Beta limits against external kink modes in tokamaks taking into account plasma outside separatrix

The pressure profile variation in relatively thin plasma layer outside the separatrix can influence global external kink mode stability and considerably change the β limit in doublet configurations. The conclusions for divertor configurations strongly depend on the choice of boundary conditions at the open field lines. Fixed boundary conditions at the divertor end plates result in stabilizing effect of the plasma outside separatrix independent of pressure gradient there. More realistic choice of boundary conditions gives a behavior similar to the doublet case. (author) 3 figs., 5 refs