Analysis of impurity confinement experiments with co- and counter-injected neutral beams in the ISX-B and PLT tokamaks

An extended impurity transport theory, which includes NBI momentum input and radial momentum transfer effects, inertial strong-rotation (vø ∼ vth) effects and radial electric field effects, has been applied to analyse the impurity accumulation experiments in ISX-B and PLT. Theory and experiment are found to be in good agreement. Counter-injection causes a central impurity accumulation that is several times larger than for co-injection, and this difference can be understood in terms of differences in transport properties between co-injection and counter-injection.