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Applied Physics Letters / Volume 89 / Issue 2 / MAGNETISM AND SUPERCONDUCTIVITY

Appl. Phys. Lett. 89, 022507 (2006); http://dx.doi.org/10.1063/1.2220059 (3 pages)

Improved oxygen diffusion model to explain the effect of low-temperature baking on high field losses in niobium superconducting cavities

Gianluigi Ciovati

Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 and Department of Physics, Old Dominion University, Norfolk, Virginia 23529

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(Received 18 August 2005; accepted 1 June 2006; published online 13 July 2006)

Radio-frequency (rf) superconducting cavities made of high purity niobium are widely used to accelerate charged particle beams in particle accelerators. The major limitation to achieve rf field values approaching the theoretical limit for niobium is represented by “anomalous” losses which degrade the quality factor of the cavities starting at peak surface magnetic fields of about 100 mT, in the absence of field emission. These high field losses are often referred to as Q drop. It has been observed that the Q drop is drastically reduced by baking the cavities at 120 °C for about 48 h under ultrahigh vacuum. An improved oxygen diffusion model for the niobium-oxide system is proposed to explain the benefit of the low-temperature baking on the Q drop in niobium superconducting rf cavities. The model shows that baking at 120 °C for 48 h allows oxygen to diffuse away from the surface, and therefore increasing the lower critical field towards the value for pure niobium.

© 2006 American Institute of Physics

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KEYWORDS and PACS

Keywords

niobium, type II superconductors, diffusion, heat treatment, surface magnetism, superconducting critical field, eddy current losses

PACS

  • 74.70.Ad

    Metals; alloys and binary compounds (including A15, MgB2, etc.)

  • 74.25.F-

    Transport properties

  • 74.25.Ha

    Magnetic properties including vortex structures and related phenomena

  • 74.25.Op

    Mixed states, critical fields, and surface sheaths

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.2220059

PUBLICATION DATA

ISSN

0003-6951 (print)  
1077-3118 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

For access to fully linked references, you need to log in.
    Q. Ma, P. Ryan, J. W. Freeland, and R. A. Rosenberg, J. Appl. Phys. 96, 7675 (2004)JAPIAU000096000012007675000001.

    G. Ciovati, J. Appl. Phys. 96, 1591 (2004)JAPIAU000096000003001591000001.

    I. Arfaoui, C. Guillot, J. Cousty, and C. Antoine, J. Appl. Phys. 91, 9319 (2002)JAPIAU000091000011009319000001.

    R. D. Blois and W. de Sorbo, Phys. Rev. Lett. 12, 499 (1964).


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