Stabilization of sawteeth instability by short gas pulse injection in ADITYA-U tokamak.

Experiments on ADITYA-U tokamak show a marked enhancement in the sawtooth period by application of short gas-puffs of fuel that cause a modification of the radial density profile. A consequent suppression of the trapped electron modes (TEMs) then leads to an increase in the core electron temperature. This slows down the heat propagation following a sawtooth crash causing a delay in achieving the critical temperature gradient inside the q = 1 surface required for the next sawtooth crash to happen. The overall scenario has strong similarities with the behavior of sawtooth under electron cyclotron resonance heating (ECRH). Our findings suggest an alternate technique for sawtooth control that may be usefully employed in small/medium sized tokamaks that do not have an ECRH or any other auxiliary heating facility.