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Register a new userAutowaves in a dc complex plasma confined behind a de Laval nozzle
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Experiments to explore stability conditions and topology of a dense microparticle cloud supported against gravity by a gas flow were carried out. By using a nozzle shaped glass insert within the glass tube of a dc discharge plasma chamber a weakly ionized gas flow through a de Laval nozzle was produced. The experiments were performed using neon gas at a pressure of 100 Pa and melamine-formaldehyde particles with a diameter of 3.43 {mu}m. The capturing and stable global confining of the particles behind the nozzle in the plasma were demonstrated. The particles inside the cloud behaved as a single convection cell inhomogeneously structured along the nozzle axis in a tube-like manner. The pulsed acceleration localized in the very head of the cloud mediated by collective plasma-particle interactions and the resulting wave pattern were studied in detail.
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An interaction of upstream extra particles with a monolayer highly-ordered complex plasma is studied. A principally new abnormal turbulent wake formed behind the supersonic upstream particle is discovered. An anomalous type of the turbulence wake clearly manifests in anomalously low thermal diffusivity and two orders of magnitude larger particle kinetic temperature compared to that of the normal wake (Mach cone) observed by Du et al [Europhys. Lett. 99, 55001 (2012)].
We report on the observation of the self-excited dust density waves in the dc discharge complex plasma. The experiments were performed under microgravity conditions in the Plasmakristall-4 facility on board the International Space Station. In the experiment, the microparticle cloud was first trapped in an inductively coupled plasma, then released to drift for some seconds in a dc discharge with constant current. After that the discharge polarity was reversed. DC plasma containing a drifting microparticle cloud was found to be strongly non-uniform in terms of microparticle drift velocity and plasma emission in accord with [Zobnin et.al., Phys. Plasmas 25, 033702 (2018)]. In addition to that, non-uniformity in the self-excited wave pattern was observed: In the front edge of the microparticle cloud (defined as head), the waves had larger phase velocity than in the rear edge (defined as tail). Also, after the polarity reversal, the wave pattern exhibited several bifurcations: Between each of the two old wave crests, a new wave crest has formed. These bifurcations, however, occurred only in the head of the microparticle cloud. We show that spatial variations of electric field inside the drifting cloud play an important role in the formation of the wave pattern. Comparison of the theoretical estimations and measurements demonstrate the significant impact of the electric field on the phase velocity of the wave. The same theoretical approach applied to the instability growth rate, showed agreement between estimated and measured values.
The plasma is generated in a low frequency glow discharge within an elongated glass tube oriented vertically. The dust particles added to the plasma are confined above the heater and form counter-rotating clouds close to the tube centre. The shape of the clouds and the velocity field of the conveying dust particles are determined. The forces acting on the particles are calculated. It is shown that convection of the dust is affected by the convective gas motion which is triggered, in turn, by thermal creep of the gas along the inhomogeneously heated walls of the tube.
Interaction of an intense electron beam with a finite-length, inhomogeneous plasma is investigated numerically. The plasma density profile is maximal in the middle and decays towards the plasma edges. Two regimes of the two-stream instability are observed. In one regime, the frequency of the instability is the plasma frequency at the density maximum and plasma waves are excited in the middle of the plasma. In the other regime, the frequency of the instability matches the local plasma frequency near the edges of the plasma and the intense plasma oscillations occur near plasma boundaries. The latter regime appears sporadically and only for strong electron beam currents. This instability generates copious amount of suprathermal electrons. The energy transfer to suprathermal electrons is the saturation mechanism of the instability.
Heat transport in a three-dimensional complex (dusty) plasma was experimentally studied in microgravity conditions using Plasmakristall-4 (PK-4) instrument on board the International Space Station (ISS). An extended suspension of microparticles was locally heated by a shear flow created by applying the radiation pressure force of the manipulation-laser beam. Individual particle trajectories in the flow were analysed and from these, using a fluid heat transport equation that takes viscous heating and neutral gas drag into account, the complex plasmas thermal diffusivity and kinematic viscosity were calculated. Their values are compared with previous results reported in ground-based experiments with complex plasmas.
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