Status of the ESSnuSB accumulator design

The 2.0 GeV, 5 MW proton linac for the European Spallation Source, ESS, will have the capacity to accelerate additional pulses and send them to a neutrino target, providing an excellent opportunity to produce an unprecedented high performance neutrino beam. The ESS neutrino Super Beam intends to measure, with precision, the charge-parity (CP) violating lepton phase at the 2nd oscillation maximum. In order to comply with the acceptance of the target and horn systems that will produce the neutrino super beam, the long pulses from the linac must be compressed by about three orders of magnitude with minimal particle loss, something that will be achieved through multi-turn charge-exchange injection in an accumulator ring, which should be able to accommodate over $2 \times 10^{14}$ protons. Several design challenges are encountered, such as strong space charge forces, low-loss injection with phase space painting, a reliable charge stripping system, efficient collimation, and e-p instabilities. This paper focuses on the status of the accumulator ring design, with multi-particle simulations of the injections procedure.