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Author: Leopoldo Carbajal
Requested Type: Pre-Selected Invited
Submitted: 2017-03-17 14:34:40

Co-authors: D. del-Castillo-Negrete

Contact Info:
Oak Ridge National Laboratory
Oak Ridge National Laboratory
Oak Ridge, Tennessee   37831

Abstract Text:
Runaway electrons (RE), thermal electrons accelerated to relativistic velocities during the rapid termination of a magnetic confinement fusion (MCF) plasma, pose a threat to ITER if they are not avoided or suppressed before they hit the wall, causing damage to plasma facing components. To develop mitigation strategies of RE in MCF plasmas, a simulation prediction capability that provides validated estimates of RE parameters is required. Synchrotron radiation (SR) emitted by RE in MCF plasmas is important for two reasons: SR is one of the main damping mechanisms for RE in these plasmas; on the other hand, SR is routinely measured in current MCF experiments. The RE distribution function parameters are inferred by interpreting the measured SR spectra and geometric properties of the radiation spatial patterns seen by the visible and infrared cameras. The inferred parameters show a great variability, depending on how the experimental data is interpreted [A. Stahl et al. PoP 20, 093302 (2013)]. We present the results of a systematic study, the first of its kind, comparing the most commonly used interpretations of the SR emission applied to synthetic diagnostic data produced via simulation for DIII-D-like magnetic fields. We use KORC, a new code to follow the RE dynamics in the full 6-D phase space which includes full-orbit effects and SR losses [L. Carbajal, D. del-Castillo-Negrete et al. PoP, submitted]. We show that the RE energy inferred from the SR spectrum can be overestimated in the case that the SR is assumed to be emitted parallel to the electrons’ velocity, compared to the case where the full angular distribution of the SR is used. Only in the latter case we do recover the wedge and tilted ellipse shapes of the SR spatial patterns often observed in experiments.

Research sponsored by the LDRD Program of ORNL, managed by UT-Battelle, LLC, for the U.S. DoE under Contract No. DE-AC05-00OR22725.