An Investigation of Neutral-Beam-Driven Impurity Flow Reversal as an Impurity Control Method in Future Tokamaks

A theory for the effect of directed neutral beam injection on impurity transport in tokamaks is extended to include temperature gradient effects. The extended theory is compared with experimental data, from PLT, and certain coefficients are adjusted to provide agreement. The adjusted theory is applied to assess the potential of NBI being used to prevent impurities from penetrating to the center of future tokamak plasmas, thereby possibly creating a cold radiating edge. The results indicate the possibility of creating a cold radiating edge in TETR and in future tokamaks represented by FED and STARFIRE.