External plate biasing and diverging magnetic field effects on radial characteristics of back diffused expanding plasma column *

Independent control of the plasma parameters distribution inside a discharge is significantly desirable to achieve plasma uniformity for microelectronic industry or in front of an ion extraction grid inside ion sources to minimize the beam divergence occurring due to spatial distribution of plasma in fusion devices. Electrode biasing is one of the popular techniques that is widely used for controlling the edge plasma density and temperature profile in magnetized plasma devices like, tokamak or linear device. Likewise, the spatial divergence in magnetic field also affects the charged particle dynamics in magnetized plasma. Therefore, the separate effect of electrode biasing and diverging magnetic field on spatial plasma properties are well known, but the combined effects of these two have not been well understood.

In this work the combined effect of electrode biasing and diverging magnetic field have been investigated from radial plasma characteristics for back-diffused, partially magnetized argon plasma column, created by hot cathode filament inside a linear plasma device.

It is seen that the radial gradient in plasma density and potential variation of back diffused plasma tend to reduce with applying a positive potential to a remotely located electrode. However, the radial gradient in plasma parameters variation inside the source and biasing region tend to increase. This observation gives a detailed insight into how the current closer/sharing between different regions of plasma column can influence the radial control of plasma parameters due to biasing of the electrode from remote location. A possible mechanism is given to explain the observed trends.