Ion cyclotron wall conditioning in reactive gases on TEXTOR

The influence of working gas on the performance of Ion Cyclotron Wall Conditioning (ICWC) has been studied in the TEXTOR tokamak. Several reactive gases (H2, D2, O2, N2, NH3) and their mixtures with He were tried and primary results about their efficiency to clean the wall from impurities and to release the retained fuel have been obtained. The experiments have demonstrated in general that low temperature plasmas produced in these gas mixtures by a conventional ion cyclotron heating system are suitable for wall cleaning. For comparison of the cleaning efficiency of different gas mixtures (except O2), the TEXTOR wall was pre-loaded with Ar and D in a glow discharge. The release of Ar atoms due to ICWC has shown a sequential reduction in series of ICWC plasma pulses. This reduction was used as a criterion for the cleaning efficiency. For the fist time ammonia has been tested for the wall conditioning in a tokamak and demonstrated Ar and D cleaning efficiencies similar to the He/H2 mixtures.