Abstract
For the Linac Coherent Light Source II (LCLS-II) project at SLAC, a 1.3 GHz superconducting rf (SRF) linac is being constructed that will generate 4 GeV electron bunches at a high repetition rate to drive x-ray free electron lasers. The LCLS-II electron source, which comprises the first three meters of the electron injector, includes two normal-conducting, continuous-wave rf cavities: a one-cell, 185.7 MHz gun and a two-cell, 1.3 GHz buncher. It also includes a gun load-lock system that allows photocathodes to be changed under vacuum. The components in this beam-line section were designed and built by Lawrence Berkeley National Laboratory based on experience from their advanced photoinjector experiment program. In combination with the SLAC UV laser system, the electron source is designed to produce beam rates up to 1 MHz with average currents up to $30\text{ }\text{ }\ensuremath{\mu}\mathrm{A}$ initially. The source was installed in mid-2018, well in advance of the SRF linac, which is now nearing completion. The source was commissioned over a two-year period, and this paper presents results including electron beam and dark current characterization.
Highlights
X-ray free electron lasers [1,2,3,4] have proven to be a revolutionary tool for photon science studies
The 12 nonevaporable getters (NEGs) were eventually identified as the source of the contamination, as it was later found they had been processed in an oil-contaminated chamber during assembly
The gun vacuum pressure level has been as low as 3 × 10−11 Torr
Summary
X-ray free electron lasers [1,2,3,4] have proven to be a revolutionary tool for photon science studies. The SLAC National Accelerator Laboratory (SLAC) Linac Coherent Light Source II (LCLS-II) project [5], which is nearing completion, represents a major advance in that it will provide up to 1 MHz bunch repetition rates, a substantial increase from the 120 Hz rate in the existing LCLS facility. This higher rate will allow experiments that require a large number of photon pulse interactions to resolve molecular structure or ultrafast molecular phenomena. The SSA can still provide >50 kW of power
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