Noise-free large-timestep RF plasma modeling with the spider stencil

We present an explicit (no matrix inversions) finite-difference time-domain

algorithm for simulating cold magnetized plasmas where the maximum timestep is

limited only by the Courant condition for RF waves [1]. We can

therefore model transient phenomena on slow time-scales such as ion

cyclotron and lower-hybrid resonances without needing to resolve fast

electron dynamics, and the simulations are numerically stable.

The algorithm applies to low-amplitude waves in cold magnetized plasmas,

such as the interaction of RF heating pulses with a tokamak edge plasma.

Our current implementation is an improvement over the algorithm described

in [1]---with a set of careful field interpolation steps, we avoid

applying any spatial smoothing operators and therefore free our simulations

from any unphysical low-frequency short-wavelength modes.

We have implemented the algorithm in Vorpal [2], and present results that

validate the physics, demonstrate numerical stability despite unresolved

electron dynamics, and benchmark performance on CPUs and GPUs.



[1] David N. Smithe, Finite-difference time-domain simulation of fusion plasmas at radiofrequency time scales, Physics of Plasmas 14, 056104 (2007)

[2] C. Nieter and J. Cary. 2004. VORPAL: a versatile plasma simulation code. J. Comput. Phys. 196, 2, 448-473.