Energy transport in discharges with off-axis neutral beam injection (NBI) has been compared with transport in similar discharges with on-axis NBI. A two fluid power balance analysis assuming purely diffusive transport indicates substantial improvements in the plasma centre in both the ion and the electron channels during off-axis NBI. The ion thermal diffusivity, χi, and the angular momentum diffusivity, χϕ, in the plasma centre improve by over 2 orders of magnitude, and χi decreases below the Chang-Hinton neoclassical level. A detailed error analysis of the energy transport has been carried out. The electron thermal diffusivity in the plasma centre improves by an order of magnitude during off-axis NBI. The predicted peak ion temperature, assuming the same ion diffusivity profile for off-axis NBI as with on-axis NBI, is nearly a factor of 2 lower than the measured ion temperature profile with off-axis NBI. In addition, assuming unchanged diffusivities, significant inward energy flow is required to explain the observed ion temperature profiles during off-axis NBI.
Toroidal rotation and ion heating during neutral beam injection in PBX-M
Measurement of local ion diffusion coefficients in the Tokamak Fusion Test Reactor