Fusion Cryostat Vacuum Vessel Insertion & Rigging Audit

Prior to rolling the 1,250-ton cryostat base from the assembly hall onto the bioshield pit rim, the temporary runway beams and permanent reinforced concrete crown ring must be audited. Dial indicators and vibrating-wire strain gauges verify that localized foundation settlement remains below 0.35 mm under full gantry self-weight plus suspended test load.

Four synchronized hydraulic strand jack units mounted on twin modular gantry girders lower the cryostat base into the 28.5-meter deep vault. An automated PLC feedback loop measures cable tension across 128 high-tensile steel strands (15.7 mm diameter) simultaneously, immediately halting motion if tension differential exceeds ±3.5%.

As the base descends within 500 mm of its final pedestal ring, an array of 8 spherical retroreflector (SMR) targets tracked by four independent laser stations calculates real-time pitch, roll, yaw, and X/Y offset. Micro-adjustment hydraulic cylinders located at gantry feet perform fine millimeter translations to achieve final alignment within ±0.5 mm of tokamak global datum.

The cryostat base maintains secondary vacuum insulation for the 4K superconducting magnets. All mating flanges utilize precision silver-plated Helicoflex resilient metal seals. The audit mandates positive-pressure clean air curtains and protective nylon elastomer shoe covers across all flange knife-edges until final mating contact is achieved.

Once lowered onto the tokamak bioshield crown pedestals, 72 high-strength M90 Inconel 718 anchor studs secure the cryostat base against Maximum Credible Earthquake (MCE) vertical and lateral shock loads. Multi-stud hydraulic tensioners apply 2,450 kN residual preload per bolt simultaneously in a criss-cross sequence to prevent flange warpage.