Further development of plasma electron gun for operation at forepump gas pressure

Summary form given only, as follows. The hollow cathode plasma electron gun was designed especially for operation at forepump (up to 0.1 Torr) gas pressure. This work is devoted to investigation of maximum values of gas pressure and accelerating voltage It was established, that the maximum. operation gas pressure as well as the electron accelerating voltage increased with the smaller emission mesh size, shorter accelerating gap and lower plasma density. Physical model to explain experimental results has been created. This model takes into account plasma penetration from discharge unit into the acceleration gap as a main reason of high voltage breakdown. This penetration occurs if thickness of sheath, that separates plasma from the emission mesh, becomes smaller then the mesh hole. From the other hand the plasma density defines electron beam current. When it exceeds some value, electrical strength of accelerating gap increases. We suppose, it is due to gas heating and hence to neutral concentration drop, that in its turn leads to breakdown voltage growth. In our experiments we observed also increase of maximum values of gas pressure, accelerating voltage and beam current when axial magnetic field is applied. We refer these facts to account of prevention of penetrating plasma motion in radial direction and therefore limitation of plasma surface. Investigations and also modification of a construction allow us to improve parameters of electron gun. Now it provides I Amp electron beam with 10 keV energy. This progress allowed us to apply electron gun for beam-plasma discharge (BPD) initiation in hydrocarbon gas. At CH/sub 4/ pressure level 30-60 mtorr and electron beam current and energy 0.5 A and 2 kV we supervised DLC films deposition with high hardness and transparence. Deposition rates varied from 10 to 50 mcm/hour depending on experimental conditions.