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 theevolution of SRF technology. In this chapter, a study of the surface treatments of Nb flatsamples and SRF single cell cavities via Gas Cluster Ion Beam (GCIB) technique will bereported. Beams of Ar, O2, N2, and NF3 clusters with accelerating voltages up to 35 kV wereemployed in the treatments. The treated surfaces of Nb flat samples were examined by ascanning field emission microscope, a scanning electron microscope equipped with an energydispersive 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 modifysurface morphology of Nb, but also change the surface oxide layer structure of Nb and reducethe number of field emission sites on the surface dramatically. Computer simulation viaatomistic molecular dynamics and a phenomenological surface dynamics was employed tohelp understand the experimental results. Due to its effectiveness at changing the depth andcomposition of the surface oxide layer structure of Nb, GCIB might be a key to understandingand overcoming the limitations of the high-field Q-slope. Based on the encouraging experimental results obtained from flat sample study, a novel setupwas constructed to allow GCIB treatments on Nb single cell cavities. First results of RF testson the GCIB treated Nb single cell cavities showed that the quality factor Q of the cavitycould be improved substantially at 4.5 K and the superconducting gap value, extracted fromRF measurements at different temperatures below superconducting transition temperature,was enhanced by oxygen GCIB treatments. This study indicates that GCIB is a promisingsurface treatment technique for Nb SRF cavities to be used in particle accelerators.
|Title of host publication||Neural Computation and Particle Accelerators|
|Subtitle of host publication||Research, Technology and Applications|
|Publisher||Nova Science Publishers, Inc.|
|Number of pages||42|
|Publication status||Published - Dec 1 2010|
ASJC Scopus subject areas