Recent developments in the production of carbon micro-ribbons for CNI polarimeters at BNL

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is the only collider in the world to collide polarized protons. In order to maximize the polarization of the proton beam in RHIC, it is critical that the polarization is measured during the acceleration process. This is accomplished with Coulomb nuclear interference (CNI) polarimeters in the Alternating Gradient Synchrotron (AGS) and RHIC. The targets for the CNI polarimeters are carbon micro-ribbons that are optimized in width for the detectors. The targets used in the AGS CNI polarimeter are 4 μg/cm2 thick (25–30 nm) and 50 mm long. The width of these targets is either 75, 125 or 250 μm. The targets used in the RHIC CNI polarimeter are the same thickness but only 25 mm long and <10 μm wide. As the beam intensity in RHIC has increased and the beam size has decreased, the lifetime of these targets has become a major issue. Efforts are underway to reduce the resistance of the targets in the hope that it will extend their lifetime. There have also been demands for unique target geometries. The technique to produce 5 mm wide targets and twisted carbon micro-ribbons is discussed.