Padamsee H.

Paper	Title	Page
MO202	Status of the Cornell ERL injector cryomodule	9
	M. Liepe, S. Belomestnykh, E. Chojnacki, V. Medjidzade, H. Padamsee, P. Quigley, J. Sears, V. Shemelin, V. Veshcherevich CLASSE, Cornell University
	Cornell University is developing and fabricating a SRF injector cryomodule for the acceleration of the high current (100 mA) beam in the Cornell ERL prototype and ERL light source. Major challenges include emittance preservation of the low energy, ultra low emittance beam, cw cavity operation, and strong HOM damping with efficient HOM power extraction. Axial symmetry of HOM absorbers, together with two symmetrically placed input couplers per cavity, avoid transverse on-axis fields, which would cause emittance growth. Fabrication of five 2-cell niobium cavities and coaxial blade tuners, ten twin high power input couplers, and six beam line HOM absorbers has finished. The injector cryomodule is presently under assembly at Cornell University with beam test planned for early 2008. In this paper we report on the cryomodule fabrication and assembly status.
	Slides(PDF)
TUP24	Studies of the high field anomalous losses in small and large grain niobium cavities	173
	A. Romanenko, G. Eremeev, D. Meidlinger, H. Padamsee CLASSE, Cornell University
	High field Q-slope in niobium cavities of all grain sizes remains to be an unexplained phenomenon. Thermometry studies performed in recent years revealed that distribution of losses in the high field Q-slope regime is not uniform, but exhibit a patchy character with some regions being hotter than other. Results of surface analysis of samples dissected from "hot" and "cold" regions of small and large BCP cavities are reported in this contribution.
TUP27	Systematic Trends for the Medium Field Q-Slope	178
	J. Vines, Y. Xie, H. Padamsee Cornell University
	The medium field Q-slope for Nb cavities has been studied in the past as a thermal feedback effect combined with the nonlinear BCS surface resistance due to currentinduced RF pair-breaking. We are systematically exploring the behavior of the medium field Q-slope with various cavity parameters such as wall thickness, residual resistance, bath temperature, Kapitza conductance, RF frequency, RRR, and phonon mean free path. We study cases involving only the standard (linear) BCS resistance as well as those including the nonlinear BCS resistance. The systematic comparison suggests specific experiments to determine the role of the nonlinear contribution.
WE101	Temperature Map Studies on Nearly Oxide-Free, Thin-Oxide and Standard-Oxide Cavities	356
	G. Eremeev, H. Padamsee CLASSE, Cornell University
	A few nanometers of niobium oxide cover niobium in niobium cavities, prepared by standard treatments. Since the RF penetration depth is a few tens of nanometers, the niobium oxide and the metal-oxide interface may play role in RF losses of superconducting niobium. In order to understand the cause of phenomena such as the high field Qslope, medium field Q-slope, and residual resistance, it is important to distinguish the contributions of the niobium oxide and its interface to losses at medium and high fields. XPS and Auger studies have shown that it is possible to reduce significantly the thickness of the oxide layer by heating to 3000C - 4000C for a few hours in vacuum. Leaving the surface in the vacuum does not re-grow the oxide layer. Applying such treatment to a cavity one can reduce the niobium oxide and measure the superconducting RF properties of a nearly oxide-free cavity. Then via controllable air exposure one can re-grow oxide and investigate the change in properties as a function of exposure. We performed these experiments and report results of nearly oxide-free, thinoxide and standard-oxide cavities.
	Slides(PDF)
WE202	Different sputtering configurations for coating 1.5 GHZ copper cavities	384
	G. Lanza, V. Palmieri, N. Patron, C. Pira, S. Stark Laboratori Nazionali di Legnaro, STITUTO NAZIONALE DI FISICA NUCLEARE E. Bemporad, F. Carassiti, M. Sebastiani University of Rome H. Padamsee Cornell University
	In the framework of the attempts to densify the sputtering discharge, two different sputtering configuration are reported: - a mixed bias magnetron sputtering technique has been explored for depositing niobium into 1,5 GHz copper cavities. Results are presented and compared with the standard CERN technique. The superconducting and high resolution morphological and mechanical properties of niobium films sputtered onto the inner walls of electropolished cavities, have been studied as a function of the deposition technique. Even if niobium films coated with the bias technique show a higher density and Tc similar to the other films, they don't present higher RRR values. Preliminary RF tests are presented. - post Magnetron sputtering in thermoelectric emission regime have been investigated and is under improvement in order to increase the RRR values of sputtered Nb: superconducting and structural properties of the obtained films have been measured to check the technique capability and its possible application for coating cavities.
	Slides(PDF)
WEP33	Realisation of a prototype superconducting CW cavity and cryomodule for energy recovery	545
	P. A. McIntosh, R. Bate, C. D. Beard, M. Cordwell, D. M. Dykes, S. Pattalwar, J. Strachan, E. Wooldridge STFC Daresbury Laboratory S. Belomestnykh, M. Liepe, H. Padamsee Cornell University A. Buechner, F. Gabriel, P. Michel FZR Rossendorf T. Kimura, T. I. Smith Stanford University J. Byrd, J. N. Corlett, D. Li, S. Lidia LBNL
	For Energy Recovery applications, the requirement for high-Q accelerating structures, operating in CW mode, at large beam currents, with precise phase & amplitude stability and modest accelerating gradients are all fundamental in achieving intense photon fluxes from the synchronised FEL insertion devices. Both Daresbury Laboratory and Cornell University are developing designs for advanced Energy Recovery Linac (ERL) facilities which require accelerating Linacs which meet such demanding criteria. The specification for the main ERL accelerator for both facilities dictates a modest accelerating gradient of 20 MV/m, at a Qo of better than 10^10, with a Qext of up to 10^8. A collaborative R&D program has been set-up to design and fabricate a 'proof-of- principle' cryomodule (which is well underway) that can be tested on ERLP at Daresbury and also on the Cornell ERL injector. This paper details the new cryomodule design, provides an insight to the design solutions employed and reports on the present status of the project.
WEP39	Status of ILC cavity processing and testing at Cornell	567
	W. J. Ashmanskas Fermilab H. Padamsee Cornell University
	As part of the coordinated U.S. effort to build up SRF infrastructure for the ILC, the Cornell SRF lab has developed tools and procedures for 9-cell 1.3 GHz cavity processing and vertical testing. Steps performed with 9-cell cavities at Cornell include tuning for field flatness, vertical electropolishing (or BCP if desired), high-pressure rinsing in ultra-pure water, baking at 110C, and RF testing at 2K in a vertical cryostat. Since spring 2006, Cornell has performed ILC cavity processing/testing cycles at a rate of about one per month. We summarize methods, results, and possible next steps.