Anomalous fast ion losses at high β on the Tokamak Fusion Test Reactor
Authors: E.D. Fredrickson, M.G. Bell, R.V. Budny, D.S. Darrow, and R. White
Abstract: This paper describes experiments carried out on the Tokamak Fusion Test Reactor (TFTR) [R J Hawryluk, et al., Plasma Phys. Control. Fusion 33 (1991) 1509] to investigate the dependence of β-limiting disruption characteristics on toroidal field strength. The hard disruptions found at the β-limit in high field plasmas were not found at low field, even for β's 50% higher than the empirical β- limit of βn ≈ 2 at high field. Comparisons of experimentally measured β's to TRANSP simulations suggest anomalous loss of up to half of the beam fast ions in the highest β, low field shots. The anomalous transport responsible for the fast ion losses may at the same time broaden the pressure profile. Toroidal Alfvén eigenmodes, fishbone instabilities, and Geodesic Acoustic Modes and are investigated as possible causes of the enhanced losses. Here we present the first observations of high frequency fishbones [F Zonca, et al., Nucl. Fusion 49 (2009) 085009] on TFTR. The interpretation of Axi-symmetric Beam-driven Modes as Geodesic Acoustic Modes and their possible correlation with transport barrier formation are also presented.
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Submitted to: Physics of Plasmas
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Download PPPL-5083 (pdf 2.3 MB / 21pp)
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