The Drift Tube Linac (DTL) for the ESS Linac will accelerate H+ beams of up to 62.5 mA peak current from 3.62 to 90 MeV. The structure consists of five cavities. The first cavity (DTL1, 21 MeV) has been commissioned with beam in summer 2022. DTL2, 3 and 4 are installed in the tunnel since the end of 2022, ready for the conditioning and commissioning starting in 2023. DTL5 is under assembly and will be transported to the tunnel after the completion of beam commissioning up to 74 MeV. The paper wants to give an overview of the activities already done and ongoing on the five DTLs: from assembly to tuning, from conditioning to beam commissioning.

A compression of the ESS proton pulse from the present 2.86 milliseconds to a few tens microseconds which is better matched to the moderator time constant of thermal neutrons would considerably boost the performance for many instruments at ESS. Generating such a proton pulse with preserved instantaneous beam power requires a storage ring to be added to the ESS accelerator. Such a ring has been studied within the ESSnuSB neutrino super-beam study. The proton pulse length extracted in single turn extraction from this ring would be 1.2 microseconds long which could be destructive for the present ESS target and is very short compared to the moderator time constant. The more desirable medium length pulse could possibly be generated by multi-turn extraction. Another way to generate the longer pulses is to extract a bunch train using fast strip line kickers but this would require a larger storage ring. Using a “bunch train” has been successfully applied at the CERN ISOLDE facility to avoid destruction of sensitive liquid metal targets used for Nuclear Physics experiments. Other challenges are linked to the injection into the storage rings and the understanding of the target, moderator and neutron extraction systems with short and medium pulse length. We will in this presentation review the technical challenges linked to a future medium pulse length ESS facility and the ways proposed to address them for the accelerator and target.

Accelerator facilities are among the most complex projects, integrating advanced engineering systems and components. At the ESS, the need to visualise the intricate integration activities has led to the development of Aggregation Diagrams (ADs). The diagrams follow the facility breakdown structure with sections and system diagrams showing their integration of the devices with enabling and interfacing systems such as the vacuum, cooling, power suppliers and control systems. Commissioning diagrams have also been developed and are used to visualise the main steps and events in the commissioning of the accelerator. The main advantage of using ADs is to help in the activities planning, provide easy access to high-level plans and develop a standard tool that could be used among the different work packages. In this paper, we present the workflow on the development of ADs giving some examples of their use in the activities planning at the ESS.