Characterization of plasma parameters in shaped PBX-M discharges

The Princeton Beta Experiment-Modification (PBX-M) was ran both with elliptical and with bean-shaped plasmas during the 1992 and 1993 operating periods. Two deuterium-fed neutral beams were used for auxiliary heating, and during 1992 the average power was ≤2.5 MW. This will be referred to as the lower neutral-beam power (LNBP) period. As many as four deuterium-fed neutral beams were used during 1993, and the average power was ≤3.2 MW. This will be referred to as the medium neutral-beam power (MNBP) period. The neutron source strength, Sn, showed a scaling with injected power P_b, Sn ∼ P_b^1.9 for both the LMBP and MNBP periods. A much wider range of shaping parameters was studied during the MNBP as compared with the LNBP period. A weak positive dependence on bean shaping was observed for the LNBP, and a stronger positive dependence on shaping was observed for MNBP, viz Sn ∼ P_b^1.95I_p^0.17κ ^2.40B_T^1.34. High values of Sn were obtained in bean-shaped plasmas for the highest values of εβ_p at q* ∼ 2.5 for the LNBP. For the MNBP the highest values of Sn and stored energy were obtained at q* ∼ 2.5, and the highest values of εβ_p were obtained at q* ∼ 3. The achievement of high Sn is aided by high neutral-beam power, high toroidal field, strong shaping, high electron temperature, and broad profiles. The achievement of high εβ_p is aided by low toroidal field, high density, less shaping, broad profiles, and access to the H-mode, viz εβ_p ∼ P_b^0.31κ^-1.52B_T ^-0.98. The achievement of high β_T is aided by strong shaping, high density, broad profiles, and access to the H-mode, viz β_T ∼ P_b^0.55I_p^1.00κ^9.10. Some comparisons with the previous higher neutral-beam (HNBP) period in 1989 are also made.