Chaos and turbulence studies in low- plasmas

Abstract

This paper describes recent experimental investigations of the nonlinear dynamics of collisional current-driven drift waves in a linear low-β discharge. It is shown that the bias of an injection grid leads to rigid-body rotation of the cylindrical plasma column that strongly destabilizes the drift waves, thus providing a control parameter for the drift-wave dynamics. In the nonlinear regime, when the control parameter is increased, the transition scenario from stability to weakly developed turbulence is studied. Two successive Hopf bifurcations, a modelocked state and its gradual destabilization to chaos and finally turbulence follow the classical Ruelle-Takens transition scenario known from neutral fluids. In addition to the temporal dynamics, the spatiotemporal evolution of drift waves is studied by means of circular Langmuir probe arrays with high spatial and temporal resolution. With each Hopf bifurcation, a drift-mode onset is associated and the bifurcation from quasi-periodicity to mode locking corresponds to the transition from non-resonant to resonant mode interaction. The mode-locked state forms a persistent spatiotemporal pattern that is destabilized by the occurrence of defects. In contrast, the turbulent state is a fully disordered, intermittent state.

Comparison of turbulence measurements and simulations of the low-temperature plasma in the torsatron TJ-K

“…From correlation experiments in linear devices [21] and in the fusion SOL [6] phases of typically π/2 are reported. Since this technique is sensitive to larger modes or events, the same ambiguity as discussed above might also exist.…”

“…Low-temperature plasmas in linear devices have already been exploited to investigate the initial transition from drift waves with a few mode numbers to a turbulent state [21]. In order to study fully developed turbulence on closed magnetic surfaces without direct wall contact, a toroidal device has to be used.…”

Lyapunov stability of charge transport in miniband semiconductor superlattices

“…[1][2][3][4][5][6][7] Such systems can demonstrate a variety of dynamical behavior, including deterministic chaos. 5,[8][9][10] However, stability analysis (even numerical) of the systems away from the equilibrium still remains a nontrivial problem. The difficulty arises because the Poisson and continuity equations are both spatially extended, i.e., have infinitely dimensional phase space.…”

Lyapunov analysis of the spatially discrete-continuous system dynamics

“…Such model was shown to demonstrate a variety of nonlinear phenomena including developing instabilities of electron transport in Pierce diode [40] and semiconductor structures [37], developing of turbulence [41] and bifurcations in plasma drift waves [42,43].…”