In December last year, and again this year in early May, pre-welding fitting tests demonstrated that steel components as tall as a four-storey building (and weighing close to 200 tonnes) could be adjusted with sub-millimetric precision.   Performed at Hyundai Heavy Industries in Ulsan, Korea, the tests consisted in matching the two main sections of a toroidal field coil case—the steel "box" that encases ITER's vertical magnets, the toroidal field coils—to within gap tolerances half the size of a grain of sand.   Achieving that level of accuracy was a truly exceptional achievement—even for the world of high-precision industry.   The fitting tests also aptly illustrated what ITER is about and the challenges its very nature entails.   The two main sections of the D-shaped coil case—the straight-backed inboard leg  and the curved outboard leg—are manufactured by companies in different countries with different industrial cultures: one leg is made in Japan by Mitsubishi Heavy Industries, the other in Korea by Hyundai Heavy Industries.   Once the fitting tests are concluded, the case sections are individually repacked and shipped from Korea to the company responsible for the insertion of the winding pack (manufactured by yet other companies) into the case and the "closure welding" operations: if the case is for a "European" coil, its sections head for the SIMIC facility in northern Italy; if the coil is part of Japan's procurement, they sail to either the Mitsubishi plant in Futami or to Toshiba in Yokohama¹.   Spread over three continents and dozen of companies, the toroidal field coil production process is the most extreme example of the "teaching and training" dimension of the ITER Project. Complexity is the price to pay to spread knowledge and experience among the participating nations. Why did ITER opt for such a ponderous and taxing work organization? Because ITER is not just about building a tokamak — it is also a teaching project, one in which all participating countries and their industry are meant to acquire expertise in fusion science and tokamak technology.   This dimension, which is sometimes overlooked in the day-to-day hardships and frustrations of such a complex, world-spanning project, remains at the core of the ITER DNA.   The toroidal field coil production process is an example—indeed the most extreme—of the constraints that ITER has imposed upon itself: conductor coils were manufactured in half a dozen countries; cases are under Japan's responsibility but partly subcontracted to Korean industry, and the cold testing and insertion operations have been entrusted to yet other companies—one in Europe and two in Japan...   This mind-boggling complexity, which no reasonable industrial venture would dare accept, is the price to pay for the ITER miracle — in the long-term project to provide future generations with a safe and inexhaustible energy source, the participating nations need both the training and the short-term technological and industrial benefits.   This is how project's Founding Fathers, more than three decades ago, intended it: accept and learn from the difficulties of building ITER today in order to acquire the capacity, tomorrow, to make fusion energy available to all.   1- The procurement of the 18 toroidal field coils (plus one space) needed for the ITER tokamak is shared between Europe and Japan.

Before embarking on the fabrication of the 54 complex steel structures that will form a ring at the bottom of the ITER machine—the divertor cassettes—the European Domestic Agency has been collaborating with industry on the development of real-size prototypes. This phase is now concluding, and the contract for the first series will soon be launched.   With a component as complex as the divertor cassette bodies ... better to be safe than sorry. These U-shaped steel structures at the bottom of the vacuum vessel act as the chassis for components facing the most blistering heat of ITER operation—the divertor dome and inner and outer targets. The cassette bodies are also designed to resist transient electromagnetic induced forces as high as 100 tonnes, provide neutron shielding for the vacuum vessel, and host diagnostic systems and cooling water channels. There are more than a dozen design variants. Since 2013 the European Domestic Agency—which is providing all 54 divertor cassettes to ITER as well as the inner vertical targets—has been working with industry to develop full-scale prototypes, a strategy that encouraged multiple suppliers to get involved and served to verify that the required quality could be achieved at acceptable cost. Two European firms carried their participation through to the end—Walter Tosto in Italy and the French-Italian CNIM-SIMIC consortium. The final dimensional checks of the initial procurement program were completed a few weeks ago and cold/hot helium leak tests were successfully performed.  With these results in hand, the European agency is preparing to issue a call for tender for the first series of divertor cassette bodies (not to exceed 20).   To find out more, please see the European Domestic Agency website.   You can download a poster of the ITER divertor here.

Towering 22 metres above ground and weighing approximately 800 tonnes, the twin sector sub-assembly tools (SSAT) are formidable handling machines that will be used to pre-assemble the vacuum vessel sectors before their installation in the Tokamak pit. SSAT 1, whose assembly began in November of last year, is now 90 percent complete. Work on an identical twin is scheduled to begin in September. To the right of the nearly completed SSAT 1, the "cradle" for its identical twin is ready. The Titan tools are designed to handle combined loads in excess of 1,200 tonnes (one vacuum vessel sector, two toroidal field coils and thermal shielding) in excess of 1,200 tonnes. Behind the fixed front columns, the rotating platforms, or "wings," will support the elements to be assembled. The main structure, rotating frames and actuator system of these hydraulic-powered tools were all tested on a 1:5-scale mockup.

The vacuum vessel, the operating theatre of the ITER machine, needs to be protected against possible damage from the hot plasma at any given time during its operation. This also applies to the First Plasma phase when most ITER plant systems are started up and functional but some in-vessel components are not yet in place. The blanket and the divertor are among those components that will not have been installed yet at the time of First Plasma. In addition to their primary functions, they also serve as vital protection for other in-vessel equipment. In their absence, temporary components will protect the vacuum vessel and other equipment already in place such as in-vessel wiring and diagnostics.*   The initial plasma will be a simple hydrogen plasma. It will have a circular shape rather than the vertically-elongated plasma shape of full fusion operation. These initial plasmas are expected to be rather unpredictable, and operators will have relatively little control over the movement of the plasma at this point. Ryan Hunt, an engineer working on the first plasma protection components, notes that, within a couple of milliseconds, the start-up plasma could move in any direction inside the vacuum vessel. "In any such cases, we want it to be running into one of our protection systems rather than into any of the in-vessel installations," says Hunt.   At the heart of this skeletal protection system are temporary limiters, in-vessel protection elements for low energy plasmas copied from existing tokamaks. In ITER they are only used for the six months of the First Plasma operation. The four D-shaped poloidal loops have the same outline as the baseline blanket and are equipped with 18 segments, with each segment shaped differently to accommodate the contour of the vacuum vessel.   This set-up keeps the plasma at a distance of about half a metre from the vessel walls at any given time, no matter in which direction it might move.   Testing the ITER Machine The First Plasma operation is in some ways analogous to the initial testing of a functional prototype. For example, when a new car engine is being developed, engineers will not run it to its top speed in the first tests. They will start by operating the functional prototype moderately, checking that all systems are working properly. Only then will they increase the speed and slowly inch towards full throttle. The same goes for the ITER machine. First Plasma—the milestone phase to start in December 2025—will be the first in a series of stages of operation. This staged approach will enable key tokamak systems to be checked and fine-tuned prior to finalizing the commissioning of all in-vessel components. And much like with the testing of a new car engine, First Plasma is conducted at lower performance levels than envisaged for the fusion phase. During First Plasma ITER aims to achieve a plasma with a current of at least 100 kA (kilo-Amperes) for a period of at least 100 milliseconds as compared to a plasma current of up to 15 MA (Mega-Amperes) for a duration of about 450 seconds under full Deuterium-Tritium fusion operation. Secondly, in the absence of the divertor at the bottom of the chamber, the temporary limiter's loops are complemented by a divertor replacement structure. Looking like an oddly shaped tennis racket, the device consists of a steel bar reaching across the vacuum vessel with a wire grid closing the gap to the very bottom. It functions as a physical interruption to any potential downward movement of the plasma.   The third element guards the vacuum vessel against possible damage by the electron cyclotron resonance heating (ECRH) beam which injects microwave energy from an upper port into the plasma to help energize and ionize it. Three copper-plated steel mirrors mounted to the inner vessel wall reflect the beam to an outboard equatorial port where a so-called "dump" absorbs the excess energy.   According to Hunt, these three First Plasma protection components—the temporary limiter, the divertor replacement structure, and the ECRH mirrors and beam dump—are in combination a simple and economical solution to protecting the vacuum vessel and already installed components against any damage during First Plasma operation.   "These elements are unique to ITER and fit the need of a simple and cost-effective protection system," says Hunt. All elements are easily installed and removed, as they are not welded but mechanically affixed to the vessel inner walls, with minimal later impact on machine operation. Components are made of steel with no costly material or high technology needed to ensure their full functionality.   * Starting the machine without the blanket and divertor will also facilitate any needed adjustment of equipment that would be difficult to be reached once the blanket and divertor are installed.  

Steven Cowley, a theoretical physicist and international authority on fusion energy, has been named director of the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL), effective July 1. Cowley has served as president of Corpus Christi College and professor of physics at the University of Oxford since 2016. From 2008 through 2016, he was chief executive officer of the United Kingdom Atomic Energy Authority (UKAEA) and head of the Culham Centre for Fusion Energy, which includes the Joint European Torus (JET) and Mega Amp Spherical Tokamak (MAST) fusion facilities. During his tenure at Culham, Cowley expanded and strengthened relations with other fusion programs in Europe and around the world, and served in key advisory roles for the U.K., U.S. and European governments. As director of PPPL, Cowley will be responsible for managing all aspects of the laboratory, including its performance in science, engineering, operations, project management and strategic planning. He will lead PPPL's scientific and technical programs in fusion energy science and technology, as well as broader investigations in plasma science, and provide leadership to the U.S. and world fusion energy efforts.  Read the original article on the PPPL website.

San Diego-based General Atomics (GA) has published a new app to help physicists work out the characteristics of plasmas on the fly. Called Plasmatica, it takes up to seven basic input parameters—ranging from magnetic field to electron temperature to ion mass factor—and outputs many fundamental properties of the plasma. The parameters are helpful to researchers because they describe intrinsic plasma behaviors, e.g., how often particles will collide with each other. "Before this, most of us just would have written a little program on our computers to do these calculations, and in fact a bunch of us have them," said David Pace, the GA physicist who spurred the development of Plasmatica. "We thought it would be nice to give back to the research community by creating a standardized app that everyone can use when they're not at their computers. It's been exciting to get some initial feedback that is guiding us to a new round of improvements." GA operates the DIII-D National Fusion Facility, the largest magnetic fusion facility operating in the U.S. and a world-renowned research center for plasma physics. Research time on DIII-D is extremely valuable—the facility can accept only about one out of every five experimental proposals—so having those calculations accessible on a mobile device can save precious minutes when researchers are trying to line up the next experiment. The app, which incorporates two formularies commonly used by plasma physicists, has been tested by researchers and is getting solid reviews. Plasmatica is available for free in both the Android and Apple app stores.

The first Fusion in Europe of 2018 has been released. This quarterly magazine, published by the European consortium EUROfusion, keeps readers abreast of the faces, facilities and feats of the very dynamic fusion research community in Europe. The latest issue offers articles on the experimental campaign underway at WEST (France), the 3D printing of small tungsten components, and plans for a neutron source oriented to DEMO (the machine after ITER). You can read or download Fusion in Europe here.