fe3O4/MgO(100) films were investigated. The Fe3O4 thin films were grown on MgO(100) substrates by laser molecular beam epitaxy (L-MBE). The Fe3O4 epitaxial film could be grown with the (200) face of MgO substrate as indicated by XRD analysis. The quality of the films was checked in situ by monitoring reflection high energy electron diffraction (RHEED) patterns and intensity oscillation during deposition. The results show that the film surface is plat, and the film growth mode is 2D layer-by-layer. AFM analysis reveals that the RMS roughness of the films is about 0.201 nm, which shows that the film surface is plat at atom level. The resistance of the films was investigated at the action of outfields such as magnetic field, temperature field and laser field. The results show that, the resistance of the films decreases generally as the temperature increases, while it has a peak at 120 K (known as the Verwey transition temperature), showing the films electrical character of semiconductor type. The resistance of the films decreases with laser field in the temperature range of 50-300 K, so the films show an instantaneously photoconductive character. The Verwey transition temperature is at 120 K for the laser off, but it ascends to 140 K for the laser on. The photoinduced resistance (PR) change increases with the temperature declining, which is due to the field-induced delocalization of charge ordered states in the films.
The outfield-induced resistance properties of Fe3O4/MgO(100) films were investigated. The Fe3O4 thin films were grown on MgO(100) substrates by laser molecular beam epitaxy (L-MBE). The Fe3O4 epitaxial film could be grown with the (200) face of MgO substrate as indicated by XRD analysis. The quality of the films was checked in situ by monitoring reflection high energy electron diffraction (RHEED) patterns and intensity oscillation during deposition. The results show that the film surface is plat, and the film growth mode is 2D layer-by-layer. AFM analysis reveals that the RMS roughness of the films is about 0.201 nm, which shows that the film surface is plat at atom level. The resistance of the films was investigated at the action of outfields such as magnetic field, temperature field and laser field. The results show that, the resistance of the films decreases generally as the temperature increases, while it has a peak at 120 K (known as the Verwey transition temperature), showing the films electrical character of semiconductor type. The resistance of the films decreases with laser field in the temperature range of 50-300 K, so the films show an instantaneously photoconductive character. The Verwey transition temperature is at 120 K for the laser off, but it ascends to 140 K for the laser on. The photoinduced resistance (PR) change increases with the temperature declining, which is due to the field-induced delocalization of charge ordered states in the films.
2012,
24: 1846-1850.
doi: 10.3788/HPLPB20122408.1846
Abstract:
The temporal profiles of two beams were obtained using comparison method , and then the energy reduction factor was acquired. The two beamsone passing through a transparent medium is clipped by laser-induced plasma, and the other transmits with a delay line come into a set of photo-electricity conversion component and oscillographin simultaneously. It is shown that the transmitted pulse energy reduction factor is 12 to 14 with the 1.064 m 1 ns laser pulse, a 100 mm focal length lens, a 100 m thick fused silica plate, and a pinhole of 80 m radius to ensure that the entire apertured area is from the plasma shuttered focal plane. Changing the thickness of the fused silica plate and the radius of the apertured pinhole respectively shows no impact on the energy reduction factor. The energy reduction factor increases while the energy of input beam enhances and the trailing edge of the clipped pulse gradually falls faster. The temporal profile of original laser pulse was reconstructed by profile stitching at the point of energy reduction.
The temporal profiles of two beams were obtained using comparison method , and then the energy reduction factor was acquired. The two beamsone passing through a transparent medium is clipped by laser-induced plasma, and the other transmits with a delay line come into a set of photo-electricity conversion component and oscillographin simultaneously. It is shown that the transmitted pulse energy reduction factor is 12 to 14 with the 1.064 m 1 ns laser pulse, a 100 mm focal length lens, a 100 m thick fused silica plate, and a pinhole of 80 m radius to ensure that the entire apertured area is from the plasma shuttered focal plane. Changing the thickness of the fused silica plate and the radius of the apertured pinhole respectively shows no impact on the energy reduction factor. The energy reduction factor increases while the energy of input beam enhances and the trailing edge of the clipped pulse gradually falls faster. The temporal profile of original laser pulse was reconstructed by profile stitching at the point of energy reduction.
2012,
24: 1851-1855.
doi: 10.3788/HPLPB20122408.1851
Abstract:
To find a solution for the high brightness, ultra-short pulse X-ray source, the betatron X-ray mechanism was studied. It is based on the interactions which generate the laser wake field acceleration (LWFA), between the ultra-intense short laser and the plasma. These accelerated electrons make betatron oscillations in the transverse fields of the bubble and emit high brightness and ultra-short X-ray pulses (about fs). Also, this kind of source has the advantages of small size, low cost. The numerical calculations of the emission of the betatron X-rays were carried out with 2D-PIC simulations and the data processing software. Synchrotron spectra with critical energy of 3 keV and 10 keV which are radiated by the lower energy electrons (about 100 MeV) and the higher energy electrons (about 170 MeV) respectively, are reported and the emission is confined to a small angle of about 8 mrad, which has a good agreement with the theoretical results.
To find a solution for the high brightness, ultra-short pulse X-ray source, the betatron X-ray mechanism was studied. It is based on the interactions which generate the laser wake field acceleration (LWFA), between the ultra-intense short laser and the plasma. These accelerated electrons make betatron oscillations in the transverse fields of the bubble and emit high brightness and ultra-short X-ray pulses (about fs). Also, this kind of source has the advantages of small size, low cost. The numerical calculations of the emission of the betatron X-rays were carried out with 2D-PIC simulations and the data processing software. Synchrotron spectra with critical energy of 3 keV and 10 keV which are radiated by the lower energy electrons (about 100 MeV) and the higher energy electrons (about 170 MeV) respectively, are reported and the emission is confined to a small angle of about 8 mrad, which has a good agreement with the theoretical results.
2012,
24: 1856-1860.
doi: 10.3788/HPLPB20122408.1856
Abstract:
The dynamic sheath model and the analytic expression of the vacuum arc plasma for mixed ion beam are presented based on the collision less model. The variations of the sheath width and electric-field strength as the function of the ion density and substrate bias voltage are calculated respectively for H-Ti mixed ion beam. The phenomena of sheath breakdown and ion beam defocusing, which usually arise in the practical application, are analyzed. It is found that the stable operating region for the mixed ion beam extremely depends on the ion density and substrate bias voltage, and reducing the ion density and increasing the substrate bias voltage can expand the stable operating region.
The dynamic sheath model and the analytic expression of the vacuum arc plasma for mixed ion beam are presented based on the collision less model. The variations of the sheath width and electric-field strength as the function of the ion density and substrate bias voltage are calculated respectively for H-Ti mixed ion beam. The phenomena of sheath breakdown and ion beam defocusing, which usually arise in the practical application, are analyzed. It is found that the stable operating region for the mixed ion beam extremely depends on the ion density and substrate bias voltage, and reducing the ion density and increasing the substrate bias voltage can expand the stable operating region.
2012,
24: 1861-1866.
doi: 10.3788/HPLPB20122408.1861
Abstract:
In fast ignition researches, fuel density is usually diagnosed by X-ray backlighting imaging with an X-ray source produced by laser irradiating metal target. The simulation on the X-ray backlighting imaging has been performed using a Monte Carlo code(MCNPs). The influence on imaging quality induced by the radius and thickness of pinhole, and the energy of X-ray source were investigated. The simulation results show that, the combination of a pinhole with 10 m radius and a X-ray source with 2.7 keV energy, corresponding to Ka line of Mo, is the optimum choice, when both the luminous flux and the spatial resolution of imaging are concerned.
In fast ignition researches, fuel density is usually diagnosed by X-ray backlighting imaging with an X-ray source produced by laser irradiating metal target. The simulation on the X-ray backlighting imaging has been performed using a Monte Carlo code(MCNPs). The influence on imaging quality induced by the radius and thickness of pinhole, and the energy of X-ray source were investigated. The simulation results show that, the combination of a pinhole with 10 m radius and a X-ray source with 2.7 keV energy, corresponding to Ka line of Mo, is the optimum choice, when both the luminous flux and the spatial resolution of imaging are concerned.
2012,
24: 1867-1870.
doi: 10.3788/HPLPB20122408.1867
Abstract:
The vacuum surface tests of cross-linked polystyrene material were carried out. Relations between the vacuum surface flashover voltage and the molecular chain structure and inner impurities of the material were respectively investigated. The results show that with the increasing of cross-linking degree, the vacuum surface flashover voltage first increases and then decreases. The structure of the cross-linked polystyrene material has an important effect on the vacuum surface flashover voltage. Moreover, the surface flashover voltage has relevance to the amount of hetero-structured molecules in the cross linked material, and the existence of the hetero-structured molecules leads to the reduction of the flashover voltage.
The vacuum surface tests of cross-linked polystyrene material were carried out. Relations between the vacuum surface flashover voltage and the molecular chain structure and inner impurities of the material were respectively investigated. The results show that with the increasing of cross-linking degree, the vacuum surface flashover voltage first increases and then decreases. The structure of the cross-linked polystyrene material has an important effect on the vacuum surface flashover voltage. Moreover, the surface flashover voltage has relevance to the amount of hetero-structured molecules in the cross linked material, and the existence of the hetero-structured molecules leads to the reduction of the flashover voltage.
2012,
24: 1871-1873.
doi: 10.3788/HPLPB20122408.1871
Abstract:
The relative calibration of a chemical vapor deposited (CVD) diamond X-ray detector has been completed on the shenguang-Ⅱ laser facility. Signals of the CVD diamond detector and an absolute-calibrated flat response X-ray diode (XRD) for X-ray radiation were obtained. The average sensitivity of the CVD diamond X-ray detector is about 1.19610-5 C/J. The difference between average sensitivity and the sensitivities in different shots is no more than 13%.
The relative calibration of a chemical vapor deposited (CVD) diamond X-ray detector has been completed on the shenguang-Ⅱ laser facility. Signals of the CVD diamond detector and an absolute-calibrated flat response X-ray diode (XRD) for X-ray radiation were obtained. The average sensitivity of the CVD diamond X-ray detector is about 1.19610-5 C/J. The difference between average sensitivity and the sensitivities in different shots is no more than 13%.
2012,
24: 1874-1878.
doi: 10.3788/HPLPB20122408.1874
Abstract:
First principles theoretical study of the elastic and thermodynamic properties of erbium dihydride in fluorite structure, such as volume, thermal expansion, bulk modulus and isochoric heat capacity at different temperatures and pressures is performed using the plane wave pseudopotential method and the quasi-harmonic Debye model. The calculated isochoric heat capacity is convergent to the Dulong-Petit limit at temperatures over 1 100 K. The calculated lattice parameter of 0.523 2 nm at 0 GPa, and 0 K is in excellent agreement with the experimental value of 0.523 0 nm. Simultaneously, the data of single point energy versus volume of primitive cell are also calculated. According to the calculated values of the elastic constants at high pressures and the mechanical stability criteria of cubic crystals, the phase transition pressure is inferred to be about 20 GPa, which is a valid theoretical reference value for further experimental work in high pressure research.
First principles theoretical study of the elastic and thermodynamic properties of erbium dihydride in fluorite structure, such as volume, thermal expansion, bulk modulus and isochoric heat capacity at different temperatures and pressures is performed using the plane wave pseudopotential method and the quasi-harmonic Debye model. The calculated isochoric heat capacity is convergent to the Dulong-Petit limit at temperatures over 1 100 K. The calculated lattice parameter of 0.523 2 nm at 0 GPa, and 0 K is in excellent agreement with the experimental value of 0.523 0 nm. Simultaneously, the data of single point energy versus volume of primitive cell are also calculated. According to the calculated values of the elastic constants at high pressures and the mechanical stability criteria of cubic crystals, the phase transition pressure is inferred to be about 20 GPa, which is a valid theoretical reference value for further experimental work in high pressure research.
2012,
24: 1879-1881.
doi: 10.3788/HPLPB20122408.1879
Abstract:
Proton acceleration experiments were performed by using an ultra-short laser to irradiate gold foils of 5 m and 2.1 m in thickness. The ultra-short laser pulse had the pulse duration of 120 fs and energy of 11 mJ. The peak focal intensity remained around 61016 W/cm2. A Thomson ion spectrometer with CR39 plastic nuclear track detectors were used to observe spectra of the accelerated protons. The spectrum of the 2.1 m foil featured a single peak around 74 keV due to the inefficiency of protons. The maximum energies and efficiencies of accelerated protons increased with decreasing the target thickness. The results were explained by the energy loss of electron transmission and a geometrical effect on hot electron recirculation.
Proton acceleration experiments were performed by using an ultra-short laser to irradiate gold foils of 5 m and 2.1 m in thickness. The ultra-short laser pulse had the pulse duration of 120 fs and energy of 11 mJ. The peak focal intensity remained around 61016 W/cm2. A Thomson ion spectrometer with CR39 plastic nuclear track detectors were used to observe spectra of the accelerated protons. The spectrum of the 2.1 m foil featured a single peak around 74 keV due to the inefficiency of protons. The maximum energies and efficiencies of accelerated protons increased with decreasing the target thickness. The results were explained by the energy loss of electron transmission and a geometrical effect on hot electron recirculation.
2012,
24: 1882-1886.
doi: 10.3788/HPLPB20122408.1882
Abstract:
To meet the high-precision requirement of microtarget assembly in inertial confinement fusion (ICF) experiments, this paper proposes a new technique for the size and position of measuring the size and position of the microsphere target in microtarget assembly. The technique employs two laser confocal probes of sub-micrometer precision to realize scanning measurement, and an algorithm based on matrix subdivision and two-step target extraction to implement calculation. The results show that a 2 m measurement precision has been achieved.
To meet the high-precision requirement of microtarget assembly in inertial confinement fusion (ICF) experiments, this paper proposes a new technique for the size and position of measuring the size and position of the microsphere target in microtarget assembly. The technique employs two laser confocal probes of sub-micrometer precision to realize scanning measurement, and an algorithm based on matrix subdivision and two-step target extraction to implement calculation. The results show that a 2 m measurement precision has been achieved.
2012,
24: 1887-1890.
doi: 10.3788/HPLPB20122408.1887
Abstract:
In inertial confinement fusion(ICF) experiments, the flat response X-ray diode(XRD) array is used to detect the evolution of radiation fluxes of the hohlraum from different directions. The spectrum response of flat response XRD is not perfectly flat, which introduces uncertainty into the recovery of the radiation flux. Thus a weighting method is developed to reduce the errors caused by the spectral shapes and local oscillations of the flat response. The condition under which the recovery ratio will be improved is studied. The method has been used to analyze ICF experiment data, and the modified time history of equivalent integral temperature obtained has a good agreement with the measurements of a multi-channel soft-X-ray spectrometer.
In inertial confinement fusion(ICF) experiments, the flat response X-ray diode(XRD) array is used to detect the evolution of radiation fluxes of the hohlraum from different directions. The spectrum response of flat response XRD is not perfectly flat, which introduces uncertainty into the recovery of the radiation flux. Thus a weighting method is developed to reduce the errors caused by the spectral shapes and local oscillations of the flat response. The condition under which the recovery ratio will be improved is studied. The method has been used to analyze ICF experiment data, and the modified time history of equivalent integral temperature obtained has a good agreement with the measurements of a multi-channel soft-X-ray spectrometer.
2012,
24: 1891-1895.
doi: 10.3788/HPLPB20122408.1891
Abstract:
X-ray phase contrast imaging experiments have been performed on micro-focus X-ray facility and Shenguang-Ⅱ laser driven plasma X-ray source. The Halo and dark zones at capsule shell interface have been found. Our work proposed the principle of light refraction to explain the halo and dark zones, and acquires the theoretic width of the halo and dark zones by sphere model and geometry optics. The theoretic width accords well with the experimental results. Thus, phase contrast imaging has an advantage over absorption imaging in low-Z material sample, and the halo and dark zones are very useful for precise diagnoses in low-Z material interface.
X-ray phase contrast imaging experiments have been performed on micro-focus X-ray facility and Shenguang-Ⅱ laser driven plasma X-ray source. The Halo and dark zones at capsule shell interface have been found. Our work proposed the principle of light refraction to explain the halo and dark zones, and acquires the theoretic width of the halo and dark zones by sphere model and geometry optics. The theoretic width accords well with the experimental results. Thus, phase contrast imaging has an advantage over absorption imaging in low-Z material sample, and the halo and dark zones are very useful for precise diagnoses in low-Z material interface.
2012,
24: 1896-1900.
doi: 10.3788/HPLPB20122408.1896
Abstract:
Experiments on interaction between intense femtosecond laser and high-purity gold were performed on the SILEX-Ⅰ laser facility. The single-photon counting X-ray CCD camera was used to measure the L-shell X-ray emission from Au plasma at different laser power densities. The experimental results show that in the process of Au plasma X-ray emission, the high-speed electrons result in the intense bremsstrahlung and thermal radiation, and all the radiation intensity increases with the laser power density.
Experiments on interaction between intense femtosecond laser and high-purity gold were performed on the SILEX-Ⅰ laser facility. The single-photon counting X-ray CCD camera was used to measure the L-shell X-ray emission from Au plasma at different laser power densities. The experimental results show that in the process of Au plasma X-ray emission, the high-speed electrons result in the intense bremsstrahlung and thermal radiation, and all the radiation intensity increases with the laser power density.
2012,
24: 1901-1906.
doi: 10.3788/HPLPB20122408.1901
Abstract:
A modified two-dimensional magnetic reconnection model is presented which focuses on the role of electrostatic field generated by charge separation in magnetic reconnection, and the E cross B drift causing the Alfvnic outflows. This reconnection model reveals that the reconnection rate described in Sweet-Parker model is strongly dependent on the ratio of the electron mass and the ion mass, and the effective local resistivity normalized by the Spitzer resistivity is proportional to the square of the ratio of the ion skin depth to the width of the current sheet. The relativistic effect and creation of electron-positron pairs in high temperature plasmas can enhance the reconnection rate. The excitation of electromagnetic waves is necessary for dissipation of magnetic energy.
A modified two-dimensional magnetic reconnection model is presented which focuses on the role of electrostatic field generated by charge separation in magnetic reconnection, and the E cross B drift causing the Alfvnic outflows. This reconnection model reveals that the reconnection rate described in Sweet-Parker model is strongly dependent on the ratio of the electron mass and the ion mass, and the effective local resistivity normalized by the Spitzer resistivity is proportional to the square of the ratio of the ion skin depth to the width of the current sheet. The relativistic effect and creation of electron-positron pairs in high temperature plasmas can enhance the reconnection rate. The excitation of electromagnetic waves is necessary for dissipation of magnetic energy.
2012,
24: 1907-1913.
doi: 10.3788/HPLPB20122408.1907
Abstract:
The evolution of plasma parameters during high pressure discharge in the microcavity with a hollow anode was numerically studied, with a two-dimensional self-consistent fluid model. The simulations were performed with argon at 13.3 kPa. The numerical results show that during the discharge the electric field around the cathode transforms from an axial field to a radial field, the plasma density gets the maximum value on the central line of the cavity and the location of the maximum density moves from the region near anode at the initial stage to the cathode vicinity at the stable stage, and the maximum electron temperature occurs in the ring sheath of cathode.
The evolution of plasma parameters during high pressure discharge in the microcavity with a hollow anode was numerically studied, with a two-dimensional self-consistent fluid model. The simulations were performed with argon at 13.3 kPa. The numerical results show that during the discharge the electric field around the cathode transforms from an axial field to a radial field, the plasma density gets the maximum value on the central line of the cavity and the location of the maximum density moves from the region near anode at the initial stage to the cathode vicinity at the stable stage, and the maximum electron temperature occurs in the ring sheath of cathode.
2012,
24: 1914-1918.
doi: 10.3788/HPLPB20122408.1914
Abstract:
The fusion reaction history is valuable information for inertial confinement fusion experiment research. The Geant4 toolkit was used to study the system performance of the fusion reaction history diagnostic facility based on gas Cherenkov detector. The material and thickness of the radiation converter were optimized along with the pressure and length of the CO2 gas cavity. Simulation results indicate that the system time resolution and conversion efficiency reach about 22 ps and 4.710-3 Cherenkov photons/gamma respectively after optimization.
The fusion reaction history is valuable information for inertial confinement fusion experiment research. The Geant4 toolkit was used to study the system performance of the fusion reaction history diagnostic facility based on gas Cherenkov detector. The material and thickness of the radiation converter were optimized along with the pressure and length of the CO2 gas cavity. Simulation results indicate that the system time resolution and conversion efficiency reach about 22 ps and 4.710-3 Cherenkov photons/gamma respectively after optimization.
2012,
24: 1919-1924.
doi: 10.3788/HPLPB20122408.1919
Abstract:
A technique of errors treatment is presented according to the negative impact of systematic errors, which is hard to eliminate in photometric measurement data, on the characterization accuracy of thin film optical parameters. In order to minimize the characterization deviations of thin film optical parameters from the real values caused by photometric measurement systematic errors, it is advised to select the photometric measurement data used in optical characterization from spectral bands characterized with opposite signs or single zero of first-order spectral coefficients partial derivatives with respect to layer thickness and refractive index for most measurement incident angles, and to exclude spectral bands characterized with the same signs or both zeros of spectral coefficients first-order partial derivatives for all measurement incident angles. The essence of this technique is to minimize the errors transfer effect of measurement data on thin film optical parameters characterization by spectral band selection with first-order partial derivatives analysis. Numerical simulations have been conducted to investigate its applicability to characterization with different polarization lights and the skills in selection of the range of measurement incident angles. The reliability of this technique is supported by replicable numerical experiments and reasonable theoretical explanations.
A technique of errors treatment is presented according to the negative impact of systematic errors, which is hard to eliminate in photometric measurement data, on the characterization accuracy of thin film optical parameters. In order to minimize the characterization deviations of thin film optical parameters from the real values caused by photometric measurement systematic errors, it is advised to select the photometric measurement data used in optical characterization from spectral bands characterized with opposite signs or single zero of first-order spectral coefficients partial derivatives with respect to layer thickness and refractive index for most measurement incident angles, and to exclude spectral bands characterized with the same signs or both zeros of spectral coefficients first-order partial derivatives for all measurement incident angles. The essence of this technique is to minimize the errors transfer effect of measurement data on thin film optical parameters characterization by spectral band selection with first-order partial derivatives analysis. Numerical simulations have been conducted to investigate its applicability to characterization with different polarization lights and the skills in selection of the range of measurement incident angles. The reliability of this technique is supported by replicable numerical experiments and reasonable theoretical explanations.
2012,
24: 1925-1930.
doi: 10.3788/HPLPB20122408.1925
Abstract:
The high-order mode coaxial cavity output circuit and the double-gap coupled cavity circuit are important for high frequency, high power and broadband klystrons. In this study, the two structures mentioned above are combined. The real part of the gap impedance of the filter-loaded double-gap output cavity is derived according to the equivalent circuit theory. In addition, the method for reducing the external quality factor of high-order mode double-gap output circuit is discussed on the basis of the microwave principle and simulation. The output circuit loaded with the designed filter has a bandwidth of 9.7%.
The high-order mode coaxial cavity output circuit and the double-gap coupled cavity circuit are important for high frequency, high power and broadband klystrons. In this study, the two structures mentioned above are combined. The real part of the gap impedance of the filter-loaded double-gap output cavity is derived according to the equivalent circuit theory. In addition, the method for reducing the external quality factor of high-order mode double-gap output circuit is discussed on the basis of the microwave principle and simulation. The output circuit loaded with the designed filter has a bandwidth of 9.7%.
2012,
24: 1931-1935.
doi: 10.3788/HPLPB20122408.1931
Abstract:
In the simulation of high frequency characteristics of coupled cavity structure, the quasi-period boundary method is usually adapted for its high precision. However, the fake solution exists in the double-cavity simulation model. In this paper, the single-cavity simulation model is proposed and studied. This model eliminates, the fake solution and reduces the mesh number by 62% and the total simulation time by 56%, while maintaining the calculation precision. Italso provides an effective way to calculate the dispersion characteristics and interaction impedance, which is favorable for the optimization of structure dimensions. The influences of structure dimensions on the high frequency characteristics are also analyzed with this model.
In the simulation of high frequency characteristics of coupled cavity structure, the quasi-period boundary method is usually adapted for its high precision. However, the fake solution exists in the double-cavity simulation model. In this paper, the single-cavity simulation model is proposed and studied. This model eliminates, the fake solution and reduces the mesh number by 62% and the total simulation time by 56%, while maintaining the calculation precision. Italso provides an effective way to calculate the dispersion characteristics and interaction impedance, which is favorable for the optimization of structure dimensions. The influences of structure dimensions on the high frequency characteristics are also analyzed with this model.
2012,
24: 1936-1940.
doi: 10.3788/HPLPB20122408.1936
Abstract:
A single-anode magnetron injection electron gun is designed and simulated according to the requirements of a 94 GHz gyrotron oscillator. On the basis of detailed theoretical analysis about the operating principle of the gun by programming, the designing of its initial parameters is performed, and its calculation module is developed based on the particle simulation software CHIPIC. The simulation results show that, the ratio of transverse velocity to axial velocity is 1.42 and the velocity spread is about 4.6%. The designed electron gun has achieved excellent beam parameters, which can meet the requirements for the electron beam in the gyrotron oscillator.
A single-anode magnetron injection electron gun is designed and simulated according to the requirements of a 94 GHz gyrotron oscillator. On the basis of detailed theoretical analysis about the operating principle of the gun by programming, the designing of its initial parameters is performed, and its calculation module is developed based on the particle simulation software CHIPIC. The simulation results show that, the ratio of transverse velocity to axial velocity is 1.42 and the velocity spread is about 4.6%. The designed electron gun has achieved excellent beam parameters, which can meet the requirements for the electron beam in the gyrotron oscillator.
2012,
24: 1941-1946.
doi: 10.3788/HPLPB20122408.1941
Abstract:
A magnet measurement method using 2D automatic rotation Helmholtz coils has been proposed to improve the measurement efficiency and accuracy of magnets in the research and development of undulators and wigglers. Theoretical analysis reveals that automatic magnet measurement can be achieved merely by 2D automatic rotation mechanism instead of 3D one, which can facilitate the automatic measurement. Such equipment has been developed successfully by using ingenuous 2D rotation mechanism, and has been applied in magnet measurement in SSRF (Shanghai Synchrotron Radiation Facility). The measurement principle and method are given in detail in this work, and the measurement errors are analyzed. This equipment can accomplish measurement of single magnet in 30 s, with the repeatability and accuracy both above 0.05%.
A magnet measurement method using 2D automatic rotation Helmholtz coils has been proposed to improve the measurement efficiency and accuracy of magnets in the research and development of undulators and wigglers. Theoretical analysis reveals that automatic magnet measurement can be achieved merely by 2D automatic rotation mechanism instead of 3D one, which can facilitate the automatic measurement. Such equipment has been developed successfully by using ingenuous 2D rotation mechanism, and has been applied in magnet measurement in SSRF (Shanghai Synchrotron Radiation Facility). The measurement principle and method are given in detail in this work, and the measurement errors are analyzed. This equipment can accomplish measurement of single magnet in 30 s, with the repeatability and accuracy both above 0.05%.
2012,
24: 1947-1950.
doi: 10.3788/HPLPB20122408.1947
Abstract:
The calculation of the minimum emittance of three-bend achromats (TBAs) made by Mathematica software can ignore the actual magnets lattice in the matching condition of dispersion function in phase space. The minimum scaling factors of two kinds of widely used TBA lattices are obtained. Then the relationship between the lengths and the radii of the three dipoles in TBA is obtained and so is the minimum scaling factor, when the TBA lattice achieves its minimum emittance. The procedure of analysis and the results can be widely used in achromats lattices, because the calculation is not restricted by the actual lattice.
The calculation of the minimum emittance of three-bend achromats (TBAs) made by Mathematica software can ignore the actual magnets lattice in the matching condition of dispersion function in phase space. The minimum scaling factors of two kinds of widely used TBA lattices are obtained. Then the relationship between the lengths and the radii of the three dipoles in TBA is obtained and so is the minimum scaling factor, when the TBA lattice achieves its minimum emittance. The procedure of analysis and the results can be widely used in achromats lattices, because the calculation is not restricted by the actual lattice.
2012,
24: 1951-1955.
doi: 10.3788/HPLPB20122408.1951
Abstract:
A high efficiency algorithm for detecting infrared dim target based on digital signal processor (DSP) is proposed. It is designed especially for thecloud edge left after the image preprocessing of irregular clouds, and it is a searching algorithm based on improved notch filter after the backgroundpredicting. A DSP-based real-time image processing platform has been used to implement and test the algorithm in real scenarios. It is proved that the algorithm can restrain the negative effect of the residual cloud edges effectively. The detection distance reaches 26 km and the real-time processing speed can reach 75 Hz. The algorithm improves the signal-to-noise ratio of images significantly, which is beneficial to target detection.
A high efficiency algorithm for detecting infrared dim target based on digital signal processor (DSP) is proposed. It is designed especially for thecloud edge left after the image preprocessing of irregular clouds, and it is a searching algorithm based on improved notch filter after the backgroundpredicting. A DSP-based real-time image processing platform has been used to implement and test the algorithm in real scenarios. It is proved that the algorithm can restrain the negative effect of the residual cloud edges effectively. The detection distance reaches 26 km and the real-time processing speed can reach 75 Hz. The algorithm improves the signal-to-noise ratio of images significantly, which is beneficial to target detection.
2012,
24: 1956-1960.
doi: 10.3788/HPLPB20122408.1956
Abstract:
The impulse of irregularly shaped space debris under laser irradiation was calculated, on the basis of the experimental phenomenon that reverse jetting under laser ablation is always normal to the irradiated surface no matter what the laser incident direction is. Fragments of sphere, cylinder and cube were selected as examples according to NASAs investigation of space debriss shape. The results indicate that for fragments of sphere and cube shapes, the impulse direction was along the laser irradiation direction, and their magnitudes of impulse are fixed proportional to cylindrical ones when the fragments materials were the same. For sylindrical fragments, both of the magnitude and direction of impulse change with thevariation of laser irradiation direction.
The impulse of irregularly shaped space debris under laser irradiation was calculated, on the basis of the experimental phenomenon that reverse jetting under laser ablation is always normal to the irradiated surface no matter what the laser incident direction is. Fragments of sphere, cylinder and cube were selected as examples according to NASAs investigation of space debriss shape. The results indicate that for fragments of sphere and cube shapes, the impulse direction was along the laser irradiation direction, and their magnitudes of impulse are fixed proportional to cylindrical ones when the fragments materials were the same. For sylindrical fragments, both of the magnitude and direction of impulse change with thevariation of laser irradiation direction.
2012,
24: 1961-1964.
doi: 10.3788/HPLPB20122408.1961
Abstract:
A system has been designed with the oblique incidence optical structure to measure the time-resolved solid-surface fluorescence spectra. The system was applied to measure the time-resolved solid-surface fluorescence spectra of ZnO films excited by 355 nm nanosecond laser pulses. The results show that the system can measure the time-resolved spectra of solid-surface fluorescence, from which the fluorescence lifetime can be obtained. The system is reliable with simple optical structure, high sensitivity, and high-speed response.
A system has been designed with the oblique incidence optical structure to measure the time-resolved solid-surface fluorescence spectra. The system was applied to measure the time-resolved solid-surface fluorescence spectra of ZnO films excited by 355 nm nanosecond laser pulses. The results show that the system can measure the time-resolved spectra of solid-surface fluorescence, from which the fluorescence lifetime can be obtained. The system is reliable with simple optical structure, high sensitivity, and high-speed response.
2012,
24: 1965-1969.
doi: 10.3788/HPLPB20122408.1965
Abstract:
The nanocrystalline silicon thin films were deposited on circular substrates with radiuses of 2.0, 2.5, 3.0, 3.5 and 4.0 cm by pulsed laser ablation in argon gas of 10 Pa at room temperature. The surface morphology and microscopic structure of the films were characterized by scanning electron microscopy, X-ray diffraction analysis and Raman spectroscopy. The results indicate that both the average size of Si nanoparticles and the damping coefficients of ablated particles are distributed symmetrically relative to the plume axis, and decrease with increasing the angle between substrate and plume axis. Meanwhile, the average size of Si nanoparticles and the damping coefficients of ablated particles decrease as the radius of circular substrate increases.
The nanocrystalline silicon thin films were deposited on circular substrates with radiuses of 2.0, 2.5, 3.0, 3.5 and 4.0 cm by pulsed laser ablation in argon gas of 10 Pa at room temperature. The surface morphology and microscopic structure of the films were characterized by scanning electron microscopy, X-ray diffraction analysis and Raman spectroscopy. The results indicate that both the average size of Si nanoparticles and the damping coefficients of ablated particles are distributed symmetrically relative to the plume axis, and decrease with increasing the angle between substrate and plume axis. Meanwhile, the average size of Si nanoparticles and the damping coefficients of ablated particles decrease as the radius of circular substrate increases.
2012,
24: 1970-1974.
doi: 10.3788/HPLPB20122408.1970
Abstract:
The study uses the particle-in-cell method to simulate the focusing of intense electron beam with the thin magnetic lens. The focusing model of intense electron beam was established and to simulate one experiment on Dragon-I accelerator. The simulation result is very close to the experimental one, which proves the validity of the model. The influences of some parameters of electron beam on focusing were simulated. In the simulations, the best envelope diameter of incident paralled beams is 20.0-22.5 mm. For the effects of beam emittance and energy spread, the simulation results agree well with theoretical ones. Moreover, the focal spot of small size can be obtained, only when the envelope diameter and the phase of incident beams are matched.
The study uses the particle-in-cell method to simulate the focusing of intense electron beam with the thin magnetic lens. The focusing model of intense electron beam was established and to simulate one experiment on Dragon-I accelerator. The simulation result is very close to the experimental one, which proves the validity of the model. The influences of some parameters of electron beam on focusing were simulated. In the simulations, the best envelope diameter of incident paralled beams is 20.0-22.5 mm. For the effects of beam emittance and energy spread, the simulation results agree well with theoretical ones. Moreover, the focal spot of small size can be obtained, only when the envelope diameter and the phase of incident beams are matched.
2012,
24: 1975-1979.
doi: 10.3788/HPLPB20122408.1975
Abstract:
A weak current measurement system is developed. It is mainly used in the accurate measurement of weak current in radiation detection. The principle of the measurement system is introduced. The interference protection measures of current-to-voltage (I-V) conversion and amplification unit, the technology of sigma-delta analog-to-digital conversion and the program design of micro-programmed control unit are described. The system communicates with the computer controlled platform by USB interface, and has functions, such as storage, range selection, data display. Its measuring range is from 0.1 pA to 2.1 mA, and resolution is 41/2 bits. The system has been successfully used in the detection of radiation.
A weak current measurement system is developed. It is mainly used in the accurate measurement of weak current in radiation detection. The principle of the measurement system is introduced. The interference protection measures of current-to-voltage (I-V) conversion and amplification unit, the technology of sigma-delta analog-to-digital conversion and the program design of micro-programmed control unit are described. The system communicates with the computer controlled platform by USB interface, and has functions, such as storage, range selection, data display. Its measuring range is from 0.1 pA to 2.1 mA, and resolution is 41/2 bits. The system has been successfully used in the detection of radiation.
2012,
24: 1980-1984.
doi: 10.3788/HPLPB20122408.1980
Abstract:
The theory of secondary electrons produced by electrons impacting the metal surface was discussed. Formulas of some important physical parameters were summarized, including secondary electron emission coefficient, and inelastically backscattered electron energy distribution. Then the secondary emission module of three dimensional PIC numerical simulation program was written. The corresponding numerical model was established. The simulation results including secondary electron emission coefficient and inelastically backscattered electron energy distribution are consistent with the theoretical predictions, which verifies the correctness of the simulation process.
The theory of secondary electrons produced by electrons impacting the metal surface was discussed. Formulas of some important physical parameters were summarized, including secondary electron emission coefficient, and inelastically backscattered electron energy distribution. Then the secondary emission module of three dimensional PIC numerical simulation program was written. The corresponding numerical model was established. The simulation results including secondary electron emission coefficient and inelastically backscattered electron energy distribution are consistent with the theoretical predictions, which verifies the correctness of the simulation process.
2012,
24: 1985-1989.
doi: 10.3788/HPLPB20122408.1985
Abstract:
In the Monte Carlo simulation, the S(,) model can only be used in some given temperature. The paper proposes the equivalent mass thermal motion model of neutron transport in water at different temperatures. The free gas thermal motion model is analyzed. Different equivalent masses are used to correct the neutron elastic scattering simulation of hydrogen in water, and the optimal equivalent mass of hydrogen in water at five different temperatures is given by comparing the result of the neutron flow through water layer with the S(,) model. According to the data of the five different temperature points, the formula of the optimal equivalent mass varying with temperature is fitted. The results of the equivalent mass thermal motion model are in accord with those of the S(,) model. The equivalent mass thermal motion model breaks the limitation of the S(,) model, and can deal with the neutron transport problems in water at arbitrary temperature between 300-800 K.
In the Monte Carlo simulation, the S(,) model can only be used in some given temperature. The paper proposes the equivalent mass thermal motion model of neutron transport in water at different temperatures. The free gas thermal motion model is analyzed. Different equivalent masses are used to correct the neutron elastic scattering simulation of hydrogen in water, and the optimal equivalent mass of hydrogen in water at five different temperatures is given by comparing the result of the neutron flow through water layer with the S(,) model. According to the data of the five different temperature points, the formula of the optimal equivalent mass varying with temperature is fitted. The results of the equivalent mass thermal motion model are in accord with those of the S(,) model. The equivalent mass thermal motion model breaks the limitation of the S(,) model, and can deal with the neutron transport problems in water at arbitrary temperature between 300-800 K.
2012,
24: 1990-1994.
doi: 10.3788/HPLPB20122408.1990
Abstract:
In order to reduce the influence of beam size, a photon beam position monitor (PBPM) called staggered-blade PBPM was designed and installed in the machine diagnostic beamline (MDBL) at the Hefei Light Source (HLS), and Libera Photon was used for data processing and output. The ratio method and the log-ratio method were put forward based on the differenceover-sum (/) method. The main performances of staggered-blade PBPM were then analyzed with the three methods. The results of online calibration match well with the calculated results. Some application researches have also been done.
In order to reduce the influence of beam size, a photon beam position monitor (PBPM) called staggered-blade PBPM was designed and installed in the machine diagnostic beamline (MDBL) at the Hefei Light Source (HLS), and Libera Photon was used for data processing and output. The ratio method and the log-ratio method were put forward based on the differenceover-sum (/) method. The main performances of staggered-blade PBPM were then analyzed with the three methods. The results of online calibration match well with the calculated results. Some application researches have also been done.
2012,
24: 1995-1999.
doi: 10.3788/HPLPB20122408.1995
Abstract:
The pulse forming line based on high dielectric constant ceramic dielectrics requires stacked Blumleins configuration with multi-switch triggering. Through the theory of pulse forming process, the effect of multiple switches dispersity of closure time on stacked Blumleins is analyzed, which contains two aspects: one is causing ladder distortions within rise and fall edges of the output rectangle pulse, the other is leading to over-voltage loaded on the parallel plate Blumleins triggered by the delayed closing switches, easily resulting in electric insulation failure for the ceramic dielectrics. A PSpice circuit program is utilized to simulate the effect on 4-stage stacked Blumleins, and the simulation results are in good agreement with analysis through the theory of pulse forming process. Practical solutions to the problem caused by the effect are presented.
The pulse forming line based on high dielectric constant ceramic dielectrics requires stacked Blumleins configuration with multi-switch triggering. Through the theory of pulse forming process, the effect of multiple switches dispersity of closure time on stacked Blumleins is analyzed, which contains two aspects: one is causing ladder distortions within rise and fall edges of the output rectangle pulse, the other is leading to over-voltage loaded on the parallel plate Blumleins triggered by the delayed closing switches, easily resulting in electric insulation failure for the ceramic dielectrics. A PSpice circuit program is utilized to simulate the effect on 4-stage stacked Blumleins, and the simulation results are in good agreement with analysis through the theory of pulse forming process. Practical solutions to the problem caused by the effect are presented.
2012,
24: 2000-2004.
doi: 10.3788/HPLPB20122408.2000
Abstract:
A set of fiber detector which consists of an optical fiber array detector and a solar-blind plug-in optical sensor was developed for multi-gap gas switch optical diagnosis. The detailed discharging process was monitored using the detector and the influence of trigger voltage, gas pressure and UV pre-ionizing on the performance of the switch was also analyzed. The timing precision of the fiber array detector is better than 0.6 ns, and its time response is 3.2 ns. The solar-blind sensor responds to light whose wavelength lies between 260 nm and 320 nm. The following results were obtained by the diagnostic system: the order of the gaps breakdown is 3rd-2nd-1st-4th-5th-6th, and statistic delay and over-voltage breakdown delay take the majority of the whole time delay. The jitter of the switch can be reduced by raising the trigger voltage, lowering the gas voltage and stabilizing the intensity of the ultraviolet light.
A set of fiber detector which consists of an optical fiber array detector and a solar-blind plug-in optical sensor was developed for multi-gap gas switch optical diagnosis. The detailed discharging process was monitored using the detector and the influence of trigger voltage, gas pressure and UV pre-ionizing on the performance of the switch was also analyzed. The timing precision of the fiber array detector is better than 0.6 ns, and its time response is 3.2 ns. The solar-blind sensor responds to light whose wavelength lies between 260 nm and 320 nm. The following results were obtained by the diagnostic system: the order of the gaps breakdown is 3rd-2nd-1st-4th-5th-6th, and statistic delay and over-voltage breakdown delay take the majority of the whole time delay. The jitter of the switch can be reduced by raising the trigger voltage, lowering the gas voltage and stabilizing the intensity of the ultraviolet light.
2012,
24: 2005-2008.
doi: 10.3788/HPLPB20122408.2005
Abstract:
The paper investigates the dielectric materials for compact pulse forming lines. According to the interrelation between parameters of pulse forming lines and dielectric properties of ceramic materials, the strategies of the material choice and assessment are presented for the solid-state pulse forming lines of dielectric materials. The microwave ceramics characteristic of adjustable dielectric constants are found to be relatively ideal candidates. The solid-state pulse forming line fabricated from the Ba-Nb-Ti microwave ceramics, can output pulses with a rise-time of 5-6 nm, a pulse length of 13 ns, and a flat top of 5-6 ns, and its breakdown strength is more than 17.5 kV/mm.
The paper investigates the dielectric materials for compact pulse forming lines. According to the interrelation between parameters of pulse forming lines and dielectric properties of ceramic materials, the strategies of the material choice and assessment are presented for the solid-state pulse forming lines of dielectric materials. The microwave ceramics characteristic of adjustable dielectric constants are found to be relatively ideal candidates. The solid-state pulse forming line fabricated from the Ba-Nb-Ti microwave ceramics, can output pulses with a rise-time of 5-6 nm, a pulse length of 13 ns, and a flat top of 5-6 ns, and its breakdown strength is more than 17.5 kV/mm.
2012,
24: 2009-2012.
doi: 10.3788/HPLPB20122408.2009
Abstract:
A six-stage gas switch with low inductance developed for fast linear transformer drivers (LTDs) is described, and the inductance of the switch with single channel and multi-channel discharges is investigated. The measured inductance ofthe switch with single channel discharge is consistent with the calculated results by the Nagaokas equation. It is affected by both the circuit loop area and the electrode azimuthal current. The triggered multi-stage switch with multi-channel discharges has the lowest inductance of 49 nH that is 4 nH more than that of the same sized cylinder, indicating that the azimuthal current along toroidal electrodes has little contribution to the inductance of the switch in practical operation.
A six-stage gas switch with low inductance developed for fast linear transformer drivers (LTDs) is described, and the inductance of the switch with single channel and multi-channel discharges is investigated. The measured inductance ofthe switch with single channel discharge is consistent with the calculated results by the Nagaokas equation. It is affected by both the circuit loop area and the electrode azimuthal current. The triggered multi-stage switch with multi-channel discharges has the lowest inductance of 49 nH that is 4 nH more than that of the same sized cylinder, indicating that the azimuthal current along toroidal electrodes has little contribution to the inductance of the switch in practical operation.
2012,
24: 2013-2016.
doi: 10.3788/HPLPB20122408.2013
Abstract:
For the plane magnetically insulated transmission line(MITL), coaxial MITL, and cone MITL, the analytical expression of initial current is derived according to the conservation of magnetic flux, and the analytical expression of initial voltage is derived according to the conservation of charge. Then, the relations of the initial current and voltage with the final steady state current and voltage are numerically calculated. The results of simulation agree well with the results of two-dimensional particle-in-cell(PIC) simulation.
For the plane magnetically insulated transmission line(MITL), coaxial MITL, and cone MITL, the analytical expression of initial current is derived according to the conservation of magnetic flux, and the analytical expression of initial voltage is derived according to the conservation of charge. Then, the relations of the initial current and voltage with the final steady state current and voltage are numerically calculated. The results of simulation agree well with the results of two-dimensional particle-in-cell(PIC) simulation.
