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Laser and Particle Beam Fusion|13 Article(s)
Using cylindrical implosions to investigate hydrodynamic instabilities in convergent geometry
J. P. Sauppe, S. Palaniyappan, E. N. Loomis, J. L. Kline, K. A. Flippo, and B. Srinivasan
Hydrodynamic instabilities such as the Rayleigh–Taylor (RT) and Richtmyer–Meshkov instabilities disrupt inertial confinement fusion (ICF) implosions through the growth of 3D perturbations. Growth of these 3D imperfections at the interfaces of an ICF capsule during implosion lead to mixing between materials that is detrimental to performance. These instabilities have been studied extensively in planar geometry, but such experiments lack the effects of convergence in spherical implosions. While several studies have been performed in spherical geometry, these often lack a direct means to measure perturbation growth. Experiments in cylindrical geometry include convergence effects while maintaining direct diagnostic access. Although cylinders have less compression than spheres, they do provide an excellent platform to validate modeling for convergent geometries. The problem with previous cylindrical implosion experiments was that the convergence ratios were limited to ～4. With the National Ignition Facility (NIF), larger cylindrical targets can be driven to convergences of 10–15 while maintaining a large enough final diameter to measure perturbation growth. This paper reviews the design process used to both benchmark radiation hydrodynamics codes and enable 1D post-processed simulations to explore design space to separate compression effects from acceleration/deceleration RT instability. Results from 1D simulations suggest that cylindrical implosions on the NIF can produce high-convergence experiments to validate RT instability growth for ICF implosions. Hydrodynamic instabilities such as the Rayleigh–Taylor (RT) and Richtmyer–Meshkov instabilities disrupt inertial confinement fusion (ICF) implosions through the growth of 3D perturbations. Growth of these 3D imperfections at the interfaces of an ICF capsule during implosion lead to mixing between materials that is detrimental to performance. These instabilities have been studied extensively in planar geometry, but such experiments lack the effects of convergence in spherical implosions. While several studies have been performed in spherical geometry, these often lack a direct means to measure perturbation growth. Experiments in cylindrical geometry include convergence effects while maintaining direct diagnostic access. Although cylinders have less compression than spheres, they do provide an excellent platform to validate modeling for convergent geometries. The problem with previous cylindrical implosion experiments was that the convergence ratios were limited to ～4. With the National Ignition Facility (NIF), larger cylindrical targets can be driven to convergences of 10–15 while maintaining a large enough final diameter to measure perturbation growth. This paper reviews the design process used to both benchmark radiation hydrodynamics codes and enable 1D post-processed simulations to explore design space to separate compression effects from acceleration/deceleration RT instability. Results from 1D simulations suggest that cylindrical implosions on the NIF can produce high-convergence experiments to validate RT instability growth for ICF implosions.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 6, 065403 (2019)
Visualizing the melting processes in ultrashort intense laser triggered gold mesh with high energy electron radiography
Zheng Zhou, Yu Fang, Han Chen, Yipeng Wu, Yingchao Du, Zimin Zhang, Yongtao Zhao, Ming Li, Chuanxiang Tang, and Wenhui Huang
High-energy electron radiography (HEER) is a promising diagnostic tool for high-energy-density physics, as an alternative to tools such as X/γ-ray shadowgraphy and high-energy proton radiography. Impressive progress has been made in the development and application of HEER in the past few years, and its potential for high-resolution imaging of static opaque objects has been proved. In this study, by taking advantage of the short pulse duration and tunable time structure of high-energy electron probes, time-resolved imaging measurements of high-energy-density gold irradiated by ultrashort intense laser pulses are performed. Phenomena at different time scales from picoseconds to microseconds are observed, thus proving the feasibility of this technique for imaging of static and dynamic objects. High-energy electron radiography (HEER) is a promising diagnostic tool for high-energy-density physics, as an alternative to tools such as X/γ-ray shadowgraphy and high-energy proton radiography. Impressive progress has been made in the development and application of HEER in the past few years, and its potential for high-resolution imaging of static opaque objects has been proved. In this study, by taking advantage of the short pulse duration and tunable time structure of high-energy electron probes, time-resolved imaging measurements of high-energy-density gold irradiated by ultrashort intense laser pulses are performed. Phenomena at different time scales from picoseconds to microseconds are observed, thus proving the feasibility of this technique for imaging of static and dynamic objects.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 6, 065402 (2019)
Plasma optics in the context of high intensity lasers
H. Peng, J.-R. Marquès, L. Lancia, F. Amiranoff, R. L. Berger, S. Weber, and C. Riconda
The use of plasmas provides a way to overcome the low damage threshold of classical solid-state based optical materials, which is the main limitation encountered in producing and manipulating intense and energetic laser pulses. Plasmas can directly amplify or alter the characteristics of ultra-short laser pulses via the three-wave coupling equations for parametric processes. The strong-coupling regime of Brillouin scattering (sc-SBS) is of particular interest: recent progress in this domain is presented here. This includes the role of the global phase in the spatio-temporal evolution of the three-wave coupled equations for backscattering that allows a description of the coupling dynamics and the various stages of amplification from the initial growth to the so-called self-similar regime. The understanding of the phase evolution allows control of the directionality of the energy transfer via the phase relation between the pulses. A scheme that exploits this coupling in order to use the plasma as a wave plate is also suggested. The use of plasmas provides a way to overcome the low damage threshold of classical solid-state based optical materials, which is the main limitation encountered in producing and manipulating intense and energetic laser pulses. Plasmas can directly amplify or alter the characteristics of ultra-short laser pulses via the three-wave coupling equations for parametric processes. The strong-coupling regime of Brillouin scattering (sc-SBS) is of particular interest: recent progress in this domain is presented here. This includes the role of the global phase in the spatio-temporal evolution of the three-wave coupled equations for backscattering that allows a description of the coupling dynamics and the various stages of amplification from the initial growth to the so-called self-similar regime. The understanding of the phase evolution allows control of the directionality of the energy transfer via the phase relation between the pulses. A scheme that exploits this coupling in order to use the plasma as a wave plate is also suggested.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 6, 065401 (2019)
Experimental study of residual activity induced in aluminum targets irradiated by high-energy heavy-ion beams: A comparison of experimental data and FLUKA simulations
Peter Katrík, Dieter H. H. Hoffmann, Edil Mustafin, and Ivan Strašík
A number of heavy-ion accelerators are either under construction (e.g., the Facility for Antiproton and Ion Research in Darmstadt and the High Intensity Accelerator Facility in China) or already in operation at many places worldwide. For these accelerators, activation of construction components due to beam loss, even during routine machine operation, is a serious issue, especially with the upcoming high-intensity facilities. Aluminum is one of the most commonly used construction materials in beam lines, collimators, and other components. Therefore, we report here on activation experiments on aluminum samples to verify and benchmark simulation codes. The analysis was performed by gamma spectroscopy of the irradiated targets. Our results on the induced activity measured in samples irradiated by uranium beams at 125 MeV/u and 200 MeV/u and a xenon beam at 300 MeV/u show activation levels significantly lower than those predicted by FLUKA simulations. A number of heavy-ion accelerators are either under construction (e.g., the Facility for Antiproton and Ion Research in Darmstadt and the High Intensity Accelerator Facility in China) or already in operation at many places worldwide. For these accelerators, activation of construction components due to beam loss, even during routine machine operation, is a serious issue, especially with the upcoming high-intensity facilities. Aluminum is one of the most commonly used construction materials in beam lines, collimators, and other components. Therefore, we report here on activation experiments on aluminum samples to verify and benchmark simulation codes. The analysis was performed by gamma spectroscopy of the irradiated targets. Our results on the induced activity measured in samples irradiated by uranium beams at 125 MeV/u and 200 MeV/u and a xenon beam at 300 MeV/u show activation levels significantly lower than those predicted by FLUKA simulations.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 5, 055403 (2019)
Analysis of three-dimensional effects in laser driven thin-shell capsule implosions
Rafael Ramis, Benoit Canaud, Mauro Temporal, Warren J. Garbett, and Franck Philippe
Three-dimensional (3D) hydrodynamic numerical simulations of laser driven thin-shell gas-filled microballoons have been carried out using the computer code MULTI-3D [Ramis et al., Phys. Plasmas 21, 082710 (2014)]. The studied configuration corresponds to experiments carried at the ORION laser facility [Hopps et al., Plasma Phys. Controlled Fusion 57, 064002 (2015)]. The MULTI-3D code solves single-temperature hydrodynamics, electron heat transport, and 3D ray tracing with inverse bremsstrahlung absorption on unstructured Lagrangian grids. Special emphasis has been placed on the genuine 3D effects that are inaccessible to calculations using simplified 1D or 2D geometries. These include the consequences of (i) a finite number of laser beams (10 in the experimental campaign), (ii) intensity irregularities in the beam cross-sectional profiles, (iii) laser beam misalignments, and (iv) power imbalance between beams. The consequences of these imperfections have been quantified by post-processing the numerical results in terms of capsule nonuniformities (synthetic emission and absorption images) and implosion efficiency (convergence ratio and neutron yield). Statistical analysis of these outcomes allows determination of the laser tolerances that guarantee a given level of target performance. Three-dimensional (3D) hydrodynamic numerical simulations of laser driven thin-shell gas-filled microballoons have been carried out using the computer code MULTI-3D [Ramis et al., Phys. Plasmas 21, 082710 (2014)]. The studied configuration corresponds to experiments carried at the ORION laser facility [Hopps et al., Plasma Phys. Controlled Fusion 57, 064002 (2015)]. The MULTI-3D code solves single-temperature hydrodynamics, electron heat transport, and 3D ray tracing with inverse bremsstrahlung absorption on unstructured Lagrangian grids. Special emphasis has been placed on the genuine 3D effects that are inaccessible to calculations using simplified 1D or 2D geometries. These include the consequences of (i) a finite number of laser beams (10 in the experimental campaign), (ii) intensity irregularities in the beam cross-sectional profiles, (iii) laser beam misalignments, and (iv) power imbalance between beams. The consequences of these imperfections have been quantified by post-processing the numerical results in terms of capsule nonuniformities (synthetic emission and absorption images) and implosion efficiency (convergence ratio and neutron yield). Statistical analysis of these outcomes allows determination of the laser tolerances that guarantee a given level of target performance.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 5, 055402 (2019)
Fuel-ion diffusion in shock-driven inertial confinement fusion implosions
Hong Sio, Chikang Li, Cody E. Parker, Brandon Lahmann, Ari Le, Stefano Atzeni, and Richard D. Petrasso
The impact of fuel-ion diffusion in inertial confinement fusion implosions is assessed using nuclear reaction yield ratios and reaction histories. In T3He-gas-filled (with trace D) shock-driven implosions, the observed TT/T3He yield ratio is ～2× lower than expected from temperature scaling. In D3He-gas-filled (with trace T) shock-driven implosions, the timing of the D3He reaction history is ～50 ps earlier than those of the DT reaction histories, and average-ion hydrodynamic simulations cannot reconcile this timing difference. Both experimental observations are consistent with reduced T ions in the burn region as predicted by multi-ion diffusion theory and particle-in-cell simulations. The impact of fuel-ion diffusion in inertial confinement fusion implosions is assessed using nuclear reaction yield ratios and reaction histories. In T3He-gas-filled (with trace D) shock-driven implosions, the observed TT/T3He yield ratio is ～2× lower than expected from temperature scaling. In D3He-gas-filled (with trace T) shock-driven implosions, the timing of the D3He reaction history is ～50 ps earlier than those of the DT reaction histories, and average-ion hydrodynamic simulations cannot reconcile this timing difference. Both experimental observations are consistent with reduced T ions in the burn region as predicted by multi-ion diffusion theory and particle-in-cell simulations.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 5, 055401 (2019)
Recent research progress of laser plasma interactions in Shenguang laser facilities
Tao Gong, Liang Hao, Zhichao Li, Dong Yang, Sanwei Li, Xin Li, Liang Guo, Shiyang Zou, Yaoyuan Liu, Xiaohua Jiang, Xiaoshi Peng, Tao Xu, Xiangming Liu, Yulong Li, Chunyang Zheng, Hongbo Cai, Zhanjun Liu, Jian Zheng, Zhebin Wang, Qi Li, Ping Li, Rui Zhang, Ying Zhang, Fang Wang, Deen Wang, Feng Wang, Shenye Liu, Jiamin Yang, Shaoen Jiang, Baohan Zhang, and Yongkun Ding
We report experimental research on laser plasma interaction (LPI) conducted in Shenguang laser facilities during the past ten years. The research generally consists of three phases: (1) developing platforms for LPI research in mm-scale plasma with limited drive energy, where both gasbag and gas-filled hohlraum targets are tested; (2) studying the effects of beam-smoothing techniques, such as continuous phase plate and polarization smoothing, on the suppression of LPI; and (3) exploring the factors affecting LPI in integrated implosion experiments, which include the laser intensity, gas-fill pressure, size of the laser-entrance hole, and interplay between different beam cones. Results obtained in each phase will be presented and discussed in detail. We report experimental research on laser plasma interaction (LPI) conducted in Shenguang laser facilities during the past ten years. The research generally consists of three phases: (1) developing platforms for LPI research in mm-scale plasma with limited drive energy, where both gasbag and gas-filled hohlraum targets are tested; (2) studying the effects of beam-smoothing techniques, such as continuous phase plate and polarization smoothing, on the suppression of LPI; and (3) exploring the factors affecting LPI in integrated implosion experiments, which include the laser intensity, gas-fill pressure, size of the laser-entrance hole, and interplay between different beam cones. Results obtained in each phase will be presented and discussed in detail.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 5, 055202 (2019)
Progress in optical Thomson scattering diagnostics for ICF gas-filled hohlraums
Hang Zhao, Zhichao Li, Dong Yang, Xin Li, Yaohua Chen, Xiaohua Jiang, Yonggang Liu, Tao Gong, Liang Guo, Sanwei Li, Qi Li, Feng Wang, Shenye Liu, Jiamin Yang, Shaoen Jiang, Wanguo Zheng, Baohan Zhang, and Yongkun Ding
Optical Thomson scattering (OTS) diagnostics have been continuously developed on a series of large laser facilities for inertial confinement fusion (ICF) research in China. We review recent progress in the use of OTS diagnostics to study the internal plasma conditions of ICF gas-filled hohlraums. We establish the predictive capability for experiments by calculating the time-resolved Thomson scattering spectra based on the 2D radiation-hydrodynamic code LARED, and we explore the fitting method for the measured spectra. A typical experiment with a simplified cylindrical hohlraum is conducted on a 10 kJ-level laser facility, and the plasma evolution around the laser entrance hole is analyzed. The dynamic effects of the blast wave from the covering membrane and the convergence of shocks on the hohlraum axis are observed, and the experimental results agree well with those of simulations. Another typical experiment with an octahedral spherical hohlraum is conducted on a 100 kJ-level laser facility, and the plasma evolution at the hohlraum center is analyzed. A discrepancy appears between experiment and simulation as the electron temperature rises, indicating the occurrence of nonlocal thermal conduction. Optical Thomson scattering (OTS) diagnostics have been continuously developed on a series of large laser facilities for inertial confinement fusion (ICF) research in China. We review recent progress in the use of OTS diagnostics to study the internal plasma conditions of ICF gas-filled hohlraums. We establish the predictive capability for experiments by calculating the time-resolved Thomson scattering spectra based on the 2D radiation-hydrodynamic code LARED, and we explore the fitting method for the measured spectra. A typical experiment with a simplified cylindrical hohlraum is conducted on a 10 kJ-level laser facility, and the plasma evolution around the laser entrance hole is analyzed. The dynamic effects of the blast wave from the covering membrane and the convergence of shocks on the hohlraum axis are observed, and the experimental results agree well with those of simulations. Another typical experiment with an octahedral spherical hohlraum is conducted on a 100 kJ-level laser facility, and the plasma evolution at the hohlraum center is analyzed. A discrepancy appears between experiment and simulation as the electron temperature rises, indicating the occurrence of nonlocal thermal conduction.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 5, 055201 (2019)
Thickness dependence of microstructure and properties in Be2C coatings as a promising ablation material
Yudan He, Lei Jin, Jiqiang Zhang, Bingchi Luo, Kai Li, Weidong Wu, and Jiangshan Luo
Beryllium carbide (Be2C) thin films have proven to be promising ablation materials, but the properties of Be2C coatings of the greater thickness required for inertial confinement fusion capsules are still unknown. In this work, Be2C coatings of various thicknesses (0.3–32.9 μm) are prepared by DC reactive magnetron sputtering. The influence of thickness on crystal properties, microstructure, and optical properties is investigated. The results indicate that the crystallinity of polycrystalline Be2C films improves with increasing thickness, while the grain size (～5 nm) and texture properties (without a preferred orientation) have only a weak dependence on thickness. A uniform featureless microstructure and smooth surface (root mean square roughness ～8 nm) are observed even in thick (32.9 μm) films, despite the presence of defects induced by contaminants. High densities (2.19–2.31 g/cm3) and high deposition rates (～270 nm/h) are realized, with the latter corresponding to the upper limit for the fabrication of Be2C coatings by magnetron sputtering. The transmittance of the films in the near-infrared region remains at a high level (>80%) and has only a weak dependence on thickness, while the transmittance in the visible region decreases with increasing thickness. In addition, the optical bandgap is estimated to be about 1.9 eV and decreases with increasing thickness owing to the presence of defects. Beryllium carbide (Be2C) thin films have proven to be promising ablation materials, but the properties of Be2C coatings of the greater thickness required for inertial confinement fusion capsules are still unknown. In this work, Be2C coatings of various thicknesses (0.3–32.9 μm) are prepared by DC reactive magnetron sputtering. The influence of thickness on crystal properties, microstructure, and optical properties is investigated. The results indicate that the crystallinity of polycrystalline Be2C films improves with increasing thickness, while the grain size (～5 nm) and texture properties (without a preferred orientation) have only a weak dependence on thickness. A uniform featureless microstructure and smooth surface (root mean square roughness ～8 nm) are observed even in thick (32.9 μm) films, despite the presence of defects induced by contaminants. High densities (2.19–2.31 g/cm3) and high deposition rates (～270 nm/h) are realized, with the latter corresponding to the upper limit for the fabrication of Be2C coatings by magnetron sputtering. The transmittance of the films in the near-infrared region remains at a high level (>80%) and has only a weak dependence on thickness, while the transmittance in the visible region decreases with increasing thickness. In addition, the optical bandgap is estimated to be about 1.9 eV and decreases with increasing thickness owing to the presence of defects.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 4, 045403 (2019)
Studies of laser-plasma interaction physics with low-density targets for direct-drive inertial confinement schemes
V. Tikhonchuk, Y. J. Gu, O. Klimo, J. Limpouch, and S. Weber
Comprehensive understanding and possible control of parametric instabilities in the context of inertial confinement fusion (ICF) remains a challenging task. The details of the absorption processes and the detrimental effects of hot electrons on the implosion process require as much effort on the experimental side as on the theoretical and simulation side. This paper describes a proposal for experimental studies on nonlinear interaction of intense laser pulses with a high-temperature plasma under conditions corresponding to direct-drive ICF schemes. We propose to develop a platform for laser-plasma interaction studies based on foam targets. Parametric instabilities are sensitive to the bulk plasma temperature and the density scale length. Foam targets are sufficiently flexible to allow control of these parameters. However, investigations conducted on small laser facilities cannot be extrapolated in a reliable way to real fusion conditions. It is therefore necessary to perform experiments at a multi-kilojoule energy level on medium-scale facilities such as OMEGA or SG-III. An example of two-plasmon decay instability excited in the interaction of two laser beams is considered. Comprehensive understanding and possible control of parametric instabilities in the context of inertial confinement fusion (ICF) remains a challenging task. The details of the absorption processes and the detrimental effects of hot electrons on the implosion process require as much effort on the experimental side as on the theoretical and simulation side. This paper describes a proposal for experimental studies on nonlinear interaction of intense laser pulses with a high-temperature plasma under conditions corresponding to direct-drive ICF schemes. We propose to develop a platform for laser-plasma interaction studies based on foam targets. Parametric instabilities are sensitive to the bulk plasma temperature and the density scale length. Foam targets are sufficiently flexible to allow control of these parameters. However, investigations conducted on small laser facilities cannot be extrapolated in a reliable way to real fusion conditions. It is therefore necessary to perform experiments at a multi-kilojoule energy level on medium-scale facilities such as OMEGA or SG-III. An example of two-plasmon decay instability excited in the interaction of two laser beams is considered.
Matter and Radiation at Extremes
- Publication Date: Jan. 01, 2019
- Vol. 4, Issue 4, 045402 (2019)
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