• Y. Iwashita, T. Sugimoto
  Kyoto ICR, Uji, Kyoto
• M. Masuzawa, T. Tauchi, K. Yokoya
  KEK, Ibaraki

Funding: Work partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (A), 18204023(2006)

Although the base line technology of the Final Focus Doublet for ILC is superconducting magnet, which is supposed to be conventional, the slender structure may be suffered from its vibration. The permanent magnets, however, do not have any vibration source in it at the steady state. The five-ring-singlet configuration, proposed by R. L. Gluckstern adds 100% strength adjustability to permanent magnet quadrupole (PMQ) lens. A prototype of this lens is fabricated and under evaluation. It was originally designed for ILC that also has the extra hole for the outgoing beam. In order to realize the beam test at ATF2, the inner bore is enlarged from D20mm to D50mm to clear the background photons from Shintake-Monitor. The magnet is described.

• G. Sikler, W. Gaertner, A. Wessner
  BNG, Würzburg
• E.S. Fischer, E. Floch, D. Krämer, J. Macavei, P. Schnizer, C. Schroeder, F. Walter
  GSI, Darmstadt

GSI had manufactured a prototype of a fast cycling superconducting dipole magnet at Babcock Noell GmbH. This is the first full size magnet for the SIS100 synchrotron at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt / Germany. In close collaboration with GSI, the magnet was technologically developed, manufactured and assembled by Babcock Noell. The system was successfully tested at GSI reaching the nominal cycling performance, including the high ramping rate of 4 T/s and the maximum field of 2.1 T. Especially the superconducting cable, the coils and the iron yoke are subject to strong mechanical and thermal stresses. Here we describe the details on the fabrication of these components and give an outlook on possible improvements of the manufacturing technologies, applicable to future prototypes and series magnets for SIS100.

• M.A. Green, D. Li, S.P. Virostek, M.S. Zisman
  LBNL, Berkeley, California
• A.B. Chen, X.L. Guo, X.K. Liu, H. Pan, L. Wang, H. Wu, F.Y. Xu, S.X. Zheng
  ICST, Harbin
• D.J. Summers
  UMiss, University, Mississippi

Funding: This work is supported by funds under the “985-2” plan of HIT. This work is also supported by the Office of Science, US-DOE under DOE contract DE-AC02-05CH11231 and by NSF through NSF-MRI-0722656.

The superconducting coupling solenoid for MuCOOL and MICE will have an inside radius of 750 mm, and a coil length of 285 mm. The MuCOOL coupling coil is identical to the MICE coupling coils. The MICE coupling magnet will have a self inductance of 592 H. When operated at it maximum design current of 210 A (the highest momentum operation of MICE), the magnet stored energy will be about 13 MJ. These magnets will be kept cold using a pair of pulse tube cryocoolers that deliver 1.5 W at 4.2 K and 55 W at 60 K. This report describes the progress on the MuCOOL and MICE coupling magnet design and engineering. The progress on the construction of the first coupling coil will also be presented.

• S.P. Virostek, M.A. Green, D. Li, M.S. Zisman
  LBNL, Berkeley, California

Funding: This work is supported by the Office of Science, United States Department of Energy under DOE contract DE-AC02-05CH11231.

The Muon Ionization Cooling Experiment (MICE) is an international collaboration that will demonstrate ionization cooling in a section of a realistic cooling channel using a muon beam at Rutherford Appleton Laboratory (RAL) in the UK. At each end of the cooling channel a spectrometer solenoid magnet consisting of five superconducting coils will provide a 4 tesla uniform field region. The scintillating fiber tracker within the magnet bore tubes will measure the emittance of the muon beam as it enters and exits the cooling channel. The 400 mm diameter warm bore, 3 meter long magnets incorporate a cold mass consisting of two coil sections wound on a single aluminum mandrel: a three-coil spectrometer magnet and a two-coil section that matches the solenoid uniform field into the MICE cooling channel. The fabrication of the spectrometer solenoids has been completed, and preliminary testing and field mapping of the magnets is nearly complete. The key design features of the spectrometer solenoid magnets are presented along with a summary of the progress on the testing and magnetic measurements.

• S.A. Kahn, R.P. Johnson, M. Turenne
  Muons, Inc, Batavia
• F. Hunte, J. Schwartz
  NHMFL, Tallahassee, Florida

High temperature superconductors (HTS) have been shown to carry significant current density in the presence of extremely high magnetic fields when operated at low temperature. The successful design of magnets needed for high energy physics applications using such high field superconductor depends critically on the detailed wire or conductor parameters which are still under development and not yet well-defined. The HTS is being developed for accelerator use by concentrating on the design of solenoid magnet that will have a useful role in cooling muon beam phase space. A conceptual design of a high field solenoid using YBCO conductor is being analyzed. Mechanical properties of the HTS conductors will be measured along with engineering current densities (JE) as a function of temperature and strain to extend the HTS specifications to conditions needed for low temperature applications. HTS quench properties are proposed to be measured and quench protection schemes developed for the solenoid magnet.

• W. Beeckman
  Sigmaphi, Vannes
• J. Simkin
  Vector Fields Ltd., Oxford
• M.N. Wilson
  Oxford Instruments, Accelerator Technology Group, Oxford, Oxon

A tender for the study and construction of a large superconducting split solenoid for the C400 carbon therapy cyclotron was issued by IBA in March 2008 and awarded to Sigamphi. Although the current density is moderate, the large radius and average field imply quite a high level of hoop stress. Simple formulas range between 140 and 180 MPa and, with such large values and uncertainties, it was felt necessary to perform a finite element analysis of the structure. Average fields in a cyclotron are very well modeled using an axially symmetrical structure and the stress was therefore studied using the stress module of the Vector Fields Opera2d suite. Different models were tried with different levels of details. A comparison is made between them as well as with the analytical results.

• Y. Ivanyushenkov, K.D. Boerste, T.W. Buffington, C.L. Doose, Q.B. Hasse, M.S. Jaski, M. Kasa, S.H. Kim, R. Kustom, E.R. Moog, D.L. Peters, E. Trakhtenberg, I. Vasserman
  ANL, Argonne
• A.V. Makarov
  Fermilab, Batavia

Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

An extensive R&D program is underway at the Advanced Photon Source (APS) with the aim of developing a technology capable of building a 2.4-m-long superconducting planar undulator for APS users. The initial phase of the project concentrates on using a NbTi superconductor and includes magnetic modeling, development of manufacturing techniques for the undulator magnet, and design and test of short prototypes. The current status of the R&D phase of the project is described in this paper.

• E.M. Mashkina, A.J. Magerl
  University Erlangen-Nurnberg, Institute of Condensed Matter Physics, Erlangen
• C. Boffo, M. Borlein, W. Walter
  BNG, Würzburg
• S. Casalbuoni, A.W. Grau, M. Hagelstein, D. Saez de Jauregui
  FZK, Karlsruhe
• N. Vassiljev
  University Erlangen-Nuernberg, Institute of Condensed Matter Physics, Erlangen

A new 15 mm period, 1.5 m long planar undulator is being fabricated by Babcock Noell GmbH (BNG) for the ANKA synchrotron light source. In order to qualify the production process and to optimize both the quench protection scheme and the magnetic field correction system, a short prototype has been fabricated. The prototype has been tested in vertical configuration and liquid helium at 4.2K in the CASPER facility at ANKA. The magnetic field has been measured along the beam axis direction by Hall probes with a positioning precision of 3 μm. We report here on the field shimming scheme and the resulting performance of the coils.

• J. Norem, J.W. Elam, M.J. Pellin
  ANL, Argonne
• C.Z. Antoine
  CEA, Gif-sur-Yvette
• G. Ciovati, P. Kneisel, C.E. Reece, R.A. Rimmer
  JLAB, Newport News, Virginia
• L. Cooley
  Fermilab, Batavia
• A.V. Gurevich
  NHMFL, Tallahassee, Florida
• Y. Ha, Th. Proslier, J. Zasadzinski
  IIT, Chicago, Illinois

Funding: DOE/OHEP

We have begun using Atomic Layer Deposition (ALD) to synthesize a variety of surface coatings on coupons and cavities as part of an effort to produce rf structures with significantly better performance and yield than those obtained from bulk niobium, The ALD process offers the possibility of conformally coating complex cavity shapes with precise layered structures with tightly constrained morphology and chemical properties. Our program looks both at the metallurgy and superconducting properties of these coatings, and also their performance in working structures. Initial results include: 1) evidence from point contact tunneling showing magnetic oxides can be a significant limitation to high gradient operation, 2) experimental results showing the production sharp niobium/oxide interfaces from a high temperature bake of ALD coated Al2O3 on niobium surfaces, 3) results from ALD coated structures.

• I. Ben-Zvi, D. Naik
  BNL, Upton, Long Island, New York

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.

A beam excited 56 MHz RF Niobium Quarter Wave Resonator has been proposed to enhance RHIC beam luminosity and bunching. As multipacting is expected, an extensive study was carried out with the Multipac 2.1 code, looking for a way to suppress it. Multipacting bands were found. Discharge occurred at cavity’s top corner above beam gap and on outer conductor up to more than half its length, moving towards the end of the cavity. We find single-point multipacting, with emission from the outer conductor, as well as two-point multipacting involving both inner and outer conductor. We found a geometric approach to suppressing multipacting. The most promising method was ripples in outer conductor. Ripples’ depth, width and gap were optimized. In shallow depth of 1 cm, electrons multiply, drift further, however they are stopped by 2 cm ripples. Width of 1 and 3 cm didn’t work as in 1 cm electrons emerge out of it, whereas, in 3 cm, they resonate and trap inside. A 2 cm wide was found good. Likewise, 2 cm gap was valuable. Finally, we find that ripples of 2 cm deep, 2 cm wide spaced by 2 cm completely suppressed multipacting, and were adopted for fabrication.

• Z.A. Conway, D.L. Hartill, H. Padamsee, E.N. Smith
  CLASSE, Ithaca, New York

Funding: Work Supported by the NSF and DOE

Superconducting RF cavity quench detection is presently a cumbersome procedure requiring two or more expensive cold tests. One cold test identifies the cell-pair involved via quench field measurements in several 1.3 GHz TM010 pass-band modes. A second test follows with numerous fixed thermometers attached to the culprit cell-pair to identify the particular cell. A third measurement with many localized thermometers is necessary to zoom in on the quench spot. We report here on a far more efficient alternative method which utilizes a few (e.g. 8) oscillating superleak transducers (OST) to detect the He-II second sound wave driven by the defect induced quench. Results characterizing defect location with He-II second sound wave OST detection, powering multiple modes of the 1.3GHz TM010 passband to locate multiple defects, and corroborating measurements with carbon thermometers will be presented.

• Z.A. Conway, E.P. Chojnacki, D.L. Hartill, M. Liepe, H. Padamsee, A. Romanenko, J. Sears
  CLASSE, Ithaca, New York

Funding: Work Supported by the U.S. Department of Energy

Cornell University’s superconducting niobium nine-elliptical-cell cavity testing and repair program is one contributor to the collaborative effort on critical SRF R&D for the ILC. The Cornell University program benefits from several unique features which provide for the rapid testing and, if necessary, repair of ILC nine-cell cavities: a continuous vertical electropolish procedure, superfluid helium second sound defect location, and tumble polishing. First, we report on the cavity 2K RF performance and the effect of micro-EP preceding the cavity test. Single-cell results at KEK have shown that micro-EP as a final surface treatment reduces the spread in gradients, but micro-EP has not yet been tried with multi-cell cavities. Secondly, we report on the highly efficient method of detecting defects using a few He-II second sound wave detectors and powering several modes of the 1.3GHz TM010 passband.

• Z.A. Conway, E.P. Chojnacki, D.L. Hartill, M. Liepe, D. Meidlinger, H. Padamsee, J. Sears, E.N. Smith
  CLASSE, Ithaca, New York

Funding: Work Supported by the NSF and the DOE

An innovative reentrant cavity design instigated the initial, highly successful, superconducting niobium reentrant-single-cell cavity tests at Cornell and KEK. Prompted by the success of the single cell program a joint effort of Cornell University and Advanced Energy Systems (AES) fabricated two multiple-cell reentrant cavities: a three-cell and a nine-cell cavity. This paper reports the development status of these two cavities. First, the results of cold tests, superfluid helium defect location and repair work on the reentrant nine-cell cavity will be presented. Second, the results of cold tests, including defect location and repair efforts of the reentrant three-cell cavity will be presented.

• N.R.A. Valles, Z.A. Conway, M. Liepe
  CLASSE, Ithaca, New York

The superheating magnetic field of a superconducting niobium 1.3 GHz reentrant cavity was measured at several points in the temperature range from (1.7 to 4.4) K. This experimental data is used to discriminate between two competing theoretical s for the temperature dependent behavior of the RF superheating field. Measurements were made with <250 us high power pulses (HPP, ~1MW) to avoid defect initiated thermal breakdown from contaminating the data. Our test incorporated oscillating superleak transducers to determine the cavity quench locations and characterize changes and the migrations of the quench locations during processing. This information provides insight into the factors which limit the ultimate achievable RF surface magnetic field.

• H. Tian, C.E. Reece
  JLAB, Newport News, Virginia
• M.J. Kelley, H. Tian
  The College of William and Mary, Williamsburg
• G. Ribeill
  North Carolina State University, Raleigh, North Carolina

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

As SRF cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on performance limitations. Micro-and nano-roughness are implicated in direct geometrical field enhancements and complications of the composition of the 50 nm surface layer in which the super-currents flow. Interior surface etching (BCP/EP) to remove mechanical damage leaves surface topography, including pits and protrusions of varying sharpness. These may promote RF magnetic field entry, locally quenching superconductivity, so as to degrade cavity performance. A more incisive analysis of surface topography than the widely-used average roughness is needed. In this study, a power spectral density (PSD) approach based on Fourier analysis of surface topography data acquired by both stylus profilometry and atomic force microscopy (AFM) is being used to distinguish the scale-dependent smoothing effects. The topographical evolution of the varied starting state Nb surface (CBP/ EBW) as a function of applied etching, polishing steps and conditions is reported, resulting in a novel qualitative and quantitative description of Nb surface topography.

• A.T. Wu, G. Ciovati, R. Manus, H.L. Phillips, C.E. Reece, R.A. Rimmer, W. Sommer, H. Tian, J.S. Williams
  JLAB, Newport News, Virginia
• F. Eozénou
  CEA, Gif-sur-Yvette
• S. Jin, L. Lin, X.Y. Lu, E. Wang
  PKU/IHIP, Beijing
• J. Mammosser
  ORNL, Oak Ridge, Tennessee

Funding: Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

A new surface treatment technique for niobium (Nb) Superconducting Radio Frequency (SRF) cavities called Buffered Electropolishing (BEP) has been developed at JLab. It was found that BEP could produce the smoothest surface finish on Nb samples ever reported in the literature. Experimental results revealed that the Nb removal rate of BEP could reach as high as 4.67 μm/min. This is significantly faster* than that of the conventional electropolishing technique employing an acid mixture of HF and H2SO4. An investigation is underway to determine the optimum values for all relevant BEP parameters so that the high quality of surface finish achieved on samples can be realized within the geometry of an elliptical RF cavity. Toward this end, single cell Nb cavities are being electropolished by BEP at both CEA-Saclay and JLAB. These cavities will be RF tested and the results will be reported through this presentation.

*Xiangyang Lu et al, to be published.

• A. Grassellino
  University of Pennsylvania, Philadelphia, Pennsylvania
• K. Fong, R.E. Laxdal, V. Zvyagintsev
  TRIUMF, Vancouver

The quality factor of superconducting radio-frequency cavities typically degrades with increasing field at moderate gradients before the on-set of field emission. The origin of the so called medium field Q-slope is not fully described and understanding it would be important in order to develop a cavity design or treatment which minimizes this effect, allowing us to produce cavities with reduced cryogenic losses. This paper will present an analysis of the medium field Q-slope data measured on cavities at different frequencies treated with buffered chemical polishing (BCP) at TRIUMF. The data is compared with existing models and agreements-discrepancies will be highlighted.

• L.J. Tavian
  CERN, Geneva

Following the incident on a LHC sector due to an electrical arc on the main dipole bus-bar circuit, post-mortem analysis of previous current plateaus has shown abnormal temperature drift in the helium II baths of some magnets in the concerned area. In order to identify other possible risky areas, a detection system based on calorimety using available precision cryogenic thermometers has been first validated by applying calibrated heating in the magnet cold-mass and then implemented in the different sectors. On the 3-km long continuous helium II cryostat of each LHC sector, this method allows detecting abnormal dissipations in the W-range , i.e. additional resistive heating due to abnormal resistance of about 20 nΩ at 7 kA and less than 10 nΩ at nominal current. The paper describes the principle and the methodology of this calorimetric method and gives the results obtained on the LHC sectors.

• F. Marhauser, T.S. Elliott, R.A. Rimmer
  JLAB, Newport News, Virginia

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

In the framework of the ongoing CEBAF 12 GeV upgrade program improvements are being made to refurbish cryomodules housing JLab’s original 5-cell cavities. Recently we have started to look into a possible simplification of the HOM-absorber design combined with the need to find alternative material candidates. The absorbers are implemented in two HOM-waveguides immersed in the helium bath and need to operate at 2K. We therefore have built a cryogenic setup to perform measurements on sample load materials to investigate their lossy characteristics and variations from room temperature down to 2K. Initial results are presented in this paper.

• D.B. Cline, X.P. Ding
  UCLA, Los Angeles, California
• R.C. Gupta
  BNL, Upton, Long Island, New York
• R.J. Weggel
  Particle Beam Lasers, Inc., Northridge

We describe preliminary study of the design of a Muon Collider using 20T Dipole Magnets such a collider could be constructed at FNAL.

• F. Hunte, J. Schwartz, H. Song
  NHMFL, Tallahassee, Florida
• R.P. Johnson, M. Turenne
  Muons, Inc, Batavia

Magnetic confinement fusion reactors (tokamaks) require the development of magnets capable of generating large fields under stringent structural constraints. High temperature superconducting magnets which are well suited to this application are however vulnerable to quench occurrence during operation. Temperature and strain sensors based on fiber optics are being developed as a countermeasure to this contingency. Optical fibers with Bragg gratings are amenable to embedding within superconducting magnets to monitor temperature, strain, irradiation, and to detect quench occurrence. In a length of YBCO tape where quench propagation velocities are slow, we show that it is possible to detect the event occurrence using fiber optic sensors even with a sampling rate as low as 1 Hz. This preliminary result demonstrates the feasibility of using fiber optic sensors to monitor the temperature and strain condition along the length within a coil. These sensors could be used to provide feedback to or trigger magnet protection systems. This would be an invaluable method for mitigating damage to superconducting magnets and increasing up-time for reactors.