Cross-beam energy transfer in flowing ICF plasmas with laser speckles and ponderomotive self-focusing

Cross-BeamEnergy Transfer (CBET) between laser beams remains an active area of research in Inertial Confinement Fusions (ICF) experiments that are related to both, indirect and direct fusion schemes. We have modelled CBET by means of numerical simulations with a wave coupling code [1], taking into account the speckle (hot spot) substructure of “smoothed” laser beams. We have shown that transfer of energy from laser hot spots of one beam to the another beam, via forward stimulated Brillouin scattering, self-focusing in the presence of a plasma flow and beam bending proves to affect considerably the angular distribution and spectra of the laser light behind the region of beam overlap for laser intensities I λ²> 10¹⁴W cm^-2 μm². For these reasons the angular distribution and spectra of transmitted light from smoothed laser beams (with speckles) is very different from the angular distribution of beam when the beam speckle structure is disregarded. We have also examined the importance of nonlinear, shock-like structures in ion waves and of plasma-induced smoothing on CBET.

[1] G. Raj and S. Hüller, Phys. Rev. Lett. 118, 055002 (2017).