Author: Grassellino, A.
Paper Title Page
MOP015 Status of the SRF Development for the Project X 117
 
  • V.P. Yakovlev, T.T. Arkan, M.H. Awida, P. Berrutti, E. Borissov, A.C. Crawford, M.H. Foley, C.M. Ginsburg, I.V. Gonin, A. Grassellino, C.J. Grimm, S.D. Holmes, S. Kazakov, R.D. Kephart, T.N. Khabiboulline, V.A. Lebedev, A. Lunin, M. Merio, S. Nagaitsev, T.H. Nicol, Y.O. Orlov, D. Passarelli, T.J. Peterson, Y.M. Pischalnikov, O.V. Pronitchev, L. Ristori, A.M. Rowe, D.A. Sergatskov, N. Solyak, A.I. Sukhanov, I. Terechkine
    Fermilab, Batavia, USA
  
  Project X is a high intensity proton facility being developed to support a world-leading program of Intensity Frontier physics over the next two decades at Fermilab. The proposed facility is based on the SRF technology and consists of two linacs: CW linac to accelerate beam from 2.1 MeV to 3 GeV and pulsed linac accelerate 5% of the beam up to 8 GeV. In a CW linac five families of SC cavities are used: half-wave resonators (162.5 MHz); single-spoke cavities: SSR1 and SSR2 (325 MHz) and elliptical 5-cell β=0.6 and β=0.9 cavities (650 MHz). Pulsed 3-8 GeV linac linac are based on 9-cell 1.3 GHz cavities. In the paper the basic requirements and the status of development of SC accelerating cavities, auxiliaries (couplers, tuners, etc.) and cryomodules are presented as well as technology challenges caused by their specifics.  
 
MOP036 New Technique and Result of Laser Welded SCRF Cavity Developed at RRCAT 186
 
  • P. Khare, R. Arya, J. Dwivedi, R. Ghosh, G. Gilankar, C. Gupta, P.D. Gupta, A. Jain, S.C. Joshi, G.V. Kane, R. Kaul, P.K. Kush, G. Mundra, S.M. Oak, C.K. Pithawa, P. Ram Sankar, S.B. Roy, V.C. Sahni, R.S. Sandha, P. Shrivastava, B.N. Upadhyay
    RRCAT, Indore (M.P.), India
  • C.A. Cooper, C.M. Ginsburg, A. Grassellino, C.S. Mishra, A.M. Rowe
    Fermilab, Batavia, USA
  
  A new technique to fabricate SCRF cavities with the help of laser welding process has been developed at Raja Ramanna Centre for Advanced Technology RRCAT), Indore, Department of Atomic Energy, India. In this technique, a pulsed Nd:YAG laser has been used and welding was performed in inert gas environment, in a specially designed welding rig. The advantages of this technique are reduced cost, small heat affected zone, no necessity to weld in vacuum and enhanced rate of production. The paper describes the technique and fabrication method of a single-cell 1.3 GHz SCRF cavity which was fabricated at RRCAT with this new technique. It also discusses the test result of this cavity which was processed and tested at Fermilab. The cavity reached an Eacc of 17MV/m with a Q0 of 1.4 E +10 at 2K. The cavity is being barrel polished for further improvement.  
 
TUIOA03
 New Insights on the Physics of RF Surface Resistance and a Cure for the Medium Field Q-Slope  
 
  • A. Grassellino
    Fermilab, Batavia, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
In this talk we will present the first deconvolution of surface resistance into BCS and residual resistance as a function of field for differently processed niobium cavities, which provides new insights on the physics of RF surface resistance. Then, new cavity results will be presented where record low values of surface resistances have been achieved. New processing strategies such as annealing and heat treatments in partial pressure of certain gases will be presented, complemented by surface studies. Via these treatments BCS resistances decreasing with the applied field have been reproducibly observed on several cavities, inverting the typical 'medium field Q-slope' trend. These findings represent a long sought solution to the the medium field Q-slope problem. 		 
slides icon Slides TUIOA03 [6.307 MB]  
 
TUIOC02 Bipolar EP: Electropolishing without Fluorine in a Water Based Electrolyte 404
 
  • A.M. Rowe, A. Grassellino
    Fermilab, Batavia, USA
  • T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor
    Faraday Technology, Inc., Clayton, USA
  
  Funding: Operated by Fermi Research Alliance, LLC under contract No. De-AC02-07CH11359 with the United States Department of Energy
For more than thirty years, preparing superconducting RF cavities for high performance has required the use of dangerous and ecologically damaging chemicals. Reducing the personnel and environmental risks associated with using these chemicals is a priority at Fermilab. Therefore, Fermilab pursued a project to adapt a non-hazardous and relatively benign bipolar electropolishing technique to SRF cavities that Faraday Technology, Inc. developed. Faraday initially developed this electropolishing technique to polish metal alloys used in automotive and semiconductor components as well as medical devices and implants. By modifying the cathodic/anodic interaction via a pulse forward/pulse reverse technique, Fermilab and Faraday Technology demonstrate the capability to polish 1.3 GHz single-cell cavities utilizing an aqueous 10% sulfuric acid electrolyte. We present the development of bipolar EP for single-cell 1.3 GHz cavities and show the results from vertical tests achieving gradients greater than 40 MV/m. 		 
slides icon Slides TUIOC02 [1.251 MB]  
 
TUP014 Fast Table Top Niobium Hydride Investigations Using Direct Imaging in a Cryo-Stage 447
 
  • F.L. Barkov, A. Grassellino, A. Romanenko
    Fermilab, Batavia, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
Performance of niobium SRF cavities can be strongly affected by hydrogen segregation into lossy niobium hydrides as known for "hydrogen Q disease" at higher concentration of dissolved H and may be a reason for the "high field Q slope" at lower concentrations. With the use of optical cryostat and laser confocal microscope we have developed a "table top technique" for direct observation of hydride precipitation, and studied formation, morphology, and time evolution of hydrides after different treatments used for cavities. Our results show that hydrides can form at the niobium surface at 90-180K depending mainly on H concentration and the cooldown rate. A lot of H is absorbed by bulk niobium during mechanical polishing, which leads to the formation of very large (>10 microns) hydrides. Both EP and BCP do not influence H concentration significantly provided that temperature during treatments is kept below 15C. 800C degassing reduces H concentration and precludes large hydride precipitation. 120C baking and mechanical deformation do not change H concentration but affect hydride precipitation through their influence on the number of nucleation centers and H binding defects. 		 
 
TUP015 Bitter Decoration Studies of Magnetic Flux Penetration Into Cavity Cutouts 451
 
  • F.L. Barkov, A. Grassellino, A. Romanenko
    Fermilab, Batavia, USA
  • L.Y. Vinnikov
    ISSP, Chernogolovka, Russia
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
Magnetic flux penetration may produce additional losses in superconducting radio frequency cavities. All the existing models for flux penetration are based on the formation of Abrikosov vortices. Using high resolution Bitter decoration technique we have investigated magnetic flux distribution patterns in cavity cutouts at the perpendicular magnetic fields of 10-80 mT. At low fields <20 mT the magnetic field penetrates in the form of flux bundles and not Abrikosov vortices, the situation characteristic of type-I superconductors. With the increase of the magnetic field up to 30 mT "bundles" first merge into a connected structure and then break up into individual Abrikosov vortices at ~60 mT and a well-known intermediate mixed state is observed. Such magnetic field driven transition from type I to type II superconductivity has never been observed before in any existing superconductor. For the case of flat samples we have observed a coexistence of both "bundles" and Abrikosov vortices in one experiment. Our results show that high-purity cavity grade niobium is a "border-line" material and behaves as a type-I superconductor at lower fields and type-II at higher fields. 		 
 
TUP019 Probing Hot Spot and Cold Spot of SRF Cavities with Tunneling and Raman Spectroscopies 466
 
  • C. Cao
    Illinois Institute of Technology, Chicago, IL, USA
  • G. Ciovati
    JLAB, Newport News, Virginia, USA
  • L.D. Cooley, A. Grassellino
    Fermilab, Batavia, USA
  • N. Groll, Th. Proslier
    ANL, Argonne, USA
  • J. Zasadzinski
    IIT, Chicago, Illinois, USA
  
  Point contact tunneling and Raman spectroscopies are presented on high purity Nb samples, including pieces from hot and col spot regions of tested SRF cavities and Nb coupons subject to similar treatment. High quality tunneling spectra were observed on cold spots, revealing the bulk Nb gap, indicating minimal surface contamination. Hot spots exhibit high smearing suggestive of pair breaking along with generally lower superconducting gap. In addition, pronounced zero bias conductance peaks were frequently observed indicative of spin-flip tunneling and thus magnetic impurities in the oxide layer. Optical microscopy reveals higher density of surface blemishes on hot spots. Raman spectra inside those blemishes show clear difference from surrounding areas, exhibiting enhanced intensity peaks identified as either amorphous carbon, hydrocarbons or the ordered NbC phase. The presence of surface NbC is consistent with TEM studies, and these inclusions exhibit enhanced second order phonon response. Such regions with high concentrations of impurities are expected to suppress the local superconductivity and may explain the formation of hot spots.  
 
TUP026 Performance of a FNAL Nitrogen Treated Superconducting Niobium Cavity at Cornell 475
 
  • D. Gonnella, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • A. Grassellino
    Fermilab, Batavia, USA
  
  Funding: NSF
In many tests of superconducting cavities, the performance of the cavity in the medium field region will be limited by medium field Q slope. For projects such as the proposed Cornell Energy Recovery Linac, high Q operation at medium fields is necessary to meet specifications for efficient CW cavity operation. A single cell cavity was prepared by Fermilab by electropolishing it and baking it at 1000°C with 1x10-2 Torr of Nitrogen, and subsequently tested at Cornell. The cavity displayed an increase in Q at medium fields between 5 and 20 MV/m at 2.0 K, opposite of the usual medium field Q slope. The material properties of this cavity were studied and correlated with performance. This analysis helps to better understand how to overcome medium field Q slope and improve cavity performance in future CW SRF machines such as the Cornell ERL. 		 
 
TUP030
 Elimination of post annealing chemistry: a route to high Q cavities and processing simplification  
 
  • A. Grassellino, A.C. Crawford, R.D. Kephart, O.S. Melnychuk, A. Romanenko, A.M. Rowe, D.A. Sergatskov, M. Wong
    Fermilab, Batavia, USA
  • M. Checchin
    INFN/LNL, Legnaro (PD), Italy
  • Y. Trenikhina
    IIT, Chicago, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
We investigate the effect of high temperature treatments followed by only high-pressure water rinse (HPR) of superconducting radio frequency (SRF) niobium cavities. The objective is to provide a cost effective alternative to the typical cavity processing sequence, by eliminating the material removal step post furnace treatment while preserving or improving the RF performance. The studies have been conducted in the temperature range 800-1000C for different conditions of the starting substrate: large grain and fine grain, electro-polished (EP) and centrifugal barrel polished (CBP) to mirror finish. An interesting effect of the grain size on the performances is found. Cavity results and samples characterization show that furnace contaminants cause poor cavity performance, and a practical solution is found to prevent surface contamination. Extraordinary values of residual resistances ~ 1 nOhm and below are then consistently achieved for the contamination-free cavities. We explore the addition of a small partial pressure of gas during the anneal to further increase the cavity quality factor by reducing the BCS resistance. 		 
 
TUP031
 Muon Spin Rotation Studies of Bulk Electropolished Cavity Cutouts and Thin Films of Alternative Materials  
 
  • A. Grassellino, A. Romanenko, D.A. Sergatskov
    Fermilab, Batavia, USA
  • T. Buck, R.E. Laxdal
    TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
  • M. Liepe, S. Posen
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • Y. Trenikhina
    IIT, Chicago, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
In the previous studies [*] magnetic flux penetration into fine and large grain BCP cavity cutouts was investigated using the muon spin rotation (muSR) technique. The technique is based on implanting muons, which serve as sensitive magnetic probes inside the material. Here we report muSR studies on fine grain EP cavity cutouts, both before and after 120C baking, and on the films of new materials.
[*] A. Grassellino et al, Phys. Rev. ST Accel. Beams 16, 062002 (2013) 		 
 
TUP038
 Field Dependence of Residual and BCS Surface Resistances Measured by Explicit Deconvolution Up to High Fields  
 
  • A. Romanenko, A. Grassellino, O.S. Melnychuk, D.A. Sergatskov
    Fermilab, Batavia, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
For both fundamental understanding of performance limiting processes and practical design of future accelerators a crucial information is the temperature and field dependence of the components in surface resistance. We report an explicit deconvolution of temperature-independent residual (Rres) and temperature-dependent BCS (Rbcs) components in multiple cavities treated by standard processing techniques (EP, BCP, 120C bake, 800C degassing) at all fields up to Brf > 100 mT. Such deconvolution allows to address the nature of the low, medium, and high field Q slopes, and provides input for accelerator parametric design optimization. 		 
 
TUP039
 Meissner Screening at Hot (Unbaked) and Cold (Baked) Spots in Electropolished Cavities Studied by Low Energy Muon Spectroscopy  
 
  • A. Romanenko, F.L. Barkov, A. Grassellino
    Fermilab, Batavia, USA
  • T. Prokscha, Z. Salman, A. Suter
    PSI, Villigen PSI, Switzerland
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
While there is a number of recent structural investigations, which shed light on possible underlying mechanisms of the high field Q slope and 120C baking effect [], there is fewer explicit superconducting investigations exploring the microscopic superconducting properties at the locations of "hot" spots in unbaked cavities. Furthermore, while the nature of the magnetic field penetration in the Meissner state into bulk niobium is predicted by BCS theory and its strong coupling extensions, it was never directly observed. Here we present a direct measurement of the magnetic field profile B(z) in the Meissner state inside a "hot" spot cutout from the electropolished cavity, and compare it to a "cold" spot from the baked electropolished cavity. We demonstrate the presence of a dead layer, a non-exponential B(z) profile, and a drastic change introduced by the 120C baking.
[*] A. Romanenko, F. Barkov, L.D. Cooley, A. Grassellino, Supercond. Sci. Technol. 26, 035003 (2013)
[**]A. Romanenko, C.J. Edwardson, P.G. Coleman, P.J. Simpson, Appl. Phys. Lett. 102, 232601 (2013) 		 
 
TUP050
 R&D Program for 650 MHz Niobium Cavities for Project X  
 
  • A. Grassellino, A.C. Crawford, C.M. Ginsburg, R.D. Kephart, T.N. Khabiboulline, O.S. Melnychuk, A. Romanenko, A.M. Rowe, D.A. Sergatskov, A.I. Sukhanov, M. Wong, V.P. Yakovlev
    Fermilab, Batavia, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
We report the first test results of several 650 MHz single cell niobium cavities processed at Fermilab. The target for the 5-cell 650 MHz cavities for Project X is CW operation at magnetic peak field ~ 60-70 mT, making high quality factors at medium accelerating fields the main goal of the surface processing R&D. We will discuss how the performance vary with the different surface processing and parameters/criteria of choice for the final surface preparation sequence. 		 
 
TUP060 Acid Free Extended Mechanical Polishing R&D 564
 
  • C.A. Cooper, A.C. Crawford, C.M. Ginsburg, A. Grassellino, R.D. Kephart, O.S. Melnychuk, A. Romanenko, A.M. Rowe, D.A. Sergatskov
    Fermilab, Batavia, USA
  
  We report the progress in the development of a centrifugal barrel polishing recipe which can lead to standard cavity performance without the need of any chemical treatments. Q ~ 1010 at 20 MV/m and gradients above 35 MV/m have already been demonstrated for cavities whose preparation sequence was CBP, degassing and no subsequent chemical treatments. Results of studies on the effect of different CBP media on RF performance will be reported, including full body T-map showing the distribution of RF losses.  
 
TUP065 Chemical Structure of Niobium Samples Vacuum Treated in Nitrogen in Parallel With Very High Q0 Cavities 583
 
  • Y. Trenikhina
    IIT, Chicago, USA
  • A. Grassellino, A. Romanenko
    Fermilab, Batavia, USA
  
  XPS in combination with subsequent material removal via Ar sputtering as well as XRD are used for the surface analysis and bulk phase characterization of nitrogen treated samples processed parallel with SRF cavities. We investigated the surface chemistry of the samples treated with nitrogen in order to understand this treatment effect on SRF cavity performance for several baking temperatures and durations in order to find cost efficient post-furnace chemistry free procedures to enable high Q-values.  
 
TUP100 Medium Field Q-Slope Studies in High Frequency Cavities 705
 
  • O.S. Melnychuk, A. Grassellino, A.I. Sukhanov
    Fermilab, Batavia, USA
  
  A phenomenon of Medium Field Q-Slope (MFQS) in superconducting RF cavities is of high importance because it occurs in the field range (5-20MV/m) that includes designed operation fields of future CW accelerators. MFQS impacts resistive losses in the cavity and, consequently, directly affects accelerator operation costs. We present studies of MFQS based on vertical test data for 1.3GHz nine-cell cavities and make comparisons of vertical test data from different laboratories.  
 
TUP101
 New Temperature Mapping Findings for the Medium Field Q-Slope  
 
  • A. Romanenko, A. Grassellino, R.V. Pilipenko
    Fermilab, Batavia, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
A problem of the medium field Q slope in cavities treated by standard surface processing techniques recently gained a lot of attention due to its importance for CW accelerators. Here we present high resolution thermometry studies of the losses in the medium field range (20-80 mT), and discuss its possible connection to the observations at high fields (>80 mT). 		 
 
WEIOC03
 Atomic Layer Deposition of Thin Superconducting Films and Multilayers: Coupons and Cavity Tests  
 
  • Th. Proslier, N. Groll, J. Klug, M.J. Pellin
    ANL, Argonne, USA
  • G. Ciovati, P. Kneisel, A-M. Valente-Feliciano
    JLAB, Newport News, Virginia, USA
  • A. Grassellino, A. Romanenko
    Fermilab, Batavia, USA
  • J. Zasadzinski
    IIT, Chicago, Illinois, USA
  
  Funding: DOE-office of Science, High Energy Physics.
I will present a summary of the work done over the last 2 years that encompasses both coupons study of thin superconducting films and multilayers and preliminary superconducting RF cavity tests coated by ALD. I will also present results of Nb onto Copper. 		 
slides icon Slides WEIOC03 [25.554 MB]  
 
THP030 Superconducting RF Cavity Development With UK Industry 966
 
  • A.E. Wheelhouse, R.K. Buckley, L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • C.A. Cooper, C.M. Ginsburg, A. Grassellino, O.S. Melnychuk, A.M. Rowe, D.A. Sergatskov
    Fermilab, Batavia, USA
  • J.R. Everard, N. Shakespeare
    Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom
  
  As part of a continuing STFC Innovations Partnership Scheme (IPS) grant, in support of enabling UK industry to address the large potential market for superconducting RF structures Daresbury Laboratory and Shakespeare Engineering Ltd are developing the capability to fabricate, process and test a niobium 9-cell 1.3 GHz superconducting RF cavity. A single-cell cavity fabricated under this grant was surface processed and tested at Fermilab, and achieved an accelerating gradient in excess of 40 MV/m at an unloaded quality factor in excess of 1.0 x 1010. This paper presents the results of the single-cell cavity testing and discusses the progress made to date in the development of the design and manufacture of a 9-cell niobium cavity, which Shakespeare Engineering Ltd will fabricate and which is anticipated to be qualified in 2014.