Trapped ion depletion by anomalous diffusion due to the dissipative trapped ion instability

Abstract

At high temperatures the Kadomtsev-Pogutse diffusion in Tokamaks can become so large as to cause depletion of trapped ions if these are replaced with free ions by means of collisions rather than being directly recycled or injected. Modified Kadomtsev-Pogutse diffusion formulas are employed in order to estimate this effect in the cases of classical and anomalous collisions. The maximum trapped-ion depletion is estimated from the Penrose stability condition. For anomalous collisions a Bohm-type diffusion is derived. Numerical examples are given for JET-like parameters (JET=Joint European Torus). Depletion is found to reduce diffusion by factors of up to 10 and more.