Hammerhead: a compact 300 kV vacuum bushing

High-voltage vacuum bushings are vital for particle accelerators, X-ray tubes, electron microscopes, fusion devices, and electron sources. Commercial bushings, however, are limited to  ~ 100 kV, and exceeding this limit has proven to be difficult. This work reports the physics-informed design, simulation, and experimental validation of Hammerhead, a compact vacuum bushing that has been tested up to 330 kV and used reliably at 300 kV. The design utilizes a coaxial electrode configuration and a ceramic insulator that bridges the gap using a flashover-resistant geometry. Compared with the state-of-the-art, Hammerhead nearly doubles the voltage holdoff per unit of volume, does not require ultra-high vacuum conditions or sub-micron polishing, and can be manufactured in a moderate cleanroom environment. It also integrates directly with a high-voltage coaxial cable, without the need for insulating fluids or pressurized gas. Here, it is shown - over 144 h of experimental testing - that Hammerhead operates stably at 300 kV with dark current below 10 μA.