A first order matched transition jump at RHIC

RHIC, the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, will be the first superconducting accelerator to cross transition, when ramping begins in 1998. All ion species except for protons will cross transition. Simulations show gold ion losses of 70%, and longitudinal emittance growth of 60%, if nothing is done to ameliorate the crossing. RHIC will also be the first accelerator to use a matched first order transition jump to modify γ_T for a short time, by pulsing a set of quadrupoles, so as to cross transition rapidly, with little beam disturbance. “First order” means that the change in γ_T is proportional to the pulse current. “Matched” means that the quadrupole arrangement minimizes optical distortions. Crucially, the maximum dispersion is only 2.30 meters, compared to the unperturbed value of 1.84 meters. This paper describes the transition jump design, and reports on its performance in the lattice RHIC92.3