IDENTIFICATION OF EXTERNAL KINK MODES IN JET

The 'outer mode' is one of the MHD modes that limits the fusion perfor mance of the hot ion H mode discharges in JET. It has previously been proposed that the outer mode is a nonlinearly saturated external kink mode. This was based on the localization of the perturbation close to the edge as observed in soft X ray (SXR), electron temperature and ele ctron density measurements. In addition, MHD stability calculations sh owed. that the plasma edge is close to the ideal external kink stabili ty boundary at the time when the outer mode is observed. The SXR data of the outer mode are compared with predictions based on the mode stru cture of the ideal n = 1 external kink mode. Excellent agreement is fo und, confirming the identification of the outer mode as an external ki nk mode.