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Joint ITER-EAST experiments | A wealth of data harvested
In January, ITER scientists teamed up with colleagues at the EAST tokamak in Hefei, China, for a run of joint physics experiments. The experiments were designed to address specific ITER questions on the reliability and operability of tungsten as a plasma-facing material. Throughout 2023 and continuing this year, teams of engineers and scientists at the ITER Organization have been focusing intensely on a re-baselining exercise intended to mitigate some of the delays experienced by the project due to the Covid-19 pandemic and some hardware issues on the main vacuum vessel and associated thermal shields. One of the key components of the re-baselining is the replacement of beryllium by tungsten as plasma-facing armour on the main chamber walls, representing some 600 m2 of material surface. Beryllium is a low-atomic-number element, so that relatively high concentrations can be tolerated in the hot plasma core before fusion burn is compromised. On the downside, the well-known issues associated with toxicity, high erosion under plasma bombardment and the tendency of eroded material to trap the tritium fusion fuel on the reactor walls mean that the benefits of a beryllium first wall for the plasma are offset by significant technological, operational and licensing issues for the plant as a whole. The particular issues of high erosion and fuel trapping, coupled with relatively low melting point, also mean that beryllium cannot be considered as a reactor-relevant wall material. On the contrary, tungsten is widely accepted as the best candidate plasma-facing material for future fusion power plants. Its main drawback is that burning plasmas can tolerate only minuscule tungsten concentrations in the hot core. While the importance for ITER of the recent JET success in producing record fusion plasmas with a beryllium first wall cannot be understated, the physics basis for 'full tungsten' ITER operation, as proposed in the new re-baseline, is also far stronger than it was when the ITER Organization was established in 2007. At that time, the ASDEX Upgrade tokamak at the Max Planck Institute for Plasma Physics in Garching, Germany, had only just made the conversion to full tungsten coverage while, in the United States, the high-magnetic-field Alcator C-Mod device had been running for about a decade with metal walls, but using mostly molybdenum—also a high-atomic-number element, but a contaminant more tolerable to fusion-grade plasmas than tungsten. Since then several tokamaks have joined the race: such as the WEST tokamak near ITER at CEA Cadarache, the EAST tokamak at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) in Hefei and, more recently, the Korean Institute of Fusion Energy's superconducting KSTAR tokamak in Daejeon, which restarted operation in late 2023 after a year-long shutdown to install a new actively cooled, ITER-like tungsten divertor. Together, the results of these experiments at ITER partner facilities provide much greater confidence that a decision to start ITER operation with tungsten and reach the project's fusion goals is no longer the high-risk option it seemed in 2007. But there remain some physics uncertainties coming both from the magnitude of the extrapolation from the medium-sized tokamaks to ITER, and the need to have key results from more than a single device. The main issues of this extrapolation are known and are being addressed in the ITER Science Division, with the help of experts in the fusion community through the ITER Scientist Fellowship Network and the International Tokamak Physics Activity (ITPA). Their involvement has been actively sought by the ITER Organization, and met by an enthusiastic response, from the very beginning of the re-baselining activity. But some of the outstanding questions require new tokamak experiments and—with ASDEX Upgrade currently in major shutdown throughout 2023 until the summer of 2024, and WEST only just restarting operation after its last 2023 maintenance period but still without sustained high confinement (H-mode) performance—time is tight to gather new data in time to support the new baseline proposal to be submitted to the ITER Council in June 2024 for a decision in November. During discussions at the 2023 IAEA Fusion Energy Conference, the ITER Organization therefore requested support from ASIPP and received, in November 2023, the extremely generous offer to place the EAST tokamak and its team at the disposal of the ITER Science Division for a mini-campaign from December 2023 up to the start of the Chinese New Year (10 February 2024) targeting ITER re-baselining activities. The offer was all the more generous taking into account that EAST has operated in the last decade with ultra-long-pulse, high-power-performance plasmas as main focus, for which the requirement for strong external current drive with a specific form of radio frequency plasma heating using so-called lower hybrid waves (not a heating scheme ITER will use) needs low density plasmas—precisely a regime in which high-atomic-number first wall materials are not ideal. To solve this, EAST has routinely used the injection of lithium powder into their discharges, providing a temporary low-atomic-number coating on plasma-facing surfaces and preventing the ingress of heavier impurities eroded from the walls. Operation to address specific ITER questions on the use of tungsten thus required significant advanced preparation for the EAST team and a clear focus for the experimental campaign. The ITER Science Division settled on three main ITER priorities for the EAST experiments: the optimization and characterization of a wall conditioning process known as boronization, plasma start-up on tungsten surfaces, and the impact on H-mode operational space of running soon after, and far in plasma operation time from, a boronization coating. While these issues have to some extent been addressed on ASDEX Upgrade and WEST operating with tungsten, the new EAST experiments have made a significant addition to the database. Targeted boronization experiments on EAST aimed to add further important data to the catalogue of experience on current devices, but also to go further and investigate the impact on the uniformity and quality of the coating as a function of the way in which the boronization is performed. In particular, comparing the efficacy of active radio frequency plasma generation, known as ion cyclotron wall conditioning (ICWC, which uses high power ion cyclotron antennas used normally for tokamak plasma heating) with the more standard technique of direct current glow discharges induced by specially designed passive anodes. ITER is being equipped to do both, but quantitative data on ICWC-induced boronization is almost non-existent. Since the thin boron coatings are quickly eroded in areas of direct tokamak plasma contact (such as the zones on the wall where tokamak plasmas are usually initiated), a key question is how easy it will be on ITER to ramp up plasmas in such 'limiter configurations' on areas where tungsten is fully exposed. In the early phases of tokamak pulses—lasting only a few seconds on ITER and usually less than one second on smaller devices—plasmas resting directly on tungsten surfaces are particularly prone to high radiation losses, when the eroded tungsten has a direct route into a still relatively fragile plasma. If that phase can be successfully navigated and the plasma is moved away from the walls to form a 'diverted configuration'—when plasma heat and particles are predominantly exhausted to a region (the divertor) distant from the main reaction chamber—another important question is how the gradual removal of the boron coating impacts the high-performance H-mode plasma operation which is required to achieve Q=10 plasmas in ITER. With these main themes in mind, experimental plans were drawn-up within the ITER Science Division through December 2023 and early January 2024, with the participation of external ITPA experts and EAST team members. While many were enjoying the Christmas festivities, the EAST team was operating and preparing for the ITER experiments which took place for the most part between 18 and 26 January, with three ITER Science Division members, Alberto Loarte, Richard Pitts and Tom Wauters, traveling to EAST to participate. By any standards, this was an intense few days of experiments, with EAST operating typically from 9:00 a.m. to 11 p.m. most days, including weekends. Fast-pulse repetition rates and a very efficient operating team combined to make for an eye-watering experimental pace, all conducted from the futuristic and quite magnificent EAST tokamak control room, which must surely rank as the finest of its kind. Remote participation is also very efficient at EAST, allowing Joerg Hobirk from the ASDEX Upgrade team and other ITER Science Division members to participate in the experiments. In all, some 6 boronization processes and over 400 tokamak pulses were executed during the campaign, providing a wealth of data which will require quite some effort and time for the EAST team, in collaboration with ITER Organization staff and external experts, to properly analyze, understand and present. Valuable new information has been obtained on boronization uniformity and process and on routine plasma start-up and stationary operation on a pure-tungsten, water-cooled outer limiter (including a record 17 sec limiter discharge). A clear demonstration has also been obtained that good H-mode confinement can be obtained in both boronized and unboronized conditions in proximity to tungsten main chamber surfaces, provided edge localized magnetohydrodynamic (ELM) activity is kept to low levels. Since this is already a condition for adequate lifetime of the ITER tungsten divertor targets, the EAST experiments provide yet more evidence for the importance of ELM control on a full-tungsten ITER. In a short break from experiments, the ITER scientists were treated to an eye-opening visit to the new CRAFT site (Comprehensive Research Facility for Fusion Technology), a short drive from the ASIPP campus. The facility was completed in early 2022 and is now prototyping components for the Chinese fusion reactor program and manufacturing coils for the next big project to follow EAST, the BEST tokamak, which will use deuterium and tritium fuel and is due to begin operation later this decade. No one spending time in the CRAFT visitors centre, even seasoned fusion campaigners, can fail to be impressed by the way in which the amazing field of fusion science and technology is communicated there to the wider public. The ITER Organization thanks ASIPP Director General Yuntao Song for opening the EAST facility for these experiments and for the generous hospitality extended to ITER scientists. Though intense, this visit to EAST was made a rewarding and efficient experience by the excellent and seamless organization provided by Xianzu Gong, Head of the Division of Tokamak Experiments, and his deputy Rui Ding. The entire EAST team (especially Jinping Qian, Manni Jia, Youwen Sun, Qingquan Yang, Ling Zhang, Xinjun Zhang and Guizhong Zuo) deserves enormous thanks and credit for working so hard before and during the experiments, and in advance for all the work to come in analyzing the data obtained. A happy new Year of the Dragon to all!
Seminar | JT-60SA team shares experience with ITER
JT-60SA, a collaboration between Europe and Japan, began operating last year as the world's largest tokamak. This week, the JT-60SA integrated project team is holding a technical coordination meeting at ITER—and taking advantage of its presence on site to share the lessons learned during the assembly and integrated commissioning phases with the broader ITER community. Since November 2019, the ITER Organization has been benefitting from the experience gained in fusion activities under the Broader Approach Agreement—and in particular the assembly, installation, integrated commissioning and operation of the tokamak JT-60SA—based on the terms of a collaboration arrangement signed in November 2019 with Japan's QST (National Institutes for Quantum and Radiological Science and Technology) and Fusion for Energy (the European Domestic Agency for ITER). Since the first collaboration activity was launched in 2020, ITER scientists have travelled to the JT-60SA site in Naka, Japan, and participated in integrated commissioning activities. The device achieved first plasma in October 2023, and celebrated the start of operation during a ceremony in December attended by ITER Director-General Pietro Barabaschi and Deputy Director-General for Science and Technology Yutaka Kamada. For its first Technical Coordination Meeting since JT-60SA became an operational tokamak, the team has chosen to gather at ITER Headquarters, and to kick off the week with a two-hour seminar for the broader ITER community (photo). With hundreds of people in attendance, in person or on line, the team went over the important lessons learned during the integrated commissioning period, and fielded technical questions from the audience. Other public talks are planned this week.
On site | Collaborating to advance tokamak integrated modelling
Present-day tokamak integrated modelling development activities put significant emphasis on the development of high-fidelity physics models to extrapolate physics understanding obtained from current experiments to future devices, on integration of the validated physics models into workflows, and on the application of automated larger-scale validation. In this context, the third meeting of Advances in Tokamak Integrated Modelling (ATIM), jointly organized by EUROfusion's TSVV11 (Theory, Simulation, Validation and Verification) task and the Dutch eScience Centre (Large-scale Validation and Uncertainty Quantification), took place at ITER Organization headquarters from 22 to 26 January 2024. The main aims of this meeting were to share recent advances in the area of tokamak integrated modelling and to align activities with ITER's integrated modelling development needs. Advanced predictive modelling of plasma operation scenarios will be required in ITER and future tokamaks not only to prepare their research plans with detailed experimental campaigns, but also to support the design and validation of tokamak components and controls, and to analyze plasma discharges obtained during experimentation. These modelling-oriented activities require validated physics models covering a wide range of physics fidelity—from fast empirical or surrogate models for control applications to high-fidelity physics models for detailed analysis. These validated models are integrated into robust modelling workflows designed to address specific use cases without loss of physics fidelity. Large-scale automated validation and uncertainty quantification (UQ) can significantly facilitate the validation of both stand-alone physics models and integrated modelling workflows, providing the ranges of validity and/or uncertainties. Recent advances in artificial intelligence (AI) can also contribute to the development of the surrogate models necessary to develop fast-plasma pulse design software and plasma control algorithms suitable for real-time application. A new Persistent Actor Framework (based upon the MUSCLE3 Multiscale Coupling Library and Environment) implemented within ITER's Integrated Modelling & Analysis Suite (IMAS) is enabling co-simulations across different software environments. All these advanced developments not only support ITER integrated modelling priorities, but also those of existing and future devices. To share recent advances in the tokamak integrated modelling area and to align various activities with ITER's integrated modelling development needs, the third in-person meeting of Advances in Tokamak Integrated Modelling (ATIM), jointly organized by EUROfusion's TSVV11 (Theory, Simulation, Validation and Verification) task and the Dutch eScience Centre (Large-scale Validation and Uncertainty Quantification), was hosted at ITER Organization headquarters from 22 to 26 January 2024. More than 50 participants, including many young modellers and scientists, took part. The meeting was organized to start with plenary sessions providing reports on recent progress and plans, and then continued with multiple parallel sessions designed to directly exchange technical expertise and information. Multiple trainings on the large-scale automated validation tool (dUQtools), IMASpy, and the iWrap actor generation tool were also provided respectively by the Dutch eScience Center and the Ignition Computing and Poznan Supercomputing and Networking Center to support ITER Integrated Modelling and Analysis Suite (IMAS) development within the ITER Members. Various advances in the high-fidelity integrated modelling platforms used throughout Europe (JINTRAC, ETS and ASTRA) were discussed to support the development of ITER's high-fidelity plasma simulator (HFPS), which is also currently based on JINTRAC (core-edge-SOL-divertor/wall transport and source modelling) in combination with DINA (free-boundary plasma equilibrium evolution). Topics covered the modelling platforms, current ramp-up modelling for validation, tungsten impurity transport modelling and prediction, and further improvements of core transport and pedestal/scrap-off-layer models. Fast-pulse design and optimization tools, including the ITER pulse design simulator (PDS), were also presented to share their status and plans. The next steps are foreseen to include further validation of physics models including multi-physics components (MHD, impurity, rotation, pedestal, etc.), improvement of physics modelling workflows (with modular and exchangeable components) and systematic validation against larger experimental databases, aligned with ITER's integrated modelling development needs.
Outreach | ITER in a spaceship
Close to 30,000 people attended the Yggdrasil festival this past weekend at EUREXPO in Lyon, France's third largest city. Named after a central element of Nordic mythology, the sacred tree Yggdrasil, the event brought together science fiction, heroic fantasy, and cosplay enthusiasts in a fantasy world bathed in exuberance and imagination. ITER was present in the Demain, mais en mieux ("Tomorrow, only better") spaceship, along with 20 other European labs, research institutes and leading companies and institutions (Airbus, Dassault, Électricité de France, the French Alternative Energies and Atomic Energy Commission CEA, the French National Research Agency, the National Centre for Space Studies and others)—all dedicated to shaping a better future for the generations to come. At the ITER booth, visitors could play with the futuristic ''holobox'' and discover the different tokamak components, take a virtual tour of the ITER platform by way of virtual reality headsets, or ask about the nature and function of an actual prototype of the divertor inner vertical target.
Image of the week | Repaired thermal shield elements leave Indian facility
Three panels from the vacuum vessel thermal shield sets that were sent to India for repair are now heading back to ITER to be reassembled. At the INOX-CVA facility in Vadodara (Gujarat), cooling pipes were removed from the panels, the pipe path was machined, and new piping was welded to the surface. It takes approximately eight months to complete repairs on one set of vacuum vessel thermal shield—an 'assembly unit' consisting of one inboard and two outboard segments. After placing a contract in June 2023 for the repair of two sets, a contract was placed in December 2023 for three additional sets to be sent to INOX-CVA for repair.
of-interest
Europe's first sector passes leak tests
The European Domestic Agency, Fusion for Energy, has announced that the first of five vacuum vessel sectors under its responsibility has passed leak testing. The tests, which assess leak tightness using nitrogen and helium, are the first in a line of factory acceptance tests that must be completed successfully before the component can ship. See the full report on the Fusion for Energy website. --View of the Europe's vacuum vessel sector 5, Westinghouse/Mangiarotti, Italy ©F4E
Nominations open: 2024 Fusion Technology Awards
The IEEE Nuclear Plasma Science Society (NPSS) Fusion Technology Standing Committee is pleased to announce that during the 31th Symposium on Fusion Engineering (SOFE 2025) in Boston, the 2024 Fusion Technology Awards will be presented to individuals who have distinguished themselves through innovation in any fusion approach that has shown significant promise or progress in the design of reactors or in the understanding of fusion plasmas. The awards each consist of a USD 3,000 cash prize, a plaque, and an invited talk at SOFE 2025. The nomination package—consisting of a letter describing the technical contributions on which the nomination is recommended and a current resume of the candidate—should be sent to the Fusion Technology Committee Awards Chair, Dr. Carl Pawley (drcpawley@ieee.org). Other supporting endorsements are encouraged. Equal consideration will be given to innovation in all fusion approaches and outstanding leadership in the fusion community. For more detailed information on eligibility, basis for judging, the nomination process or a list of past award recipients, please visit the IEEE-NPSS website and go to the "Fusion Technology Awards" section. The nomination deadline for the 2024 Fusion Technology Awards is 11 March 2024.
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