Phase contrast imaging measurements of reversed shear Alfveneigenmodes during sawteeth in Alcator C-Mod

摘要

Reversed shear Alfven eigenmodes (RSAEs) have been observed with the phase contrast imagingdiagnostic and Mirnov coils during the sawtooth cycle in Alcator C-mod [M. Greenwald et al., Nucl.Fusion 45, S109 (2005)] plasmas with minority ion-cyclotron resonance heating. Bothdown-chirping RSAEs and up-chirping RSAEs have been observed during the sawtooth cycle.Experimental measurements of the spatial structure of the RSAEs are compared to theoreticalmodels based on the code NOVA [C. Z. Cheng and M. S. Chance, J. Comput. Phys. 71, 124 (1987)]and used to derive constraints on the q profile. It is shown that the observed RSAEs can beunderstood by assuming a reversed shear q profile (up chirping) or a q profile with a local maximum(down chirping) with q ≈1.