Measurements and modeling of runaway electron radial transport in quiescent, low-density MST tokamak plasmas

Understanding the creation and radial transport of runaway electrons (RE) in tokamak plasmas is vital for safety and preventing machine damage during plasma disruptions. We use a Multi-energy Soft X-Ray (ME-SXR) camera on the Madison Symmetric Torus (MST) to probe the radial and energy distribution of photon emission using a 450 um silicon detector. Low-density (10^17 – 10^18 m^-3) quiescent plasmas, with B_T = 0.13 T and T_e ~ 100 eV are tailored such that a RE population with energy ~ 10-100 keV grows during the plasma current flat-top and produces SXR radiation via pitch-angle scattering. Ongoing work is being completed to model RE acceleration and diffusion rates in MST using the Fokker-Planck code CQL3D with a synthetic ME-SXR diagnostic. Also discussed are temporal variations in the SXR emission; shot-to-shot reproducibility and ensemble-averaging efforts; and plans for further RE studies using the ME-SXR diagnostic.