A six vane, single radial output slot relativistic magnetron revisited

The behavior of a six vane relativistic magnetron with a single radial output slot has been studied in detail by 3D PIC simulations. We find that a delicate electro-dynamic imbalance caused by impedance mismatch is responsible for the shortening of the radiated power pulse. When the power pulse drops the voltage reduces and the current increases which points towards under-matched impedance of the magnetron relative to the generator providing its input power. We demonstrate this here by changing the radius of the cathode. When the impedances match the radiated power pulse no longer shortens and it can be increased considerably. This relatively simple electrical power balance is the result of intricate dynamics involving the electron flow within the magnetron, out of the interaction cavity through the axial flow and the electro-magnetic modes supported by the structure.

I. Introduction

Radiated power pulse shortening has been found to be a shortcoming in the operation of relativistic magnetrons [1]. Ways have been found to increase the radiated power efficiency and overcome the shortening of the pulse [2]–[11] yet the mechanism responsible for pulse shortening has not been definitively explained. Cathode plasma expansion has been pointed out as responsible [1] and it has been accepted as the most plausible reason for pulse shortening, yet in recent experiments no plasma expansion has been observed in the cathode-anode gap [8].