TUIXA01
JLab, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
SRF cavities subjected to heat treatment below 200 °C in the presence of nitrogen showed an improvement in quality factor while maintaining an accelerating gradient above 25 MV/m. Here, we report the rf performance of several single-cell superconducting radio frequency cavities with frequency ranging from 0.75 - 3.0 GHz subjected to low temperature heat treatment in nitrogen environment. The cavities were treated at temperature 120 - 175 oC for 24 - 48 hours in low partial pressure of ultra-pure nitrogen gas. The improvement in Q₀ with Q-rise was observed when nitrogen gas was injected ~300 °C during the furnace treatment. The surface modification was confirmed by the change in electronic mean free path and near surface elemental analysis by SIMS. The field dependence of the rf losses is strongly correlated to the cavity frequency. The analysis of experimental data with available theoretical models as well as comparison with similar study on high temperature nitrogen doped cavities will be presented.
TUIXA02
Fermilab, Batavia, Illinois, USA
Bulk niobium SRF cavities remain as a leading technology in the realization of the next generation of particle accelerators and serve as the highest Q₀ platform for 3-D quantum computing architectures. Whether utilized in kilometer long accelerators or 10 cm long quantum processors, the performance of these cavities is largely determined by the material properties within the 100 nm from the inner RF surface. This talk will discuss advancements made in the development and understanding of surface engineering techniques (doping with O or N, N-infusion, and low/mid temperature baking) on niobium SRF cavities in different regimes: mK and single photon levels for quantum computing and high Q/high G accelerator applications. By coupling material science and resonator measurements, we delineate the role of different impurities in enabling excellent performance in each of these regimes.
TUIXA03
KEK, Ibaraki, Japan
UBC & TRIUMF, Vancouver, British Columbia, Canada
TRIUMF, Vancouver, Canada
UVIC, Victoria, Canada
TUIXA05
UVIC, Victoria, Canada
In SUST 30 (12), 125012, we reported that coating a superconductor with a larger penetration depth on niobium can increase the field of first vortex penetration Hvp from niobium¿s lower critical field Hc1 to its superheating field Hsh. This was interpreted as an energy barrier at the superconductor-superconductor interface, analogous to the Bean-Livingston barrier at vacuum-superconductor interfaces. A smaller but significant increase in Hvp was observed for low-temperature baked (LTB) niobium. Results from muon spin rotation with variable implantation depth in the micrometer range and vibrating sample magnetometry (Scientific Reports 12 (1), 5522) suggest that the apparent Hvp increase in LTB niobium was due to surface pinning and not an actual Hvp increase. Low-energy muon spin rotation results further support that interpretation as a distinct bipartite magnetic screening profile is observed for actual bilayers (arXiv:2304.09360) but not for LTB niobium (PR Applied 19 (4), 044018 and arXiv:2305.02129). This suggests that the reason why some LTB niobium SRF cavities reach surface magnetic fields beyond Hc1 is specific to RF effects, such as the nucleation time.