Runaway electron plateau current profile reconstruction using synchrotron emission imaging in DIII-D*

Current profile reconstructions are obtained for the first time in high current (≅500 kA) post-disruption runaway electron (RE) beam plasmas plateaus in DIII-D.

A reliable current profile is critical for the study of RE instabilities behind deconfinement and final loss dynamics to minimize post-disruption wall damage

for safe operation of reactor-scale tokamaks. A novel method of analyzing synchrotron emission (SE) imaging is presented here, enabling an accurate spatial

localization of the MHD modes which form in RE plateaus at high Ip: both a locked, steady edge (2/1) mode and episodic, fast growing/crashing central (1/1) mode. The current profile is reconstructed using the observed radii of (m/n) = (2/1) and (1/1) modes, allowing localization of the safety factor q = 2 and q = 1 surfaces. Current profiles estimated using SE agree with line-integrated Ar-II line polarization measurements and are compared with predictions by two codes: a Fokker-Planck code (DREAM) and a kinetic test particle code (IonBalance), both

giving good agreement. The reconstructed current profile is peaked on the magnetic axis, it is not hollow as the SE profile might suggest.