Abstract
Recently, it was demonstrated that significant reductions in field emission on Nb surfaces could be achieved by means of a new surface treatment technique called gas cluster ion beam (GCIB). Further study as shown in this paper revealed that GCIB treatments could modify surface irregularities and remove surface asperities leading to a smoother surface finish as demonstrated through measurements using a 3D profilometer, an atomic force microscope, and a scanning electron microscope. These experimental observations were supported by computer simulation via atomistic molecular dynamics and a phenomenological surface dynamics. Measurements employing a secondary ion mass spectrometry found that GCIB could also alter Nb surface oxide layer structure. Possible implications of the experimental results on the performance of Nb superconducting radio frequency cavities treated by GCIB will be discussed. First experimental results on Nb single cell superconducting radio frequency cavities treated by GCIB will be reported.
Highlights
Recent experiments [1,2,3,4] have shown that the gas cluster ion beam (GCIB) technique is a highly desirable tool for treating Nb surfaces to reduce field emission
We report on the results of the measurements on the surfaces of Nb samples treated by various GCIB gas species employing a 3D profilometer, an atomic force microscope (AFM), a scanning electron microscope (SEM), and a dynamic secondary ion mass spectrometry (SIMS)
This paper reported on the investigation of the change of Nb surface morphology and oxide layer structure by GCIB treated via measurements by a 3D profilometer, an AFM, an SEM, and a dynamic SIMS system
Summary
Recent experiments [1,2,3,4] have shown that the gas cluster ion beam (GCIB) technique is a highly desirable tool for treating Nb surfaces to reduce field emission. Computer simulation via atomistic molecular dynamics and a phenomenological surface dynamics was employed to understand the experimental observations. It will be demonstrated in the following that GCIB treatments can modify surface morphology of Nb and change its surface oxide layer structure. By adjusting GCIB treatment parameters and agent, it is possible to reduce field emission significantly and improve superconducting properties on the Nb surface, leading to a better performance for Nb based superconducting radio frequency (SRF) cavities
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