Characterisation of Tungsten coating on Graphite samples

The first wall of RFX-mod is entirely made of polycrystalline Graphite that completely covers the Inconel vacuum vessel. The full Carbon first wall assured very safe operation also at the highest feasible plasma current of 2 MA, when strong localized plasma-wall interaction events can cause thermal load to the wall up to tens of MW/m 2 . On the other hand, due to the high retention of H2, the graphite wall dramatically affected density control during operation and recently the possibility to move to metal plasma facing components is under study. The material chosen for RFX is Tungsten, but bulk tiles are not usable since theirmuch higher weight with respect to graphite ones would imply a major modification of the mechanical structure of RFX-mod. For this reason, a research activity has started in order to determinewhich is the deposition technique that will assure the Tungsten coating on Graphite tiles with the best resistance to the interaction with RFX plasmas. The coating techniques under test are Plasma Spray and different types of Plasma Vapour Deposition, with coating thicknesses in the range of hundreds and tens of microns respectively. A manipulator has been setup in order to allow the insertion of large coated samples up to the envelope of the first wall of RFX-mod, and the poloidal section where the manipulator is installed has been equipped with IR piro-bolometer and fast camera for the measure of thermal load during exposure and spectroscopic monitors for the evaluation of erosion. The samples temperature is also measured by means of integrated thermocouples. Finally, the manipulator comprises a built-in Thermal Desorption Spectroscopy diagnostic, that will allow in-situ studies of gas retention. The exposure of samples to cyclic heath loads has also been done. The characterization of the coating after exposure both to RFX plasma and cyclic heating was essentially based on SEM imaging of the surface and the first results of these studies are the subject of this contribution.