Mitigation of cross-beam energy transfer in direct-drive inertial-confinement-fusion implosions with enhanced laser bandwidth*

Cross-beam energy transfer (CBET) is a special category of stimulated Brillouin scattering in which two overlapping laser beams exchange energy by means of an ion acoustic wave in an under-dense expanding plasma [C.J. Randall \textit{et al.}, Phys. Fluids \textbf{24}, 1474 (1981)]. CBET can cause the incident laser energy to be misdirected in direct-drive inertial-confinement-fusion (ICF) implosions, thereby reducing both the maximum ablation pressure achieved and the overall symmetry of the implosion [J.F. Myatt \textit{et al}., Phys. Plasmas \textbf{21}, 055501 (2014)]. One strategy for mitigating CBET may be to increase the bandwidth of the laser light, thereby disrupting the coherent wave-wave interactions underlying this resonant parametric process. In this presentation, we report on results of two-dimensional planar simulations performed with the code LPSE-CBET that demonstrate a significant reduction in CBET for bandwidths between 2 and 5 THz. Although large compared to OMEGA and NIF values (about 1 and 0.3 THz, respectively), it may be possible to reach such bandwidths with existing ICF lasers using a technique based on stimulated rotational Raman scattering [D. Eimerl \textit{et al}., Phys. Rev. Lett. \textbf{70}, 2738 (1993)], which is a subject that we also briefly discuss.