Model for collisional fast ion diffusion into Tokamak Fusion Test Reactor loss cone

An analytic model is developed to estimate the classical pitch angle scattering loss of energetic fusion product ions into prompt loss orbits in a tokamak geometry. The result is applied to alpha particles produced by deutrium–tritium fusion reactions in a plasma condition relevant to Tokamak Fusion Test Reactor (TFTR) [Proceedings of the 14th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Wurzburg, 1992 (International Atomic Energy Agency Vienna, 1992)]. A poloidal angular distribution of collisional fast ion loss at the first wall is obtained and the numerical result from the transp [‘‘A standard D–T supershot simulation’’ (to be published in Nucl. Fusion, 1994)] code is discussed. The present model includes the effect that the prompt loss boundary moves away from the slowing‐down path due to reduction in banana thickness, which enables one to understand, for the first time, the dependence of the collisional loss rate on Zeff.