Plasma potential and geodesic acoustic mode evolution with Helium puffing in the ECRH regime on the T-10 tokamak

The evolution of the Geodesic Acoustic Mode (GAM) and mean plasma electric potential were examined in the regime with short (5 ms) Helium puffing into Electron Cyclotron Resonance heated discharge of the T-10 tokamak. It was shown that a Helium pulse leads to temporal perturbation of the plasma electron temperature and density and concomitant evolution of the mean potential, happening in the diffusive time-scale ∼âƒ' 30 ms. Afterwards, the potential restores to the new stationary level with the same time-scale. On top of that GAM amplitude reduces sharply (within 2-5 ms) and GAM frequency also decreases within 30 ms after Helium puffing. Afterwards GAM amplitude and frequency relax to a new stationary level within about 50-70 ms. The evolution of electron density, electron and ion temperatures, total stored energy and plasma density turbulence is discussed in order to clarify their links with potential and GAM evolution. (paper)