Current profile control and fluctuation reduction in MST via electrostatic current injection

Summary form only given, as follows. We have designed and are conducting a current profile control experiment aimed at reducing fluctuations and improving confinement in RFP plasmas. Profile modification will be achieved via electrostatic injection of electrons from /spl sim/30 miniature plasma sources. Each source produces a 1 kA electron beam which is dense (/spl sim/150 kA/cm/sup 2/ at 70 cm from the source), highly directional, and without large impurity content. An initial multi-injector experiment in which a total current of 5 kA was injected is completed. Results from this experiment will be discussed. One of the promising results is an apparent increase in the plasma density by 50% and associated increase in the particle confinement time. Low impurity influx from the sources is essential for scaling up the injection system. MHD computations predict a current of /spl sim/30 kA is necessary to suppress fluctuations in Madison Symmetric Torus (MST) and future experiments will employ an increasing number of injectors until this level is reached.