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Metal alloy cathodes based on alloys Pt-Ba, Pd-Ba, Ir-La, Ir-Ce, Os-Th and Re-Th are described. These metal alloy cathodes have a unique combination of emission, thermal and physical properties and found a wide application in vacuum microwave devices (traveling-wave tubes, backward-wave oscillators, klystrons, magnetrons). Cathode design of these metal alloy cathodes is described and will be presented.
The commercial, off-the-shelf (COTS) industrial heating magnetrons are the most powerful non-relativistic Microwave Vacuum Electronic Devices (MVED) operating in the upper part of the UHF band (800-1000 MHz). There are limitations imposed on the magnetron operation by the thermionic cathodes operating in the thermal electron emission mode. Among the most severe limitations are (i) the time the magnetron...
The UM/L-3 relativistic magnetron operates at -300 kV, 2-5 kA, for durations of 500 ns and is capable of generating microwave pulses of 100's MW output power at 1 GHz for 100's ns. Previous research at UM utilized Metal-Oxide- Junction (MOJ) cathodes to exploit triple point field enhancement to stimulate electron emission. These MOJ cathodes generated fast current turn-on, however, the lifetime of...
In the present paper the 3-D model is employed to analyze the electron hub generation process in a magnetron diode with a secondary-emission cathode whose operation is stimulated by priming electrons from ancillary side cathode. It is shown that the electron emitted from the cold cathode areas at the diode ends has an effect upon the rate of space charge density, it is needed to trigger the secondary...
Recent gyrotron operations indicate that nonuniform cathode emission is prevalent in many, if not most, magnetron injection guns. A nonuniform emission can result in degradation of the RF performance and increase heating in the collector. This paper describes research to improve cathode emission by addressing temperature uniformity and work function issues. A new cathode design is proposed, and a...
Summary form only given. To provide fast start microwave oscillatios in relativistic magnetrons, we proposed the transparent cathode, which is essentially a longitudinally slit cylindrical cathode comprising multiple strip electron emitters arranged in a circle. The fast start is achieved due to both cathode and magnetic priming, and the presence of strong electromagnetic field within the electron...
Previous experiments at the University of Michigan have explored the mechanism of electron emission from triple points (vacuum-conductor-dielectric interface) for application to high current cathodes. Recent experiments have fabricated metal-oxide junction (MOJ) cathodes consisting of hafnium oxide (HfO2) coatings over metal (#304 stainless steel) substrates. High dielectric constant HfO2 coatings...
The transparent cathode is a novel cathode design intended to provide rapid startup in pulsed, relativistic magnetrons (Fuks and Schamiloglu, 2005). The transparent cathode consists of separate longitudinal metal strips arranged on a cylindrical surface that act as electron emitters. The cathode may also contain a center conductor to provide mechanical support for the cathode strips
Summary form only given. Initial magnetic priming experiments performed on the UM/Titan relativistic magnetron (6-vane, -300 kV, 5-10 kA, 0.3-0.5 mus) have shown improvements in magnetron performance over baseline operation. In the current experimental setup, three, 4-cm magnetic wires (Mu-Metal) are located within the cathode structure, centered beneath the emission region, and spaced 120 degrees...
Summary form only given. Relativistic magnetrons are very powerful and compact sources of high power microwaves. The transparent cathode is a very simple cathode design in which longitudinal strips are removed from a thin walled tubular cathode. This geometry allows the azimuthal electric field of the operating wave, E_, which is responsible for motion of electrons to the anode, to penetrate to the...
Summary form only given. We present results of emission non-uniformity studies by 3D modeling and experiments on a 96 kV, 40 A magnetron injection gun (MIG) for use in a 1.5 MW 110 GHz gyrotron. Non-uniform beam current density is attributed to emitter surface roughness, surface temperature inhomogeneity, and variation of the work function along the emitting cathode ring. The emission nonuniformity...
Summary form only given. Experiments have been performed on a relativistic magnetron using innovative monolithic metal cathodes (Al). These new types of cathodes are fabricated utilizing KrF laser ablation of metal surfaces to enhance the local E field. Two new types of cathodes invented are: projection ablation lithography (PAL) and ablation line focused (ALF) cathodes. PAL cathodes are fabricated...
Summary form only given. The gap between the cathode and anode in a relativistic magnetron is, as a rule, much smaller than the radii of the electrodes in order to provide synchronous interaction between the electrons and the operating wave. However, the inadvertent production of plasma on the cathode during explosive electron emission quickly fills the anode-cathode (A-K) gap, thereby limiting the...
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