Mitigation of hot electrons from laser-plasma instabilities in high-Z, highly ionized plasmas

• Published in: Physics of plasmas 2017-03, Vol.24 (3)
• Main Authors: Fein, J. R., Holloway, J. P., Trantham, M. R., Keiter, P. A., Edgell, D. H., Froula, D. H., Haberberger, D., Frank, Y., Fraenkel, M., Raicher, E., Shvarts, D., Drake, R. P.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Balances (scales); Electron density; Electron density profiles; Electron plasma; Foils; Hot electrons; Landau damping; Lasers; Plasma physics; Plasma waves; Raman spectra
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.4978625

Hard x-ray measurements are used to infer production of hot electrons in laser-irradiated planar foils of materials ranging from low- to high-Z. The fraction of laser energy converted to hot electrons, f hot , was reduced by a factor of 103 going from low-Z CH to high-Z Au, and hot electron temperatures were reduced from 40 to ∼20 keV. The reduction in f hot correlates with steepening electron density gradient length-scales inferred from plasma refraction measurements. Radiation hydrodynamic simulations predicted electron density profiles in reasonable agreement with those from measurements. Both multi-beam two-plasmon decay (TPD) and multi-beam stimulated Raman scattering (SRS) were predicted to be above threshold with linear threshold parameters that decreased with increasing Z due to steepening length-scales, as well as enhanced laser absorption and increased electron plasma wave collisional and Landau damping. The results add to the evidence that SRS may play a comparable or a greater role relative to TPD in generating hot electrons in multi-beam experiments.