Ion accumulation by a dust cloud in a dc discharge

Abstract

The ion accumulation within the negatively charged dust cloud embedded in a plasma of dc glow discharge has been studied numerically under the conditions corresponding to recent experiments. The characteristics of neon plasma in a positive column of dc discharge with various densities of micron-sized particles have been simulated by a diffusion-drift model with the use of experimental values of parameters of dust clouds. The model considers an additional gas heating associated with the presence of a dust component. It has been shown that the injection of dust particles into a plasma can either reduce the density of ions due to their recombination on dust particles or increase it due to the formation of an ion concentrator. Conditions under which the plasma-dust cloud represents an ion concentrator have been found; the density of ions in this trap can be several times higher than that in a discharge without dust particles. The method of elevating the ion density with dust particles has been shown to be more efficient than increasing the discharge current without dust particles and the value of relative overheating of the discharge with dust particles is many times less. The possibility of obtaining the desired ion density in a dust cloud at different neon pressures and the same discharge current has been demonstrated; it should be emphasized that this is impossible in a discharge without dust particles.

On the optical measurement of microparticle charge using quantum dots

“…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.…”

Ion confinement efficiency and ionization balance in a complex DC discharge plasma

“…The relative overheating coefficient η Q is useful, first of all, for technologies and processes at low and cryogenic temperatures, when heating is undesirable [24][25][26][27][28]. As was demonstrated in [18], at low discharge currents (I < 1 mA) a gain in the relative heating is quite large (η Q > 10), but it disappears with increasing the discharge current. For instance, for a discharge in neon containing microparticles of several microns in diameter within the pressure range of 40 to 120 Pa, the relative overheating coefficient is less than one (η Q < 1) at the current I > 2 mA.…”

“…For instance, such conditions are realized in a nonequilibrium low-temperature plasma of self-sustaining low-pressure electric discharges [21][22][23]. From the viewpoint of heat release, gas-discharge plasma with charged microparticles represents a more efficient system, which produces and concentrates ions [18,19].…”

“…Within a certain range of parameters, such a complex plasma can release less heat than plasma without microparticles, and its efficiency is determined by the relative overheating coefficient η Q [18]. This coefficient indicates how much more heat is released in the discharge plasma without microparticles in comparison with the complex plasma upon maintaining equal ion density.…”

“…Direct determination of ion parameters using experimental methods of plasma diagnostics [30] is not always realizable. In such cases, numerical simulation methods are employed [18]. In our previous study [19], based on the synergistic paradigm of processes in complex plasma, we demonstrated how the microparticle number density, the ion density, and the relative ion density in the ion trap in the positive glow-discharge column can be determined using the calculated electric fieldcurrent diagrams.…”