(EX/6-3) Alfvén Instabilities in DIII-D: Fluctuation Profiles, Thermal-Ion Excitation, and Fast-Ion Transport

W.W. Heidbrink1), G.J. Kramer2), R. Nazikian2), M.A. Van Zeeland3), M.E. Austin4), H.L. Berk4), K.H. Burrell5), N.N. Gorelenkov2), Y. Luo1), G.R. McKee6), T.L. Rhodes7), G. Wang7), DIII-D Team
 
1) University of California-Irvine, Irvine, California, United States of America
2) Princeton Plasma Physics Laboratory, Princeton, New Jersey, United States of America
3) Oak Ridge Institute for Science Education, Oak Ridge, Tennessee, United States of America
4) University of Texas, Austin, Texas, United States of America
5) General Atomics, San Diego, California, United States of America
6) University of Wisconsin, Madison, Wisconsin, United States of America
7) University of California, Los Angeles, California, United States of America

Abstract.  To understand and predict alpha-particle driven instabilities and the resultant alpha-particle transport in ITER, it is essential to measure fast-ion transport arising from Alfvén instabilities in present day experiments. In DIII-D, several diagnostic systems have improved sensitivity and bandwidth for the detection of Alfvén modes, including the interferometer, reflectometer, beam-emission spectroscopy, and electron cyclotron emission diagnostics. A new technique, fast-ion Dα (FIDA) spectroscopy, measures the spatial fast-ion profile. These diagnostics are applied to the toroidicity-induced Alfvén eigenmodes (TAE), reversed-shear Alfvén eigenmodes (RSAE), and compressional Alfvén eigenmodes (CAE) that are driven by deuterium neutral beam ions in DIII-D. FIDA measurements indicate large reductions in the fast-ion density at the center of the plasma during Alfvén activity. The measured fluctuations indicate spatial localization of RSAEs near the minimum q surface, as theoretically expected. Unstable toroidal mode numbers as large as n = 40 are inferred with measured poloidal wavenumbers on the thermal ion gyroradius scale. Calculations indicate the high n modes are excited by the thermal ion population.
* Work supported by US DOE under SC-G903402, DE-FG03-97ER54415, DE-FC02-04ER54698, DE-FG03-95ER54309, DE-AC02-76CH03073, DE-FG03-96ER54373, DE-FG03-01ER54615, and DE-AC05-76OR00033.

Full paper and slides available (PDF)