Positive ion speed at the plasma–sheath boundary of a negative ion‐emitting electrode

Abstract

One‐dimensional fluid model for a planar sheath in front of a negative ion‐emitting electrode surface immersed in a collision‐less, non‐magnetized, electronegative plasma is presented. It was found that the positive ion speed at the plasma–sheath boundary (PSB) increases linearly with negative ion emission from the electrode but attains a saturation value as soon as a virtual cathode is formed near the electrode surface. The effect of negative ion emission on the pre‐sheath region shows that the potential drop increases across the pre‐sheath in accordance with the rise in positive ion speed at the PSB. The sheath width obtained using the present model shows a similar trend as the Child‐Langmuir law, but its magnitude is found to be consistently higher compared with a non‐emitting electrode. A plausible explanation has been given to explain these effects.