ESS Installs First Two Cryomodules in the Linac

First Spoke CM
One of the first two cryomodules, subject to installation in its permanent place the ESS accelerator tunnel. All images and video: Ulrika Hammarlund/ESS

ESS this week began the installation of cryomodules in the ESS superconducting linac.  This follows a long period of design, manufacturing and extensive testing and marks another significant milestone on the Road to Science.

In line with the re-baseline project plan, this week ESS started the installation of cryomodules in the superconducting section of the linear accelerator.

The pilot installation of one double-cavity spoke cryomodule and one medium beta elliptical cryomodule containing four cavity strings paves the way for serial installation of cryomodules to begin this summer. Ultimately, there will be a total of 43 cryomodules installed in the superconducting linac.

ESS Accelerator - schematic

A schematic drawing of the 600-metre-long Linear Accelerator. The area highlighted in blue is the superconducting part where the cryomodules are installed.

Illustration: Mamad Eshraqi/ESS

MB cryomodule

The first medium beta cryomodule on route to the superconducting part of the linac.

The ESS Linac group is overseeing the installation with the Superconducting RF section working in close collaboration with various teams such as Rigging, SAM, Vacuum, RF, Cryogenics, contractor Powerheat and several ESS In-Kind partners who delivered the Cryogenic Distribution System (CDS) and cryomodule components and are participating in the testing and installation tasks.


The ESS Superconducting Linac, where 43 cryomodules will be installed, is more than 300 metres long.

The CNRS (French National Centre for Scientific Research contributed 13 spoke cryomodules each with two cavities, developed at the IJC Laboratory in France and fully tested at the Freia Laboratory at Uppsala University, Sweden. CEA (Alternative Energies and Atomic Energy Commission) in France is responsible for nine medium-beta and 21 high-beta cryomodules each with four elliptical cavity strings provided as in-kind from INFN/LASA-Italy and STFC-UK respectively.

Spoke CM SAM

The ESS Survey, Alignment and Metrology (SAM) team is ready to take measurements of the first cryomodule in place.

All elliptical cryomodules are fully tested in the ESS on-site test stand before installation. This involves exciting the cavities, cooled down to the operational temperature of 2K, with radiofrequency power – which is in principle the same that will happen in the accelerator tunnel, only the proton pulse is missing in the test phase. These ongoing tests are conducted by the Polish in-kind team from IFJ PAN in collaboration with the ESS Linac and  Cryogenics groups.

To date, ESS has received 12 of the 13 spoke cryomodules, seven of the nine medium beta and six out of the 21 high beta cryomodules. For initial operations and Beam-on-Target only seven medium beta and two high beta cryomodules are required.

Paolo Pierini

Paolo Pierini, SRF Section Lead and Machine Section Coordinator, Superconducting Linac (SCL). In the background: Henry Przybilski, CM Installation Package Lead.

The two cryomodules will be connected to the valveboxes of the cryogenic distribution system, the waveguides of the RF distribution system and the vacuum envelopes of the Linac Warm Units.

The pilot installation will inform the detailed plan for the cryomodule serial installation scheduled to start this summer.

At the same time, repairs and optimisation of the cryogenic distribution system will proceed with the next cooldown foreseen for this summer.

Watch this video of the first two cryomodules arriving to the ESS accelerator tunnel for installation in their permanent position.

Learn more: What is a cryomodule?

A cryomodule is a large tank with thermal shielding which contains a series of superconducting radio frequency (SRF) cavities. The cavities are cooled down to 2 Kelvin (-271 degrees Celsius) using a cryogenic system distributing cold helium.

The SRF cavities inside the cryomodule are designed to create an alternating electromagnetic field that accelerates protons as they pass through the string of connected cavities. By using a superconducting material (niobium) and cooling the cavities to extremely low temperatures, the cavities will allow for very high acceleration of the particles. At ESS the final proton speed will exceed 95% the speed of light.


Cross-section of ESS spoke and elliptical cryomodules with two and four superconducting cavities.