NON-THERMIONIC CATHODE FOR HIGH POWER, LONG PULSE, LONG LIFETIME MAGNETRONS

A non-equilibrium plasma is proposed as a source to generate repetitive high current, electron beams for microwave production in a slow wave structure.  Due to the gas environment inside the hollow cathode electrode, the electron beam will generate a plasma channel minimizing beam space-charge effects allowing self-focusing.  Since the non-equilibrium plasma is effectively the electron gun cathode, the properties of the cathode and hence the generated electron beam may be adjusted by changing the parameters of the plasma.  Due to the plasmas supple structure and pulse shaping properties, the non-equilibrium plasma generated electron source is compact being built around a finite in length, cylindrical anode tube possibly terminated by a diaphragm with orifice housing.  The diaphragm acts as a filter to shape the extracted electron beam and allows for some differential control in vacuum pumping if desired.   External heating units, used in thermionic emission, are not needed and large electron beam accelerating potentials may be relaxed.  The electron beam current and energy will be high enough to inject the beam into a metal plug attached to a needle inserted into the magnetron.  The source will be designed such that the electron beam energy is high enough to yield a low probability of secondary electron emission.  With special attention to capacitive coupling effects, the injected charge collected by the plug redistributes appropriately over the surface of the needle increasing the field for field emission to occur.  The cylindrical symmetry of the needle allows for uniform emission.  Instead of a solid cathode electrode, the cathode is a grid encapsulating the needle providing the appropriate potentials between cathode and anode for magnetron operation.   BENEFIT: At the end of this program (Phases I & II), we will be positioned to advance the development of the technology to produce next generation prototypes of plasma cathode-based electron injectors for use with high-power magnetrons.  It is anticipated that such development will lead directly to commercialization of these devices for military applications. If the Phase I research is successful in the tasks outlined above, the Air Force Office of Scientific Research will have an entirely new, prototypical plasma cathode for use with magnetrons and high-power fast switching applications.  The work will lay a foundation for Phase II research in which the initial development is transitioned into applications of this new technology.)