A flying "squirrel" over the ITER worksite

Over the past few years, the ITER worksite has been photographed from a helium balloon, a glider, a small airplane, a crane…

Last Friday, the French gendarmerie helicopter that took the ITER Director-General on a flyover of the ITER Itinerary (an Ecureuil AS 350 B, or Squirrel) provided another opportunity to capture the spectacular vista of the ongoing construction works.

The monster that pulled people out of their homes

The passage of an exceptional convoy is a common sight for the inhabitants of the villages of Berre, Rognac, La Fare-les-Oliviers or Lambesc. The area, close to the harbour in Marseille, is heavily industrialized: steelworks, refineries, the aircraft industry … all depend on the delivery and expedition of large-size loads that travel the roads to the general indifference of the local population.

It takes something really exceptional to pull people out of their homes, old and young alike, and bring them to the roadside to ogle and gawk.

On Monday night, 16 September, the 352-wheel, 800-ton trailer mimicking an actual ITER convoy did just that. As it commenced its four-night journey between Berre and the ITER site in Saint Paul-lez-Durance, hundreds of people were lined up along the roads, some of them in nightshirts and pyjamas, to watch the long procession of men and vehicles slowly advance along the first stage of the 104-kilometre ITER Itinerary.

The event, which aims to monitor the behaviour of roads and bridges under the extreme ITER loads, was the culmination of five years of hard work and complex calculations by the French public roads administration and the technical services of the Bouches-du-Rhône département. As ITER Deputy Director-General Rem Haange explained prior to the departure of the convoy, „The ITER Itinerary is essential to the project. It is the indispensable link between component fabrication in the factories of the ITER Members and the assembly of the machine by the ITER Organization.”

It was around 10:00 p.m. when the convoy, organized by logistics service provider DAHER, left its parking area in Berre. Night had fallen one hour earlier and the headlights of the trailer, accompanying vehicles and gendarmerie motorcycles contributed to the eerie atmosphere—the monster had awakened and was ready to take to the road.

Its first stop, two hours and five kilometres later, was at the railroad bridge in Rognac, the first of the 35 bridges that dot the Itinerary. The bridge had been equipped with a whole array of sensors to measure the deflexion of the structure under the strain of the convoy. Calculations had anticipated some 32 mm of deflexion, measurements yielded 30 mm.

The test convoy will continue another three nights to the ITER site. As it progresses along the Itinerary, the measurement operations will be repeated at every bridge. Manoeuvring space and operational margins will also be checked at every turn and roundabout. Processing the accumulated data will take about one month and a half, but early on Tuesday morning, Pierre-Marie Delplanque, the man in charge of overseeing operations for Agence Iter France, was satisfied … and relieved.

„We had a couple of very small issues,” he said, „and in two or three places we can still make small improvements. However we did not identify any major obstacle and I do not anticipate any issue when the actual convoys are organized.”

The convoy arrived in a secure zone in the village of Lambesc at 5:45 a.m. Tuesday, 16 September. Operations resume on Tuesday night at 9:30 p.m., when the convoy will take to the road again and—following the same pattern of measurements—will proceed another 15 to 20 kilometres.

The test convoy is expected to arrive at ITER in the wee hours of the morning on Friday 20 September.

View more photos here.
View local (LCM-Marseille) and regional (France 3) public TV coverage in French.

Ministerial representatives reaffirm the importance of ITER

Convening on 6 September for a meeting at ministerial level in Saint Paul-lez-Durance, France, high-level representatives of the seven ITER Members acknowledged the progress achieved in the construction of one of the most complex scientific and engineering projects in the world today, the ITER international collaboration for fusion.

Ministerial representatives reaffirmed the importance of fusion for the world’s energy future and stressed the importance of the ITER experimental device as an indispensable step on the path to the development of fusion energy—a virtually limitless and environmentally benign energy source. The participants also emphasized the role played by the ITER international partnership in defining a new model of worldwide scientific collaboration.

Read the full press release in English and in French.
See the first photos from the meeting here.

Manufacturing milestone achieved in Europe

The first step in the fabrication of the full-size, superconducting prototype of a toroidal field coil double pancake has been successfully carried out in Europe. Winding was completed at the beginning of August at the ASG premises in La Spezia, Italy.

The European Domestic Agency, Fusion for Energy, is responsible for procuring ten toroidal field coils (and Japan, nine). These D-shaped coils will be operated with an electrical current of 68,000 amps in order to produce the magnetic field that confines and holds the plasma in place. Toroidal field coils will weigh approximately 300 tons, and measure 16.5 m in height and 9.5 m in width.

Each one of ITER’s toroidal field coils will contain seven double pancakes. These double pancakes are composed of a length of superconductor, which carries the electrical current, and a stainless steel D-shaped plate called a radial plate, which holds and mechanically supports the conductor through groves machined on both sides along a spiral trajectory.

The first stage of toroidal field coil manufacturing—the winding of the double pancakes—is the most challenging. It consists of bending the conductor length along a D-shaped double spiral trajectory. As the conductor must fit precisely inside the radial plate groove, it is vital to control its trajectory in the double pancake and in the groove of the radial plate with extremely high accuracy. The trajectory of the conductor, in particular, must be controlled with an accuracy as high as 0.01 percent.

For this reason, the winding line employs a numerically controlled bending unit as well as laser-based technology to measure the position and the dimensions of the conductor. The winding takes place in an environment with a controlled temperature of 20 °C +/-1 C, at an average speed of 5 m of conductor per hour.

For the European commitments to ITER, a consortium made up of ASG (Italy), Iberdrola (Spain) and Elytt (Spain) will manufacture the full-size, superconducting prototype as well as the production toroidal field coil double pancakes in the future.

The next steps in the manufacturing process are: heat-treatment of the double pancakes at 650 °C in a specially constructed inert atmosphere oven, electrical insulation; and finally the transfer of the double pancakes into the grooves of the stainless steel radial plates. After assembly and the application of electrical insulation on the outside of the radial plate, the module is finally impregnated with special radiation-resistant epoxy resin to form the prototype double pancake module.

Work on the module is scheduled to be completed by the beginning of next year, in time to allow for the prototype to be tested at -77 K in order to assess the effect of the low temperature. The module will then be cut in sections in order to analyze the impregnation of the insulation.

Read the detailed article on the F4E website here.

The dream of his life

ITER owes much to a few. At different moments in the history (and prehistory!) of the project, a handful of individuals made moves that were to prove decisive. Among this band of godfathers—whether scientists, politicians, diplomats or senior bureaucrats—Umberto Finzi stands prominently.

Finzi, who retired from the European Commission in 2004 but continued to advise the Director General of Research until the conclusion of the ITER negotiations in 2006, belongs to the generation who embraced fusion research in the early 1960s at a time when plasma physics was still in its infancy.

A physicist turned bureaucrat—he was called to Brussels to take care of setting up JET in 1978 and was appointed Head of the European Fusion Programme in 1996—Finzi played a key role in the negotiations that led to building ITER in Europe. An ITER godfather in his own right, he nevertheless insists on the „collective action” that, under four successive European presidencies, led to this decision.

Time has passed. The „paper project” whose roots go back to the late 1970s, years before the seminal 1985 Reagan-Gorbatchev summit  in Geneva, is now a reality, as tangible as it is spectacular. When he toured the ITER worksite on 30 July, Umberto Finzi took the full measure of the progress accomplished since his last visit in 2006, when all there was to see was a hilly, wooded landscape and a high pole marking the future location of the Tokamak.

„During most of my professional life,” he said, „ITER was a dream. You can imagine my emotion seeing these tons of steel and concrete. This reminds me of the famous message by Hergé¹ to Neil Armstrong: „By believing in his dreams, man turns them into reality.” 

„ITER is a difficult venture,” he added, „and difficult ventures requiretime and patience. The effort is not only scientific or technological. It lies also, and maybe essentially, in the planning and coordination.”

ITER, with 35 participating nations, could have been a Tower of Babel. „On the contrary,” says Finzi, „it is the exact opposite of a Tower of Babel, a beautiful demonstration of worldwide understanding. No project has ever associated so many different nations. To me, this is the most important aspect of ITER, a historical dimension that reaches beyond the project’s scientific and technological objectives.”

(1) Hergé (1907-1983) was a Belgian cartoonist, creator of the world-famous characters Tintin and Snowy. Between 1930 and 1986, Hergé published 23 albums of The Adventures of Tintin, selling a total of 200 million copies in 70 languages. Fifteen years before Neil Armstrong, Tintin, Snowy and other recurrent characters in the series walked on the Moon in the 1954 album "Explorers on the Moon."

ITER featured on BBC Evening News

On Wednesday  7 August, BBC world ran a feature on ITER in their evening news program. Science Presenter David Shukman and his team had spent two full days on the ITER site investigating about "the world’s most ambitious attempt to harness fusion as a source of power"…See the video to hear his conclusions.

ITER features on BBC evening news

On Wednesday this week, 7 August, BBC world ran a feature on ITER in their evening news program. Science Presenter David Shukman and his team had spent two full days on the ITER site investigating about "the world’s most ambitious attempt to harness fusion as a source of power"…See the video to hear his conclusions.

A call to arms for making fusion happen

To the members of the wider fusion community, the name Dan Clery most likely rings a bell. News editor for the magazine Science since 1993, Dan has closely followed the excitement and frustrations of the quest for fusion energy and, of course, the „making of” ITER. Over the years he has gathered more than enough information to fill regular magazine pages and so he decided to, temporarily, swap the fast beat of a news reporter for the reclusiveness of a book author.

A Piece of the Sun draws the bow from the Big Bang, to Prometheus, to the first scientists working out the details of the fusion reaction, the first machines and experiments, and finally to modern times. None of this is new and may have appeared before in print, but don’t be mistaken! Dan is not only an eloquent writer, but also a skilled journalist with a mission. In his hands, the book is far more than a technical narration of the good old days: it is a political statement … a rousing call to arms for making fusion happen.

„The world energy industry is worth trillions of dollars—divert only a tiny fraction of that into researching fusion and we will soon know if it is workable,” Dan passionately argues. „Some technological dreams just take time to come to fruition,” he writes, drawing the parallel with the Wright brothers and Virgin Galactic’s spacefaring pleasure aircraft. „The cost and time it will take to make fusion work has to be balanced against the enormous benefits it will bring. It won’t damage the climate, won’t pollute and it won’t run out. How can we not try?”

Read an interview of Dan Cleary on the PPPL website.

Русский День at ITER

Do Russians drink vodka for lunch? ITER DDG Alexander Alekseev made the point that they didn’t but Vladimir Pozdnyakov, Russia’s Consul General in Marseille, said he was „not so sure”, suggesting that they might, „just a little bit, on some special occasions…”

Vodka was the only thing Russian that was missing (along with Slavic melancholy) at the celebration of ITER’s Russia Day on Friday 19 July. For the rest, it was all there: the food, the songs, the dances, the images of Mother Russia…

More than 600 ITER staff and contractors participated in the event that Olga Star and Igor Sekachev had organized.

Experts on Russian singing and dancing (and there are at least 26 at ITER) assured that the five singers and dancers of Marseille’s Alliance franco-russe were among the best they had ever seen.

Vladimir Vlasenkov, Deputy Head of the Russian Domestic Agency, who was participating in the Unique ITER Team week at ITER, said „it [was] not very common, even for [him] to witness such a beautiful expression of Russian traditions.”
Click here to view more pictures of Russia Day at ITER.

Pair of safe hands to handle up to 1,500 tons

Fusion for Energy (F4E), the Domestic Agency managing Europe’s in-kind contribution to ITER, has signed a contract with the NKMNOELL-REEL consortium formed by NKMNoell Special Cranes GmbH, Germany and REEL S.A.S., France (part of Groupe REEL) for the design, certification, manufacturing, testing, installation and commissioning of the four cranes that will be used to assemble the Tokamak, as well as the Tokamak cargo lift that will move the casks containing components. The budget of the contract is in the range of EUR 31 million and it is expected to run for five years.

The cranes will be located within the Tokamak Building and the Assembly Building and will operate like a pair of safe hands to move the heavy components between the two areas and position them during assembly with extreme precision. The consortium will deliver two 750-ton cranes that, in tandem, will lift up to 1,500 tons during assembly, two 50-ton auxiliary cranes, and the Tokamak cargo lift.

Sophisticated engineering combined with advanced safety lifting and remote handling technologies are some of the elements that describe the nature of the work undertaken by the two companies.

How will the cranes work?

The four electric overhead travelling cranes will move between the Assembly Building and the Tokamak Building, which is divided in two areas housing the Tokamak and a crane hall above the machine.

The major heavy lifting requirements shall be met by the two 750-ton cranes. Each will be equipped with two trolleys carrying a single 375-ton hoist each. In total, the four 375-ton hoists will provide a maximum lifting capacity of 1,500 tons—the weight of 187 London double-decker buses. The cranes shall be capable of working in tandem to provide a fully synchronized lift and precise positioning. Two auxiliary cranes of 50-ton capacity will be used for other lifting activities, working independently of one another.

Which components?

The principal purpose of the Tokamak crane system is to lift and receive heavy components, support assembly operations, move the cryostat components, and transport the assembled vacuum vessel sectors and other major components. When the Tokamak machine becomes operational there will be no further planned use for the cranes. The 750-ton cranes will remain parked and electrically isolated while the 50-ton cranes will continue to be used in the Assembly Building.

How will the Tokamak cargo lift work?

The Tokamak cargo lift shaft will be located in the Tokamak Building with connecting doors to the Hot Cell. The lift will carry the casks that contain machine components. The cask is 3.7 metres high by 2.7 metres wide and 8.5 metres long—the approximate size of a London double-decker bus, weighing 60 tons when empty. Automated transfer systems and high tech remote handling systems will be deployed to transfer the casks between the various levels of the Tokamak Building and the Hot Cell by remote control. All components involved in the transfer need to be integrated in a seamless manner.

Bracing for a busy September

The summer recess at ITER (the site will be closed the week of 12-18 August) will be followed by a flurry of activity.

On 6 September, on the initiative of Günther Oettinger, European Commissioner in charge of Energy, representatives at ministerial level of the seven ITER Members will convene at the ITER Headquarters to review the main progress accomplished. This will be the second time in the project’s history that the highest-level government representatives of the seven ITER Members meet; the last time was 21 November 2006, on the day after the signature of the ITER Agreement.

Ten days later, the first technical tests will be performed on the ITER Itinerary. Organized jointly by Agence Iter France (AIF) and the DAHER Group, the operation will consist in verifying that the engineers’ calculations agree with the reality of travelling the whole length of the Itinerary (104 km) with a convoy that mimicks the most exceptional ITER loads — 800 tons in weight, 40 metres in length, 9 metres in width, and 11 metres in height.

The „measurement campaign,” as it is officially called by AIF, will be performed at night negociating the 16 roundabouts and crossing the 30 bridges that punctuate the Itinerary. The vehicle — an 88-axle self-propelled platform — will remain stationary during the day in order not to interfere with the heavy summer traffic. The public will be able to share in the spectacular event from two specifically designed viewing areas, one in Berre l’Etang where the platform will be stationed on 16 September and one in Peyrolles where it will arrive two days later.

In order to confirm that the organization among all involved entities is appropriate, a complete dress rehearsal, with all the logistics of an actual Highly Exceptional Convoy, will be organized in the following months. The first supersized ITER components (the US-manufactured drain tanks) should be delivered on site in June 2014.

As it has for the past six and a half years, Newsline will continue to report on all the events, large and small, that make the daily life and history of ITER.

We’ll be back with more news on 26 August!

India will participate in upper port plug manufacturing

ITER-India and the ITER Organization signed a Memorandum of Understanding (MoU) for the Common Manufacture of Port Plugs on 16 July 2013 during the Unique ITER Team week at ITER. This MoU enables the participation of India in the common manufacture of the upper port plug that includes the Generic Upper Port Plug (GUPP) and applicable customizations. ITER-India is responsible for providing Upper Port No. 9 Integration components, of which Upper Port Plug No. 9 is one of the components.

The main functions of the upper port plug are to hold the diagnostics in position, shield diagnostics from neutron streaming and act as the first closing boundary at the vacuum vessel port flange. This upper port plug will be a stainless steel structure of nearly 6 metres in length and a little more than 1 metre in width and height, weighing approximately 25 tons.


An Associated Laboratory in fusion was established earlier this month between the Chinese Academy of Sciences (CAS) and the French Commission of Atomic Energy (CEA) to develop cooperation on two long-pulse tokamaks, EAST and Tore Supra, soon to be equipped with an ITER-like tungsten divertor — the project WEST.

The creation agreement was signed on 3 July by Prof Li, director of the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) and Gabriele Fioni, director of CEA’s Physics Science Division, CEA, at the French Embassy in Beijing. French nuclear counselor Pierre-Yves Cordier hosted the signing ceremony, with André Grosman, deputy director of the Institute of Magnetic Confinement Fusion Research (IRFM/CEA) and consular assistant Shunming Ding. 

The associated laboratory has been created to develop cooperation on CEA’s long-pulse tokamak WEST* and ASIPP’s EAST, particularly in the fields of actively cooled, metallic plasma-facing components; long-duration plasma operation in an actively cooled, metallic environment; long-pulse heating and current drive; ITER technology support; and the preparation of „Generation ITER” (see this issue’s Of Interest entry) in all of the above-mentioned areas.

Xavier Litaudon and Yuntao Song are appointed as the associated laboratory’s co-directors. They will be responsible for leading and coordinating the performance of the projects under the Associated Laboratory Agreement.

„I am enthusiastic about the CAS/ASIPP-CEA collaboration,” said Prof Li after the signature. „The cooperation between EAST and WEST will be good for all fusion communities.”

As a first step, ASIPP has already sent two young researchers to IRFM to work for one year on WEST component design and engineering.

* WEST = W (tungsten) environment for steady state tokamak

Toroidal field coils: strand production passes 400 tons

„Toroidal field strand procurement is going rather well,” reports Arnaud Devred, who heads the Superconductor Systems & Auxiliaries Section at ITER. „We are on schedule.”

Manufactured by suppliers in six ITER Domestic Agencies—China, Europe, Japan, Korea, Russia and the USA—production of niobium-tin (Nb3Sn) superconducting strand for ITER’s toroidal field coils began in 2009 and has now topped 400 tons.

That’s more than 80,000 kilometres of strand—enough to go around the world twice at the Equator.

Worldwide capacity has had to ramp up significantly to meet the Project’s demand. There are eight qualified suppliers for ITER, including three that are new to the market (one in China, one in Korea and one in Russia). In 2011 and 2012, these eight suppliers, together, turned out over 100 tons annually.

„One hundred tons per annum represents a spectacular increase in the worldwide production of this multifilament wire which was estimated, before ITER production, at a maximum of 15 tons per year,” says Devred. „As you would expect, the price has come down, and this 'surge’ in production for ITER may well open up new markets.”

Eighteen toroidal field coils will be produced for ITER plus a nineteenth (a spare). That’s approximately 420 tons of strand, give or take a bit of spare material planned by each Domestic Agency. The production curve will begin to flatten in 2013 (see graph above) as contracts are brought to a close in several Domestic Agencies.

Devred estimates the market value of the toroidal field strand procurement at over EUR 200 million.

„It has been very satisfying to see this procurement unfold and to watch our international collaboration develop at every step in the process,” says Devred. „In addition to the sheer scale of this procurement, what is also remarkable is the quality control and quality assurance that we have been able to set into place.”

Four of the ITER suppliers are using a production technique called internal tin, while another four are using a bronze process. „It has been up to us to demonstrate that we can control both types of production within technical requirements,” explains Devred, „We weren’t sure of ourselves since this is the first time there has been such a large-scale production of internal tin. Test data shows that we can do it effectively.”  

Quality testing for ITER calls for statistical process control on critical parameters, systematic low-temperature measurements on strands, and regular low-temperature measurements on full-size conductors (25 percent of toroidal field conductor unit lengths are tested). This testing data is stored, like manufacturing data, in ITER’s conductor database, which is currently fed by approximately 150 users, including suppliers and Domestic Agencies. Some 350,000 individual objects are stored in this web database—created to monitor the quality assurance/quality control processes of the conductor Procurement Arrangements.

Devred credits the „early days” with setting up the processes and systems that are proving to work today for conductor procurement: before the signature of the first ITER Procurement Arrangement, the specifications for ITER conductors were written by a committee made up of worldwide experts in large conductor procurement. Very tight quality control was developed that imposes many control points at each stage of fabrication verified by the Domestic Agencies and the ITER Organization. „I believe this will be the key to our final success," says Devred. "I am confident that what is coming off of the manufacturing lines is as good as can be made.”

Read more on how strand is produced in Newsline 140.

Thirty four and counting

It was foreseen by the authors of the ITER Agreement, signed in 2006 by the seven ITER Members.

As a research organization, the ITER Organization may conclude scientific collaboration agreements with other international organizations and institutions in the interest of promoting cooperation on fusion as an energy source.

For ITER, collaboration agreements keep ITER scientists and engineers in close touch with work going on in precise domains relating to fusion science and technology; for the laboratories and institutes, they are an opportunity to collaborate with the fusion community’s most advanced experiment.

Since January 2008, the ITER Organization has signed 34 scientific collaboration agreements and another 4 are currently in the preparatory stages. A common thread amongst these agreements is the training of young researchers.

„In the coming years, I envision more and more of this type of scientific exchange for the ITER Organization,” says the Director-General of the ITER Organization, Osamu Motojima. „I would like to open ITER’s door to younger people who will in fact take on a lot of the responsibility for fusion in the future. ITER will be the foremost research laboratory for magnetic fusion. Scientific collaboration agreements enrich the experience of our scientists, and provide training for the next generation of fusion scientists. The ITER Organization is a Centre of Excellence in this area.”

Under these scientific collaboration agreements, the ITER Organization and research institutes can cooperate in academic and scientific fields of mutual interest. „Some of the ideas for collaboration come from our scientists. We have compiled a database of agreements signed by the ITER Organization so that when we’re approached, we can inform them whether we already have an agreement with the institute in question,” says Anna Tyler of Legal Affairs.

Typically, the agreements cover the following type of collaboration: joint supervision of students working on Master’s or PhD theses; joint training and exchange of young scientists, engineers, interns and experts; joint research projects (particularly in plasma physics); and joint seminars.

Collaboration agreements have been signed with laboratories and institutes in Austria , China France, Germany, India, Italy, Japan, Korea, Monaco, the Netherlands, Spain, Switzerland, Japan,  and the UK—the most recent to date was signed just last month with the Department of Civil and Industrial Engineering at the University of Pisa (Italy).

David Campbell, head of ITER Plasma Operation Directorate, has been able to see the practical benefits of such exchanges. „Because we are aiming to develop ITER as centre of excellence in fusion research, such agreements allow us to develop scientific and technology exchanges with leading fusion research institutions around the world, building a network of fusion research activities which not only supports the preparations for ITER operation, but also contributes to the longer-term realization of the potential of fusion energy.

One of the more exciting aspects of the collboration agreements relates to the training activities and the opportunities they provide for younger researchers to participate in the ITER Project, according to Campbell. "The transfer of knowledge between generations is a key element of the scientific enterprise and an integral component of the development of ITER as an international centre of fusion research.”

800-ton dummy load to test Itinerary in September

Many of the ITER components that will come off of the fabrication lines in the factories of the ITER Members are particularly large and heavy. In order to permit their transport to ITER, France has adapted a special 104 kilometre-long Itinerary—widening roads, adapting roundabouts and reinforcing bridges between Port-de-la-Pointe, on the shores of the Étang de Berre, and the ITER site in Saint Paul-lez-Durance.

Work on the ITER Itinerary began in January 2008 and was completed three years later. In March 2012 the ITER Organization awarded a framework contract for the transport of the machine’s components to the DAHER Group. In advance of the test convoys planned for September (technical) and October (logistics and organization) 2013, final adjustments to the ITER Itinerary were carried out between April and June this year.

On 16-20 September, travelling at night, a test convoy will be organized jointly by Agence Iter France (the CEA agency that acts as an interface between ITER and France) and the DAHER Group. After having crossed the inland sea of Étang de Berre, a dummy load made of 360 concrete blocks will be loaded onto a special self-propelled platform (88 axles) to travel the whole length of the Itinerary. Its weight and dimensions—800 tons, 40 metres long, 9 metres wide, 11 metres high—will mimic the most exceptional ITER loads.

This first test, officially a „measurement campaign,” aims at verifying that the reality of bypassing 16 villages, negotiating 16 roundabouts and crossing more than 30 bridges corresponds to the engineers’ calculations.

According to Agence Iter France, an „enormous technical, administrative and regulatory machine” has had to be fine-tuned in order to bring about this first campaign.

Two viewing areas—one close to Berre-l’Étang and the other in the rest area close to the village of Peyrolles-en-Provence—will allow the public to share in the event … for many, a spectacular introduction to the exceptional dimensions of the ITER machine.

Click here to read the latest issue of Agence Iter France’s publication Itinéraire News (in French).

Design Review for tungsten divertor shows way ahead

Last week, the ITER Organization concluded the Final Design Review for a full-tungsten ITER divertor. In this three-day assessment, which was the culmination of eighteen months of design, analysis, testing and development, the readiness and the feasibility of a full-tungsten variant capable of withstanding the extreme conditions in ITER were assessed. Challenges related to the specific nature of tungsten were identified and dealt with. „The completed design now requires some refinement with respect to the local shaping of the tungsten monoblocks,” said Philippe Mertens from the Research Centre in Juelich, Germany, who chaired the review.

Almost five years ago, in its 60th issue, the ITER Newsline announced the upcoming Final Design Review of the divertor system. At that moment, the ITER approach was to begin plasma operations with carbon fibre composite (CFC) on the regions of the divertor’s vertical targets that are expected to receive the highest heat loads. All other plasma-facing surfaces would have been armoured with tungsten.

So much for the non-active phases of plasma operation. The ITER approach for the following phase—nuclear operation with deuterium and tritium—was to replace the carbon-tungsten divertor with a full-tungsten variant.

Carbon presented two major drawbacks as divertor armour material: it reacts chemically with the plasma fuel tritium and it traps the fuel like a sponge, leading to enhanced material erosion and unacceptable levels of tritium retention within the machine. Tungsten (W), on the other hand, has the advantage of not absorbing tritium, but at the same time it doesn’t offer the same forgiving behaviour as carbon in terms of compatibility with the plasma.

In September 2011 budget restrictions forced the ITER Organization to reconsider its Baseline divertor strategy. By launching operations with a full-tungsten divertor from day one, one of the three divertors planned for ITER’s 20-year operational phase would be eliminated.

A comprehensive investigation was launched in 2011—the Tungsten Divertor Qualification Program—in consultation with the procuring Domestic Agencies in Russia, Europe and Japan. The program comprised full-scale prototype manufacturing and testing.

While many of the features of the existing CFC/W Baseline design are applicable to a full-tungsten divertor for ITER, there are some key differences. Employing metal in high heat flux areas for example requires particular attention—where carbon was known to have favorable properties for the „plasma machining” of misaligned edges (due to manufacturing and assembly tolerances) these do not to apply for tungsten.

Attention must also be paid to the global shaping of the upper baffle areas of a tungsten divertor, where off-normal events such as a sudden vertical displacement of the plasma are predicted to lead to extremely heavy heat loads. Through the slight tilting of the targets and through particular shaping of the outer baffle (very much like the shaping of the first wall of the blanket) some promising results have been obtained that were presented during the design review.

_To_56_Tx_High heat flux tests performed last year at the newly completed ITER Divertor Test Facility in Russia—with prototypes manufactured by Japanese industry that were exposed to 10 MW/m2 over 5000 cycles and 20 MW/m2 over 1000 cycles—demonstrated no macroscopic cracks, de-bonding or traces of melting. Similar tests run for 300 cycles at 20 MW/m2 have been performed by European industry with optimistic results. 

A „melt experiment” consisting in the deliberate melting of tungsten tiles has been proposed for JET this summer to better understand the behaviour of the molten layer and the consequences of operating a machine on re-solidified W layers.

„It is now expected to report the last findings on this full-tungsten divertor variant to the next ITER Council Science and Technology Advisory Committee (STAC) in October 2013, to obtain a recommendation on the divertor armour for ITER. The objective would be to implement the decision into the Baseline by the end of the year,” said Frederic Escourbiac, leader of the Tungsten Divertor Section, who was clearly satisfied by the outcome of the particularly intense three-day design review.