Published online by Cambridge University Press: 13 March 2009
Detailed computational results are presented for the stability of linear tearing modes in low-q cylindrical tokamaks with various radial profiles. The stability properties of a widely used ‘classical’ profile are compared with those of a ‘piecewise’ profile. It is shown that the stability properties of low-q tokamak discharges show a sensitive dependence on small changes in the current density profile near the singular surface. While the ‘classical’ profile is stable for a large range of q0, where q0 is the value of the safety factor on the magnetic axis, a similar ‘piecewise’ profile is unstable for the same set of parameters.