Geodesic mode instability driven by electron and ion fluxes during neutral beam injection in tokamaks

摘要

Abstract The effect of a minor concentration of energetic particles produced by parallel NB injection on Geodesic Acoustic Modes (GAM) spectrum is analyzed using fully kinetic equation. It is found that the GAM frequency is reduced by the effective mass renormalization due to that new energetic GAM appears with higher frequency. The electron current in combination with NB driven ion flow, modeled by shifted Maxwell distribution, may overcome the ion Landau damping thus resulting in the GAM instability when electron current velocity is larger than the effective parallel GAM phase velocity Rqω. Qualitative agreement of the theory with co/counter NB injection experiments in COMPASS tokamak is demonstrated. Highlights ? Effect of a minor concentration of the energetic particles due to NB injection on geodesic acoustic mode (GAM) spectrum is analyzed. ? Using shifted Maxwell distribution for all plasma species, fully kinetic treatment is applied to study GAMs. ? The instability occurs due to its cross term of the electron supersonic velocity of the current with ion flow, as well as with energetic ion drift. ? Splitting of GAM spectrum by the effective mass renormalization of energetic particles is found. ? Qualitative confirmation of the theory with co/counter NB injection experiments in COMPASS tokamak is demonstrated. ]]>