Studying non-Maxwellian ion velocity distributions in ICF-relevant conditions using Thomson scattering on a diagnostically-accessible OMEGA platform

Recent ICF experiments at both the NIF and OMEGA have yielded experimental signatures which are inconsistent with hydrodynamic models, which assume locally-Maxwellian ion velocity distributions, but questions remain regarding the exact origin of these signatures. A diagnostically-accessible platform that mocks up an ICF implosion with a planar geometry is fielded on OMEGA with the aim of making progress towards addressing these questions. The platform consists of two opposing CD foils which are driven from the backs into a D₂ gas jet that propagates in between the foils. Collective optical Thomson scattering is used to probe the electron and ion velocity distributions at the center of the configuration where the fusion volume is expected to be located. The inferred velocity distributions are compared to neutron data as well as to both hydrodynamic and kinetic simulations. A preliminary analysis of the Thomson data suggests the presence of fast ion beams in the fusion volume which could contribute to kinetic effects in ICF.

The experiment was conducted at the Omega Laser Facility with the beam time through the National Laser Users’ Facility (NLUF) under the auspices of the U.S. DOE/NNSA by the University of Rochester’s Laboratory for Laser Energetics under Contract DE-NA0003856 and was funded by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Award Number DE-SC0024306.