It is shown that a class of disturbances exists which have a cumulative effect on the migration of the stable (or feedback stabilized) toroidal burning plasma along the curve of marginal ignition. However, the migration path can be compensated for and the working point on the ignition curve can be adjusted along a stable path by suitable prescriptions for the feedback system of the vertical field. Regulation of the burn and position of the plasma column on a finer scale, using a succession of small stable cycles around the chosen working point, is also discussed. Since the path R(t) = const is unstable in the pressure-position space (near the thermally unstable points of the ignition curve), the stable cycles do not involve isovolumic branches.