ANALYTICAL APPROXIMATION OF FUSION REACTIVITY PROFILES

It is shown that any representation of the functional dependence of th ermal fusion reactivity on plasma temperature can be rewritten in an e xact alternative form as a power law function and the appropriate powe r exponent is given. Based on this alternative representation, a simpl e but accurate generalized parabolic approximation is found for the ra dial profile of the fusion reactivity, given corresponding approximati ons for ion temperature and density. The usefulness of the approximati on is illustrated by deriving an explicit expression for the ion therm al conductivity from a recently published investigation based on the o bserved decay of 2.5 MeV neutron emission from a neutral beam heated d euterium plasma after the beams have been shut off.