Undesirable electron field emission (a.k.a. dark current) in high gradient RFphotocathode guns deteriorates the quality of photoemission current and limitsthe operational gradient. To improve the understanding of dark currentemission, a high-resolution (~100 um) dark current imaging experiment has beenperformed in an L-band photocathode gun operating at ~100 MV/m of surfacegradient. Dark current from the cathode has been observed to be dominated byseveral separated strong emitters. The field enhancement factor, beta, ofselected regions on the cathode has been measured. The post scanning electronmicroscopy (SEM) and white light interferometer (WLI) surface examinationsreveal the origins of ~75% strong emitters overlap with the spots where rfbreakdown have occurred.
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