A layered sombrero roof crowns the European Spallation Source in Sweden

Breakthroughs in modern science have always occurred in tandem with the evolution of experimental equipment, with its development allowing for studies in more extreme conditions over the years. Presently, in the domain of particle physics, the preferred method of inquiry involves smashing together minute particles at extremely high speeds - comparable to that of the speed of light itself - to observe what emerges from their interactions. Naturally, the apparatus used for these kinds of experiments are quite complex, sensitive, and in need of vast amounts of energy for operation, and hence, the structures housing them require intensive detailing in their design and construction. Prominent examples of such structures include the famous Large Hadron Collider (LHC) at CERN in Geneva, Switzerland, or the Relativistic Heavy Ion Collider (RHIC) in Upton, New York, USA. Now, the city of Lund in Sweden is home to another facility of a similar persuasion, in the form of the world’s most powerful pulsed neutron source, dubbed the European Spallation Source (ESS). Completed by a team that included the likes of Buro Happold, Henning Larsen, Cobe led by Dan Stubbergaard, as well as SLA (Stig Lennart Andersson), the project is an immense achievement of engineering and structural design, on a massive scale.

Equipped to house a 500-metre long linear proton accelerator, the facility is touted to be among the most powerful of its kind in the world on completion. While much of the enveloping structure and supplementary facilities have been fully constructed, the remaining work of fully prepping the structure for experimentation is expected to stretch to 2027, with the first research findings from this process anticipated in 2023. The facility has been conceived to specialise in experiments that involve nuclear spallation - a process in which fast moving particles (usually protons) are made to bombard a heavy target (tungsten in this case) in order to produce a neutron beam. Such a process involves the consumption and liberation of massive amounts of energy and comes with an associated level of risk which were some of the vital considerations taken into account by the designers throughout the process of developing the ESS.

Consisting of a number of buildings that house the actual spaces for equipment where the research will be conducted, in addition to offices and auxiliary areas, the complex is massive in its extent, but united under the cover of a sombrero-style roof composed of a layered sequence of steel trusses. This element of the facility’s design consolidates the assortment of structures that constitute it, crafting a singular visual presence that is immediately identifiable. Cantilevered up to a distance of 35 metres at certain edges, the roof assembly has been configured to assist in counterbalancing deflections in the building’s steelwork trusses while withstanding extreme environmental loads, such as strong winds, blankets of snow that are upto seven metres thick, as well as earthquakes of magnitude several times higher than any recorded within the region’s recent history. Such resistance to adverse conditions is crucial for a building of this nature, where high energy reactions will take place.

Adam Pekala, Project Leader at Buro Happold, explains in a statement, “The cladding of the overhanging roof is made up of L-shaped aluminium lamellas mounted onto panels. The nature of these panels prevents detrimental snow accumulation on the overhang, reducing the total load acting on the larger sections. We used parametric modelling to define the optimum shape and layout of the panels and reduced the number of bespoke assemblies by 87 per cent. This helped to minimise wastage by using materials and production resources in a more sustainable way, while enabling much faster fabrication and assembly.”

From the outside, the complex is made up of a series of staggered rectilinear blocks, with open spaces and landscaped stretches configured between and around them. Consolidated under the roof truss, the entire structure is quite immense in its scale, but with a façade design that serves to counteract it by the virtue of the lightness of its material palette. Cold and impersonal in its identity, the predominantly glass and ridged metal envelope imparts the structure with an almost warehouse-like quality, despite the prevalence of both these materials in contemporary Scandinavian architecture. As per the Danish architects, a façade panellisation study was conducted by them alongside the façade specialists while devising this external skin. Inside the building, most of the areas accommodating research equipment were designed with long spans, allowing for minimal obstructions inside the spaces. Hence, the building’s scale has been astutely exploited, creating cavernous spaces that reduce users to mere ants in comparison.

To move heavy equipment in and out of the experiment halls, the building has been fitted with an advanced system of overhead operating cranes. While developing arrangements and configured settings for these devices, the design team made use of computational processes in order to account for the nearly two million loading scenarios that had to be accounted for. As commercially available software was incapable of this intense degree of analysis, Buro Happold developed a program to conduct this pre-design research in-house. Safety was also pivotal to this automated layer of the complex’s design, and the crane in the central target building is testament to this attention to detail. Capable of lifting 115 tons, the crane is tasked with handling very heavy components as well as activated material from the spallation process at certain times - both high-risk scenarios that need to be carefully addressed. Furthermore, the outer shell of the ESS is also capable of withstanding the loads and stress induced when all the cranes operate simultaneously, in addition to its high tolerance for environmental loads.

Paul Roberts, Project Director at Buro Happold, concludes in a statement, “It has been a close collaboration with the architects and the client right from the beginning of the project, starting with the very first hand-drawn sketches that we worked on together. Seeing the result of this impressive roof structure that marks a significant milestone for ESS is truly amazing. We are proud of our contribution to the world’s most powerful neutron source that will help address some of the most important societal challenges of our time: enabling scientific breakthroughs in research related to materials, energy, health and the environment.”

Project Details

Name: European Spallation Source
Location: Lund, Sweden
Architects: Henning Larsen and Cobe
Landscape Architect: SLA
Engineers: Buro Happold, NNE Pharmaplan, and Transsolar
Consultant: Bent Lauritzen, Head of Division, Center for Nuclear Technologies, Radiation Physics