Experiments showing the dynamics in the self-organization of surface wave sustained discharges are presented. Microwave ͑2.4 GHz͒ discharges maintained in an argon gas in a continuous wave regime at a constant applied power and varying gas pressure are studied. The evolution of the discharge from a stationary plasma column at comparatively low pressure (pр10 Torr) to a plasma torch at atmospheric pressure passes through different stages of self-organization of the wave-field↔plasma nonlinear structure showing evidence of the general trends of behavior of nonequilibrium dissipative systems. The measurements are carried out at the stage of the discharge self-organization into a filamentary structure with an azimuthal rotation. Macroscopic characteristics ͑number, size, velocity of rotation͒ of the filaments and their dependence on the gas pressure and its time variation are given. The total light emission of the plasma considered as giving information about the plasma density is measured and different methods of signal processing ͑including correlation-spectrum analysis͒ are applied. Oscillations of the filament ends are also observed. The different types of interrelation between plasma density and field intensity, registrated in the different pressure ranges, call for variety in the instability mechanisms. Although the scenario of the discharge self-organization is stressed in the discussions, the observations are important with their relation to the discharge applications, which require avoiding conditions of development of instabilities.

No abstract

The problem of envelope solitons of surface waves is considered on the basis of results for the nonlinear dispersion relation of the waves in a plasma column. The soliton solutions are derived as particular cases of the general solutions obtained by a universal procedure and expressed in terms of Jacobi elliptic functions. Since the two types of interactions, namely the (ω + ω) – ω and the (ω – ω) + ω interactions (where ω is the frequency of the carrier wave) included in the nonlinear dispersion relation act in opposite ways, existence both of bright and dark solitons is shown to be possible. The effect of the ponderomotive force that in our case is expressed through the contribution of the (ω – ω) + ω interaction leads to the formation of dark solitons. The effect of the losses is also considered.

The nonlinear behaviour of surface waves propagating along a plasma column is investigated. The experiments include (i) measurements of the nonlinear dispersion of the waves and (ii) observation of the evolution of the shape of the wave envelope and of the wave spectrum when the waves are excited with an amplitude-modulated signal. Comparison with theory shows that (i) the measured nonlinear wavelength shift corresponds to increasing wave phase velocity with increasing wave amplitude, (ii) the observed narrowing of the wave envelope can be associated with the formation of periodic nonlinear waves described by dn Jacobi elliptic function solutions of the nonlinear Schrödinger equation and (iii) the observed strong changes of the wave spectrum are mainly related to a nonlinear effect of phase modulation.

No abstract