Linear stability studies using NIMROD's continuum drift kinetic (CDK) model

The interaction of thermal and energetic particles with macroscopic fluid modes in magnetized fusion plasmas affects both stability and transport. In order to better understand these interactions from the perspective of a plasma fluid code, continuum solutions to the linearized drift kinetic equation (DKE) for thermal electrons and ions and energetic particles have been implemented in the NIMROD code and applied successfully in studies of linear tokamak stability. The continuum approach in NIMROD efficiently employs (1) a fully implicit solution to the DKEs that can be iterated with fluid variables to effect a nearly fully implicit, simultaneous advance at large time step, (2) a finite-element approach in pitch-angle that efficiently resolves resonances in velocity space and, (3) nonclassical quadrature schemes in the normalized speed coordinate that provide rapid convergence for the CGL pressure tensor closures in this hybrid fluid/kinetic model. Growth and rotation rates from verification and validation exercises show agreement for several instabilities including the ideal internal kink, external kink, reverse shear Alfven eigenmodes and peeling ballooning modes.