Deposition and Thermalization of Fusion Products in a Tokamak Plasma

As suprathermal fusion products (fp's) slow down in a Tokamak, their average drift is inward. The effect that this drift has on the spatial distribution profile for suprathermals approaching thermal energies, on the energy distribution, and on the plasma heating profile, is examined for five reactor cases ranging from near-term low-current devices to conceptual power reactors. In-situ energy deposition is shown to be a reasonable assumption for the higher current machines, differing in the plasma heating evaluation by only a few percent compared to a more exact Monte Carlo-like treatment (SYMALF). However, for lower current Tokamaks the SYMALF method (or, for approximate work, in-situ modified by a loss fraction) appears necessary. It is also shown that, for certain cases, the fp energy distribution near the plasma edge has a positive slope with increasing energy, representing a possible driving mechanism for micro-instabilities.