Monte Carlo simulation of minority ion bootstrap current by off-axis ion cyclotron heating in tokamaks

The characteristics of the ion current driven by localized minority ion cyclotron heating in tokamaks in the presence of a well enhanced high energy tail are examined by fully toroidal Monte Carlo guiding centre simulations. The contribution of the diamagnetic current to the minority current drive has been found to be of importance as it dominates the resulting fast ion current in the presence of significant toroidal trapping of RF heated minority ions, and also because it is excited even with symmetric launching, thus requiring no directivity in the antenna system. The driven currents from the simulation are compared with a functional form approximating the trapped ion contribution to the minority ion diamagnetic current in the strong heating limit. The bidirectional current profile, the dependence on wave intensity and the increase of the current generation efficiency with electron temperature and with the inverse major radius as predicted by the Monte Carlo simulations are satisfactorily reproduced by the estimate