Investigations of surface quality and SRF cavity performance

Improvement of the first flux entry field by laser post-treatment of the thin Nb film on Cu

“…The results show that the first flux entry field was mostly influenced by the localized enhanced magnetic field created by the many sources such as grain boundaries [46], pits [47], microparticles [3], microscopic surface roughness [16] or crystalline defects [17]. As the laser irradiation led to compactness/ uniformity of the grains at the surfaces (figure 4), the enhancement of the localized magnetic field at a grain boundaries became lowered [46].…”

“…It is well known that the surface of the superconductor provides a barrier against the field penetration [11,12] and therefore the surface quality of the inner wall of the cavity has a significant impact on its performance [13,14]. Defects such as microscopic roughness and pitting occurring on the cavity surface can cause enhancement of the local magnetic field and premature flux penetration [15][16][17]. The improvement of the Nb surface can be achieved by mitigation of the surface defects [18] with a small, disordered Nb grains, and slightly strained lattice parameters [19].…”

Proposal: Apparatus for Sensing the Effect of Surface Roughness on the Surface Resistance of Metals

“…To mention a few examples, the performance of electrochemical electrodes, which is in fact directly dependent on their roughness coefficient [ 1 , 2 , 3 ], the quality of the contact between two conductors, or the failing of copper wires under long-term mechanical stress [ 4 , 5 ]. Particular attention has been devoted to treatments to reduce the roughness of the conducting surface of accelerating cavities to minimize the residual resistance at radio and microwave frequencies [ 6 , 7 ]. This widespread interest in the effects of surface roughness on various physical properties stimulated the development of several methods to evaluate the surface roughness, either in contact or contactless setups [ 8 ].…”