• A.T. Wu
  JLAB, Newport News, Virginia
• Z. Insepov
  ANL, Argonne
• D.R. Swenson
  Passport Systems Inc, Billerica, Massachusetts

Recently, it was demonstrated1 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 revealed that GCIB treatments could also modify surface irregularities and remove surface asperities leading to a smoother surface finish as demonstrated through measurements using a 3-D 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.

1: A.T. Wu et al, invited contribution to the book “Neural Computation and Particle Accelerators: Research, Technology, and Applications”, NOVA Science Publishers, New York, USA, 2009, In press

• A.T. Wu
  JLAB, Newport News, Virginia
• D.R. Swenson
  Passport Systems Inc, Billerica, Massachusetts

Field emission is one of the major obstacles for achieving constantly high accelerating gradient for Nb superconducting radio frequency (SRF) cavities, although various techniques and procedures have been adopted trying to keep the inner surfaces of Nb SRF cavities clean and free from field emission in the past a couple of decades. In this report, it is shown that significant reductions in field emission on Nb surfaces can be achieved by means of a new surface treatment technique called gas cluster ion beam (GCIB). When a relevant treatment agent is selected with optimal treating parameters, it is demonstrated a reduction in field emission as much as 87.5% is possible through measurements using a home-made scanning field emission microscope. Possible mechanism regarding the suppression of field emission on Nb surfaces by GCIB treatments will be discussed.