The Greek philosopher Aristotle (384-322 BC) knew nothing about tokamaks. But when he stated in his famous aphorism that "Nature abhors a vacuum,"¹ he anticipated one of the problems that tokamak designers would face 25 centuries later. Vacuum occupies a large part of ITER, both literally and figuratively—vacuum volumes are huge and vacuum challenges daunting. Successful plasma operation rests on the quality of the vacuum in the (aptly named) vacuum vessel, but also in the cryostat, the neutral beam injection system, and many other systems.   A vessel under vacuum is submitted to pressure from the external environment ... and the higher the vacuum, the more aggressive is the attack of particles from the environment and surfaces.   Gases and liquids will find the tiniest breach in a structure under vacuum. "A crack the width of a human hair is enough to alter the vacuum quality and halt fusion performance," emphasizes ITER Vacuum Section Leader Robert Pearce. Nature not only abhors a vacuum, it conspires by all available means to destroy it ...   Close to ten years ago, an intense R&D program was started to develop risk-mitigating concepts for leak detection and localization. The Procurement Arrangement that was recently signed between the European Domestic Agency, Fusion for Energy, and the ITER Organization is a direct outcome of this decade-long effort.   Under this agreement and the Amendment which is under preparation, Fusion for Energy will deliver a whole suite of ITER-designed systems and instruments to detect and localize leaks throughout the vast volumes of the vacuum vessel and cryostat, and also in smaller areas such as the neutral beam injectors or the cryopumping systems.   "Basically it's about ensuring the integrity and leak testing the totality of the machine: the 2,000 m³ of the vacuum vessel, the 8,500 m³ cryostat (pumping volumes);  the primary vacuum for the neutral beam, not to mention the tens of kilometres of piping carrying gases and fluids that could leak into these volumes," explains ITER Vacuum Section leader Robert Pearce.   Although the risk of leakage is minimized by design as well as best practices and quality control throughout the fabrication and assembly processes, it cannot be reduced to nil. "There should be no leaks," says Vacuum team member Liam Worth, "but experience tells us that if we achieve this it will be a 'miracle.' To date, all tokamaks, stellarators, particle accelerators, and other vacuum installations of large size and complexity have experienced a certain number of leaks."   Achieving and maintaining the required vacuum in the ITER machine is an immense task that the Vacuum Team took on more than one decade ago. Some leaks are "tolerable" but others are not. "There are thresholds," explains Liam. "We can cope with the thermal shield or magnet system leaking a minute quantity of helium into the cryostat. But a leak into the vacuum vessel, whether of air or water, starts to affect plasma performance as the size increases and so cannot be easily tolerated."   Once detected and localized, leaks can of course be fixed, generally by cutting, replacing, bypassing, or isolating the faulty part. In some cases it is relatively easy; in others—for example in the case of a leak occurring in one of the in-cryostat helium lines—it would be a "huge job" to repair, according to Liam.   Among the systems and tools presented at the recent design review is a spectacular device—a self-propelled "in-pipe inspection tool" that can wiggle its way into the smallest and most contorted piping networks (see video) and find its way deep into the cryostat.   In the ITER vacuum lab, a vacuum flange is inspected for small scratches which could potentially cause a leak. New tools and technologies will enable the localization and detection of leaks smaller than the width of hair divided by one million. Conceptualized by the ITER Organization and developed by Doosan Babcock in Scotland, the working prototype of the articulated tool can propel itself inside pipes no larger than 40 millimetres in diameter, move forward and backward, take a 90-degree turn and, thanks to a tiny video camera and built-in lighting system, provide high-resolution images (better than 0.01 mm) of potential cracks or faulty welds. The device, which is evocative of an ultraminiaturized freight train or an oversized, segmented tapeworm, is equipped with inflatable "bladders" that can isolate and locate leaks in precise sections.   Although basic in-pipe inspection tools are standard in industry for much larger pipes, the articulated tool is unique. "Nothing in the world can do what it does," says Liam. "It's reduced size means, for instance, that 100 percent of the thermal shield manifolds² are accessible for inspection and leak localization."   "With the exception of the drive mechanism, all the prototype tool's components, including motors, are off-the-shelf or slightly modified off-the-shelf," says Liam. "The concept design has been demonstrated but the tool can be significantly improved with the use of bespoke components that are smaller and lighter."   "In the more distant future, with advances in material and electronic technologies, such a tool could be further miniaturized by a factor of 10 and provide an even more powerful tool for leak localization and repair for fusion devices and many others," concludes Pearce.   Achieving and maintaining the required vacuum in the ITER machine is an immense task that the Vacuum Team took on more than one decade ago. As ITER is now gearing up for assembly operations, the team is moving forward with a new set of tools and technologies that potentially enable the localization and detection of leaks smaller than the width of hair divided by one million.   ¹-Aristotle couldn't have known that at the atomic scale, Nature—that is, the material world—is essentially made of ... vacuum.   ²-A manifold is an arrangement of interconnected pipes. In the ITER thermal shield, the manifolds supply cryogens to the shield's panels.   Read a related story on the Fusion for Energy website.

Room by room, level by level, the raw concrete of the Tokamak Complex is being covered with coats of smooth, shiny white paint. The figures are mind-boggling: in the lowest level of the Tokamak Building (B2) where the teams are working currently, close to 28 tonnes of resin, primer and paint are needed to cover the floor, walls and ceiling of the vast galleries surrounding the central Tokamak Pit. An equivalent tonnage will be required for each of the other main levels of the concrete building, bringing the total to approximately 150 tonnes. The same treatment will be applied to the inner walls of the Tokamak Pit—a total surface of more than 3,000 m²—and to the Diagnostics and Tritium buildings.   In the Diagnostics Building, paint provides for cleanliness and a dust-free environment. Everywhere else in the Tokamak Complex, it is an element of nuclear safety. In a nuclear building, the coating on the floors, walls and ceilings must present a perfectly smooth surface in order to be decontaminated in case of an incident or accident. (Proven decontamination techniques include water projection, adhesive foam, etc.)   Just like in a home-painting job, surfaces must be prepared and elements such as switches, electrical outlets and door frames must be protected by masking tape. In ITER, these simple tasks take on mammoth proportions: sandblasting the walls and ceiling prior to applying the primer, for example, requires more than 100 tonnes of abrasive material per level, and there are up to 19,000 embedded steel plates per level in the Tokamak Building that require masking.   Like at home ... but on a much larger scale. These workers use rollers around the pre-taped embedded plates. Home painting jobs rarely include floors but in ITER they do—and the quality of the job is paramount in terms of nuclear safety. Floors need to be perfectly leak-tight and act as a "drip tray" in case of a leakage of effluents.   Whereas walls and ceiling are sandblasted to optimize paint adherence, the floors are submitted to the "bombardment" of small steel balls—a technique called "shot peening"—that creates a pockmarked surface facilitating the binding of the first layer of coating to the concrete surface.   The shot-peening operation is followed by the application of a coat of thick primer, followed by four layers of super-smooth resin—not only on the floor proper but up the wall to a height of about 30 centimetres. All in all, a six-millimetre-thick resin coating.   One of the reasons why home paint jobs are preferably done in the spring is air temperature. A balmy 20 °C is ideal, but in the vast volumes of the Tokamak Building this is not easy to achieve—particularly in the Tokamak Pit, whose open volume is in excess of 25,000 m³.   Next week, when painting begins inside this 30-metre high, 30-metre-in-diametre cylinder, the inside temperature will not rise above 10 °C. Teams have planned industrial hot air blowers to progressively bring the temperature to the required 20 °C and maintain it throughout the 2.5-month duration of the works.   The Tokamak Building in raw concrete conveyed a feeling of brute force, consistent with the massive challenges of construction. Once painted white, it will provide a pristine jewel box for the most complex and sophisticated research installation ever built.

The 2019 ITER International School has concluded successfully in Korea, after five days of discussion on the challenge of exhausting heat from tokamaks.   It's a crisp and sunny winter week in Daejeon, South Korea—a techno hub located 140 km south of the capitol Seoul. The dynamic city, whose name derives from the old Korean term hanbat or "big land," is also the base for Korea's leading science and research university, KAIST (Korea Advanced Institute of Science and Technology). The ultra-modern KAIST campus neighbours the National Fusion Research Institute (NFRI), home of the KSTAR superconducting tokamak and the Korean Domestic Agency for ITER.   Gathered at 9:00 a.m. on Monday 21 January in the Yang Seung-Tack auditorium are more than 100 masters, graduate and postdoctoral students representing almost all the ITER partner countries, eagerly awaiting the start of five days of lectures and discussion to be offered by the 2019 edition of the ITER International School. Co-sponsored by KAIST, the Korean Domestic Agency and NFRI, this is the tenth in the series, which alternates between sites in Aix-en-Provence, France, organized by the University of Aix-Marseille, and external hosts within the ITER Member countries.   The topic of the school this year? One of the most important challenges facing magnetic confinement fusion—how to cope with the burning plasma heat exhaust.   ITER is a transitional step, where surfaces in direct contact with the peripheral plasma will together have to remove up to about 850 MW of total power continuously, and locally up to 20,000 times the power density felt on the Earth's surface on a summer day with the Sun at its zenith.   High as these numbers are, they can be dealt with by the sophisticated, water-cooled plasma-facing components that ITER will deploy. However, the walls of commercial fusion reactors based on the ITER line will have to cope with four to five times this total power, and heat handling is already recognized as a serious potential issue that scientists and engineers must start to think about now, even before ITER fires up.   One thing common to both ITER and future tokamak reactors is that transient heat flux surges to first wall armour (mostly provoked by magnetohydrodynamic instabilities) must be strongly mitigated or completely eliminated. ITER will play a major role in showing how this can be done at reactor scale and is itself watching and working carefully with the R&D community within the ITER partners to develop and perfect the techniques which will be required.   At the School, leading specialists from research organizations within the ITER partners and from the ITER Organization delivered more than 24 hours of accessible lecture material on the science and technology of the tokamak heat exhaust challenge, interspersed with long and often stimulating discussion sessions in which students could interact directly with the speakers. Outside the auditorium, there was room for more exchange in coffee breaks or the poster sessions where students presented their own research material. Two gold and four silver poster prizes were awarded based on scores recorded by the lecturers, with the gold winners walking away with an engraved sample of ITER niobium-tin superconducting cable.   Hosted by KAIST's Wonho Choe, the 2019 ITER International School was a fine example of the value and importance of giving young scientists and engineers a taste of the stimulating, multi-disciplinary and challenging field which is magnetic fusion.

Dutch research institutes TNO and DIFFER will be joining with Active Space Technologies (Europe) and Chromodynamics (Netherlands) to develop a diagnostic tool capable of measuring the impurity content of the plasma—important information for regulating neutral beam heating power on ITER. The visible spectroscopy reference system (VSRS) will "look" into the plasma along a single sightline at a precisely defined angle. By analyzing the light emitted by the plasma along that line, it provides important information on the average impurity content, or "transparency" of the plasma.   The visible spectroscopy reference system (VSRS) operates a single viewing chord at a precisely defined angle to measure the visible light emitted by the ITER plasma. By collecting information on impurity content—and thus the relative transparency or opaqueness of the plasma—the diagnostic can provide an early warning for neutral beam shine through that could damage the ITER walls. For ITER's main source of external heating, neutral beam injection, plasma impurity content is an important parameter. If the level if impurities is too high, the beam of neutral particles will be slowed—even stopped—in its trajectory and not enough energy will reach the centre of the plasma. If on the other hand impurity content is too low, the neutral beam could potentially "shine through" and hit the vacuum vessel wall, heating and possibly damaging inner wall components.   By monitoring the absorption rate of the beam's energy by the plasma, the visible spectroscopy reference system provides an early warning to trigger a reduction in neutral beam power before wall heating takes place.   A Cooperation Agreement was signed on 19 February for the design of the visible spectroscopy tool with the Netherlands Organisation for Applied Scientific Research (TNO), the Dutch Institute for Fundamental Energy Research (DIFFER), the European company Active Space Technologies and the Dutch startup Chromodynamics.   An early version will be made available for First Plasma in 2025 to survey the visible light emitted by the plasma and to help identify the types of impurities present. An updated version—optimized to monitor the absorption of heating neutral beam power—will be available by 2028 for later stages of pre-fusion power operation.

Whether you are a physicist or an engineer, a journalist or a businessperson, a student or a tourist ... the ITER Communication visits team can plan a visit for you. The ITER Communication visits team shares its unique experience and knowledge of the ITER Project all year round*, tailoring each visit program to the type of guest or group. Welcoming on average two visitor groups per day, the team strives to answer any and all questions from visitors with diverse interests and educational backgrounds.   Depending on the visitor profile, presentations and tours can focus on ITER science, ITER construction, engineering and manufacturing, international collaboration, or the complex organization of a project of this scale. This is the magic of visiting ITER.   The "fusion journey" of the curious mind usually begins at ITER's state-of-the-art Visitor Centre, where guests can enjoy a rich and immersive experience. During a one-hour presentation, the audience learns about fusion in the universe, fusion on Earth, the advantages of the ITER machine, and ITER's mission and history.   Guiding the audience through the complex ITER universe represents a double challenge. The person "running the show" must sense the needs of each group and adapt the presentation timely and efficiently, while explaining complex technological concepts in an accessible manner. Every group is different; every "ITER journey" is unique. One thing that does not change from visit to visit, from group to group, is the "good vibe" that visitors and their guide share. It comes naturally: the audience shares the guide's enthusiasm while gradually taking steps into the ITER world. The excitement is catching. Questions are asked and answered.   People from neighbouring towns are happy to learn that ITER is creating jobs. Visitors from abroad enjoy deeper explanations about the international aspects of the project and the challenging logistics put into place to bring ITER components from all over the world to southern France. Those following the project closely are eager to hear about progress on the buildings that will soon house the ITER machine and systems.   And—worksite conditions permitting—every visit ends with a tour of the ITER construction site by bus. The excitement at this point usually puts stars in the eyes of our visitors ...   We invite you to look at the project's website for more information about visiting ITER.   ITER also participates in the organization of local and regional events, competitions and conferences to raise awareness about the project and nuclear fusion in general. In particular, our biannual ITER Open Doors days are a great opportunity for the public to learn more about the project (follow the link in blue above).*14,000 people visited ITER last year—7,500 visitors were accompanied by the ITER Communication visits team, 1,500 by the Director-General's Cabinet VIP team, and 5,000 local schoolchildren by Agence Iter France.

The sequel of the ITER manga is out. Taiyô Tenno, the young Japanese art student who had visited Provence and had been introduced to ITER by French scientist Soléane, has returned to France. He spends his summer vacation as an intern at ITER's Communication Department where he and his two intern colleagues are tasked to come up with an idea of how to reach out to people all over the world and spread the word about ITER. Taiyô meets Soléane again who introduces him to ITER's Deputy-Director Eisuke Tada. During a weekend walk on the Sainte Victoire mountain near Aix-en-Provence with Mr. Tada, Taiyô learns about the diversity at ITER, with experts coming from all over the world, sharing ideas in an open and frank atmosphere. Taiyô is inspired and returns to work full of ideas. To find out how the story ends, read the new installment "A small sun on Earth. Volume 2: Internship chapter" published by ITER Japan. It is available in Japanese, English and French. Download the manga on the ITER Japan website here or directly from the ITER Publications page (Comics).