Characteristics of Short Wavelength Compressional Alfven Eigenmodes
Authors: E.D. Fredrickson, N.N. Gorelenkov, M. Podesta, A. Bortolon, N.A. Crocker, S.P. Gerhardt, R.E. Bell, A. Diallo, B. LeBlanc, F. M. Levinton, and H. Yuh
Abstract:
Most Alfven activity in the frequency range between Toroidal Alfven
Eigenmodes and roughly one half of the ion cyclotron frequency on NSTX [M.
Ono, et al., Nucl. Fusion 40 (2000) 557], that is, approximately 0.3 MHz up to
~1.2 MHz, are modes propagating counter to the neutral beam ions. These
have been modeled as Compressional and Global Alfven Eigenmodes (CAE
and GAE) and are excited through a Doppler-shifted cyclotron resonance with
the beam ions. There is also a class of co-propagating modes at higher
frequency than the counter-propagating CAE and GAE. These modes have
been identified as CAE, and are seen mostly in the company of a low
frequency, n=1 kink-like mode. In this paper we present measurements of the
spectrum of these high frequency CAE (hfCAE), and their mode structure. We
compare those measurements to a simple model of CAE and present a
predator-prey type model of the curious non-linear coupling of the hfCAE and
the low frequency kink-like mode.
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Submitted to: Physics of Plasmas (December 2012)
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