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The ITER Newsline is a globally-distributed publication released weekly by the Office of Communication of the ITER Organization.
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Plasma physics | Be clean, be strong

ma, 16/04/2018 - 17:33

To achieve maximum fusion efficiency in a tokamak device it is essential to limit the impurities in the plasma. But this can be a challenge, as interaction between the hot plasma and the material surfaces of the vacuum vessel causes material particles to detach and enter the swirling cloud of gas.
The laws of physics dictate the maximum plasma density that can be achieved for a given current in a tokamak, which means that in ITER—as in other tokamak devices—there will be an upper limit to the number of atoms that can be confined.
Within this limit, it is important that the plasma contain as many atoms as possible that are capable of reacting to produce fusion—in ITER's case, atoms of deuterium and tritium.
Even in trace amounts, other atoms ("impurities") dilute the core of the plasma by taking the space that could be occupied by the fusion fuels, resulting in fewer reactions and a reduction in energy production. And because fusion reactions occur in a roughly proportional manner to the square of fuel density, the "multiplier" effect sets in quickly—fewer fuel atoms result in a dramatic drop-off in fusion reactions, while more fuel results in a rapid increase.
Impurities originate from vacuum vessel and the in-vessel component materials ... iron from the steel components, beryllium from the top layers of the first-wall panels protecting the vacuum vessel, and tungsten from the divertor targets. 
Impurities not only dilute the plasma but—depending on the physical properties of the atoms involved (the number of electrons)—they can also cool it to differing degrees. "The process is similar to that in a fluorescent lamp," explains Alberto Loarte, who leads the Confinement & Modelling Section at ITER. "The electrons of the impurity atoms run into the electrons in the plasma and drain their energy, re-emitting it as electromagnetic radiation—including visible light."
The heavier elements, in particular, drain a lot of energy from the plasma through radiation because of a high number of electrons (tungsten has 74). The energy lost through impurity radiation cools the plasma down and the fusion reactions stop.
In ITER, to keep these radiative losses to a minimum, the divertor will be working from its position at the bottom of the machine to continually exhaust impurities from the plasma and limit contamination.
The very properties that make impurities unwelcome in the core of the plasma, however, can be applied to beneficial effect in the plasma edge region.
Because the energy confinement provided by the machine's magnetic fields is not perfect, large power fluxes can find their way to the edge of the plasma and onto the divertor targets. To avoid localized depositions that would be too high for the material components to withstand, scientists will inject impurity gases at the plasma edge. The radiative properties of the impurities will act to reduce the power fluxes to the material elements by dissipating their energy over a larger zone.
As the plasma in this edge/divertor region is already at temperatures much lower than those required to produce fusion power, this plasma cooling will not affect fusion power production in ITER.

Ring coils | Hot resin before the deep cold

ma, 09/04/2018 - 16:23



It has been almost one year since the fabrication of the first ring coil was launched in the on-site Poloidal Field Coil Winding Facility by European Domestic Agency contractors. Out of the eight "double pancake" conductor windings needed to finalize the 350-tonne magnet, three have been wound and are ready to pass through the resin-impregnation phase—an operation that contributes to both electrical insulation and structural strength.
On one of the circular platforms on the southern end of the silent, clean and temperature-controlled facility, a double pancake sits, still attached by 24 lifting points to the circular spreader beam that has just moved it from the stacking station.
A few metres away, technicians are busy assembling the vacuum containment vessel—the "mould"—that will enclose the double pancakes throughout the lengthy and delicate resin impregnation process.
"During impregnation, we inject some 600 litres of epoxy resin at a temperature of 55-60 °C through entry ports in the mould," explains Gian Battista Fachin of the European Domestic Agency, who works in the facility where Europe is fabricating the four largest ITER poloidal field coils. "At that temperature the resin is as liquid as water and easily penetrates through the fiberglass wrapping of the double pancake."
Once extra pressure has been applied inside the leak-tight mould to insure that all micro spaces are properly filled, the resin's temperature is ramped up first to 100 °C for a few hours of "gelling," then to 140 °C for a full day and a half of "curing." By then, the resin has become rock solid and the shining white double pancake has turned into a massive block the colour of caramel.
The resin impregnation process was tested and validated on a "dummy" conductor winding that is presently stored at the far end of the building.
"We learned a lot from the dummy, right from the beginning operations that began in November 2015," confirms Gian. "We established metrics and procedures, refined bending parameters, impregnation and injection durations ... everything a dummy is for."
The dummy is a perfect replica of an actual double pancake for the 17-metre-in-diameter poloidal field coil #5 (PF5). For reasons of cost however, it is wound from copper conductor rather than from superconducting niobium-titanium alloy.
When all eight double pancakes for PF5 are finalized (winding is underway on the fourth in the series now) they will be stacked to form a winding pack—the coil's very core—which will be wrapped with insulating fiberglass tape and impregnated with resin as one single component.
The winding pack will then receive additional equipment such as clamps, protection covers and pipes. At that point, one last crucial operation remains to be performed before the component can be considered fit for duty.
When ITER enters operation, liquid helium circulating inside the conductor will bring the coil temperature down to 4 K (minus 269 °C) to create the physical conditions for superconductivity in the niobium-titanium conductor.
Throughout the manufacturing process, sample tests and quality control have insured that the conductor's performance in such extreme conditions is in line with the magnet system's requirements.
What remains to be tested however, is the coil's behaviour as a whole. How is it affected by the thermal contractions generated by the ultra-cold temperature? Does the liquid helium circuit within the cable-in-conduit conductor remain leak-tight? Can cracks develop in the resin and hinder electrical insulation?
These questions can be answered without having to cool the coil all the way down to 4 K. At the temperature of liquid nitrogen (80 K or minus 193 °C) thermal contractions have already reached their maximum and all the potential issues can be identified. Also, cooling with liquid nitrogen is much cheaper and easier to implement than cooling with liquid helium.
In May, the cold testing equipment will arrive from Italy for installation in the northern end of the workshop. The four coils manufactured on site (ranging from 17 to 24 metres in diameter) will be tested one after the other in the cold testing vacuum vessel, as will a smaller coil (10 metres in diameter) that is being manufactured in China under an agreement with Europe.
Cold-testing operations are scheduled to begin in the summer of 2019 and last for more than one year.

Plant systems | Entering the stage, one by one

ma, 26/03/2018 - 17:19

As buildings rise out of the earth and equipment is progressively installed, ITER's Science & Operations Department is busy making plans to commission the first plant systems.
Commissioning is the final check that each of the components and plant systems have been designed, manufactured and installed correctly. It is an opportunity to transfer knowledge to the operations team, test all the procedures, and get ready to start the first experiments.
To commission a facility as complicated as ITER it is necessary to proceed in small and gradual steps—checking each part before moving onto the next, and bringing together more and more pieces of the puzzle until the whole facility is working as one. At that point we will be ready to turn on the Tokamak and make plasma.
We will start this year by energizing the electrical distribution systems, since without electricity nothing can work. ITER is directly connected to France's 400 kV public transmission network. Transformers and switchgears located on the ITER platform will "propagate" this power all over the site to provide the correct voltage for each of the clients.
Last year, a test was performed with the first energization of a 400 kV bay, in order to validate all procedures and contractual requirements with French transmission system operator.
Once power is available, the central control system will be turned on and made ready to control, monitor and record data from each of the systems to come. The first task for the control system will then be to start up the cooling water systems and the cooling towers, testing each pump and valve before starting the circulation and flow tests.
_To_134_Tx_With power, control and cooling in place we will begin commissioning the production and distribution networks for various gases and liquids, as well as the air conditioning to remove heat generated by the plant in each building. We then start up the nitrogen and helium production facilities in the cryogenic plant and the various auxiliary vacuum pumping systems.
The specialized Tokamak systems come next—the electron cyclotron system that generates megawatts of microwave energy to heat the plasma, cryogenic pumping systems able to produce ultra-high vacuum, and the power supplies needed to energize the superconducting magnets.
When all of these systems have passed their tests we are ready: the construction phase of ITER is complete and we can start the operations phase with integrated commissioning of all systems working together. All air will be evacuated out of the vacuum vessel and cryostat to bring the pressure inside to one millionth of normal atmospheric pressure; the magnets will be cooled down to -269 °C and energized to create the magnetic confinement field; and a tiny amount of hydrogen gas will be injected and heated up to produce a critical milestone for ITER—First Plasma.
Once this has been achieved we will press on—turning up the current on the magnets to full power and completing their stress testing under all the various field combinations.
At that point we will have shown that the ITER machine is ready for the researchers.

Blanket shield blocks | Full-scale prototype passes key test in China

ma, 19/03/2018 - 16:22


A full-scale prototype of a blanket shield block manufactured in China successfully passed acceptance tests, including the challenging hot helium leak testing in February. An important qualification milestone has been achieved in the ITER blanket program ...

On 14 February, two days before the start of the Chinese New Year, the Chinese Domestic Agency successfully accomplished the last in a series of back-to-back qualification milestones in its program to procure 50 percent of the blanket shield blocks required by ITER.
The ITER blanket consists of 440 individual modules covering a surface of 600 m² inside of the vacuum vessel. The plasma-facing surface of the blanket—the first wall—is attached to massive components called shield blocks that provide neutron shielding for the vessel and magnet coil systems. These thick steel blocks, weighing up to four tonnes apiece, interface with many other systems, in particular a large number of diagnostics. For this reason there are a total of 28 major design variants and 150 or more minor design variants. The Chinese and Korean Domestic Agencies are each providing 220 shield blocks.
In December 2017, Chinese suppliers in Guangzhou completed an 18-month program to manufacture a full-scale prototype of shield block SB09A. The next month, a dedicated facility for hot helium leak testing was commissioned in Chengdu—just in time to begin test activities on the SB09A prototype. From 6 to 14 February, hot helium leak tests were carried out according to ITER Organization accepted procedures, and witnessed by ITER Organization representatives. The results met all relevant ITER requirements.
The shield block module SB09A, located in the upper region inside the vacuum vessel, represents probably the most complex type of shield block structure—making it the most challenging to manufacture of all shield blocks to be procured by China. It has the most complex geometry, with several cut-outs to accommodate interfacing systems and diagnostics, and is largely tapered. For this reason it was selected as a full-scale prototype to qualify the manufacturing technologies that will be used in series production.
Chinese manufacturers started on the full-scale prototype in July 2016, progressively accomplishing all of the fabrication steps including machining datum, drilling the deep holes of the cooling channel, side machining, welding of cover plates, and final machining. From nine tonnes of original stainless steel forgings, the final full-scale prototype after machining was 2.8 tonnes. Many tests were performed throughout the fabrication process to verify quality—such as preliminary dimensional examination, non-destructive examination, and hydraulic pressure tests, which all showed acceptable manufacturing results.
The shield blocks, like all the in-vessel components, have to operate under ultra-high vacuum conditions (ten billion times lower than atmospheric pressure). Therefore stringent design, manufacturing and testing provisions have to be planned in order to ensure that the demanding vacuum requirements are met. In this regard, the so-called hot helium leak test represents the definitive demonstration of the fitness for purpose of the component to operate in an ultra-high vacuum environment. This test foresees the cycling of the components up to the operational temperature and pressure in order to be able to detect the tiniest microleaks, which would not be detectable by other means.
During commissioning tests at the dedicated hot helium leak test facility in Chengdu, operators verified that the sensitivity of the helium detector and the background helium leak rate could reach ITER requirements; in both cases the facility performed well.
During two full cycles of testing on the full-scale prototype, results showed that the maximum helium leakage rate was well within ITER requirements. As the first hot helium leak test on a large ITER blanket component, the results provide valuable reference data for the further investigation of the acceptance criteria of ITER blanket components. They also provide an important benchmark for developing hot helium leak test standards for the large vacuum components of future tokamaks.
See the gallery of photos below.

Out WEST | A purple haze on the screens

ma, 26/02/2018 - 15:50


Numbers, graphs and a wobbling purple haze on the monitoring screens—this is what a plasma shot looks like when seen from the control room of the WEST tokamak.
Since its first plasma in December 2016, the former Tore Supra tokamak has logged some 2,500 shots. Upgraded, transformed, equipped with an actively cooled tungsten divertor, and graced with a new name—WEST (Tungsten (W) Environment in Steady-State Tokamak)—the machine is being groomed to act as a test bed for ITER, minimizing industrial and financial risks and obtaining experimental data to prepare for operation.
On 16 February, WEST shot the last plasmas of a campaign that had begun one month earlier with the coupling of the machine's two lower hybrid antennas. By the end of this year, the plasma heating system, including three ion cyclotron resonance heating antennas procured by China, should be fully operational.
WEST is now well advanced on the way to becoming an "ITER-like" machine. Out of the 456 actively cooled plasma-facing units in tungsten that make up the divertor, six (three procured by Japan and three by China) are already in place and six more (procured by Europe) will be installed in the coming months. The full actively cooled tungsten divertor configuration should be ready for operation at the end of 2019.
In the meantime, operators in the control room are "learning to drive." Although several features from the "old" Tore Supra have been preserved, WEST is definitely a new machine with a different magnetic configuration (extra coils have been installed under the divertor) that allows for the production of ITER-like D-shaped plasmas.
Over the past few months, the WEST team has been busy fine-tuning the coils, adjusting the position and power of the first lower hybrid antenna, and monitoring the behaviour of the plasma-facing components. Jérôme Bucalossi, who heads the WEST project at CEA's Institut de Recherche sur la Fusion Magnétique (IRFM), is confident that by the time the tungsten divertor is complete, WEST will have reached the high confinement mode ("H mode") that will be ITER's operational regime.
Although almost routine by now (WEST produces an average of 30 pulses per operating day) the pulsating haze on the screens makes a fascinating sight—deuterium nuclei spinning madly for a few seconds inside a magnetic cage. Not quite fusion yet ... but a foretaste in anticipation of the real thing.
Click here to view a video of a plasma shot in WEST.

Nuclear safety | "A pragmatic and creative approach"

ma, 19/02/2018 - 17:22

Safety is at the core of all nuclear activities. Over the past seven decades—since the first experimental reactor was brought to criticality in 1942—codes, standards, procedures and regulations have been established, along with regulatory bodies and international guidelines to ensure plant safety and the protection of nuclear workers, neighbouring populations and the environment.
Until ITER however, all nuclear activities and installations were founded on fission—the splitting of heavy elements such as uranium. With ITER, a new form of nuclear energy, based on the fusion of light elements, has entered the stage.
ITER is the first fusion device fully categorized as a nuclear installation. Although the physics of fusion and associated risks are radically different from fission, some of the issues ITER has to manage are familiar to nuclear safety experts.
Others—such as the extremely energetic neutrons produced by the fusion reaction or the quantities of tritium present in the installation—are unprecedented.
"Generic" safety studies for ITER began in the mid-1990s, at a time when a site had yet to be chosen to host the installation. Adapted to the present location in France, and in the logic of continuous improvement and refinement, these studies continue to this day ... requiring further exploration, simulation and demonstration.
In compliance with the 2006 ITER Agreement, ITER observes French safety regulations and, like any nuclear installation in France, submits to the stringent controls and inspections, both "notified" and "unscheduled," of the country's regulatory body—the Autorité de sûreté nucléaire (ASN).
The ASN demanded the same approach as for any nuclear installation in France, where it is the responsibility of the nuclear operator (the installation "owner") to define safety objectives and functions, identify risks, and describe means to mitigate and minimize them.
This approach is particular to France: safety regulations here are not "prescriptive," meaning that they don't mechanically correlate an identified risk with a pre-defined protection.
_To_133_Tx_"It's a pragmatic, graduated approach," says Joëlle Elbez-Uzan, who was part of the early 2000 European ITER Site Studies (EISS) and who now heads the ITER Environmental Protection & Nuclear Safety Division. "The French regulations define the objectives, and let the nuclear operator propose the means to meet these objectives. Solutions have to be proportional to what is a stake in terms of safety. It's a creative and adaptive process ..."
"Oversizing" protection is an obvious option when seeking to mitigate risks. But oversizing has consequences not only in terms of cost but also in terms of robustness. "The more massive a protective measure gets, the more complex and the less robust it becomes. By applying a 'just required' approach we minimize costs and achieve better robustness," adds Joëlle.
Such a philosophy is well adapted to a fusion installation whose potential risks cannot be compared to those of a fission installation.
Joëlle remembers that when she moved from fission to fusion the first thing that struck her was the fundamental difference in physics. "What happens in the core of a fusion reactor is intrinsically safe—if parameters cease to be nominal, the reaction simply stops. And of course this is something we had to take advantage of."
Whereas a fission reactor contains more than one hundred tonnes of solid fuel (enriched uranium of mixed uranium-plutonium oxide), there is never more than a few grams of gaseous fuel in the ITER vacuum vessel at any given time. As a direct consequence, the stored energy is minimal.
This and other fusion-specific characteristics have led safety experts to rely as much as possible on "passive solutions" for ITER. The cooling water system is not classified as a "safety function" in a fusion reactor, for instance. It comprises a single loop only, whereas in a fission reactor a second loop must be able to take over from the first in an emergency situation.
Although some of the safety parameters for the ITER design were established by extrapolating from the fission world, safety analysts were confronted with a number of never-before-encountered situations.
Because of its operational needs, ITER will have to manage significant quantities of tritium—a situation Joëlle describes as "completely new for a nuclear installation."
In dealing with tritium [see box], the "lessons learned" approach proved essential. Feedback from CANDU reactors, the Karlsruhe Tritium Laboratory and even the JET (European) and TFTR (US) tokamaks, which handled minute quantities of tritium during experiments in the 1990s, provided a basis to develop R&D tritium handling programs up to prototype scale.
The vacuum vessel also raised specific safety issues, as there was no readily available code applicable to this unique component and the stresses/forces it will be subjected to. Codes applying to fission reactor vessels were adapted to the specific geometry of the ITER vessel and to the conditions it will face (for instance the impact and subsequent irradiation of the inner walls by energetic neutrons, or unique stresses and movements—such as vertical displacement events).
"ITER operation and its progressive ramp-up will provide a unique opportunity to confirm our hypotheses, validate the safety methodology and refine the regulatory framework and international guidelines for fusion installations," says Joëlle.
For decades, nuclear safety was not central to fusion research, as only two experiments—and only very briefly—had ever employed nuclear fuel in fusion operations.
Now, with ITER, everything has changed. "Ensuring the safety of an installation goes way beyond establishing codes and procedures," says Joëlle. "It is about embedding a 'safety attitude' into each and every action we take. What is at stake here is nothing less than the project's success."

Gravity supports | First production unit in China

ma, 12/02/2018 - 18:03


Bolted in a perfect circle to the pedestal ring of the cryostat base, 18 gravity supports will brace the curved outer edge of each toroidal field coil. These unobtrusive elements are in fact a marvel of engineering, designed to support 10,000 tonnes of dead weight and yet have the flexibility to withstand the displacement of the coils during cooldown and operation.
In China, the first production unit stands 2.65 metres tall on the shop floor at the company HTXL, a sub-supplier of the Center for Fusion Science of the Southwestern Institute of Physics (SWIP). Built from 20 tonnes of ITER-grade 316LN stainless steel, the assembly resembles a Roman column, with 21 vertical plates inserted into pedestals at top and bottom and helium cooling pipes in a curled arrangement welded to each plate near the top.
ITER's 18 interlinked toroidal field coils provide the superstructure that anchors the entire superconducting magnet system, including six poloidal field coils, the central solenoid and an array of correction coils. From their position at the bottom of the machine, then, the toroidal field coil gravity supports will be confronted with about 10,000 tonnes of magnet dead weight—or 580 tonnes per support.
At the same time the gravity supports must withstand the electromagnetic forces of operation, seismic loads (if they occur), and thermal gradient deformation, which causes the top of the support to shrink toward the centre of the machine (~32 mm) while the bottom remains stable.
This push and pull represented a severe design challenge for engineers, requiring many years of prototyping, load analyses and testing. Working from an ITER Organization design, engineers in China worked closed under the coordination of the ITER Magnet Division, the Chinese Domestic Agency and SWIP. In 2013, an engineering test platform was built at SWIP to apply the loads—and load combinations—that are expected during operation at ITER on these qualification mockups.
The solution is a mix of flexibility and rigidity—a sandwich of 21 flexible plates, 30 mm thick, divided by spacers that are pre-assembled and clamped together at bottom and top with pre-stressing bars and tie rods; these bars and rods are pre-tensioned with stud tensioners. Active cooling provided at two-thirds of the height of the assembly smooths the transition between the toroidal field magnets at 4 K on top and the room temperature at the base of the structure.
"The gravity support will have to be able to resist the toroidal and vertical motion and related forces of the toroidal field coils during the Tokamak operation, but also allow their radial motion during cooldown and warmup," explains Cornelis Beemsterboer, structural engineer for the Magnets Division and technical responsible officer for the different magnet supports. "At the same time each vertical plate is designed to support 27 tonnes of the overall gravity load. Analysis has shown that the design meets all requirements for both room and operating temperature conditions."
The first production module in China has performed well in factory acceptance tests, including a thermal shock test, helium leak tests on the active cooling pipes, and pressure tests. Still to come is the final assessments on the final applied pre-loading of the bolts. "The gravity supports are impossible to replace and we need to be sure that the bolts will keep the vertical plates together for the full duration of ITER operation," emphasizes Beemsterboer.
The full set of gravity supports is expected on site in mid-2019 for installation in the machine on the pedestal ring ahead of the toroidal field magnets. China is also manufacturing other magnet supports for the poloidal field and correction coils—in all, more than 400 tonnes of equipment.

Construction management | Bringing all the strands together

ma, 05/02/2018 - 16:47

With a project as complex as the construction of the ITER machine and plant it is easy to lose sight of the big picture over the many intricate details. Angie Jones from the MOMENTUM consortium makes sure that this doesn't happen. She fiercely defends the need to look at the construction project with the eye of an eagle.
The MOMENTUM consortium joined ITER's quest for fusion energy in the summer of 2016 as Construction Manager-as-Agent (CMA). Its main task, according to Project Director Angie Jones, is to bring all the strands together and make sure that the ITER machine and plant are assembled and installed on time, safely and in compliance with budget.
"Our mission is to manage, coordinate, and supervise assembly and installation activities on behalf of the ITER Organization. As CMA, we share industry best practice for large construction projects, and adapt it for implementation at ITER." 
MOMENTUM is led by Wood (UK, formerly Amec Foster Wheeler) in partnership with Assystem (France) and KEPCO Engineering and Construction (Korea).
Based on already completed scientific and engineering work, MOMENTUM puts together controllable construction work packages for the contractors, who in turn break them down into installation work packages. "These detailed packages allow us to monitor and measure the work as the construction manager," says Jones.
Jones and her 70 colleagues are fully focused on their mission as ITER's construction management partner. They deliver processes and procedures for all phases: construction preparation, project management, contract management, interface management, site coordination, construction supervision and completion.
The biggest part of her job is integration—bringing all the elements together and identifying gaps. This means raising the focus from specific engineering and manufacturing tasks to the long-term goal--achieving First Plasma in 2025.
It all comes down to perspective, according to Jones. "Chickens keep pecking on the ground, never looking up to see what's going on elsewhere. But the eagle can see everything from a great height," says Jones. "We must shift to a project delivery culture in which construction needs drive the engineering and procurement priorities.
_To_131_Tx_She calls it the "right-to-left approach," where the end goal—completing the installation—defines the construction project schedule in all its phases.  
Jones named her high-level strategy meeting with the MOMENTUM leadership team the "eagle meeting." This is where the team works together to identify transversal challenges and to bring solutions to the ITER Organization. 
As might be expected, it took some time for the CMA partner to find its place among pre-existing ways of working. The political nature of ITER was also a new challenge for Jones—requiring the team to go beyond industrial construction expertise and be diplomats as well. And in front of engineers, scientists and project administrators who, for some, had already spent a decade on this project, it was necessary for the MOMENTUM team to persuade others that it shared the same commitment to making ITER a reality. "Today, I feel more of a partner than ever before," she says. 
Jones has begun to see the fruit of her persistent efforts. The MOMENTUM delivery organization has evolved along with the ITER Organization to prepare for the phase ahead, and it is now fully aligned with clear lines of authority for quick decision making to deliver on the construction objectives. "It's been worth it to work so hard for these synergies over the last 17 months," she concludes.

Sixty years ago | How the "Zeta fiasco" pulled fusion out of secrecy

ma, 29/01/2018 - 21:34



In those days—the late 1950s—pinch machines ruled the world of fusion. Although tokamaks were already under development in the Soviet Union, it would be more than a decade before they became the dominant form of fusion device.
In the West, scientists were founding their expectations on machines such as the Perhapstron in the US or Zeta (Zero Energy Thermonuclear Assembly) in the United-Kingdom—machines that used strong magnetic fields to compress ("pinch") the plasma and, hopefully, produce fusion reactions.
Fusion research at the time was mostly national, classified and competitive. Although scientists throughout the world were eager to engage in international collaboration (as Igor Kurchatov's 1956 visit to Harwell, the Holy of Holies of Britain's nuclear research, had demonstrated), governments were reticent to open their labs and facilities.
The "Zeta fiasco," as it came to be known, was to throw into stark relief the need to pull fusion research out of secrecy.
The Zeta fiasco began with a triumphant claim and ended in utter embarrassment. What happened sixty years ago this week, at the end of January 1958, was a blow to fusion research and yet at the same time a first step towards its refoundation.
Zeta entered operation in July 1957. Its first results were highly encouraging: in previous machines plasmas had rarely lasted more than a few microseconds; in Zeta they passed the millisecond mark—a full three orders of magnitude jump and a remarkable achievement.
By August, the machine's operators had switched from hydrogen to deuterium, increasing current to 200,000 amps. Suddenly, on the evening of the 30th—bingo!  Zillions of neutrons began flooding out of the five-million-degree plasma.
Zeta's experiments were still secret. But the news was too good to be contained and leaks began appearing in the press. In November, a spokesman from the United Kingdom Atomic Energy Authority (UKAEA) hinted that "fusion energy [had] been achieved" and, by January, the UK government decided that it was time for a full-blown press conference.
Nobel Prize winner John Cockcroft, who headed British nuclear research and was responsible for the Zeta program, opened the conference with a cautiously worded statement: "Neutrons have been observed in about the numbers to be expected if thermonuclear reactions were proceeding," he said. However, "in no case have the neutrons been definitely proved to be due to the random motion of the deuterium associated with a temperature on the order of five million degrees ..."
Was it indeed thermonuclear fusion, or not? Had Zeta harnessed the power of the Sun? Had the UK beaten the rest of the world in the quest for unlimited energy? At Harwell, 400 howling reporters demanded to know for sure.
Pressed with questions Cockcroft eventually said that he was "90 percent certain" that Zeta's neutrons came from fusion reactions. The media needed nothing more—and the presses started rolling.
"A Sun of our own!" trumpeted the London Daily Sketch the following morning. "Unlimited fuel for millions of years," echoed the Daily Mail. Cockcroft presented what the UK scientists had achieved as "a greater achievement than Sputnik," (the artificial satellite that the USSR had launched a few months before). The world was enthralled. For the French daily Le Monde Zeta—dubbed "the magic tube"—marked the "first step in harnessing thermonuclear energy."
The press conference at Harwell had been timed to coincide with the publication of a Nature article, which also included results (although not as spectacular as Zeta's) from the Los Alamos Perhapstron and Columbus machines. Included in the coverage, but largely unnoticed by the general media, was a note by Lyman Spitzer, the father of fusion research in the US.
Spitzer, an astrophysicist who had invented the concept of magnetic confinement and had built the first fusion machine in 1951, was highly skeptical of Zeta's results. There was a contradiction, he wrote, between the predictions of theory and the numbers reported, that suggested that "some unknown mechanism would appear to be involved." Fusion could not happen at 5 million degrees.
Others, like Lev Artsimovitch in Moscow, were more brutal in their refutation. As increasingly detailed analyses sowed more and more doubt, the Zeta triumph turned into an embarrassment.
Less than four months after the January 1958 news conference, "the H-men from Harwell"—as newspapers called the Zeta team—had to issue a corrective news release, acknowledging that the neutrons they had observed had nothing to do with the fusion of deuterium nuclei, but rather owed their existence to complex phenomena originating in plasma instabilities.
The Zeta affair dealt a severe blow to the credibility of fusion research; too many expectations and too much excitement had resulted in a huge disappointment. But there were precious lessons to be learned. One of the most important was that fusion research was doomed if it was to be pursued in the secrecy of national laboratories. Peer review, the sharing of information and doubts, and a common analysis of failures or potential successes were essential not only to the credibility of fusion research but also to its success.
One month later in Geneva, the "Second United Nations International Conference on the Peaceful Uses of Atomic Energy" (Atoms for Peace) opened the door to such collaboration. And ten years later at the Novosibirsk fusion conference, when Lev Artsimovitch presented the exceptional results obtained in the soviet T-3 and TM-3 tokamaks (a 20-millisecond plasma at a temperature of 10 million degrees) it was a British team that was invited to do the checking and that eventually confirmed the breakthrough.
As for Zeta—for some time, the largest fusion machine in operation—it went on to have a very productive career in plasma studies. But its species belonged to an evolutionary dead end. By the late 1960s the time of the tokamak had come.

Tokamak cooling system | Final design achieved

ma, 22/01/2018 - 17:14


To remove the heat from the components closest to the plasma, the tokamak cooling water system will rely on over 36 kilometres of nuclear-grade piping and fittings as well as a large number supports, valves, pumps, heat exchangers and tanks—all integrated into the limited space of the Tokamak Complex. The way has now been cleared for the fabrication and assembly of this complex system, after a final design review was held successfully held in November for the elements that need to be in place by First Plasma.   At your home, water is delivered to the tap at a flow rate of 0.1 m³/ second, a velocity of 1 metre/ second, and at a pressure of around 3.5 bars. 
In contrast, the water will surge through the pipes of ITER's tokamak cooling water system (TCWS) at a flow rate of 5 m³/second, a velocity of 10 metres/second, and a pressure of 14 bars (up to 50 bars at the pump outlet).
The TCWS is a one-of-a-kind nuclear system that is similar in complexity and scope to the cooling systems in a commercial nuclear power plant but—because of the unique design architecture of the machine—is much larger in size. The cooling system will have the capacity to remove up to a gigawatt of heat from the Tokamak. (For perspective, a gigawatt—one billion watts—provides enough power for the needs of a small city.) The TCWS will also provide capabilities that are not used in power plants, such as baking and drying in-vessel components, leak detection, and tokamak maintenance. The system will interface with the secondary cooling system, provided by India, as well as with other ITER plant systems.
System layout and design have been challenging for a number of reasons, including limited space, a large number of interfacing systems, and the fact that—as a safety-important system for the containment of radioactive water—TCWS components must comply with French nuclear pressure equipment directives. All 36 kilometres (1,200 tonnes) of piping and fittings, along with 12,000 structural supports, 3,000 valves, and 100 pieces of equipment will all need to be installed in tight spaces inside the Tokamak Complex.
An innovative arrangement was founded in 2013 to ensure that the procurement and integration could be carried out in the most efficient and cost-effective manner possible. While the global responsibility for the TCWS remains with the US Domestic Agency, part of the scope (including final design, and the procurement of piping) was transferred to a US-funded team based at ITER Organization headquarters, which is carrying out these activities on behalf of US ITER.
Moustafa Moteleb heads the Tokamak Cooling Water System Division at ITER. "With a team of fewer than 30 people at ITER Headquarters, we have been able to produce high-quality work ... improving the initial design of the system, reducing cost, and bringing the first-round of components to the required level of maturity. We have been using Earned Value Management from the start to monitor our own performance against the schedule and to track cost savings."
The final design solution proposed by the ITER TCWS team addresses the important issue of the protecting electronics inside the Tokamak from the effect of activated cooling water—an issue that had been flagged at an earlier design stage. Through the use of specialized expertise and precise modelling tools, the team was able to propose a solution that meets all project requirements on safety.
"The design incorporates a configuration that was approved by Director-General Bigot in June 2015, which significantly improved the investment protection of electronics," says Moustafa. "For many areas, the strategy focused on additional shielding, relocation, and/or the qualification of electronics to withstand the harsh environment. While planning for in-service inspection of TCWS components remains a challenge due to the congestion of equipment, worker exposure rates inside the Tokamak are well below acceptable norms in fission plants."
Now the design of the TCWS piping and components has been confirmed—first at a design readiness review held at US ITER in September, followed by two design integration reviews at ITER in October, and finally in a three-day final review in November attended by approximately 40 experts from the ITER Organization, US ITER, and the industry.
The manufacturing of critical components like heat exchangers and pressurizers, expected on site from 2021 on, can begin.
"It is very exciting to be entering this new phase, with a major part of the design behind us and manufacturing contracts planned in 2018," says Moustafa. "The TCWS team at the ITER Organization dedicates this successful final design review for first-phase components to Responsible Officers Jan Berry and Brad Nelson, who have recently retired from US ITER. They have been involved since the system conceptual design, and without their strong contributions over the years we could not be where we are today."
As for the TCWS team at ITER, they have their work set out for them with the design of second-phase components as well as pre-fabrication engineering studies to reduce the amount of pipe welding carried out on site. Pipe installation will begin in late 2019 inside the Tokamak.

Vacuum vessel | First segment completed in Korea

ma, 15/01/2018 - 16:26

The technically challenging fabrication of the ITER vacuum vessel is progressing in Korea, where Hyundai Heavy Industries has completed the first poloidal segment for sector #6. From manufacturing design and material procurement to cutting, forming, machining, welding, non-destructive examination, and final dimensional measurements—the industrial effort to forge the building blocks for ITER's double-walled steel plasma chamber is one of the most complex of the ITER Project.  

On 11 December 2017, Hyundai Heavy Industries (HHI) completed dimensional checks on the inboard (poloidal) segment of vacuum vessel sector #6—the first-completed segment of the vacuum vessel construction program.
All inspection and test results demonstrated that safety requirements are fully satisfied and that the tolerances of the completed segment, measured at ± 4.0 millimetres, are well within the ITER requirement of ± 10.0 millimetres.
With this successful realization the ITER Project celebrates both an industrial and a programmatic milestone, as the first production unit is the result of a lengthy program to establish, qualify and implement manufacturing and test procedures for a one-of-a-kind component, and also respects the calendar of ITER Council milestones that has been established to track project progress.
"It was very challenging to reach this level of technical maturity and achievement," says Wooho Chung, the technical responsible officer for the vacuum vessel at ITER Korea. "Because the vacuum vessel will act as the first safety confinement barrier, all of our procedures and activities had to be qualified and approved by the Agreed Notified Body (a company authorized by the French Nuclear Regulator to assess conformity of components in the pressure equipment category, ESPN)."
Since signing a Procurement Arrangement with the ITER Organization in November 2008, teams in Korea have developed—and received authorization for—detailed manufacturing procedures for forming, welding, and non-destructive examination (especially ultra-sonic examination and remote visual examination).
"After successfully completing the manufacture of the first poloidal segment, we will now be able to move more smoothly on the basis of confirmed manufacturing processes and procedures," states Chung. "We know that we have still remaining challenges—such as the completion of the outboard segments for sector #6 as well as factory acceptance tests—but we are confident that we can achieve these steps this year."
The ITER doughnut-shaped vacuum vessel will be welded in the Tokamak Pit at ITER from nine steel sectors. Each 40° vacuum vessel sector is a double walled steel component weighing 500 tonnes and measuring 12 metre in height and 7 metres in width, with multiple port openings and in-wall shielding contained within its walls in the form of modular blocks.
Key to the good progress on the challenging procurement of the vacuum vessel, according to Chung, is very constructive and cooperative collaboration between the members of the Vacuum Vessel Project Team and industries.
Fabrication responsibility is shared by four ITER Domestic Agencies—Europe (five main vessel sectors); Korea (four main vessel sectors plus equatorial and lower ports); Russia (upper ports); and India (in-wall shielding)—plus the ITER Organization and a large number of industrial contractors. The Vacuum Vessel Project Team was created to make one team of these participants for promoting synergies, the sharing of experience, and the rapid resolution of fabrication issues.
Collaboration meetings among participants of the Vacuum Vessel Project Team are organized regularly; (please see the report of the latest meeting on the European Domestic Agency website). All vacuum vessel components are currently being manufactured with good quality assurance and quality control at various industrial locations worldwide.
With the results achieved for the first segment, Hyundai Heavy Industries has identified how tolerance control can be improved for the next segments through experience. The results are also undergoing detailed, integrated analysis at the ITER Organization Design & Construction Integration Division, taking into account all interfacing systems.
The Korean Domestic Agency plans to complete the first sector (#6) and start the mass production of all remaining sectors/ports in 2018.

First toroidal field coil structure | Submillimetric tolerances achieved

ma, 08/01/2018 - 18:05


In major news for the ITER superconducting magnet program, the first toroidal field coil case has passed all fitting tests. The two sides of the huge component—as tall as a four-storey building and machined from 20-centimetre-thick steel—were matched within gap tolerances of 0.25 mm to 0.75 mm, an accuracy of more than one order of magnitude in relation to conventional high-precision welded structures of comparable size.
On 18 and 19 December 2017, precision laser trackers were used to measure the alignment of inboard and outboard legs of the first toroidal field coil case as well as the precise position and orientation of the heavy steel segments. The measurement results were sent electronically to the ITER Organization for detailed analysis, where it was confirmed that giant steel structures matched at all welding grooves with gaps ranging from 0.25 mm to 0.75 mm, fully respecting specified tolerances.
"This is a technological achievement of the highest order," declared Eisuke Tada, ITER Deputy Director-General, as he attended a ceremony on 26 December at the testing site. "A component that is 16 metres in height, weighing 190 tonnes, has been successfully machined to within sub-millimetre tolerances by multiple manufacturers. The international nature of this achievement makes it all the more remarkable."
The toroidal field coils cases provide protective covers for the toroidal field winding packs, the superconducting core of the magnets wound from approximately 5.5 kilometres of niobium-tin conductor. The thick steel cases also have a structural role to play, anchoring the poloidal field coils, the central solenoid and the correction coils and withstanding huge electromagnetic loads inside the machine.
Japan* is responsible for producing 19 toroidal field coil structures (for ITER's 18 toroidal field coils plus one spare). Nine of the structures will encase the toroidal field coil winding packs produced in Japan, while ten—including this first unit—will be shipped to Italy for the insertion of winding packs produced in Europe.
Toroidal field cases are D-shaped components, with the inboard leg corresponding to the straight-backed portion of the letter and the outboard leg corresponding to the rounded portion.
The inboard leg of the first coil case was manufactured at Mitsubishi Heavy Industries, Ltd. (Kobe, Japan). During fitting tests in July 2017 the two sections of the inboard leg—the U-shaped sub-assembly ("AU") that will contain the superconducting core plus a cover plate ("AP")—were successfully paired with gap tolerances of 0.25 mm to 0.75 along the entire 14-metre-long weld groove.
The outboard leg was contracted by Japan to Hyundai Heavy Industries in Ulsan, Korea. The ultimate test was then to verify that structures manufactured in two locations following stringent ITER Organization specifications would fit together perfectly. "Ultimately, the story of the toroidal field coil cases is the occasion to showcase the spirit that underlies the ITER Project in its entirety—the "One-ITER" spirit of teamwork that unites us around one design, one schedule and one mission," stressed Deputy Director-General Tada.
At Hyundai, the outboard leg sub-assemblies ("BU" and "BP") were first fitted together to verify manufacturing precision. Then, on 18 and 19 December the principal segments of the coil case ("AU," manufactured in Japan and shipped to Korea, and "BU" manufactured in Korea) were positioned and measured. (Please see the photo gallery below for further explanations.)
The required tolerances of bevels at the welding grooves were respected across the board at less than 1 millimetre—with gap variations ranging from 0.25 mm to 0.75 mm. Witnesses on hand during the fitting tests included representatives of the ITER Organization, the Japanese and Korean Domestic Agencies, the European Domestic Agency (which will be receiving the component), and manufacturers Mitsubishi Heavy Industries and Hyundai Heavy Industries.
The successful fitting trials of the first toroidal field coil case demonstrates that the final assembly—the insertion of the superconducting winding pack followed by closure welding—can be achieved within the tight tolerances required. This is excellent news, as work proceeds on the fabrication and precision machining of elements for the 18 other cases.
The first case is now on its way to SIMIC (Italy), where the first European winding pack has been delivered for insertion.
*QST—Japan's National Institutes for Quantum and Radiological Science and Technology—is responsible for the procurement of all components allocated to Japan by the ITER Organization.