Limitation of leakage current in the a6 relativistic magnetron

Abstract

Summary form only given. The feeding of a relativistic magnetron using a high current electron accelerator from one side leads to inevitable leakage of axial current from the interaction space along the magnetic field lines. This leakage current decreases the magnetron efficiency because it does not contribute to energy exchange with the electromagnetic (EM) field. An evident way to decrease these losses is to limit the leakage flow of electrons by their own space charge, transporting this flow into a channel with a larger diameter than that of the magnetron anode along the applied magnetic field. The value of the space-charge-limited current can be controlled by varying the magnetic field. This limitation of the leakage current is associated with the formation of a virtual cathode in the channel near the interaction space with the electron flow reflected from it. In the virtual cathode there is a position where electrons stop; therefore, the Lorentz force keeping electrons on the magnetic field lines disappears, whereas the greatest density of electrons in this position results in strong Coulomb forces pushing electrons aside. Thus, electrons return to the interaction space along trajectories with larger radii. Reentry of reflected electrons into the interaction space can increase magnetron efficiency as well as decrease it. If their trajectories lead them near the cathode surface, then reflected electrons are almost indistinguishable from electrons emitted from the cathode. In this case they play a useful role in energy exchange, moving towards the anode in a favorable phase of the synchronous field of the operating wave. If reflected electrons return to the interaction space near the anode surface, they take energy away from the electromagnetic field, moving towards the cathode in an unfavorable phase of the field decreasing magnetron efficiency. In this present work, the problems related to the limitation of leakage current based on the formation of a virtual cathode are studied for the A6 magnetron parameters using the 3D particle-in-cell code MAGIC