Superconducting Radiofrequency Technology for Accelerators

3 Nitrogen-Doping

3.1 Introduction

Nitrogen doping (N-doping) has been a surprising and exciting discovery, followed by substantial developments and applications. The phenomenon was discovered by Grassellino in 2012 at Fermilab [99]. N-doping is a surface treatment for niobium cavities to absorb nitrogen atoms as interstitial impurities into the niobium lattice. This treatment gives rise to an unexpected field-dependent Q increase at medium fields (15–25 MV/m, 60–100 mT), known as the “anti-Q-slope” or “positive Q-slope.” The surprising aspect of the discovery is that standard cavity treatments normally show Q decreases with increasing field called the medium field Q-slope (MFQS). Interstitial N lowers the mean free path of the RF penetration ...