Physics-driven specifications for the EIC ESR magnet power supply ripple

To avoid unacceptable proton emittance growth via beam-beam interaction, the EIC electron storage ring (ESR) requires very stringent tolerances for beam position and size stability at the interaction point. These tolerances imply tight specifications for several accelerator systems, including magnet power supplies (PS). While the magnetic field ripple requirements are most stringent at the betatron frequency and harmonics, the main PS challenges occur below ~1 kHz, where the ripple attenuation due to the vacuum chamber is insufficient. In the original ESR dipole powering scheme with ~20 families, the dipole PS current ripple specifications were found to be near or beyond the state-of-the-art. A recently adopted scheme with a single ESR main dipole PS relaxes these requirements to ~10 parts per million (ppm) rms, which is achievable. Additionally, the vacuum chambers of non-standard cross-sections required at some dipoles must be modified to match the field penetration time constant to that of the standard vacuum chamber. The paper presents the physics reasoning and simulations behind the latest PS ripple specifications, ranging from 5 to 100 ppm rms, depending on the magnet type.