Abstract:
The article presents the results of studying the grid electrodes made of anisotropic pyrolytic graphite (APG) as part of the cathode-grid unit (CGU) of a powerful pulsed traveling-wave tube (TWT). It was found that the grid electrodes made of APG demonstrated high antiemission properties in the temperature range of 800–900$^\circ$C at cathode temperatures of 1080–1150$^\circ$C. It was found that during testing the CGU as part of a TWT device for 900 hours in the forced mode (the cathode temperature exceeded the operating temperature by 70$^\circ$C), there was no parasitic thermionic current in the cathode-control grid circuit. This result can be explained by an increase in the electron work function of the APG with a barium oxide film adsorbed on its surface. The results of calculations using the density functional method and quantum molecular dynamics modeling for the structure of APG with a BaO film having a hexagonal lattice showed that the value of its electron work function was $\sim$ 5.14 eV, which is significantly higher than the work function of APG ($\sim$ 4.7 eV) and barium oxide ($\sim$ 1–1.6 eV).
Keywords:parasitic thermal emission, cathode-grid unit, anisotropic pyrolytic graphite, density functional theory, adsorption, molecular dynamics modeling.
Fulltext:
PDF file (1799 kB)