Comment on Electromagnetic Global Gyrokinetic Simulation of Shear Alfven Wave Dynamics in T.pdfVIP

Comment on “Electromagnetic Global Gyrokinetic Simulation of Shear Alfvén Wave Dynamics in Tokamak Plasmas” [Phys. Plasmas 14, 042503 (2007)] Bruce I. Cohen, Andris M. Dimits, and William M. Nevins University of California, Lawrence Livermore National Laboratory, Livermore, California 94550 Abstract This comment clarifies the relation of the research in a recently published article [Phys. Plasmas 14, 042503 (2007)] to other prior publications addressing the inclusion of electromagnetic and drift-kinetic electron physics in gyrokinetic simulation, raises a concern related to the inclusion of kinetic electrons in a system with magnetic shear, and discusses alternatives in the face of an important limitation on the general applicability of the algorithm described therein. The research published in Ref. 1 addresses extensions of a global, particle-in-cell (PIC), gyrokinetic, simulation algorithm to include the coupling of electrostatic drift-type modes to electromagnetic Alfvénic modes using a hybrid, fluid-kinetic, electron model. This comment seeks to clarify the relation of the research in Ref. 1 to other publications predating Ref. 1, raises a concern related to the inclusion of kinetic electrons [Eq.(12) in Ref. 1] in the presence of mode rational surfaces, and points out some alternatives in the face of an important limitation on the general applicability of the algorithm in Ref. 1. Reference 1 presents simulations in global geometry with fluid electrons and formulates the perturbative inclusion of kinetic effects for |ω/k v | 1, but does not || e 1 include electron kinetic effects in any of the si