Determination and control of ion parameters in a 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.