Plasma auto-biasing during Ohmic H-mode in the STOR-M tokamak

Summary form only given. Applying a short current pulse on nominal Ohmic discharge in the STOR-M tokamak triggers ohmic H-mode characterized by reduced H/sub /spl alpha radiation, increased global energy confinement time, reduced edge density and magnetic fluctuations, and suppression of sawtooth oscillations. Measurements of plasma floating potential at the plasma edge and in the scrape-off layer indicate that the Ohmic H-mode is accompanied by negative plasma autobiasing, which leads to a steeper radial electric field profile at the edge. Since the duration of the current pulse (/spl les/20 kA, 100 /spl mu/s) is shorter than the resistive skin time (/spl sime/1 msec), preferential edge heating is expected, which is believed to be responsible for the changes in the edge discharge condition favorable for inducing ohmic H-mode. The electron density profile becomes steeper at the edge during the H-mode, and clear formation of a density pedestal has been seen.