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Nantista, C. D.

Paper Title Page
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.

WEPMS018 Superconducting Materials Testing with a High-Q Copper RF Cavity 2370
  • A. Canabal, T. Tajima
    LANL, Los Alamos, New Mexico
  • G. B. Bowden, V. A. Dolgashev, J. R. Lewandowski, C. D. Nantista, S. G. Tantawi
    SLAC, Menlo Park, California
  • I. E. Campisi
    ORNL, Oak Ridge, Tennessee
  Magnesium diboride (MgB2) has a transition temperature (Tc) of ~40 K, i.e., about 4 times higher than niobium (Nb) that has been used for recent accelerators. The studies in the last 3 years have shown that it could have about one order of magnitude less RF surface resistance (Rs) than Nb and much less power dependence compared to high-Tc materials such as YBCO up to ~400 Oe. The tests to check the RF critical magnetic field, an important parameter to determine the feasibility for accelerator application, are underway. We are planning to test different thickness films and with different coating methods. This paper describes the results obtained so far. One of the objectives is to verify Gurevich's theory of getting higher critical field than Nb by adding a very thin layer (less than penetration depth) to Nb. In addition, some CW tests on power dependence up to higher magnetic fields are planned and some results will be shown if available at the time of conference.  
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.

WEPMS039 High Power Tests of Normal Conducting Single-Cell Structures 2430
  • V. A. Dolgashev, C. D. Nantista, S. G. Tantawi
    SLAC, Menlo Park, California
  • Y. Higashi, T. Higo
    KEK, Ibaraki
  Funding: This work was supported by the U. S. Department of Energy contract DE-AC02-76SF00515.

We report results of the first high power tests of single-cell traveling-wave and standing-wave accelerating structures. These tests are part of an experimental and theoretical study of RF breakdown in normal conducting structures at 11.4 GHz*. The goal of this study is to determine the gradient potential of normal conducting, RF powered particle beam accelerators. The test setup consists of reusable mode converters and short test structures powered by SLAC?s XL-4 klystron. This setup was created for economic testing of different cell geometries, cell materials and preparation techniques with short turn-around time. The mode launchers and structures were manufactured at SLAC and KEK and tested in the klystron test laboratory at SLAC.

* V. A. Dolgashev et al., "RF Breakdown In Normal Conducting Single-Cell Structures," SLAC-PUB-11707, Particle Accelerator Conference (PAC 05), Knoxville, Tennessee, 16-20 May 2005, pp. 595- 599.

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.

THPMS096 Development of a Dielectric-Loaded Test Accelerator 3211
  • S. H. Gold
    NRL, Washington, DC
  • W. Gai, R. Konecny, J. Long, J. G. Power
    ANL, Argonne, Illinois
  • C.-J. Jing
    Euclid TechLabs, LLC, Solon, Ohio
  • A. K. Kinkead
  • C. D. Nantista, S. G. Tantawi
    SLAC, Menlo Park, California
  Funding: Work supported by DoE and ONR.

A joint project is underway by the Naval Research Laboratory (NRL) and Argonne National Laboratory (ANL), in collaboration with the Stanford Linear Accelerator Center (SLAC), to develop a compact X-band accelerator for testing dielectric-loaded accelerator (DLA) structures.* The accelerator will use a 5-MeV injector previously developed by the Tsinghua University in Beijing, China, and will accommodate test structures up to 0.5 m in length. Both the injector and the structures will be powered by an 11.4-GHz magnicon amplifier that can produce 25 MW, 200-ns output pulses at up to 10 Hz. The injector will require ~5 MW of rf power, leaving ~20 MW to power the test structures. This paper will present a progress report on the construction and commissioning of the test accelerator, which will be located in a concrete bunker in the Magnicon Facility at NRL.

* S. H. Gold et al., Proc. PAC 2005.