LCLS-II prototype cryomodule: a success story

Rich Stanek

A project is like a good book: As you complete one chapter you start the next, but sometimes you cannot wait and you read ahead.

The LCLS-II project, a next-generation X-ray light source being built at SLAC, one that is based on a superconducting RF electron linac operating in continuous-wave mode, has completed Chapter One – the prototype cryomodule (pCM). And now we are already well into the assembly of the second, third and fourth cryomodules.

As one of the partner labs, Fermilab is responsible for the design of LCLS-II’s 1.3-gigahertz cryomodules, as well as assembly and testing for 19 of them. (LCLS-II will have a total of 40 of these cryomodules, and Jefferson Lab is assembling the rest.) Additionally, Fermilab is designing and will assemble and test three 3.9-gigahertz cryomodules and has responsibility for the procurement of the cryogenic distribution system for the LCLS-II linear accelerator.

The pCM assembly and testing have been very successful, due in large part to the technical skills and dedication to quality of our entire team. Still, it was a learning experience, which has made our SRF and cryogenic organizations in the Accelerator and Technical divisions stronger and more tightly connected.

More than 150 people at Fermilab have contributed to the design and assembly of the prototype cryomodule for LCLS-II. Photo: Reidar Hahn

The pCM met most of its acceptance criteria, to the point where it could be used in the LCLS-II linac. The majority of the design has been verified; the energy gain exceeds the specification; the average quality factor exceeds the goal and sets a new world record (3.0 x 1010); the superconducting magnet meets specification; the new tuner design was verified; the modified fundamental power coupler (in continuous-wave operation) was shown to meet specification; instrumentation and controls worked as planned; and the implementation of magnetic hygiene (first time in a cryomodule) was very successful.

The one issue that remains is to reduce the microphonics levels so as to allow better amplitude and phase control of the cryomodule’s eight accelerating cavities, which must operate in unison.

I must stress again how this success was driven by our team effort. Particularly evident in the pCM testing was the ability of the Technical and Accelerator division personnel to work together to accomplish the task at hand.

The challenge to design, build and test the prototype CM drew on the work of a wide range of team members across many organizations. From beginning to end, the team functioned well. Contributions were made by staff responsible for design, procurement, part inspection, component handling and transportation, cavity testing and qualification, machining and welding, string assembly, cryomodule assembly, leak checking, installation, RF power and controls, cryogenics, and testing.

In all, more than 150 individuals at Fermilab are contributing to the LCLS-II effort, and each has reason to be proud of their work. I am very fortunate to be able to lead this team, and I’m thankful for their dedication and strong efforts.

Just as with a good book, once you start reading you cannot put it down; the better the book, the more motivated you are to complete reading it. So it is with this project as we are now into the execution phase. We have gotten a taste of our first success and look forward to the next chapters of the story and to completing our work.

Rich Stanek is the Fermilab LCLS-II senior team leader.