  The Landau form of the Fokker-Planck equation is the gold standard for
plasmas dominated by small angle collisions, however its $\Order{N^2}$ work
complexity has limited its practicality. This paper extends previous work on a
fully conservative finite element method for this Landau collision operator
with adaptive mesh refinement, optimized for vector machines, by porting the
algorithm to the Cuda programming model with implementations in Cuda and
Kokkos, and by reporting results within a Vlasov-Maxwell-Landau model of a
plasma thermal quench. With new optimizations of the Landau kernel and ports of
this kernel, the sparse matrix assembly and algebraic solver to Cuda, the cost
of a well resolved Landau collision time advance is shown to be practical for
kinetic plasma applications. This fully implicit Landau time integrator and the
plasma quench model is available in the PETSc (Portable, Extensible, Toolkit
for Scientific computing) numerical library.
