Alpha particle confinement in tokamaks

An assessment of diffusive tokamak transport mechanisms of concern for alpha particles indicates that the ‘‘stochastic regime’’ is the only one that appears to pose a real danger for adequate alpha confinement. This fact, in conjunction with the threshold character of that mechanism, allows one to decide whether an alpha born at a given location will be lost or confined, according to a very simple criterion. Implementing this criterion numerically results in a new code for the assessment of alpha confinement, which is orders of magnitude faster than earlier codes used for this purpose.