THE EUROPEAN SPALLATION SOURCE

The 5 MW European Spallation Source (ESS) – to be built in Lund, Sweden – is typical of the generation of mulit-MW superconducting proton linacs currently under design and discussion. The Accelerator Design Update (ADU) collaboration of mainly European institutions will deliver a Technical Design Report at the end of 2012. First protons are expected in 2018, and first neutrons in 2019. HIGH POWER SPALLATION LINACS Spallation is the nuclear process that emits neutrons at a spectrum of energies after highly energetic particles bom-bard heavy nuclei – for example, when the ESS proton beam strikes a liquid heavy-metal or rotating disk target. These neutrons are cooled in moderators adjacent to the target, before exiting target ports to be transported through neutron guides to experimental instruments [1]. Long Pulses Pulsed neutron sources like the Spallation Neutron Source (SNS) and the ESS are more efficient than continu-ous sources, in a majority of applications [2]. The neutron time-of-flight, and therefore the neutron energy, are read-ily measured at a pulsed source. Unlike the SNS, the ESS does not need an accumulator (compressor) ring [3]; the ESS macro-pulse length is 2.0 ms rather than ∼1 µs. In addition to the advantage of eliminating the ring, a “long pulse ” implementation permits H+ operation, and main-tains relatively low currents in all beamilines. High leve