2024 – Recombination Neutral Pressure Window for the Low-Z Benign Termination Strategy

Recombination Neutral Pressure Window for the Low-Z Benign Termination Strategy

2024 Research Campaign, Disruption Mitigation

Purpose of Experiment

The purpose of this experiment is to improve the physics basis for the low-Z benign termination strategy. This strategy has the potential to be an alternative collisionless approach for mitigating an existing runaway electron (RE) beam, which will be of critical importance in future large plasma current tokamak devices like ITER and SPARC. This strategy seeks to increase the wetted area of the RE deposition by triggering a high amplitude MHD instability. It has been shown that this MHD event is facilitated by two crucial steps: recombination and low q_a.

Experimental Approach

The approach is broken down into two sections: 1. Neutral pressure threshold for recombination and reionization of the companion plasma as a function of plasma current and argon quantity. This pressure will be scanned in both directions in a single discharge using a combination of D2 MGI and the fueling valves. The pressure will then be decreased by allowing the material to be pumped out of the plasma 2. Impact of RE current and compression rate on benign termination in high neutral pressure scenarios which is defined as the neutral pressure window in which the free electron density is an increasing function of the neutral pressure.