The RFX graphite tiles: Design and tests

The paper, after a brief introduction covering the basic concepts underlying the design of the RFX first wall, describes the main features of the graphite tiles and presents their predicted operating conditions in the presence of applied heat fluxes and electrodynamic forces. On the basis of the results of experimental tests performed to measure the tile-vessel contact conductance, the thermal behaviour is analyzed by means of numerical models which simulate the real operating conditions of the first wall and vacuum vessel, with its forced gas cooling system and its thermal insulation. The safety margin, preventing tile rupture due to electrodynamic extraction forces during fast plasma current terminations, is then investigated by means of mechanical tests closely reproducing the real load distribution. Finally, the stresses due to machining allowances on the tiles and on their grooved seats are analyzed by means of a finite-element model, under the load produced by the bayonet keys which clamp the tiles to the vacuum vessel stiffening rings.