The 2.0 GeV, 5 MW proton linac for the European Spallation Source, ESS, will have the capacity to send extra pulses to a neutrino target, giving an excellent opportunity to produce a high performance neutrino beam, the ESS neutrino Super Beam (ESSnuSB). The neutrino target focusing system needs pulses in the order of a few micro-seconds. These short pulses will be produced in an accumulation ring, capable of storing 2.86 ms long linac pulses with 1.1 $10^{15}$ protons in each pulse. One of the main challenges of this accumulator ring is the injection of the particles. The injection method presently used in the design is H- stripping and painting. Some other ideas like lossless, multi-turn and multi-plane injection of protons will also be investigated. The evolution of the beam distribution is studied during accumulation in order to make sure that the beam properties meet the requirements for the extraction region, the transfer line and the target system. Simulation results and plans for future work on the accumulator design in view of the ESSnuSB design report, work partly funded by EU (H2020) are discussed.