re Spherical Tokamak (MAST) [A. Sykes, R. J. Akers, L. C. Appel et al., Nucl. Fusion 00, 0000 (0000)], the Joint European Torus (JET) [P. H. Rebut et al., Nucl. Fusion 00, 0000 (0000)], and ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 00, 000 (0000)]. In the MAST simulation, prompt losses of beam ions injected counter to the plasma current drive up a radial electric field that saturates at a level such that beam ions subsequently injected are confined electrostatically. Although the actual radial electric fields in counterinjected MAST discharges are lower than this, the scenario explored in the simulation would be approached in MAST plasmas with sufficiently low collisionality. The JET simulation, although unrealistic, shows that a similar process could be driven by losses of fusion 