Abstract
The effect of the helical instabity on the internal magnetic field in the positive column, is theoretically investigated, under the assumptions that the densities of electrons and ions are perturbed independently and that the perturbed densities have finite amplitudes. The theoretical values are confirmed by the experiment.
We draw a conclution that the direction of the internal magnetic field produced by the helical instability above Bc is parallel to that of the applied magnetic field.
