Accelerator Design Progress for the Future Electron-Ion Collider at Brookhaven National Laboratory

The Electron-Ion Collider (EIC), which is currently being designed for construction at Brookhaven National Laboratory, will collide polarized electron beams (5-18 GeV) with polarized hadron beams of protons (41-275 GeV) or nuclei ranging from light ions (d, He) to heavy ions (e.g. Au, U) at luminosities up to 10³⁴ cm⁻² s⁻¹. The only lepton-hadron collider since HERA at DESY, the EIC combines high polarization of both beams, a wide center-of-mass energy coverage, diverse ion species, and substantially higher luminosities. These properties will make it an ideal machine for exploring the mass and spin dynamics of nucleons. Recently, the design of the accelerators has matured considerably with a number of key design decisions taken to advance the project and reduce risk. These include locating the rapid cycling synchrotron, which serves as the injector to the electron storage ring, in a new tunnel, and planning for a phased ramp-up to full energy and luminosity. The 3.8-kilometer electron and hadron rings are now at a high maturity level, both in terms of overall design and the design of individual components and systems. In this talk I will outline the status of the accelerator design, focusing on the electron storage ring, and highlight some important recent developments and design decisions.