Short-wavelength-and-broad-bandwidth mitigation of laser-plasma instabilities

The U.S. Naval Research Laboratory is engaged in an ongoing research effort to demonstrate the benefits of an argon-fluoride (ArF) laser driver for inertial confinement fusion (ICF). Compared to the frequency-tripled Nd:glass lasers used in most ICF experiments today, an ArF laser provides several distinct advantages, including: 1.) a shorter wavelength (193 nm versus 351 nm); and 2.) a broader native bandwidth (5 - 10 THz versus ≤ 1 THz) — both of which help to suppress deleterious laser-plasma instabilities (LPIs). In this talk, we present numerical simulations of ICF-relevant LPIs that were performed using the LPSE code. Our numerical models incorporate multi-beam laser geometries as well as realistic plasma conditions and we compare results for ArF and Nd:glass drivers. In the case of cross-beam energy transfer, for example, we find that an ArF driver provides a 40% increase in the time-averaged, inverse-bremsstrahlung absorption in the plasma surrounding an OMEGA-scale target. Moreover, in studies of the absolute two-plasmon-decay and stimulated-Raman-scattering instabilities for both OMEGA and NIF-scale implosions, threshold intensities are found to be consistently higher using ArF laser light. This work suggests that an ArF driver would facilitate larger ablation pressures in ICF target designs, which would, in turn, permit the use of thicker- walled pellets that are more resistant to hydrodynamic instabilities.