Undergraduate Research at Jefferson Lab

Beam Emittance Characterization of the 180 kV Gun for CEBAF

Student: Tariq Kerr

School: Christopher Newport University

Mentored By: Alicia Hofler

The injector of the Jefferson Lab Continuous Electron Beam Accelerator Facility (CEBAF) provides the optimal emittance for running experiments in any of the four halls on the site. A recent upgrade to the injector increased its full energy to 123 MeV, as part of the CEBAF energy upgrade to 12 GeV, which expanded the volume of experiments scientists could run. The focus of this experiment is to test if at a higher gun operating voltage the emittance will be better preserved since space charge effects and the initial ratio between transverse and longitudinal momentum should be reduced. Space charge effects cause the particles to spread away from each other which can increase the emittance. Through the use of two software analyzing tools, qsUtility and the General Particle Tracer (GPT), we were able to measure and simulate the evolution of the beam characteristics for each running condition (spot size on cathode and operating voltage charge). The gun was operated at two operating voltages (130 kV and 180 kV), and combined with the Expando lens, we measured the emittance under the four conditions of gun operating voltage setting and Expando lens inclusion.