Challenges and 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, interleaved with the proton pulses for neutron production, and send them to a neutrino target, providing an excellent opportunity to produce an unprecedented high- performance neutrino beam, the ESS neutrino Super Beam (ESSnuSB), to measure, with precision, the CP violating phase at the 2nd oscillation maximum. In order to comply with the acceptance of the target and horn systems that will form 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 in an accumulator ring. This ring will accommodate about 1015 protons, which means that several design challenges are encountered. Strong space charge forces, low-loss injection, efficient collimation, and e-p instabilities are some of the aspects central to the design work. Different pulse structures and injection painting schemes have been studied, with the goal of mitigating space charge effects and of minimizing the heating of the stripping foil despite the very high beam intensity. This paper presents the status of the accumulator ring design, with multi- particle simulations of the injection procedure