Thomas H. Stix Award for Outstanding Early Career Contributions to Plasma Physics Research: Developing Broadband Laser Drivers for a Step Change in ICF Performance through Laser-Plasma Instability Mitigation

Increasing ablation pressure to >200 Mbar is crucial for accessing the region of design space where robust ignition would be expected for a MJ-class laser driver. Currently, crossed-beam energy transfer (CBET) severely limits the ablation pressure in directly driven implosions. Operating intensities are further constrained by the need to avoid fuel preheat by suprathermal electrons generated by the two-plasmon decay (TPD) and stimulated Raman scattering instabilities. Simulations suggest that fractional bandwidths of ≈1.5% (Δω/ω)—about 50 larger than what is available currently—would completely eliminate all laser-plasma instabilities (LPI) in OMEGA-scale implosions and thereby recover the advantages for energy coupling that were expected for direct drive (i.e., >200 Mbar ablation pressures) [1-2].To test these predictions, LLE is building the first UV long-pulse prototype beamline to have that amount of bandwidth—the Fourth-generation Laser for Ultrabroadband eXperiments (FLUX). FLUX utilizes high-efficiency amplification of broadband spectrally incoherent pulses based on optical parametric amplifiers [3] along with a novel sum frequency generation technique that preserves the large bandwidth into the third harmonic [4]. FLUX will be coupled to the OMEGA-60 target chamber to enable focused physics studies using the LPI platform, with operation expected to begin in early 2024. Platform development in anticipation of FLUX has been underway for some time. We will discuss plans to study the impact of laser bandwidth on a wide range of processes, including CBET, hot-electron generation, filamentation, plasma characterization, laser imprint, and more. This material is based upon work supported by the DOE NNSA under Award Number DE-NA0003856, the DOE Fusion Energy Sciences program under Award Number DE-SC0021032, the University of Rochester, and the New York State Energy Research and Development Authority.

[1] R. K. Follett et al., Physics of Plasmas 28, 032103 (2021).

[2] R. K. Follett et al., Physics of Plasmas 30, 042102 (2023).

[3] C. Dorrer et al., Optics Express 28, 451-471 (2020).

[4] C. Dorrer et al., Optics Express 29, 16135-16152 (2021).