Diffusion in tokamaks with impurities in the Pfirsch-Schlueter regime

The transport in tokamaks due to collisions between impurity ions in the Pfirsch-Schlueter regime and light ions is considered. The diffusion coefficients for the particles have a Pfirsch-Schlueter-like structure for all the regimes of light ions. They experience, however, a transition from a set of values (A) to a different set of values (B), when the quantity v2sub(thl)tausub(Dl)tausub(Ml)(qR)-2 varies through a value of the order unity. (vsub(thl) and tausub(Dl), tausub(Ml) are the thermal velocity and the relaxation times for deflection and Maxwellization of light ions, respectively.) The values (A) (applicable, in particular, when the light ions are in the banana and plateau regimes) allow, in principle, plasma purification by the ion temperature gradient. (author)