INFLUENCE OF ACTIVE PUMPING ON DENSITY AND CONFINEMENT BEHAVIOR OF JET PLASMAS

This paper describes the confinement characteristics of high density E lmy PI-modes obtained in the JET Mark I experimental campaign. Plasma pulses carried out with and without the in-vessel cryopump operational (approximate to 240 m(3) s(-1) pumping speed for deuterium) are compa red. In all cases, it is found that the PI-mode density limit is not d isruptive, but manifests itself as a loss of confinement, accompanied by an increase of neutral pressure at the plasma edge. The interpretat ion of the H-mode density limit in terms of the Greenwald scaling is d iscussed. It is also shown that the loss of confinement correlates to the onset of detachment in the divertor, and that operation at high de nsity in H-mode is compatible with partial detachment but not with ful l detachment.