Cross-Beam Energy Transfer (CBET) and Stimulated Brillouin Scattering (SBS) in NIF Hohlraums

We explore the role of CBET and SBS in recent NIF experiments, which use relatively low hohlraum gas fill density ≤ 0.6 mg/cm³, and short laser pulses ≤ 10 ns. Even with no wavelength shift between “inner” (polar angle vs. hohlraum axis θ=21.2^o–32.7^o) and outer laser beams (θ=42.2^o–52.4^o), Lasnex simulations [1] with the self-consistent or “inline” CBET model [2] indicate transfer from inner to outer beams, induced by plasma flow. Especially for high-power shots, this CBET brings simulated implosion shape closer to measurements. These experiments also have moderate SBS from the outer beams, usually coming late in peak laser power. An inline SBS model has been implemented, and its effects will be presented. CBET may also be important in understanding the angular distribution of outer-beam SBS, which tends to be mostly from the highest θ beams (θ=52.4^o). Namely, CBET from the θ=42.2^o-47.7^o beams to the θ=52.4^o beams may be important. To assess this, including beam polarization, we use the “offline” CBET code Vampire [3].

1. G Zimmerman and W Kruer, Comments PPCF 2, 85 (1975)

2. D Strozzi, D Bailey et al., PRL 118, 025002 (2017)

3. A Colaitis, T Chapman et al., PoP 25, 033114 (2018)