Design & manufacturing of cooled immersion tubes for divertor bolometry in Wendelstein 7-X

Abstract

After the successful Operation phase 1.2b experimental campaign Wendelstein 7-X was upgraded for steady-state operation with pulse duration of 1800s and up to 18 GJ energy input. Heat management in steady-state requires active water-cooling of the in-vessel components, in particular if temperature-stable environments are required for diagnostics such as bolometry. Two new, actively cooled bolometer immersion tubes (IT) with two camera housings (5–7 detector heads each) have been designed and manufactured for W7-X. By installing the two IT in the same module viewing the poloidal plasma cross-section from opposite sides provides a complete coverage with lines of sight. This allows tomographic reconstruction of the plasma radiation, but make accurate knowledge of the diagnostic geometry essential. This makes accurate manufacturing and assembly essential.An additional design challenge in W7-X is the suppression of Electron Cyclotron Resonance Heating (ECRH) stray-radiation as well as undesired particle deposition from plasma deposition, dust and boronization in the interior of the IT. This was realized with a welded sheet metal shell and a shutter system for each IT. In the design of the cooling channel, a high degree of temperature stability in particular for the detector heads was required. This resulted in complex components that were challenging for conventional manufacturing approaches. Selective laser melting might be an improvement for future projects.