Vacuum Tight Threaded Junctions (VTTJ): a new solution for reliable heterogeneous junctions in ITER

A new technique, called Vacuum Tight Threaded Junction (VTTJ), has been developed and patented by Consorzio RFX, permitting to obtain low - cost and relia ble non welded junctions, able to maintain vacuum tightness also in aggressive environments (high temperature and high mechanical loads). The technique can be applied also if the materials to be joint are not weldable and for heterogeneous junctions (for e xample, between steel and copper) and has been tested up to 500 bar internal pressure and up to 200° C, showing excellent leak tightness in vacuum conditions and high mechanical resistance. The main advantages with respect to existing technologies (for exa mple, friction welding and electron beam welding) are an easy construction, a low cost, a precise positioning of the junction and a high repeatability of the process. Due to these advantages, the new technique has been adopted for several components of the SPIDER experiment and is proposed for ITER, in particular for the ITER Heat and Current Drive Neutral Beam Injector and for its prototype to be tested at Consorzio RFX, the MITICA experiment. This paper gives a detailed description of the VTTJ technique, of the samples manufactured and of the qualification tests that have been carried out so far.