Description: Two distinct conditions where the rf phase velocity is directed opposite to the ohmically induced electron drift have been studied experimentally: (1) rf current ramp-up (f/sub p/ > 0), where an induced electric field opposes the current increase; (2) rf current ramp-down, where waves are launched opposite the electron drift direction for a decaying plasma current. The time behavior of the electron tail is inferred from hard x-ray (30 to 750 keV) emission as a function of angle to B. In cases (1) and (2) we find that the emission amplitude in the reverse (opposite the LH phase velocity) direction increases throughout the rf pulse, while it is constant in the forward direction. This increase indicates that some high energy electrons are accelerated or are even running away in the direction opposite to the main rf produced tail. It also indicates for case (1) that the electric field in the plasma center has been reversed by the rf current drive.
Date: June 1, 1983
Creator: Stevens, J.; Von Goeler, S.; Bernabei, S.; Chu, T.K.; Hooke, W.; Jobes, F. et al.
Partner: UNT Libraries Government Documents Department