LCLS-II “High Energy” upgrade
LCLS-II-HE is an upgrade to the LCLS-II superconducting X-ray free-electron laser. The upgrade includes the addition of 23, 1.3 gigahertz cryomodules jointly built by Fermilab and Jefferson Lab, each housing eight 1.3 gigahertz nine-cell SRF cavities. The cryomodule design remains nearly unchanged from the original LCLS-II superconducting linac. However, there is a significant change in cavity performance specifications.
Motivated by limitations in available tunnel length, the average accelerating gradient is increased from 116 megavolts per meter in LCLS-II to 20.8 megavolts per meter in LCLS-II-HE, for a total module voltage of 173 megavolts. Like the original LCLS-II cryomodules, the LCLS-II-HE cryomodules will operate in continuous wave mode, making high Q0, or intrinsic quality factor, performance essential to keep the cryogenic heat load manageable. This upgrade will significantly boost the accelerator’s performance, enabling new scientific discoveries in materials science, chemistry and biology.
Fermilab’s scope of work for LCLS-II-HE
As part of the LCLS-II-HE effort, Fermilab is:
- Leveraging its High Gradient (High Q₀) R&D Program, the breakthrough nitrogen-doping technology to enhance the quality factor of SRF cavities, reducing both cryogenic infrastructure and operating costs. In collaboration with Jefferson Lab and SLAC, Fermilab co-developed a new cavity processing protocol and successfully transferred the technology to industry.
- Designing, fabricating, testing and delivering 14 high-performance cryomodules, each operating at 1.3 gigahertz.
- Sharing component procurement responsibilities with Jefferson Lab.
- Leading the mechanical and cryogenic design of specialized cryomodules, such as the Buncher Capture Cavity.
- Supporting SLAC in designing and procuring assistance for the cryogenic distribution system and cryomodule interconnect components.
- Providing installation and commissioning support at SLAC.
Progress and achievements
Fermilab successfully completed its work for the original LCLS-II project and delivered the final LCLS-II cryomodule to SLAC in March 2021. The experience gained during LCLS-II provided valuable lessons in SRF cryomodule production and quality assurance, laying a solid foundation for the LCLS-II-HE effort.
Since then, Fermilab has delivered most of the LCLS-II-HE cryomodules to SLAC, demonstrating effective collaboration both internally and externally. The work at Fermilab has produced exceptional results, demonstrating its ability to produce cryomodules with world-record performance that meet both schedule and budget requirements.
