SRF Cavity Development for Lower Cost and Sustainable Accelerators*

Superconducting radio-frequency (SRF) cavities are building blocks of modern particle accelerators for fundamental research. They are typically made of high-purity bulk Nb, requiring cooling at around 2 K for efficiency. The size, cost and complexity of the associated sub-cooled LHe cryoplant has limited the application of SRF technology mostly to large machines. Beyond large scientific instruments, particle accelerators have many industrial and societal applications. Examples include environmental remediation (water, waste treatment), medical instrument sterilization, medical isotopes production, engineering of material and surfaces with altered properties radiation driven chemistry, food preservation... These applications need a new class of compact, high-power electron accelerators, with drastically reduced cryogenic requirements so they can be located on a mobile platform, in a university or hospital room.

Cryocoolers are reliable, compact, closed-cycle refrigerators, less expensive and easier to operate than liquid He ones. Recent technological advances have led to cryocoolers with increasing power capacity at 4.2 K. Recent strides in SRF technology have allowed drastic reduction of SRF losses at 2 and 4 K with developments of enhanced surface processing, materials and structures more efficient than bulk Nb combined with higher thermal conduction substrates. These improvements in efficiency have driven recent work on SRF cavities conduction cooled by a cryocooler, operational in continuous wave with low power dissipation and without thermal breakdown. Such successful developments can lead to a paradigm shift in superconducting accelerator technology.

On-going SRF cavity technology developments aiming at reducing the operation cost and increasing the efficiency and sustainability of particle accelerators for science and societal needs will be reviewed.