Magnetron assembly to show.

Magnetron assembly to show. A magnetron is a 'crossed-field' microwave electron tube capable of efficiently generating high-power microwaves (1-100 kW, up to 10 MW for short pulses) in the frequency range of 1-40 GHz. Magnetrons have been used since the 1940s as pulsed microwave radiation sources for radar tracking, for both ground radar stations and aircraft. More recently, they have been used for rapid microwave cooking. The central portion of the magnetron is cylindrical, with a hollow central cylindrical cathode, and a larger concentric anode. The anode consists of a series of quarter-wavelength cavity resonators placed symmetrically about the axis. Fixed permanent magnets provide a magnetic field parallel to and coaxial with the cathode. A radial DC electric field (perpendicular to the cathode) is applied between anode and cathode. When the cathode is heated, electrons are emitted. The combination of electric and magnetic fields ('crossed-field') causes the electrons to orbit the cathode (moving in a direction perpendicular to both e and b fields). The motion of the swarm of circulating electrons generates electrical noise currents in the surface of the anode, exciting the resonators in the anode so that microwave fields build up at the resonant frequency. The parameters of the tube, especially the velocity of the electrons, have been chosen so that the microwave fields are maximized (by a process called 'electron-bunching'). Thus a relatively small tube can be very efficient. The microwaves exit the magnetron through the output waveguide. Reference: Mac Graw Hill Encyclopedia of Science and Technology, Vol.10, p 340-343, Physics Library
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