MHD Stability of Optimized Shear Discharges in JET
The main limitation to the performance of the JET optimized shear discharges is due to MHD instabilities mostly in the form of a disruptive limit. The structure of the MHD mode observed as a precursor to the disruption as measured from soft x-ray and ECE diagnostics shows a global ideal MHD mode. The measured mode structure is in good agreement with calculated mode structure of the pressure driven kink mode. The disruptions occur at relatively low normalized beat in good agreement with calculated ideal MHD stability limits for the n=1 pressure driven kink mode. These low limits are mainly due to the extreme peaking factor of the pressure profiles. Other MHD instabilities observed in the JET optimized shear discharges include, usually benign, chirping modes. These modes, which occur in bursts during which the frequency changes, have the same mode structure as the disruption precursor but are driven unstable by fast particles.
Bibliographic Reference: Article: JET-P(99)06 (1999) 1-23
Record Number: 199910900 / Last updated on: 1999-06-18
Original language: en
Available languages: en