Boronization in TEXTOR
The liner and limiters of TEXTOR have been coated in situ with a boron containing carbon film using a RG discharge in a throughflow of 0.8 He + 0.1 B(2)H(6) + 0.1 CH(4). The average film thickness was 30-50nm and the ratio of boron and carbon in the layer was about 1:1 according to Auger Electron Spectroscopy. Subsequent tokamak discharges are characterised by a small fraction of radiated power (<0.3) even during high power ICRF heating (2.6 MW, 1.6 s). A concomitant strong increase of the convective power loading of the limiters is observed. Values of Z(eff) lower than 1.2 are derived from conductivity measurements. The most prominent change in the impurity concentration compared to good conditions in a carbonised surrounding is measured for oxygen. The value O VI/n(e) of the O VI intensity normalized to the average plasma density n(e) decreases by more than a factor of four. The decrease in the oxygen content manifests itself also as a reduction of the CO and CO(2) partial pressures measured during and after the discharge with a sniffer probe. The carbon levels are reduced by a factor of about two as measured by the normalized intensity C II/n(e) of the C II line and via the ratio of the C fluxes and deuterium fluxes measured at the limiter (CI/D(alpha)). The wall shows a pronounced sorption of hydrogen from the plasma, easing the density control and the establishment of low recycling conditions. The beneficial conditions did not show a significant deterioration during more than 200 discharges, including numerous shots at ICRH power levels > 2MW.
Bibliographic Reference: Article: Journal of Nuclear Materials, Vol. 162-164 (1989), pp. 713-723
Record Number: 198911041 / Last updated on: 1994-12-01
Original language: en
Available languages: en