Selection of dispenser cathode impregnant types

Summary form only given. The dispenser cathode consists of a porous tungsten matrix impregnated with a barium rich impregnant material. This impregnant material reacts with the tungsten matrix to produce barium which, in conjunction with oxygen, produces a barium-oxygen dipole monolayer on the cathode surface. Many types of impregnant materials have been used over the years. These are identified by their constituent molar ratios of barium oxide (BaO), calcium oxide (CaO) and aluminum oxide (Al₂O₃). This paper discusses the relative advantages and disadvantages of several commonly used impregnant types including 5-3-2, 4-1-1, 3-1-1, and 6-1-2. Barium evaporation rate, resistance to poisoning, and common operating temperatures are discussed.