The interaction of intense, ultra-short microwave beams with the plasma generated by gas ionization

Results of the non-linear interaction of an extremely short (0.6 ns) high power (∼500 MW) X-band focused microwave beam with the plasma generated by gas ionization are presented. Within certain gas pressure ranges, specific to the gas type, the plasma density is considerably lower around the microwave beam axis than at its periphery, thus forming guiding channel through which the beam self-focuses. Outside these pressure ranges, either diffuse or streamer-like plasma is observed. We also observe high energy electrons (∼15 keV), accelerated by the very high-power microwaves. A simplified analytical model of this complicated dynamical system and particle-in-cell numerical simulations confirm the experimental results.