Reece C.E.

Paper	Title	Page
TUP18	Recent XPS Studies of the Effect of Processing on NB SRF Surfaces	158
	H. Tian, B. Xiao, M. J. Kelley JLab & College of William and Mary C. E. Reece JLab A. DeMasi, L. Pipe, K. E. Smith Boston University
	XPS studies have consistently shown that Nb surfaces for SRF chiefly comprise of a few nm of Nb2O5 on top of Nb metal, with minor amounts of Nb sub-oxides. Nb samples after BCP/EP treatment with post-baking at the various conditions have been examined by using synchrotron based XPS. Despite the confounding influence of surface roughness, certain outcomes are clear. Lower-valence Nb species are always and only associated with the metal/oxide interface, but evidence for an explicit layer structure or discrete phases is lacking. Post-baking without air exposure shows decreased oxide layer thickness and increased contribution from lower valence species, but spectra obtained after subsequent air exposure cannot be distinguished from those obtained prior to baking, though the SRF performance improvement remains.
TUP62	Hydrodynamic Thermal Modeling of 9-cell ILC Cavity Electropolishing and Implications for Improving the EP Process	275
	C. E. Reece, J. Mammosser JLab J. Ortega Blue Ridge Numerics
	Multi-cell niobium cavities often obtain the highest performance levels after having been subjected to an electropolishing (EP) process. The horizontal EP process first developed at KEK/Nomura Plating for TRISTAN[1] cavities is being applied to TESLA-style cavities and other structures for the XFEL and ILC R&D. Jefferson Lab is presently carrying this activity in the US. Because the local electropolishing current density is highly temperature dependent, we have created using CFDesign?? a full-scale hydrodynamic model which simulates the various thermal conditions present during 9-cell cavity electropolishing. The results of these simulations are compared with exterior surface temperature data gathered during ILC cavity EP at JLab. Having benchmarked the simulation, we explore the affect of altered boundary conditions in order to evaluate potentially beneficial modifications to the current standard process.
WE104	Novel Characterization of the Electropolishing of Niobium with Sulfuric and Hydrofluoric Acid Mixtures	370
	H. Tian, M. J. Kelley TJNAF and College of William and Mary S. G. Corcoran Virginia Tech C. E. Reece TJNAF
	Niobium surfaces are commonly electropolished in an effort to obtain optimally smooth surfaces for high-field SRF cavity applications. We report the first use of controlled electrochemical analysis techniques to characterize electropolishing of Nb in a sulfuric and hydrofluoric acid electrolyte. Through the use of a reference electrode we are able to clearly distinguish the anode, cathode polarization potentials as well as the electrolyte voltage drop that sum to the applied power supply voltage. We then separate the temperature and HF concentration dependence of each. We also report the first use of Electrochemical Impedance Spectroscopy (EIS) on this system. EIS results are consistent with a presence of a compact salt film at the Nb/electrolyte interface that is responsible for the limiting current. Microscopic understanding of the basic Nb EP mechanism is expected to provide an appropriate foundation with which to optimize the preparation of high-field niobium cavity surfaces. The implication of EIS for monitoring Nb surface during electropolishing shows this technology could be potentially used as a source of on-line feedback.
	Slides(PDF)
WEP04	Surface roughness characterization of niobium subjected to incremental BCP and EP processing steps	438
	H. Tian, M. J. Kelley TJNAF/College of William and Mary G. Ribeill North Carolina State University C. E. Reece TJNAF
	The surface of niobium samples polished under incremental Buffered Chemical Polish (BCP) and Electro- Polishing (EP) have been characterized through Atomic Force Microscopy (AFM) and stylus profilometry across a range of length of scales. The results were analyzed using Power Density Spectral (PSD) technique to determine roughness and characteristic dimensions. This study has shown that the PSD method is a valuable tool that provides quantitative information about surface roughness at different length scales.
WEP31	Optimization of the SRF Cavity Design for the CEBAF 12 GeV Upgrade	536
	C. E. Reece, E. F. Daly, J. Henry, W. R. Hicks, J. Preble, H. Wang, G. Wu JLab
	Based on initial testing of the "HG" and "LL" 7-cell cavities in the prototype cryomodule Renascence, several opportunities for improved optimization were identified. The HOM damping configuration was refined so as to meet the requirements for damping key dipole modes while simultaneously dramatically reducing risk of HOM pickup probe heating and also creating beamline clearance for mounting the tuner to stainless steel helium vessel endplates (rather than NbTi/Ti transitions to a titanium helium vessel). Code modeling and bench measurements were performed. The new design maintains the 7-cell LL cells and incorporates a brazed transition between Nb and the SS helium vessel. The resulting configuration is now called the "C100" design. Cavity design details as well as vertical dewar and horizontal test bed performance are presented.
WEP32	Performance of the CEBAF prototype cryomodule renascence	540
	C. E. Reece, E. F. Daly, G. K. Davis, M. Drury, W. R. Hicks, J. Preble, H. Wang JLab
	The prototype cryomodule Renascence was constructed as an energy building block for securing 6 GeV operation of CEBAF and to validate design elements for future CEBAF upgrade modules. These elements include the new "HG" and "LL" 7-cell cavity designs and a new tuner design.[1,2] Issues were identified during initial testing in 2005. The module has been reworked to address the issues with thermal stability, component breakage, and tuner motion. In addition, opportunity was taken to employ upgraded cleaning and assembly techniques for the cavity string. The HOM coupler heating issue was resolved, and seven of the eight cavities in the cryomodule have run stably at an average of 20 MV/m CW. The cryogenic, rf, and mechanical performance of the cryomodule are presented. Commissioning in CEBAF has just been completed in October 2007.
WEP49	Flexible application of the JLab pansophy information system for project reports, process monitoring, and R&D sample tracking	601
	V. Bookwalter, B. Madre, C. E. Reece JLab
	The use and features of the JLab SRF Institute IT system Pansophy1,2 continue to expand. In support of the cryomodule rework project for CEBAF, a full set of webbased travelers has been implemented and an integrated set of live summary reports has been created. A graphical user interface within the reports enables navigation to either higher-level summaries or drill-down to the original source data. In addition to collection of episodic data, Pansophy is now used to capture, coordinate, and display continuously logged process parameter that relate to technical water systems and clean room environmental conditions. In a new expansion, Pansophy is being used to collect and track process and analytical data sets associated with SRF material samples that are part of the surface creation, processing, and characterization R&D.
WEP62	Diagnosis, analysis, and resolution of thermal stability issues with HOM couplers on prototype CEBAF SRF cavities	656
	C. E. Reece, E. F. Daly, G. K. Davis, W. R. Hicks, T. Rothgeb, H. L. Phillips, J. Preble, H. Wang, G. Wu TJNAF
	During initial testing of the prototype cavities incorporated into the developmental cryomodule Renascence severe thermal stability issues were encountered during CW operation. Additional diagnostic instrumentation was added. This enabled identification of an unanticipated thermal impedance between the HOM coupler probe feedthrough assembly and the cavity beamtube. Subsequent detailed FE analysis successfully modeled the situation and indicated the need for alternate cooling path for the couplers on those cavities. HOM damping was measured to be adequate employing only two of the four HOM couplers. The two pickup probes on the couplers at the input power coupler side of each cavity were removed, the remaining HOM probe feedthroughs were heat stationed to two-phase helium supply piping, and a novel heat sink was added to station both the inner and outer conductors of the remaining HOM rf cables. The characterization measurements, analysis, modifications, and resulting performance are presented.
WEP85	Waveguide coupler kick to beam bunch and current dependency on SRF cavities	721
	G. Wu Fermilab H. Wang, C. E. Reece, R. A. Rimmer JLab
	JLAB SRF cavities employ waveguide type fundamental power couplers (FPC). The FPC design for the 7-cell upgrade cavities was optimized to minimize the dipole field kick. For continuous wave (CW) operation, the forwarding RF power will be at different magnitude to drive the different beam current and cavity gradient. This introduces some deviation from optimized FPC field for varying beam loading. This article analyzes the beam behavior both in centroid kick and head-tail kick under different beam loading conditions.