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As buildings rise out of the earth and equipment is progressively installed, °ÄÃÅÁùºÏ²Ê¸ßÊÖ's Science & Operations Department is busy making plans to commission the first plant systems. Commissioning is the final check that each of the components and plant systems have been designed, manufactured and installed correctly. It is an opportunity to transfer knowledge to the operations team, test all the procedures, and get ready to start the first experiments.   To commission a facility as complicated as °ÄÃÅÁùºÏ²Ê¸ßÊÖ it is necessary to proceed in small and gradual steps—checking each part before moving onto the next, and bringing together more and more pieces of the puzzle until the whole facility is working as one. At that point we will be ready to turn on the Tokamak and make plasma.   We will start this year by energizing the electrical distribution systems, since without electricity nothing can work. °ÄÃÅÁùºÏ²Ê¸ßÊÖ is directly connected to France's 400 kV public transmission network. Transformers and switchgears located on the °ÄÃÅÁùºÏ²Ê¸ßÊÖ platform will "propagate" this power all over the site to provide the correct voltage for each of the clients.   Last year, a test was performed with the first energization of a 400 kV bay, in order to validate all procedures and contractual requirements with French transmission system operator.   Once power is available, the central control system will be turned on and made ready to control, monitor and record data from each of the systems to come. The first task for the control system will then be to start up the cooling water systems and the cooling towers, testing each pump and valve before starting the circulation and flow tests.   First commissioning task: electrical distribution Commissioning of electrical supplies will begin this year with the energization of the four 400 kV transformers connected directly to the French national electrical network, an operation that will be performed jointly with RTE (Réseau de transport d'électricité), the transmission system operator. These transformers will then be used to progressively energize the 22 kV switchgear for distribution of this "steady-state" baseline electrical supply to the load centres spread around the °ÄÃÅÁùºÏ²Ê¸ßÊÖ site serving different client systems. Later, this process will be repeated for the transformers providing the 66 kV and 22 kV supply to the pulsed power network for the superconducting magnets and other systems that require the supply of electricity during a plasma pulse. With power, control and cooling in place we will begin commissioning the production and distribution networks for various gases and liquids, as well as the air conditioning to remove heat generated by the plant in each building. We then start up the nitrogen and helium production facilities in the cryogenic plant and the various auxiliary vacuum pumping systems.   The specialized Tokamak systems come next—the electron cyclotron system that generates megawatts of microwave energy to heat the plasma, cryogenic pumping systems able to produce ultra-high vacuum, and the power supplies needed to energize the superconducting magnets.   When all of these systems have passed their tests we are ready: the construction phase of °ÄÃÅÁùºÏ²Ê¸ßÊÖ is complete and we can start the operations phase with integrated commissioning of all systems working together. All air will be evacuated out of the vacuum vessel and cryostat to bring the pressure inside to one millionth of normal atmospheric pressure; the magnets will be cooled down to -269 °C and energized to create the magnetic confinement field; and a tiny amount of hydrogen gas will be injected and heated up to produce a critical milestone for °ÄÃÅÁùºÏ²Ê¸ßÊÖ—First Plasma.   Once this has been achieved we will press on—turning up the current on the magnets to full power and completing their stress testing under all the various field combinations.   At that point we will have shown that the °ÄÃÅÁùºÏ²Ê¸ßÊÖ machine is ready for the researchers.

Living without a partner dramatically reduces one's life expectancy. And what is true for human beings is even truer for neutrons. Bound to a proton inside an atomic nucleus, a neutron can expect to live forever; alone in the world it barely survives more than ten minutes. Lone—or "free"—neutrons are created naturally by cosmic rays interacting with the upper layers of the atmosphere. During their short trip to the Earth's surface, their destiny depends on what they encounter.   Because matter is mostly void, a fair amount of "cosmogenic" neutrons will zip through the air, not encountering anything. Others will collide with whatever particle—nitrogen, oxygen, carbon—that happens to be in their way.   Depending on the incoming neutron's energy—and some of them can be extremely energetic¹—and depending also on the latitude and altitude of the encounter and on the nature of the particle, different things may happen. Michael Loughlin, °ÄÃÅÁùºÏ²Ê¸ßÊÖ Nuclear Shielding & Analysis Coordinator, explains: "A neutron can kick out a proton or another neutron from the nucleus it collides with; it can be absorbed and give birth to an isotope (that's how carbon 14 is created); or it can just bounce off the 'surface' of the nucleus and lose energy in the process."   Of all the neutrons produced in the atmosphere, only a few will reach the Earth's surface. Depending on the location and altitude of their landing, they will rain down at the rate of 100-300 neutrons per second per square metre. Over eons of evolution, living things have adapted to cope with this neutron drizzle.   If they have retained enough energy—and if their lifespan has not expired—neutrons may get a last chance to join a nucleus. The soil on the surface of the Earth offers more mating options than the atmosphere, so the cosmogenic neutrons can be absorbed by iron, silicon, potassium, etc.   When a neutron's time is up it dies a quick death, decaying into a proton, an electron and a neutrino².   Free neutrons are also created artificially for research purposes: an intense neutron beam can probe deep into solid objects and reveal their intimate molecular structure.   And of course neutrons are central to fusion energy, both as a blessing and as a safety issue.   The neutrons from the fusion reaction inside the vacuum vessel generate the heat that, in a fusion plant, will initiate the electricity-producing process. They will also be put to use, in a later operational stage, to experiment tritium production inside the machine.   At full power, the °ÄÃÅÁùºÏ²Ê¸ßÊÖ machine will generate one hundred billion billions highly energetic neutrons per second. Compared to the natural drizzle, it will be a non-stop hurricane. And this is something living things and the environment needs to be protected from.   The rules governing °ÄÃÅÁùºÏ²Ê¸ßÊÖ's fusion neutrons are the same as those governing the passage of cosmogenic neutrons through the atmosphere, but the environment they will encounter is radically different. Instead of thin air, the fusion neutrons travelling at approximately 51,000 kilometres per second (17 percent of the speed of light!) will face a succession of daunting physical obstacles, some of them exceptionally dense.   Beryllium in the shielding blankets; high-strength copper and stainless steel in the vacuum vessel's first wall; ultra-dense neutron-hungry borated concrete³ in the bioshield—these materials will contribute to absorbing the neutron flux from the fusion reaction and keep radiation escaping to the environment to a minimum. But given the proportion of void in even the densest materials, some neutrons will pass all the obstacles unscathed.   How many? "A handful," answers Michael. And nothing, really, to worry about—the survivors will be so few that they will be undistinguishable from the natural background neutron noise.   ¹ A small proportion of cosmogenic neutrons have energy in the range of 28 MeV — twice that of fusion neutrons. ² The electron and the proton will slow down and eventually combine with other protons and electrons to form a new nucleus. As for the neutrino, it will head off into space never to be seen again. ³ The isotope Boron 10 has a strong appetite for neutrons. In the areas of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ bioshield that are the most exposed to the neutron flux, a concrete formulation that includes 0.3 percent of boron will be used.  

Three years ago in late March, the most imposing features on the °ÄÃÅÁùºÏ²Ê¸ßÊÖ platform were the workshops for the cryostat (left) and the poloidal field coils (right)—vast facilities where the manufacturing and/or assembly of some of °ÄÃÅÁùºÏ²Ê¸ßÊÖ's largest components was set to begin. Construction of the Assembly Hall had just begun, and the first steel pillars had been installed on opposite sides of the building's concrete floor slab. In the 90 x 130 metre area reserved for the Tokamak Complex, nothing yet had emerged above the platform level—work was concentrated at the level of the B2 slab, where preparatory works were underway for the construction of the bioshield.   Three years later the difference is striking. In this picture taken last week from the same angle, the 60-metre-tall Assembly Hall and its poster of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Tokamak are a towering presence that completely hides the Cryostat Workshop from view. To the right, the Poloidal Field Coils Winding Facility is masked by a cluster of plant buildings.   And in the area of the Tokamak Complex, some of the walls now stand four storeys above platform level and the massive 30-metre-tall bioshield has been finalized.   However impressive the photo comparison may be, a large part of the progress that °ÄÃÅÁùºÏ²Ê¸ßÊÖ has achieved since 2015 cannot be detected in these snapshots. Hundreds of components, both large and small, have been manufactured and safely delivered to the construction site. Many more—among them some of the largest and most challenging °ÄÃÅÁùºÏ²Ê¸ßÊÖ components—are in various stages of advanced fabrication or factory acceptance testing.   According to the stringent metrics that monitor project performance °ÄÃÅÁùºÏ²Ê¸ßÊÖ has now completed 53.7% of the total work scope on the road to First Plasma (calculated on the base of all design, construction, manufacturing, delivery, assembly, installation, and commissioning activities).

Last week's Newsline reported on the participation of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Director-General in a US Congressional hearing on 6 March focused on the US fusion research program, including °ÄÃÅÁùºÏ²Ê¸ßÊÖ. Rarely has such a visit seemed more timely. Eight days later, on Wednesday 14 March, the House of Representatives issued a revised draft of budget legislation that almost doubled US fiscal year 2018 (FY2018) funding for °ÄÃÅÁùºÏ²Ê¸ßÊÖ—from the $63 million originally proposed to $122 million. A mere 48 hours later, the draft "omnibus spending bill" had been approved by House and Senate and signed into law by President Trump. Of course, cause and effect is never that simple: it would be a mistake to characterize the 6 March hearing as the sole basis for the °ÄÃÅÁùºÏ²Ê¸ßÊÖ funding increase. But as °ÄÃÅÁùºÏ²Ê¸ßÊÖ Director-General Bigot commented, the increase can be taken as "a strong positive signal," especially since it represents bipartisan consensus across both houses of Congress. Critically, as Bigot notes, "If the $122 million is properly applied, we should be able to avoid any delays to the °ÄÃÅÁùºÏ²Ê¸ßÊÖ schedule in 2018."  The new legislation did not attempt to address the shortfall in US in-cash contributions for 2016 or 2017. The Director-General hopes this will be addressed soon, when the US finishes its review of °ÄÃÅÁùºÏ²Ê¸ßÊÖ under the ongoing Nuclear Energy Policy Review.   On a broader note, it is also worth noting the increases to overall US science funding as part of the same legislation. The Department of Energy's Office of Science, which had requested about $5.347 billion for FY2018, was allocated about $6.260 billion, a sizable increase. Within the Office of Science, Fusion Energy Sciences also increased sharply, from the $310 million requested to about $570 million. Additional details can be read here. (For Fusion Energy Sciences and °ÄÃÅÁùºÏ²Ê¸ßÊÖ, see page 40).

The first poloidal field coil to be installed during the °ÄÃÅÁùºÏ²Ê¸ßÊÖ machine assembly phase may be one of the smallest in terms of lateral dimensions, but it tops out its five sister coils in weight due to the number of stacked layers (or double pancakes) that go into its construction.  At the Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP) in Hefei, China, an 80-person team is involved in the fabrication of poloidal field coil #6 (PF6) on behalf of the European Domestic Agency*. Each poloidal field coil is unique. Depending on the number of double pancakes (the building block of the coil) stacked to form the final assembly and the number of "turns" in each layer, °ÄÃÅÁùºÏ²Ê¸ßÊÖ's poloidal field coils vary in weight from 193 tonnes (PF1) to 396 tonnes (PF6), and in diameter from 9 metres (PF1) to 24 metres (PF3 and PF4).   The sixth coil is the only one of the poloidal field set with nine double pancakes, compared to six or eight for the others. It also has double the number of spiral-like turns of the similar-sized PF1—meaning that more conductor is required. Finally, the clamp arrangement for the assembled PF6 coil will be heavier than the others due to an exceptionally thick bottom plate.   By September of this year, the contractor expects to have completed the fabrication process for the nine double pancakes—including winding, impregnation, and the creation of helium and electrical joints.   This will open the way to final assembly activities on the 10-metre-in-diameter coil, such as stacking, joining, ground insulation and final impregnation. Please see the full report on the European Domestic Agency website. *The second-smallest ring magnet for °ÄÃÅÁùºÏ²Ê¸ßÊÖ is being fabricated in China on the basis of an agreement concluded with the European Domestic Agency.

Halo currents—electrical currents that flow from the hot, charged plasma that fuels fusion reactions and strike the walls of fusion facilities—could damage the walls of fusion devices like °ÄÃÅÁùºÏ²Ê¸ßÊÖ. Such currents occur during plasma disruptions and channel large amounts of electrical current from the plasma to the vessel walls. "These findings provide scientific guidance to the °ÄÃÅÁùºÏ²Ê¸ßÊÖ team as they work to address the disruption problem," said physicist Clayton Myers, lead author of a paper that reported the findings in the journal Nuclear Fusion.   The findings "place additional importance on the reliability of °ÄÃÅÁùºÏ²Ê¸ßÊÖ's disruption mitigation system, which can alleviate the effects of halo current rotation," said Myers, who led the research project while at the US Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) and now is a researcher at Sandia National Laboratories, another DOE national laboratory.   In the halo current study, researchers compiled a database gathered from five tokamaks located around the world. The database contains information gleaned from more than 800 total discharges by the five machines, each of which confines plasma within magnetic fields to produce fusion reactions. "The goal of assembling such a database is to try to understand, based on all the work that's been done so far, whether we can project certain phenomena to next-generation devices like °ÄÃÅÁùºÏ²Ê¸ßÊÖ," Myers said.   The machines included ASDEX-Upgrade, in Germany; Alcator C-Mod at the Massachusetts Institute of Technology; DIII-D, the national fusion facility operated by General Atomics for the DOE in San Diego; the National Spherical Torus Experiment (NSTX) at PPPL that has since been upgraded; and the Joint European Torus (JET) in the United Kingdom.   Halo currents occur when the plasma undergoes large shifts within the vacuum chamber caused by lack of confinement during a disruption. These shifts can cause the plasma to come in contact with the chamber walls, allowing current to flow between the plasma and the walls. Such currents interact with the magnetic field of the tokamak to generate potentially damaging forces against the walls.   These forces become more concerning if the halo currents bunch up on one side of the doughnut, pushing on one part and pulling on another part of the walls. Furthermore, the forces become more concerning still if the bunched currents also rotate around the tokamak in resonance with the structural components of the machine. The effect is similar to the combined resonance that can occur between soldiers marching in step and the structural elements of a bridge.   The researchers examined the database and compared the behavior of halo currents in different machines to see how the velocity and duration of the halo current rotation changes in machines of different sizes. They then extrapolated the results to the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Tokamak. "°ÄÃÅÁùºÏ²Ê¸ßÊÖ is on the boundary of suffering from this problem," Myers said. "The take-away is that we cannot rule out the possibility of this phenomenon occurring."   Halo currents pose less risk in present-day tokamaks because the frequencies at which the currents rotate do not resonate with the structure of the machines. Moreover, the forces in today's tokamaks are mild compared to the forces expected in the huge, 23,000-tonne °ÄÃÅÁùºÏ²Ê¸ßÊÖ.   Going forward, scientists hope to study the magnitude of the asymmetric, or bunched, currents in order to project their strength for °ÄÃÅÁùºÏ²Ê¸ßÊÖ. "Understanding the expected halo current magnitude would be another piece of the puzzle in terms of answering the question of how damaging the amplified forces could be in °ÄÃÅÁùºÏ²Ê¸ßÊÖ," Myers said.   This study was conducted under the auspices of the International Tokamak Physics Activity, an agreement organized by °ÄÃÅÁùºÏ²Ê¸ßÊÖ to help develop fusion research. Funding was provided by the DOE Office of Science, the Euratom research and training programme, and the RCUK Energy Programme in the United Kingdom. Coauthors include Nicholas Eidietis, from General Atomics; Sergei Gerasimov, Tim Hender, and colleagues from Britain's Culham Centre for Fusion Energy; Stefan Gerhardt, from PPPL; Robert Granetz, from MIT's Plasma Science and Fusion Center; and Gabriella Pautasso, from Germany's Max Planck Institute for Plasma Physics.   Read the original article on the PPPL website.

Drawing inspiration from the robotic tasks that will be faced at °ÄÃÅÁùºÏ²Ê¸ßÊÖ during installation and maintenance activities, the annual °ÄÃÅÁùºÏ²Ê¸ßÊÖ Robots contest challenges students of different ages to imagine, design, and program Lego robots. Launched in 2012 by Agence Iter France and the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization, the program is growing every year. As Newsline reported last June, the 2017 °ÄÃÅÁùºÏ²Ê¸ßÊÖ Robots competition involved 600 students from 27 schools organized into 46 teams. This year, the competition will expand to about 70 teams and also offer a new program—°ÄÃÅÁùºÏ²Ê¸ßÊÖ Robots Junior—for primary age students in 4th, 5th and 6th grade (12 additional teams). And who better to help design the new junior competition than 14-year-old Camylle Jordan, who spent one week as an intern in °ÄÃÅÁùºÏ²Ê¸ßÊÖ's Remote Handling Section. According to Jean-Pierre Martins, the °ÄÃÅÁùºÏ²Ê¸ßÊÖ remote handling engineer who supervised Camylle, "she solved every issue she encountered in a pragmatic manner." In addition to becoming familiar with the complexity of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Project, Camylle had to adapt her programming skills to work with a Thymio robot and to learn the basics of SolidWorks ®, a Computer Assisted Design tool. The young intern left the °ÄÃÅÁùºÏ²Ê¸ßÊÖ engineers impressed with her efficiency and confidence. She successfully tested the proposed curriculum and competition design, proactively suggesting and demonstrating ways to improve the robot mission. She participated in the official kick-off meeting of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Robots Junior challenge, interacting with people from °ÄÃÅÁùºÏ²Ê¸ßÊÖ, Agence Iter France and the French education system (Education Nationale). And she found time to fit in a tour of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ worksite and virtual reality room, and to give an on-camera Facebook interview to student journalists. Most importantly, she documented her progress systematically, keeping a logbook of written records, photos, and videos, to ensure the contribution of her workweek at °ÄÃÅÁùºÏ²Ê¸ßÊÖ would not be lost.