Beta and confinement scaling studies with neutral-beam heating in the ISX-B tokamak

Abstract

Experiments to investigate the scaling of volume-averaged beta <β> and a global energy confinement time for neutral-beam-heated (Pb ≤ 2.5 MW) discharges in the ISX-B tokamak are described. The results are condensed into a set of empirical scaling formulas which can be used as a guide for other theoretical and experimental studies of confinement in high-beta, neutral-beam-heated plasmas. The dependence on toroidal field BT, plasma current Ip, and line-averaged electron density n̄e was determined by varying each of these while keeping other external variables fixed. Magnetic diagnostics were used to obtain global properties, and Thomson-scattering-based profile analysis was carried out to permit more detailed investigation of selected cases. The poloidal beta, βp, is found to be independent of BT and n̄e at fixed beam power Pb; confinement is found to deteriorate with increasing Pb but to improve with IP, consistent with previous results. The mechanisms which govern this confinement scaling have not been discerned, but it apparently does not depend on ⟨β⟩, BT, or the (m = 1; n = 1) MHD activity, which typically dominates the MHD diagnostic signals. Losses are primarily through the electron channel, and the scaling of electron energy confinement time is similar to that of .