Observation of nonlinear effects in the propagation of m=0 torsional hydromagnetic waves

A report is presented on the observation of nonlinear effects in the propagation of axisymmetric (m = 0) torsional hydromagnetic waves in a partially ionized helium afterglow plasma. In accordance with the predictions of a weakly nonlinear theory, magnetic field perturbations oscillating at twice the frequency of the primary wave have been observed. Good quantitative agreement between the experimental data and theoretical calculations is obtained for moderate primary wave amplitudes. (author)