Development of the ITER Magnet Protection in the Case of Paschen Condition Detection

The ITER superconducting magnet electrical insulation is designed and manufactured to be Paschen proof. The ITER cryostat and the feeder vacuums are also designed to provide a level of vacuum where Paschen conditions should not occur in case of insulation failure. The high voltage insulation failure coincident with degraded vacuum has been identified as a risk with major consequences. The level of magnetic energy stored in the superconducting coils, up to a maximum value of about 50 GJ, could result in electrical arcs leading to severe damages on the magnet system. The present paper focus on the operation, control and protection to mitigate the risk of Paschen discharge: vacuum monitoring, detection and protective actions are discussed: what the baseline strategy is and what should be further developed and improved for the ITER magnet system based on the return of experience of large scale superconducting magnet tests.