Pump depletion and the "Raman gap" in ignition-scale plasmas*

After inertial confinement fusion (ICF) achieved ignition on National Ignition Facility (NIF), direct drive ICF becomes an attractive fusion energy source candidate due to its high laser-target coupling efficiency. Ongoing work is geared towards understanding LPI at ignition scales but more work remains. We investigated the cause of ”Raman gap” using two-dimensional Particle-in-Cell simulations with a combination of in-plane (PP) and out-of-the-plane (SP) lasers. By utilizing SP incident lasers and intentionally setting the intensity of PP lasers lower than that of the SP laser, we highlighted the crucial role of pump depletion in the formation of the Raman gap under NIF and OMEGA EP conditions.