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Author: Zehua Guo
Requested Type: Poster
Submitted: 2017-03-17 14:18:52

Co-authors: X.Z. Tang, C. Mcdevitt

Contact Info:
Los Alamos National Laboratory
P.O. Box 1663
Los Alamos,   87545
US

Abstract Text:
Generation of runaway electrons (RE) can lead to perhaps the most deleterious effect of tokamak disruptions on plasma facing components. Recently, a number of numerical calculations [1,2] have confirmed the formation of a RE bump in their energy distribution by taking into account Synchrontron radiation damping due to RE's gyromotions. Here, we discuss in more detail how the bump location in energy changes at different pitch-angle and the characteristics of the RE pitch-angle distribution at different energy. Although REs with zero pitch-angle are preferably accelerated and then populate the phase-space of larger pitch-angle at higher energy mainly through diffusions, an off-axis peak can still form due to the presence of a vortex structure which causes accumulation of REs at low pitch-angle. A simplified Fokker-Planck model and its semi-analytical solutions based on local expansions will be used to illustrate the characteristics of RE distribution around the O point of the vortex
structure in phase-space. The calculated energy of the O point together with the off-axis peak of the RE distribution agree with the full simulation result [2].

Work supported by DOE OFES.

[1] A. Stahl et al, PRL 114, 115002 (2015); J. Decker et al, PPCF 58, 025016 (2016)
[2] Z. Guo et al, PPCF 59, 044003 (2017)

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