Outgassing measurements for the ITER EC H&CD Upper Launcher

Abstract

In most of applications involving both vacuum and high temperatures, outgassing of structural materials is a critical issue. For instance, this is the case of fusion test devices, where the gas released from the vessel walls contaminates the plasma. Four upper ports in the ITER vacuum vessel are reserved for Electron Cyclotron Heating and Current Drive (EC H&CD) Upper Launchers (UL), which have to provide plasma MHD stabilization by localized deposition of high power microwave beams. The structural material foreseen for the UL is the 316L(N)-IG stainless steel. It has to withstand temperatures in the range 120–150 °C during normal operation and 240 °C during the baking process. One of the preferred manufacturing routes for the UL is the Hot Isostatic Pressing (HIP) which is a very sophisticated method to manufacture structural components of complex geometry with good mechanical properties. The materials for use in the ITER vacuum systems have to comply with the outgassing limits given in the ITER vacuum handbook, but no outgassing data for HIPed stainless steel are available in literature, thus they must be obtained by experimental measurements. In this paper, measurements of partial outgassing rates are shown and discussed for stainless steel prototype samples AISI 316LN (on which the 316L(N)-IG is based) and AISI 317LMN, obtained by powder and solid HIPing method. A variant of the gas throughput method in vacuum systems was used for the measurements which were carried out over periods larger than 8 h and at different temperatures.