AMPLITUDE COLLAPSE OF NONLINEAR DOUBLE-LAYER OSCILLATIONS

The negative differential resistance of a double layer can give rise t o large amplitude oscillations in the potential drop over the double l ayer. Such oscillations are investigated in a triple-plasma machine fo r weak nonlinearity, implying approximately harmonic oscillations at l ow frequencies (omega much less than omega(pi)). The amplitude of the potential oscillations can approach the dc potential drop over the dou ble layer. The oscillation exists within a certain interval of dc drop s and vanishes outside this interval. An interesting nonlinear phenome non that we call amplitude collapse is observed. The amplitude does no t always decrease smoothly from its maximum value to zero when the dc drop is increased, but there is a sudden jump to vanishing amplitudes. For a decreasing dc voltage the corresponding sharp amplitude increas e occurs at a lower voltage. This phenomenon, which is not predicted b y the classical van der Pol equation, is shown to follow from the gene ralized van der Pol equation that describes the actual system, by usin g asymptotic solutions for weak nonlinearity.