Abstract Details
Abstracts
Author: Don Daniel
Requested Type: Pre-Selected Invited
Submitted: 2019-02-20 10:46:17
Co-authors: W.T.Taitano,LChacón
Contact Info:
Los Alamos National Laboratory
T-5
Los Alamos, 87545
USA
Abstract Text:
Upon application of a sufficiently strong electric field, electrons break away from thermal equilibrium and approach relativistic speeds. These highly energetic ‘runaway’ electrons (∼ MeV) play a crucial role in understanding tokamak disruption events, and therefore their accurate understanding is essential to develop reliable mitigation technologies. For this purpose, we have developed a fully implicit, 0D2P, scalable relativistic Fokker-Planck kinetic electron solver [1].
The relativistic Fokker-Planck collision operator models Coulomb collisional effects between species under the assumption of small angle binary collisions [2]. Similar to its non-relativistic counterpart, the operator is well-posed, and supports strict conservation of species number density, total momentum and total energy. We ensure discrete energy and momentum conservation for the electron-electron interactions. Electron-ion interactions are modeled using the Lorentz operator, and synchrotron damping using the Abraham-Lorentz-Dirac reaction term.
We use positivity-preserving finite-difference schemes for both advection [3] and tensor diffusion terms [4]. Using multi-grid preconditioned Anderson Acceleration fixed-point iteration scheme for our nonlinear solves, we demonstrate parallel scalability up to 4096 cores and algorithmic scalability with time steps approximately 1000 times larger than the explicit time steps.
The proposed numerical treatment enables the accurate investigation of phenomena spanning a wide range of temporal scales. We demonstrate the proposed scheme with numerical results ranging from small electric-field electrical conductivity measurements to accurate reproduction of runaway tail dynamics when strong electric fields are applied.
[1] Daniel, Taitano, Chacón, J. Comp. Phys., submitted, 2019
[2] Braams, Karney. Phy. Rev. Lett., 1987
[3] Gaskell and Lau, Int. J. Numer. Meth. Fluids, 1988
[4] D’Toit, O‘Brien, Vann., Comp. Phys. Com, 2018
Comments:
1) Computer Simulation of Plasmas
