Gyrokinetic particle simulations of reversed shear Alfven eigenmodes in fusion plasmas

A nonlinear gyrokinetic simulation model, which recovers the ideal magnetohydrodynamic (MHD) theory in the linear long-wavelength regime is formulated for studying kinetic MHD processes in magnetized plasmas. This comprehensive formulation enables gyrokinetic simulation of both pressure gradient-driven and current-driven instabilities including ideal and kinetic ballooning modes, kink modes, and shear Alfven waves, as well as their nonlinear interactions in multi-scale simulations.;Implemented in the gyrokinetic toroidal code (GTC), the new formulation is verified in simulations of reversed shear Alfven eigenmode (RSAE) in fusion plasmas. The antenna excitation of RSAE provides verifications of its mode structure, frequency and damping rate from the initial perturbation simulation with kinetic thermal ions. When excited by fast ions, their non-perturbative contributions modify the mode structure relative to the ideal MHD theory. With inclusion of thermal plasma pressure, the mode frequency increases due to the elevation of the Alfven continuum by the geodesic compressibility. The GTC simulations have been benchmarked with extended hybrid MHD-gyrokinetic simulations.;The verified gyrokinetic simulation model is applied to studying the linear properties of RSAE driven by density gradient of neutral beam injected fast ions in a well-diagnosed DIII-D tokamak experiment (discharge ;As a prelude to nonlinear simulations of RSAE and associated fast ion transport, properties of microturbulence in reversed shear plasmas are also studied.