EXPERIMENTAL-STUDY OF SHEATH CURRENTS IN THE SCRAPE-OFF LAYER DURING ICRH ON TEXTOR

In our previous study on TEXTOR it has been shown that an excited Fara day-shielded fast-wave antenna draws a large DC electron current from the plasma due to the sheath rectification effect. In the present stud y, it is shown for the first time that this DC current (up to 400 A) e xtends toroidally all around the circumference of the machine and retu rns to the wall via conducting objects which are electrically connecte d to the wall. Preliminary measurements of r.f. currents in the scrape -off layer were performed using a specially designed Rogowski coil.