15th International Conference on Plasma Surface Interactions in Controlled Fusion Devices de 27 Abril a 3 de Maio de 2002, Gifu, Japão

	Influence of Electrode and Limiter Biasing on the ISTTOK Boundary Plasma
	C. Silva, H. Figueiredo, J. A. C. Cabral, B. Gonçalves, I. Nedzelsky e C. A. F. Varandas
	Resumo
	In this contribution limiter and electrode biasing experiments are compared, in particular in what concerns their effects on the edge plasma parameters. For positive limiter bias, an increase in the average plasma density is observed, although, without a significant increase in the gross particle confinement. In spite of the lower density, particle confinement is higher for negative polarization due to low turbulent transport.For electrode bias changes in the plasma parameters are more significant. For positive bias, a substantial increase (>50%) in the average plasma density is observed, without significant changes in the edge density, leading to steeper profiles. The ratio ne/ Ha also increases significantly (>20%), indicating an improvement in gross particle confinement. The plasma potential profile is strongly modified as both the edge Er and its shear increase significantly. Good correlation between confinement modifications and ExB shear has been found.