Instability of a plasma sheath near an emitting cathode

The analytical model of the instability of plasma sheath near cathode is presented. It is assumed that this phenomenon recently observed experimentally close to the instability of the plasma sheath near an anode. However, the physical mechanism of the instability is different. The normal mode of the plasma oscillations in the anode sheath exists and can be pump by the electron current flowing to the anode. There is no such mode in the cathode sheath since the energy of the normal waves in the ion current propagates to the cathode only. Nevertheless, the presence of the secondary electrons knotted out of the cathode by the ions can lead to the emergence of feedback in this system. The current of the secondary electrons can be high because, usually the surface of the cathode is impure