11 Jan 2021 to 18 Jan 2021
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Cryostat thermal shield | A "strong back" for a fragile component
The lower cryostat thermal shield is a large silver-plated component, circular in shape and five metres tall, which fits inside the depression in the cryostat base to form a heat barrier to protect the superconducting magnets. Twenty metres in diameter and weighing approximately 50 tonnes, it is so thin (10 millimetres) that crane operators use the word 'skin' to describe it. Lifting such a fragile component and preventing potential deformation throughout the lifting, transfer and installation operations, called for a 'strong back.' What operators call a 'strong back' is an extremely rigid circular lifting device that interfaces with the component through 18 attachments, equally distributed around its circumference. The 23-tonne device is attached to the overhead crane by a single hook, which facilitates the centring of the load and ensures perfect balance. Following the installation of the cryostat base and lower cylinder, in May and August of last year respectively, the operation on Thursday 14 January was another memorable moment in the assembly of the ITER device. The aspect of the component, whose silvery surface reflected the colours and distorted shapes of the environment, its apparent fragility, and its delicate rigging all contributed to the grace of the event. In a sequence that is now familiar the load was first lifted a few centimetres while its balance was checked and metrology was performed, before it was hoisted to cruising altitude some 23 metres above the floor of the Assembly Hall. Once aligned with the axis of the assembly pit, the journey began—approximately 100 metres at the relatively fast speed of 2 metres per minute, marked by the delicate passage over the tall assembly tools along the way and over the wall that separates the Assembly Hall proper from the opening of the Tokamak pit. When the component was positioned directly above the pit, it remained stationary for a time as real-time metrology was performed once again. During its transfer however, the load had rotated a few degrees and the temporary vertical rails inside the component, designed to fit into the guiding device of the 'alignment tools' at the bottom of the pit, were slightly off target. As is often the case in the last stages of installing large components, the final approach is prepared by delicately pulling on ropes until perfect alignment is achieved. In last Thursday's operation, this routine technique was made more difficult because of the presence of a recently installed coil gravity support whose protruding anchor bolts left very little room to manoeuver. Such 'unexpected difficulties,' stemming from the small gaps and complex interfaces between components are, and will be, quite common throughout the ITER machine installation phase. On Thursday, operators dealt with it just as they have always done—with reactivity and ingenuity. A little past 4:30 p.m., two hours after having reached the pit and five since the beginning of the lift, the lower cryostat thermal shield was in the expected position at the bottom of the pit. Three hours later, the load was transferred from the crane to an array of hydraulic jacks positioned on the base. Final adjustments required another couple of hours and at 9:30 p.m., following final metrology, the operation was declared a success. Like matryoshka nesting dolls, the lower cryostat thermal shield is now inserted into the lower section of the cryostat base, which itself is nestled in the concrete cylinder of the assembly pit. In a few months, in an operation that promises to be even more spectacular, another piece will be inserted into the circular open space—the 400-tonne poloidal field coil #6.
Diagnostic shielding | B4C ceramic bricks prove their worth
A number of materials can effectively shield diagnostic equipment from the neutron flux coming from the plasma. To find the best one, the diagnostics team at ITER had to match efficacy with a number of other requirements, including overall weight. The 25 diagnostic-hosting port plugs in the ITER Tokamak serve two main purposes. One is to protect diagnostic equipment from neutron flux—either by either completely blocking the flux or by reducing it several orders of magnitude. The other is to provide the diagnostic equipment with a view into the plasma through windows and holes. On the plasma-facing ends of the equatorial port plugs are three diagnostic shield modules—drawer-like structures that consist of a stainless steel frame and a diagnostic first wall. Behind the stainless steel frame, shielding material will be the last line of defense, reducing or blocking the neutron flux to protect sensors and auxiliary equipment. Choosing material with the right properties Choosing the right material to use for shielding was a process that required a number of steps, and input from several organizations. Not only would the material have to provide the right amount of protection, but it also had to respect a number of constraints. One constraint is that each fully equipped port can weigh no more than 48 tonnes, which limits the kinds of shielding that can be used. 'You can create a solid shield alternating layers of stainless steel and water,' says Maxim Ivantsivskiy, Project Associate in the Diagnostic Engineering Section. 'This would meet our requirements for reducing the neutron flux, but unfortunately this solution would be absolutely outside of the weight limit.' To find a solution that would remain within the weight limit, the ITER Organization and the US and Russian Domestic Agencies conducted independent studies. All three organizations came to the conclusion that boron carbide (B4C) would be the best material to use. B4C is a very strong material, used for example in bulletproof vests and as armor for some modern tanks. B4C also has another advantage: whereas stainless steel and water slow down the neutron flux, B4C blocks the neutrons—providing even better protection. What's more, B4C is almost four times lighter than stainless steel. Choosing the right form of the material 'Once it became clear that B4C was the right material, we had to figure out in what form,' says Ivantsivskiy. 'B4C can take the form of dust or sand, with which you can fill a box to provide shielding, or it can take one of several ceramic forms. We discussed different solutions with the working group and agreed that the best solution would be B4C in ceramic bricks, which would be much easier to manipulate.' The next step was to find out how to distribute the ceramic bricks to achieve the optimal tradeoff between shielding and weight. The team started by designing the shielding tray, which contains the B4C bricks. 'We opted for a modular design, where you can alter the dimensions of the trays according to the shape of the diagnostic equipment,' says Ivantsivskiy. The idea is to house the optical sensors and mirrors inside the diagnostic shielding module, which is surrounded with shielding trays. One advantage of this approach is that if equipment is damaged, it is easy to remove only a small number of the shielding trays to reach it. However if the space is completely filled with bricks, the weight limit is exceeded. 'We found a solution that is quite elegant,' says Ivantsivskiy. 'We make a big hole in the center of each brick, which has the added advantages of creating a fixation on one side that can be used to attach the other structures. By making this hole bigger or smaller, we can manage the average density.' Another challenge that had to be overcome was the outgassing rate. 'During the early stages of the project, the designers calculating the outgassing rates for pumps budgeted for each part of the tokamak,' says Ivantsivskiy. 'The budget included outgassing from port plugs too. But the ceramic bricks add to the surface area, and they weren't considered in the original exercise. A port plug can have up to 40,000 bricks, with a total surface area of 407 m², which is a lot of extra surface to take into account.' To determine if the port plug would remain within the outgassing budget, the missing piece of the calculation was the outgassing rate of each brick of B4C ceramic. The Russian Domestic Agency set out to find out what that was. 'We took 638 pieces of ceramics and cleaned them—first with ultrasound, then in water for 20 minutes—and then dried them at 120 degrees Celsius,' says Ivantsivskiy. 'The pieces were then baked for 4 hours in an oven at 1000 degrees. We put these bricks into a vacuum vessel and tested them according to ITER requirements.' 'After just 5 hours of testing we demonstrated that we fall within the requirements. After 24 hours, it was even better. To take it a step further, we pumped and measured for one whole year. The outgassing rate decreased by a factor of 3.5.' After months of research, design tradeoffs and experimentation, B4C ceramic bricks have been shown to protect diagnostic equipment, and also meet the constraints of operating within diagnostic-hosting port plugs.
Image of the week | The cryostat top lid, batch after batch
Batch after batch, the elements for the top lid of the ITER cryostat keep arriving from India. As of today, 7 out of the 12 required segments have been delivered. The lid is a complex component that integrates a number of auxiliary elements such as a central cover, a central cylinder, a manway, lip seals, fasteners and several supports for the thermal shield. The circular component pictured at the forefront of this image is the top lid central cover (8.2 metres in diameter, and weighing slightly in excess of 30 tonnes), which arrived at ITER in September 2020. In the rear is one of the segments (#1) that was part of last Thursday's delivery to the ITER site, along with segment #7 and the top lid's central cylinder. At 665 tonnes, the cryostat top lid is the second heaviest component of the whole machine. Only the cryostat base at 1,250 tonnes tops it on the scale.
Europe: new fusion technology transfer award
The European Domestic Agency for ITER, Fusion for Energy, has opened a contest to reward companies for the commercial use of fusion technologies in non-fusion markets. Open to all European companies and organizations, the Technology Transfer Award competition aims to encourage and promote projects where a fusion technology or know-how is used or is planned to be used outside of fusion applications. Applications will be evaluated according to the resources and efforts deployed by the candidate to achieve commercial use of the technology in a non-fusion market, as well as the socio-economic impact of the project on the market. The selected project will receive a sole prize of €10,000. Applications are open from 18 January 2021 to 18 March 2021 at this link.
Russian-language film on ITER
ITER Russia (ROSATOM) has teamed with documentary film makers to create a 38-minute feature on fusion and ITER called "On the Way to the Sun" (На пути к Солнцу). In 2021, the film makers will present it at leading international and domestic festivals. You can view it free of charge on YouTube (in Russian) at this address.
IAEA: Fusion Crowdsourcing Challenge Launched
The International Atomic Energy Agency (IAEA) and the European Fusion Education Network (FuseNet) are calling on fusion enthusiasts around the world to review scientific literature and online resources to find as many zero-dimensional, or independent, design parameters as possible for active fusion tokamak and stellarator experimental reactors in the IAEA's interactive Fusion Device Information System (FusDIS) database. The data collected through the challenge, which is aimed at students and young professionals with an understanding of fusion without being experts, will prove useful for simulations, modelling and design studies to advance fusion research. The challenge is looking for submissions that include the following parameters: radii, plasma current, magnetic field strength, material composition of device wall and divertor, plasma shape, elongation and triangularity. Participants have until 31 January 2021 to submit their answers here. Click to see the IAEA and FuseNet announcements.
New documentary on fusion energy: Engineering the Future
A new fusion documentary follows the efforts underway at ITER, JET, and First Light Fusion to realize "the ultimate energy solution." Produced by Bigger Bang Communications (UK) and narrated by actor Patrick Stewart (known for his distinct voice), the 60-minute film is part of a six-part series called Engineering the Future. "A global industrial revolution is underway, driven by passionate, dedicated individuals intent on shaping a new world. A cleaner world. A greener world. Together, they are pushing engineering to its limits to create extraordinary machines that can protect our planet for the future.' The episode on fusion can be viewed on Curiosity Stream and HBO Max (paywalls).
Link to the recordings of the "Fusion and the Climate" Webinar
Kernfusion: Die ENERGIE der SONNE nutzen
Fusion For Energy launches Technology Transfer Award
Swiss-built laser trackers take leading role in assembly of the very large structures at the ITER project
FuseNet and IAEA launch a challenge and you can win prizes!
ИТЭР в 2020 году, часть вторая
전남도, 차세대에너지 '인공태양'프로젝트 뛰어든다
Expert panel approves the next DEMO design phase
Iter / Italy's Ansaldo Nucleare Completes Crucial Welding Project
Renowned fusion laboratory honors pioneering physicist Richard J. Hawryluk
Ansaldo Nucleare, commessa da 105 milioni per Cadarache
Final major contracts signed for Iter Tokamak Complex assembly
Contract signed for ITER emergency electrical power