Signatures of resistive ballooning modes for ASDEX high beta discharges

The signatures of resistive ballooning modes in ASDEX high beta discharges are investigated. It is shown that the growth rates of these modes increase significantly when βp reaches its maximum value during the discharge and therefore they can be used to explain the 'hard βp saturation' behaviour. A simple estimate of the corresponding electron heat conductivity gives values of χe>1m2·s-1, in agreement with expectations from the observed confinement deterioration at maximum beta. (author). Letter-to-the-editor. 5 refs, 4 figs