Abstract
A parametric decay of a whistler wave into an upper sideband whistler and a corresponding low frequency wave, both with harmonic structure, is investigated. The decay has been observed over a wide range of pump frequencies, 0.45<or= omega / omega ce<or=0.95 and has a threshold of approximately 1 W. The waves satisfy the energy conservation condition omega o= omega u+ omega l, where the subscripts o, u and l denote the pump, the upper sideband, and the negative energy low frequency waves, respectively. Wavelengths and directions of propagation of the pump and upper sideband are measured and found to be nearly equal and in the same direction. As implied by the wave momentum conservation equation, ko=ku+kl, the low frequency wave has no measurable axial phase shift, nor does it have a measurable radial phase shift over the central part of the column.