Polarized imaging of visible synchrotron emission from runaway electron plateaus in DIII-D

Popović, E. M. Hollmann, D. Del-Castillo-Negrete, I. Bykov, R. A. Moyer, J. L. Herfindal, D. Shiraki, N. W. Eidietis, C. Paz-Soldan, A. Lvovskiy

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Abstract

A new approach to estimate the pitch angle of highly energetic postdisruption runaway electrons is presented by imaging the polarized runaway electron synchrotron emission. The vertical to horizontal polarization ratio is found to range between 3 and 14 in image-average studies looking at repeated shots as well as the polarization in a single discharge. Numerical studies with guiding center and full orbit simulations performed with the SOFT and KORC codes are given and compared to the experiment. The pitch angle evolution analyzed using a 1D impurity diffusion model in combination with kinetic simulations is also presented. These studies find agreement in the magnitude of the pitch angle, but not in the temporal rate of change of pitch angle. The measured pitch angle evolution timescale of order 50 ms falls between a modeled timescale of 20 ms in an equilibrium model and ≫100 ms in a nonequilibrium model.

Original languageEnglish
Article number082510
JournalPhysics of Plasmas
Volume28
Issue number8
DOIs
StatePublished - Aug 1 2021

Funding

The authors gratefully acknowledge assistance with SOFT from M. Hoppe and L. Stagner. This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award Nos. DE-FG02-07ER54917, DE-FC02-04ER54698, DE-AC05-00OR22725, DE-AC52-07NA27344, DE-FG02-04ER54744, and DE-AC05-06OR23100. D. d.-C.-N. was sponsored by the U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research and Office of Fusion Energy Science, Scientific Discovery through Advanced Computing (SciDAC) program, at the Oak Ridge National Laboratory, which is operated by UT-Battelle, LLC, for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.

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