Toroidal rotation and ion heating during neutral beam injection in PBX-M

Determination of the profiles of the ion temperature and the plasma toroidal rotation has been accomplished by charge exchange recombination spectroscopy in PBX-M. The angular momentum and the thermal ion energy transport have been studied mainly during the H mode phase of a high β_p discharge (I_p ≃ 330 kA, 3.5 × 10¹⁹ ≤ n _e ≤ 6.5 × 10¹⁹ m^-3) having different heating beam configurations (combination of two perpendicular and two tangential neutral beam injections, abbreviated as 2 perp. NBI and 2 parall. NBI). The toroidal rotation velocity V_φ rises substantially in the region of r/a ≥ 0.5 after the L-H transition, and the V_φ profile (peakedness) is more highly dependent on the beam configuration than the T _i profile. The angular momentum confinement time varies from 147 ms (rigid rotation for 2 perp. NBI) to 39 ms (viscous rotation for 2 parall. NBI). In contrast, the thermal energy confinement time is 44-48 ms and is almost independent of the configuration. The transport analysis shows that the radial angular momentum diffusion is caused mainly by the viscous losses and that the angular momentum diffusivity χ_φ is reduced substantially in the outer minor radius region during the 2 perp. NBI H mode. The neoclassical friction effect between the bulk ions and the impurities may influence the χ_φ profiles locally, where the ion temperature gradient is steep.