Sensitivity of the kink instability to the pressure profile.

The stability of the n=1 ideal kink in DIII-D-like [Fusion Technol. 8, 441 (1985)] configurations is found to depend critically on the details of the current density and pressure profiles. The maximum stable normalized β, β[sub N]=β/(I/aB) (I in MA, a in meters, and B[sub 0] in tesla), is found to increase dramatically as the peak in the pressure gradient is shifted from the central region toward the plasma boundary. Further, for peaked pressure profiles, the β limit is insensitive to the internal inductance, l[sub i], whereas for broad pressure profiles, the β limit depends more strongly on l[sub i] and can increase with l[sub i] almost up to the point where the q profile becomes hollow. With broad pressure profiles and a conducting wall at 1.5 minor plasma radii, kink-stable β[sub N] values of 5.8—significantly above both the Troyon limit and the ballooning limit—have been found. [ABSTRACT FROM AUTHOR]