Confinement of Injected Silicon in the Alcator-ATokamak

Results of injected-impurity transport studies on the Alcator-$A$ tokamak are presented. It is found that injected silicon diffuses throughout the plasma and is then observed, contrary to the predictions of neoclassical theory, to leave the discharge, having confinement times much shorter than the discharge length. There is no observed buildup of silicon on the axis of the device. The impurity confinement is found to increase with plasma current and background-ion mass. Scalings with electron density and toroidal field are also discussed.