A 29.2 GHz electron cyclotron resonance-primary proton source for the relativistic heavy ion collider optically pumped polarized H- ion source

A 29.2 GHz dc electron cyclotron resonance (ECR) source produces a primary proton beam in the relativistic heavy ion collider (RHIC) optically pumped polarized H- ion source. A proton beam of a 50-100 mA is extracted from the ECR plasma at 2.0-3.0 keV energy by a 121-hole, three-grid ion extraction system. Polarized beam injection to RHIC requires only 300-500 μs pulses at 0.2-6 2/3 Hz repetition rate. Pulsed source operation was studied and resulted in a significant current increase at greatly reduced average microwave power and hydrogen gas consumption. A molecular H2+ ion beam component out of the ECR source might cause polarization dilution, when H20 molecular beam is dissociated in the sodium ionizer cell with the production of H- ions (having half the energy of the main component) with lower polarization. Admixture of oxygen gas reduces the H2+ beam component. A reduction to less than 5% was observed also in pulsed ECR operation. As a result of the ECR-source optimization, the RHIC optically pumped polarized H+ ion source intensity was increased up to 0.5-1.0 mA at routine operation (maximum current 1.5 mA). A polarization of 80% was measured in a 200 MeV polarimeter