Reversed Shear Alfvén Eigenmodes Associated with the Ellipticity and Triangularity Alfvén Gaps
Authors: G.J. Kramer and G-Y. Fu
Date of PPPL Report: June 2006
Submitted to: Plasma Physics and Controlled Fusion
Based on numerical simulations with the magnetohydrodynamic code NOVA, reversed shear Alfvén Eigenmodes (RSAE) associated with the ellipticity-induced and non-circular triangularity-induced Alfvén Eigenmode gaps were found. An analytical model for large aspect ratio plasmas confirms the existence of those modes with a pressure gradient threshold that agrees very well with the NOVA calculations. It is predicted that these higher gap RSAEs might be observed in existing large tokamaks in the early phase of reversed shear discharges when the minimum value of the magnetic safety factor is high (larger that two). Because the pressure-gradient threshold decreases with major radius these modes might readily show up in ITER plasmas.