| The virtual cathode oscillator, or vircator, is a microwave source capable of generating extremely high levels of microwave power (;In an attempt to increase the microwave production efficiency of the vircator, a completely different geometry is being investigated. The cathode is on the inside surface of a grounded cylinder and the positively pulsed anode is a semi-transparent cylinder located concentric to, and inside of, the cathode. This geometry is termed a coaxial vircator. Electrons are emitted from the cathode and accelerated across the anode-cathode gap, they continue inward radially until the space charge from the electrons forms a virtual cathode. This virtual cathode oscillates in amplitude and radial position causing microwaves to be generated and propagated down an attached cylindrical waveguide. In addition, some electrons are repelled from the virtual cathode and oscillate between the real and virtual cathodes, also generating microwaves.;Extensive particle-in-cell simulations were employed to develop a prototype coaxial vircator. The coaxial vircator was tested in three different configurations and the experimental results are compared to simulation models. The coaxial vircator was shown to generate microwaves at an efficiency similar to a planar vircator, but the efficiency is very dependent on small geometry differences. Based on the results of the coaxial vircator experiments, improvements which may greatly increase the efficiency of a second-generation coaxial vircator, are suggested for future implementation. |
