Effects of multiple ion species on two-dimensional trapped-electron modes

Previous calculations for the two-dimensional spatial structure of drift and trapped-electron modes in tokamaks are generalized to include an arbitrary number of ion species. Thus, it is possible to determine the influence of light or heavy impurity ions, and of multiple hydrogen isotopes, on these instabilities. As an example, results are presented for the case of a single light impurity species. Here, the effect is found to be either stabilizing or destabilizing, depending on specific parameters such as the equilibrium density profiles. Moreover, if a sufficiently idealized model is adopted, beam ion effects can also be studied. In the case considered, corresponding to the neutral-beam-heated Princeton Large Torus, these effects are found to be stabilizing.