H-mode density limit and detachment in JT-60U

High-density discharges in JT-60U have been analysed with the aim of establishing a mechanism for the H-mode density limit (DL). The data support the view that the density behaviour in the H-mode is mainly affected by confinement, with the hard limit on the H-mode density being imposed by the H-L transition. Analysis of highly radiating NBI-heated plasmas with MARFE and detachment has enabled one to discriminate between detachment and the H-L transition as mechanisms for the H-mode DL. Although strong detachment is observed near the H-L transition in JT-60U, by itself it was found to impose no limit on the density rise.