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The LCLS-II injector source includes a 186MHz CW rf-gun, a 1.3 GHz CW rf-buncher, a loadlock system for photocathode change, two main solenoids, and a few essential diagnostics. The electron beam is designed to operate at a high repetition rate, up to 1-MHz. Since summer of 2018 we started LCLS-II injector source commissioning immediately after the major installation was completed. Initial commissioning showed the rf-gun was severely contaminated with hydrocarbons and very limited power 600W could be fed into the gun cavity. After a few significant processes, we eventually removed the hydrocarbons and successfully delivered desired rf power of 80 kW to the gun. This paper reports first com-missioning results including gun bakeout and vacuum processing, CW RF-gun and buncher operation with nom-inal power, and measurements of rf stability and dark current., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Accelerator operation history data are used to train neural networks in an attempt to understand the underly-ing causes of performance drifts. In the study, injection efficiency of SPEAR3 [1] over two runs is modelled with a neural network (NN) to map the relationship of the injection efficiency with the injected beam trajectory and environment variables. The NN model can accurately predict the injection performance for the test data. With the model, we discovered that an environment parameter, the ground temperature, has a big impact to the injection performance. The ideal trajectory as a function of the ground temperature can be extracted from the model. The method has the potential for even larger scale application for the discovery of deep connections between machine performance and environment parameters., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

The Early Injector Commissioning program for LCLS-II aims to demonstrate CW electron beam production this year in the first two meters of the injector that includes the room-temperature 185.7 MHz single-cell gun and the 1.3 GHz two-cell buncher cavity. These cavities were designed and built by LBNL based on their experience with similar ones for their Advanced Photo-Injector Experiment (APEX) program. With the 258 nm laser system and Cs2Te cathodes, bunches of up to 300 pC are expected at rates as high as 1 MHz. The paper presents results from this program including the vacuum levels achieved, RF processing and field control experience, dark current measurements and laser and beam characterization., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The first in situ high resolution field emission (FE) imaging experiment has been carried out on an L-band photocathode gun test stand at Argonne Wakefield Accelerator facility (AWA). Separated strong emitters have been observed to dominate the field emission. Field enhancement factor, beta, of small regions on the cathode has been measured with the imaging system. It is shown that most strong emitters overlaps with the high beta regions. The post surface examinations reveal the origins of ~75% strong emitters overlap with the spots where rf breakdown have occurred. Detailed results are presented in this paper., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

Building more compact accelerators to deliver high brightness electron beams for the generation of high flux, highly coherent radiation is a priority for the photon science community. A relatively straightforward reduction in footprint can be achieved by using high-gradient X-Band (11.4 GHz) RF technology. This talk presents the all X-band photo-injector facility at SLAC, covering the benefits of using this technology and highlighting the performance achieved., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

Precisely locating field emission (FE) emitters on a realistic surface in rf structures is technically chal-lenging in general due to the wide emitting phase and the broad energy spread. A method to achieve in situ high resolution FE imaging has been proposed by using solenoids and a collimator to select electrons emitted at certain phases. The phase selection criterion and imaging properties have been studied by the beam dynamics code ASTRA. Detailed results are presented in this paper., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

The localized high electric field enhancement or low work function is the trigger for strong field emission, which however has yet been well experimentally studied. Using an L-band photocathode gun test stand at Argonne Wakefield Accelerator Facility (AWA), we’ve constructed an imaging beam line to observe field emission current from predefined emitters on cathode. Preliminary experiment results are present. Future plan is discussed., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

A pin cathode has been installed into an L-band photocathode gun to study the influence of stored energy on field emission. The stored energy was varied by tuning the recess of the cathode in order to have the same E-field on the cathode tip. We have observed 5 times difference of dark current level at the same E-field, while by varying the stored energy by three fold. Dynamics study reveals the difference is not caused by transmission, but by emission process itself. We'll present experiment results and discuss possible mechanisms about the phenomena., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

The LCLS-II 4 GeV SC electron linac will use 280 TESLA cavities and TTF3 couplers, modified for CW operation with input power up to about 7 kW. The coupler modifications include shortening the antenna to achieve higher Qext and thickening the copper plating on the warm section inner conductor to lower the peak temperature. Another change is the use a waveguide transition box that is machined out of a solid piece of aluminum, significantly reducing its cost and improving its fit to the warm coupler window section. This paper describes the changes, simulations of the coupler operation (heat loads and temperatures), rf processing results and CW tests with LCLS-II dressed cavities., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada