GYCOM Ltd. has technologies for manufacture of high- and low-temperature cathodes used in gyrotrons.
The high-temperature cathodes are made of lanthanum hexaboride (LaB6). They have an operating temperature of about 1500oC and are subdivided into two types: cerametallic (cermet) and sintered ones. Such cathodes are highly resistant to ion an electron bombardment, stable against poisoning with residual gases, and have low secondary-emission coefficient and good renewability of emissive properties in the case of operation in long-pulse and continuous-wave regimes with current densities up to 3 A/cm2.
Cermet cathodes are made of a metal-ceramic mixture (10% of lanthanum hexaboride and 90% of rhenium). Rhenium reduces the value of the electronic work function and, therefore, the operating temperature, down to ~1450ºС).
The technological cycle of manufacturing the emittive coating includes the following operations:
- chemical and thermal preprocessing of the core;
- preparation of the metal-ceramic mixture on a binder;
- layer-by-layer deposition and sintering of the emitting composition in vacuum;
- final lathing of the core with the emitter.
High-temperature sintered cathodes are made of pure lanthanum hexaboride. The operating temperature of such cathodes is equal to ~1550ºС at the maximum current densities of up to 4 A/cm2. The technological manufacture cycle includes the following operations:
- formation of a porous rhenium sponge with preset dimensions;
- impregnation of the sponge with lanthanum hexaboride;
- sintering in vacuum.
Operations of sponge formation and impregnation are performed on a binder.
Low-temperature impregnated cathodes have long lifetimes and can ensure current densities up to 10 A/cm2. The operating temperature is about 1000ºС. Such cathodes survive long storage periods under the atmospheric conditions well and can be used in different devices many times. The manufacture process includes the following operations:
- plasma deposition of tungsten sponge;
- impregnation of the sponge with barium aluminate and calcium aluminate;
- sintering in hydrogen;
- polishing to the specified size.
When a cathode is manufactured, the above-listed emitting coating is formed on a molybdenum core. For operation in gyrotrons, the cathodes are equipped with indirect cathode heaters. Tungsten spirals are used as heating elements. When a gyrotron is assembled, the cathode is mounted on the cathode heater unit and fixed on it.