Cryo-Rated Vacuum Feedthroughs
Every analog channel crosses the vacuum and cryogenic boundary through a hermetic, cryo-rated feedthrough that must preserve signal integrity without leaking heat or vacuum.
The boundary problem
A fusion machine is a high-vacuum, partly cryogenic pressure vessel. Telemetry must cross that wall without breaking vacuum, without conducting a heat load into the cryostat that feeds the high-field REBCO magnets, and without corrupting the signal. The feedthrough is the component that does this — a hermetic seal carrying a conductor from the cold, evacuated interior to the warm, atmospheric acquisition side.
What 'cryo-rated' demands
- Hermeticity to ultra-high vacuum, verified by helium leak rate, maintained across thermal cycling.
- Low thermal conductance so the feedthrough is not a heat leak into the magnet cryostat.
- Controlled impedance so fast Mirnov and ECE signals arrive with bandwidth and phase intact.
- Radiation tolerance against the 14 MeV neutron field in the breeder and the 5.44%-fraction neutron flux in the burner.
Signal integrity across the wall
Differential wiring and careful shielding cross the feedthrough to reject common-mode pickup from the megampere-class currents nearby (9.66 MA plasma current in the breeder). The feedthrough's parasitic capacitance and inductance are characterized and stored as part of each channel's calibration, so the acquisition chain can de-embed them. Without this, a 16.84 T machine's electromagnetic environment would swamp low-level diagnostic signals.
Thermal budget coupling
Because the feedthrough touches the cryogenic system that also drives the ICE-PISTON magnet preload cycle, its heat leak is accounted in the same thermal budget the twin tracks. Strain and temperature telemetry from the feedthrough region feeds structural-health monitoring, closing the loop between the data path and the machine it measures.
Feedthrough specifications are engineering design targets for the machines whose construction begins Q2 2027; the numbers here are canonical design values, not measurements from a built device.