Boffo C.

Paper	Title	Page
TUP49	ECR Plasma Cleaning: An In-situ Processing Technique for RF Cavities	243
	G. Wu, H. Jiang, T. Khabiboulline, I. Pechenezhskiy, T. Koeth, J. Reid, W. Muranyi, B. Tennis, E. Harms, Y. Terechkine, H. Edwards, D. Mitchell, A. Rowe, C. Boffo, C. Cooper, L. Cooley, R. Schuessler Fermilab W. -D. Moeller DESY Hamburg C. Antoine CEA-Saclay A. Romanenko Cornell University
	A condition for Electron Cyclotron Resonance (ECR) can be established inside a fully assembled RF cavity without the need for removing high-power couplers. As such, plasma generated by this process can be used as a final cleaning step, or as an alternative cleaning step in place of other techniques. We will describe the current effort to study plasma cleaning by ECR in a 3.9GHz cavity.
TUP70	Optimization of BCP Processing of Elliptical NB SRF Cavities	308
	C. Cooper, G. Galasso, A. Rowe Fermilab C. Boffo Babcock Noell GmbH
	At present, electropolishing (EP) is considered a key technology in fabricating Nb SRF cavities performing at or above 35 MV/m. Nevertheless buffer chemical polishing (BCP) is still a cheaper, simpler and effective processing technique for single grain high gradient and polycrystalline lower gradient cavities. BCP has also been adopted to chemically process the third harmonic 3.9 GHz cavities, operating at or above 14 MV/m, being fabricated at Fermilab [1]. The dimensions and the shape of these cavities pose the problem of uneven material removal between iris and equator of the cells. This paper describes the thermal-fluid finite element model adopted to simulate the process, the experimental flow visualization tests performed to verify the simulation and a novel device fabricated to solve the problem.
WE105	An Investigation of the influence of grain boundaries on flux penetration in high purity large grain niobium for particle accelerators
	Z. H. Sung, P. J. Lee, A. Gurevich, A. A. Polyanskii, D. C. Larbalestier NHMFL, FSU C. Antoine Saclay C. Boffo, H. T. Edwards Fermilab
	Grain boundaries (GBs) in niobium cavities may be one of the important causes of extra power dissipation by reducing the field of first vortex penetration because the superconducting gap and the local depinning current density Jb on the GB are reduced. It is therefore important to measure the critical current density Jb and investigate the microstructure at grain boundaries to better understand whether or how grain boundary weakness can affect SRF cavity performance. Our experiments are currently correlating the global (by magnetometer) and local magnetization (by magneto-optical imaging), transport critical current density and atomic scale structure of Nb samples so that a DC analog of the RF surface currents can be developed for real Nb surfaces prepared using cavity optimization treatments. To measure Jb we apply transport current as a function of perpendicular magnetic field on BCP-treated bi-crystals of as-received, high-purity, large-grain niobium sheet. After measurement, we thin the very same grain boundary so that we image the microstructure of the external surface adjoining each GB by scanning transmission electron microscopy (STEM) in conjunction with EELS (Electron Energy Loss Spectroscopy). EELS has shown the presence of stoichiometric niobium oxide on the topmost layers, well within the typical superconducting niobium penetration depth (~ 50nm). 1. now at SACLAY
	Slides(PDF)