A short-period in-vacuum undulator for the NSLS X-ray Ring has been de
veloped in a collaboration between SPring-8 and the NSLS, and has achi
eved its project design goals during commissioning studies. The device
is called IVUN (in-vacuum undulator) and employs magnet arrays (31 pe
riods, with an 11 mm period) developed at SPring-8, while the requisit
e vacuum chamber and mechanical systems were developed at the NSLS. At
a magnet gap of 3.3 mm, IVUN produces 4.6 keV radiation in the fundam
ental, with useful photon fluxes in both the second and third harmonic
s. The magnet gap is adjustable between 2 and 10 mm. A brief overview
of IVUN is presented, together with initial commissioning results: the
dependence of electron-beam lifetime and bremsstrahlung on magnet gap
, and the output radiation spectrum.