Study of the Effect of Compressional Alfvén Modes on Thermal Transport in the National Spherical Torus Experiment
Authors: E.D. Fredrickson, N. Gorelenkov, C.Z. Cheng, R. Bell, D. Darrow, D. Gates, D. Johnson, S. Kaye, B. LeBlanc, D. McCune, J. Menard, L. Roquemore, and S. Kubota
Date of PPPL Report: February 2002
Published in: Physics of Plasmas 9 (May 2002) 2069-2076. (Presented at the American Physical Society Division of Plasma Physics in Long Beach, CA, October 29 through November 2, 2001.)
With the first injection of neutral beams into the National Spherical Torus Experiment (NSTX) [Ono, et al., Nucl. Fusion 40 (2000) 557] a broad spectrum of fluctuations consisting of nearly equally spaced peaks in the frequency range from about 0.2 to 1.2 times the ion cyclotron frequency was observed. The frequencies scale with toroidal field and plasma density consistently with Alfvén waves. From these and other observations, the modes have been identified as Compressional Alfvén Eigenmodes (CAE). It has also recently been found that the ratio of the measured ion and electron temperatures in NSTX during neutral-beam heating is anomalously high [Bell, Bull. Am. Phys. Soc. 46 (2001) 206]. To explain the anomaly in the ratio of ion to electron temperature, it has been suggested that the CAE, driven by the beam ions, stochastically heat the thermal ions [Gates, et al., Phys. Rev. Lett. 87 (2001) 205003]. In this paper it is shown through studies of the power balance that stochastic heating of the thermal ions by the observed CAE alone is not solely responsible for the anomaly in the ion to electron temperature ratio.