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MODIFICATION OF SURFASE LAYERS BY IMPULPSE PLASMA FLUXES AS ONE OF THE WAYS FOR IMPROVING THE TECHNOLOGY OF EFFECTIVE THERMOCATHODE PRODUCTION

Keywords:

O.Yu .Maslennikov, N.Ya. Roukhlyada, I.P.Lee, I.A. Chusov, A.S.Shelegov


Pulse plasma obtained by a linear pinch is used for treating porous-metal cathodes with cylindrical emitting surfaces. The installation design and parameters are described. Cathode surface treatment by pulse plasma results in a grid or cell structure which improves the cathode emission characteristics, i.e. reduces the effective work function by 0,2 eV, improves the surface emission uniformity and contributes to a 1,5-fold increase in the secondary electron emission coefficient. Optimal emission characteristics of cylindrical cathodes are obtained by varying pulse counts, all other installation parameters being preserved: argon pressure 0,1 Pa, discharge chamber electrode voltage 20 keV, pulse duration 1 µs. The lowest effective work function value 1,9 eV is observed after surface treatment by 10 pulses. A transient thermal conductivity equation is solved to calculate the cathode depth temperature distribution. The surface layer fusion penetration is calculated depending on the voltage applied. There is a good agreement between calculations and experimental data. A layer-by-layer analysis with Auger and laser mass spectrometry has shown that in the surface layer (at depth of 0,2 µm) of pulse plasma-irradiated cathodes the content of oxygen and calcium is higher as compared to non-irradiated ones. Oxygen is responsible for Ba – O – W structure on the surface with the double electrical layer that reduces the work function up to 1,9 eV. The increased coefficient of secondary electron emission is explained by changes in the physico-chemical composition of the cathode surface layer caused by its refusion
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