Determination and control of ion parameters in complex plasma of a DC discharge

Abstract

Complex plasmas, comprising a low-pressure DC discharge plasma and charged microparticles, form traps that can accumulate and localize ions. A loss of ions and electrons always occurs on the surfaces of the microparticles, which can lead to a decrease in the ion and electron densities in the plasma bulk. However, in most cases, the collective effect of the interaction between the discharge plasma and the dust cloud leads to an increase in the ion density-both around and inside the dust cloud-in comparison with that in pure plasma at the same discharge currents. Complex plasmas are open dissipative synergetic systems. Feedback between plasma processes allows one to control their properties using the external influences of various physical fields. Such influences thus represent a tool for controlling the dust cloud parameters and the ion density. In this letter, we report a method for determining the ion density inside a dust cloud using an electric field-current diagram (ECD). This method is based on the statement that only a single electric field can relate the particular values of the ion density, the discharge, and the dust cloud parameters. Our method includes a procedure for superimposing the ECD on the ion density-current diagram. To calculate the plasma parameters, a fluid model of a DC discharge with microparticles is employed. The method proposed herein allows us to find the conditions under which the ion density in a plasma with microparticles is less than that in pure plasma without microparticles-or vice versa, increases up to five times.

On the optical measurement of microparticle charge using quantum dots

“…It was shown in experiments [50,51] and calculations [23,52] that microparticles immersed in plasmas should heat up from several K to several tens K with respect to the neutral gas due to the kinetic and potential energy, the electrons, ions and excited atoms deposit on their surfaces. On the other hand, QD photoluminescence is known to experience the red shift on the increase of the QD temperature [40,[53][54][55].…”

“…A certain group of methods requires assumptions on the spatial distribution of plasma parameters [15,16] and/or rely on the exact values of plasma parameters [19]. Values of the plasma parameters are often taken from measurements in dust-free plasmas, whereas it has been shown that dust strongly affects the local values of plasma parameters as well as their global distributions [9,[20][21][22][23]. All the above-mentioned issues limit the accuracy of the measurements.…”

Quantum dot on a plasma‐facing microparticle surface: Requirement on thermal contact for optical charge measurement

“…[26][27][28] Charged particles bring their kinetic as well as potential energy to the plasma-facing surface, which is cooled by neutral gas as well as by thermal radiation. [29][30][31][32] Heating is, therefore, along with charging, an unavoidable consequence of the exposure of the surface to any ionized medium. The spectral shifts caused by these two phenomena have to be therefore distinguished.…”

Quantum dot on a plasma-facing microparticle surface: Thermal balance

“…Experiments of [25] have shown that exposure of QDs to the fluxes of charged particles is connected not only with the surplus-charge-induced Stark shift, but also with the thermal shift of the photoluminescence spectrum [28][29][30]. Charged particles bring their kinetic as well as potential energy to the plasma-facing surface, which is cooled by neutral gas as well as by thermal radiation [31][32][33][34]. Heating is, therefore, along with charging, an unavoidable consequence of the exposure of the surface to almost any ionized medium.…”