Magnesium diboride (MgB2) is attractive for RF cavityapplication for particle accelerators because it might not show an increaseof RF surface losses at high magnetic surface fields, a phenomenon that hasprevented high-Tc superconducting materials such as YBCO from beingused for this application. We have measured the RF surface resistance (Rs)at 21 GHz of a MgB2 sample fabricated using Hot Isostatic Press (HIP) at200 Mpa and 1000 °C. The results show that polishing with 0.1-microndiamond lapping film followed by a 1500-psi DI water rinse in a clean roomreduced the Rs by a factor of 6.2 at 15 K and it is the lowest compared toother published data. The Rs data near the lowest temperature (~13 K)scatter between 0.6 and 1.3 mΩ. The penetration depth λ(0) and energy gap2 /kBTc were estimated to be 263 nm and 1.9-2.7, respectively, for thepolished surface.
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