Tests on the VTTJ technique (Vacuum Tight Threaded Junctions) and qualification for the use 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 reliable non welded junctions, able to maintain vacuum tightness also in heavy loading conditions (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 example, between steel and copper) and has been tested up to 500 bar internal pressure and up to 700 °C, showing excellent leak tightness in vacuum conditions and h igh mechanical resistance. The main advantages with respect to existing techno logies (for example, friction welding and electron beam welding) are an easy construction, a low cost, a pr ecise positioning of the junction and a high repeat ability of the process. Due to these advantages, the new techn ique has been adopted for several components of the SPIDER experiment and it is proposed for ITER, in particular for the ITER Heat and Current Drive Neutral Beam Injector and for its prototype, the MITICA experiment, to be tested at Consorzio RFX. This report gives a detailed description of the VTT J technique, of the samples manufactured and of the qualification tests that have been carried out so far.