Multi-metallic conduction cooled superconducting radio-frequency cavity with high thermal stability

Abstract

Superconducting radio-frequency cavities are commonly used in modern particle accelerators for applied and fundamental research. Such cavities are typically made of high-purity, bulk Nb and are cooled by a liquid helium bath at a temperature of ∼ 2 K. The size, cost and complexity of operating a particle accelerator with a liquid helium refrigerator makes the current cavity technology not favorable for use in industrial-type accelerators. We developed a multi-metallic 1.495 GHz elliptical cavity conductively cooled by a cryocooler. The cavity has a ∼ 2 µm thick layer of Nb3Sn on the inner surface, exposed to the rf field, deposited on a ∼ 3 mm thick bulk Nb shell and a bulk Cu shell, of thickness 5 mm deposited on the outer surface by electroplating. A bolt-on Cu plate 1.27 cm thick was used to thermally connect the cavity equator to the second stage of a Gifford-McMahon cryocooler with a nominal capacity of 2 W at 4.2 K. The cavity was tested initially in liquid helium at 4.3 K and reached a peak surface magnetic field of ∼ 36 mT with a quality factor of 2 × 10 9 . The cavity cooled by the crycooler achieved a peak surface magnetic field of ∼ 29 mT, equivalent to an accelerating gradient of 6.5 MV/m, and it was able to operate in continuous-wave with as high as 5 W dissipation in the cavity for 1 h without any thermal breakdown. This result represents a paradigm shift in the technology of superconducting accelerator cavities.

Next-Generation Superconducting RF Technology based on Advanced Thin Film Technologies and Innovative Materials for Accelerator Enhanced Performance and Energy Reach

“…First proof-of-principle experiments have demonstrated successful operation of Nb 3 Sn coated cavities cooled with commercial, off-the-shelf cryocoolers, paving the way for completely cryogenfree operation for SRF based accelerator technology for applications beyond science [32,33,38]. The emergence of reliable, energy efficient high Q systems, based on highly performing filmbased SRF cavities along with transformative development with cryocoolers would combine into cost effective compact superconducting accelerators with reduced footprint and capital investment, transformational for societal applications.…”

Soft Superconductors: Materials and Applications

“…Thin film production techniques are applicable for superconductor materials. Magnetron sputtering [75], Radio-Frequency sputtering [73], photolithography [70], electron beam evaporation [75], cold spray [76], vacuum plasma spraying [77] are some of the techniques which are used in superconductor thin film claddings. Techniques for thin film production may be adapted to produce superconducting films.…”

A White Paper on Design and Fabrication of SRF Deflecting Cavities for Elletra-2

“…In this case, instead of a LHe vessel, a conductive cooling system should be designed. Similar cooling schemes have recently been developed and successfully tested for single-cell cavities at Fermilab, Cornell, and JLab [17][18][19]. Figure 16 shows conductive cooling straps mounted on a 2.6-GHz cavity at Cornell.…”