Speaker
Description
Dark current has presented operational challenges at LCLS-II due to its deleterious effects on diagnostics, heating of collimators, and other undesirable impacts. Until recently, it was necessary to use a 20 mm-diameter collimator and a non-optimal tuning of the first solenoid to mitigate the issues caused by dark current. However, recent changes to the cathode plug design have reduced the dark current to a much more tolerable level, with some designs yielding a reduction by three orders of magnitude. In this contribution, we present various modifications of the cathode plug shape and insertion depth. We then discuss the results of our measurements of the resulting dark current magnitudes and distributions, as well as what that implies for both the distribution of the emission sites and the resulting downstream dark current orbits.
Funding Agency
Work supported by the U.S. Department of Energy under Contract No. DE-AC02-76SF00515.
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