AN OVERVIEW OF MHD ACTIVITY AT THE TERMINATION OF JET HOT ION H-MODES

In nearly all hot ion H modes in JET, a magnetohydrodynamic (MHD) even t is clearly observed just before the time the stored plasma energy sa turates and the neutron yield starts to decline. The results of a syst ematic analysis of MHD observations for a large number of discharges i s reported. The relationship between MHD phenomena and the onset of co nfinement limitation is discussed, as are aspects of the three main ty pes of performance limiting MHD: (a) low-n modes in the outer regions of the plasma, (b) sawteeth and. (c) giant edge localized modes (ELMs) . Model simulations indicate how the transport is affected and allow a n assessment of how much the neutron yield would be improved if the MH D activity were absent.