Undergraduate Research at Jefferson Lab

Electron Beam Dynamics, Astra Modeling and Measurement

Student: Robert Parker-Mason

School: Morehouse College

Mentored By: Fay Hannon

Jefferson Lab uses a particle-tracking algorithm called Astra in their Gun Test Stand (GTS). The GTS contains a direct current gun that uses high voltage with a multi alkali photocathode to accelerate electrons down a beam line. This photocathode was chosen because it has a high quantum efficiency and it is thought to have long lifetime. The beam line at the GTS comprises of solenoids, viewers and a faraday-cup. The purpose of the GTS is to study how electron beams behave and eventually, run the electron beam at 5 mA without a fluctuation in vacuum. The focus of this project was to simulate the electron beam in the GTS using Astra and confirm those results with measurements. Simulations were then validated with beam measurements. The measurements and simulations agreed well at low current. However, at high current halo was introduced. Halo is unwanted electrons caused by illuminated parts in the photocathode from the multiple reflections of the laser beam. Simulations were then run to determine at which cathode radius the halo would become a problem.