Abstract
It is demonstrated that a spontaneously excited ionization wave in a small radius positive column is suppressed resonantly by an externally launched wave at some discrete frequencies. Waves whose frequency is not equal to these discrete frequencies have only a small effect of suppression. Results suggesting a feedback effect through the column are shown. It has been found that asynchronous quenching as described by van der Pol's equation should be modified. Also, the energy relation between the wave deviates from that given by van der Pol's relation. These characteristics are explained by considering nonlinearities of ionization rate and loss factor in Pekarek's equation.