FIRE, a novel concept of massive gas injection for disruption mitigation in ITER: Validation on Tore Supra

Disruptions in large size tokamak like ITER must be mitigated to reduce detrimental effects on the device. Massive impurity injection prior to disruption is a promising mitigation technique. Many injector designs have already been tested on nowadays tokamaks. A novel concept of injector has been designed and tested on Tore Supra. It is based on the use of high pressure cartridges sealed with a bursting disc. For firing, an electric arc is generated inside the cartridge close to the rupture disc. This initiates a shock wave which breaks the disc. Tests show that the opening is achieved in less than 400 μs. A detailed modeling of the fast injector operation is presented. One result is that the gas is expelled in about 2 ms and an outflow rate as large as 4.2 × 1025 atoms/s can be achieved at the nozzle exit (1 cm diameter). Massive neon gas injections have be performed on stable plasma to validate the concept. The gas penetration into the plasma prior to disruption is followed by a fast camera. Comparison with a ferromagnetic-valve based injector was also carried out. It is found that the velocity of the cold front penetration into the hot plasma is larger using this new injector.