CHARACTERIZATION OF PLASMA PARAMETERS IN SHAPED PBX-M DISCHARGES

The Princeton Beta Experiment-Modification (PBX-M) was run both with e lliptical and with bean-shaped plasmas during the 1992 and 1993 operat ing periods. Two deuterium-fed neutral beams were used for auxiliary h eating, and during 1992 the average power was less than or equal to 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 1 993, and the average power was less than or equal to 3.2 MW. This will be referred to as the medium neutral-beam power (MNBP) period. The ne utron source strength, Sn, showed a scaling with injected power P-b, S n similar to 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 w ith the LNBP period. A weak positive dependence on bean shaping was ob served for the LNBP, and a stronger positive dependence on shaping was observed for MNBP, viz Sn similar to P-d(1.95) I-p(0.17) kappa(2.40) B-T(1.34). High values of , Sn were obtained in bean-shaped plasmas fo r the highest values of epsilon beta(p) at q similar to 2.5 for the L NBP. For the MNBP the highest values of Sn and stored energy were obta ined at q similar to 2.5, and the highest values of epsilon beta(p) w ere obtained at q similar to 3. The achievement of high Sn is aided b y high neutral-beam power, high toroidal field, strong shaping, high e lectron temperature, and broad profiles. The achievement of high epsil on beta(p) is aided by low toroidal held, high density, less shaping, broad profiles, and access to the H-mode, viz epsilon beta(p) similar to P(b)(0.31)kappa(-1.52)B(T)(-0.98). The achievement of high beta(T) is aided by strong shaping, high density, broad profiles, and access t o the H-mode, viz beta(T) similar to P-b(0.55) I-p(1.08) kappa(9.10). Some comparisons with the previous higher neutral-beam (HNBP) period i n 1989 are also made.