Efficiency enhancement in a6 magnetron with transparent cathode

Abstract

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 center of the axis. This leads to a large value of E_ in the vicinity of the emission region, thereby providing faster start of oscillations. In addition, because of the presence of the strong azimuthal electric field on any thickness of electron flow, the magnetron efficiency can be increased through a concomitant increase in the applied voltage and magnetic field. Simulations were performed for the parameters of the A6 magnetron using the 3D particle-in-cell code MAGIC with both a transparent cathode and traditional solid cathode for different voltages. Results indicate that the output characteristics (e.g., microwave power, efficiency and time of start of oscillations) of the A6 magnetron were improved with the transparent cathode for any applied voltage. For the case of the solid cathode, concomitantly increasing the applied voltage and magnetic field (to maintain synchronous interaction) ultimately leads to unstable generation and degradation of output characteristics because the E_ field becomes too small on the electron flow in order to capture electrons to the anode. However, for the transparent cathode, the magnetic field range in which the magnetron operated in the desired 2_ mode becomes narrower as the applied voltage increases. This leads to the situation when the 2_ mode appears only during the early part of the simulation and later switches to the undesirable 4_/3 mode for small deviation of the value of the magnetic field from the optimal one. Introducing an external signal equal in frequency to the 2_ mode assists in locking the operating mode to the 2_ mode