Study On Grid Emission Suppression And Application Of Cold Cathode In Microwave Tubes

Pulse-controlled grid traveling-wave tubes (TWTs) are widely used in the field of space and defense for navigation and directing of radar, aircraft, satellite, and guided missiles because of the high gain, high power, wide work frequency band, small volume, light weight, good reliability of TWTs. In order to attain higher frequencies and powers, gun designs for modern microwave tubes have utilized grids, which are in close proximity and bonded to the cathode. Unfortunately, the active electron-emission substances (Ba, BaO) from the cathode are inevitably deposited onto the surface of the grid because of the close proximity of the grid to the hot cathode, which greatly lowers the work function of the grid. This leads to electron emission from the grid, (grid emission,) which impairs grid cut-off characteristics and the working condition of pulse-controlled grid TWTs. Grid emission is a long-term technological problem in vacuum microwave tubes. Supported by a grant from 973-Program of the Ministry of Science and Technology of China (No.G2000067207-2), the electron emission suppression properties of hafnium and platinum film on molybdenum using ion beam assisted deposition (IBAD) were investigated, studied the mechanism of grid emission suppression, and further explored the new anti-emission coating materials. Due to BaHfO₃ compounds and Ba-Hf diffusion, the grid coated with Hf film by IBAD can effectively reduce the accumulated electron-emission substances on the grid surface from the cathode. Meanwhile steady BaHfO₃ compounds and Ba-Hf diffusion may destroy the structure...