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Kuchnir, M.

Paper Title Page
MOPAN118 High Field HTS Solenoid for Muon Cooling 446
  • S. A. Kahn, M. Alsharo'a, R. P. Johnson, M. Kuchnir
    Muons, Inc, Batavia
  • R. C. Gupta, R. B. Palmer, P. Wanderer, E. Willen
    BNL, Upton, Long Island, New York
  • D. J. Summers
    UMiss, University, Mississippi
  Funding: Work supported by U. S. Department of Energy under Contract DE-AC02-98CH1088 and SBIR Grant DE-FG02-04ER86191

The ability of high temperature superconducting (HTS) conductor to carry high currents at low temperatures makes feasible the development of very high field magnets for uses in accelerators and beam-lines. A specific application of a very high field solenoid is to provide a very small beta region for the final cooling stages for a muon collider. This paper will describe a conceptual design of a 50 Tesla solenoid based on Bi-2223 HTS tape, where the magnet will be operated at 4.2 K to take advantage of the high current carrying capacity at that temperature. A 25 Tesla solenoid has been run using a 5 Tesla Bi-2212 insert. The current carrying capacity of the BSCCO wire has been measured to be 266 Amps/mm2 at 4.2 K at the NHFML. This paper will describe the technical issues associated with building this 50 Tesla magnet. In particular it will address how to mitigate the large Lorentz stresses associated with the high field magnet and how to design the magnet to reduce the compressive end forces.

  • M. BastaniNejad, A. A. Elmustafa
    Old Dominion University, Norfolk, Virginia
  • M. Alsharo'a, P. M. Hanlet, R. P. Johnson, M. Kuchnir, D. J. Newsham
    Muons, Inc, Batavia
  • C. M. Ankenbrandt, A. Moretti, M. Popovic, K. Yonehara
    Fermilab, Batavia, Illinois
  • D. M. Kaplan
    Illinois Institute of Technology, Chicago, Illinois
  Funding: Supported in part by DOE STTR grant DE-FG02-05ER86252

Microscopic images of the surfaces of metallic electrodes used in high-pressure gas-filled 800 MHz RF cavity experiments are used to investigate the mechanism of RF breakdown. The images show evidence for melting and boiling in small regions of ~10 micron diameter on tungsten, molybdenum, and beryllium electrode surfaces. In these experiments, the dense hydrogen gas in the cavity prevents electrons or ions from being accelerated to high enough energy to participate in the breakdown process so that the only important variables are the fields and the metallic surfaces. The distributions of breakdown remnants on the electrode surfaces are compared to the maximum surface gradient E predicted by an ANSYS model of the cavity. The surface local density of spark remnants, presumably the probability of breakdown, shows a power law dependence on the maximum gradient, with E10 for tungsten and molybdenum and E7 for beryllium. This is reminiscent of Fowler-Nordheim behavior of electron emission from a cold cathode, which is explained by the quantum-mechanical penetration of a barrier that is characterized by the work function of the metal.