Wu G.

Paper	Title	Page
TU204	Review of SRF Materials Workshop	94
	G. Wu, L. Cooley, H. Edwards Fermilab C. Antoine CEA-Saclay
	The performance of niobium cavities has approached the theoretical hard limit. Yet the consistent achievement of higher performing cavities remains the greatest challenge. To further understand the basic materials science, a workshop was held at Fermilab in May 2007 to present and discuss the fundamental and experimental limitations, and propose new ideas.
	Slides(PDF)
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.
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.
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.