21st Fusion Energy Conference, 13-21 de Outubro, Chengdu, China

	Transport and fluctuations during electrode biasing experiments on the TJ-II stellarator
	Pedrosa, M.A., C. Silva, C. Hidalgo, K. McCarthy, B. Gonçalves, J. Herranz, I. Pastor e a Equipa TJ-II
	Resumo
	The effect of electrode biasing on plasma confinement, turbulence and plasma flows has been investigated in the TJ-II stellarator. Experimental results show that it is possible to modify global confinement and edge plasma parameters with biasing. In addition evidence of electric field induced improved confinement has been found. The plasma response is different at densities below and above the threshold value to trigger the spontaneous development of ExB sheared flows in TJ-II. Two different time scales have been observed in the modification of the edge plasma potential both during spontaneously driven and in biasing induced radial electric fields experiments. The measured fast decay times are in the range of few turbulence correlation times. These results can help to test critically neoclassical and anomalous damping mechanisms in fusion plasmas. Non-exponential decays of plasma parameters in the scrape-off layer (SOL) have been observed in TJ-II. By means of externally applied radial electric fields the level of fluctuations and the radial velocity of turbulent events are reduced and non-exponential tails observed in the SOL disappear.