High gradient superconducting niobium cavities. A review of the present status

Abstract

Superconducting niobium cavities used in particle accelerators are limited in their rf performance by two phenomena: quench field levels below the theoretical limit of the material caused by defects, and field emission loading resulting from artificial contamination of the superconducting surfaces during surface treatment and assembly procedures. In recent years the community involved in SEW technology developments has successfully improved cavity performances by applying advanced surface treatment methods such as chemical polishing, electropolishing, tumbling, high temperature heat treatment, high pressure rinsing, "in situ" high peak power processing and clean room assembly procedures. In addition, improvements in the material properties such as thermal conductivity by "solid state gettering" and very strict QA methods, both in material inspection and during cavity fabrication, have resulted in cavity performance levels of E,,, up to 40 MV/m in monocells and gradients in the vicinity of 30 MV/m in multicell structures at Q-values of = 10" at a temperature of 2K.More recently the fabrication of "seamless" cavities by spinning is being pursued with encouraging results. This process eliminates electron beam welds, which sometimes are the causes of performance degradations.

Nb3Sn superconducting radiofrequency cavities: fabrication, results, properties, and prospects

“…Niobium has properties that make it extremely useful in superconducting radiofrequency (SRF) cavities, such that it is by far the material of choice for modern SRF accelerators [1][2][3][4][5][6][7]. Over years of development, researchers have pushed the performance of niobium cavities, overcoming a number of nonfundamental limitations-see overview of development in [8,9] and [10][11][12][13][14] for examples of mitigation: multipacting, field emission, high field Q-slope-and now cavities are being produced that reach close to the fundamental limits of this material. To continue to increase the reach of particle accelerators for frontier scientific research and to open new industrial applications for accelerators, researchers are examining the potential of alternatives to niobium with superior SRF properties.…”

Analysis of materials properties of niobium tube from the results of a virtual bulge test

“…Superconducting radio frequency (SRF) cavities of niobium (Nb) or Nb-plated Cu are beginning to replace normal-conducting cavities for accelerating either hadrons or leptons in high energy particle accelerators because of their advantages in terms of BCS surface resistance, residual surface resistance, peak surface field, field emission, thermal breakdown, and Q 0 degradation [1][2][3]. An increasing demand for electron and positron accelerators is calling for improvements in SRF cavity performance and fabrication techniques.…”