  Collisional processes are critical in the understanding of non-Maxwellian
plasmas. The Landau form of the Fokker-Planck equation is the gold standard for
modeling collisions in most plasmas, however O(N^2) work complexity inhibits
its widespread use. We show that with advanced numerical methods and GPU
hardware this cost can be effectively mitigated. This paper extends previous
work on a conservative, high order accurate, finite element discretization with
adaptive mesh refinement of the Landau operator, with extensions to GPU
hardware and implementations in both the CUDA and Kokkos programming languages.
This work focuses on the Landau kernels and on NVIDIA hardware, however
preliminary results on AMD and Fujitsu/ARM hardware, as well as end-to-end
performance of a velocity space model of a plasma thermal quench, are also
presented. Both the fully implicit Landau time integrator and the plasma
thermal quench model are publicly available in PETSc (Portable, Extensible,
Toolkit for Scientific computing).
