High power microwaves generation from intense relativistic electron beam using Kali-1000 pulse power system

Intense relativistic electron beam (IREB) is generated using Kali-1000 (Kilo Ampere Linear Injector) pulse power system, providing input electric power of 4 GW and stored energy of 1000 J. IREB is used for generating Non Ionizing (High Power Microwaves, HPM) and Ionizing (Flash X-rays) radiation. The present manuscript discusses generation of HPM by Kali-1000 system using an axial Virtual cathode oscillator. Kali-1000 pulse power system is a low impedance (4 Omega) high voltage generator, consisting of Radial Tesla transformer to step up the voltage from 28 to 300 kV in 5 mu s, which energizes the line, pulse discharged by a self triggered pressurized SF6 closing switch across a Relativistic Electron Beam (REB) diode load. The typical electron beam parameters are 300 kV, 15 kA and 100 ns with a current density of 3-4 hundreds of amperes per square centimeter. Experiments are carried with a REB diode consisting of graphite cathode and SS anode mesh. Measured pulse duration of HPM pulse (FWHM) varies from 70 to 110 ns on shot-to-shot basis. The major operating output frequencies have been measured to be 5.8 and 6.2 GHz within a range of 4.8-6.7 GHz using B-dot magnetic field sensor coupled to high frequency digital oscilloscope. Microwave output power from the virtual cathode oscillator has been measured to be 50 MW using double ridged waveguide horn antenna coupled with Schottky detector diode. The estimated beam to microwave power conversion efficiency is thereby found to be 1.1%. Particle-in-Cell (PIC) simulation has been performed for a set of Vircator experiments being driven by the Kali-1000 system. Experimentally measured cathode current, dominant output frequency, radiation pattern, etc., have been compared with simulation results and are in good agreement. The dominant emission mode from the virtual cathode oscillator is shown to be the TE01 mode based on the emission pattern of microwave induced air breakdown in this experiment.