Experimental study of energy spread in a space-charge dominated electron beam

Characterization of beam energy spread in a space-charge dominated beam is very important to understand the physics of intense beams. It is believed that coupling between transverse and longitudinal direction via Coulomb collisions will cause an increase of the beam longitudinal energy spread. At the University of Maryland, experiments have been carried out to study the energy evolution in such intense beams. To measure the energy spread, a high-resolution retarding field energy analyzer has been developed. In this paper, we present the initial experimental results using this energy analyzer. The temporal beam energy profile along the beam pulse has been characterized at the exit of the electron gun. It is the first time that we measure the energy profile of the head and tail of the bunched beams in the experiment. The measured mean energy variation along the beam pulse is in excellent agreement with direct measurement of the cathode-grid pulse waveform. The measured rms energy spread is very close to the theoretical prediction of Coulomb scattering