Comparative study of a relativistic magnetron performance with various cathodes

Cathode plasma expansion into a vacuum gap is one of the major physical mechanisms affecting the relativistic magnetron (RM) performance and causing a so-called pulse shortening. Therefore, development of new cathode technologies may lead to a significant enhancement of the microwave pulse length, efficiency and power of RMs. The authors are currently conducting a series of experiments with various cathodes with an aim towards improving the RM characteristics. The first results of this research were reported at the BEAMS'98 Conference (Haifa, Israel). In this paper, a more detailed analysis of the experimental data is presented. A primary objective in this research was to determine how the cathode geometry and type of the emission surface would influence major RM characteristics such as microwave pulse duration, output power and magnetron efficiency. The authors found that the cathode geometry influences strongly the RM operation but that the type of emission surface has much less significance. The cathode end caps, which have been mostly abandoned after transition from classical to relativistic magnetrons, were shown to be able to increase the microwave power and RM efficiency without facilitating the pulse shortening effect.