<title>High-power microwave(HPM) air breakdown</title>

Abstract

ABSTRACT The results of the breakdown of microwave pulses in air have been described in this paper. The experimental study has beendone in a waveguide, with the frequency of 9.37GHz, the peak power up to 200kW, pulse width from O.3ts to 2.Ots, singleshot and repetition rate up to 970Hz, and the processes of the breakdown of repetitive pulse were also been recorded for tenpulses. The analytic methods for threshold power density are presented also. The comparisions between the theoretical andthe experimental results for the breakdown threshold are presented, and in good agreement. Keywords: high power microwave, propagation, breakdown, plasma, ionization, attachment, recombination, pulse, threshold, repetition rate 1. INTRODUCTION The propagation of HPM through the air is a process that strongly concerns on such factors as air breakdown efffect, the airabsorption and scattering, and reflection, diffraction and scattering of HPM from all kinds of earth obstacles. The high powerdensity ofHPM makes air breakdown effect the most significent phenomina for the study of the propagation of HPM throughatmosphere. There are several events may arise while the 11PM air breakdown happens. These events are: the decay of HPMpulse, tail-erosion, and the power reflection from the air breakdown point. The decay and tail-erosion of the HPM pulselimits the power can be transmitted to targets, and consquently decrease the efficiency of the HPM source; at the same time,the reflected power from the air breakdown plasma may be dangerous to the HPM source. Especially for the design of HPMsystems, it is very important for the designers to have in-depth understanding of the physics of HPM air breakdown andrelated experimental data, including the breakdown thresholds for different HPM parameters(frequency, pulse duration,repetition rate, and power).A waveguide system was employed to study HPM air breakdown, at the same time, theoretical analysis were made tounderstand the physics of air breakdown. The experimental and theoretical results were compared and some conclusionswere drawn.The high density plasma generated by HPM air breakdown results not only in the reflection, absorption, and tail-erosion ofHPM, but also in such phenomina as enhancement of amplitude, widening of spectrum, and self-focus of HPM if certainconditions could be satisfied. The enhancement ofthe 11PM amplitude may due to the dispersion characteristic of the plasma,sometimes the amplitude of the field can be higher than that of the injected 11PM pulse. As to the widening of HPM spectrum,the main reason is that the pulse duration of the incident HPM is shorted by the breakdown plasma. When the density ofthe breakdown plasma satisfies some conditions, the transmitted HPM pulse will focus. As the first step, the work reported in