ICRF assisted low voltage start-up in TEXTOR-94

Successful ICRF assisted low voltage start-up was demonstrated for the first time on TEXTOR-94. Plasma current ramping up to 400 kA during approx. 0.25 s was achieved with E approx. 0.5 V/m. ICRF pre-ionization, target plasma production and preheating have been performed in the standard second harmonic ICRH regime at PRF approx. 350-500 kW by using the existing two double loop antennas, one without and the other wit Faraday screen. Reproducible low voltage start-up was possible in the presence of a compensated stray (error) magnetic field of the order of /B-barv/ ≤ 10 G and a gas pressure of (2-4) x 10-5 mbar. Without ICRF pre-ionization (n-bare0 approx. 0.2-0.8) x 1012 cm-3), no start-up at low loop voltage was achieved. ICRF assisted start-up at conventional electric field operation (E approx. 1.09 V/m) gives ∼ 10% reduction in the volt-second consumption, evaluated at the beginning of the current flat-top. (author). 13 refs, 6 figs