The Role of Apex Angle of a Cone-Shaped Hollow Cathode on Plasma Parameters

An analytical model based on particle and energy conservation equations has been developed to determine the plasma parameters inside conical and cylindrical hollow cathodes. Using this model, the effective plasma size and its dependence on the apex angle of the cathode has been formulated. The study shows that the plasma density falls monotonically, while electron temperature rises as the apex angle of the cone increases. This is caused due to a contraction in the effective plasma size inside the conical cathode. The plasma parameters obtained from the experimental measurements inside conical and cylindrical cathodes are found to be in qualitative agreement with the model.