Experimental investigations on the role of e x B flow shear in improved confinement

Edge transport and confinement changes induced by radial electric fields, externally imposed in TEXTOR-94 by means of electrode biasing, were investigated. The edge profiles of the electric field E_r were measured continuously by a specially developed nine-tip Langmuir probe, thus allowing the study of the relative spatial and temporal dynamics of E_r and its radial gradient and possible ensuing transport changes. A particle transport barrier is found to be built up as the electric field gradient increases, thus strengthening the conjecture that E x B stabilization is a viable mechanism for improved confinement in tokamaks.