Helicity injection and dissipation in the edge region on a reversed field pinch

Helicity injection and dissipation in the edge plasma region are studied in the REPUTE-1 reversed field pinch (RFP) device. Increases in one-turn loop voltage V1 and magnetic fluctuations with nearly constant ion temperature are found advancing movable limiter or injection probe into the plasma. A drastic in V1 is observed with an insertion of ∼8cm from the plasma edge. This V1 increase under various conditions is discussed comparing with theories. The induced voltage between parallel plates (poloidal direction) is measured (<60V) as a function of the insertion depth, which shows the presence of the high energy electrons (at least more than 20eV with a relative population of less than several %). The first dc helicity injection is tried applying a voltage between two parallel plates (injection probe) inserted to the plasma edge, and effects on plasma performance are studied. The injected current up to 9kA is nearly proportional to the applied voltage VH with a small offset voltage. A transient increase in the toroidal flux by ∼10% and a decrease in the poloidal field by <10% are found (plasma takes the more relaxed state) near the injection port, regardless of the polarity of VH. An analysis of electrical circuit is also done to estimate the load of the probe part. (author)