Comparison of collisionless plasma models identifies a robust candidate for nonlinear phenomena

Simulating collisionless plasma has been a longstanding issue. Simple fluid models ignore collisionless wave-particle interactions, but more complex, fully kinetic models are resource intensive.

Jikei and Amano examined two middle-of-the-road fluid models for collisionless plasmas that incorporate some kinetic effects to see what applications suit the models. They compared a classical Chew-Goldberger-Low (CGL) model, which includes a finite Larmor radius and the Landau closure for the longitudinal mode, and a cyclotron resonance closure (CRC) model that accounts for cyclotron and Landau resonances.

“Although fluid-based modeling of collisionless plasmas has been studied for a long time, its use in nonlinear simulations was limited, and the reason for that has not been obvious,” said author Taiki Jikei. “In this paper, we were pleased to clarify the reason the CGL-based models are not suited for nonlinear simulations.”

Using a simulation of a parallel firehose instability, which in early stages is a low frequency phenomenon, Jikei and Amano tested the two models. Their results showed the CGL model failed once high frequency fluctuations appeared, but the CRC model remained robust. The findings suggest using collisionless damping is essential for such models.

“We are excited to confirm our recently developed CRC model is a good candidate for a wide range of collisionless plasma simulations,” Jikei said. “By making further corrections to the CRC model, we may be able to simulate collisionless plasma phenomena without using fully kinetic models, which are very resource heavy.”

The authors hope their findings will help in the development of a new, better collisionless fluid model that could unlock new discoveries in fusion and space plasma physics.

Source: “Critical comparison of collisionless fluid models: Nonlinear simulations of parallel firehose instability,” by Taiki Jikei and Takanobu Amano, Physics of Plasma (2022). The article can be accessed at https://doi.org/10.1063/5.0077064 .