Platform development for broadband laser mitigation of stimulated Raman scattering and two-plasmon–decay instabilities on OMEGA

Target preheat by superthermal electrons generated by stimulated Raman scattering and two-plasmon–decay instabilities is a potential concern for direct-drive inertial confinement fusion. The development of broadband laser technology can help suppress deleterious laser–plasma instabilities (LPI’s). An experimental platform is being developed at the Omega Laser Facility to study LPI mitigation using the FLUX laser, which will be available at the beginning of 2024 and have a frequency bandwidth of ~1.5%. FLUX beam interaction with a preformed coronal plasma, generated by nine OMEGA beams incident onto a planar or open-cone target, will be studied experimentally. Two-dimensional hydrodynamic DRACO simulations predict that coronal plasmas with a density scale length at the n_c/4 surface, ranging from 150 to 400 µm, will be available. We present DRACO simulations and the first experiments to utilize a narrow-bandwidth P9 interaction beam, which studied the regimes of LPI without mitigation. Simulations using the LPI code LPSE show advantages of small f-number optics to study the regimes of LPI relevant to direct-drive implosions.