VAN DER POL BEHAVIOR OF RELAXATION OSCILLATIONS IN A PERIODICALLY DRIVEN THERMIONIC DISCHARGE

The nonlinear dynamics of the frequency entrainment process in periodi cally driven, self-oscillating thermionic discharges is investigated e xperimentally. The periodically interrupted frequency entrainment proc ess, known as periodic pulling, is demonstrated to be an essential fea ture of the transition region between the quasiperiodic state and the entrained state: A detailed comparison of experimental findings with t he analytical and numerical study of the driven van der Pol equation x - epsilon(1 - beta x(2))w(0)x + w(0)(2)x = w(0)(2)E cos(w(i)t) confir ms the relevance of this dynamical model for nonlinear plasma oscillat ions. A physical explanation is developed based on results from partic le-in-cell simulations of periodic pulling in thermionic discharges.