Positive ion impediment across magnetic field in a partially magnetized plasma column

Abstract

The radial characteristic of a partially magnetized plasma column created by a hot cathode filament is presented. It is found that in the absence of magnetic field, plasma potential and density varies similarly according to Boltzmann distribution. However when magnetic field increases, a clear divergence is seen as the plasma density becomes more pronounced in the centre whereas a corresponding minima is observed in plasma potential; which impede the radial diffusion of positive ions towards the grounded sidewalls. A phenomenological model based on short-circuiting effect is developed, which fairly explains this contrasting behaviour.

Equilibrium potential profile across magnetic field in inhomogeneous electronegative plasma

“…In certain apparatus, radial potential distribution across the magnetic field can be affected in the presence of a conducting end-plate [12,13,17]. Whereas in the present case, the electrodes geometry does not prefers a short-circuit effect but rather shows independent flux balance in the axial (as confirmed by the zero mean current over a RF cycle) as well in the radial direction (as also confirmed by this radial flow fluid model).…”

“…Whereas in the present case, the electrodes geometry does not prefers a short-circuit effect but rather shows independent flux balance in the axial (as confirmed by the zero mean current over a RF cycle) as well in the radial direction (as also confirmed by this radial flow fluid model). As a matter of fact the model cannot explain the experimental data reported in [12], which was the case when the plasma body was in contact with the grounded chamber wall, thus providing a short-circuiting path for the electrons through the metallic body of the chamber. Thus the bottom-line is that the radial potential, density and temperature in an inhomogeneous plasma system created due to application of magnetic field, pressure or distributed sources will follow a Boltzmann like distribution, provided that the conducting plasma boundaries do not influence the potential profile inside the plasma.…”

“…As a result, the plasma density and potential distribution inside the plasma follow a Boltzmann distribution. However, it has been seen that the spatial potential distribution inside the plasma can be highly system specific as it depends on various other experimental conditions, like external magnetic field [12], the discharge source [13], and the type of gases used [14]. Numerous examples can be found in the literature, which shows significant deviation from the theoretical prediction of plasma potential with regard to the experiments [12,13,15,16,17].…”

“…However, it has been seen that the spatial potential distribution inside the plasma can be highly system specific as it depends on various other experimental conditions, like external magnetic field [12], the discharge source [13], and the type of gases used [14]. Numerous examples can be found in the literature, which shows significant deviation from the theoretical prediction of plasma potential with regard to the experiments [12,13,15,16,17]. Particularly, the magnetized plasma systems is one such example where the presence of external electrodes in contact with the plasma body are found to dramatically alter the equilibrium properties of plasma from the Boltzmann to a non-Boltzmann potential distribution profile, particularly across magnetic fields [12,13,17].…”

“…Numerous examples can be found in the literature, which shows significant deviation from the theoretical prediction of plasma potential with regard to the experiments [12,13,15,16,17]. Particularly, the magnetized plasma systems is one such example where the presence of external electrodes in contact with the plasma body are found to dramatically alter the equilibrium properties of plasma from the Boltzmann to a non-Boltzmann potential distribution profile, particularly across magnetic fields [12,13,17]. In another case of electro-negative discharges, the negative ions are known to affect the plasma potential distribution between the discharge plates.…”