Hop structure optimization

Abstract

Summary form only given. Traditionally, the cathodes used in Microwave Vacuum Electron Devices (MVEDs) have been thermionic cathodes. While thermionic cathodes are extremely reliable and well developed, they do have their disadvantages. Thermionic cathodes require heater power and do not allow for spatial or temporal control. The advances of processing techniques have enabled Field Emitter Arrays (FEAs) to emit the electrons with nearly the same current as thermionic cathodes and with gate voltages on the order of 100 Volts. FEAs are more efficient and allow spatial control. While the use of thermionic cathodes in MVEDs is well explored, the use of FEAs is not. Our study focuses on the use of FEAs in a linear Cross-Field Amplifier (CFA) configuration. To inject the electrons into this configuration, a plate with slits is used to protect the FEAs. The plate is fabricated from Low Temperature Co-fired Ceramic (LTCC). The sloped wall slits form hop funnels. These hop funnels use the secondary electron emission properties of a dielectric surface to concentrate electron emission from a FEA and enhance uniformity and spatial distribution. The injected electrons will cycloid down the tube with the E×B velocity and will interact with the RF wave on a slow wave circuit. In this work we will look at the effects of using hop structures with slit geometries as well as standard hop funnel holes using different wall slopes. Two different hop funnels will be tested each with a different wall slope. Measurements will include the funnel IV characteristics and the electron energy distribution at the funnel exit. We will also look at the electron trajectories down the length of the CFA tube. We will monitor the emitter current and will measure the currents into the anode, collector, FEA gate, and hop electrode in order to track the electron movement. These structures will be modeled using the particle trajectory simulation Lorentz2E2 and compared to the experimental results.