Operation of a relativistic magnetron with a "cut cathode"

Summary form only given. The consistent increase of applied voltage and magnetic field in magnetrons to maintain the synchronous interaction of electrons with the operating wave leads to a decrease in radiated power and efficiency. Moreover, it leads to unstable RF generation. The reason is that the synchronous azimuthal electric field decreases in the electron flow over the cathode and the flow thickness decreases as H/sup -2/. A good solution, if possible, would be to use a transparent cathode for this electric field, which is responsible for capturing electrons into spokes forming an anode current, because for any magnetic field it provides a strong synchronous electric field everywhere in the narrow interaction space (compared with the cathode radius). We suggest to use a cathode that has many longitudinal narrow bands in order to facilitate penetration of the azimuthal electric field into the cathode. It is possible to use a high current cathode that has minimal plasma formation to achieve this, as well as ordinary explosive emission cathodes because of the deceleration of plasma filling the interaction space as plasma expands in all directions. Above all, the plasma becomes transparent for strong microwave fields that are found in high power magnetrons. We use the A6 magnetron, which has the best characteristics operating in the 2/spl pi/ mode with voltage U=350 kV when a solid cathode is used, and we study its operation using a "cut cathode" (a cathode with many longitudinal bands cut along it that allows for partial penetration of the fields into the cathode). The results of computer simulations using the MAGIC PIC code are: i) the formation of electron spokes occurs after the appearance of a solid electron ring around the cathode; ii) the magnetron shows steady state operation in /spl pi/ mode for applied voltages 0.35-1.5 MV for a wide range of magnetic field; iii) the radiated power increases more quickly than the voltage, and the efficiency exceeds 30% - or any voltage.