Non-linear Modulation of Short Wavelength Compressional Alfven Eigenmodes
Authors: E. Fredrickson, et. al.
Abstract:
Most Alfvenic activity in the frequency range between toroidal Alfven eigenmodes and roughly
one half of the ion cyclotron frequency on National Spherical Torus eXperiment [Ono et al., Nucl.
Fusion 40 , 557 (2000)], that is, approximately 0.3MHz 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 counterpropagating
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.
__________________________________________________
Submitted to: Physics of Plasmas (December 2012)
__________________________________________________
Download PPPL-4886 (pdf 499 MB 10 pp)
__________________________________________________