Kinetic Radial Transport and RF Quasilinear Diffusion of Runaway Electrons Calculated with CQL3D

Runaway electron (RE) distributions which are driven by large toroidal electric fields induced by rapid Te-drops in a tokamak, e.g., due to plasma disruption or pellet injection, are comprehensively simulated by the toroidal 3D bounce-average Fokker-Planck solver CQL3D [1], including the Ampere-Faraday equations. CQL3D has been extensively applied to calculate plasma kinetic distributions f(vpar,vperp,rho,t) resulting from RF induced quasilinear and collisional diffusion. For runaways, we present results of the combined effects of (1) radial diffusion and pinch terms, which can strongly reduce the RE population [2]; and (2) injection and/or instability of RF which can pitch angle scatter the RE distribution thus increasing their synchrotron radiation, thereby reducing their energetic potency. The background time-dependent plasma profiles, including radial diffusion, are obtained from the NIMROD code [4]. [1] R.W. Harvey and M. McCoy, “The CQL3D Fokker Planck Code,” www.compxco.com/cql3d.html. [2] R.W. Harvey, V.S. Chan, S.C. Chiu et al., Phys. Plasmas 7, 4590 (2000). [3] Pavel Aleynikov and Boris Breizman, Nucl. Fusion 55, 043014 (2015). [4] V.A. Izzo and P.B. Parks, Phys. Plasmas 24, 060705 (2017).