The Effect of Plasma Beta on High-n Ballooning Stability at Low Magnetic   Shear
  An explanation of the observed improvement in H-mode pedestal characteristics with increasing core plasma pressure or poloidal beta, as observed in MAST and JET, is sought in terms of the impact of the Shafranov shift, d', on ideal ballooning MHD stability. 
J W Connor, C J Ham, R J Hastie
physics.plasm-ph