The Relativistic Heavy Ion Collider (RHIC) was designed for head-on collisions in the Interaction Regions. However, RHIC operation in recent years necessitated crossing angles to limit collisions to a narrow longitudinal vertex region, which created operating conditions with a large Piwinski angle (LPA). The angles were implemented by adjusting the shunt currents of four dipoles, the D0 and DX magnets, near the IP. The longitudinal bunch profile often deviates from Gaussian due to the utilization of high-order RF cavities, adding complexity to calculating luminosity reduction with crossing angle. This paper introduces two methods for implementing crossing angles, discusses resultant aperture concerns, conducts numerical calculations of luminosity reduction, and compares these findings with experimental observations.

For the 2024 100 GeV proton run at RHIC, the new sPHENIX detector will require a maximum amount of collisions within ±10 cm of its central Interaction Point (IP), and preferably few or no collisions outside this range. To maximize the collisions within the vertex, a large crossing angle of up to 2 mrad will be used, operating the Large Piwinski Angle (LPA) scheme. To compensate for the reduction in luminosity from the large Piwinski angle, a β=50 cm lattice has been designed and supported with dynamic aperture simulations. To further compensate the luminosity reduction, injector studies have been performed to support up to a 45% increase in the injected intensity relative to the previous 100 GeV run in 2015.1

The Relativistic Heavy Ion Collider (RHIC) Run 23 program consisted of collisions of 100 GeV gold beams at two collision points for the first time since 2016; the sPHENIX collaboration used the beam to commission their new detector systems while STAR took physics data. Completion of sPHENIX construction pushed the start of the run to May, forcing the collider complex to operate over the summer months and incurring lower than normal availability due to heat and power dip related problems. Issues with dynamic pressure rise during acceleration through transition resulted in a slower ramp up of intensity compared to prior years. Finally, a failure of a warm-to-cold current lead interface in the valve box for the Main Magnet power supply forced the run to end. This paper will discuss the progress made by each experiment and the failure mode, repair and mitigation efforts in preparation for Run 24.