Density profile and DC electric field measurements in the TEXTOR boundary for ohmic and ICRF-heated discharges

TEXTOR is a medium size tokamak with circular cross-section equipped with the ALT II toroidal pumped limiter. The major and minor radii are 1.75 m and 0.46 m, respectively, and ALT II, consisting of eight movable graphite blades, is situated at the outside about 45o below the equatorial plane. Two antenna pairs extending poloidally from 15o below the outer midplane to 7.5o from the top of the machine are installed for auxiliary heating in the ion cyclotron frequency range. TEXTOR is dedicated to plasma wall interaction studies towards a better understanding of the scrape-off layer (SOL) and the plasma at the limiter edge. TEXTOR is equipped with active and passive diagnostics for the SOL/edge region such as continuous thermal Li-beam spectroscopy (T=550oC, 2x1014 particles/sec, 128 Si-diode array), laser ablation technique (LiF/C target, 1 J ruby laser, E<10 eV, n=1015m-3, same type of camera), a reciprocating Langmuir probe (150 voltage sweeps per probe plunge, 500 Hz, total transit time for 30 cm of 0.3 s), a rotating Langmuir double probe (rotation frequency 2 Hz, 200 voltage sweeps per rotation), and a collector probe head instrumented with four flush mounted Langmuir double probes (two at each toroidal side, one voltage sweep every 5 ms). (author) 13 refs., 3 figs