A study of secondary electron emission properties of the molybdenum cathode doped with RE 2O 3

Abstract

The secondary electron emission properties of rare-earth-doped molybdenum emitter made by aqueous solution–solid doping method, its microstructure and surface behavior are discussed in this paper. The experimental results show that adding rare-earth oxides La 2O 3,Y 2O 3 and Gd 2O 3 into molybdenum raises the maximum secondary electron yield δ m from 1.25 of clean Mo to 2.0–3.24 of doped molybdenum when heated to 1100–1600 °C in vacuum. With increasing percentage content of doped rare-earth oxide δ m is enhanced in some extent. δ m remains nearly constant during 1000 h of test period when cathodes are operated at 1100 °C and under primary electron bombardment with bombarding energy of 1000 eV and bombarding power of 300 W/cm 2. This demonstrates such cathodes have good anti-bombing insensitivity. A work function of about 2.7–2.8 eV is obtained from Richardson lines. SEM observations and EDS analysis show that distribution of rare-earth oxides in the cathode body is inhomogeneous and tends to aggregate at molybdenum grain boundaries. By AES analysis it is found, that atomic concentrations of La and Y on the surface are about 2.5 times higher than in the bulk for a sintered body and further increase after activation. We believe the rare-earth atoms segregated at the grain boundaries diffuse along the grain boundary during the process of cathode activation. Therefore, the surface of the cathode is covered by a certain amount of rare-earth oxide. As a result, the secondary electron yield is improved.