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Adolphsen, C.

Paper Title Page
WEPMN070 High Power Test of an X-band Slotted-Iris Accelerator Structure at NLCTA 2191
  • S. Doebert, R. Fandos, A. Grudiev, S. T. Heikkinen, J. A. Rodriguez, M. Taborelli, W. Wuensch
    CERN, Geneva
  • C. Adolphsen, L. Laurent
    SLAC, Menlo Park, California
  The CLIC study group at CERN has built two X-band HDS (Hybrid Damped Structure) accelerating structures for high-power testing in NLCTA at SLAC. These accelerating structures are novel with respect to their rf-design and their fabrication technique. The eleven-cell constant impedance structures, one made out of copper and one out of molybdenum, are assembled from clamped high-speed milled quadrants. They feature the same heavy higher-order-mode damping as nominal CLIC structures achieved by slotted irises and radial damping waveguides for each cell. The X-band accelerators are exactly scaled versions of structures tested at 30 GHz in the CLIC test facility, CTF3. The results of the X-band tests are presented and compared to those at 30 GHz to determine frequency scaling, and are compared to the extensive copper data from the NLC structure development program to determine material dependence and make a basic validation of the HDS design.  
WEPMS017 High-Power Coupler Component Test Stand Status and Results 2367
  • B. Rusnak
    LLNL, Livermore, California
  • C. Adolphsen, G. B. Bowden, L. Ge, R. K. Jobe, Z. Li, B. D. McKee, C. D. Nantista, J. Tice, F. Wang
    SLAC, Menlo Park, California
  • R. Swent
    Stanford University, Stanford, Califormia
  Funding: This work was performed under the auspices of the U. S. DOE by the University of California, LLNL under Contract No. W-7405-Eng-48. SLAC Work supported under Contract No. W-7405-Eng-48.

Fundamental power couplers for superconducting accelerator applications like the ILC are complicated RF transmission line assemblies due to their having to simultaneously accommodate demanding RF power, cryogenic, and cleanliness constraints. When these couplers are RF conditioned, the observed response is an aggregate of all the parts of the coupler and the specific features that dominate the conditioning response are unknown. To better understand and characterize RF conditioning phenomena toward improving performance and reducing conditioning time, a high-power coupler component test stand has been built at SLAC. Operating at 1.3 GHz, this test stand was designed to measure the conditioning behavior of select components of the TTFIII coupler independently, including outer-conductor bellows, diameter changes, copper plating and surface preparations, and cold window geometries and coatings. A description of the test stand, the measurement approach, and a summary of the results obtained are presented.

WEPMS028 Converter-Modulator Design and Operations for the ILC L-band Test Stand 2397
  • W. Reass
    LANL, Los Alamos, New Mexico
  • C. Adolphsen, T. G. Beukers, C. Burkhart, R. L. Cassel, M. N. Nguyen, G. C. Pappas, R. Swent, A. C. de Lira
    SLAC, Menlo Park, California
  • D. E. Anderson
    ORNL, Oak Ridge, Tennessee
  Funding: This work supported by Stanford Linear Accelerator Center, Oak Ridge National Laboratory, and the Department of Energy.

To facilitate a rapid response to the International Linear Collider (ILC) L-Band development program at SLAC, a spare converter-modulator was shipped from Los Alamos. This modulator was to be a spare for the Spallation Neutron Source (SNS) accelerator at ORNL. The ILC application requires a 33% higher peak output power (15 MW) and output current (130 Amp). This presents significant design challenges to modify the existing hardware and yet maintain switching parameters and thermal cycling within the semiconductor component ratings. To minimize IGBT commutation and free-wheeling diode currents, a different set of optimizations, as compared to the SNS design, were used to tune the resonant switching networks. Additional complexities arose as nanocrystalline cores with different performance characteristics (as compared to SNS), were used to fabricate the resonant "boost" transformers. This paper will describe the electrical design, system modifications, modeling efforts, and resulting electrical performance as implemented for the ILC L-band test stand.

WEPMS037 RF Distribution Optimization in the Main Linacs of the ILC 2424
  • K. L.F. Bane, C. Adolphsen, C. D. Nantista
    SLAC, Menlo Park, California
  Funding: Work supported by the U. S. Department of Energy under contract DE-AC02-76SF00515.

The nominal design gradient for the ILC is 31.5 MV/m, but the L-band superconducting cavities built to date have demonstrated a range in sustainable gradient extending below this goal, limited by Q-dropoff and quenching. An economically feasible cavity acceptance rate will include in the linacs a certain percentage of sub-performing cavities. We examine how, with a customizable RF distribution scheme, one can most efficiently distribute power from one klystron amongst 24 nine-cell cavities. The nominal cavity fills to the design gradient at the time the beam arrives, after which the beamloading voltage exactly cancels any further rise, yielding constant gradient during the bunch train. Along with adjustable RF power, we assume adjustable cavity coupling, or loaded quality factor, so that the gradient can be leveled in non-nominal cavities, to avoid quench-inducing overshoots. We explore these and related issues for the ILC linac high-power RF.

WEPMS041 Multipacting Simulations of TTF-III Coupler Components 2436
  • L. Ge, C. Adolphsen, K. Ko, L. Lee, Z. Li, C.-K. Ng, G. L. Schussman, F. Wang
    SLAC, Menlo Park, California
  • B. Rusnak
    LLNL, Livermore, California
  Funding: This work was supported by US DOE contract No. DE-AC02-76SF00515. This work was performed under the auspices of the US DOE by the University of California, LLNL under Contract No. W-7405-Eng-48.

The TTF-III coupler adopted for the ILC baseline cavity design has shown a tendency to have long initial high power processing times. A possible cause for the long processing times is believed to be multipacting in various regions of the coupler. To understand performance limitations during high power processing, SLAC has built a flexible high-power coupler test stand. The plan is to test individual sections of the coupler, which includes the cold and warm coaxes, the cold and warm bellows, and the cold window, using the test stand to identify problematic regions. To provide insights for the high power test, detailed numerical simulations of multipacting for these sections will be performed using the 3D multipacting code Track3P. The simulation results will be compared with measurement data.

WEPMS043 An RF Waveguide Distribution System for the ILC Test Accelerator at NML 2442
  • C. D. Nantista, C. Adolphsen, G. B. Bowden, B. D. McKee, R. Swent
    SLAC, Menlo Park, California
  Funding: Work supported by the U. S. Department of Energy under contract DE-AC02-76SF00515.

An ILC R&D facility is being constructed in the NML building at Fermilab which, in addition to an injector and beam dump with spectrometer, will contain up to three cryomodules worth of ILC-type superconducting 9-cell cavities, 24 in all. This linac will be powered by a single klystron. As part of SLAC?s contribution to this project, we will provide a distribution network in WR650 waveguide to the various cavity couplers. In addition to commercial waveguide components and circulators and loads developed for TESLA, this sytem will include adjustable tap-offs, and customized hybrids. In one configuration, the circulators will be removed to test pair-wise cancellation of cavity reflections through hybrids. The system will be pressurized with nitrogen to 3 bar absolute to avoid the need for SF6 at windows or circulator. The full distribution for the first cryomodule will be delivered and installed later this year. We describe the design of the system and completed RF testing.

WEPMS048 Modelling Imperfection Effects on Dipole Modes in TESLA Cavity 2454
  • L. Xiao, C. Adolphsen, V. Akcelik, A. C. Kabel, K. Ko, L. Lee, Z. Li, C.-K. Ng
    SLAC, Menlo Park, California
  Funding: Work supported by DOE contract DE-AC02-76SF00515

The actual cell shape of the TESLA cavities differ from the ideal due to fabrication errors, the addition of stiffening rings and the frequency tuning process. Cavity imperfection shift the dipole mode frequencies and alter the Qext's from those computed for the idea cavity. A Qext increase could be problematic if its value exceeds the limit required for ILC beam stability. To study these effects, a cavity imperfection model was established using a mesh distortion method. The eigensolver Omega3P was then used to find the critical dimensions that contribute to the Qext spread and frequency shift by comparing predictions to TESLA cavity measurement data. Using the imperfection parameters obtained from these studies, artificial imperfection models were generated and the resulting wakefields were used as input to the beam tracking code Lucretia to study the effect on beam emittance. In this paper, we present the results of these studies and suggest tolerances for the cavity dimensions.

THPMS049 Investigations of the Wideband Spectrum of Higher Order Modes Measured on TESLA-style Cavities at the FLASH Linac 3100
  • S. Molloy, C. Adolphsen, K. L.F. Bane, J. C. Frisch, Z. Li, J. May, D. J. McCormick, T. J. Smith
    SLAC, Menlo Park, California
  • N. Baboi
    DESY, Hamburg
  • N. E. Eddy, L. Piccoli, R. Rechenmacher
    Fermilab, Batavia, Illinois
  • R. M. Jones
    UMAN, Manchester
  Funding: US DOE Contract #DE-AC02-76SF00515

Higher Order Modes (HOMs) excited by the passage of the beam through an accelerating cavity depend on the properties of both the cavity and the beam. It is possible, therefore, to draw conclusions on the inner geometry of the cavities based on observations of the properties of the HOM spectrum. A data acquisition system based on two 20 GS/s, 6 GHz scopes has been set up at the FLASH facility, DESY, in order to measure a significant fraction of the HOM spectrum predicted to be generated by the TESLA cavities used for the acceleration of its beam. The HOMs from a particular cavity at FLASH were measured under a range of known beam conditions. The dipole modes have been identified in the data. 3D simulations of different manufacturing errors have been made, and it has been shown that these simulations can predict the measured modes.

FRYC01 ILC RF System R&D 3813
  • C. Adolphsen
    SLAC, Menlo Park, California
  Funding: Work Supported by DOE Contract DE-AC02-76F00515

The ILC Linac Group at SLAC is actively pursuing a broad range of R&D to improve the reliability and reduce the cost of the L-band (1.3 GHz) rf system and normal-conducting accelerators. Current activities include the development of a Marx-style modulator and a 10 MW sheet-beam klystron, operation of an L-band (1.3 GHz) rf source using an SNS HVCM modulator and commercial klystron, construction of an rf distribution system with adjustable power tap-offs and custom hybrids, tests of cavity coupler components to understand rf processing limitations, simulation of multipacting in the couplers, optimization of the cavity fill parameters for operation with a large spread in sustainable cavity gradients and operation of a 5-cell prototype positron capture cavity. This paper surveys the results from the past year and reviews L-band R&D at other labs, in particular, that at DESY for the XFEL project.

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FRPMN090 A Prototype Energy Spectrometer for the ILC at End Station A in SLAC 4285
  • A. Lyapin, F. Gournaris, B. Maiheu, D. J. Miller, M. Wing
    UCL, London
  • C. Adolphsen, R. Arnold, C. Hast, D. J. McCormick, Z. M. Szalata, M. Woods
    SLAC, Menlo Park, California
  • S. T. Boogert, G. E. Boorman
    Royal Holloway, University of London, Surrey
  • M. V. Chistiakova, Yu. G. Kolomensky, E. Petigura, M. Sadre-Bazzaz
    UCB, Berkeley, California
  • V. N. Duginov, S. A. Kostromin, N. A. Morozov
    JINR, Dubna, Moscow Region
  • M. Hildreth
    Notre Dame University, Notre Dame, Iowa
  • H. J. Schreiber, M. Viti
    DESY Zeuthen, Zeuthen
  • M. Slater, M. Thomson, D. R. Ward
    University of Cambridge, Cambridge
  The main physics programme of the international linear collider requires a measurement of the beam energy with a relative precision on the order of 10-4 or better. To achieve this goal a magnetic spectrometer using high resolution beam position monitors (BPM) has been proposed. A prototype spectrometer chicane using 4 dipole magnets is currently under development at the End Station A in SLAC, intending to demonstrate the required stability of this method and investigate possible systematic effects and operational issues. This contribution reports on the successful commissioning of the beam position monitor system and the resolution and stability achieved. Also, the initial results from a run with a full spectrometer chicane are presented.