|hudson_icc2006.pdf||2006-03-02 15:17:41||Ben Hudson|
Fast Ion Confinement In MST
Author: Ben F Hudson
Submitted: 2006-01-19 14:46:24
Co-authors: G. Fiksel, R. M. Magee, A. D. Beklemishev, Y. Tsidulko
University of Wisconsin - Madison
1150 University Ave.
Madison, WI 53706
A high power (20 kV, 30A), short-pulse (1.5 ms) neutral beam injector is used to study fast ion confinement and the feasibility of neutral beam heating of an RFP. The injected fast deuterium ions undergo D-D fusion with the bulk ions and the product 2.45 MeV neutron flux is measured outside the vessel with a scintillator and a photomultiplier tube. The observed neutron signal indicates the presence of a well-confined fast ion population with a characteristic loss time in excess of 30 ms. MHD activity (sawtooth crashes), with the related increase in magnetic perturbations, is seen to increase the loss rate to a level that would be commensurate with stochastic losses for the duration of the crash. Counter-injection has been found to result in poor confinement, as expected based on simulation. Analytical and computational studies show that the guiding center drifts alter the safety factor of the guiding center motion and tend to bring it out of resonance with the background magnetic field. As a result, the stochasticity of the fast ion population is reduced. The ions are predicted to become stochastic after having lost sufficient energy that their rotational transform approaches that of the background magnetic field.
Work supported by D.O.E. and N.S.F.