Potential profile near the virtual cathode in presence of charged dust

Abstract

In this work, concept of virtual cathode and its existence in dusty plasma has been studied by theoretical and numerical analysis. Using basic equations of charge dust, ions, and electrons, the non‐monotonic behaviour of the potential in presence of charged dust has been calculated and plotted as a function of dust density. It has been found that there is a change in potential between cathode and sheath potential and subsequently changes the threshold wall temperature as compared to that of without dust conditions. The threshold wall temperature has been increased due to the ability of micro‐particles acquiring electron charge and hence, reducing potential at the wall. Further, for different values of α (depends on dust density); threshold temperature remained the same for observed virtual cathode. Hence, behaviour of potential has been plotted as a function of α with increasing wall temperatures for two dust charge values (1 and 1,000). Considering no dust charge, it has been observed that, at lower dust density, double layer like structure is formed near the emissive wall. But this double layer structure gets diminishes with increasing dust density. Hence, below a threshold dust density, virtual cathode near to the emissive wall is not possible. While for Zd = 1,000, the formation of virtual cathode appeared even at very small dust density. However, irrespective of variation of potential difference near the wall and existence of virtual cathode at different emission regime the threshold wall temperature remains same. Effect of dust potential dependency on threshold wall temperature has also been discussed in this study.

Comment on “Potential profile near the virtual cathode in presence of charged dust”

“…It has been claimed that dust density is a function of the potential distribution, which is true in the case of dusty plasma experiments. There is a lack of density variation function with the potential in the manuscript.…”

“…In a very recent paper, Rathod et al have studied the potential profile near the virtual cathode in the presence of charged dust. The virtual cathode formation in a plasma sheath region of an emitting cathode is an interesting topic and has been studied theoretically and experimentally .…”

“…The set of equations are used to get solution of potential distribution in the sheath region including the dust density ( n d ), dust charge number ( Z d ), the density of emitted electrons (), etc. From the set of Equations (Equation 1–20), authors derive the conditions for the existence of virtual cathode in presence of the charged dust grains. The virtual cathode forms when ϕ vc − ϕ w < 0, where ϕ vc and ϕ w are potential at virtual cathode and emitting wall respectively.…”

“…In Figures 5 and 6, I see either a zero or almost steady variation in ϕ vc − ϕ w with increasing T w from lower to a threshold value ( T th > 52,000 K), where a double layer like potential structure or virtual cathode is formed. An almost steady or zero variation of ϕ vc − ϕ w against T w below the threshold temperature does not follow the Equation (1) which is used to understand the role of dust grains in the virtual cathode formation . The density of emitted electrons () can be estimated by expressions , where j rd = and v w = .…”

“…The density of emitted electrons () can be estimated by expressions , where j rd = and v w = . Here A = 1.2 × 10 6 Am −2 K −2 and W f ∼ 4.5 eV are the Richardson constant and work function of the tungsten wall . Since the density of emitted electrons is function of the cathode or wall temperature, it increases with increasing T w .…”