EDGE PLASMA CONDITIONS AND PLASMA-SURFACE INTERACTIONS IN EXTRAP T1

The T1 device is a toroidal machine with R/a = 0.5 m/0.06 m and stainless steel wall. It has been used to study high current density reversed field pinch plasmas. The edge plasma has been extensively investigated with double and triple Langmuir probes, heat flux probes and passive probes. Discharges with 40-90 kA plasma current is characterized by an edge density n(e)(a) approximate to 10(19) m(-3), T-e(a) approximate to 10 eV and a high asymmetric parallel heat flux. A drift perpendicular to the magnetic field can be inferred from Langmuir probe measurements and passive probes and appears to be largely diamagnetic. Edge ion temperatures T-i greater than or equal to 100 eV are inferred from the saturation behaviour of hydrogen ions implanted in passive probes, from the high q(i parallel to) and from the inferred sputtering rate of metals.