Internally driven spatiotemporal irregularity in a dc glow discharge

Spatiotemporal dynamics of an undriven de glow discharge at intermediate pr essures (p(0)r(0) = 6.2 Torr cm, i < 50 mA) is investigated experimentally. Spatiotemporal irregularity and windows of regular nonlinear waves occur a nd are found to depend on the discharge current. Above a threshold current column head oscillations arise and inject high-frequency ionization waves i nto the positive column that decay towards the anode through nonlinear wave coupling with a discrete eigenmode of the positive column. Regularity was found to be a result of commensuration of both waves and obeys a devil's st aircase. Since column head oscillations occur in the transition region from cathode fall to positive column as result of discharge formation, the irre gularities were internally driven. Spatiotemporal analysis by means of bior thogonal decomposition gives insights into the mechanism of irregularity an d can be employed for characterization of spatiotemporal complexity.