Abstract Details

Add files

Ion heating and classical impurity ion confinement in the RFP

Author: John S Sarff
Requested Type: Poster Only
Submitted: 2012-12-07 16:41:17

Co-authors: A.F. Almagri, J.K. Anderson, B.C. Chapman, D.J. Den Hartog, S. Eilerman, G. Fiksel, S.T.A. Kumar, R. Magee, J.A. Reusch, J. Titus, V. Mirnov

Contact Info:
University of Wisconsin-Madison
1150 University Ave
Madiosn, WI   53706
USA

Abstract Text:
Ions are heated to high temperature in MST by a non-collisional process related to tearing magnetic reconnection. Several recent measurements reveal key characteristics of the heating that can be compared with several proposed mechanisms. Since the heating power is not known precisely, it is difficult to evaluate ion thermal confinement. However, the impurity ion particle confinement has been measured in improved-confinement plasmas obtained with inductive control (PPCD), revealing that the ions attain classical confinement when magnetic fluctuations are small.

Measurements of the ion dynamics on MST are facilitated by several key diagnostics: CHERS, Rutherford scattering, and neutral particle analyzers. The heating is very powerful during sawtooth crash relaxation. The impurity ion temperature measured by CHERS shows that the heating is anisotropic, with T_perp>T_parallel. Collisional equilibration occurs soon after the crash. Neutral particle analyzers observe this heating, but also reveal an energetic ion tail extending to at least 30 keV. This tail has a power-law character. The tail ions are well-confined, consistent with the good confinement observed for NBI-generated 25 keV ions (see J. Anderson this meeting). Passive Doppler spectroscopy measurements of a number of edge-localized ions in lower charge states reveals a Z/m dependence that might be consistent with cyclotron-like heating through a turbulent magnetic energy cascade.

CHERS measurements of fully-stripped carbon density reveal the formation of a hollow profile following the application of inductive profile control (PPCD). An analysis of classical (collisional) transport in the RFP shows good agreement with the measured profile and its evolution. Unlike the tokamak or stellarator, mod(B) tends to be everywhere normal to magnetic surfaces in the RFP, so banana orbit widths are smaller than the gyro-radius. Hence the irreducible collisional transport is classical rather than neoclassical. The hollow profile is expected, resulting from the anti-pinch associated with temperature screening.

Characterization: 4.0

Comments: