Cylindrical Tearing Mode Equation
The magnetic structure of a tearing perturbation is determined by the socalled cylindrical tearing mode equation, (3.35), which can be written in the form [4,14]

(3.60) 
where

(3.61) 
is a dimensionless measure of the toroidal current density profile.
Note that Equation (3.60) is singular at the socalled rational magnetic fluxsurface, radius , at which

(3.62) 
At the rational surface,
, where is the equilibrium magnetic field, and
the wavevector of the tearing perturbation.