Schottky-Enabled Photoemission and Dark Current Measurements-Toward an Alternate Approach to Fowler-Nordheim Plot Analysis

Field-emitted dark current, a major gradient-limiting factor in RF cavities, is usually analyzed via FowlerNordheim (FN) plots. Traditionally, field emission is attributed to geometrical perturbations on the bulk surface whosefield enhancement factor (beta) and the emitting area (A) can be extracted from the FN plot. Field enhancement factors extracted in this way are typically much too high (1-2 orders of magnitude) to be explainable by either the geometric projection model applied to the measured surface roughness or by field enhancement factors extracted from Schottky-enabled photoemission measurements. We compare traditional analysis of FN plots to an alternate approach employing local work function variation. This is illustrated by comparative analysis of recent dark current and Schottky-enabled photoemission data taken at Tsinghua Sband RF gun.