Design of the Transferline to the ESS Target and Beam Dump at Reduced Beam Energy

The European Spallation Source (ESS) linac transfer-lines to the target and beam dump are designed for the 2 GeV beam energy. The commissioning and operation of the accelerator will start at a reduced energy of 571 MeV with the high beta part of the linac unpowered. The beam power at this energy is still above 1 MW and a proper transport from the last accelerating cavity to the target is essential. Beam dynamics design of the High Energy Beam Transport (HEBT) and Accelerator to Target (A2T) are studied based on this reduced energy in this paper, including phase advance optimization and rematch. Among the factors which are analyzed are the envelope and beam size on the target which are kept close to their values at 2 GeV and losses along the linac and the transfer lines.