European Spallation Source (ESS): Target Building Roof

Lund, Sweden

The opening of the ESS will herald a new era of particle science research. The facility will include state-of-the-art particle accelerators and spallation technology which will transmit neutron beams 100 times brighter than available today, making it the most powerful spallation source in the world.

Spallation sources are a high-flux source in which protons are accelerated at high energy rates into targets which creates the emission of neutrons. This science is used to drive innovation in the fields of energy, physics, engineering, chemistry, and medicine.

The vision of the Lund Science Village is to create a pioneering research environment between two major research institutions: the MAX IV next generation synchrotron radiation facility and the ESS.

The two key elements of the ESS facility are the 600 metre long linear proton accelerator and a 4-tonne tungsten target wheel, which working in tandem create particle science data that scientific teams can use in their research. Buro Happold was commissioned to design an extraordinarily strong yet lightweight large steel-framed roof structure to cover the target wheel and associated Experimental Halls in the advent of extreme winter weather and seismic activity. The dramatic roof will be the focal point and iconic visual identity for the ESS.


Given the nature of potential risks in particle research, it is of paramount importance to ensure that the steel roof structure is engineered to withstand extreme wind, snow and earthquake scenarios over a return period much longer than the anticipated design life of the building. Moreover the roof design needed to allow for the changing needs of the research facility.

The sheer size and loading applied to the roof, covering a footprint of 200×150 metres, were the first set of challenges for our engineering design team. The profile of the roof includes cantilevers up to 35 meters beyond the perimeter of the building, which can increases the risk of vulnerability to environmental factors such as high wind and the heavy build-up of snow.

ESS target
The ESS facility includes a 600m long linear proton accelerator and a 4-tonne tungsten wheel target. Image: Henning Larsen/COBE Architects


In order to overcome these issues, our team developed a semi-porous ribbed roof facade system that reduces the magnitude of environmental loading. The extra benefit of this approach allowed us to reduce the quantity and thus the cost of the steelwork. In close collaboration with the architectural team and facade specialists, we developed a design for the external facade of the cantilevered roof to incorporate aluminium fins. We used parametric tools to optimise the shape, length and thickness of the fins. Nesting on the rib steelwork, the fins are specially shaped to allow wind to pass through and proportions of snow to fall to the ground without compromising the integrity of the cantilevered roof. Working in collaboration with specialist testing companies, the effects of wind and snow were verified with scale model testing and computational fluid dynamic (CFD) analysis. Our team also created a parametric modelling tool connected to the Building Information Modelling (BIM) model that allowed the adjustment of steel truss heights, spacing and pitch to ensure an optimal engineering design.

ESS target
The Buro Happold engineered roof, which covers the target wheel and Experiment Halls will be the focal point and iconic visual identity for the ESS. Image: Henning Larsen/COBE Architects

Further adding value, we considered the construction process during the early stages of the project, ensuring efficiency. Solutions include standardising steelwork elements despite the complex geometry of the roof and specifying prefabricated roofing panels, allowing them to be quickly and safely installed on-site. Demonstrating our experience with working on complex structures, a specialist parametric modelling tool was produced to significantly reduce the number of different types of facade panels required for the cantilevered roof. This resulted in great efficiencies in terms of fabrication and installation from a sustainability perspective, while the amount of material wastage in this system is significantly reduced.

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Carefully engineered fins on the steel work of the cantilevered roof allow wind and snow to pass through without compromising the integrity of the roof. Image: Henning Larsen/COBE Architects


After 20 years of planning, by 17 countries around the globe, the European Spallation Source facility is destined to further our understanding of the universe, providing insight that was not previously possible to achieve. Our contribution to the project entailed engineering innovation and careful planning to ensure the ESS Target Building Roof will be built strong enough to shield the world’s most powerful neutron testing facility from a variety of extreme environmental factors, yet remain flexible in design to accommodate the future of particle science.

European Spallation Source (ESS): Target Building Roof
Image: Henning Larsen/COBE Architects

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