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RSS2015 Vol. 27, No. 03
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2015,
27: 032001.
doi: 10.11884/HPLPB201527.032001
Abstract:
In the scheme of electron-driven fast ignition of inertial confinement fusion (ICF), MeV relativistic electron beams driven by ultraintense petawatt laser pulses are required and electron energy of several tens of kilojoules should be deposited in the compressed core of an imploded DT shell. The beam quality is crucial to the success of fast ignitor. In order to study the generation and transport of the relativistic electron beam, a three-dimensional high-performance parallel particle-in-cell code is developed and improved. In this review, this paper shows the researches on the generation of high-quality electron beams and the method of beam divergence controlling of our research group. Two main reasons for poor beam quality are firstly introduced: pre-plasma effect and random scattering of the magnetic field produced by the beam instability. In addition, enhancement of electron beam flux and collimation of its propagation are investigated. Four ways to obtain collimated electrons are put forward: 1) reduce the pre-plasma effect with a double cone target; 2) collimate fast electrons in specially engineered targets with the spontaneously generated magnetic field during its transportation; 3) collimate fast electrons with external magnetic field; 4) control the beam instability at the laser-plasma interface.
In the scheme of electron-driven fast ignition of inertial confinement fusion (ICF), MeV relativistic electron beams driven by ultraintense petawatt laser pulses are required and electron energy of several tens of kilojoules should be deposited in the compressed core of an imploded DT shell. The beam quality is crucial to the success of fast ignitor. In order to study the generation and transport of the relativistic electron beam, a three-dimensional high-performance parallel particle-in-cell code is developed and improved. In this review, this paper shows the researches on the generation of high-quality electron beams and the method of beam divergence controlling of our research group. Two main reasons for poor beam quality are firstly introduced: pre-plasma effect and random scattering of the magnetic field produced by the beam instability. In addition, enhancement of electron beam flux and collimation of its propagation are investigated. Four ways to obtain collimated electrons are put forward: 1) reduce the pre-plasma effect with a double cone target; 2) collimate fast electrons in specially engineered targets with the spontaneously generated magnetic field during its transportation; 3) collimate fast electrons with external magnetic field; 4) control the beam instability at the laser-plasma interface.
2015,
27: 032002.
doi: 10.11884/HPLPB201527.032002
Abstract:
High Mach number compressible turbulent flow is a multi-process physical phenomenon with multi-scale properties. To explore its physical mechanism, the motion compressible turbulence is divided into shear and dilation processes, and the effect of dilation on the statistic and dynamics of turbulence is investigated. At first, a new compact-WENO scheme is developed to simulate the turbulent field accurately. The multi-scale properties of shear and dilation process and their effect on the particle transportation are analyzed. The effect of shock on turbulence field is investigated. It is proved that the energy flux due to convection and pressure are constant, then there exists the inertial range for kinetic energy cascade. It is also proved that both the shear and compressible parts of kinetic energy flux are constant in the inertial range. The contribution from subgrid scale stress and subgrid mass flux to the kinetic energy cascade is analyzed.
High Mach number compressible turbulent flow is a multi-process physical phenomenon with multi-scale properties. To explore its physical mechanism, the motion compressible turbulence is divided into shear and dilation processes, and the effect of dilation on the statistic and dynamics of turbulence is investigated. At first, a new compact-WENO scheme is developed to simulate the turbulent field accurately. The multi-scale properties of shear and dilation process and their effect on the particle transportation are analyzed. The effect of shock on turbulence field is investigated. It is proved that the energy flux due to convection and pressure are constant, then there exists the inertial range for kinetic energy cascade. It is also proved that both the shear and compressible parts of kinetic energy flux are constant in the inertial range. The contribution from subgrid scale stress and subgrid mass flux to the kinetic energy cascade is analyzed.
2015,
27: 032003.
doi: 10.11884/HPLPB201527.032003
Abstract:
Wigner distribution function method includes diffractive effects into the conventional ray tracing model of laser beams. However, there are some difficulties when using this method in hydra-dynamics codes. Wigner distribution function method needs a large number of laser rays to describe laser energy distribution in phase space, which results in efficiency reduction in hydra-dynamic simulations. This paper proposes a phenomenal model which is based on Wigner distribution function. This model can describe the macroscopical intensity distribution of practical laser beams on positions at and off the focal spot. And the continuous phase plate (CPP) can also be described in this model.
Wigner distribution function method includes diffractive effects into the conventional ray tracing model of laser beams. However, there are some difficulties when using this method in hydra-dynamics codes. Wigner distribution function method needs a large number of laser rays to describe laser energy distribution in phase space, which results in efficiency reduction in hydra-dynamic simulations. This paper proposes a phenomenal model which is based on Wigner distribution function. This model can describe the macroscopical intensity distribution of practical laser beams on positions at and off the focal spot. And the continuous phase plate (CPP) can also be described in this model.
2015,
27: 032004.
doi: 10.11884/HPLPB201527.032004
Abstract:
This paper presents our study of stimulated backward Raman scattering (SRS) and stimulated backward Brillouin scattering (SBS) instabilities, which appeared when the pump laser passed through the hohlraum plasma in the indirect driven inertial confinement fusion (ICF). It mainly introduces the physical model of the spectral analysis code in detail and the simulated processes of SRS and SBS under different plasma parameter conditions. Influence of hohlraum plasma parameter on spectral characteristics of SRS and SBS are analyzed, and the beneficial parameters to restrain the instabilities are presented, which provide references to the relevant target design.
This paper presents our study of stimulated backward Raman scattering (SRS) and stimulated backward Brillouin scattering (SBS) instabilities, which appeared when the pump laser passed through the hohlraum plasma in the indirect driven inertial confinement fusion (ICF). It mainly introduces the physical model of the spectral analysis code in detail and the simulated processes of SRS and SBS under different plasma parameter conditions. Influence of hohlraum plasma parameter on spectral characteristics of SRS and SBS are analyzed, and the beneficial parameters to restrain the instabilities are presented, which provide references to the relevant target design.
2015,
27: 032005.
doi: 10.11884/HPLPB201527.032005
Abstract:
In this article, the compressing and forming mechanism of hot spot in the implosion of shock ignition is analyzed using the method of simulation. Firstly, the implosion of conventional central ignition is discussed. The hot spot experiences shock compression and inertial compression in conventional central ignition, and ignition is achieved mainly by inertial compression. Then, the implosion of shock ignition is analyzed in detail. Shock ignition is not a two-step scheme that the assembly of the fuel is separated from ignition. Ignition is simultaneous with assembly. The ignitor shock participates in the assembly and has little direct impact on the hot spot. Ignition is still mainly achieved by inertial compression in shock ignition. Finally, the physical mechanism of the hot spot pressure improvement is analyzed according to the hot spot pressure scaling law of inertial compression and the impact of shock collision on the shell. The improvement of hot spot pressure results from the enhancement of shell density due to the collision of the ignitor shock and the return shock in the shell.
In this article, the compressing and forming mechanism of hot spot in the implosion of shock ignition is analyzed using the method of simulation. Firstly, the implosion of conventional central ignition is discussed. The hot spot experiences shock compression and inertial compression in conventional central ignition, and ignition is achieved mainly by inertial compression. Then, the implosion of shock ignition is analyzed in detail. Shock ignition is not a two-step scheme that the assembly of the fuel is separated from ignition. Ignition is simultaneous with assembly. The ignitor shock participates in the assembly and has little direct impact on the hot spot. Ignition is still mainly achieved by inertial compression in shock ignition. Finally, the physical mechanism of the hot spot pressure improvement is analyzed according to the hot spot pressure scaling law of inertial compression and the impact of shock collision on the shell. The improvement of hot spot pressure results from the enhancement of shell density due to the collision of the ignitor shock and the return shock in the shell.
2015,
27: 032006.
doi: 10.11884/HPLPB201527.032006
Abstract:
Due to the fuel surrounded by a high-Z pusher, the double-shell target differs from the cryogenic single-shell case, and it requires volume ignition of the whole fuel. In the paper, the ignition condition for the fuel surrounded by a high-Z pusher is analyzed, and an indirect-drive cryogenic double-shell ignition target is designed and analyzed, which releases a comparable energy to the hot-spot ignition target to be performed at National Ignition Facility (NIF). The collision between the outer and inner shell is the key in the energy transport. By adjusting the ratio of the mass between the two shells, the efficiency of the energy from the outer shell to the inner shell can be highly elevated, with a purpose of reducing the size of the target and the required energy to achieve ignition. For the double-shell ignition, a new preheating mechanism by the radiative shock is pointed out, which can help stabilize the Rayleigh-Taylor (RT) instability occurring at the outer surface of the inner shell. The preheat of radiative shock, as a potential effect in double-shell target, should be seriously realized and underlined.
Due to the fuel surrounded by a high-Z pusher, the double-shell target differs from the cryogenic single-shell case, and it requires volume ignition of the whole fuel. In the paper, the ignition condition for the fuel surrounded by a high-Z pusher is analyzed, and an indirect-drive cryogenic double-shell ignition target is designed and analyzed, which releases a comparable energy to the hot-spot ignition target to be performed at National Ignition Facility (NIF). The collision between the outer and inner shell is the key in the energy transport. By adjusting the ratio of the mass between the two shells, the efficiency of the energy from the outer shell to the inner shell can be highly elevated, with a purpose of reducing the size of the target and the required energy to achieve ignition. For the double-shell ignition, a new preheating mechanism by the radiative shock is pointed out, which can help stabilize the Rayleigh-Taylor (RT) instability occurring at the outer surface of the inner shell. The preheat of radiative shock, as a potential effect in double-shell target, should be seriously realized and underlined.
2015,
27: 032007.
doi: 10.11884/HPLPB201527.032007
Abstract:
This paper introduces the radiation-hydrodynamic code LARED-Integration, including its physical background, model equations, numerical algorithms and numerical results. The code is developed by Institute of Applied Physics and Computational Mathematics (IAPCM) and mainly implemented to simulate the whole process of the indirect-drive laser inertial confinement fusion (ICF). The code can also be used to study the direct-drive laser fusion process and the radiation-drive capsule implosion process. Compared with the experimental data and the numerical results of the 1D radiation-hydrodynamic code, the reliability of the LARED-Integration code is validated. The numerical simulation of the NIF ignition target is realized by the LARED-Integration code and this code is widely used in the physical research of ICF now.
This paper introduces the radiation-hydrodynamic code LARED-Integration, including its physical background, model equations, numerical algorithms and numerical results. The code is developed by Institute of Applied Physics and Computational Mathematics (IAPCM) and mainly implemented to simulate the whole process of the indirect-drive laser inertial confinement fusion (ICF). The code can also be used to study the direct-drive laser fusion process and the radiation-drive capsule implosion process. Compared with the experimental data and the numerical results of the 1D radiation-hydrodynamic code, the reliability of the LARED-Integration code is validated. The numerical simulation of the NIF ignition target is realized by the LARED-Integration code and this code is widely used in the physical research of ICF now.
2015,
27: 032008.
doi: 10.11884/HPLPB201527.032008
Abstract:
Using quantum molecular dynamic simulations, we studied the molecular dissociation and the equations of states of hydrogen and its isotopes under extreme conditions, and provided fitting parameters. By introducing the first order quantum corrections to the molecular and atomic fluid motions, the isotopic nuclear effect was discussed, and the difference of the dissociation ratio between hydrogen and deuterium was found. The Hugoniot curve was obtained according to the first principle equations of states, and the results were accordant with gas gun, chemical explosive, Z-pinch, and high power laser experiments. The isotopic effects appeared in the Hugoniot data for hydrogen and deuterium were also shown and discussed.
Using quantum molecular dynamic simulations, we studied the molecular dissociation and the equations of states of hydrogen and its isotopes under extreme conditions, and provided fitting parameters. By introducing the first order quantum corrections to the molecular and atomic fluid motions, the isotopic nuclear effect was discussed, and the difference of the dissociation ratio between hydrogen and deuterium was found. The Hugoniot curve was obtained according to the first principle equations of states, and the results were accordant with gas gun, chemical explosive, Z-pinch, and high power laser experiments. The isotopic effects appeared in the Hugoniot data for hydrogen and deuterium were also shown and discussed.
2015,
27: 032009.
doi: 10.11884/HPLPB201527.032009
Abstract:
A series of ARTI experiments have been performed in Shenguang Ⅱ(SGⅡ) laser facility of China. The simulation results from the LARED-S code for the planar foil trajectory experiment indicate that the energy flux at the hohlraum wall is obviously less than that at the laser entrance hole (LEH). Furthermore, the non-Planckian spectra of X-ray source can affect the dynamics of the foil flight and the perturbation growth. The images of evident growth of the ARTI initiated by a small-amplitude perturbation and the spike-bubble pattern initiated by large-amplitude perturbation were observed. The data of the growth of the second and the third harmonics were also obtained by increasing the spatial resolution in the experiments. The simulation results are in general consistent with the experimental results. The reliability of the LARRED-S code has been tested and validated through the comparison with the experiment results.
A series of ARTI experiments have been performed in Shenguang Ⅱ(SGⅡ) laser facility of China. The simulation results from the LARED-S code for the planar foil trajectory experiment indicate that the energy flux at the hohlraum wall is obviously less than that at the laser entrance hole (LEH). Furthermore, the non-Planckian spectra of X-ray source can affect the dynamics of the foil flight and the perturbation growth. The images of evident growth of the ARTI initiated by a small-amplitude perturbation and the spike-bubble pattern initiated by large-amplitude perturbation were observed. The data of the growth of the second and the third harmonics were also obtained by increasing the spatial resolution in the experiments. The simulation results are in general consistent with the experimental results. The reliability of the LARRED-S code has been tested and validated through the comparison with the experiment results.
2015,
27: 032010.
doi: 10.11884/HPLPB201527.032010
Abstract:
Energy deposition of ultra-intense laser driven fast electrons into the highly compressed fuel core plasmas is of great importance in assessing the overall coupling efficiency in fast ignition scheme. In this paper, a relativistic kinetic model is established based on fundamental principles of plasma collisions to explore the energy deposition process. The relativistic Fokker-Planck equation is derived, including both the binary collision and the contribution from plasma collective response. It is formulated in a differential form with the help of analogous Rosenbluth potentials. Its explicit expression in three-dimensional momentum space is obtained via spherical harmonics expansion method, in which only simple differentiations and integrations are involved. Corresponding numerical algorithms are developed as well as the kinetic code. Typical fast ignition physical cases are presented, and it is used to make a preliminary analysis for the coming FI experiments in Shengguang Ⅱ laser facility.
Energy deposition of ultra-intense laser driven fast electrons into the highly compressed fuel core plasmas is of great importance in assessing the overall coupling efficiency in fast ignition scheme. In this paper, a relativistic kinetic model is established based on fundamental principles of plasma collisions to explore the energy deposition process. The relativistic Fokker-Planck equation is derived, including both the binary collision and the contribution from plasma collective response. It is formulated in a differential form with the help of analogous Rosenbluth potentials. Its explicit expression in three-dimensional momentum space is obtained via spherical harmonics expansion method, in which only simple differentiations and integrations are involved. Corresponding numerical algorithms are developed as well as the kinetic code. Typical fast ignition physical cases are presented, and it is used to make a preliminary analysis for the coming FI experiments in Shengguang Ⅱ laser facility.
2015,
27: 032011.
doi: 10.11884/HPLPB201527.032011
Abstract:
Hohlraum radiation flux is the source of the capsule implosion in the indirect drive fusion, which strongly affects the capsule compression properties. It is very important to study the angular distribution of the hohlraum radiation temperature in order to understand the radiation properties inside the hohlraum. In this work, the angular distribution of the hohlraum radiation temperature is studied through theoretical analysis and multi-group radiation transfer simulations with LARED. It is found that the angular distribution of the radiation temperature is mainly determined by the ratio of the radiation flux between the hot spot and non-spot region, the ratio of the hot spot area in the detected line of sight, and the component of the volume emission. The theoretical analysis agrees very well with the LARED simulation in the two dimensional laser cone case. It is found that the two dimensional LARED simulation can be effectively used to study the angular distribution of the radiation temperature in the SGIII-P hohlraum experiments with three dimensional laser spot structures. An improved method is proposed to measure the angular distribution of the radiation temperature with more significant variation of the radiation temperature.
Hohlraum radiation flux is the source of the capsule implosion in the indirect drive fusion, which strongly affects the capsule compression properties. It is very important to study the angular distribution of the hohlraum radiation temperature in order to understand the radiation properties inside the hohlraum. In this work, the angular distribution of the hohlraum radiation temperature is studied through theoretical analysis and multi-group radiation transfer simulations with LARED. It is found that the angular distribution of the radiation temperature is mainly determined by the ratio of the radiation flux between the hot spot and non-spot region, the ratio of the hot spot area in the detected line of sight, and the component of the volume emission. The theoretical analysis agrees very well with the LARED simulation in the two dimensional laser cone case. It is found that the two dimensional LARED simulation can be effectively used to study the angular distribution of the radiation temperature in the SGIII-P hohlraum experiments with three dimensional laser spot structures. An improved method is proposed to measure the angular distribution of the radiation temperature with more significant variation of the radiation temperature.
2015,
27: 032012.
doi: 10.11884/HPLPB201527.032012
Abstract:
Laser and plasma interaction (LPI) and Rayleigh-Taylor instability (RTI) are two main ingredients affecting the success of ignition. The gas fill near the Au wall along the inner laser cone is the main region where SRS instabilities occur. At this region, pressure balance and energy balance between the inside and the outside of inner laser cone path are obtained. A plasma scaling model in ignition hohlraum of ICF is developed. Considering the scaling formula in capsule, an index is proposed which describes the stability performance. Designing of ignition targets is directed by using this index to obtain more margin for LPI and RTI.
Laser and plasma interaction (LPI) and Rayleigh-Taylor instability (RTI) are two main ingredients affecting the success of ignition. The gas fill near the Au wall along the inner laser cone is the main region where SRS instabilities occur. At this region, pressure balance and energy balance between the inside and the outside of inner laser cone path are obtained. A plasma scaling model in ignition hohlraum of ICF is developed. Considering the scaling formula in capsule, an index is proposed which describes the stability performance. Designing of ignition targets is directed by using this index to obtain more margin for LPI and RTI.
2015,
27: 032013.
doi: 10.11884/HPLPB201527.032013
Abstract:
In the field of indirect-drive inertial-confinement-fusion, to acquire high spatial resolution X-ray radiation images is the foundation for hydrodynamic instabilities and imploded process researches. Kirkpatrick-Baez (KB) microscope, which is based on the principles of grazing-incidence X-ray imaging, is an X-ray diagnosis device presenting an extra-high spatial resolution and a big total solid angle of collection. The KB microscope has been an international key X-ray diagnosis device on ICF facilities. We have investigated KB devices on SG-Ⅱ and SG-Ⅲ prototype facilities and made remarkable progresses on optical design, optical component preparation and assemblage technology of objective mirrors. A large object-field KB microscope and a multi-energy KB microscope have been developed. These KB microscopes have been applied in the hydrodynamic instabilities and implosion experiments, and performed high-resolution high-magnification images of key physical data for laser-fusion plasma research.
In the field of indirect-drive inertial-confinement-fusion, to acquire high spatial resolution X-ray radiation images is the foundation for hydrodynamic instabilities and imploded process researches. Kirkpatrick-Baez (KB) microscope, which is based on the principles of grazing-incidence X-ray imaging, is an X-ray diagnosis device presenting an extra-high spatial resolution and a big total solid angle of collection. The KB microscope has been an international key X-ray diagnosis device on ICF facilities. We have investigated KB devices on SG-Ⅱ and SG-Ⅲ prototype facilities and made remarkable progresses on optical design, optical component preparation and assemblage technology of objective mirrors. A large object-field KB microscope and a multi-energy KB microscope have been developed. These KB microscopes have been applied in the hydrodynamic instabilities and implosion experiments, and performed high-resolution high-magnification images of key physical data for laser-fusion plasma research.
2015,
27: 032014.
doi: 10.11884/HPLPB201527.032014
Abstract:
Hohlraum physics is fundamental to the indirect drive inertial fusion. The ultimate goal of laser-driven hohlraum is to create a radiation environment that ablatively implodes a capsule to ignite and burn. To obtain high fusion yield with minimum laser energy, the hohlraum radiation drive must meet both the high X-ray conversion and excellent uniformity. By optimizing the hohlraum structures and materials, the hohlraum performance could be improved in flux intensity, uniformity and spectrum. The hohlraum physics study focuses on the laser propagation through the underdense plasma, x-ray conversion by the laser interacting with the high-Z material and X-ray heating of high-Z walls. All of these issues are important for understanding the hohlraum. On the Shenguang-Ⅲ prototype laser facility, extensive experiments have been performed to characterize laser-heated hohlraum. We have demonstrated good understanding of the hohlraum energetics and radiation feature. Experimental study on vacuum hohlraum energetics obtains the scaling of the scattered light and radiation temperature with laser energy and hohlraum size. Gas-filled hohlraum impedes the motion of ablated wall plasma with the low-density, low-Z gas plasma, and exhibits a reduction of Au M-band flux that might adversely preheat the capsule. Several quantitative studies that concentrate on the specific regions inside the hohlraum have been performed. The laser spot movement with different flux limiter according to electron heat conduction has been investigated. The movement of laser heated corona plasma could be controlled by varying initial gas density. The ratio of the X-ray emission between the laser spot and the reemitting wall was measured in the same shot, which might contribute to the optimization of the hohlraum flux symmetry.
Hohlraum physics is fundamental to the indirect drive inertial fusion. The ultimate goal of laser-driven hohlraum is to create a radiation environment that ablatively implodes a capsule to ignite and burn. To obtain high fusion yield with minimum laser energy, the hohlraum radiation drive must meet both the high X-ray conversion and excellent uniformity. By optimizing the hohlraum structures and materials, the hohlraum performance could be improved in flux intensity, uniformity and spectrum. The hohlraum physics study focuses on the laser propagation through the underdense plasma, x-ray conversion by the laser interacting with the high-Z material and X-ray heating of high-Z walls. All of these issues are important for understanding the hohlraum. On the Shenguang-Ⅲ prototype laser facility, extensive experiments have been performed to characterize laser-heated hohlraum. We have demonstrated good understanding of the hohlraum energetics and radiation feature. Experimental study on vacuum hohlraum energetics obtains the scaling of the scattered light and radiation temperature with laser energy and hohlraum size. Gas-filled hohlraum impedes the motion of ablated wall plasma with the low-density, low-Z gas plasma, and exhibits a reduction of Au M-band flux that might adversely preheat the capsule. Several quantitative studies that concentrate on the specific regions inside the hohlraum have been performed. The laser spot movement with different flux limiter according to electron heat conduction has been investigated. The movement of laser heated corona plasma could be controlled by varying initial gas density. The ratio of the X-ray emission between the laser spot and the reemitting wall was measured in the same shot, which might contribute to the optimization of the hohlraum flux symmetry.
2015,
27: 032015.
doi: 10.11884/HPLPB201527.032015
Abstract:
In the research of laser indirect-drive inertial confinement fusion, the capsule is imploded symmetrically using radiative ablation. Then, the implosion kinetic energy is converted into the hotspot thermal energy in the deceleration phase so as to achieve the ignition condition and the resulting burn propagation. According to current knowledge, the most important factors that determine the implosion performance are the implosion symmetry, adiabatic factor, implosion velocity, and mix. The purpose of the experimental studies of the implosion physics is to develop the methods that can quantitatively characterize these factors, to investigate the scaling laws of these factors as the design parameters are changed, and to establish the ways to tune these factors. Considering the implosion symmetry, Bi sphere reemission experiments were carried out in order to characterize the incident flux asymmetry in the first 2 ns of the ignition pulse. With respect to the implosion velocity, the platform of homochromatic stream-line using spherical bent crystal was developed to measure the implosion velocity and the remaining mass. In the subject of mix, we performed implosion experiment using the capsule of doped inner layer, and ring-shaped images were obtained. Finally, comprehensive implosion experiments using DT gas were conducted on SGⅡ and SGⅢ prototype laser facilities. The correlations between neutron yield and initial target parameters were studied.
In the research of laser indirect-drive inertial confinement fusion, the capsule is imploded symmetrically using radiative ablation. Then, the implosion kinetic energy is converted into the hotspot thermal energy in the deceleration phase so as to achieve the ignition condition and the resulting burn propagation. According to current knowledge, the most important factors that determine the implosion performance are the implosion symmetry, adiabatic factor, implosion velocity, and mix. The purpose of the experimental studies of the implosion physics is to develop the methods that can quantitatively characterize these factors, to investigate the scaling laws of these factors as the design parameters are changed, and to establish the ways to tune these factors. Considering the implosion symmetry, Bi sphere reemission experiments were carried out in order to characterize the incident flux asymmetry in the first 2 ns of the ignition pulse. With respect to the implosion velocity, the platform of homochromatic stream-line using spherical bent crystal was developed to measure the implosion velocity and the remaining mass. In the subject of mix, we performed implosion experiment using the capsule of doped inner layer, and ring-shaped images were obtained. Finally, comprehensive implosion experiments using DT gas were conducted on SGⅡ and SGⅢ prototype laser facilities. The correlations between neutron yield and initial target parameters were studied.
2015,
27: 032016.
doi: 10.11884/HPLPB201527.032016
Abstract:
In laser indirect-driven inertial-confinement-fusion (ICF), the capsules with multi-layered structure are subjected to hydrodynamic instabilities. Rayleigh-Taylor instability growth at the ablation front and the interface between the DT ice and central gas plays a key role in the success of the fusion ignition. A series of radiation-driven ablation-front RT growth experiments were conducted on Shenguang Ⅱ laser facility. Face-on radiographies were obtained for an extensive set of conditions: different initial amplitude (0.3, 0.44, 1.4, and 2.7 m), different perturbation wavelengths (20, 30, 50, and 72m), and different materials (C50H47Br3, C50H44Br6, C8H8). The onset of second and third harmonics and their growth were well observed in the experiments. The experimental results provide useful database for the validation of our hydrocode simulation.
In laser indirect-driven inertial-confinement-fusion (ICF), the capsules with multi-layered structure are subjected to hydrodynamic instabilities. Rayleigh-Taylor instability growth at the ablation front and the interface between the DT ice and central gas plays a key role in the success of the fusion ignition. A series of radiation-driven ablation-front RT growth experiments were conducted on Shenguang Ⅱ laser facility. Face-on radiographies were obtained for an extensive set of conditions: different initial amplitude (0.3, 0.44, 1.4, and 2.7 m), different perturbation wavelengths (20, 30, 50, and 72m), and different materials (C50H47Br3, C50H44Br6, C8H8). The onset of second and third harmonics and their growth were well observed in the experiments. The experimental results provide useful database for the validation of our hydrocode simulation.
2015,
27: 032017.
doi: 10.11884/HPLPB201527.032017
Abstract:
Compared with central ignition of laser fusion, fast ignition separates compression and ignition thus it can relax the requirements for the implosion symmetry and the driven energy. Indirect drive pre-compression of cone-in-shell target for fast ignition was performed on Shenguang Ⅱ laser facility. The temporal evolution of the target was observed by the X-ray backlight framed camera. The density and areal density of the compressed fuel which were obtained from the backlight figures are 30 g/cm3 and 50 mg/cm2 separately. To minimize the mixing of the compressed fuel and cone high-Z vapor produced by the M-line emission from the gold holhraum, a CH foil was coated on the full outer surface of the cone. Experimental results and simulation results demonstrated that the coated CH foil could minimize the mixing effectively.
Compared with central ignition of laser fusion, fast ignition separates compression and ignition thus it can relax the requirements for the implosion symmetry and the driven energy. Indirect drive pre-compression of cone-in-shell target for fast ignition was performed on Shenguang Ⅱ laser facility. The temporal evolution of the target was observed by the X-ray backlight framed camera. The density and areal density of the compressed fuel which were obtained from the backlight figures are 30 g/cm3 and 50 mg/cm2 separately. To minimize the mixing of the compressed fuel and cone high-Z vapor produced by the M-line emission from the gold holhraum, a CH foil was coated on the full outer surface of the cone. Experimental results and simulation results demonstrated that the coated CH foil could minimize the mixing effectively.
2015,
27: 032018.
doi: 10.11884/HPLPB201527.032018
Abstract:
By comparing and analyzing various frequency conversion schemes, a compatible harmonic generation system has been designed. With type-Ⅱ-type-Ⅱ crystal combination configuration, polarization mismatch third harmonic generation and type-Ⅱ orthogonal quadrate second harmonic generation can be quickly switched. The thicknesses were optimized to be 10mm for both crystals by numerical simulation method, as a result, the requirements of high efficiency for long pulse with low intensity, as well as high stability for short pulse with high intensity, can be satisfied.
By comparing and analyzing various frequency conversion schemes, a compatible harmonic generation system has been designed. With type-Ⅱ-type-Ⅱ crystal combination configuration, polarization mismatch third harmonic generation and type-Ⅱ orthogonal quadrate second harmonic generation can be quickly switched. The thicknesses were optimized to be 10mm for both crystals by numerical simulation method, as a result, the requirements of high efficiency for long pulse with low intensity, as well as high stability for short pulse with high intensity, can be satisfied.
2015,
27: 032019.
doi: 10.11884/HPLPB201527.032019
Abstract:
In Thomson scattering experiment on SG-Ⅱ laser facility, X-ray radiation produced by laser interaction with Au hohlraum was used to heat the Fe/Al sample. The scattering spectra of the probe laser beam were measured at 90. The self-emission from the sample plasma was also recorded. Analyzing and fitting these two spectra, the average electron temperature was 360 eV, and the ionization degree of Fe was 18.8.
In Thomson scattering experiment on SG-Ⅱ laser facility, X-ray radiation produced by laser interaction with Au hohlraum was used to heat the Fe/Al sample. The scattering spectra of the probe laser beam were measured at 90. The self-emission from the sample plasma was also recorded. Analyzing and fitting these two spectra, the average electron temperature was 360 eV, and the ionization degree of Fe was 18.8.
2015,
27: 032020.
doi: 10.11884/HPLPB201527.032020
Abstract:
With the safety requirements of detectors in the gas hohlraum experiments, a technique of pulsed bias application on X-ray diodes is studied preliminarily. A new synchronization method is presented based on the signal generator and the 8 ps laser equipment. And the technology of X-ray diodes with pulsed bias is proved by experiments on the laser equipment. The differences of rising time and FWHM between the detector with DC and pulsed bias voltage are no more than 10%. Temporal performances of X-ray diodes with pulsed bias are in agreement with one of diodes with DC bias. The results show that application of pulsed bias on X-Ray Diodes is technically feasible. The main requirements of pulsed high-voltage power, is given at the end. The pulse width should be 110 s and the time when the voltage is unloaded should be 2.11 ns after zero time.
With the safety requirements of detectors in the gas hohlraum experiments, a technique of pulsed bias application on X-ray diodes is studied preliminarily. A new synchronization method is presented based on the signal generator and the 8 ps laser equipment. And the technology of X-ray diodes with pulsed bias is proved by experiments on the laser equipment. The differences of rising time and FWHM between the detector with DC and pulsed bias voltage are no more than 10%. Temporal performances of X-ray diodes with pulsed bias are in agreement with one of diodes with DC bias. The results show that application of pulsed bias on X-Ray Diodes is technically feasible. The main requirements of pulsed high-voltage power, is given at the end. The pulse width should be 110 s and the time when the voltage is unloaded should be 2.11 ns after zero time.
2015,
27: 032021.
doi: 10.11884/HPLPB201527.032021
Abstract:
The titanium hohlraum as a bright X-ray source was explored on the Shenguang-Ⅲ prototype laser facility. It shows that the multi-keV X-rays are mainly generated near the cylinder axis. The multi-keV X-ray emission region and the duration increase with the increase of the hohlraum inner diameter, but the X-ray flux decreases, thus the optimal hohlraum inner diameter is in the range of 1000-1300 m for Shenguang-Ⅲ prototype laser facility. The presence of the bottom foil for the hohlraum can enhance the X-ray emission. The maximum X-ray conversion efficiency of the titanium hohlraums is 4.7% in 4 space, which is larger than that of the solid planar target.
The titanium hohlraum as a bright X-ray source was explored on the Shenguang-Ⅲ prototype laser facility. It shows that the multi-keV X-rays are mainly generated near the cylinder axis. The multi-keV X-ray emission region and the duration increase with the increase of the hohlraum inner diameter, but the X-ray flux decreases, thus the optimal hohlraum inner diameter is in the range of 1000-1300 m for Shenguang-Ⅲ prototype laser facility. The presence of the bottom foil for the hohlraum can enhance the X-ray emission. The maximum X-ray conversion efficiency of the titanium hohlraums is 4.7% in 4 space, which is larger than that of the solid planar target.
2015,
27: 032022.
doi: 10.11884/HPLPB201527.032022
Abstract:
This paper mainly introduced some researches about calibration of scintillatorssensitivity using standard radio -active sources 241Am, 133Ba and 152Eu in Beijing Institute of Atomic Physics. As a scintillator could be used for single photon counting, are developed a new method to calibrate a scintillators sensitivity by measuring detectors' charge spectrum with radioactive sources' incidence. The experiment also calibrated QDC(quantity-to-digital convertor), and got the results of sensitivity for Filter-Fluorescer spectrometer in ICF experiments. The data's uncertainty (10%) was lower than that with traditional methods (15%), and calibration energy range increased up to more than 100 keV. Finally, we compared experimental data with Geant4 simulating results, and they were in good accordance.
This paper mainly introduced some researches about calibration of scintillatorssensitivity using standard radio -active sources 241Am, 133Ba and 152Eu in Beijing Institute of Atomic Physics. As a scintillator could be used for single photon counting, are developed a new method to calibrate a scintillators sensitivity by measuring detectors' charge spectrum with radioactive sources' incidence. The experiment also calibrated QDC(quantity-to-digital convertor), and got the results of sensitivity for Filter-Fluorescer spectrometer in ICF experiments. The data's uncertainty (10%) was lower than that with traditional methods (15%), and calibration energy range increased up to more than 100 keV. Finally, we compared experimental data with Geant4 simulating results, and they were in good accordance.
2015,
27: 032023.
doi: 10.11884/HPLPB201527.032023
Abstract:
Gold foam is one of the most important materials used in ICF experimental research, while it is hard to precisely measure the volume of the gold foam in its density characterization. Here we reported one method of volume reconstruction by using X ray CT technology. By using this method, the density of our prepared gold foam with abnormal surface is determined to be 978.68 mg/cm-3. To validate the accuracy of this method, comparison experiments between this method and a specific gravity bottle method have been performed by using plasticine samples. The results show that the relative error value is less than 1%.
Gold foam is one of the most important materials used in ICF experimental research, while it is hard to precisely measure the volume of the gold foam in its density characterization. Here we reported one method of volume reconstruction by using X ray CT technology. By using this method, the density of our prepared gold foam with abnormal surface is determined to be 978.68 mg/cm-3. To validate the accuracy of this method, comparison experiments between this method and a specific gravity bottle method have been performed by using plasticine samples. The results show that the relative error value is less than 1%.
2015,
27: 032024.
doi: 10.11884/HPLPB201527.032024
Abstract:
The main point of inertial-confinement-fusion (ICF) lies on the concept that via capsule-based implosion fuel inside capsules can be pressured to high temperature, high density plasma to approach ignition. Capsules, taken as fuel containers and being related with hydrodynamic instability and compression symmetry during implosion, must meet some specifications on spherecity, wall-thickness, surface smoothness and doping level. In order to meet these specifications, a series of techniques are developed, such as microencapsulation technique, degradable mandrel technique and glow discharge polymerization method and dried gel method to prepare polymer capsules and hollow glass microspheres respectively. ICF capsules are relatively small, light, and fragile and possess smooth surfaces which are subject to deface, different techniques are developed to characterize the capsule profile, component , doping level and fuel density, such as contact X-ray radiography, wall-mapping technique and white light interferometry. These techniques make the preparation and characterization of ICF capsules, such as multilayer polymer capsules, hollow glass microspheres, poly--methyl styrene mandrel capsules and doped glow discharge polymerization capsules advance quickly in these years. These capsules succeed in implosion experiments held on SG series facilities.
The main point of inertial-confinement-fusion (ICF) lies on the concept that via capsule-based implosion fuel inside capsules can be pressured to high temperature, high density plasma to approach ignition. Capsules, taken as fuel containers and being related with hydrodynamic instability and compression symmetry during implosion, must meet some specifications on spherecity, wall-thickness, surface smoothness and doping level. In order to meet these specifications, a series of techniques are developed, such as microencapsulation technique, degradable mandrel technique and glow discharge polymerization method and dried gel method to prepare polymer capsules and hollow glass microspheres respectively. ICF capsules are relatively small, light, and fragile and possess smooth surfaces which are subject to deface, different techniques are developed to characterize the capsule profile, component , doping level and fuel density, such as contact X-ray radiography, wall-mapping technique and white light interferometry. These techniques make the preparation and characterization of ICF capsules, such as multilayer polymer capsules, hollow glass microspheres, poly--methyl styrene mandrel capsules and doped glow discharge polymerization capsules advance quickly in these years. These capsules succeed in implosion experiments held on SG series facilities.
2015,
27: 032025.
doi: 10.11884/HPLPB201527.032025
Abstract:
The spatial distribution of deuterium (D2) or deuterium-tritium (DT) ice condensed inside the inertial confinement fusion (ICF) spherical cryogenic target is determined by the temperature field around the target. In the deuterium cryogenic target, the uniform liquid is formed by the vapor-liquid interfacial tension gradient resulting from the vertical temperature gradient, which counterbalances the gravity-induced fuel sagging. The uniform D2 solid layer can be achieved by slow cooling toward the triple point of D2. The layering process of D2 ice in a glow discharge polymer (GDP) shell of 1mm diameter and 30m thickness is demonstrated experimentally by imposing vertical temperature gradient combined with control of cooling rate. Calculated from the bright ring in backlit shadowgraphy, the average thickness and uniformity of D2 ice layer are 185.56 m and 80.2% respectively, the inner surface roughness of the ice from mode 2 to 100 in power spectrum is about 2.26 m.
The spatial distribution of deuterium (D2) or deuterium-tritium (DT) ice condensed inside the inertial confinement fusion (ICF) spherical cryogenic target is determined by the temperature field around the target. In the deuterium cryogenic target, the uniform liquid is formed by the vapor-liquid interfacial tension gradient resulting from the vertical temperature gradient, which counterbalances the gravity-induced fuel sagging. The uniform D2 solid layer can be achieved by slow cooling toward the triple point of D2. The layering process of D2 ice in a glow discharge polymer (GDP) shell of 1mm diameter and 30m thickness is demonstrated experimentally by imposing vertical temperature gradient combined with control of cooling rate. Calculated from the bright ring in backlit shadowgraphy, the average thickness and uniformity of D2 ice layer are 185.56 m and 80.2% respectively, the inner surface roughness of the ice from mode 2 to 100 in power spectrum is about 2.26 m.
2015,
27: 032026.
doi: 10.11884/HPLPB201527.032026
Abstract:
Low-density high-Z oxide aerogels are easy to shrink or crack due to the formation of the end group of metal-oxygen double bond in their precursors solution. Rare-earth oxide aerogels were prepared via coordination environment adjustment and dispersed inorganic sol-gel method. Lanthana-based aerogel and yttria-based aerogel exhibit good formability, and have the lowest densities of about 0.05 gcm-3 and 0.06 gcm-3 respectively. Their main compositions are hexagonal phase La(OH)3 and Y(OH)3 respectively, while the ions are coordinated with carboxyl groups in polyacrylic acid via bridge mode. Both the two kinds of aerogels are obviously composed of hierarchical microstructure, exhibiting similar spherical secondary structure but different primary structure composed of fiber and sheet/sphere, respectively. Their specific surface areas are 229.1 m2g-1 and 229.6 m2g-1, respectively. Given the low density and nanoscale homogeneity of the rare-earth oxide aerogels prepared via this method, they exhibit application potentials in the field of backlight targets.
Low-density high-Z oxide aerogels are easy to shrink or crack due to the formation of the end group of metal-oxygen double bond in their precursors solution. Rare-earth oxide aerogels were prepared via coordination environment adjustment and dispersed inorganic sol-gel method. Lanthana-based aerogel and yttria-based aerogel exhibit good formability, and have the lowest densities of about 0.05 gcm-3 and 0.06 gcm-3 respectively. Their main compositions are hexagonal phase La(OH)3 and Y(OH)3 respectively, while the ions are coordinated with carboxyl groups in polyacrylic acid via bridge mode. Both the two kinds of aerogels are obviously composed of hierarchical microstructure, exhibiting similar spherical secondary structure but different primary structure composed of fiber and sheet/sphere, respectively. Their specific surface areas are 229.1 m2g-1 and 229.6 m2g-1, respectively. Given the low density and nanoscale homogeneity of the rare-earth oxide aerogels prepared via this method, they exhibit application potentials in the field of backlight targets.
2015,
27: 032027.
doi: 10.11884/HPLPB201527.032027
Abstract:
Using low pressure plasma polymerization technology, glowing discharge polymer films were fabricated at different coating pressures. Surface roughness, chemistry structure and optical properties were measured by atomic force microscopy, infrared absorption spectroscopy and ultraviolet-visible transmittance spectroscopy, respectively. The results show that as the coating pressure increases, the surface roughness of the GDP film and content of the olefinic carbon bonds decrease, while the hydrogen and SP2 CH2 concentration and the optical band gap of GDP films increases.
Using low pressure plasma polymerization technology, glowing discharge polymer films were fabricated at different coating pressures. Surface roughness, chemistry structure and optical properties were measured by atomic force microscopy, infrared absorption spectroscopy and ultraviolet-visible transmittance spectroscopy, respectively. The results show that as the coating pressure increases, the surface roughness of the GDP film and content of the olefinic carbon bonds decrease, while the hydrogen and SP2 CH2 concentration and the optical band gap of GDP films increases.
2015,
27: 032028.
doi: 10.11884/HPLPB201527.032028
Abstract:
Taking advantage of low pressure plasma chemical vapor deposition technology, the hydrocarbon glow discharge polymer (GDP) and deuterated glow discharge polymer (D-GDP) films were fabricated by glow discharge polymerization technology. The deposition rates, the chemical structures and mechanical properties of films were studied by FTIR spectra, surface profiler and nano-indentation. The results show that the deposition rate of GDP/D-GDP almost linearly increases with the increase of gas flow, the deposition rate of GDP films is higher than that of D-GDP films. The cross-link degree of D-GDP films is lower than that in GDP films. The D-GDP films might be more favorable for IR heating on the DT ice of ICF target. The mechanical property of GDP is better than that of D-GDP.
Taking advantage of low pressure plasma chemical vapor deposition technology, the hydrocarbon glow discharge polymer (GDP) and deuterated glow discharge polymer (D-GDP) films were fabricated by glow discharge polymerization technology. The deposition rates, the chemical structures and mechanical properties of films were studied by FTIR spectra, surface profiler and nano-indentation. The results show that the deposition rate of GDP/D-GDP almost linearly increases with the increase of gas flow, the deposition rate of GDP films is higher than that of D-GDP films. The cross-link degree of D-GDP films is lower than that in GDP films. The D-GDP films might be more favorable for IR heating on the DT ice of ICF target. The mechanical property of GDP is better than that of D-GDP.
2015,
27: 032029.
doi: 10.11884/HPLPB201527.032029
Abstract:
Via measuring results of phase compatibility and interference effects between polystyrene (PS) and polyvinyl benzyl chloride (PVBCl), the influence on the phase separation status of the two substances in the cured film and shell from solution mixed with PS and PVBCl was studied using the infrared microscopic chemical image, and the phase separation of the two polymers of the microspheres obtained under different processing conditions was studied by the infrared microscopic chemical image. The results indicated that the established method can be used to analyze the phase separation of PS and PVBCl in the shell of microspheres by qualitative or semi-quantitative, and the large testing uncertainty caused by the interference effects in polymer microspheres, can be optimized at 40 ℃ because of the better phase separation of these two polymer substances. This study provides a method to investigate the conditions of preparation of heterogeneous dual hemispherical polymer, and to characterize the phase separation of polymer by infrared microscopic chemical image. However, this method affected by the spatial resolution is not suitable for the sample with size less than 6.25 m6.25 m.
Via measuring results of phase compatibility and interference effects between polystyrene (PS) and polyvinyl benzyl chloride (PVBCl), the influence on the phase separation status of the two substances in the cured film and shell from solution mixed with PS and PVBCl was studied using the infrared microscopic chemical image, and the phase separation of the two polymers of the microspheres obtained under different processing conditions was studied by the infrared microscopic chemical image. The results indicated that the established method can be used to analyze the phase separation of PS and PVBCl in the shell of microspheres by qualitative or semi-quantitative, and the large testing uncertainty caused by the interference effects in polymer microspheres, can be optimized at 40 ℃ because of the better phase separation of these two polymer substances. This study provides a method to investigate the conditions of preparation of heterogeneous dual hemispherical polymer, and to characterize the phase separation of polymer by infrared microscopic chemical image. However, this method affected by the spatial resolution is not suitable for the sample with size less than 6.25 m6.25 m.
2015,
27: 032030.
doi: 10.11884/HPLPB201527.032030
Abstract:
To research the effect of molecular weight on the solidification rates of the emulsion particles in the microencapsulation process of poly (-methyl styrene) (PAMS) hollow shells, three different kinds of PAMS with molecular weights 300, 440 and 800 kgmol-1 respectively as oil phase were further studied. In the curing process, the diameter of PAMS/FB droplets, the PAMS concentration and the evolution of FB diffusion flux under PVA and PAA solution were experimentally measured. The results show that the PAMS concentration increased slowly with the decreasing molecular weight. Especially, the summit of FB diffusion evolution flux achieved the minimum when the molecular weight of PAMS was 300 kgmol-1. Therefore, the curing time could be prolonged by reducing the molecular weight of PAMS and the diffusion rates of FB could be accordingly decreased, and during the key phase of the solidification process of double emulsions, the droplets could have enough time to adjust to obtain better sphericity.
To research the effect of molecular weight on the solidification rates of the emulsion particles in the microencapsulation process of poly (-methyl styrene) (PAMS) hollow shells, three different kinds of PAMS with molecular weights 300, 440 and 800 kgmol-1 respectively as oil phase were further studied. In the curing process, the diameter of PAMS/FB droplets, the PAMS concentration and the evolution of FB diffusion flux under PVA and PAA solution were experimentally measured. The results show that the PAMS concentration increased slowly with the decreasing molecular weight. Especially, the summit of FB diffusion evolution flux achieved the minimum when the molecular weight of PAMS was 300 kgmol-1. Therefore, the curing time could be prolonged by reducing the molecular weight of PAMS and the diffusion rates of FB could be accordingly decreased, and during the key phase of the solidification process of double emulsions, the droplets could have enough time to adjust to obtain better sphericity.
2015,
27: 032031.
doi: 10.11884/HPLPB201527.032031
Abstract:
A device is designed to deposit metals on double-shell targets. The plating mechanism is described in detail, as well as structure and function. The special structure of the tank make the growing speed of upper surface faster than that of the lower. Rotation and revolution of the micro spheres make the deposit grow uniformly. The special flow pattern of plating bath reduces the number of parameters, and make the process easy to control. Determinants of layer thickness and uniformity were researched. The results show that the new plating tank has a better performance than the old one. Layer thickness is determined by depositing time, metal density, solution density, equivalent density of the micro spheres.
A device is designed to deposit metals on double-shell targets. The plating mechanism is described in detail, as well as structure and function. The special structure of the tank make the growing speed of upper surface faster than that of the lower. Rotation and revolution of the micro spheres make the deposit grow uniformly. The special flow pattern of plating bath reduces the number of parameters, and make the process easy to control. Determinants of layer thickness and uniformity were researched. The results show that the new plating tank has a better performance than the old one. Layer thickness is determined by depositing time, metal density, solution density, equivalent density of the micro spheres.
2015,
27: 032032.
doi: 10.11884/HPLPB201527.032032
Abstract:
A new structure for the fast ignition target was presented, setting a flat tip in the front cone to avoid plasma escaping, and a micro-nanometer dot on centre of flat tip to emit thermal electron. The limited condition of Alfvn principle might arise when the array of micro-nano-meter-dot was fabricated on the tip-flap. An energy formula of thermal electron was presented, following multi-project to research to improve the structure and the performance.
A new structure for the fast ignition target was presented, setting a flat tip in the front cone to avoid plasma escaping, and a micro-nanometer dot on centre of flat tip to emit thermal electron. The limited condition of Alfvn principle might arise when the array of micro-nano-meter-dot was fabricated on the tip-flap. An energy formula of thermal electron was presented, following multi-project to research to improve the structure and the performance.
2015,
27: 032033.
doi: 10.11884/HPLPB201527.032033
Abstract:
To obtain the cleaning methods in high power laser system, the beampath cleanliness experiments and the effects of laser induced damage owing to contamination are studied. The numbers and components of the aerosols are analyzed using the commercial particle counters and SEM. The SiO2 film on K9 is put in the beampath for a certain time, and the transmittance spectra and the morphologies are studied. The laser induced damage threshold of the K9 glass is studied using the 1-on-1 method. The results show that the aerosols keep high concentrations about 7 class after one laser shot with the energy about 5000 J. In this environment, the transmittance of the film descends seriously (about 2.5%), and the aerosols moved onto the surface for clearance in the film. The laser induced damage threshold fluence descends linearly with the cleanliness level of the surface to the maximum decrease of about 10%. The dust and the metal particles are the main contaminations in the beampath, and the source of typical airborne molecular contaminations is discussed and the removal methods are suggested to prolong the life of optics.
To obtain the cleaning methods in high power laser system, the beampath cleanliness experiments and the effects of laser induced damage owing to contamination are studied. The numbers and components of the aerosols are analyzed using the commercial particle counters and SEM. The SiO2 film on K9 is put in the beampath for a certain time, and the transmittance spectra and the morphologies are studied. The laser induced damage threshold of the K9 glass is studied using the 1-on-1 method. The results show that the aerosols keep high concentrations about 7 class after one laser shot with the energy about 5000 J. In this environment, the transmittance of the film descends seriously (about 2.5%), and the aerosols moved onto the surface for clearance in the film. The laser induced damage threshold fluence descends linearly with the cleanliness level of the surface to the maximum decrease of about 10%. The dust and the metal particles are the main contaminations in the beampath, and the source of typical airborne molecular contaminations is discussed and the removal methods are suggested to prolong the life of optics.
2015,
27: 032034.
doi: 10.11884/HPLPB201527.032034
Abstract:
Two different laser conditioning methods including n% raster scanning and R-on-1 test were conducted to investigate the conditioning effect of 532 nm high reflectors. The Nd: YAG second harmonic laser was employed to do 1-on-1 test for 532 nm high reflectors prepared by electron beam evaporation. Afterwards, n% raster scanning and R-on-1 test were done for comparison. The analysis of damage probability and damage morphologies shows that, laser conditioning could eliminate the defects with low threshold in coatings, thus enhancing the laser damage threshold of 532 nm high reflectors (by 38% and 30% in n% raster scanning and k-on-1 test, respectively).
Two different laser conditioning methods including n% raster scanning and R-on-1 test were conducted to investigate the conditioning effect of 532 nm high reflectors. The Nd: YAG second harmonic laser was employed to do 1-on-1 test for 532 nm high reflectors prepared by electron beam evaporation. Afterwards, n% raster scanning and R-on-1 test were done for comparison. The analysis of damage probability and damage morphologies shows that, laser conditioning could eliminate the defects with low threshold in coatings, thus enhancing the laser damage threshold of 532 nm high reflectors (by 38% and 30% in n% raster scanning and k-on-1 test, respectively).
2015,
27: 032035.
doi: 10.11884/HPLPB201527.032035
Abstract:
High speed plasma jets are generated by ablating half-cylinder-shell targets with two laser bunches on Shenguang Ⅱ Laser Facility. Using optical and X-ray diagnostics, the parameters of the plasma jets have been measured. Propagating in vacuum, the jets are collimated. One-dimensional hydrodynamic simulation is used to indirectly calculate the jet velocity. The collimation of the jets may be attributed to the expansion cooling of plasma bubbles ablated by main laser pulses. Radiative cooling of the high-Z plasmas might collimate the plasma jets as well. Having some geometrical similarities with young stellar object (YSO) jets, the jets have potential application to simulating YSO jets in laboratories.
High speed plasma jets are generated by ablating half-cylinder-shell targets with two laser bunches on Shenguang Ⅱ Laser Facility. Using optical and X-ray diagnostics, the parameters of the plasma jets have been measured. Propagating in vacuum, the jets are collimated. One-dimensional hydrodynamic simulation is used to indirectly calculate the jet velocity. The collimation of the jets may be attributed to the expansion cooling of plasma bubbles ablated by main laser pulses. Radiative cooling of the high-Z plasmas might collimate the plasma jets as well. Having some geometrical similarities with young stellar object (YSO) jets, the jets have potential application to simulating YSO jets in laboratories.
2015,
27: 032036.
doi: 10.11884/HPLPB201527.032036
Abstract:
In order to overcome the space charge influence over the transport of the high-current particle beams in laser acceleration, we propose a new scheme to realize the acceleration of a neutral plasma block. It is carried out by injecting an ultraintense laser pulse with intensity about 1022 W/cm2 and pulse duration about 5T (T is laser period) upon two thin solid-density plasma blocks. By optimizing the plasma parameters, we have obtained an accelerated plasma block, which is almost neutral and propagates for a quite long distance in the space. The ion and electron energies are of GeV and 100 MeV magnitude respectively.
In order to overcome the space charge influence over the transport of the high-current particle beams in laser acceleration, we propose a new scheme to realize the acceleration of a neutral plasma block. It is carried out by injecting an ultraintense laser pulse with intensity about 1022 W/cm2 and pulse duration about 5T (T is laser period) upon two thin solid-density plasma blocks. By optimizing the plasma parameters, we have obtained an accelerated plasma block, which is almost neutral and propagates for a quite long distance in the space. The ion and electron energies are of GeV and 100 MeV magnitude respectively.
2015,
27: 032037.
doi: 10.11884/HPLPB201527.032037
Abstract:
The main active particles produced by excitation of dielectric barrier discharge plasma on air were analyzed with emission spectrometry, the evolution rules of the active particles were simulated with plasma kinetic model, and the chemical kinetics mechanism of O-atom assisted ignition was revealed via sensitivity analysis and reaction path analysis. The results show that the main excited particles of N2 and O2 are generated with excitation of plasma on air, and the excited particles increase with the increase of voltage which will be to rapidly convert into free radicals and O-atom is the largest concentration of free radicals, and that the ignition delay time decreases about an order of magnitude, the oxidized pathway of CH3 changes to HO2 and O-atom from O2 for auto-ignition, and the latter reaction rate is much faster, that is why O-atom decreases the ignition delay time.
The main active particles produced by excitation of dielectric barrier discharge plasma on air were analyzed with emission spectrometry, the evolution rules of the active particles were simulated with plasma kinetic model, and the chemical kinetics mechanism of O-atom assisted ignition was revealed via sensitivity analysis and reaction path analysis. The results show that the main excited particles of N2 and O2 are generated with excitation of plasma on air, and the excited particles increase with the increase of voltage which will be to rapidly convert into free radicals and O-atom is the largest concentration of free radicals, and that the ignition delay time decreases about an order of magnitude, the oxidized pathway of CH3 changes to HO2 and O-atom from O2 for auto-ignition, and the latter reaction rate is much faster, that is why O-atom decreases the ignition delay time.
2015,
27: 032038.
doi: 10.11884/HPLPB201527.032038
Abstract:
There is an important application for laser-driven plasma wakefield in electrons acceleration field. The idea of capillary plasma improving the effect of electron acceleration is put forward. Based on an analytical model of laser plasma wake, the interaction between laser and capillary plasma is investigated. It is shown that the amplitude of plasma wakefield in capillary is influenced by the radius of the capillary, and it rises with decreasing of the radius of capillary. With the same laser and plasma parameters, in capillary plasma these main physical quantities, such as the longitudinal scale of electron bubble, the peaks of electrostatic field and azimuthal magnetic field, increase 60% compared to that in unbound plasma. These results indicate that the plasma wake in capillary is in favor of electrons acceleration.
There is an important application for laser-driven plasma wakefield in electrons acceleration field. The idea of capillary plasma improving the effect of electron acceleration is put forward. Based on an analytical model of laser plasma wake, the interaction between laser and capillary plasma is investigated. It is shown that the amplitude of plasma wakefield in capillary is influenced by the radius of the capillary, and it rises with decreasing of the radius of capillary. With the same laser and plasma parameters, in capillary plasma these main physical quantities, such as the longitudinal scale of electron bubble, the peaks of electrostatic field and azimuthal magnetic field, increase 60% compared to that in unbound plasma. These results indicate that the plasma wake in capillary is in favor of electrons acceleration.
2015,
27: 032039.
doi: 10.11884/HPLPB201527.032039
Abstract:
In order to obtain focal spot size and spatial resolution of X-ray driven by the ultra-intense laser, a new method was designed to diagnose with a 0.2-m-thick knife-edge attached two different meshes, one copper mesh of 400 meshes and another nickel of 394 line pairs per centimeter. The X-ray was obtained by X-ray CCD. Tisapphire laser (1 J/40 fs/10 Hz) with an intensity of approximately 4.41018 W/cm2 shot the disc Cu target by repetition frequency. The experiment was carried out successfully on a 25 TW laser device at CAEP, in which the first focal spot and the X-ray image of the meshes were both obtained. The estimated focal spot of the X-ray was 43 m, and the estimated spatial resolution was 34 m. The results showed that the method of knife-edge and two meshes was suitable for the measurement of focal spot size of X-ray driven by ultra-intense laser.
In order to obtain focal spot size and spatial resolution of X-ray driven by the ultra-intense laser, a new method was designed to diagnose with a 0.2-m-thick knife-edge attached two different meshes, one copper mesh of 400 meshes and another nickel of 394 line pairs per centimeter. The X-ray was obtained by X-ray CCD. Tisapphire laser (1 J/40 fs/10 Hz) with an intensity of approximately 4.41018 W/cm2 shot the disc Cu target by repetition frequency. The experiment was carried out successfully on a 25 TW laser device at CAEP, in which the first focal spot and the X-ray image of the meshes were both obtained. The estimated focal spot of the X-ray was 43 m, and the estimated spatial resolution was 34 m. The results showed that the method of knife-edge and two meshes was suitable for the measurement of focal spot size of X-ray driven by ultra-intense laser.
2015,
27: 032040.
doi: 10.11884/HPLPB201527.032040
Abstract:
According to the characteristics of and application requirements for pulsed plasma, a time of flight mass spectrometry diagnosis system for pulsed plasma has been developed using orthogonal-injection, grid reflecting and two-stage space focusing method. The mass resolution, the range of detecting energy, and the time resolution are about 1690 (FWHM), 3-150 eV and about 0.45 s respectively. The important characters, such as ion mass spectrometry and ion energy distribution function, have been achieved by time of flight mass spectrometry researching and analyzing of typical pulsed plasma. The dominating components are Tin+ ions with different charge state, and the most probable energies of Ti+ and Ti2+ ions are nearly 23 eV and 48 eV respectively.
According to the characteristics of and application requirements for pulsed plasma, a time of flight mass spectrometry diagnosis system for pulsed plasma has been developed using orthogonal-injection, grid reflecting and two-stage space focusing method. The mass resolution, the range of detecting energy, and the time resolution are about 1690 (FWHM), 3-150 eV and about 0.45 s respectively. The important characters, such as ion mass spectrometry and ion energy distribution function, have been achieved by time of flight mass spectrometry researching and analyzing of typical pulsed plasma. The dominating components are Tin+ ions with different charge state, and the most probable energies of Ti+ and Ti2+ ions are nearly 23 eV and 48 eV respectively.
2015,
27: 032041.
doi: 10.11884/HPLPB201527.032041
Abstract:
In order to study the transmission of electromagnetic waves in the non-uniform plasma sheath, the Z Finite-Difference Time-Domain（Z-FDTD） numerical method is combined with experiments. Electromagnetic waves transmission characteristics experiments are carried out under L-band(1.575 GHz) in plasma with thicknesses of 2,4,6,8,10 cm. The attenuations of electromagnetic wave are 9，15.8，24.9，36.4，45.5 dB. The results agree well with simulation results.
In order to study the transmission of electromagnetic waves in the non-uniform plasma sheath, the Z Finite-Difference Time-Domain（Z-FDTD） numerical method is combined with experiments. Electromagnetic waves transmission characteristics experiments are carried out under L-band(1.575 GHz) in plasma with thicknesses of 2,4,6,8,10 cm. The attenuations of electromagnetic wave are 9，15.8，24.9，36.4，45.5 dB. The results agree well with simulation results.
