Ion confinement in NBI heated START plasmas

The novel use of neutral beam injection (NBI) in tight aspect ratio tokamaks with relatively low edge magnetic fields is being investigated in the START tokamak. Predictions from the ASTRA transport code, which includes tight aspect ratio effects, are in good agreement with observations of ion confinement in START Ohmic plasmas. NBI heating of the START tokamak is most evident in the ion temperature which typically increases from ~100eV to ~300eV. Assuming ion neoclassical confinement during NBI, the required heating from the fast ions to account for the observations is consistent with that predicted from a Monte--Carlo fast ion transport code. Similar T_e(r) and T_i(r) profiles are found and at the highest NBI heating to date (500kW) the magnitudes are also similar.