title: In Situ Observation of Dark Current Emission in a High Gradient rf Photocathode Gun.
abstract: Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (∼100  μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ∼100  MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. The postexaminations with scanning electron microscopy and white light interferometry reveal the origins of ∼75% strong emission areas overlap with the spots where rf breakdown has occurred.
authors: Department of Engineering Physics, Tsinghua University Beijing 100084, P.R. China.|Argonne National Laboratory, Lemont, Illinois 60439, USA.
authors: Jiahang
authors: J
authors: Shao
authors: Department of Engineering Physics, Tsinghua University Beijing 100084, P.R. China.
authors: Jiaru
authors: J
authors: Shi
authors: Argonne National Laboratory, Lemont, Illinois 60439, USA.|Euclid Techlabs LLC, Bolingbrook, Illinois 60440, USA.
authors: Sergey P
authors: SP
authors: Antipov
authors: Argonne National Laboratory, Lemont, Illinois 60439, USA.|Euclid Techlabs LLC, Bolingbrook, Illinois 60440, USA.
authors: Sergey V
authors: SV
authors: Baryshev
authors: Department of Engineering Physics, Tsinghua University Beijing 100084, P.R. China.
authors: Huaibi
authors: H
authors: Chen
authors: Argonne National Laboratory, Lemont, Illinois 60439, USA.
authors: Manoel
authors: M
authors: Conde
authors: Argonne National Laboratory, Lemont, Illinois 60439, USA.
authors: Wei
authors: W
authors: Gai
authors: Argonne National Laboratory, Lemont, Illinois 60439, USA.
authors: Gwanghui
authors: G
authors: Ha
authors: Argonne National Laboratory, Lemont, Illinois 60439, USA.|Euclid Techlabs LLC, Bolingbrook, Illinois 60440, USA.
authors: Chunguang
authors: C
authors: Jing
authors: SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors: Faya
authors: F
authors: Wang
authors: Argonne National Laboratory, Lemont, Illinois 60439, USA.
authors: Eric
authors: E
authors: Wisniewski