Boronization of ASDEX
Boronisation is the plasma-chemical deposition of thin boron/carbon or pure boron films onto the inner wall of a tokamak device. Since mid-April 1989 the ASDEX vessel has been boronised seven times in glow discharges at room temperature vessel walls. Local surface analysis of the deposited layers yielded thicknesses of up to 2000 Å. Boronisation provided considerably improved plasma conditions. In ohmic discharges, reductions of CO by a factor of more than five in the divertor chamber and of two for H(2)O were observed, in relation to a reduction of oxygen by a factor of more than five, as measured by spectroscopy, but the reduction of hydrocarbons was only marginal. Iron disappeared from the spectra and even copper, the target plate material, was significantly reduced. As a consequence, Z(eff) was less than 1.5 for n(e) greater than 3x1.0E19/m3. The density limit was improved by 25% and more. The oxygen-diminishing effect of boron/carbon and pure boron layers was found to be longer lasting than the suppression of metal impurities. Deteriorated wall conditions occurred only after hundreds of discharges, including numerous additional heating shots with ICRH, NI, LH and combined scenarios, but pre-boronisation conditions were never reached.
Bibliographic Reference: Report: IPP III/166 EN (1990) 17 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199011672 / Last updated on: 1994-12-02
Original language: en
Available languages: en