The construction of a new beamline at the Diamond Light synchrotron poses several challenges with no room for error. Jo Stimpson reports on this unique project that required intricate foundations.
The giant, silvery doughnut that dominates the tidy surroundings of the Oxfordshire village of Chilton is exciting and futuristic from first sight.
But what inhabits the Diamond Light synchrotron research facility is even more astonishing. The building contains a machine that uses electrons to generate what is known as synchrotron light in the form of x-rays, ultraviolet and infrared beams.
The beams must hit a tiny target 250m away from their source… equivalent to hitting a 5mm wide spot from a distance of 100km
Phase 1 of construction, costing £263M, saw the building and the first seven beamlines open in 2007. Phase 2, costing £120M and comprising 15 further beamlines, is now under way and includes one beamline whose construction commands special attention.
Unlike most of the others, which are contained within the central doughnut-shaped structure, the I13 will run within the doughnut before extending 130m outside the main structure through a concrete duct. The beamline will then enter an external building which houses the experimental stations, running a total length of 250m.
Contractor Kier Moss is charged with building the duct and external facility, which was designed by consultant Capita Symonds.
Work began on site in June and comprises the 130m long, 4m wide duct − which has 250mm thick concrete walls and lead sections to protect from electromagnetic radiation − and the external building at the duct’s end, which has a footprint of 35m by 20m. This houses an optics hutch and experiments hutch for each of the two
branches, as well as laboratories and a workshop.
The work has progressed well so far, says Diamond’s chartered engineer Andy Peach. “There’s nothing that has been technically unexpected. “
“You can create whatever vibrations you like inside the building but it can’t penetrate the concrete shell of the hutches.”
Principal beamline scientist for I13 Professor Christoph Rau regularly visits the construction site to check on progress. The only problems have been minor ones, he says. “There are always hiccoughs. We thought we were two weeks behind, but we are back on track now.”
Although that work is progressing smoothly, the project is not without its challenges. Far from it − Rau says there are often jokes on site that something has been built at a slightly wrong angle or a fraction too low. The
joke’s popularity is testament to the miniscule room for error. The beams must hit a tiny target 250m away from their source. To give an idea of scale, it is the equivalent of hitting a 5mm wide spot from a distance of 100km.
For this reason, the accuracy and steadiness of the structure is vital, and the foundations play a crucial role in preventing movement. The imaging line has 16 piles (six under the optics hutch; and 10 under the experiments
hutch which sits behind it) while the coherence line has 29 (eight under optics; and 21 under experiments).
These 35 friction piles have a diameter of 600mm and a depth of 14m. “The piling was really important,” says Rau. “If you don’t pay attention to detail it can ruin the whole thing.”
Experiments will also have to be protected from external vibration. This meant that in effect the optics and experiments hutches needed to be isolated from the remaining superstructure to mitigate the effects of any
vibration that might occur. One innovative design solution was the use of a void formation system called Clayboard to create a 50mm gap between the 800mm thick floor of the hutches and the building, effectively insulating them.
“We are trying to protect the floor from external vibration, so the walls are on seperate foundations.”
“We are trying to protect the floor from external vibration, so the walls are on separate foundations and cast on Clayboard,” says Peach. “You can create whatever vibrations you like inside the building but it doesn’t penetrate the concrete shell of the hutches.”
Clayboard consists of a strongyet biodegradable paper-like honeycomb core set between plastic facings. The core is designed to disintegrate upon contact with water − so once the concrete had set, site workers flushed out the Clayboard interlayer with a hosepipe, letting the water fill the whole void and then wash away, leaving an empty space. The hutches’ floors stand on the piles with no contact to the subsoil.
The design has worked well on previous beamlines, and it has captured the imagination of engineers working on other synchrotron facilities. “I would say quite a lot of people copy our design with the isolated floor,” Rau says.
The existing geography of the site posed further obstacles. The undulating landscape limited the length of the beam − although Rau explains that this was not too problematic.
“With this layout you get a couple of hundred microns of coherence, which is best for the kind of experiments we want to do,” Rau says. Being situated outside the main building also allowed I13 to have longer hutches than other beamlines.
But I13 has come up against some vital infrastructure. The concrete duct, which has an internal height of around 1m, crosses two roads from the large doughnut-shaped building to the small external one.
The team had to dig up the roads, elevate them, then build ducts underneath for the beams to pass through. They opted to build road ducts close by at the same time for the I14 beamline, another long beamline which is
due to be built next.
It was also discovered that power cables were worryingly close to I13’s path − including the main power cable for the whole synchrotron facility. “Cables are not always where you think they are on the plans,” says Peach.
As well, the project had to contend with a nursery school whose grounds overlapped with the beamline’s site. The nursery has been relocated and now stands empty, likely to be demolished if Diamond cannot find a use for it.
Race against time
Time has been another major challenge for I13’s construction. The synchrotron machinery is so complex and will take so long to set up that the beamline scientists are keen to get construction finished as soon as possible.
It is hoped that the structure will be complete by March next year, with the equipment installed inside in time for the first I13 experiments to take place in October 2011.
Diamond’s facilities are so unique and popular that there is already a queue of users lining up to use I13 in their research. Even a small postponement of the opening date would prove expensive for Diamond, and veryproblematic for the researchers. “With the amount of funding, a delay of a week is significant,” says Rau.
When users come in, Rau will be responsible for looking after them, as well as having the opportunity to carry out his own research. Diamond has hosted a wide range of research projects, including some with civil engineering applications.
One group has used the facility to study stress corrosion cracks, and another looked at the phenomenon of pit corrosion − both of which could be instrumental in creating safer nuclear plant and nuclear waste storage, or be applied in pipelines.
“A great number of people want to collaborate with us. Everyone wants to get started with their beamlines.”
Professor Christoph Rau
The science is extremely complicated − but its exciting possibilities are evident when Rau describes the “magic” of the speeds reached by the synchrotron light, and again when an engineer on site likens the beamlines to “toys for scientists”.
The continuing development of Diamond Light’s synchrotron is inspiring scientists globally. Other synchrotron facilities are “coming up like mushrooms everywhere,” says Rau. “A great number of people want to collaborate with us. Everyone wants to get started with their beamlines.”