Measurements of the Return-Current Instability with Ion-Acoustic Thomson Scattering

Return-current instability (RCI), the process by which a cold current is driven to compensate for heat flux leading to ion-acoustic turbulence, has been proposed as a mechanism to limit the heat flux in inertial confinement fusion experiments. Here, the threshold for the instability was studied experimentally as a function of temperature gradient scale length. Temporally resolved ion-acoustic wave Thomson-scattering measurements showed the red-shifted wave grew consistently with electron Landau damping feeding the instability. Measurements of the ion-acoustic wave growth at multiple spatial locations and heating levels showed the level of growth was associated with the temperature gradient scale length in the plasma. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.