Rare Earth Oxide Refractory Metal Salt Impregnated W Based Directly-Heated Cathode

Cathode plays an important role in the magnetron. In order to enhance the emission current, reduce the operation temperature and prolong the lifetime of the pure W cathode applied in the magnetron, a new La sub(2) O sub(3)/Y sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated W based directly-heated cathode was developed. The thermionic emission properties of the La sub(2) O sub(3)/Y sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated cathode were measured. The results show that the La sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated cathode can provide more than 0.18 A /cm super(2) current density for the space charge limitation(SCL) at 1600[degrees]C. Under the same thermionic emission level, the working temperature of the La sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated cathode is at least 300[degrees]C lower than that of the pure W cathode. Lifetime of the La sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated cathode reaches 2100 h at 1750[degrees]C with dc load of 0.5 A/cm super(2). The Y sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated cathode can provide more than 0.6 and 3.4 A /cm super(2) current density for SCL at 1400[degrees]C, 1700[degrees]C, respectively. Under the same thermionic emission level, the working temperature of the Y sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated cathode is at least 400[degrees]C, lower than that of the La sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated cathode. Lifetime of the Y sub(2) O sub(3)-Gd sub(2) O sub(3)-ZrO sub(2) impregnated cathode reaches 2600 h at 1600[degrees]C with dc load of 1.5 A/cm super(2). At last, the thermionic emission mechanisms of the two new impregnated cathodes are discussed reasonably.