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ELFIE - Study of anomalous electron heating produced by kinetic saturation processes of LPI's in picosecond time scale (C. Rousseaux)

Among  problems  issued  from  the  laser-plasma  interaction  domain,  laser  parametric  instabilities  (LPI)  are  oneof  the  most  complex ones for ICF issues. Besides worrying backward stimulated Raman scattering (SRS) reflectivities from the inner laser cone as well as significant energy transfer between the inner cones and outer cones, as reported from NIF experiments, the hot electron populations generated by stimulated Raman scattering and other instabilities producing electron plasma waves (EPW) are generally pointed out for issues relevant to the preheat of the compressed target. However, we are interested here in additional effects of these hot electron populations that are related to basic  properties  of  plasmas:  as  the  velocity  distribution functions (VDF) of the particles are no more Maxwellian, the hot electron populations, even in small proportions, may significantly alter either heating transport coefficients, or damping rates of waves in the plasma, or radiation properties of high Z materials in the indirect drive scheme of ICF. The aim of this proposal is to investigate how far from thermal equilibrium would be the plasmas experiencing strong local, kinetic heating generated during LPI saturation processes (the thermal equilibrium state refers to a plasma where the VDFs of particles  (electrons  and  ions)  are  Maxwellian).  The  most  suitable  diagnostics  for  this  purpose  are  highly  space- and  time-resolved  Thomson  imaging  systems  that  are  regularly  used  on  the  ELFIE  facility.  Particular  attention  will  be  paid  to detect thermal ion acoustic and electron plasma waves that inform on local plasma characteristics, as  local  electron  temperature (and gradients) or macroscopic particle drifts (or currents). As thermal Thomson measurements are challenging in the short pulse interaction context, the driven electrostatic waves of a  second,  weak  laser  pulse  fired  just  after  the  main  perturbing laser pulse will be also diagnosed by means of a second 3ω Thomson probe.

ELFIE : S26-30 / 2016
co-PI : S. Baton (LULI)