Design and development of lab scale 80K Cryostat for the Arc detection in Cryogenic Environment

In SST-1 like superconducting (SC) Tokamak machines, SC magnets are insulated with Cryo-grade glass fibre epoxy with resins for electrical isolation of wind to wind insulation in magnets as well as with other nearby potentially grounded surfaces. SST-1 tokamak has such 16 nos. of SC toroidal field (TF) magnets as well as 9 nos. of poloidal field (PF) magnets. These magnets are connected with Vapour Cooled Current Leads (VCCL) which acts as SC magnet feeder system to connect SC magnets with room temperature power supply feeders. These VCCL interfaces with SC magnets of SST-1 tokamak are situated in the Current Feeder System (CFS) where both systems are thermally isolated by different vacuums. Recently we had observed an event of flash arcing inside this interface between PF SC bus bars and its Cryostat surfaces which are at ground potential compare to SC bus bars. To avoid further such accidents we have decided to conceptualize a fibre optic-based arc detection system to mount on it which is very complex due to less working space and cryogenics environment. To visualise such flash arcs on Cryogenic cooled surfaces and understand the phenomena, we have designed and developed a lab-scale 80 K cryostat to test arc detection system along with optical window performance at liquid nitrogen temperatures. This paper describes on development and results of Cryostat testing in lab-scale conditions as well as options for further development and testing of cryogenic components like Cryogenic compatible optical windows to test their performance at low temperatures. (author)