Multiscale Gyrokinetic Simulations Including the Reversal Surface in Reversed-Field Pinch Plasmas

Multiscale, gyrokinetic simulations are important in understanding the full behavior of turbulence in magnetically confined plasmas. In reversed-field pinch (RFP) plasmas, the gyrokinetic code GENE is used to capture tearing modes, drift waves and their interactions. In an RFP equilibrium, the toroidal field reverses sign. The mapping between the toroidal flux and the radius is double valued. Since gyrokinetic codes commonly use the toroidal field to label magnetic flux and include factors of the inverse safety factor in coordinate definitions, changes to the framework are required to treat radial regions that include the reversal surface where the field crosses zero.

In this work, we introduce such changes to the GENE code and perform tests for flux-tube simulations that include the reversal surface. These results set the stage for planned global simulations covering most of the device, including the reversal surface, to study tearing modes and microturbulence in the RFP.