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Four times as large as the Vatican City State, but slightly smaller than the Principality of Monaco, the ±¬×ߺÚÁÏ international enclave covers 180 hectares, of which about half is occupied by buildings and infrastructure. The land was conceded by France to the ±¬×ߺÚÁÏ in 2010, and will be returned once ±¬×ߺÚÁÏ has completed its scientific program. Whether working directly for the ±¬×ߺÚÁÏ, for an ±¬×ߺÚÁÏ Domestic Agency, or for one of the approximately 700 institutions or contracting companies present on site at any given moment, almost 6,500 people hold an ±¬×ߺÚÁÏ "passport" in the form of an access badge to the ±¬×ߺÚÁÏ enclave. Few places, if any, host a more cosmopolitan community on such a small stretch of land. The people working on ±¬×ߺÚÁÏ territory hail from 90 countries (up from 68 in 2020), from "A" like Afghanistan to "V" like Venezuela. Reflecting the important presence of French companies on site and the necessary interaction with the host country, the largest cohort is French (3,885). Italians come second (421), followed by Spaniards (335), Indians (254), Chinese (214), Portuguese (165) and Romanians (119). There are almost as many Americans (42) as there are Algerians (44) or Moroccans (46), all involved in one way or the other in the realization of ±¬×ߺÚÁÏ.Twenty-eight countries—Bangladesh, Cyprus, Gambia, Madagascar and Mali among them—have only one representative on site, as does a little-known administrative entity called the "United States Minor Outlying Islands"¹ made up of a string of small islands and atolls in the Pacific and the Caribbean. Albania, Argentina, Jordan, Mauritius, Congo and Tanzania have two; Lebanon and Gabon have four (at the time of this writing). There are 7 Ukrainians, 3 Serbs, 1 Kosovar and 96 Russians working to build ±¬×ߺÚÁÏ.Of close to 6,500 people, approximately 1,600 are directly attached to the ±¬×ߺÚÁÏ either as staff (1,066), ±¬×ߺÚÁÏ Project Associates (216) or interim personnel (359). The largest contractors present on the ±¬×ߺÚÁÏ construction site are Assystem (152)—part of the ±¬×ߺÚÁÏ's Construction Management-as-Agent MOMENTUM consortium and a variety of engineering support contracts—followed by the European Domestic Agency's Architect Engineer Engage (102) and the construction company GTM Sud (94). Of the 707 contracting companies or institutions represented on the construction site, 50 have more than 20 employees; their area of intervention includes construction (Valérian, Demathieu Bard, Ferrovial-Agroman), fabrication (CNIM, ASG Superconductors), logistics (DAHER), crane operations (FOSELEV, Ponticelli Frères, Vernazza Autogru), scaffolding management (Entrepose Échafaudages), services (Sodexo, Onet Services) and other support activities. The rest of the workforce is distributed among 158 companies that have between 5 and 20 employees and another 368 companies (half of the total) that have only one representative on site.Since construction began in the summer of 2010, an estimated 15,000 people from 5,000 companies have been involved in the myriad activities that building ±¬×ߺÚÁÏ requires. Since construction began in the summer of 2010, an estimated 15,000 people from 5,000 companies, small and large, have been involved in the myriad activities that building ±¬×ߺÚÁÏ requires. English is the lingua franca of the ±¬×ߺÚÁÏ enclave. As a mother tongue however, it is only spoken by a small proportion of its denizens: 15 percent within the ±¬×ߺÚÁÏ, certainly much less for the construction workforce. But communication on the ±¬×ߺÚÁÏ site is not an issue: supervisors have sufficient command of the language to interact with ±¬×ߺÚÁÏ or Domestic Agency responsible officers and they can pass on the information to their team. Many workers have a basic understanding of English and, when falling short, resort to smartphone apps that prove efficient in conveying simple messages.The culture that the denizens of the ±¬×ߺÚÁÏ enclave have developed over the years transcends nationality and language. In all aspects—large and small—it reflects the nature and values of the unique international project they are committed to.¹ Other islanders hail from French Polynesia (2), Cape Verde (1), the Canaries, which belong to Spain (1) and the Caribbean microstate of Saint Kitts and Nevis (1).

The future of fusion rests on the availably of two hydrogen isotopes, deuterium (one proton, one neutron) and tritium (one proton, two neutrons). Extracting deuterium from water is a relatively simple and proven industrial process, used mainly to produce the "heavy water" that acts as a coolant and neutron moderator in certain fission reactors. The only source of readily available tritium, a radioactive element which exists naturally only in trace amounts, is a type of fission reactor called CANDU where tritium is created by neutron capture in the heavy water coolant. Over the course of its scientific program, ±¬×ߺÚÁÏ will acquire and consume the totality of the world's tritium inventory, which amounts to only a few dozen kilos. Developing solutions to breed large quantities of tritium is therefore a precondition for the development of industrial and commercial fusion reactors. Breeding tritium is an integral part of ±¬×ߺÚÁÏ, inscribed in the ±¬×ߺÚÁÏ Council-approved Project Specifications document: "±¬×ߺÚÁÏ should test tritium breeding module concepts that would lead in a future reactor to tritium self-sufficiency, the extraction of high grade heat and electricity production." The project will experiment with tritium production within the vacuum vessel by way of test blanket modules (TBMs). The research activity runs in parallel to the ±¬×ߺÚÁÏ research plan and is considered "a project within the project."Test blanket modules are based on a simple physics principle: when a neutron impacts a lithium nucleus, the reaction produces one atom of tritium. An intense flux of neutrons will be generated once ±¬×ߺÚÁÏ enters full power operation and the Earth's crust contains abundant reserves of lithium. The challenge the ±¬×ߺÚÁÏ Test Blanket Module Program is facing is to turn a physics principle into an efficient tritium-producing and extraction system.Test blanket modules are the breeding elements of the tritium breeding blanket systems that are being designed independently by China, Europe, and Japan. In addition, Korea and Europe are collaborating to develop a joint test blanket module concept¹. This collaboration was formalized by the signature of the Test Blanket Module Partnership Agreement between the two Members at ±¬×ߺÚÁÏ Headquarters on 1 March 2023. A second document called a Test Blanket Module Arrangement—involving the ±¬×ߺÚÁÏ as nuclear operator—was signed one week later. A week later, an additional document (the Test Blanket Module Arrangement) was signed by Korea's Kijung Jung (right), European Domestic Agency representative Juan Knaster (left), and Pietro Barabaschi, Director-General of the ±¬×ߺÚÁÏ (nuclear operator). These signatures marked the culmination of a multiyear process, and officially launched the start of design, construction and procurement activities by the fully integrated single-project Korean/European test blanket module team. Considering the sensitive and strategic nature of test blanket modules, and the considerable industrial and commercial implications of tritium breeding, the collaboration was hailed by all stakeholders as an exceptional example of trust, determination and team spirit.¹ Four different test blanket module concepts are being developed by the ±¬×ߺÚÁÏ Members and will be integrated into two equatorial ports for testing on ±¬×ߺÚÁÏ: water-cooled lithium-lead (Europe); water-cooled ceramics breeder (Japan); helium-cooled ceramics breeder (China); and helium-cooled ceramic pebbles (Europe/Korea). All ±¬×ߺÚÁÏ Domestic Agencies are carrying out R&D on different aspects of the test blanket systems (i.e., coolant, materials, tritium extraction...). Learn more about the ±¬×ߺÚÁÏ Test Blanket Module Program in this recent ±¬×ߺÚÁÏ Talk.

Punctuating the inner surface of the vacuum vessel are many strategically placed windows that will be used by diagnostic systems to "observe" the plasma. "The windows are an indispensable component of ±¬×ߺÚÁÏ," says Sunil Pak, Boundary Penetration and Port System Group Leader of the Diagnostic Engineering Section. ±¬×ߺÚÁÏ half of the ±¬×ߺÚÁÏ diagnostics are optical or microwave diagnostics—systems that operate from a protected location inside a port plug and peer into the plasma through small windows covered by transparent material. Because these windows are part of the vessel, they must also—in addition to providing transparency for viewing—reproduce some of the critical functions of the wall. They need to be leak proof so that the vacuum in the vessel is preserved, and they must be able to maintain nuclear confinement. A total of just over one hundred windows are built into diagnostic ports around the vacuum vessel. "We try to standardize as much as possible, so different systems can share a window," explains Pak. "On average, one standardized window is used by three or four diagnostics." Critical design features Almost all window assemblies will be based on a double-disc design with an interspace that is monitored. But beyond that common feature, different design attributes will be used to meet the requirements of specific diagnostic or groups of diagnostics. Aperture discs (the transparent part of the assembly) range in size from 25 to 160 millimetres in diameter. The material used depends on the diagnostic frequency ranges—for example, infrared, visible, or ultraviolet all require different materials—and on the expected power load. The choice of materials includes fused silica, quartz, sapphire, zinc selenide, and diamond.   Almost all window assemblies share this double-disc design with an interspace that is monitored. The transparent material is diffusion bonded to the metal structure. Regardless of the material, signals must pass through the transparent surface with minimal attenuation and disturbance. Window bending must be avoided to prevent skews in the measurements. Reflection, another potential source of skew, is minimized by slightly tilting the transparent part of the window. As an additional measure, about 70 percent of the transparent surface of the windows is covered with a very thin coating of anti-reflection material.The window assemblies must also be leak free to preserve the vacuum in the plasma chamber and maintain confinement. To monitor for leaks, the service vacuum line is connected to the interspace between the two discs, where it measures pressure continuously during machine operation. To prevent leaks at the seams, bonding or sealing methods are used to tightly join the transparent material to the surrounding metal."One technique is to put the stainless steel and the transparent material in a vacuum and then place a thin aluminum layer between them," says Pak. "We raise the temperature up to 500 °C and keep it there for two hours until the aluminum starts to melt. Then we put pressure on the disc and cool it down slowly over a period of one to four hours. This technique, called diffusion bonding, causes the aluminum to diffuse into the glass and metal."Diffusion bonding requires very good axial symmetry. As the temperature is lowered from 500 °C to room temperature, the metal shrinks more than the glass, compressing the disc along the way. Asymmetry might cause localized compression, which could lead to the formation of defects during ±¬×ߺÚÁÏ's lifetime. These window prototypes are in an oven for thermocycling tests (500 cycles from room temperature to 240 °C) to demonstrate that even at peak stress, the glass will not crack. The windows are designed to last the lifetime of the ±¬×ߺÚÁÏ machine, but on-board monitoring and some inspection tests are planned. Another technique, sealing, is used for aperture materials like zinc selenide, which cannot survive the high temperatures required for diffusion bonding. At temperatures higher than 250 °C, zinc selenide starts to oxidize, so a metal seal has to be used."We have a very high peak stress on the glass due to this small metal seal, so there is a higher chance for a crack," explains Pak. To eliminate that risk, the team performed thermocycling experiments on prototypes—and those tests proved they got it right.Another challenge is electron cyclotron (ECH) stray heat on the window due to power injections that are not absorbed in the plasma. This stray heat can propagate to the window through optical paths and may cause damage on the disc. To mitigate this risk, the inner surface of the optical path is coated with electromagnetic wave absorption material, a mixture of aluminum oxide (Al2O3) and titanium dioxide (TiO2). Moreover, every window is equipped with a sensor that continuously monitors for ECH stray power.  Maintenance and repair during operationsThe diagnostic window design is based on the windows used on the European tokamak JET, but with several modifications to meet ±¬×ߺÚÁÏ requirements. They must demonstrate that they can keep the confinement function in ±¬×ߺÚÁÏ against all the normal and abnormal loading conditions. Furthermore, to ensure the soundness of the windows for the duration of the machine's lifetime, a more rigorous set of inspection and maintenance procedures are required, starting with protocols for both preventive and corrective maintenance.The windows are designed to last the lifetime of ±¬×ߺÚÁÏ and they also have on-board monitoring. However it is still planned that they be inspected at least once during their lifetime, starting with a check for visible cracks and for any peeling of the antireflective coating. A second helium leak test will be performed by injecting helium in the transparent surfaces to make sure there are no fissures. Stray heat from the electron cyclotron system that reaches the diagnostic windows could cause disc damage. To mitigate this risk, every window is equipped with a sensor (1). Image (2) shows one sensor mounted on the Wendelstein 7-X stellarator for testing; in image (3), the sensor's electromagnetic-absorbing coating is subjected to a steam exposure test. To allow observation of windows that cannot be seen directly, ±¬×ߺÚÁÏ is developing an endoscopic inspection tool. In this case, cameras will be inserted into tubes and guided to windows to check for cracks.The road aheadEach type of window follows a different timeline for design, manufacturing and testing. The nuclear safety qualification activities for fused silica windows have started and the prototype that will be used for a qualification test is being manufactured. The qualification test will be completed by the end of 2024."In the meantime," says Pak, "we are finalizing the design for three other types of windows—zinc selenide for the interferometer diagnostic systems, small aperture windows for the high-field reflectometry system, and CVD diamond windows for the collective Thomson scattering system."The diagnostic windows provide eyes to observe the plasma—and at the same time, they are safety important components, maintaining the primary torus vacuum and contributing to the safety confinement barrier. The ±¬×ߺÚÁÏ window team is committed to the delivery of high-quality windows meeting those essential requirements.

Registration for the 28th International Conference on Magnet Technology (MT-28) is open on the conference website beginning today, 13 March 2023. See all fee information here, including reductions for retired participants, students and one-day attendees. The registration fee includes access to the exhibition, all technical sessions, all poster sessions, and receptions. The conference will take place in Aix-en-Provence, France (only 30 minutes from the ±¬×ߺÚÁÏ site) from 10 to 15 September 2023. To register to MT-28, see this link.

The ±¬×ߺÚÁÏ World, ±¬×ߺÚÁÏ's second podcast miniseries, debutes this week for International Women's Day with Episode 1: "The Women at ±¬×ߺÚÁÏ." It is available directly through the ±¬×ߺÚÁÏ website or through the following channels: Amazon Music, Apple Podcasts, Google Podcasts, PodBean, Spotify, Tune In and World Radio Paris.  Season 1 of the ±¬×ߺÚÁÏ podcast, All ±¬×ߺÚÁÏ ±¬×ߺÚÁÏ, took a look at what nuclear fusion is and how one of the largest, most complex science experiments on Earth is taking shape in the south of France. Season 2 begins to orbit this world in order to understand its multifaceted inhabitants, their motivations and challenges. From hearing about their love for fusion, to meeting some of the women involved or gaining a first-hand perspective on what it's like to be a part of this extraordinary, once-in-a-lifetime global project. Six episodes are planned, with host Kruti Mawani Fayot. See the podcast page of the ±¬×ߺÚÁÏ website.

Women in Fusion¡ªthe one-year-old global platform established to highlight the role that women play in advancing cutting-edge research and technology in fusion and to promote networking and advocacy¡ªhas launched a new initiative: mentoring.By connecting mentors with mentees, the Women in Fusion program aims to support women with backgrounds in science, engineering, legal or administration in all aspects of their career development, including goal setting, leadership, and work/life balance. Expand your network and foster your career growth as a mentee, or grow your leadership skills and assist an early-career professional as a mentor.All details are available on this page of the Women in Fusion website.