Conduction cooling paves the way toward compact SRF-based electron-ion accelerators

Abstract

This is a viewpoint on the letter by Ciovati et al (2020 Supercond. Sci. Technol. 33 07LT01).The development of the conduction-cooled superconducting radio frequency (SRF) cavity is a big step towards industrial/commercial applications of SRF accelerator technology. In this paper, Ciovati et al [1], demonstrate a reasonably high-quality factor (Q 0 ) of 5 × 10 8 at 4.5 MV m −1 , 4.3-7.0 K in an Nb 3 Sn on Nb 1.5 GHz cavity. The cavity performed at the above Q 0 with no performance degradation for at least 1 h run without any thermal instability in continuous wave (CW) operation with total 5 W rf power. Together with the advancement of RF couplers, cryo-cooler capacity for 4 K service, and development of high-performance Nb 3 Sn coatings, the possibility of a conduction-cooled cavity or variations thereof can pave the way forward for commercial accelerator applications in the future.SRF Nb (T c ∼ 9.2 K) technology has been an essential driver for the production of high-quality beams for high energy physics experiments and light sources for the past 30 years [2,3]. The current Nb technology can deliver very high E acc (>30 MV m −1 ) with a high-quality factor >10 10 [4-7]. For CW applications, the minimization of the overall AC plug power limits the optimal gradient to <25 MV m −1 [8,9]. High energy accelerators SRF Nb accelerators like the ones proposed International Linear Collider can be operated in pulse mode using Nb cavities, providing an accelerating gradient above 25 MV m −1 . However, Nb cavities delivering high beam energies operating ∼2.0 K required a large capacity on-site He cryogenic plant for reliable operation. Lower beam energy applications could work economically with SRF cavities coupled with cryo-coolers up to 10 W capacity for 4.2 K operation, opening up the application landscape beyond fundamental physics research or light sources.Current high gradient (>20 MV m −1 ) and high Q 0 (>10 10 ) SRF-based linear accelerators can provide electron beams with energies beyond 10 MeV, beam power in the range of several tens of kilowatts within an accelerating length much less than a meter [10]. The compactness of the system makes them attractive since it reduces infrastructure costs and makes them appealing for applications such as isotope production, chemical management, national security, and defense. A lower electron beam energy range of 1-10 MeV is of interest for industries involving polymerization and applications such as waste management that need to reduce half-lives of long decay time toxic chemicals. A cryo-cooler which couples the cooling power to a compact accelerator provides a standalone unit with greater mobility and would thus further the application of SRF technology. High E acc and Q 0 of accelerators are important for compactness, increased efficiencies, and cost of the system.Development in Nb 3 Sn (T c ∼ 18 K) coatings for SRF cavities provides a viable technology path for cryo-cooler-based systems operating at temperatures in the vicinity of 4.2 K, as demonstrated by Ciovati et al ...