European Spallation Source Accelerator Research Articles

First Protons in the ESS LINAC

The European Spallation Source (ESS), currently under construction in Lund, Sweden, will be the world’s brightest neutron source, driven by a linear accelerator (LINAC) with an average beam power of 5 MW at 2.0 GeV beam energy. The LINAC accelerates a proton beam of 62.5 mA peak current at 4% duty cycle (2.86 ms at 14 Hz). The accelerator uses a normal conducting front-end bringing the beam energy to 90 MeV, beyond that the acceleration up to 2 GeV is performed using superconducting structures. The first protons were extracted at the ESS site during the commissioning of the ion source and low energy beam transport that started earlier this year and will continue to the next stage of the commissioning up to 21 MeV early next year. This paper gives an overview of the status of the ESS accelerator and the commissioning of the ion source and the low energy beam transport.

Commissioning of the Warm Compressor System for the ESS Accelerator Cryoplant

The accelerator cryoplant (ACCP) providing the cooling for the cryomodules and the cryogenic distribution system for the cold part of the ESS proton linac is being built and commissioned at the European Spallation Source (ESS) in Lund, Sweden. The ACCP warm compressor system (WCS) consists of several compression stages. The sub-atmospheric pressure stage (SP) is used to compress helium coming from the cold compressors directly to middle pressure (MP) level. The low pressure stage (LP) compresses the helium from LP level to the same MP level, being merged with additional flow from the cold box and the flow from the SP stage. The total flow is compressed in a single compression stage (HP) from MP to HP. The oil-flooded screw compressors are chosen in a way that the flow in each stage SP, LP and MP is compressed by a single screw compressor. Both, SP and LP compressors are equipped with a variable frequency drive (VFD) to adapt the compressor capacities to the various load cases. The ACCP had been contracted to Linde Kryotechnik AG in 2015 and all compressors are made by the Aerzener Maschinenfabrik GmbH, Germany. Following successful installation and commissioning in 2018, the final 100 hours test run at maximum nominal design condition and the part load tests under various ACCP operation modes were carried out at the beginning of 2019. The key parameters, including mass flow, power consumption, isothermal and volumetric efficiencies, are well fulfilled with the design data. The paper describes the system features, project challenges, lessons learned and acceptance test results.

The Opportunity Offered by the ESSnuSB Project to Exploit the Larger Leptonic CP Violation Signal at the Second Oscillation Maximum and the Requirements of This Project on the ESS Accelerator Complex

The European Spallation Source (ESS), currently under construction in Lund, Sweden, is a research center that will provide, by 2023, the world’s most powerful neutron source. The average power of the proton linac will be 5 MW. Pulsing this linac at higher frequency will make it possible to raise the average total beam power to 10 MW to produce, in parallel with the spallation neutron production, a very intense neutrino Super Beam of about 0.4 GeV mean neutrino energy. This will allow searching for leptonic CP violation at the second oscillation maximum where the sensitivity is about 3 times higher than at the first. The ESS neutrino Super Beam, ESSnuSB operated with a 2.0 GeV linac proton beam, together with a large underground Water Cherenkov detector located at 540 km from Lund, will make it possible to discover leptonic CP violation at 5σ significance level in 56% (65% for an upgrade to 2.5 GeV beam energy) of the leptonic CP-violating phase range after 10 years of data taking, assuming a 5% systematic error in the neutrino flux and 10% in the neutrino cross section. The paper presents the outstanding physics reach possible for CP violation with ESSnuSB obtainable under these assumptions for the systematic errors. It also describes the upgrade of the ESS accelerator complex required for ESSnuSB.

Strategy for the engineering integration of the ESS accelerator

The European Spallation Source (ESS), currently under construction in Lund, Sweden, will be the world’s most powerful source of neutrons. The goal is to deliver neutrons to users in 2019 and reach full power sometime in the middle of the following decade. One of the key issues for ESS is to develop a strategy, along with the proper innovative tools, to efficiently communicate and smoothly collaborate between divisions and groups inside ESS and with its outside collaborators, so-called In-Kind Contributors (IKC). Technical requirements related to the scope to be delivered are among the most important technical information to be exchanged. This information exchange is facilitated by using a commercial requirements management database that is accessible through the web. The physics multidisciplinary needs are linked with the engineering integration through LinacLego, which is a tool that provides all updated lattice data for the accelerator. The lattice information is then gathered and utilized to control the physical positioning of the mechanical engineering components for the accelerator. The precision for this operation is provided by a dedicated mechanical design skeleton in a Computer Aided Design (CAD) environment. Finally, the realization of all these steps is supervised in detail and continuously evaluated. In this way the required ESS machine design can be delivered, both in terms of the engineering and the physics aspects.

ESS Accelerator Cryoplant Process Design

The European Spallation Source (ESS) is a neutron-scattering facility being built with extensive international collaboration in Lund, Sweden. The ESS accelerator will deliver protons with 5 MW of power to the target at 2.0 GeV, with a nominal current of 62.5 mA. The superconducting part of the accelerator is about 300 meters long and contains 43 cryomodules. The ESS accelerator cryoplant (ACCP) will provide the cooling for the cryomodules and the cryogenic distribution system that delivers the helium to the cryomodules. The ACCP will cover three cryogenic circuits: Bath cooling for the cavities at 2 K, the thermal shields at around 40 K and the power couplers thermalisation with 4.5 K forced helium cooling. The open competitive bid for the ACCP took place in 2014 with Linde Kryotechnik AG being selected as the vendor. This paper summarizes the progress in the ACCP development and engineering. Current status including final cooling requirements, preliminary process design, system configuration, machine concept and layout, main parameters and features, solution for the acceptance tests, exergy analysis and efficiency is presented.

Specification of the ESS Accelerator Cryoplant

The European Spallation Source (ESS) is a neutron-scattering facility being built with extensive international collaboration at Lund, Sweden. The ESS accelerator will deliver protons with 5 MW of power to the target at 2.0GeV, with a nominal current of 62.5mA. The superconducting part of the accelerator is about 300 meters long and contains 43 cryomodules. The ESS accelerator cryoplant will provide the cooling for the cryomodules and the cryogenic distribution systeminterconnecting cryoplant and cryomodules. The cryoplant will cover three cryogenic circuits: bath cooling for the cavities at 2K, the thermal shields at around 40-50K and 4.5K forced helium cooling for the power couplers. This paper describes project stages,the cryogenic architecture andthe design basis including cooling capacity, operation modes and interfaces. The important design choices comprising no liquid nitrogen pre-cooling,one integrated cold box, waste heat recovery and process control system strategy as well as the principles of evaluation are presented. All the topics above are implemented and addressed in the technical specification, which has been finished and issued in June 2014. That is a very important step in the development of the ESS cryogenics system.

ESS accelerator cryogenic plant

The European Spallation Source (ESS) is a neutron-scattering facility being built with extensive international collaboration at Lund, Sweden. The ESS accelerator will deliver protons with 5 MW of power to the target at 2.5 GeV, with a nominal current of 50 mA. The superconducting section of the ESS accelerator consists of a total of 208 SRF cavities in cryomodules (CMs) cooled with superfluid helium to 2 K. The CM contains one thermal radiation shield operating from 40 to 50 K. Additionally, 4.5-K gas helium is used to provide forced cooling to the fundamental power couplers for the cavities. The cryogenic cooling for these CMs is provided by one cryogenic plant connected to CMs via a cryogenic distribution line. This article describes the requirements and preliminary design decisions for the ESS accelerator cryoplant. The expected capacity, temperature levels and operating modes are given. Design choices to address important issues of turn-down capability, high availability, and timely restart after plant trips are discussed. Procurement options and schedules are described.