Investigation of cathode layer in the discharge with oscillating electrons

Summary form only given. We have investigated the structure and emission characteristics of the cathode layer in the ion source with cold cathodes. It has been shown that if we take into consideration electron oscillations along magnetic field, it is possible to form the space charge layer near the cathode under condition /spl gamma/> 1/2 /spl radic/(m/sub i//m/sub e//spl middot/U/sub 0//U)/spl middot/L//spl lambda/, where /spl gamma/-secondary ion-electron emission rate, U, U/sub 0/-potential drop in the anode and cathode layer accordingly, L-size of the system along magnetic field, X-length of free path of electrons. In this case the cathode layer structure is analogous to the double Langmuir layer with the potential minimum near the cathode, this value is determined by the average energy of the secondary emission electrons. The formation of the double electric layer leads to the restriction of the emissive capacity of the cathode and a reduced discharge current. Electric field of the negative space charge on the cathode prevents to formation of the cathode spots and electric break-down in discharge system. Experimental investigation of the double layer has been realized by test stream of thermions from the cathode side. Under low pressures it´s observed heavy restriction of the thermion current towards the discharge gap. It´s provides evidence of a potential barrier existence for thermions near the cathode. In this range of pressure the injected thermionic current is slowly increased with the growth of heating current, pressure, discharge voltage but it doesn´t depend on the value of magnetic field. Under pressure that is over critical value p/spl ap/10/sup -4/ Torr the potential barrier near the cathode disappears and thermionic current to the discharge gap is abruptly increased.