Observation of reverse shear Alfv\'{e}n eigenmodes in Alcator C-Mod and their modeling with NOVA*

The phase contrast imaging (PCI) system on Alcator C-Mod has observed reverse shear Alfv\'{e}n eigenmodes (RSAE) during the current ramp with early ICRF heating. Using the ideal MHD code NOVA$^{1}$, the frequency chirping characteristics of these modes can be modeled with good accuracy. It is noted that the minimum frequency may be interpreted as the geodesic deformation of Alfv\'{e}n continuum at low frequency$^{2}$. RSAEs observed with PCI show intermittent behavior that suggests a significant continuum interaction. Ignoring fast particle effects, the MHD eigenmode solutions from NOVA are compared to the experimental data. The central shear and q$_ {min}$ are adjusted until a good fit is achieved. Possible q profiles based on this analysis will be presented. \\ \\$^{*} $Work supported by USDOE Contract DE-AC02-76-CH0-3073 and Coop. Agree. No. DE-FC02-99-ER54512\\ \\$^{1}$C.Z. Cheng and M.S. Chance, J. Comp. Phys. \textbf {71}, 124 (1987).\\ $^{2}$M.S. Chu et al., Phys. Fluids B \textbf{4}, 3713 (1992).