The ideal localized ballooning mode stability criterion has been analysed using equilibria obtained in Doublet III. Near the experimental beta limit, portions of the flux surfaces could have developed the pressure gradient set by this stability criterion. At low q (≤3.2), this is not sufficient to affect the trend in the development of the plasma internal inductance, , and total βt. At high q (≥3.5), both and βt achieve stationary values. This correlates well with the hypothesis that a large portion of the plasma reaches the ballooning mode limit for more than one energy confinement time.
Ballooning stability of JET discharges