April 15-17

Abstract Details

files Add files

Abstracts

Author: Lee F. Ricketson
Requested Type: Pre-Selected Invited
Submitted: 2019-02-21 16:29:01

Co-authors: L. Chacon

Contact Info:
Lawrence Livermore National Laboratory
7000 East Ave
Livermore, CA   94550
USA

Abstract Text:
Tremendous progress has been made on implicit particle-in-cell (PIC) schemes in recent years. They feature exact energy conservation and have been shown to be more robust to the finite grid instability than their explicit counterparts, making them very powerful for long-time simulation. Simultaneously, there has been increasing interest in implicit, full-orbit kinetic simulation that steps over the gyration time-scale as an alternative to gyrokinetics. Such an approach would have noteworthy advantages: being able to handle widely varying levels of magnetization within the domain, arbitrarily sharp gradients in background density and temperature profiles, and general boundary conditions. We present a new full-orbit time integrator at the intersection of these two ideas. The integrator is built on Crank-Nicolson and preserves the crucial exact energy conservation property of implicit PIC, but it also reproduces all first-order guiding center drifts and the correct gyroradius when stepping over the gyration time-scale, all while converging to the full orbit dynamics for small time-steps. The key innovations are 1) the ability to capture the grad-B drift and mirror force without breaking energy conservation and 2) a detailed understanding of the scheme’s time-step restrictions along with an adaptive time-step strategy that ensures these restrictions are respected. Results from several test problems are presented demonstrating the scheme’s effectiveness. Notably, the scheme predicts trapped/passing boundaries, adiabatic invariance of magnetic moment, and behavior when passing through unmagnetized regions much more accurately than prior efforts.

*Work performed under the auspices of the U.S. Department of Energy by LLNL and LANL under contracts DE-AC52-07NA27344, DE-AC52-06NA25396, and supported by the Exascale Computing Project (17-SC-20-SC), a collaborative effort of the U.S. Department of Energy Office of Science and the National Nuclear Security Administration.

Comments:
Computer Simulation of Plasmas