Current profile reconstructions are obtained for high current ( kA) post-disruption runaway electron (RE) plateau plasmas in DIII-D. Two novel methods of measuring the RE current profile in high-current RE plateaus are introduced and compared: localization of the q = 2 rational surface using visible synchrotron emission (SE) imaging and the measurement of the polarization angle of line-integrated Ar-II line emission. The two methods are found to be consistent with each other within the data uncertainties. Different simulations of the RE current profile are compared with the measurements: the toroidal fluid RE model is found to best fit the data, within the measurement uncertainties. In addition to introducing two novel methods to measure the RE current profile and validating present simulation capabilities, this work demonstrates that instabilities can grow at q = 2 and q = 1 surfaces without necessarily causing a RE final loss instability. Numerical simulations are also presented to elucidate the role of these instabilities on synchrotron emission.
This paper introduces two novel methods to measure the current profile of high-current runaway electron (RE) plateaus after disruptions in the DIII-D tokamak. The methods use synchrotron emission imaging and Ar-II line polarization to localize the q=2 and q=1 rational surfaces, which are important for understanding RE instabilities. The measurements are consistent with simulations, showing that instabilities can grow at these surfaces without causing a final RE loss.