Effects of charge depletion in dusty plasmas

Abstract

The charge reduction effect is studied in dense dust clouds. The saturation currents of Langmuir probes are used to derive the density of ions and electrons, which are calibrated with the plasma oscillation method. The plasma potential inside the dust cloud is measured with an emissive probe, which also yields the floating potential in a heated nonemitting mode. The presence of the dust also affects the density and the plasma potential of the ambient plasma. The ion densities inside the dust cloud and in the ambient plasma are found equal, while the electron density is reduced inside the dust cloud. The measured potentials are compared with current models. Inclusion of the bi-Maxwellian distribution of the electrons leads to an improved description in the limit of low dust density. The strong increase of the floating and cloud potential for high dust density, predicted by the constant ion density model, is not confirmed.

Study of glow discharge positive column with cloud of disperse particles

“…In spite of disperse particles deplete the high-energy wing of EEDF and influence the ionization efficiency of gas, however the observed in our experiment concentrations of particles could not lead to the EEDF depletion yet, as it was concluded in [16], nor change the electron temperature inside the dust cloud, as it show measurements represented in [7]. Still, at higher particle concentrations the effect of particle charge reduction observed in [7], should be also regarded.…”

“…Therefore, the simplified homogeneous particle distribution within the cloud seems to be good approximation for simulation. Here the radial distribution of disperse particles was simulated by axially symmetrical flat profile with slight end blurring: n d (r) = n d,0 , r r d , (6) n d (r) = n d,0 e (r d −r)/0.1R , r > r d , (7) where the characteristic linear size of distribution r d is independent of discharge parameters and disperse particle concentration on the discharge tube axis n d,0 .…”

“…In [6] the plasma parameters were measured in RF discharge with very low concentration of plastic tracer particles. Still, the recent probe measurements were successfully carried out even in dense dust clouds using especial procedure of cleaning and fast probe data collection [7]. The measurement of disperse particle concentration in low pressure discharge is also complicated because this procedure usually cannot be carried out using optical methods: the matter is that the detectable influence on plasma properties may be produced by rather high concentration of particles.…”

Computer tomography of large dust clouds in complex plasmas

“…This effect is called electron depletion and is typically described by the Havnes parameter. 15,16 On the other hand, the temperature of the remaining free electrons is often found to be increased 17,18 compared to a dust-free plasma. At high dust densities, a change of the discharge operation mode due to the dust was observed in capacitively coupled radio frequency (ccrf) plasmas.…”

Direct measurement of the speed of sound in a complex plasma under microgravity conditions

“…At high microparticle densities, such as in the given study, most of the electrons are collected by the microparticles. This has various effects on the plasma [39]. In particular, it leads to a lower electron density than in the microparticle-free case and, correspondingly, to a decrease of the microparticle charge [40] and also of the probe particle charge.…”