Compressional magnetic field fluctuation in global gyrokinetics

The gyrokinetic framework has been successful in simulating a variety of phenomena in fusion and astrophysical plasmas. Past research has mostly focused on electrostatic and shear-magnetic fluctuations, neglecting compressional magnetic fluctuations. We derive a radially global gyrokinetic framework which includes compressional fluctuations. Using finite element functions, we construct the field equations. The low-β constraint is relaxed by including the full coupling of electrostatic, shear-magnetic, and compressional-magnetic fluctuations. We present an initial implementation of this new set of equations in the gyrokinetic turbulence code GENE. With the compressional magnetic fluctuations included in GENE, the Gradient-driven Drift Coupling instability found in the high-β experiments in the Large Plasma Device, as well as magnetic reconnection in the solar corona, can be studied to finer precision.