Details

IT02 · Internal Alfvén Eigenmode Observations on DIII-D

M.A. Van Zeeland^a, M.E. Austin^b, T.N. Carlstrom, T. Deterly^c, D.K. Finkenthal^c, G.J. Kramer^d, M.A. Makowski^e, G.R. McKee^f, R. Nazikian^d, W.A. Peebles^g, T.L. Rhodes^g, W.M. Solomon^d, E.J. Strait

General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
^aOak Ridge Institute for Science Education, Oak Ridge, Tennessee, USA
^bUniversity of Texas at Austin, Austin, Texas, USA
^cPalomar College, San Marcus, California, USA
^dPrinceton Plasma Physics Laboratory, Princeton, New Jersey, USA
^eLawrence Livermore National Laboratory, Livermore, California, USA
^fUniversity of Wisconsin, Madison, Wisconsin, USA
^gUniversity of California-Los Angeles, Los Angeles, California, USA

To whom correspondence should be addressed (vanzeeland@fusion.gat.com)
(Dated: January 17, 2006)

Abstract: Recent upgrades to many of the diagnostic systems on DIII-D [J.L. Luxon, Nucl. Fusion 42, 614 (2002)] such as the CO₂ interferometer, far-infrared scattering, beam-emission spectroscopy, and quadrature reflectometer have significantly extended their capabilities and made possible the experimental study of Alfv´en eigenmodes (AEs) through observation of the AE induced density perturbation. Measurements have revealed the presence of several different classes of AEs in DIII-D discharges including the toroidal Alfv´en eigenmode (TAE), reverse shear Alfv´en eigenmode (RSAE or Alfv´en cascade), and ellipticity induced Alfv´en eigenmode (EAE). Based on a simple model for the RSAE frequency, a sensitive diagnostic for the evolution of the minimum magnetic safety factor (q_min) is presented and results are compared with motional Stark effect (MSE) measurements. Strong localization of high toroidal mode number RSAEs to regions near the minimum of the magnetic safety factor is exhibited on CO2 interferometer and beam emission spectroscopy (BES) measurements. Based on this observation, a method for providing constraints on the radial location of q_min is demonstrated and a favorable comparison to MSE measurements is made. Detailed measurements of TAEs using a new all-digital large bandwidth two-color CO2 interferometer system show a strong asymmetry between vertical and radial viewing interferometer chords confirming previously reported results. Additionally, effects related to line-integrated observations are clearly illustrated by comparison to local BES measurements and potential issues related to this are discussed.

Note: In special issue in Nuclear Fusion - volume 46, issue 10
http://www.iop.org/EJ/toc/0029-5515/46/10

Synopsis (pdf)