Study of tungsten filaments for indirectly heated LaB₆ cathode assemblies

Tungsten filaments of two different configurations, helical spring coil type and spiral type, are studied, fabricated and tested for development of LaB₆ cathode assemblies. These assemblies are used in electron injectors for RF and DC accelerators of the division. The helical spring coil filament is of length about 190 mm and is fabricated in house. These filaments indirectly heat the LaB₆ cathode pellet so as to extract a maximum beam current of more than 1 A. Some filaments have failed due to hot spot generation and some due to failure in spot welding joint to the tantalum holders. Typically the filament life is more than 1000 hours. This paper describes the comparison of performance of the cathode assemblies with the two types of filaments, their life estimation, their testing and failures under different conditions. (author)