In-vessel inspection system: Development and testing activities of high vacuum and temperature technologies for fusion remote handling

The In-Vessel Inspection System (IVIS) is remote handling in-service system to perform visual inspections of the SST-1 scale tokamak under vacuum and high temperature in between the plasma shots. The IVIS system is approximately 4 m in length and has 5- degrees of freedom (DOF), consisting of four rotary joints and one linear motion for deployment inside the tokamak. The IVIS system is designed to support a cantilevered payload of approximately 1 kilogram while maintaining a positional accuracy of <2 mm. Initially, the IVIS system is stored in a vacuum chamber that is approximately 5 m long and maintained under Ultra-High Vacuum (UHV) conditions. This storage vacuum chamber (SVC) is separated from the Vacuum Vessel (VV) by a UHV gate valve. When performing visual inspections, the gate valve is opened, allowing the IVIS to be deployed within the VV. It then carries out the inspection procedure and subsequently returns to its initial position outside the VV. IVIS structural components are five links of arms made of aluminium alloy 6061-T6 and base link, lugs, stiffeners and shafts made of SS 304. Each module can provide rotation (±90° in the horizontal plane). With varying lengths, simulations were performed in virtual reality model to arrive at the present configuration. Based on the VR simulation, it was found that IVIS with a total of 5 links, 1 fixed link & maximum link lengths of 0.7 m (joint to joint) is sufficient to encompass the 180° sector inside SST-1 like machine. This paper offers an overview of the conceptual design, development, and testing phases of the IVIS and SVC to perform visual inspections on the SST-1 scale tokamak while it is under vacuum conditions in the intervals between plasma shots. The paper presents theoretical calculations, a comprehensive kinematic assessments, and structural integrity analyses. Additionally, it discusses strategies for optimizing the design based on these results. A feasibility assessment was conducted to evaluate the appropriateness of technologies for operating the IVIS under conditions resembling those of SST-1, including vacuum and temperature. The IVIS components are designed to withstand temperatures of approximately 100 °C during VV inspection and vacuum conditions (with a pressure of less than 1 × 10−8 mbar) for conditioning before entering the VV. The restrictions on out-gassing within the VV impose significant limitations on the design. The COTS components selection and availability (actuators, bearings, encoders, vacuum feed-throughs & cable tray) to match the performances compatible with high temperature, UHV requirements and to overcome pollution issues of the tokamak environment are discussed in this paper.