Micro-particle injection experiments in ADITYA-U tokamak using an inductively driven pellet injector

A first-of-its-kind, inductively driven micro-particle (Pellet) accelerator and injector have been developed and operated successfully in ADITYA-U circular plasma operations, which may ably address the critical need for a suitable disruption control mechanism in ITER and future tokamak. The device combines the principles of electromagnetic induction, pulse power technology, impact, and fracture dynamics. It is designed to operate in a variety of environments, including atmospheric pressure and ultra-high vacuum. It can also accommodate a wide range of pellet quantities, sizes, and materials and can adjust the pellets’ velocities over a coarse and fine range. The device has a modular design such that the maximum velocity can be increased by increasing the number of modules. A cluster of lithium titanate/carbonate (Li₂TiO₃/Li₂CO₃) impurity particles with variable particle sizes, weighing ∼50-200 mg are injected with velocities of the order of ∼200 m s⁻¹ during the current plateau in ADITYA-U tokamak. This leads to a complete collapse of the plasma current within ∼5-6 ms of triggering the injector. The current quench time is dependent on the amount of impurity injected as well as the compound, with Li₂TiO₃ injection causing a faster current quench than Li₂CO₃ injection, as more power is radiated in the case of Li₂TiO₃. The increase in radiation due to the macro-particle injection starts in the plasma core, while the soft x-ray emission indicates that the entire plasma core collapses at once.