Undergraduate Research at Jefferson Lab

Constructing and Testing a Photocathode Preparation Chamber

Student: Sam Girdzis

School: The College of William and Mary

Mentored By: Marcy Stutzman

The CEBAF accelerator at Jefferson Lab uses wafers of gallium arsenide (GaAs)-based materials to produce the electron beam. Laser light strikes the wafer (also referred to as a photocathode), which emits polarized electrons by the photoelectric effect. My project focused on constructing and testing a preparation chamber for a new polarimeter system, which will be used to evaluate photocathode materials. Construction involved mounting components such as thermocouple feedthroughs and a heater assembly onto the chamber, as well as making minor modifications when hardware conflicts occurred. Testing consisted of leak-checking the chamber, calibrating the heater, and running a photocathode through an activation cycle by heating it and applying layers of cesium and nitrogen trifluoride. We were successful in activating a wafer of bulk GaAs, achieving 3.87 µA of photocurrent. However, the necessary addition of a lock-in amplifier complicated the application of chemicals to the photocathode. Further testing will be needed to optimize the preparation procedure for this new system.