Kinetic Simulations of Highly Magnetized Plasmas

Link

Efficiently modeling highly magnetized plasmas is essential for applications ranging from astrophysics to fusion, yet first-principles simulations become prohibitively expensive when high gyrofrequencies must be resolved.
We develop and test two special-relativistic particle pushers using the guiding center approximation (GCA) within the state-of-the-art OSIRIS particle-in-cell (PIC) framework.


The first, the GCA pusher, updates the parallel velocity explicitly and advances the guiding center position implicitly via fixed-point iteration, extending prior work by including both the mirror force and the Grad-B drift.
The second, the GCA-correction pusher, modifies the Boris pusher by retaining its parallel update while imposing guiding center drifts on the perpendicular motion; extending previous attempts that considered only the EXB drift.
We benchmark both against the Boris pusher using test particles in prescribed electromagnetic fields, from simple analytical configurations isolating individual drifts to turbulent fields self-generated by a three-dimensional PIC simulation of the Weibel instability.


Our results show that, unlike the Boris pusher, the GCA pusher accurately captures particle dynamics when the gyrofrequency is underresolved, provided spatial scales of the electromagnetic field variation are well resolved and the GCA remains valid. The GCA-correction pusher is currently less robust due to time-centering issues, but achieves comparable accuracy in some regimes while offering higher efficiency.


These findings demonstrate that GCA-based pushers enable accurate modeling of kinetic physics in strongly magnetized plasmas with much larger time-steps than conventional PIC, opening a path to significant computational speedups, improving our ability to model both astrophysical and laboratory fusion plasmas over relevant scales.