Session KP01 - Poster Session III.
POSTER session, Tuesday afternoon, March 23
Exhibit Hall, GWCC
The present work describes a simple model for determining the energy confinement time in a reversed field pinch (RFP). The model is motivated by the idea that the region interior to the Bz reversal point is in a highly turbulent state resulting from tearing mode instabilities. It has been suggested, in fact, that the profiles adjust themselves so as to be in a state of nearly marginal stability against tearing modes. This conjecture further suggests that one approach to deduce the energy confinement time in an RFP is to determine the marginally stable profiles, consistent with MHD pressure balance, and use these profiles to evaluate tau using the standard definition. This somewhat heuristic approach is obviously less rigorous than a self consistent calculation of anomalous thermal conductivity and the resulting implied profiles, but is, nevertheless, much simpler to implement.
The original goal of the research was to develop the "marginally stable tearing mode" transport model. Even with such a simplified approach, it soon became apparent that a significant level of computational work would be required to determine profiles that were marginally stable to tearing modes. As a prelude to this work, it was decided to first develop a framework and formulation of the calculation based on a simpler local marginal stability criterion, the Suydam criterion. Once the analytic and computational machinery were set up, the more complicated, non-local tearing mode criterion would be implemented. The original expectation was that the Suydam criterion model, based on ideal MHD, would be more optimistic than the tearing mode model based on resistive MHD.
The calculation based on Suydam’s criterion has been completed. Somewhat to our surprise, the expression for tau agrees remarkably well with the existing experimental data in terms of both scaling and magnitude. This unexpected result is the motivation for the present paper. Details of the calculation and results will be presented at the meeting.