title: Surface-emission studies in a high-field RF gun based on measurements of field emission and Schottky-enabled photoemission.
abstract: We report on investigations into the fundamental surface emission parameters, the geometric field enhancement factor (β) and the work function (φ), by making both field emission and Schottky-enabled photoemission measurements. The measurements were performed on a copper surface in the Tsinghua University S-band RF gun in two separate experiments. Fitting our data to the models for each experiment indicate that the traditionally assumed high value of β(≈50-500) does not provide a plausible explanation of the data, but incorporating a low value of φ at some sites does. In addition, direct measurements of the surface conducted after the experiment show that β is on the order of a few, consistent with our understanding of the electron emission measurements. Thus we conclude that the dominant source of electron emission in high gradient RF cavities is due to low φ sites, as opposed to the conventionally assumed high β sites. The origin of low φ at these sites is unclear and should be the subject of further investigation.
authors.affiliation: Department of Engineering Physics, Tsinghua University, Beijing 100084, China.
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Du
authors.forename: W
authors.initials: W
authors.lastname: Gai
authors.forename: A
authors.initials: A
authors.lastname: Grudiev
authors.forename: J
authors.initials: J
authors.lastname: Hua
authors.forename: W
authors.initials: W
authors.lastname: Huang
authors.forename: J G
authors.initials: JG
authors.lastname: Power
authors.forename: E E
authors.initials: EE
authors.lastname: Wisniewski
authors.forename: W
authors.initials: W
authors.lastname: Wuensch
authors.forename: C
authors.initials: C
authors.lastname: Tang
authors.forename: L
authors.initials: L
authors.lastname: Yan
authors.forename: Y
authors.initials: Y
authors.lastname: You