Proof-of-principle demonstration of Nb3Sn superconducting radiofrequency cavities for high Q applications

Abstract

Many future particle accelerators require hundreds of superconducting radiofrequency (SRF) cavities operating with high duty factor. The large dynamic heat load of the cavities causes the cryogenic plant to make up a significant part of the overall cost of the facility. This contribution can be reduced by replacing standard niobium cavities with ones coated with a low-dissipation superconductor such as Nb3Sn. In this paper, we present results for single cell cavities coated with Nb3Sn at Cornell. Five coatings were carried out, showing that at 4.2 K, high Q0 out to medium fields was reproducible, resulting in an average quench field of 14 MV/m and an average 4.2 K Q0 at quench of 8 × 109. In each case, the peak surface magnetic field at quench was well above Hc1, showing that it is not a limiting field in these cavities. The coating with the best performance had a quench field of 17 MV/m, exceeding gradient requirements for state-of-the-art high duty factor SRF accelerators. It is also shown that—taking into account the thermodynamic efficiency of the cryogenic plant—the 4.2 K Q0 values obtained meet the AC power consumption requirements of state-of-the-art high duty factor accelerators, making this a proof-of-principle demonstration for Nb3Sn cavities in future applications.

Performance-defining properties of Nb3Sn coating in SRF cavities

“…While construction of Fermilab's Nb 3 Sn coating facility was in progress [10], we initiated extended characterization of the first Nb 3 Sn coated cavity (ERL1-5) from Cornell University. Though subsequent cavities coated at Cornell showed much higher quality factors [11], this 1.3G Hz single cell Nb 3 Sn coated cavity exhibited a fairly poor (for Nb 3 Sn) low-field Q 0 on the order of 10 9 at 4.2 K as well as Q-slope reminiscent of that observed previously at U Wuppertal (Wupp. Cav 2) [6], as shown in figure 1.…”

“…A physical vapor deposition apparatus constructed at Cornell University for the production of Nb 3 Sn coatings on Nb cavities [4,5] has produced 1.3 GHz 1-cell cavities that do not exhibit the strong Q-slope degradation-i.e. increase in surface resistance with accelerating gradient-that had been observed previously, notably in experiments at U Wuppertal [6].…”

Theoretical estimates of maximum fields in superconducting resonant radio frequency cavities: stability theory, disorder, and laminates

“…Will the new, more complex materials be fundamentally more challenging to optimize? Our preliminary experimental cavities using Nb 3 Sn appear already to be operating above H c1 [64], but are not yet delivering anywhere near to the theoretically predicted superheating field. Just as we have been exploring the fundamental theoretical limits to the fields for ideal surfaces, in this section we explore the fundamental theoretical challenges in minimizing the effects of dirt, flaws, and defects in lowering the barriers to vortex entry.…”

Radio Frequency Magnetic Field Limits of Nb andNb3Sn

“…The Nb 3 Sn preparation procedure carried out at Cornell was recently shown to avoid a strong dissipation mechanism observed in previous experiments (see Refs. [29][30][31] for additional details of Cornell's Nb 3 Sn fabrication process and results).…”