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

Experiments to investigate the scaling of volume-averaged beta <#betta#> and a global energy confinement time tausub(E)* for neutral-beam-heated (Psub(b) <= 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 Bsub(T), plasma current Isub(P), and line-averaged electron density n-barsub(e) 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, #betta#sub(p), is found to be independent of Bsub(T) and n-barsub(e) at fixed beam power Psub(b); confinement is found to deteriorate with increasing Psub(b) but to improve with Isub(P), consistent with previous results. The mechanisms which govern this confinement scaling have not been discerned, but it apparently does not depend on <#betta#>, Bsub(T), 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 tausub(E)*. (author)