Superconducting radio-frequency cavities made from medium and low-purity niobium ingots

Abstract

Superconducting radio-frequency cavities made of ingot niobium with residual resistivity ratio (RRR) greater than 250 have proven to have similar or better performance than fine-grain Nb cavities of the same purity, after standard processing. The high purity requirement contributes to the high cost of the material. As superconducting accelerators operating in continuous-wave typically require cavities to operate at moderate accelerating gradients, using lower purity material could be advantageous not only to reduce cost but also to achieve higher Q 0 -values. In this contribution we present the results from cryogenic RF tests of 1.3-1.5 GHz single-cell cavities made of ingot Nb of medium (RRR=100-150) and low (RRR=60) purity from different suppliers. Cavities made of medium-purity ingots routinely achieved peak surface magnetic field values greater than 70 mT with an average Q 0 -value of 2×10 10 at 2 K after standard processing treatments. The performances of cavities made of low-purity ingots were affected by significant pitting of the surface after chemical etching.

Field-dependent nonlinear surface resistance and its optimization by surface nanostructuring in superconductors

“…For Nb with T c = 9.2 K, ∆ = 1.9T c , τ 1 = 3·10 −12 s, and τ 2 = 8·10 −11 s 68 , Eq. (19) gives τ r ∼ 4 · 10 −8 s and τ s ≃ 2 · 10 −8 s at T = 2 K. As T increases to 4K, the time constants τ r ≃ 4 · 10 −10 s and τ s ≃ 2 · 10 −9 s diminish but remain much longer than the relaxation time constant of the superconducting condensate,h/∆ ∼ 10 −12 s. At T ≪ T c and ω ≪ ∆/h an exponentially small density of quasiparticles has practically no effect on the dynamics of the condensate which reacts nearly instantaneously to the timedependent currents. As a result, the spectral function M in Eq.…”

Secondary ion mass spectrometry for superconducting radiofrequency cavity materials

“…[1,2,3,4,5] However, extensive evidence from cavity processing and testing indicates that introduction of small amounts of nitrogen and perhaps other interstitials can markedly improve energy efficiency, as characterized by quality factor Q 0 . [6,7,8,9,10] Difficulties encountered in current efforts to implement doping technology for the Linac Coherent Light Source II (LCLS II) suggest that deeper understanding is needed. [11,12] Another potential path to improvement is the creation of a micron-thick layer of Nb 3 Sn on the cavity interior surface.…”

Engineering Topological Many-Body Materials in Microwave Cavity Arrays

“…Resonator linewidths of κ ∼ 20 Hz for superconducting coaxial resonators [21] have been achieved in zero field. Realizing such small linewidths in a magnetic field may be challenging, but recent works have achieved Q ∼ 10 9 in microwave cavities with rf field strengths just below H c1 [51]. Since significant timereversal breaking can be achieved at fields below H c1 , linewidths in the range of κ ∼ 10-100 kHz should be achievable for our system.…”