Specialised Technical Services

The Specialised Technical Services Group provides cryogenic, vacuum, cooling, electrical power and test stand systems for the ESS project consistent with project scope, cost and schedule. This work extends throughout ESS, supporting the accelerator, target and instrument projects in these areas.

The cooling and electrical power activities provide the link between the conventional facilities and the users of technical equipment requiring these utilities. Operation of the cryogenic, vacuum and test stand systems are also the group’s responsibility. The group’s work is designed not only to successfully complete the ESS project but also to enable long-term capacity in cryogenics, vacuum, cooling, electrical power and cryomodule development infrastructure for the ESS Laboratory.

Also located in STS are the senior engineer responsible for QA/QC strategy within the accelerator project and deputy work package managers that provide the connection to the in kind contributors for the Normal Conducting Front End and Beam Delivery work packages.


The group will be available to provide advice and assistance in cryogenics and vacuum systems throughout ESS and will, of course, carry out its work in a safe, collaborative and open manner.

The group will develop a centre of excellence in cryogenics, vacuum, cooling, electrical power and test stands by: committing to the ongoing development of personnel and the continued recruitment of talented people, working with universities in the education and training of both undergraduate and graduate students, establishing collaborations with other institutions (e.g. MaxLab, DESY, GSI, CERN, RAL, FNAL), participating in public outreach programmes, participating in international conferences and publishing in the scientific literature.

The Specialised Technical Services group is lead by John Weisend and it has two sections, Cryogenics and Vacuum, and is developing the ESS Accelerator test stands.

This 50-tonne high-tech Coldbox is used to cool down compressed Helium gas and even liquefy it. Helium is used at ESS to maintain the low temperature of the superconducting cavities that accelerate the proton beam and to cool the target system.



Cryogenics is the science and technology of phenomena below a temperature of 120 K (-153°C).

Cryogenics plays an important role at the European Spallation Source, where three principal applications of cryogenics are found: The SRF cryomodules of the ESS proton linac require cooling at 2 K, 4.5 K and 40 K; the hydrogen moderator surrounding the target that produces neutrons requires cooling through 16 K helium; and liquid helium and nitrogen are required for many of the scientific instruments. These needs will be met by a set of three cryogenic refrigeration/liquefaction plants and an extensive cryogenic distribution system.

Accelerator Cryoplant (ACCP)

The accelerator cryoplant (ACCP) is the largest and most complicated of the ESS cryoplants, and mainly serves to cool the superconducting RF cavities in the cold part of the linac. There are 13 spoke cavity cryomodules, nine medium beta elliptical cryomodules and 21 high beta elliptical cryomodules. There is also contingency space in the accelerator lattice for an additional 14 high beta cryomodules that might be required to achieve the nominal beam energy of 2 GeV. All the SRF cavities operate in saturated 2 K He II baths. Each of the cryomodules also contains a 40 K thermal shield and a helium cooling circuit for the RF power couplers.

Cryogenic Distribution System (CDS)

The cryogenic distribution system (CDS) connects the ACCP to the cryomodules in the ESS tunnel. Vacuum barriers separate each cryomodule’s isolation vacuum from that of the distribution line. Each cryomodule is connected to the corresponding valve box on the distribution line via an all welded vacuum insulated jumper connection. 2 K helium is created separately for each cryomodule. The cryogenic distribution line supplies helium at 4.5 K and 3 bar, which is passed through a pre-cooling heat exchanger and then expanded via a Joule-Thompson valve into the 2 K bath surrounding the SRF cavities. Sub-atmospheric vapour pumped off the 2 K bath passes back through the pre-cooling heat exchanger and is returned to the ACCP.

Target Moderator Cryoplant (TMCP)

The target moderator cryoplant (TMCP) provides cooling for the 20 K supercritical hydrogen moderators that surround the target. These moderators reduce the energy of the neutrons to values more interesting to researchers. Heat deposited in the moderators is absorbed by a hydrogen cooling loop, which is in turn connected via a heat exchanger to a 16 K helium flow from the TMCP. As such, the TMCP is the heat sink for the heat deposited in the moderator.

Test and Instruments Cryoplant (TICP)

The Test and Instruments Cryoplant (TICP) has two roles: During the construction phase, it provides cooling to the elliptical cryomodule test stand at the ESS site, and during operations it will provide liquid helium to the scientific instruments, as well as providing cooling for the occasional cryomodule test.

Auxiliary Equipment

Auxiliary equipment for the overall cryogenic system consists of helium gas storage at medium pressure, liquid helium storage tanks for the ACCP and the TICP, a helium recovery system with gas collectors, high pressure compression, purification system and high pressure storage. Additionally, there will be a liquid nitrogen supply at different locations and a helium infrastructure with mobile dewars for LHe supply and satellite recovery systems in the neutron instruments halls.

This high-level block diagram shows the ESS cryogenic system and its connections to other ESS components

Welcome to the world of vacuum, where nothingness is a sign of a job well done.

The ESS Vacuum Section is responsibile for all ESS vacuum systems. Activities are currently directed mainly towards to the fabrication of the accelerator components, developing fabrication process for the target monolith vessel and the design details for all the neutron instruments.

vacuum test stand

The vacuum test stand at ESS


The accelerator vacuum system design will be conventional; where turbo molecular pumps are planned for pumping the ion source, low energy beam transport, and the radio frequency quadrupole, sputter ion pumps, and NEG are currently planned for pumping all other systems.

As with all accelerators incorporating superconducting technology, one of the critical features of the vacuum design will be the minimisation of gas and particles flow into the SRF cavities. During the assembly process, vacuum connections will need to be made under clean room conditions to minimise the potential for particulates being transported into the cavities that would reduce cavity performance due to field emissions. Design of the vacuum systems for instruments and neutron guides has already begun and will reflect the requirements for operating base pressure and cycle time.

One of the biggest vacuum challenges identified to date will be in the target monolith and the vicinity of the proton beam window interface, where alignment, vacuum connections, and water and liquid hydrogen cooling will present a challenge for leak testing, which will be carried out remotely due to the anticipated residual radiation levels.

The ESS Vacuum Section also face plenty of challenges in developing the vacuum systems necessary for the world’s most powerful spallation source.


This page is managed by the ESS Vacuum Group and is designed to specifically address vacuum issues that arise as the ESS vacuum systems evolve from preliminary design through to operations. In later updates it is planned to address other topics of interest to the vacuum community.

ESS Vacuum Handbook


Part 1: General Requirements
Part 2: Standardisation
Part 3: Design and Fabrication
Part 4: Test Manual



Marcelo Ferreira

Section Leader


ACCSYS work package 10 covers the test stands for the main accelerator components in Uppsala and in Lund

Test Stand 1 concerns the main RF equipment prototype soak tests

One modulator prototype and one klystron prototype will be acceptance-tested in a dedicated test stand, which consists mainly of a hall equipped with requisite electrical power, electrical grounding, cooling water and HVAC. This will provide a solid base for the acceptance of the prototypes.

Test Stand 2 concerns the Site Acceptance Tests (SAT) of the series production cryomodules (elliptical cavities)

All cryomodules will go through their SAT on a dedicated test stand, which consist mainly of an RP bunker, a test stand cryoplant and RF power sources. The Lund test stand will provide facilities for testing the elliptical cavity cryomodules of both varieties: elliptical medium beta and elliptical high beta. Testing of the spoke cavity cryomodule series production is foreseen to take place on the Uppsala test stand.

The Lund TS2 will allow the SAT of cryomodules with full cryogenic load at the final operating temperature and with full RF load on all cavities in parallel.

The Uppsala test stand FREIA will be used to do parts of the tests of the spoke cavity prototype, the spoke cavity cryomodule prototype and the spoke cavity cryomodule series SAT