Vacuum Leak Detection
A single small leak can spoil the vacuum and, in a tritium plant, breach containment, so leak detection runs before and during operation.
Kinds of leak
A real leak lets air in through a physical path; a virtual leak is trapped gas slowly outgassing from a pocket or a poor weld. Both raise pressure, but only a real leak admits atmospheric gases. Distinguishing them matters because a real leak is a containment problem while a virtual leak is a cleanliness problem.
Detection methods
The standard tool is a helium leak detector: helium sprayed on the outside of a suspected joint is drawn through any real leak and detected inside by a mass spectrometer tuned to helium. The response time and location of the signal pinpoint the leak. During operation, residual-gas analysers watch the chamber's gas composition, and a rise in nitrogen or oxygen signals an in-leak of air.
Control integration
Leak detection is wired into the vacuum state machine and the safety interlocks. Base pressure and leak rate must be within limits before plasma operation is permitted. During a pulse, an unexpected pressure rise or a composition shift triggers an alarm and, if severe, a controlled shutdown. In a tritium plant, containment monitors add a further layer that acts on any sign of a breach.
- Real leaks admit air; virtual leaks are trapped gas
- Helium spray plus mass spectrometry locates real leaks
- Residual-gas analysis catches in-leaks during operation
- Leak criteria gate permission to operate
Tritium containment
In a D-T device a leak can work both ways: air in, or tritium out. Detritiation systems, glovebox under-pressure, and room monitors form the containment that leak detection protects. In the Kronos breeder design study, tritium containment is integral to the fuel cycle and blanket; leak detection is part of keeping the modeled tritium inventory accounted for and contained. The machine is a simulation and design case.
Finding a leak the size of a pinhole before it matters is a routine but essential control task.