The ESS will have the capacity to offer an additional 5 MW of beam power, which provides an excellent opportunity to produce an unprecedented high performance neutrino beam that intends to measure, with precision, the charge-parity (CP) violating lepton phase at the 2nd oscillation maximum. In order to comply with the neutrino target and horn systems, each long pulse from the ESS linac must be split into 4 sub-pulses and compressed up to three orders of magnitude before impinging on the target. A chopping system will be adopted in the linac to split the pulses while an accumulator ring will be used to compress the pulses from the linac. Multi-turn charge-exchange injection to the accumulator will be adopted since it allows high beam intensity injection with minimal beam loss. Several challenges of the accumulator ring design are encountered, such as low-loss beam injection, a reliable charge stripping system, a set of collimation system with high efficiency, and e-p instabilities. This paper focuses on the accumulator ring design, with numerical simulations of the injection procedure.