Thermalization times and scaling laws for alpha particles and hydrogen isotopes in Tokamak plasmas

Thermalization times of light ions in fusion plasmas are calculated using quantum and semiclassical dielectric models for the interaction of external particles with plasma electrons and ions. An accurate analytical approximation is obtained, which combines a classical Bohr-type description for the interaction with plasma ions with a quantum description for the interaction with plasma electrons. Scaling laws for thermalization times are found for different light ions in a characteristic range of intermediate energies of special interest for tokamak systems composed of pure deuterium and deuterium-tritium plasmas. The study covers a range of temperatures between 10^{7} and 10^{9}K and electron densities from 10^{13} to 10^{15}cm^{-3}. A useful fitting formula for the thermalization time is proposed and applied to the cases of plasma heating using energetic deuterium beams and the thermalization of alpha particles produced by D-T fusion reactions. Finally, a set of useful tables with reference values for these cases is provided.