Numerical Analysis of High-Power X-Band Sources, at Low Magnetic Confinement, for Use in a Multisource Array

Abstract

High-power microwave sources are typically relativistic in nature, employing multi-kilo-ampere electron beams that require significant magnetic confinement for efficient operation. As the desired output power increases, so does the complexity, and overall energy requirements, of the source. It can, therefore, be advantageous to consider the use of several, moderate-power, sources operating as a phased array; for an array of N sources, the far-field peak intensity scales as N², and the peak-of-field may be steered electronically by varying the relative phases of the different output signals. In this article, we present the numerical analysis of a short-pulse (~1 ns) X-band backward-wave oscillator, driven by a 210-keV, 1.4-kA electron beam, suitable for use as the radiative element in such an array. The investigation of the required magnetic confinement showed two peaks in performance, with the highest efficiency, of 43%, predicted at the low magnetic confinement peak at 0.3 T, corresponding to 125-MW peak output power. The magnitude and timing of the peak in the output pulse were functions of the rise time of the electron beam energy, with longer rise times resulting in delayed peak-of-field and lower peak output power. When operating in an array, to maintain effective output in the region of N², it was determined that the beam rise times, across all sources, should be ≤150 ps with the adjustment of the relative timing between output's being ±30 ps.