Commissioning of the SLAC Linac Coherent Light Source II electron source

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 high repetition rate to drive x-ray free lasers. The LCLS-II source, which comprises first three meters of injector, includes two normal-conducting, continuous-wave cavities: one-cell, 185.7 MHz gun and two-cell, buncher. It also load-lock system allows photocathodes be changed under vacuum. components in this beam-line section were designed built by Lawrence Berkeley National Laboratory based on experience from their advanced photoinjector experiment program. In combination with SLAC UV laser system, source produce beam rates up 1 average currents $30\text{ }\text{ }\ensuremath{\mu}\mathrm{A}$ initially. was installed mid-2018, well advance SRF linac, now nearing completion. commissioned over two-year period, paper presents results including dark current characterization.