  A DC cylindrical magnetron sputtering system has been commissioned and
operated to deposit Nb3Sn onto 2.6 GHz Nb SRF cavities. After optimizing the
deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on
flat samples by multilayer sequential sputtering of Nb and Sn, and later
annealed at 950 {\deg}C for 3 hours. X-ray diffraction of the films showed
multiple peaks for the Nb3Sn phase and Nb (substrate). No peaks from any Nb3Sn
compound other than Nb3Sn were detected. Later three 2.6 GHz Nb SRF cavities
are coated with ~1 $\mu$m thick Nb3Sn. The first Nb3Sn coated cavity reached
close to Eacc = 8 MV/m, demonstrating a quality factor Q0 of 3.2 x 108 at Tbath
= 4.4 K and Eacc = 5 MV/m, about a factor of three higher than that of Nb at
this temperature. Q0 was close to 1.1 x 109, dominated by the residual
resistance, at 2 K and Eacc = 5 MV/m. The Nb3Sn coated cavities demonstrated Tc
in the range of 17.9 - 18 K. Here we present the commissioning experience,
system optimization, and the first results from the Nb3Sn fabrication on flat
samples and SRF cavities.
