Application of the novel VTTJ technique (Vacuum Tight Threaded Junction) to fusion reactor relevant geometry and materials

Highlights: • Heterogeneous junctions represent a critical issue in nuclear fusion experiments. • The new VTTJ technique is a low cost and reliable alternative to welding. • VTTJ has been accepted by ITER for the usage in the SPIDER and MITICA experiments. • New tests demonstrated its applicability to the divertor and other components. - Abstract: A new technique, called Vacuum Tight Threaded Junction (VTTJ), has been developed and patented by Consorzio RFX, permitting to obtain low-cost and reliable vacuum-compatible non-welded junctions. The technique has been tested up to an internal pressure of 500 bar and up to a temperature of 700 °C . The main advantages with respect to existing technologies are an easy construction, a low cost and a high repeatability of the process. Due to these advantages, the new technique has been adopted for several in-vacuum components of the SPIDER experiment and has been also recently accepted by the ITER vacuum group for the usage in the MITICA experiment, the full prototype of the ITER Neutral Beam Injectors. This paper reports the test and qualification, according to the ITER criteria, of the VTTJ technique with geometry and materials compatible with the divertor and other components of future fusion reactors. Namely, a set of junction samples have been manufactured, joining CuCrZr to AISI 316L stainless steel and using tube-to-tube geometry.