Effects of compressional magnetic perturbation on kinetic Alfven waves

Kinetic Alfven waves play a very important role in the dynamics of fusion as well as space and astrophysical plasmas. The compressional magnetic perturbation $\delta $B\textbar \textbar can play important role in kinetic Alfven waves (KAW) and various instabilities at large plasma $\beta $. It could affect the nonlinear behavior of these modes significantly even at small $\beta $. In this study, we have implemented $\delta $B\textbar \textbar in gyrokinetic toroidal code (GTC). The perpendicular Ampere's law is solved as a force balance equation. Double gyroaveraging is incorporated in the code to treat the finite Larmor radius effects related to $\delta $B\textbar \textbar terms. KAW is studied in slab geometry as a benchmark case. A scan in $\beta $ for the KAW dispersion relation shows that as $\beta $ approaches 1 (\textgreater 0.3), the effects of $\delta $B\textbar \textbar becomes important. Connections are made with other existing studies of KAWs in the fusion and space plasma literature. This new capability of including $\delta $B\textbar \textbar in GTC could be applied to nonlinear simulations of modes such as kinetic ballooning and tearing modes.