An elongated plasma column in the presence of an axial magnetic field has been formed using a cylindrical hollow cathode (HC) and a constricted anode (CA). The plasma characteristics of the central line have been found to vary with the magnetic field strength and the axial distance from the source. It is believed that the primary electrons constituting the discharge current are steered by the axial magnetic field to undertake ionizing collisions along the plasma column. The current carrying electrons from the HC reach the anode by cross-field diffusion towards the central line. The above observation has been substantiated using a phenomenological model which links the observed characteristics of the source with the plasma column. The experimental results are found to be in qualitative agreement with the model.

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.

A: The article presents an experimental investigation on Langmuir probe measurements in a magnetized plasma column which exhibits two-temperature electron populations. It is a known fact that probe I(U) traces follow the usual exponential law if the measurements are performed with a reference electrode in good contact with plasma; which is usually a grounded discharge electrode. However in the present case, as the grounded probe reference is not a part of the discharge circuit the resulting I(U) analysis is not straightforward. It is found that owing to the high impedance between bulk plasma and probe reference, the probe measurement results in lower values of electron saturation current as compared to the ideal scenario. An appropriate correction is thus required to account actual electron saturation current and thereby to extract subsequent plasma parameters. Therefore, a simple analysis technique has been proposed to interpret probe I(U) traces resulting from such magneto-plasma devices, where reference to the probe is in partial/ poor contact with the bulk plasma. K: Plasma diagnostics -probes; Data analysis; Nuclear instruments and methods for hot plasma diagnostics; Plasma generation (laser-produced, RF, x ray-produced) 1Corresponding author.

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