More and more particle accelerators are using Nb Superconducting Radio Frequency (SRF) technology due to the steady progress made during the last few decades in the SRF field. Improvement of the surface treatments of Nb SRF cavities is an indispensable part of the evolution of SRF technology. In this chapter, a study of the surface treatments of Nb flat samples and SRF single cell cavities via Gas Cluster Ion Beam (GCIB) technique will be reported. Beams of Ar, O2, N2, and NF3 clusters with accelerating voltages up to 35 kV were employed in the treatments. The treated surfaces of Nb flat samples were examined by a scanning field emission microscope, a scanning electron microscope equipped with an energy dispersive x-ray analyzer, a secondary ion mass spectrometry, an atomic force microscope, and a 3-D profilometer. The experiments revealed that GCIB technique could not only modify surface morphology of Nb, but also change the surface oxide layer structure of Nb and reduce the number of field emission sites on the surface dramatically. Computer simulation via atomistic molecular dynamics and a phenomenological surface dynamics was employed to help understand the experimental results. Due to its effectiveness at changing the depth and composition of the surface oxide layer structure of Nb, GCIB might be a key to understanding and overcoming the limitations of the high-field Q-slope. Based on the encouraging experimental results obtained from flat sample study, a novel setup was constructed to allow GCIB treatments on Nb single cell cavities. First results of RF tests on the GCIB treated Nb single cell cavities showed that the quality factor Q of the cavity could be improved substantially at 4.5 K and the superconducting gap value, extracted from RF measurements at different temperatures below superconducting transition temperature, was enhanced by oxygen GCIB treatments. This study indicates that GCIB is a promising surface treatment technique for Nb SRF cavities to be used in particle accelerators.
|Title of host publication||Niobium|
|Subtitle of host publication||Properties, Production and Applications|
|Publisher||Nova Science Publishers, Inc.|
|Number of pages||41|
|Publication status||Published - Dec 1 2011|
ASJC Scopus subject areas
- Chemical Engineering(all)