BNL, Upton, Long Island, New York, USA
There is a strong interest in running RHIC at low ion beam energies of 7.7-20 GeV/nucleon [1]; this is much lower than the typical operations with 100 GeV/nucleon. The primary motivation for this effort is to explore the existence and location of the critical point on the QCD phase diagram. Electron cooling can increase the average integrated luminosity and increase the length of the stored lifetime. A cooling system is being designed that will provide a 30 – 50 mA electron beam with adequate quality and an energy range of 1.6 – 5 MeV. The cooling facility is planned to be inside the RHIC tunnel. The injector will include a 704 MHz SRF gun, a 704 MHz 5-cell SRF cavity followed by a normal conducting 2.1 GHz cavity. Electrons from the injector will be transported to the Yellow RHIC ring to allow electron-ion co-propagation for ~20 m, then a 180 degree U-turn electron transport so the same electron beam can similarly cool the Blue ion beam. After the cooling process with electron beam energies of 1.6 to 2 MeV, the electrons will be transported directly to a dump. When cooling with higher energy electrons between 2 and 5 MeV, after the cooling process, they will be routed through the acceleration cavity again to allow energy recovery and less power deposited in the dump. Special consideration is given to ensure overlap of electron and ion beams in the cooling section and achieving the requirements needed for cooling. The instrumentation systems described will include current transformers, beam position monitors, profile monitors, an emittance slit station, recombination and beam loss monitors.
BNL, Upton, Long Island, New York, USA
The electron lenses installed in RHIC are equipped with two independent transverse beam profiling systems, namely the Pinhole Detector and YAG screen. A small Faraday cup, with a 0.2mm pinhole mask, intercepts the electron beam while a pre-programmed routine automatically raster scans the beam across the detector face. The collected charge is integrated, digitized and stored in an image type data file that represents the electron beam density. This plungeable detector shares space in the vacuum chamber with a plunging YAG:Ce crystal coated with aluminum. A view port at the downstream extremity of the Collector allows a GigE camera, fitted with a zoom lens, to image the crystal and digitize the profile of a beam pulse. Custom beam profiling software has been written to import both beam image files (pinhole and YAG) and fully characterize the transverse beam profile. The results of these profile measurements are presented here along with a description of the system and operational features.
* W. Fischer, et al, "… head-on beam-beam compensation in RHIC", ICFA (BB3013), CERN (2013).
**T. Miller, et al, “… eLens pin-hole detector and YAG…“, BIW2012, Newport News, VA, TUPG039
BNL, Upton, Long Island, New York, USA
The Relativistic Heavy Ion Collider (RHIC) electron lenses, being commissioned to attain higher polarized proton-proton luminosities by partially compensating the beam-beam effect, require good alignment of the electron and proton beams. These beams propagating in opposite directions in a 5T solenoid have a typical rms width of 300 microns and need to overlap each other over an interaction length of about 2 m with deviations of less than ~50 microns. A new beam diagnostic tool to achieve and maintain this alignment is based on detecting electrons that are backscattered in close encounters with protons. Maximizing the intensity of these electrons ensures optimum beam overlap. The successful commissioning of these devices using 100 GeV/amu gold beams is described. Future developments are discussed that will further improve the sensitivity to small angular deviations.