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Fusion world | Translating JET into ITER

With an inner wall made of beryllium and tungsten, the European tokamak JET is the only tokamak in the world to share the same material environment as ITER. When it begins a new experimental campaign with ITER fuels in January 2021, JET will be a crucial source of experimental data. We asked the head of ITER Physics at EUROfusion¹, Xavier Litaudon, where preparations stand and what we can expect to learn. The start of the new campaign with tritium and  deuterium-tritium mixture is planned in just two months. Can you tell us how the teams are preparing? JET is now in the final stages of preparing for experiments with tritium and deuterium-tritium (D-T) fuel mixtures. Indeed, important progress on plasma scenario development—as well as the completion of a major program of enhancement in the active gas handling system for the tritium cycle—led the EUROfusion General Assembly, in July 2020, to approve JET readiness for D-T operation unanimously. Over the past year, significant progress with deuterium plasmas—showing reliable and steady high power operation—has contributed to the development of stationary fusion performance for durations typically lasting 5 seconds, i.e., significantly above the performance obtained previously when JET was equipped with a carbon wall. However, our main objective is to provide good understanding of the consequences for ITER, not just to achieve sustained fusion performance. In this context, progress has also been made in enhancing JET's measurement capabilities in order to deliver high quality data. This data, accompanied by a strong theory and simulation programme so that the underlying physics of the deuterium-tritium plasma can be better understood, means that the JET results will translate to ITER with more confidence. On the technical side, the commissioning of a critical element for operating JET with tritium—the exhaust detritiation system—was completed during summer 2020. The expansion of the tritium boundary from the active gas handling system² to the JET torus and the neutral beam injection boxes was completed in September, and the commissioning of the heating neutral beams in tritium is now underway. I am particularly impressed by the way the team was able to make all of this progress in the context of a very challenging year, despite the interruption of our campaign in March 2020 due to COVID-19 and subsequent reductions in experimental days per week. Before entering the D-T phase, JET will begin by experimenting with "pure tritium" plasmas—a first in the history of fusion research. What will these experiments teach us? The pure tritium experiments will reveal a number of things: how the change of the plasma fuel mass³ will modify the turbulent plasma transport processes in the core and pedestal region; the conditions for the transition from low to high confinement operation (L to H transition); the beryllium wall erosion mechanisms and migration in the scrape off layer to the divertor region; and the divertor detachment under highly radiative plasmas conditions for example. The pure tritium campaign will have a huge impact on the field and on our understanding of the underlying physics of isotope effects. All that is highly relevant for the tritium experiments to come in ITER and in fact in any fusion reactor that wants to run on deuterium-tritium fuel. Indeed, the development of "pure tritium" plasmas will require an extremely high level of preparation to optimize the use of tritium and to strictly respect the new operation boundary (see next paragraph). In this challenging context, a significant effort has been made to prepare very precise and detailed reference discharges that have been recently rehearsed in pure deuterium (or hydrogen) to reach the required level of reproducibility for pure tritium experiments. Today, thanks to the hard work of the whole JET team, all the reference pulses for repeating in tritium are now available and ready for the coming experimental campaign.  On the operational aspects, the JET safety case limits the amount of releasable tritium inside the vacuum vessel stored on the cryopanels of the pumping system to 11 g. To stay within the set limit, it is planned to carry out daily regeneration (overnight) of all cryopanels, which requires approximately 8 hours. In order to keep up with tritium reprocessing and accounting the campaign will be on a five-week cycle, with three weeks of operation following by one week of tritium reprocessing and one week of tritium accounting. The JET scientists will have to learn to carry out experiments with these new operational challenges. We have already rehearsed best practices in tritium operation by operating with pure deuterium this September. The pure tritium plasma experiments heated with tritium neutral beam power will be executed from the beginning of January up to mid-May 2021, followed by the deuterium-tritium campaign lasting until August 2021 and a subsequent tritium clean-up phase. Past results on JET have been extrapolated to predict your future campaign, and those results will be extrapolated to ITER. What is the process? We have computer models, validated using the International Tokamaks Physics Activity (ITPA) worldwide database, of how hot plasmas will behave under certain conditions based both on theory and on previous experiments. We have done much work to validate these models and develop them further, so that now we can routinely predict how future experiments will go. The models include aspects such as plasma turbulent transport, plasma stability, heating and current drive, and the behaviour of fast, hot particles and how that all influences overall performance. We have used our best modelling tools, developed and validated during more than 20 years on JET, and worldwide databases to prepare and extrapolate our present and future operation. We wish to predict first before carrying out the experiments, both to optimize our experimental development effort and to efficiently guide us on the missing physics that needs to be added if the predictions do not match the observed results. This is the fascinating aspect of our work that could lead to new discoveries and a better understanding of the physics processes. It is not enough to just study isolated process; we want to know how they influence each other so we can catch any non-linear behaviour in our predictions!  Indeed, the physics knowledge of D-T plasmas is still limited and ITER will be essential to making further progress. We have to disentangle all kinds of physics processes. For instance, the change of the fuel mass from deuterium to a mixture of deuterium-tritium, or processes related to the alpha heating effects by the reaction product of the D-T fusion reaction. JET has developed a scientific program where similar discharges in D-D, T-T and D-T will be performed, compared and simulated with the models and codes used to predict ITER performance. If new physics processes are discovered they will be implemented in our modeling suite and the simulation will be compared to the latest experimental results to shed light on the physics of the future burning plasma. This effort will contribute to optimizing the transition from D-D to D-T plasma operation in ITER.    Let's also add that, with this campaign, we have a unique opportunity to educate a new generation of young scientists and engineers that then can be involved in ITER operation in the future. The European experimental team involved in the JET D-T campaign involves more than 300 scientists, 25 percent of whom are from the new generation of scientists (PhD, post-doc, or young engineers) who will also have the opportunity to participate in ITER D-T operation in the future—a unique experience for them! Lots of things are happening in the fusion world these days, with ITER now well into the machine assembly phase, MAST having just produced first plasma, JT-60 SA close to producing its own, WEST scheduled to launch Phase II in the summer of 2021, etc. As someone who has been involved in fusion research for a long time, how do you feel about this 'planetary conjunction'? Since the start of my career in fusion more than 30 years ago, what I have liked best is that fusion research is a collective and international endeavour. It gives me the reassuring feeling that we can achieve significant progress when we join our efforts in a common goal that could not be achieved individually. The recent groundswell of progress is the result of every actor making a small contribution on a daily and regular basis, with the collective result surpassing individual contributions to produce significant achievements. So yes, a 'planetary conjunction' is possible when worldwide we work together to resolve challenging goals that transcend us. It is a great feeling of happiness for me, especially in the times we're living through because of the pandemic. ¹ JET, based at the Culham Centre for Fusion Energy, is collectively used under EUROfusion's management by more than 40 European laboratories. Some 300 to 350 scientists and engineers from all over Europe contribute to the JET program.² The active gas handling system stores, supplies and recycles tritium going to and from JET.³ As the tritium nucleus comprises one proton and two neutrons, a tritium plasma is heavier than a pure deuterium or deuterium-tritium plasma.

Worksite | Major progress you don't see from the air

There was a time when aerial pictures of the ITER worksite taken at six-month intervals showed spectacular change. Buildings and structures sprouted from previously vacant lots, new levels were added to existing constructions, and progress was strikingly visible. Today, most of the action takes place inside the buildings, where equipment is being installed, components unpacked and tools prepared for upcoming assembly tasks. Progress remains steady, but it is now rarely visible from the air. As a consequence, playing 'spot the differences' between an aerial photograph from a few days ago with one taken in late May is becoming a difficult game. Still, the differences are there. Can you spot them?

Diagnostic first walls | Pushing manufacturing to the limit

A unique set of challenges calls for a unique set of manufacturing approaches. The ITER Organization is partnering with industry to demonstrate the advanced manufacturing techniques required for ITER's first line of defense for diagnostic systems—the diagnostic first wall.During the final design review of the diagnostic first walls, several concerns were raised with regards to the feasibility of manufacturing approaches suppliers would have to use to meet specifications. To clear up these concerns, a decision was made to build an experimental mockup to demonstrate the efficacy of these methods in terms of robustness and their application in serial production. At the end of 2019, a reduced-scale mockup produced by the Spanish firm IDONIAL was presented in an expert design review and the techniques were approved. 'This extra step of constructing a reduced-scale mockup was useful because it helped us develop new manufacturing procedures and to discard others,' says Julio Guirao, Common Port plug Components Engineer. 'Our mockup validated the combined use of several techniques —gun drilling machining, circular TIG (tungsten inert gas) welds, PAW (plasma arc-welding), ArcTIG (an innovative version of the tungsten inert gas for mechanized joint welding), and ESW (electroslag welding) overlays. We were able to test the structural integrity and thermal hydraulic performance resulting from each approach.'Demonstrating a number of special techniques on a reduced scaleDiagnostic first walls play an essential role for the systems that measure what is happening in the ITER Tokamak during a pulse. One of three main protective components of equatorial port plugs, diagnostic first walls provide thermal and nuclear shielding to both the diagnostic shielding modules and the diagnostic systems themselves. (The other two protective components are the port plug structures, part of the confinement barrier, and the diagnostic shielding modules, the frames which house diagnostics and provide extra shielding).Diagnostic first walls must provide line of sight for the diagnostic systems through cutouts in the walls, but because each of the diagnostic systems operates differently, each of the 82 first walls requires different apertures. For example, some diagnostics shine a laser beam into the plasma. The beam needs to pass through a cutout and also have some freedom of movement to shine from different angles. The holes have to be big enough for the diagnostics—but to maximize protection, they can be no bigger than necessary. 'The cutouts are random penetrations that create a complex geometry, making it all the more challenging to implement the dense cooling network that we need at the front of the port plug to protect against thermal radiation,' says Guirao. To manufacture the network, you can only do straight drills. We have proposed rigid procedures, including gun drilling in vertical and horizontal lines.'Also challenging to manufacture are the connective tabs that will attach each diagnostic first wall to a diagnostic shielding module. To protect them from heat, cooling channels must be implemented in the tabs. 'This has required the development of specific welding procedures to close the pockets around the apertures,' says Guirao. 'With standard TIG welding, we run the risk of having thermal distortions as we would need several passes and welds are quite close to each other. Instead, on the reduced-scale mockup we showed that plasma welding could weld the whole thickness in one pass, minimizing distortions. We are also testing newer processes based on arcTIG welding to bring more flexibility to the manufacturing. Once procedures are developed, we recommend them to the manufacturer.'Progressing to the manufacturing phaseSince the successful expert design review, the ITER Organization has completed a tender process and is now preparing a manufacturing contract for all 82 diagnostic first walls.'Although we have already demonstrated that the advanced manufacturing techniques work in a reduced scale mockup, to minimize production risks we now need to test how these methods work together in a life-sized component,' says Guirao. 'To do this, IDONIAL is building a full-scale mockup that demonstrates a number of combinations—for example, that massive gun drilling works with rather close welding.'The team expects to finish this full-scale mockup by the first quarter of 2021. 'This is around the time we intend to start working with the supplier on the final manufacturing design,' says Guirao. 'All the documentation and knowledge generated by this mockup will be transferred to the supplier. In the end, the supplier decides how it intends to manufacture the diagnostic first walls—but the outcome of the mockup will provide very good guidance in anticipating risks.' The final stage is the manufacturing readiness review, during which the ITER Organization makes its final assessment before giving its green light.

In memoriam | Todd Evans, a pioneer in three-dimensional magnetic fields

The fusion community is without one of its most creative members with the passing away of Todd Evans last month. Todd dedicated most of his career to furthering the theoretical and experimental understanding and application of three-dimensional (3-D) magnetic fields in fusion devices. He played a key role in this area of international research, contributing to the design of 3-D magnetic field systems on a large number of devices across the ITER Members R&D fusion institutes, such as the tokamaks TEXT and DIII-D (USA), JIPPT-IIU (Japan), Tore-Supra and TEXTOR (Europe).Of particular importance for ITER was his discovery that specially designed 3D magnetic fields can avoid the triggering of edge magnetohydrodynamic instabilities (so-called Edge Localized Modes or ELMs for short) in H-mode plasmas. In this regime, energy confinement is improved by the formation of a "transport barrier" at the very periphery of the plasma, providing improved insulation from the hot core plasma. Operation in H-mode is required for ITER to demonstrate the project's high fusion power gain (Q) goals, but is accompanied by rapid and periodic bursts of energy and particle losses associated with ELMs. Although the ELMs themselves usually have relatively minor effects on the plasma, leading to losses of only a small percent of the plasma energy, they generate repetitive, fast transient plasma heat pulses on the in-vessel components facing the plasma. Left unmitigated they would, on ITER, greatly increase surface erosion of these components, significantly reducing their lifetime. Todd Evans led the initial effort to demonstrate that these ELM instabilities can be avoided by applying specially tailored 3D magnetic fields called resonant magnetic field perturbations (or RMPs), while the plasma retains the desirable features of the H-mode regime. He led the first pioneering experiments on the DIII-D tokamak by using a system of coils located inside the tokamak vacuum vessel and originally installed to control a different magnetohydrodynamic plasma instability (the resistive wall mode). In 2006, he published a seminal paper in Nature Physics demonstrating, for the first time, an 'ELM suppression' scheme compatible with the edge plasma conditions expected in ITER.Todd's achievement had a profound impact on the fusion community and on the ITER design itself. A whole host of fusion devices (such as ASDEX-Upgrade, COMPASS, JET and MAST (Europe); EAST (China); KSTAR (Korea); and LHD (Japan)) followed his lead, either by deploying existing coil sets or installing completely new systems to study this innovative ELM control scheme so important to the future success of ITER.  As part of the ITER Design Review carried out in 2007-2008, the ITER Organization also started a series of studies to incorporate an in-vessel coil system to provide ELM control within the ITER baseline design. This required a series of engineering and physics studies, to which Todd was an essential contributor. The design effort to incorporate a comprehensive ELM control coil set into the ITER machine proved to be an extremely complex challenge, but was ultimately successfully completed. This was recognized by the ITER Council Science and Technology Advisory Committee in 2013 with its recommendation that these coils be formally included in the ITER baseline design. The ELM coils completed their final design review in 2019 and are presently being manufactured. Throughout this long process, Todd was always ready to advise and support the ITER Organization in many of the specific design decisions that had to be taken to make the ELM control coils in ITER a reality.In addition to his direct contribution to the ITER design, Todd Evans has been a leading figure in driving R&D for the application of resonant magnetic field perturbations for the resolution of specific issues affecting ITER plasma performance, core-edge plasma integration and the development of the ITER Research Plan. Among the issues, are the use of resonant magnetic field perturbations for ELM suppression in helium plasmas during ITER's Pre-Fusion Power Operation phase*, and the fuelling of ELM-suppressed plasmas with pellets. His curiosity, perseverance, and willingness to help others understand complicated physics issues and to produce results of practical application to fusion development will be missed by the fusion community and by the ITER Organization.Todd E. Evans died on 26 October 2020; click here to read an obituary published on the DIII-D website.**During this phase of ITER operation, hydrogen and helium plasma scenarios will be developed to allow the full commissioning of all tokamak sub-systems (except those involving the use of deuterium or tritium) with plasma.

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Apply now: 100+ ITER internship opportunities

The ITER Organization has kicked off its 2021 internship program with the publication of 116 offers on the ITER website (visit Jobs/Internships here: https://www.iter.org/jobs/internships). These opportunities are geared toward undergraduate and postgraduate students, with a broad array of topics across scientific, technical and support departments. Control and data acquisition, systems engineering, business operations, construction and installation, safety and security, and science and technology are all represented in this year's batch of internship opportunities. Positions are offered for up to six months; some categories are extendable to one year. Apply before 28 February 2021 through the online e-recruiting system. (Please note that internship opportunities are limited to nationals from countries participating in the ITER Project, i.e., China, the European Union plus Switzerland, India, Japan, Korea, Russian Federation and the United States.)

JT-60SA tokamak enters cooldown

The JT-60SA fusion experiment in Naka, Japan, has entered its integrated commissioning phase—one of the last steps before first plasma. This collaborative project, financed and executed jointly by Europe and Japan under the Broader Approach agreement, will soon be running experiments to support the operation of ITER and to investigate how best to optimize the design and operation of fusion power plants built after ITER. Preparing the newly upgraded device for its first plasma is step-by-step operation that began with the evacuation of all air from the vacuum vessel and surrounding cryostat, and was followed by the current phase of slowly cooling down the device's superconducting magnets to the temperature of 4 K (- 269 °C). This phase started on 10 October 2020 and is expected to last several weeks. (You can follow the progression of cooldown here.)  Once the magnets reach the desired temperature, the team will heat up the vacuum vessel to 200 °C to rid it of moisture and any possible residual contaminants. Energizing the magnets come next, first each magnet separately before the full group together. The final step, before injecting hydrogen for making a plasma, is to test the electron cyclotron resonance heating. Read more at Fusion for Energy.

ITER makes world's "most influential projects" list

The ITER Project has been selected as one of the world's most influential projects by the Project Management Institute in its 2020 ratings, released in November. The professional organization's Top 50 list singles out 'compelling efforts across industries and around the world that have achieved significant milestones' during the year. 'In a time of uncertainty and upheaval, bold projects are paving the way to a new future.' Each effort is 'a distinct masterclass in how to navigate change and deliver results.' The ITER Project is #34 overall and #3 in the Top 10 list for projects in the domain of energy, recognized for 'boldly exploring next-gen nuclear energy.' Find out more here: https://www.pmi.org/most-influential-projects.

press

1st Spanish Fusion High Performance Computing Workshop 2020: 27 November (online)

Most Influential Projects 2020

Los 10 proyectos de Energía más influyentes del 2020

Challenges for humanity (ITER: from 21:45)

документальный фильм "Вызовы человечеству" (ITER from 21:45)

Hexagon Inaugurates Preferred Supplier Partnership With ITER

General Atomics wins ITER contract

How to carry the diagnostic signals from the ITER vacuum vessel outside

Med igranjem boga in iskanjem svetega grala

The Shape of This Machine Could Finally Move Fusion Forward

울산시, UNIST·현대重과 '인공태양 프로젝트' 추진

UKAEA's £55m device successfully takes a step closer to fusion power

International Thermonuclear Experimental Reactor project: 'Sun machine' could provide world with clean energy

General Atomics Awarded Contract to Develop Key Component for ITER

A hombros de gigantes - La energía de fusión, cada vez mas cerca

Team achieves first plasma on upgraded MAST, ready to test Super-X divertor

MAST Upgrade achieves first plasma

Acceso il reattore sperimentale a fusione britannico

Dansk forsker i fornemt selskab på fusionsreaktor