Overview of the International Research on Ion Cyclotron Wall Conditioning
This paper gives an overview of the experimental and modeling activity on Ion Cyclotron Wall, Conditioning (ICWC), with hydrogen as working gas, in order to assess the applicability of this technique on ITER for recovery from disruptions, vent or air leak, recycling control and mitigation of the tritium inventory build-up. Experimental results obtained on TORE SUPRA, TEXTOR, ASDEX-Upgrade, JET, KSTAR and LHD are presented. The conditions for safely producing RF plasmas with conventional ICRH antennas have been carefully investigated. Discharge homogeneity has been improved by adding a small poloidal component to the toroidal field. Proper choice of the duty cycle RF on/off allows mitigating re-implantation of wall desorbed particles reionized in the ICWC discharge. A 0-D model of ICWC plasmas in He and H2 has been developed which reproduces experimentally determined electron density, neutral and ion fluxes. The installation in 2010/11 of the ITER like wall (ILW) in JET, allows now assessing the efficiency of ICWC for fuel removal on the ITER material mix. Experimental observations in carbon devices and modeling seem to indicate that ICWC, like other plasma-based conditioning techniques, interacts preferentially with transient reservoirs rather than in codeposited layers. An attempt is made to extrapolate the found fuel removal rates to ITER.