The Spanish contribution to ITER

Spain’s relationship with ITER is especially close as the city of Barcelona hosts the European agency Fusion for Energy, which manages the European contribution to the Project.

Spanish research centres—led by CIEMAT and in cooperation with other European partners—play a crucial role in ITER by contributing to the development of diagnostic systems, plasma heating components, test blanket modules, and control and data acquisition systems.

The Centre for the Industrial and Technological Development (CDTI) promotes the participation of Spanish industry and acts as a focal point between companies and ITER. For Spanish industry, ITER is a unique opportunity to develop cutting-edge technologies, but also an occasion to foster commercial products in industrial areas outside fusion energy. This cross-fertilization will contribute to the scientific and technological progress in the coming decades.

Since 2008, Spanish companies have earned an increasing number of contracts for ITER, with a peak in 2012. According to the latest estimates, Spanish industry has won over EUR 400 million in contracts in a highly competitive market, with many opportunities for participation ongoing. Spanish industrial capabilities cover a wide range of technological areas, making it possible to participate in the fabrication of many ITER components such as the vacuum vessel, magnets, buildings, test blankets modules, plant systems, in-vessel components, remote handling, safety, instrumentation and control and CODAC, to name but a few.

Spanish companies have also won important contracts in other fusion facilities such as the European tokamak JET, TJ-II (CIEMAT) and W7X (Germany) and have taken on significant challenges in the supply of components for the Spanish in-kind contributions to the Broader Approach projects IFMIF-EVEDA and JT-60.

Many of the developments for ITER and fusion projects have been made in collaboration with other European industries either through consortia or through the supplier chain, showing that the effort for fusion is really framed inside a wide European dimension.

Who’s got the biggest?


At ITER, we don’t brag. But we do like to mention the exceptional dimensions of the machine we are building: the ITER Tokamak will indeed include components that, in their category, are by far the largest in the world.

In talks and presentations to the public it has become routine, for instance, to assert that the ITER cryostat will be the largest high-vacuum chamber ever built.

But recently, a young postdoc attending a presentation on ITER at the Institute of Plasma Physics in Prague took issue with this claim. It’s NASA’s Space Power Facility, the student said, that holds the blue ribbon for the largest high-vacuum chamber.

Located in Sandusky, Ohio (USA), the Space Power Facility was built in 1969 to create an environment comparable to that encountered in deep space, on the Moon or on planet Mars. It comes complete with high-vacuum, extreme cold (down to minus 195°C) and solar radiation simulation.

NASA has been using the facility for more than four decades to expose rocket components, space capsules, landing vehicles and satellite hardware to the harsh conditions of outer space. Its futuristic setting has also inspired movie makers: in 2012 the opening sequences of the blockbuster The Avengers were filmed there.

The cylindrical vacuum chamber is 30 metres in diameter and 37 metres in height—bigger, it’s true, than the 29.4 x 29 metre ITER cryostat. There is however an important difference between the two: while the aluminium Space Power Facility’s test chamber is spectacularly empty (after all, rocket stages have to fit in) the steel ITER cryostat is a very crowded place.

In ITER, because of the volume occupied by components such as magnets, support structures, the thermal shield and the vacuum vessel itself, the pump volume inside the cryostat—that is, the total volume of the chamber minus that of the components—is reduced to 8,500 cubic metres. At the NASA facility, it is almost three times larger (23,500 cubic metres).

In order to achieve high vacuum up to 10-6 Torr, one millionth time more tenuous than the Earth’s atmosphere, both installations use mechanical roughing pumps to go down to ~ 0.1 Torr, and then cryopumps to achieve the required high vacuum. While NASA’s installation can achieve high vacuum in 8 to 12 hours, the ITER cryostat will require about twice this time.

„However, the two systems are quite different," notes Matthias Dremel, an engineer in the ITER Vacuum Section. „The ITER cryostat contains thermal shields cooled to 80 K that act as pumps by condensation of the gases. What’s more, the magnets behind the thermal shield, cooled to ~4K, also act as pumps by condensation.”

Because these components are extremely cold, they significantly contribute to removing the impurities that remain in the chamber. Atoms, molecules and particles are all captured by cold surfaces: the more intense the cold … the more irresistible its holding power.

In the ITER cryostat and in NASA’s Space Power Facility we have two high vacuum chambers of approximately the same size but the latter, however spectacular, is but a big empty aluminium cylinder. The ITER cryostat, on the other hand, is a highly complex structure that must remain absolutely leak-tight despite the thousands of lines and feed-throughs that penetrate it for cryo, water, electricity, sensors, etc.

So it’s a NASA win (but not by much) when it comes to size, but when it comes to complexity—the ITER cryostat remains unchallenged by far.

Three cities, two Procurement Arrangements

During the week of 26 August, ITER Director-General Motojima travelled to Russia, visiting three cities and signing two Procurement Arrangements in four days.

Accompanied by Deputy Director-General Alexander Alekseev, head of the Tokamak Directorate, the ITER Director-General began his trip at the Institute of Nuclear Physics in Novosibirsk, where he signed the Procurement Arrangement for Equatorial Port 11 Engineering, for the engineering of diagnostic systems into vacuum vessel Port 11. The Budker Institute will be responsible for the scope of work.

The Budker Institute already plays a key part in the development of high-tech electron equipment, engineering of diagnostic systems into the vacuum vessel ports, and research into the investigation of high-temperature plasma impact on reactor’s first wall materials as well as developing, manufacturing, and testing equipment for the ITER machine.

According to the Head of the Russian ITER Domestic Agency, Anatoly Krasilnikov, equipment development for ITER’s plasma diagnostics engineering will take five to seven years and will require constant interaction with the ITER Project’s other partners. In all, the Budker Institute will develop five engineering systems for ITER’s vacuum vessel ports.

The delegation from ITER also visited the Institute of Applied Physics and the enterprise GYCOM in Nizhniy Novgorod, where gyrotron component manufacturing and assembly are conducted as well as the development of infrastructure equipment such as cryomagnetic systems, measurement and technological devices, and part of the energy sources required for the gyrotrons. Procurement of the ITER gyrotrons is a matter of special pride to the Institute of Applied Physics, because it was here that this device was invented. More than half of existing experimental fusion facilities in the world currently use gyrotrons from Nizhniy Novgorod.

The final destination stop was in Moscow. At Project Center ITER (the Russian Domestic Agency for ITER), Director-General Motojima signed the Procurement Arrangement for the Thomson Scattering diagnostic system, one of 21 systems that Russia will deliver to ITER before 2024.

Melting tungsten for a good cause



Over the past two years ITER physicists and engineers, along with many scientific colleagues within the fusion research community, have been working to establish the design and physics basis for a modified divertor—the component located at the bottom of the huge ITER vacuum vessel responsible for exhausting most of the heat and all of the particles which will continuously flow out of ITER’s fusion plasmas. 

Our current Baseline begins plasma operations with divertor targets armoured with carbon fibre composite (CFC) material in the regions that will be subject to the highest heat flux densities. After the initial years of ITER exploitation, in which only hydrogen or helium will be used as plasma fuel producing no nuclear activation, this divertor is to be replaced. The replacement—a variant of the first component but fully armoured with tungsten—would be the heat and particle flux exhaust workhorse once the nuclear phase, using deuterium and then deuterium/tritium fuel, begins.

In 2011 the ITER Organization proposed to eliminate the first divertor and instead go for the full-tungsten („full-W”) version right from the start. This makes more operational sense and has the potential for substantial cost savings. By June 2013, the design was at a sufficiently advanced stage and we were confident that the necessary tungsten high heat flux handling technology was mature enough to invite external experts to examine our progress during the full-W divertor Final Design Review

But making a choice to begin operations with tungsten in the most severely loaded regions of the divertor is not just a question of having a design ready to build. 

Tungsten, a refractory metal with high melting temperature (3400 Celsius), is a much more difficult material than carbon when it comes to handling very high heat loads and running the plasmas which ITER will require to reach good fusion performance. Why? For two principal reasons: as a metal, tungsten will melt if the heat flux placed on it is high enough; also, as an element with high atomic number it can only be tolerated in minute concentrations in the burning plasma core.

Carbon, on the other hand, does not melt but sublimes (passing directly from solid to vapour) and is low atomic number, so can be tolerated in much higher quantities in the core plasma. Unfortunately, carbon is a difficult option for ITER nuclear phase operations as a result of its great capacity for swallowing up precious tritium fuel and efficiently trapping it inside the vacuum vessel. Tungsten retains fusion fuel only at comparatively low levels.

Why is melting such a problem? Because a melted metal surface is no longer the flat, pristine surface which is installed when the component is new. One of the ways the ITER divertor is able to handle the enormous power flux densities which will be carried along the magnetic field lines connecting to the target surfaces is to make the target intersect the field lines at very glancing angles, so that the power is spread over a wider surface. But a small angle means that any non-flat feature on the surface will receive a higher-than-average heat flux and can be further melted, producing a cascade effect.

The ITER full-W divertor design goes to great lengths to make sure that there is no possibility—on any of the many thousands of high heat flux handling elements—of an edge sticking up (for example, as a result of mechanical misalignment) that could overheat and begin to melt under the relentless bombardment these components receive during high power operation. However ITER’s size means that it will have the capacity to reach a value of stored energy in the plasma more than a factor of 10 higher than the largest currently operating tokamak, JET (EU). When some of this energy is released in a rapid burst (for example due to very transient magnetohydrodynamic events such as ELMs), some melting is possible—even if all edges have been hidden by clever design.

We intend to stop this happening as much as possible by applying ELM control techniques, but occasional larger events cannot always be excluded. So one of the big physics questions we have tried to answer over the past two years is: what exactly happens when a burst of energy, sufficient to melt tungsten, strikes our divertor targets?

Until recently we had only rather complex computer simulations with which to establish the physics design specifications. One of the main worries was not just that energy bursts could roughen up and damage divertor component surfaces, but that the very rapid melting induced by the burst could lead to the expulsion, or spraying, of micro-droplets of tungsten back into the plasma leading to intolerable contamination and a decrease in performance.

The computer simulations say this shouldn’t happen, but the process of melt ejection is so complex that experiment is the only sure test. But how to test the behaviour under conditions which only ITER can create? Well, as far as tokamaks are concerned, the only place where this was even conceivable was at JET, in which natural ELM energy bursts can be generated at levels similar to those expected for controlled ELMs in ITER. The problem is that these comparatively benign transients will not melt a tungsten surface!

In an experiment proposed and planned jointly between JET and the ITER Organization over the past two years, a small region of one of the full-W modules in the JET divertor was carefully modified to create a situation which every divertor designer would do anything to avoid—a deliberately misaligned edge.

The JET divertor modules are made up of about 9,000 small tungsten plates („W lamellas”), bound together by a complex spring loading system. The lamellas are only 5 mm wide and about 60 mm long with 1 mm gaps between neighbouring elements. For the experiment, a few lamellas were machined to make a single element stand up out of the crowd, presenting an edge of about 1.5 mm on average to the plasma in one of the hottest zones of the divertor.
The result: reassuringly unsurprising! Although there was some evidence suggesting the occasional ejection of very small droplets from the melted area, there was very little impact on the confined plasma. As the ELM plasma bursts repetitively melted the edge of the misaligned lamella, the molten material continuously migrated away from the heat deposition zone, accumulating harmlessly into a small mass of re-solidified tungsten (see video at left, courtesy of EFDA-JET). The JET plasmas with 3 MA of plasma current were able to produce ELM plasma pulses very similar to the lowest amplitude events we need to guarantee for 15 MA operation in ITER—a fact which makes the experiments very relevant from a plasma physics point of view.

Much more analysis is required to see how the results can be matched quantitatively by simulation, but the observations are clearly in qualitative agreement with theory. That’s the most reassuring part: that physics codes used to assist in component design for ITER tomorrow can be validated on experiments performed today. We will have to wait another year now for the damaged lamella to be retrieved from JET before the full picture of these important experiments can be completed, but this is already extremely valuable physics input for the important decisions coming up later this year with regard to our divertor strategy.

Korean contract advances neutral beam ports

The Korean Domestic Agency signed an important contract in July for the fabrication of neutral beam port in-wall shielding with Korean supplier Hyundai Heavy Industries Co., LTD (HHI). Through this contract, installation of the in-wall shielding into the port stub extensions will begin in mid-2015 with fabrication completed by early 2016. Hyundai Heavy Industries is also manufacturing two sectors of ITER vacuum vessel as contractor to the Korean Domestic Agency, as well as seventeen equatorial ports and the nine lower ports

The vacuum vessel’s neutral beam ports are composed of a connecting duct, port extension, and port stub extension. The spaces between the inner and outer shells of the port extension and port stub extension are filled with preassembled blocks called in-wall shielding. The main purpose of in-wall shielding is to provide neutron shielding for the superconducting magnets, the thermal shield and the cryostat.

In order to provide effective neutron shielding capability with the cooling water, 40-millimetre-thick flat plates (steel type 304B4) are used in almost all areas of the volume between port shells.

In-wall shielding is composed of shield plates, upper/lower brackets and bolt/nut/washers. Pre-assembled 368 in-wall shielding blocks will be assembled into the neutral beam port extension and port stub extension during port fabrication, while 160 field joint in-wall shielding blocks will be assembled after field joint welding on the ITER site. The total net weight of all neutral beam in-wall shielding approximates 100 tons.

Ki-jung Jung, Director-General of the Korean Domestic Agency, commented during the signature: „ITER Korea takes very seriously the demands of the vacuum vessel schedule and quality requirements by ITER.”

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.

Plasma seeking plasma

It has been an unusual July so far in Provence. Thunderstorms have broken over the site almost every afternoon, causing work to be stopped until the storm front moves on.

Storms over the ITER platform do not come unannounced: when one approaches, the French storm forecast agency Metéorage (a subsidiairy of Météo-France) sends an alert to security personnel, who activate the appropriate siren. Depending on the distance of the incoming storm, the siren sounds an „orange alert,” stopping only the heavy activity, or a „red alert,” requiring full site evacuation.

This spectacular bolt of lightning was captured last Wednesday from a fifth floor window in the ITER Headquarters building after a red alert was sounded.

Lightning is a high current electric discharge in the air that generates a ramified column of plasma. This specific bolt might have been looking for its kindred—the plasma that will be created within the ITER vacuum vessel. The place was right but the time some seven years too early.

STAC Chair reflects on latest meeting


The 14th meeting of the Science and Technology Advisory Committee (STAC) took place recently at the ITER Headquarters, from 14-16 May. We had the honour to be the first committee that met in the impressive Council Room after it was inaugurated by the ITER Council last November.

The STAC advises the ITER Council on two areas: the monitoring of ongoing project activity and the assessment of new proposals which imply a change in the ITER Baseline. The work at every meeting is based on the „STAC charges” adopted by the ITER Council. We assess the input from the ITER Organization that replies to recommendations made by the STAC and answers questions implied in the STAC charges.

The preparation of each STAC meeting involves an important work load on key ITER Organization staff and, as Chair of the STAC, I am aware that we must be careful with the amount of work that our requirements put on ITER Organization resources. I must also recognize the high overall quality of the reports and presentations delivered to our committee.
 
One of the first agenda points since I have participated in the STAC is the review of the project schedule from a technical point of view. Essentially, we analyze the technical causes of delays, including aspects which are midway between the technical and the managerial world such as configuration control, quality control, process control, etc.

As is happened in previous meetings, STAC 14 continued to express its concern about delays in the project. A number of systems are „critical or supercritical,” which means that they drive the First Plasma schedule, amongst them buildings, vacuum vessel, the poloidal field coils … and even the toroidal field coils could come into this category if delays are not stemmed. In addition, the „microschedule” reflected in the milestone achievement index and similar management parameters also indicates delays. However my personal perception, and to some extent that of many STAC members, is that the processes are improving and that the project schedule will soon consolidate. The STAC also acknowledged the organizational efforts and the implementation of recovery plans in order to mitigate the delays.

As I explained during the meeting with the staff in the afternoon of 16 May, my personal view on the delays is that they are not dangerous per se for the project but they undermine our credibility in front of stakeholders and society and this is the actual danger. In order to rebuild credibility our best tool is to keep working hard, as everyone involved is already doing. The ITER project is not only extremely complicated technically, it is also a nuclear project, which adds complexity. It was conceived with a complicated collaborative structure and, unfortunately, an underestimated allocation of resources. The fact that it is effectively progressing and that many components are actually being constructed should encourage all of us.

In addition to the technical analysis of the schedule STAC also looked at deferrals, i.e., procurements which are proposed to be delayed in order to free resources for other items that are needed in earlier phases of the project. We were worried about the deferred implementation of some systems, in particular diagnostics, and we have requested the ITER Organization to make every possible effort to implement those systems in time in order to avoid delays to the deuterium-tritium campaign derived from a slow implementation of the research plan.

During STAC-14 we noted that the organization and the progress of neutronics analysis has improved, for which we commended the ITER Organization. We have requested further detail on the results obtained for the next meeting of the STAC, in particular in relation to the heating of toroidal field coils and shutdown dose rates near the ports.

The news presented to the STAC on the central solenoid conductor was very good: in the last tests of a new cable developed by the Japanese Domestic Agency it showed very good stability—in fact, the degradation noted in earlier samples was essentially non-existing. Thus, we are now confident that the construction of the central solenoid can go ahead while keeping ITER’s performance as originally planned.

This STAC had the responsibility to make a clear recommendation on an important technical decision: whether or not to include in-vessel coils for ELM control in the Baseline. After we evaluated the specific problems that a lack of ELM control could cause, in particular when operating with a tungsten divertor, our unanimous recommendation was to include the coils in the ITER Baseline. STAC concluded that the potential benefits of the use of the coils in achieving ITER’s mission outweigh the risks, which were found to be very modest taking into account the solid design of the coils and the fact that they will be thoroughly tested during the non-nuclear phase.

STAC expects to make a recommendation next October for another key technical decision: the material for the first ITER divertor (tungsten or carbon).

At STAC-14 we analyzed the input from the ITER Organization regarding progress in divertor technology and tungsten divertor physics and the preliminary report prepared by the ITPA topical groups, which provided an excellent in-depth review of what is known today concerning tokamak operation with high Z* walls. The results from JET and other devices give a positive view of the operation with tungsten divertor in ITER but impose some scenario restrictions that must be further considered for ITER. Experiments to be carried out at JET in the near future, aiming at local melting of some tungsten elements of the divertor, will provide important input for a final recommendation by the STAC on its next meeting.

A final element in the last STAC meeting was the monitoring of progress in a number of areas: remote handling, quality control, ion cyclotron, and negative neutral beam heating. On this last item STAC looks forward with interest to the recent start of activities in the ELISE facility, which will provide important input to the physics and engineering design of the neutral beam injection sources for ITER.

In summary, STAC 14 corroborated important steps in the progress in the ITER project, which we expect to see reinforced next October thanks to the continued effort of all ITER Organization staff.

* A high Z element, like tungsten, is an element with a high
atomic number—its nucleus includes a large number of protons.

Let there be light!

Once the components of the ITER Tokamak are assembled and individually verified, a delicate and complex series of operations will be necessary before lighting the fire of First Plasma.

Commissioning, as this phase is called, means that all the different systems of the machine—vacuum, cryoplant, magnets—will be tested together in order to verify that the whole installation behaves as expected.

These commissioning operations all converge toward one point: the breakdown of the gas inside the vacuum vessel.

It happens in the following way: Initially, the toroidal field coils are electrically charged. Then the varying electrical current in the central solenoid and poloidal field coils generates an electric field around the torus of the tokamak causing the atoms in the gas to collide with the accelerated electrons. The gas in the vacuum vessel becomes ionized (electrons are stripped from the atoms) and reaches the state of plasma.

„At this moment,” explains Woong Chae Kim who joined ITER two months ago as Section Leader for Commissioning and Operations, „First Plasma will be achieved and the commissioning process will be over.”

ITER commissioning is expected to last more than two years and every step—from vacuum vessel leak-testing to the electrical charging of the magnets—will bring its own challenges. Woong Chae, however, is confident. „In the long history of tokamaks, start-up operations have never failed. Technically, I am not afraid. I’ve done it before …”

„Before” was five years ago, when Woong Chae was in charge of plasma commissioning at KSTAR. On 13 June 2008, following six months of commissioning operations, the large Korean tokamak (and the first to implement superconducting niobium-tin coils) achieved a First Plasma that surpassed the original target parameters.

From a technical perspective, commissioning KSTAR was close to what it will be at ITER. The difference lies in the regulatory status of the two devices—ITER is a nuclear installation, KSTAR is not—and in the inner workings of the organization.

„I participated in several design reviews for ITER components over the past four years and have had many opportunities to experience the complexity of the decision-making process within the ITER Organization. It is indeed a very complex machinery, even more than I had anticipated …”

KSTAR, which he joined in 1995 when the project was launched, taught something essential to Woong Chae: „While doing your own job on your own system or component, it is essential to have an overview of the whole device. If you don’t, coordination and interfacing becomes very, very difficult …”

Woong Chae chose to train as a fusion physicist/engineer because he felt fusion was „cool.” „It’s ideal as an energy-producing source, fascinating in terms of physics and technology and so different from the things one comes across in daily life.”

The first fusion device he encountered at graduate school in Seoul was the small tokamak SNUT-79 that Korea had developed in the late 1970s—the country’s first significant step onto the fusion stage. At the time, says Woong Chae, „the device was already a museum piece standing at the centre of the laboratory.” He then worked on the mirror machine HANBIT („Great Light”) in Daejeon, a partial reincarnation of the MIT’s 25-metre-long TARA, where he „learned how to manage big projects.”

After spending 18 years at KSTAR, Woong Chae felt that ITER was the „natural playground" for people like him—people who thrill at the challenge of „organizing men and procedures in order to make things happen.” Several ITER colleagues like Chief Engineer Joo Shik Bak or CODAC Section Leader Mikyung Park made a similar choice.

Woong Chae has moved to Aix-en-Provence with his wife, who spent a year in France as a graduate student, and their 16 year old son. They live near „Painters Ground” and have a beautiful view of Mount Sainte-Victoire. „Although I do not speak much French and am not what you would call a specialist in impressionism, I’m on familiar ground. In the early days of my marriage, we lived in Daejeon, close to restaurant named … Cézanne.”

Armed and ready to identify leaks

In constructing ITER, one of the key challenges is to ensure a leak-free machine. The US Domestic Agency has recently completed the bulk of delivery for the test equipment required to confirm the vacuum leak-tightness of components as they arrive on site and during the construction of the machine. At right,  vacuum team members are pictured with some of the leak detection tools-of-the-trade: helium spray guns and highly sensitive mass spectrometer-based detectors.

„This procurement is the very first US ITER procurement to be delivered to the ITER site,” rejoices Mike Hechler, the responsible officer within the US vacuum team. „Hence it should be celebrated as a real success. Being first we were like guinea pigs having to sort out how to deal with transport, VAT charges, customs, CE marking. It was not easy, but opens up the way for future US deliveries.”

„The basic method of leak detection is simple,” explains Liam Worth, member of the ITER vacuum team  and responsible for the test program. „You evacuate your vacuum vessel, surround it with helium gas, and then use the leak detector to look for helium leaking in—these instruments can detect in the minutest quantities.” However the size, complexity and number of the ITER vacuum systems make this a far from simple task. „We estimate that from acceptance to the final commissioning of the machine, no fewer than 94 man-years of vacuum testing will have to be performed.”

In Korea, a week of meetings for key ITER components


An important week of meetings took place recently in Korea for the ITER vacuum vessel and thermal shield—for both of these key components industrial suppliers have been selected and manufacturing, pre-manufacturing or kick-off works have begun.

The 52nd ITER Vacuum Vessel Integrated Product Team (IPT) meeting and Domestic Agency collaboration meeting held on 8-10 April brought together over 30 experts from the ITER Organization, the European, Indian, Korean and Russian Domestic Agencies, and Korean industry (Hyundai Heavy Industry & AMW). During meetings hosted at the National Fusion Research Institute (NFRI) and at Hyundai Heavy Industry, participants shared the technology and experience of fabrication of the ITER vacuum vessel, ports and in-wall shielding, and discussed the development pathway for fabrication issues. A visit was organized to the KSTAR Tokamak at NFRI.

During a bilateral collaboration meeting held on 11 April, participants from the Korean and European Domestic Agencies—plus industrial suppliers Hyundai Heavy Industry and AMW—focused more particularly on the new technologies for fabrication of ITER vacuum vessel sectors, especially welding, nondestructive examination (NDE) and optical dimensional measurement. All parties agreed that such valuable collaboration would be continued in the future.

On Friday 12 April, the kick-off meeting for the ITER thermal shield was held—this key component will be installed between the magnets and the vacuum vessel/cryostat in order to shield the magnets from radiation. The contract for the design and fabrication of the thermal shield was awarded by the Korean Domestic Agency in February to SFA Engineering Corp, which is also the supplier selected by Korea for ITER’s assembly tooling. SFA presented the implementation plan for the procurement of the thermal shield during the meeting.

More than 20 responsible persons from the Korean Domestic Agency, SFA and the ITER Organization were present including Domestic Agency head Kijung Jung, SFA Chief Operating Officer Myung Jae Lee, and head of the ITER Vacuum Vessel Division Carlo Sborchia. Prior to the kick-off meeting, representatives from ITER and the Korean Domestic Agency agreed to collaborate closely to solve urgent design change requests related to assembly and interface issues.

„The thermal shield is one of the most critical procurement items in the ITER project. We will do our best in collaboration with the ITER Organization for its successful procurement,” stressed Kijung Jung.

Green light for ITER’s blanket design



After three days and 29 presentations, a comprehensive design review with probably the largest participation in the history of the ITER project was completed last week. More than 80 experts from the ITER Organization, Domestic Agencies and industry attended the Final Design Review of the ITER blanket system.

„The development and validation of the final design of the blanket system is a major achievement on our way to deuterium-tritium operation—the main goal of the ITER project,” Blanket Integrated Product Team Leader (BIPT) and Section Leader Rene Raffray concluded at the end of the meeting, obviously relieved at the success of this tremendous endeavour. „We are looking at a first-of-a-kind fusion blanket which will operate in a first-of-a-kind fusion experimental reactor.”

The ITER blanket system provides the physical boundary for the plasma and contributes to the thermal and nuclear shielding of the vacuum vessel and the external machine components such as the superconducting magnets operating in the range of 4 Kelvin (-269°C). Directly facing the ultra-hot plasma and having to cope with large electromagnetic forces, while interacting with major systems and other components, the blanket is arguably the most critical and technically challenging component in ITER.

The blanket consists of 440 individual modules covering a surface of 600 m2, with more than 180 design variants depending on the segments' position inside the vacuum vessel and their functionality. Each module consists of a shield block and first wall, together measuring 1 x 1.5 metres and weighing up to 4.5 tons—dimensions  that not only demand sophisticated remote handling in view of maintenance requirements during deuterium-tritium operation, but also an approach to attaching the modules which is far from trivial when considering the enormous electromagnetic forces. 

The first wall is made out of shaped „fingers.” These fingers are individually attached to a poloidal beam, the structural backbone of each first wall panel through which the cooling water will be distributed. Depending on their position inside the vacuum vessel, these panels are subject to different heat fluxes. Two different kinds of panels have been developed: a normal heat flux panel designed for heat fluxes of up to 2 MW/m2 and an enhanced heat flux panel designed for heat fluxes of up to 4.7 MW/m2.

The enhanced heat flux panels are located in areas of the vacuum vessel with greater plasma-wall interaction and they make use of the hyper-vapotron technology which is similar to that used for the divertor dome elements. All panels are designed for up to 15,000 full power cycles and are planned to be replaced at least once during ITER’s lifetime. A sophisticated R&D program is currently under way in Japan for the development of remote handling tools to dismantle and precisely re-position the panels.  

Due to the high heat deposition expected during plasma operation—the blanket is designed to take a maximum thermal load of 736 MW—ITER will be the first fusion device with an actively cooled blanket. The cooling water is fed to and from the shield blocks through manifolds and branch pipes. Furthermore, the modules have to provide passage for the multiple plasma diagnostic technologies, for the viewing systems, and for the plasma heating systems.

Because of its low plasma-contamination properties, beryllium has been chosen as the element to cover the first wall. Other materials used for the blanket system are CuCrZr for the heat sink, ITER-grade steel 316L(N)-IG for the  steel structure, Inconel 718 for the bolts and cartridges, an aluminium-bronze alloy for the pads that will buffer the electromechanical loads acting on the segments, and alumina for the insulating layer. 

The procurement of the 440 shield blocks is equally shared between China and Korea. The first wall panels will be manufactured by Europe (50%), Russia (40%) and China (10%). Russia will, in addition, provide the flexible supports, the key pads and the electrical straps. The assembly of the blanket is scheduled for the second assembly phase of the ITER machine starting in May 2021 and lasting until August 2022. The work will be performed with the help of two in-vessel transporters working in parallel.

In assessing the work presented at the Final Design Review, Andre Grosman, deputy head of Magnetic Fusion Research Institute at CEA and chair of the review panel, enthusiastically commended the BIPT for its achievements since the Preliminary Design Review in December 2011 which were „beyond the expectation of the panel.” He added: „We have singled out the continuity and benefit of the work done by the ITER Organization and the Domestic Agencies within the BIPT framework with a sharing of risk and information among all stakeholders.”

The panel nevertheless pointed out some remaining issues, including a few challenging issues that need to be addressed at the project level. But thanks to the excellent quality of work performed by the BIPT, the ITER blanket design can today be called „approved.” The BIPT can now turn its focus to addressing the feedback received at the Final Design Review, applying the final touches to the design, and preparing for the Procurement Arrangements, where fabrication is handed over to the Domestic Agencies, starting at the end of 2013.

DivSOL wagon rolls EAST



With the EAST tokamak in the middle of an extended maintenance period—during which the ASIPP team in Hefei, China will take the audacious step of installing an ITER-like, full tungsten divertor in the upper part of the vacuum vessel by the end of this year—what better place to hold the latest in the series of regular meetings of the International Tokamak Physics Activity (ITPA) Topical Group on Divertor and Scrape-Off Layer physics. Known in ITPA circles as the DivSOL TG, this group focuses on issues of importance to ITER in the area of heat and particle exhaust from the tokamak plasma and the unavoidable plasma-surface interactions which occur at the plasma-materials boundary. 

Plasma and materials physicists work together within DivSOL to address a host of questions, from movement of material by the plasma and tritium trapping in surfaces, to turbulent transport of heat in the plasma boundary and plasma-facing component lifetime under intense heat fluxes. In common with all ITPA groups, DivSOL is reactive to urgent ITER physics R&D issues and works to find answers to specific requests.

One such example is the flurry of activity stimulated by the ITER Organization proposal in autumn 2011 to eliminate one of the two divertors planned for the first years of ITER operation, up to achievement of burning plasmas. The idea is to go the whole way with a single unit in which tungsten (chemical symbol W) would be the only material intercepting the majority of the tokamak heat exhaust. A single divertor would be a major cost saving to the project, but it is a calculated risk: W is a harder material to work with from the plasma point of view than the carbon fibre composite in originally planned first divertor.

Finding out just how much of a risk, and making sure that a workable design with qualified technology can be ready in time for procurement which must begin next year, was the task set by the ITER Council to the ITER Organization, with a reporting deadline near the end of 2013. All the ITPA groups are lending a helping hand by trying to assess the physics risks of „beginning full-W.” DivSOL has a major role to play given that most, but by no means all, of the issues concern the plasma-materials interface.

Not surprisingly, living with tungsten was a major theme in the 18th DivSOL meeting, hosted by ASIPP from 19-22 March. It was also a record breaking meeting that reunited over 90 representatives from the ITER Members, including about 50 Chinese participants representing universities and technology institutes from all over China. Such high attendance reflects the importance of plasma-materials interaction not just to ITER, but to the long-term future of fusion as a viable energy source. The meeting was also a good example of the less visible, but essential, role which ITPA fulfills in addition to supporting ITER as a vehicle through which newcomers can take part in lively discussions and presentations, in a workshop atmosphere, with experts from across the ITER Members.

The success of any workshop or conference depends to a large part on organization. Our Chinese hosts led by Houyang Guo of ASIPP (and ITPA DivSOL co-chair), provided a seamless environment for the first DivSOL meeting ever to be held at the Institute. The next DivSol TG will be held in Japan in January 2014.

ITPA DivSOL wagon rolls EAST



With the EAST tokamak in the middle of an extended maintenance period—during which the ASIPP team in Hefei, China will take the audacious step of installing an ITER-like, full tungsten divertor in the upper part of the vacuum vessel by the end of this year—what better place to hold the latest in the series of regular meetings of the International Tokamak Physics Activity (ITPA) Topical Group on Divertor and Scrape-Off Layer physics. Known in ITPA circles as the DivSOL TG, this group focuses on issues of importance to ITER in the area of heat and particle exhaust from the tokamak plasma and the unavoidable plasma-surface interactions which occur at the plasma-materials boundary. 

Plasma and materials physicists work together within DivSOL to address a host of questions, from movement of material by the plasma and tritium trapping in surfaces, to turbulent transport of heat in the plasma boundary and plasma-facing component lifetime under intense heat fluxes. In common with all ITPA groups, DivSOL is reactive to urgent ITER physics R&D issues and works to find answers to specific requests.

One such example is the flurry of activity stimulated by the ITER Organization proposal in autumn 2011 to eliminate one of the two divertors planned for the first years of ITER operation, up to achievement of burning plasmas. The idea is to go the whole way with a single unit in which tungsten (chemical symbol W) would be the only material intercepting the majority of the tokamak heat exhaust. A single divertor would be a major cost saving to the project, but it is a calculated risk: W is a harder material to work with from the plasma point of view than the carbon fibre composite in originally planned first divertor.

Finding out just how much of a risk, and making sure that a workable design with qualified technology can be ready in time for procurement which must begin next year, was the task set by the ITER Council to the ITER Organization, with a reporting deadline near the end of 2013. All the ITPA groups are lending a helping hand by trying to assess the physics risks of „beginning full-W.” DivSOL has a major role to play given that most, but by no means all, of the issues concern the plasma-materials interface.

Not surprisingly, living with tungsten was a major theme in the 18th DivSOL meeting, hosted by ASIPP from 19-22 March. It was also a record breaking meeting that reunited over 90 representatives from the ITER Members, including about 50 Chinese participants representing universities and technology institutes from all over China. Such high attendance reflects the importance of plasma-materials interaction not just to ITER, but to the long-term future of fusion as a viable energy source. The meeting was also a good example of the less visible, but essential, role which ITPA fulfills in addition to supporting ITER as a vehicle through which newcomers can take part in lively discussions and presentations, in a workshop atmosphere, with experts from across the ITER Members.

The success of any workshop or conference depends to a large part on organization. Our Chinese hosts led by Houyang Guo of ASIPP (and ITPA DivSOL co-chair), provided a seamless environment for the first DivSOL meeting ever to be held at the Institute. The next DivSol TG will be held in Japan in January 2014.

Management Advisory Committee meets in Barcelona


For the second time in its history, the ITER Council Management Advisory Committee (MAC) convened for an extraordinary session in order to assess the status of the ITER project schedule and the implementation of corrective actions.

The meeting took place from 18-19 March at the headquarters of the European Domestic Agency in Barcelona in the attendance of high-level representatives of the ITER Organization and seven ITER Members.

Since the last special MAC meeting held in August 2012, the ITER Organization has worked closely with Domestic Agencies to complete the integration of Detailed Work Schedules (DWS)—detailed schedules that exist for every component or system. The IO and DAs completed the integration of the remaining DWS, namely Main Vacuum Vessel, IC Antenna, PF Coils and TF Structure, which will allow for monitoring of the schedule.

MAC requested that the Unique ITER Team continue to make significant efforts to take action focusing on super-critical milestones and to take all possible measures to keep to the Baseline schedule. The ITER Organization and Domestic Agencies are committed to doing their best to implement this request.

Hot, hotter, hottest



Temperature, from a physicist’s perspective, is not only a measure of hot or cold.

It is also a measure of the energy carried by atoms and molecules: temperature tells us how rapidly these atoms or molecules move within a solid, a liquid or a gas.

Temperature is different from heat. To feel heat on your fingers, you need density: the higher the density, the more heat is transferred to your skin—this explains why a neon tube containing a very hot (~10,000°C) but very tenuous plasma can be touched without harm.

In temperature, there is a theoretical absolute cold („absolute zero”) but no absolute hot: a particle can always move more rapidly but it cannot be more immobile than … immobile.

When we talk about a 150- to 300-million-degree plasma in ITER, we’re describing an environment where particles (the deuterium and tritium ions and the freed electrons) move around at tremendous speed: so fast and with such a high energy that when they collide head on the miracle of fusion happens. The electromagnetic barrier that stands between nuclei is overcome and the nuclei can fuse.

How will the ITER plasma be brought to such extreme temperatures—ten times higher, or more, than the core of the Sun?

Plasma heating in ITER will begin with an electrical breakdown, quite similar to what happens when we turn on the switch of a neon light. In the very tenuous gas mixture that fills the vacuum vessel (one million times denser than the air we breathe) the electrical discharge strips the electrons from the atoms and the gas becomes a plasma—a particle soup of electrically charged electrons and ions.

„The electrons from the current collide with and communicate their energy to the ions from which they have been stripped,” explains Paul Thomas, ITER Deputy Director-General for CODAC, Heating & Diagnostics. „Current intensity grows steadily and, as plasma resistance increases due to the collisions between electrons and ions, temperature also rises—this is Ohmic heating, like in a bread toaster or an electrical radiator.”

However, contrary to what happens in metals, plasmas have an unusual property in terms of resistivity: the hotter they get, the less resistive they become. This means that Ohmic heating can heat a plasma only up to a point.

„For a long time,” Paul recalls, „some fusion physicists dreamed they would achieve fusion with Ohmic heating alone by increasing the magnetic field. Even today, the project called Ignitor is based on this assumption. The problem is that the more intense the magnetic field, the stronger the mechanical strain on the machine’s structure…”

Ohmic was the only heating source on the Soviet T-3, which achieved plasma temperatures in the range of 10 million degrees in the late 1960s—an achievement that left the nascent world fusion community agog and launched the tokamak race worldwide.

Achieving fusion, however, requires temperatures approximately ten times higher than what Ohmic heating alone can provide. In the 1970s, the fusion community began experimenting with additional heating techniques based on radio frequency (RF) waves, or the injection of energetic atoms into the plasma.

Yes, radio waves can heat. Whether at 40-55 MHz, like shortwave radio (ion cyclotron; a few GHz like microwave ovens (lower hybrid) or many tens to hundreds of GHz like very advanced radar (electron cyclotron), sending electromagnetic into the plasma can deliver enough energy to push it into the fusion regime. ITER will be equipped with an electron cyclotron and an ion cyclotron heating system, both delivering 20 MW of power.

But the workhorse of additional heating in tokamaks has been neutral beam heating—the injection of high-energy neutralized particles deep into the plasma.

Neutral beam heating is a bit like heating the milk in a pot by using a jet of hot steam from the espresso machine, what French garçons de café systematically do when you order cappuccino. As hot molecules from the steam jet collide with those of the cold milk, energy is transferred and hot milk is ready to be poured in the coffee cup.

„Exploitation of the neutral beam technologies we will use was pioneered in Japan,” says Paul. We have a very strong collaboration with our friends in Naka. Neutral beam technology is also used on JET (ITER’s neutral beam system will deliver seven times the energy of JET’s).

The challenging technology of ITER’s neutral beam system will be tested in a dedicated installation that was inaugurated a year ago almost to the day: the PRIMA Neutral Beam Test Facility in Padua, Italy. In parallel, IPP Garching is developing ELISE, an ion source half the size of ITER’s; success on this test bed will greatly reduce the risk associated with the final development of the full-size ITER ion source at the SPIDER test facility.

ITER’s three heating systems—electron cyclotron, ion cyclotron and neutral beam—feature different levels of technical complexity, maintainability and ease or convenience of use. The balance between these features is such that all three should be tested on ITER and developed to the point where a decision can be taken on which should heat a reactor, according to Paul.

„The reason we’ll have all three systems in ITER is to have them compete in the nuclear environment — this is precisely what the 'technological viability' demonstration is about.”

Korea awards contract for ITER thermal shields


The Korean Domestic Agency signed a contract with SFA Engineering Corp. for ITER thermal shields on 28 February. The contract covers the detailed design of manifolds/instrumentation, the manufacturing design and the fabrication of the thermal shield system. „For us, this is a big step forward for the Korean contribution to ITER,” said Myeun Kwon, president of the National Fusion Research Institute, after the signing.

SFA is a leading company in industrial automation with much experience in the procurement of advanced equipment related to fusion, accelerator, and space technology. SFA was deeply involved in the manufacturing and assembly of the Korean tokamak KSTAR.

The ITER thermal shield will be installed between the magnets and the vacuum vessel/cryostat in order to shield the magnets from radiation. The thermal shield consists of stainless steel panels with a low emissivity surface (<0.05) that are actively cooled by helium gas, which flows inside the cooling tube welded on the panel surface. The temperature of helium gas is between 80 K and 100 K during plasma operation. The total surface area of the thermal shield is approximately 4000 m2 and its assembled body (25 m tall) weighs about 900 tons.

The key challenges for thermal shield manufacturing are tight tolerances, precision welding, and the silver coating of the large structure. The thermal shield also has many interfaces with other tokamak components. „The Korean Domestic Agency is satisfied with this contract because the thermal shield is one of the most critical procurement items in the ITER project. We will do our best in collaboration with the ITER Organization to successfully procure the ITER thermal shield,” said Hyeon Gon Lee, DDG of the Korean Domestic Agency, on the occasion of the contract signature.

Fusion, with a touch of science fiction



An imposing object stands at the heart of the Tom Hunt Energy Hall in the recently opened Perot Museum of Nature and Science in Dallas, Texas.

The four-metre-high structure is a mock-up of the ITER Tokamak—or, rather, a designer’s „interpretation” of the science of fusion and of the flagship device of fusion research.

Those familiar with the arrangement of components that make up an actual tokamak—central solenoid, vacuum vessel, toroidal and poloidal field coils, divertor, piping and feeders—will be a bit lost when gazing upon the towering mockup.

This is intentional. „Our goal was to create a sense of wonder in our visitors that might inspire them to learn more about the subject,” explains Paul Bernhard, whose team designed and installed the 700-square-metre Tom Hunt Energy Hall. „We see our tokamak as based in science, but coloured by a future vision influenced by science fiction—a somewhat cinematic element that you might imagine seeing in a new Star Trek film…”

The result is indeed spectacular. Although Bernhard’s tokamak looks a bit like a thermonuclear mushroom cloud—a „purely coincidental” similarity due to the geometry of the large rounded shape containing the brightly glowing "plasma" suspended over the narrower central core—it is a truly astonishing work of science art.

The moment of awe passed, visitors can experiment with a neon/argon plasma, manipulating it with a magnet; have a hands-on experience with actual toroidal field coil and central solenoid conductor sections provided by the US Domestic Agency; or watch video clips.

Impressed by the „amazing potential of fusion energy,” Bernhard and his team sought to „pass along [their] sense of inspiration.” In stimulating curiosity and enthusiasm for the sciences, a bit of artistic license can’t do any harm.