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Cathodes for High-Current Electronics

#0687


Development of Cathodes Intended for High-Current Electronics on the Base of Intercalated Laminar materials with High Electron Emission

Tech Area / Field

  • MAT-ELE/Organic and Electronics Materials/Materials

Status
3 Approved without Funding

Registration date
04.07.1996

Leading Institute
Kurchatov Research Center, Russia, Moscow

Project summary

All kinds of cathodes currently available (various metal alloys, LaB6, oxide, impregnated, Cs and Ba film, etc.) are characterized by low emissivity of 0.5-1.5 A/cm2 at relatively low temperatures of 600-800° C in stationary conditions, and by emissivity of up to 10 A/cm2 in the pulse mode with high relative pulse duration. A demand for cathodes with emissivity that is order of magnitude higher is rather pressing, especially for such applications, as high-current electronics, commercial (green) lasers, and direct energy conversion systems. These problems could be solved through the use of laminate materials based, for example, on graphite or dichalcogenates, intercalated with alkali metals or barium. It was found in preliminary studies performed, among others, by the project authors, that pyrolitic graphite-based materials intercalated with cesium or barium show promise for attaining extremely high current densities of up to 100 A/cm2 at low accelerating voltages of 3-5 V and rather moderate temperatures around 700° C. Analysis of optimum structures of the material surface, investigation into sorption processes taking place in the metal-graphite system, as well as peculiarities of combining various kinds of electron emission from the cathode surface are key issues to be solved in this competitive project. The final stage consists in development of the manufacturing process, and fabrication of prototypic cathodes.

The work will be done in RRC "KI" on instrumentation of plasma diode voltage-current characteristics and multifunctional thermion microscope.

The following experimental results shall be obtained in this effort:


1. Voltage-current characteristics for a plasma diode with emitter of graphite-cesium, barium system over a wide range of temperatures, working medium vapor pressures and accelerating voltages. And it is proposed therewith to study emitter materials of varying phase composition.
2. Investigation will be performed of sorption and diffusion processes using a thermion microscope, photographs will be obtained of the emitter surface emissive state at different temperatures, compositions of graphite-cesium, barium system and temporal parameters.
3. Intercalated laminate structures and their emissive properties have been investigated in Russia only, including the project authors who studied these issues on cesium-graphite and barium-graphite systems. Voltage-current characteristics of a diode with emitter of laminate structures were studied in these investigations. High electron current densities of order 100 A/cm2 were detected at accelerating voltages of 3-5 V.
4. Mechanism of emission in studied systems is not understood. Because of this, it appears promising to study thermionics with simultaneous monitoring of the surface state in donor addition-graphite system. Besides, when investigating voltage-current characteristics of a plasma diode, variation in the cathode temperature at emission current removal will be measured. It is proposed also to develop a procedure for assessment of work function of the surface of donor addition-graphite system by voltage-current characteristic of a plasma diode in low-voltage arc mode.
5. Comparison of expected results with those previously obtained will allow to state a qualitative working model of the emission mechanism, and to propose ways of optimizing the surface composition and structure in order to upgrade efficiency of laminate emitters.


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