Physics Open (Dec 2020)
Nitrogen doping and infusion in SRF cavities: A review
Abstract
Advances in SRF technology over the last 40 years allowed achieving accelerating gradients ~50 MV/m corresponding to peak surface magnetic fields close to the theoretical limit of niobium. However, the quality factor decreases significantly with increasing accelerating gradient. This decrease is expected since increasing the rf field increases the number of quasiparticles and therefore the rf losses. Recently, a new phenomenon of increase in quality factor with an accelerating gradient has been observed when SRF cavities are doped with certain non-magnetic impurities. In particular, the diffusion of nitrogen into the niobium cavities’ inner surface has been successfully implemented into the commercialization of SRF technology. The quest is still ongoing towards process development to achieve high accelerating gradient SRF structures with high-quality factors for future high energy accelerators. Here, we present the review of the research on process development to this date via nitrogen diffusion, material analysis, and present the summary of current theoretical understanding behind high Q0 SRF cavities.
