Velocity Perturbation
The fluxfreezing constraint of marginallystable idealMHD takes the form

(3.55) 
[See Equation (2.379).] Taking the curl of the previous equation, combining with Maxwell's equations, and linearizing, we obtain

(3.56) 
where

(3.57) 
and use has been made of Equation (3.50), as well
as the facts that
.
The radial component of the previous equation yields

(3.58) 
where use has been made of Equations (3.9), (3.19), (3.32), (3.52), and (3.53).
Equations (3.54) and (3.58) imply that

(3.59) 
Hence, we deduce that the perturbed plasma flow associated with a tearing mode in a low, large aspectratio, tokamak plasma is divergencefree [see Equations (3.51) and (3.59)], and is specified by Equations (3.57) and (3.58).