When cooled to the temperature of 4.5 Kelvin (around minus 269 degrees Celsius), ITER's magnets will become powerful superconductors. The electrical current surging through a superconductor encounters no electrical resistance, allowing superconducting magnets to carry the high current and produce the strong magnetic fields that are essential for ITER experiments.

Superconductivity can be maintained as long as certain thresholds conditions are respected (cryogenic temperatures, current density, magnetic field). Outside of these boundary conditions a magnet will return to its normal resistive state and the high current will produce high heat and voltage. This transition from superconducting to resistive is referred to as a quench.

During a quench, temperature, voltage and mechanical stresses increase—not only on the coil itself, but also in the magnet feeders and the magnet structures. A quench that begins in one part of a superconducting coil can propagate, causing other areas to lose their superconductivity. As this phenomenon builds, it is essential to discharge the huge energy accumulated in the magnet to the exterior of the Tokamak Building.

Despite 23,000 tons of steel, the ITER machine won't be a rigid, unmoving block. As the magnets are cooled down progressively, or as they are powered up according to ITER's plasma scenarios, the machine will "breathe" and move. Quenches may occur as the result of mechanical movements that generate heat in one part of the magnet. Variations in magnetic flux or radiation coming from the plasma can also cause quenches, as well as issues in the magnet cryogenic coolant system.

Magnet quenches aren't expected often during the lifetime of ITER, but it is necessary to plan for them. "Quenches aren't an accident, failure or defect—they are part of the life of a superconducting magnet and the latter must be designed to withstand them," says Felix Rodriguez-Mateos, the quench detection responsible engineer in the Magnet Division. "It is our job to equip ITER with a detection system so that when a quench occurs we react rapidly to protect the integrity of the coils."

"A quench is not an off-normal event," confirms Neil Mitchell, head of the Magnet Division. "But we need a robust detection system to protect our magnets, avoid unnecessary machine downtime, and also as a safety function to discharge large stored energy and avoid damage to the first confinement barrier—the vacuum vessel."

Quench management will be a two-fold strategy in ITER: first quench detection, then magnet energy extraction. The time between detection and action has to be short enough to limit the temperature increase in the coil and avoid any damage. "We have on the order of 2-3 seconds to detect a quench and act," says Felix.

The primary detection system—called the investment protection quench detection system—will monitor the resistive voltage of the superconducting coils (there is also a secondary detection system, see box below). Why the voltage? "Whereas during superconducting operation the resistive voltage in a coil is practically zero, a quench would cause it to begin to climb," explains Felix. "By comparing voltage drops at two symmetric windings for instance, the instruments will detect variations of only fractions of a volt."

Above a threshold level, these variations trigger a signal that is sent to the central interlock control system. In order to avoid unnecessary machine downtime, specific signal processing is required within the quench detection system to discriminate the resistive voltage from the inductive one due to the variations of the magnetic field—that is, to distinguish "true" signals from "false."

In addition to its primary quench detection system, ITER will have a safety class quench detection system that performs the safety function of initiating a fast discharge of the toroidal field coils in the event that a quench has failed to be detected by the primary system. The purpose of this safety action is to safely discharge the large stored energy, removing the hypothetical risk of damage to the vacuum vessel and its extensions that provide the first confinement barrier for the in-vessel radioactive material inventory.

"The Tokamak environment will be a very noisy one for our instruments—that's one of the challenges of quench detection in ITER," says Felix. "The difficulty will be to cull out false triggers while at the same time not allowing a real quench to go undetected," says Felix. "We have tried to build enough redundancy into the system so as to minimize false signals. We don't want to discharge the coils and lose machine availability if we don't have to."

If a quench is confirmed, the switches on large resistors connecting coil and resistors are thrown open and the magnetic energy of the coil is rapidly dissipated, avoiding any damage to the coils. For the toroidal field coils that have the largest amount of stored energy, 41 GJ, achieving total discharge can take about one a half minutes.

To detect the start of a quench in any part of the magnet system, voltage measuring instruments (over 3,000 sensors) will be integrated at regular distances onto ITER's coils, feeding bus bars, and current leads. Following the Manufacturing Readiness Review for coil instrumentation last December, the Magnet Division is currently in the phase of preparing over 20 individual tenders (~EUR 25 million). The instruments imply a variety of components and technologies to compensate inductive signals. Much process and material development has gone into the design of these systems. 

In addition, an R&D collaboration has been underway at the superconducting Korean tokamak KSTAR since 2009 to learn more about compensating the electromagnetic fields. ITER is collaborating with the KSTAR magnet team to gather information on the electromagnetic signals picked up by the superconducting cables during plasma disruptions. This data will assist the ITER team in designing compensation systems to separate the electromagnetic noise of a disruption from a quench.

"Quench detection in ITER is the most challenging around," concludes Felix, who has approximately 25 years of experience in the field. "At the Large Hadron Collider (LHC), for instance, we were working with faster detection times. But in ITER, there will be a tremendous amount of interference for the instruments to sort through—electromagnetic noise, swinging voltages, couplings, perturbations. At ITER, we are also dealing with higher current, bigger common mode voltages, and larger stored energy. We'll be pushing quench detection and protection to the limit of technology today."

Drain tank fabrication for ITER's tokamak cooling water system is progressing steadily under the leadership of US ITER, which is managed by Oak Ridge National Laboratory for the US Department of Energy. The drain tanks will be among the first major hardware items shipped to the ITER site in France. The US production timing will accommodate the installation sequence for the ITER fusion facility.

Joseph Oat Corporation, a sub-contractor to AREVA Federal Services based in Camden, New Jersey, has begun fabrication activities for four 10-metre-tall, 78 metric ton drain tanks and one 5-metre-tall, 46 metric ton drain tank. Another industry partner, ODOM Industries in Milford, Ohio, is fabricating the ten tank heads as a sub-contractor to the Joseph Oat Corporation.

ODOM will ship each tank head as it is fabricated, and will complete delivery to Joseph Oat Corporation by the end of 2013. Joseph Oat, which specializes in industrial fabrication of pressure vessels and heat exchange technologies, expects to stagger completion of drain tanks throughout the summer and fall of 2014.

"Because the tanks are so large, the ITER Organization will install the tanks one at a time and do so before the neighbouring building is constructed," Chris Beatty, US ITER tokamak cooling water systems engineer, said.

Beatty noted that the Hot Cell building will permanently block access to the drain tanks in the Tokamak Complex once the ITER facility is complete. The tanks, which are built to last 40 years, are expected to perform beyond the duration of the ITER project.

The tokamak cooling water system includes over 20 miles of piping in an intricate network that wraps around the ITER Tokamak. The primary cooling water system is responsible for transferring heat from Tokamak hardware to the secondary cooling system. The tokamak cooling water system also supports operations such as the baking of in-vessel components, chemical control of water provided to client systems, and draining and drying for maintenance.

"There are many ways to cool a reactor, but ITER uses water to cool the internal parts," said Juan Ferrada, US ITER tokamak cooling water senior systems engineer and technical project officer.

When the water isn't being used for operations, such as cooling the system through the network of pipes, it can be stored in the four large drain tanks that hold up to 63,000 gallons of water each. Two 78-tonne tanks are reserved for normal maintenance and operations. During maintenance, the smaller, 46-tonne tank will store coolant for the neutral beam injector that pelts high-energy atoms into the Tokamak to heat the plasma.

The other two 78-tonne tanks, known as the safety drain tanks, are primarily used for storage in case water should leak into the vacuum vessel. Because fusion reactions use tritium and the plasma-facing wall is made of beryllium, the safety tanks are designed to hold water with radioactive particles such as dust, tritium and activated corrosion products.

The pressurized, stainless steel drain tanks must meet French regulations, giving these US fabricators the opportunity to gain experience implementing French regulations for nuclear pressure equipment.

"Compliance with French nuclear pressure equipment regulations is new to most manufacturers in the US," says Glen Cowart, US ITER quality assurance specialist. "In addition, tank fabrication must meet the ITER Organization's requirements as well as engineering and quality criteria established by AREVA Federal Services and US ITER."

"We have to make sure our design criteria meet the French regulations so the tanks can be used for ITER nuclear operations in France," Beatty explains.

Following approved designs, the tanks are being fabricated out of stainless steel plates. Typical plates are 2.7 metres wide and nearly 10 metres long, with each plate weighing over 8.5 tonnes. The design requires that each tank have two hemispherical heads—comprised of a curved top cap and a base, fabricated from six segments (called petals) that are welded together. Joseph Oat has begun bevelling and welding the plates, and rolling them into a cylindrical shape. The caps and base will then be welded to the cylindrical body to form the approximately 6-metre-diameter tanks.

Although the drain tanks are simple equipment from an engineering standpoint when compared to many parts of ITER, their sheer size and weight, in addition to being the first set of US ITER-provided equipment fabricated under the French nuclear regulatory framework, make the fabrication and delivery process extremely demanding.

"Even moving the plates is time consuming," Beatty said. "It takes about an hour to move them from the bevelling machine to where they will be welded. Once they're welded, the plates are even larger, so it can take half a day just to flip them over."

Once the tanks are completed, approved for nuclear pressure safety and delivered to the ITER site in France, they will pose one more challenge: Positioning the heavy tanks inside the Tokamak Complex. To meet this challenge, plans are already in place for using specialized air pads to manoeuvre the tanks to their permanent home in the ITER facility.

 

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.

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 tonnes.

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."

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."

It's that time of year again. With the last days of August upon us and a busy September just around the corner, it's a good time to stop and take measure of the evolution of the ITER Organization. The 2012 ITER Organization Annual Report, just released, recounts one year in the life of the ITER Project—the highlights in every technical department, the organizational challenges faced (and the solutions set into motion), and milestones in construction and manufacturing.

In 2012, the ITER project entered the third year of its Construction Phase. The ground support structure and seismic isolation system for the future Tokamak Complex was completed, work began on the site of the Assembly Building, the ITER site was connected to the French electrical grid, and part of the ITER team—approximately 500 people—moved into the completed Headquarters building.

The year 2012 was also witness to the accomplishment of a major licensing milestone when, in November, ITER became the world's first fusion device to obtain nuclear licensing.

The project made a definitive shift in 2012 from design work and process qualification to concrete manufacturing and production. To match this important evolution, the 2012 Annual Report introduces a new feature—the last pages of the report (pp. 40-48) are now reserved for reports from the Domestic Agencies. How is the procurement of ITER systems divided among the Domestic Agencies? Where are activities for ITER taking place in each Member? What percentage of work has been signed over by the ITER Organization in the form of Procurement Arrangements? And, finally: What major manufacturing milestones were accomplished in 2012?

The ITER Organization 2012 Annual Report and 2012 Financial Statements are available online at ITER's Publication Centre.

Despite appearances, this picture does not frame a late-summer apéritif. End of August or not, the Sun still shines fiercely down on the Tokamak Pit and for workers preparing the anchoring of the equipment-supporting plates, a bit of shade is most welcome.

Some 60,000 of these plates will be embedded into the slab and walls of the Tokamak Complex. Depending on the equipment they will support, their size range from 30 x 30 to 90 x 90 centimetres.