Design of the RFX-mod2 first wall

RFX-mod2 is the latest upgrade of the reversedfield pinch machine operated at Consorzio RFX. A significantmodification consists of replacing thefirst wall tiles, proposed as a key factor to improve the gas density withreduction of hydrogen retention. Polycrystalline graphite has been identified as tile material given its highthermal conductivity (up to about 165 Wm-1K-1), uniformity and small grain size (about 20?m), and highmechanical strength (100 MPa compressive strength, 30 MPa tensile strength).With respect to RFX-mod, the mechanical resistant section of tiles has been increased coherently with themagnetic front-end modification that foresees the tiles supported by the existing MHD passive stabilising shell, sodecreasing the maximum stress at 3.5 MPa calculated fromfinite element analysis that simulates the operatingcondition. This low stress level together with a measurement of the experimental loads during next RFX-mod2operations could qualify the use of extruded graphite for a possible furtherfirst wall change in the future. Indeed,extruded graphite is considered attractive given its high directional thermal diffusivity (about 50 % better thenpolycrystalline graphite) to enhance the heat transmission and so improving the gas density control, and the lowstress induced may allow use of this mechanically less performing graphite.