Electron tube with dispenser cathode

DETAILED DESCRIPTION An object of the invention is to provide a vacuum tube with substantially increased electron current density.
A further object is to provide an electron tube having substantially increased life.
A further object is to provide an electron tube which may be speedily outgassed.
A further object is to provide a tube whose reliability is not degraded by cathode-to-anode arcs.
A further object is to provide a tube for generating increased power at microwave frequencies.
A further object of the invention is to provide an improved thermionic cathode capable of emitting higher current density than previously available cathodes.
A further object is to provide a cathode having 10 amperes per square centimeter cw emission.
A further object is to provide a cathode which will outgas readily.
A further object is to provide a cathode with long life and low rate of evaporation of active material.
A further object is to provide a cathode which is resistant to degradation by arcs and ion bombardment.
To achieve these objectives, the tube incorporates a thermionic cathode comprising a porous metallic matrix in which iridium is a bulk constituent instead of merely a surface layer.
The matrix is completely impregnated with a molten alkaline earth aluminate.
The resulting complete filling of the pores of the matrix provides a structure which outgases quickly.
A matrix composed of a mixture of particles of iridium and tungsten has been found good and other metals such as molybdenum, mixed with iridium may be used.
However, a matrix of pure iridium is an alternate embodiment.
The metallic particles are pressed and lightly sintered.
Heating only to the temperature required to impregnate may be sufficient to sinter.
The impregnant is primarily barium aluminate.
Alternatively, lesser quantities of other alkaline earth oxides may be added to the barium aluminate.
It has been found that tubes embodying these cathodes can be operated with up to 10 or more amperes per square centimeter emission current density compared to 3 amperes for prior art cathodes