Influence of cold hollow cathode geometry on the radial characteristics of downstream magnetized plasma column

Abstract

In this paper, the effect of cathode geometry on the radial characteristics of a downstream plasma column is presented for a cold cathode type of hollow cathode (HC) system. It is observed that when an axial magnetic field is applied to a cylindrical cathode, the downstream plasma exhibits an off-centered peak in the plasma density. However, as the magnetic field increases, the discharge extinguishes rapidly above a critical value, due to the suppression in secondary electron emission from the cylindrical cathode surface. On the other hand, by replacing the hollow cylinder with a cone-shaped cathode an oblique sheath is formed with respect to the axial magnetic field. This configuration helps in sustaining the discharge at twice the magnetic field than in the cylindrical case. It is also found that the downstream plasma exhibits a peak plasma density at the center for the case of the conical cathode. The above experimental observations for each HC setup has been qualitatively explained with the help of a phenomenological model.

Secondary electron emission under magnetic constraint: from Monte Carlo simulations to analytical solution

“…It acts along the entire trajectory of the secondary electrons, assuming that the sheath thickness is twice as large as the Larmor radius of the secondary electrons. This is a valid assumption for magnetic fields of the order of , as in magnetron sputtering devices 30 and tokamaks 39 , but it may fail for lower magnetic fields ( ), as in Hall thrusters 9 or hollow cathode discharges 28 , 29 . The schematic representation of magnetic field B , electric field E and secondary electron velocity vectors is plotted in Fig.…”

“…The effective SEY is obtained by subtracting the number of recaptured electrons from the number of secondary electrons released by a single primary particle. It is a crucial parameter in various applications assisted by a magnetic field, such as: magnetically confined plasma in fusion devices 27 , Hall thrusters 8,9 , hollow cathode discharges 28,29 , or magnetron sputtering reactors 16,30,31 ; electron guidance by magnetic immersion lenses in scanning electron microscopy 32 ; magnetic suppression of the SEE from the beam screen of a high-energy accelerator 33 or from the negative electrode of a beam direct energy converter 34 . Therefore, the effective secondary electron emission under magnetic field influence has been investigated, independently or in connection with the mentioned applications.…”

Secondary electron emission under magnetic constraint: from Monte Carlo simulations to analytical solution

“…The electric field acts along the entire trajectory of the secondary electrons, assuming that the sheath thickness is larger than the Larmor radius of the secondary electrons. This is a valid assumption for magnetic fields of the order of 0.1−1 T, as in magnetron sputtering devices [19] and tokamaks [25], but it may fail for lower magnetic fields (∼ 0.01 T), as in Hall thrusters [6] and hollow cathode discharges [17,18].…”

“…The SEE is influenced and may be controlled by the presence of a magnetic field at the emitting surface. It is the case of various applications: magnetically confined plasma in fusion devices [16], Hall thrusters [5,6], hollow cathode discharges [17,18] or magnetron sputtering reactors [13,19,20]; electron guidance by magnetic immersion lenses in scanning electron microscopy [21]; magnetic suppression of the SEE from the beam screen of a high-energy accelerator [22] or from the negative electrode of a beam direct energy converter [23].…”

Understanding Langmuir probe characteristics of a magnetized plasma column in partial contact with grounded probe reference

“…bulk electrons and hot electrons). Hence, the effective electron temperature is given by the harmonic average of the individual species [15,18,19]. Therefore, the actual value of electron saturation current is essential to account bulk and hot electron densities individually.…”