Edge plasma control by rf electric field in the compact helical system (CHS)

The reduction of the plasma heat flux on the material limiter and the stabilization of the fluctuations at the plasma boundary by the use of an rf ponderomotive potential barrier on the limiter (rf limiter) have been demonstrated in the compact helical system (CHS) for the ECH heated plasma. The rf current on a graphite limiter surface along magnetic field lines produces a ponderomotive potential barrier, which is large at the limiter edges. The high heat load on the limiter edges, which is measured using an infrared TV camera, has been shown to be reduced by an rf power of 1.4 kW at a frequency of 10 MHz (ωci<ω<<ωce). Another remarkable effect of the ponderomotive potential barrier on the limiter that has been observed is the suppression of density fluctuations (<100 kHz) at the plasma boundary. (orig.)