Comparative study of the surface potential of magnetic and non-magnetic spherical objects in a magnetized radio-frequency discharge

Abstract

We report measurements of the time-averaged surface floating potential of magnetic and non-magnetic spherical probes (or large dust particles) immersed in a magnetized capacitively coupled discharge. In this study, the size of the spherical probes is taken greater than the Debye length. The surface potential of a spherical probe first increases, i.e. becomes more negative at low magnetic field ( $B < 0.05\ \textrm {T}$ ), attains a maximum value and decreases with further increase of the magnetic field strength ( $B > 0.05\ \textrm {T}$ ). The rate of change of the surface potential in the presence of a $B$ -field mainly depends on the background plasma and types of material of the objects. The results show that the surface potential of the magnetic sphere is higher (more negative) compared with the non-magnetic spherical probe. Hence, the smaller magnetic sphere collects more negative charges on its surface than a bigger non-magnetic sphere in a magnetized plasma. The different sized spherical probes have nearly the same surface potential above a threshold magnetic field ( $B > 0.03\ \textrm {T}$ ), implying a smaller role of size dependence on the surface potential of spherical objects. The variation of the surface potential of the spherical probes is understood on the basis of a modification of the collection currents to their surface due to charge confinement and cross-field diffusion in the presence of an external magnetic field.

Magnetized dusty plasma: On issues of its complexity and magnetization of charged dust particles

“…[1,68] (f) It is also expected to observe a finite effect of collisions (background neutral density) on the charging currents in the presence of the magnetic field due to the I e⊥ and I i⊥ dependence on collisional relaxation time. [1,55] It should be noted that the estimation of accurate charge on dust grains in weakly/strongly magnetized plasma is necessary to understand the dynamics/characteristics of dusty plasma. In the last few years, theoretical as well as experimental works have been carried out to estimate the charge on dust grains in magnetized plasma.…”

“…Melzer et al [69] adopted normal mode analysis of the dust cluster in the magnetized rf plasma for extracting charge on nm-to micron-sized dust grains. At the same time, Choudhary et al [55] estimated charge on magnetic and nonmagnetic spherical probes (large dust grains) in magnetized rf discharge. Theoretical study and computational experiments have been performed to understand the charging mechanism in magnetized plasma background [59,68,[70][71][72][73] However, there are inconsistencies in the numerically estimated and experimentally observed values of the dust charge in weakly magnetized dusty plasma.…”

“…In recent years, dedicated experimental devices are built to study the strongly magnetized dusty plasma where massive charged particles (nm to μm) can be magnetized. [52][53][54][55] However, there are many challenges to magnetizing the solid-charged dust particles in the ambient plasma background after application of a strong B-field. Thomas et al [98] suggested the strength of magnetic field (few Tesla) to magnetize the charged dust particles (nm to μm) in the plasma background.…”

“…The electrons are magnetized at a lower magnetic field (B < 0.05 T) but a higher B‐field (B > 0.1 T) is required to magnetize ions in typical dusty plasma experiments. [ 55 ] In magnetized plasma, the currents $$$ {I}_e $$$ and $$$ {I}_i $$$ to the dust surface are expected to change due to the following reasons: (a) magnetic field reduces the loss of energetic electrons from the plasma region to the wall of the experimental chamber. The confinement of energetic electrons may change the average energy or electron temperature of bulk plasma electrons.…”

“…It is a fact that strong magnetic field is required for the study of strongly magnetized dusty plasma. There are few dusty plasma devices based on permanent magnet [52] and superconducting electromagnet [53][54][55] to conduct dusty plasma studies with strong magnetic field (few Tesla). Researchers are continuously working to explore the effect of strong magnetic field on low-temperature plasma and dusty plasma phenomena such as patterns formation, [56,57] imposed structure formation, [58] computational modeling of dust charging, [59] study of dust acoustic modes, [60,61] vertical oscillation of dust grain, [62] rotational and vortex motion, [25,63] crystallization and melting of dust grain medium, [64] Mach cone formation, [65] dusty plasma crystal as tunable terahertz (THz) filter, [66] etc.…”