Commissioning of RHIC p-carbon CNI polarimeter.

An innovative polarimeter based on proton carbon elastic scattering in the Coulomb Nuclear Interference (CNI) region has been installed and commissioned in the Blue ring of RHIC during the first RHIC polarized proton commissioning. The polarimeter consists of ultra-thin carbon targets and four silicon detectors. All elements are in a 1.6 meter target chamber. It worked very well as a pivotal tool during the commissioning. It demonstrated that the RHIC snake magnets rotate spin to the expected direction. The results also show that polarized proton beam has been accelerated in RHIC and the polarization is maintained up to 29 GeV.