Crossed-field device

Details Crossed-field device Crossed-field device

1999-02-26

2001-05-22

Lee, Benny T. (Department: 2817)

Electric lamp and discharge devices: systems

Combined load device or load device temperature modifying...

Discharge device load with distributed parameter-type...

C315S039630, C315S039670, C330S047000

Reexamination Certificate

active

06236161

ABSTRACT:

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to pulsed or intermittently operated crossed-field devices such as magnetrons and crossed field amplifiers (CFAs). By way of example, U.S. Pat. No. 3,255,422 shows one such CFA device wherein a microwave entry waveguide provides radio frequency energy to an entry port for a slow wave propagating structure on an anode. A cathode is opposed to this anode across a gap. A solenoid maintains a magnetic field perpendicular to the applied electric field. The cathode is formed of a material having a secondary emission ratio greater than unity so that electrons emitted from the cathode due to the electric field follow re-entrant trajectories in the magnetic field and bombard the cathode to cause further electron emission. Energy exchange between the emitted electrons and the rf field results in amplification of the input signal, which is then coupled out at a microwave outlet port as an amplified signal.
Because the cathode is formed of a material selected to copiously emit secondary electrons, such devices, if not provided with a means for shutting down the electron emission, could continue to run spontaneously even when the input rf is removed. Thus, as set forth in the aforesaid U.S. Pat. No. 3,255,422, it is customary to provide a control electrode which during a turn-off phase is pulsed near anode potential to capture electrons and end the secondary electron re-emission. However, the control electrode requires a relatively high-powered pulse and high potential to dependably quench the electron flux. This may result in an inflexibility of operating characteristics, so that the device does not work dependably with power supplies or drivers having slightly different characteristics, or fails to shut down after hot, relatively long, operating cycles. Thus, for example, when used to amplify or supply high energy radar pulse sequences, shut down may become erratic when used with different models of power supply or pulse timing units.
Accordingly, it would be desirable to provide a crossed-field device having improved shut-down characteristics.
It would further be desirable to provide such a device wherein the control electrode operates at a lower potential or energy.
SUMMARY OF THE INVENTION
The present invention overcomes deficiencies of known devices by providing a crossed-field device such as a crossed-field amplifier or magnetron wherein a distributed cathode body is spaced from an anode to provide an electric field in a traveling wave region between an rf inlet and an rf outlet. The traveling wave region is arranged to have a magnetic field oriented perpendicular to the electric field, so that some electrons emitted by the cathode cycle back to the cathode. A control electrode is positioned to interrupt the operation of the device by collecting some of the circulating electron flux in the gap, and by diverting the remainder of the electron flux to an auxiliary electrode. The diversion of electron flux to an auxiliary electrode reduces the energy requirements on the control electrode. In a preferred embodiment, the cathode extends along a cylindrical arc, and the control electrode occupies a segment extending along a minor portion of the periphery and spaced from, but along a generally continuous contour with, the cathode. The auxiliary electrode is positioned in a gap, and preferably behind the cathode syrface, so that electrons traveling along the amplification path are diverted away from the cathode and the traveling wave path before reaching the control electrode.
Preferably, the cathode is dimensioned appropriately for the frequency of the input rf drive, with the dimensions of height and diameter under several inches each for the case of L-band operation. The cathode is carried by an insulating support structure and the auxiliary electrode may be a rod which extends axially parallel to but spaced from the cathode, in a gap between the cathode and control electrode. The auxiliary electrode may be positioned in a counterbore in the cathode support structure, where it operates as a second anode in the crossed field to capture electrons from the gap. Preferably the auxiliary electrode is operated above cut-off so that electrons are rapidly and completely collected.


REFERENCES:
patent: 2967264 (1961-01-01), Dench
patent: 2971121 (1961-02-01), Dench
patent: 3255422 (1966-06-01), Feinstein et al.
patent: 3577172 (1971-05-01), Dench
patent: 3614515 (1971-10-01), Wilczek
patent: 3619709 (1971-11-01), Dudley
patent: 5280218 (1994-01-01), Smith
patent: 5412281 (1995-05-01), Farney et al.

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