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ELFIE - Direct measurement of ion acoustic wave damping in multispecies plasmas and of self-generated magnetic field in monospeckle laser-plasma interaction (C. Rousseaux)

In most experiments relevant to ICF studies, laser parametric instabilities (LPIs) such as stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) are excited in multispecies plasmas. The multispecies plasmas are present in gas‐filled hohlraums (for example, hydrocarbon or helium/hydrogen mixes in the indirect drive scheme of ICF), and around the interface between two expanding plasmas: expansion of the gold plasma into the heated gas and/or with the ablated capsule, expansion of the exploded foils at laser‐entrance‐holes (LEHs) into the gas. In heavy/light ion mixes and near LEH, SBS and crossed‐beam‐energy transfer (CBET) are expected to develop significantly. The growth and the saturation of these instabilities involving ion acoustic waves (IAWs) closely depend on the IAW damping which in turn is poorly understood in perturbed plasmas that undergo LPIs. The goal of this proposal is to use short laser pulses (i) to provide direct measurements of this damping rate, for plasma mixtures relevant to ICF, and (ii) to improve the characterization of the limited plasma volume where the IAWs are driven. Indeed, high amplitude IAWs are initially amplified by backward‐SBS in the same plasma region where SRS has also saturated and generated hot electron populations; consequently, the velocity distribution functions(VDF) of the particles are no more Maxwellian, and local ion flows may dramatically alter the IAW damping rates. In the proposed experiment on the multibeam ELFIE facility, we will use highly space‐ and time‐resolved diagnostics to characterize both the IAWs (Thomson scattering) and the plasma volume (local density profile by interferometry, electron currents and self‐generated B field by Faraday's rotation).

ELFIE - S27-31 / 2018