Cooldown of Cryomodule 2 marks major achievement in Fermilab SRF program

Cryomodule 2 was successfully cooled to 2 Kelvin on Nov. 12. Photo: Reidar Hahn

On Tuesday, Nov. 12, the Accelerator Division successfully cooled down Cryomodule 2, the first ILC-type cryomodule in which all component cavities were processed and tested in the United States, to a temperature of 2 Kelvin.

The cooldown is a major step in the laboratory’s program on superconducting radio-frequency technology, known as SRF. Nearly all proposed large-scale particle accelerators are based on SRF, and the technology has promising applications in industry, medicine and other fields of science.

Now that CM2 is ultracold, the Accelerator Division SRF team at Fermilab can power it up and begin testing. Once testing is complete, CM2 will form an important element of Fermilab’s proposed Advanced Superconducting Test Accelerator and could be the technology of choice for upgrades to the Fermilab accelerator complex.

CM2 contains eight so-called cavities, which look like giant metal strings of pearls, through which the particle beam travels. The higher the cavity’s gradient, the more energy the particle beam gains in a given distance. The Technical Division SRF team contributed a great deal to cavity R&D, processing and testing cavities as well as assembling the cryomodule.

CM2 is the first cryomodule built in the United States to achieve the ambitious operating gradients required by the proposed International Linear Collider, which Japan might build. The ILC gradient goal, 31.5 megavolts per meter on average, pushes the current state of the art in SRF technology. Each of CM2’s eight cavities has exceeded that goal in tests of both bare and fully dressed cavities. The goal of the CM2 test is to validate that the high gradient can be maintained once the cavities are fully integrated into a cryomodule.

This latest CM2 milestone is the culmination of months of effort by the entire SRF team at Fermilab. Numerous individuals and groups were involved in the cryomodule’s assembly, transport, installation and cooldown, as well as its many associated subsystems.

“This was a significant effort that required great attention to detail and close collaboration among many groups within the lab, as well as from our collaborating partners at other laboratories,” said NML Project Engineer Jerry Leibfritz. “The safe and successful execution of this work is a testament to the dedication of all those involved.”

Over the next several weeks, the SRF team will carry out cavity conditioning and characterization to prepare for the full-power testing of CM2.