Low-energy electron gun

As an offshoot of our torsion-balance experiments, our group was involved in technology development for the Laser Interferometer Space Antenna, a proposed three-spacecraft space mission to detect gravity waves. These spacecraft were to stay in a perfect free-fall orbit by tracking a free-floating “test mass” contained within each spacecraft. We were investigating the effects of electrical charge buildup on the test masses. To do this, we needed a reliable method to move electrons onto and off of an electrically isolated body. Removing electrons from the body is easily achieved with a UV LED via the photoelectric effect, but forcing electrons onto the body proved to be more difficult. My first contribution to the project was to develop and build a UV-LED-based low-energy electron gun. Other types of electron guns were available, but were too high-energy, required high voltages, would introduce unwanted material or ions into the experimental chamber, or were too large for the chamber.

ElectronGun_hatched

The electron gun was designed to minimize the amount of UV light escaping from the barrel to avoid ejecting electrons from the gold-plated target body.  To further reduce this effect, the donor surface in the gun was coated with magnesium, which has a work function lower than that of gold, and a  longer-wavelength UV LED was used.

mounted_gun

This project involved CAD work, numerical modeling of the electron trajectories, and machining.

An open-access preprint of the academic paper describing the full project is available here.