Vacuum vessel manufacturing | Last phase for Korean sector #6

ITER - ma, 16/09/2019 - 22:22

On 7 September, contractors from Hyundai Heavy Industries in Ulsan, South Korea, initiated the final fabrication activities for vacuum vessel sector #6: the assembly of four completed segments into the final D-shaped component, plus the installation of upper and lower port stub extensions. At the end of this first-of-a-kind undertaking, the first 440-tonne ITER vacuum vessel sector will be ready for shipment to France.
On the shop floor in Ulsan, a curtained-off clean space has been created around the assembly platform that supports the building blocks for ITER first vacuum vessel sector: four poloidal segments ranging in weight from 35 to 125 tonnes. When assembled and welded, the final D-shaped component will measure 13.8 metres in height, 6.6 metres in width, and 7.8 metres in length.
All nine sectors needed to form ITER's toroidal plasma chamber are currently in fabrication in the factories of two ITER Members—Korea (for four sectors) and Europe (for five sectors). As the first sector programmed for arrival at ITER, sector #6 has the honour, and the challenge, of "proceeding first" through every fabrication stage. The lessons learned on sector #6 will facilitate the way for all other sectors.
"We are definitely breaking new ground," says project director Kyungho Park at Hyundai. "The ITER vacuum vessel is an absolutely unique component with very complex geometry, hundreds of interfaces to other components, and very strict nuclear safety compliance requirements. Each step of the process has been challenging, from manufacturing qualification and procedures, machining, and welding, to non-destructive examination and tolerances. We are learning and problem solving as we go, and we are making sure that the knowledge and experience we acquire benefits the other sectors."
The vacuum vessel is a double-walled component, with 34 to 75 cm of space between the inner and outer steel shells. "Space" is rather a misnomer, however, because the interspace will be nearly completely filled with in-wall shielding blocks (packs of borated stainless steel plates), cooling water channels, and steel supporting ribs. The interspace of Sector 6, for example, contains 850 blocks of in-wall shielding and 850 supporting ribs. Inside the vessel, 172 flexible support housings are welded for the attachment of the blanket shield blocks while outside, two port stub extensions are attached to the sector's upper and lower port stubs through splice plates.
All of this complexity makes the final assembly stage quite challenging. Activities will be carried out in the following order: TIG welding of the inner shell (full penetration welds), followed by welding of structural ribs (so-called "t-ribs") and flexible support housings, keys, the installation of in-wall shielding, and—in the final activity to complete the segments—TIG welding of the outer shell (full penetration welds). One hundred percent volumetric inspection is required as a nuclear safety requirement.
Taking all assembly activities on sector #6 into account, the Hyundai team estimates the total length of full penetration welds at 1,380 metres.
In order to increase confidence that the stringent tolerance requirements for the final geometry can be achieved, the Hyundai team—in collaboration with the ITER Organization and the Vacuum Vessel Project Team¹—performed  a "virtual fitting" this summer in which all available dimensional measurements of the completed poloidal segments were processed with specialized software (Space Analyzer)  and matched virtually. "This process was key," explains Chang Ho Choi, who leads the ITER Vessel Division. "It allows the demanding tolerances to be achieved by identifying the areas that require reverse engineering to compensate welding deformation and shrinkage."
From 7 to 15 September, the team completd the inner shell welding on all poloidal segments. Six Project Team inspectors, two Agreed Notified Body² inspectors, and the Hyundai quality departments are performing continuous quality control—day and night—as the work advances. A total of 45,000 inspection points are planned and 500 manufacturing documents, including reports, have been developed.
¹ The Vacuum Vessel Project Team reunites staff from the European, Korean, Indian and Russian Domestic Agencies with staff from the ITER Organization in regular meetings to improve the overall efficiency of vacuum vessel procurement execution.
² An Agreed Notified Body (ANB) is a private company authorized by the French Nuclear Regulator ASN to assess the conformity of components in the pressure equipment category (ESPN).

Vacuum technology | Record-breaking sealing performance

ITER - ma, 09/09/2019 - 19:45

The ITER vacuum vessel, its ports and port extensions, and port plugs all provide the vacuum boundary and first safety confinement barrier of the ITER machine. In this context, the leak tightness of the large metallic vacuum seals around the ports is critical. In order to leave nothing to chance, the ITER Organization is testing vacuum sealing on a real-size test rig. Recent test results were excellent.
The high-performance vacuum sealing of the ITER vacuum vessel's 50+ large ports is a "first of a kind" challenge due to the rectangular shape of the ports, their large size, and the need to remove and replace port plugs (large, stainless-steel components that "plug" the openings and also play a role as structural host to systems such as diagnostics).
Eamonn Quinn is responsible officer for the Large Seal Test Rig (LSTR) program. "To leave nothing to chance, a full-size replica of the largest equatorial ports was designed, manufactured and installed on site with the purpose of testing the vacuum sealing of what will be the largest ports ever built on a tokamak."
The equipment was installed in the European Poloidal Field Coils Winding Facility on site, where the "clean" conditions were ideal for the tests, and space was made available courtesy of the European Domestic Agency.
The test rig is of an impressive size (nearly 5 metres in height and as many in length) and it weighs around 19 tonnes. It gives a preview of how the ITER machine will look when seen through the equatorial ports cells, as they are starting now to take shape on the construction site. It was built and installed by Indian high-tech company Vacuum Techniques.
There was much preparation, along with repeated inspections and some anxiety as the first large, double all-metallic seal was positioned on the flange. The flanges were brought together with the repeated tightening of 100 bolts, and after a number of hours of muscle flexing the seals were compressed.
Then came the leak tests: first a quick one—no leak found. Then the thorough one, during which the leak rate across each seal was <10-11 Pa.m3.s-1 —a world-record-breaking sealing performance for the largest non-circular all metal vacuum seal! (In lay terms, that means that no more than the volume of air contained in a glass would leak over a period of ... 100 million years.)
The performance on this first test was well beyond the requirements, beyond all expectation. In short, a world record breaker!  
The metal seals were made by Technetics (US). Company Vice President Bob Panza had time to comment: "I heard the wonderful news yesterday. This is a result of good collaboration between our companies and we should all be proud of the results."
The seal test rig not only allows the largest demountable rectangular seals to be tested, but also enables us to prepare installation techniques which will be critical to achieving the required vacuum quality.
Since the first test, the validation program has successfully continued with heating the flanges to 100 °C and then on to 240 °C and still the sealing performance has been maintained.

Testing of JT-60SA’s Power Supplies kicks off

F4E News - wo, 04/09/2019 - 02:00
Testing verifies that the power supply equipment that F4E has delivered and the power supply components provided by QST work well together.

Critical steps in manufacturing the European Vacuum Vessel sectors reached

F4E News - ma, 02/09/2019 - 02:00
Critical steps in the manufacturing the five European Vacuum Vessel sectors have been reached – three major tasks have been completed.

Cryoplant installation completed for ITER Neutral Beam Test Facility

F4E News - do, 08/08/2019 - 02:00
F4E and Air Liquide bring cooling power to MITICA experiment.

Europe and Japan celebrate major milestone in validating LIPAc

F4E News - ma, 05/08/2019 - 02:00
Components of the world’s highest beam perveance accelerator pass tests.

Assembly | A colossal task made manageable

ITER - ma, 29/07/2019 - 17:25

For the execution of work during the next project phase—machine and plant assembly up to First Plasma—the ITER Organization has chosen a contractual approach that emphasizes manageably sized work packages with strong risk management. Nine major assembly and installation contracts are foreseen.
Starting in March 2020 with the first major lift operation—the delivery of the cryostat base to the Tokamak Pit—and ending with the closure of the cryostat lid, the first phase of ITER assembly covers the construction of the core machine and the installation of plant systems needed for First Plasma.
While the ITER Organization is responsible for the surveillance of all construction activities and final compliance with requirements, including nuclear safety requirements in France, the work will be carried out by contractors selected for their industrial know-how, experience, resources, skills and proven track record.
"The relationship between the oversight body—the ITER Organization, and its Construction Management-as-Agent MOMENTUM—and the executors (contractors) is of primordial importance," says Christophe Dorschner, of the Procurement & Contracts Division. "All together, we will be carrying out what is probably the most difficult sequences of assembly and installation works ever attempted in a first-of-a-kind construction project, and we need to do so in full respect of safety, specification, schedule and cost."
The ITER Tokamak is a one-of-a-kind machine, with 15 major sub-systems and as many as 300 very heavy, very large components. The size and weight of the major components, the precise assembly tolerances, the specialized tooling required, the diversity of manufacturers, the tight schedule, the multiple contractors ... all combine to make ITER an engineering and logistics challenge of enormous proportions. "As a first-of-a-kind device, there are areas for which no prior industrial knowledge exists," says Katsumi Okayama, acting head of the Construction Department. "The ITER Organization will be providing input to inform the works in these cases based on R&D, trials and studies."
In developing its strategy for the assembly of the ITER machine and plant, the ITER Organization began by looking carefully at other large construction projects and benchmarking best practices. This groundwork led to the development of a number of core principles for the tendering and contract phases:
  • Strive for cost and schedule control and flexibility through manageable lots;
  • Minimize interference and interfaces between the different contractual scopes;
  • Secure timely work execution by foreseeing temporary backup;
  • Benefit from industry knowledge and know-how wherever possible;
  • Allow industry to propose methods or processes within well-defined boundaries to accelerate or optimize work.
_To_160_Tx_For the purpose of tendering, assembly and installation work on the ITER construction platform has been organized in three zones—the Tokamak Complex (except the machine); the Tokamak machine (Tokamak Pit, Assembly Hall and Cleaning Building); and the balance of plant (all plant and auxiliary buildings; see the colour coding in the diagram below.) Each zone is as physically isolated as possible, with its own access paths and laydown locations in order to minimize interference.

Within these zones, work will be executed under nine major assembly and installation contracts.

"We have chosen to divide the assembly scope into manageable work packages with time phasing and clear responsibility for performance in order to permit better schedule and cost control throughout the lifetime of the contracts," says Katsumi. "This approach will give us the flexibility we need to work with uncertainty—either in the effective handover dates of certain work zones, the availability of tooling, or the risk that some components may be delayed or require adjustment on arrival."

Time phasing means that work will be carried out based on construction work packages that are released by the ITER Organization in achievable—and trackable—batches. In some cases, contractors will be involved in the engineering development of the work packages to provide early input on construction optimization and methodology.

For the most complex and time-sensitive areas—the Tokamak machine and the Tokamak Complex—the choice has been made to preserve peer competition by splitting the works in these areas between at least two contractors. It also protects the ITER Organization in the case of contract default, as one contractor can take over in a relatively short amount of time from the other.

Contracts are awarded through competitive call for tender. First, the ITER Organization invites companies from the ITER Members to express interest through the "Call for Nomination" process. This stage is followed by a pre-selection of candidate tenderers (the "Pre-Qualification Application"), and finally the tender invitation is effectively issued ("Call for Tender"). (See more about the ITER procurement process here.)

The global tendering phase for the assembly and installation contracts is now drawing to a close. All Balance of Plant contracts have been issued; the two Tokamak Assembly (TAC) contracts have been awarded (but not yet signed); and the two Tokamak Complex (TCC) tenders are under evaluation.

The ITER Newsline will have a full report on contract awards in September.

Electrifying success for MITICA High Voltage tests

F4E News - wo, 24/07/2019 - 02:00
The moment of truth for European and Japanese equipment at ITER Neutral Beam Test Facility.

A "magic moment" | Cryostat 60% complete

ITER - di, 23/07/2019 - 20:23

When a seafaring vessel is launched, naval tradition requires that a bottle be broken on its hull to invite good luck. Although the ITER cryostat will never take to the sea, it is indeed a vessel—and a most spectacular one at that.

In the Cryostat Workshop, where the India-procured component is assembled and welded, ITER Director-General Bernard Bigot, India's Ambassador to France Vinay Mohan Kwatra, and the former chairman of the Atomic Energy Commission of India, Anil Kakodkar, symbolically smashed a bottle of French champagne on a large chunk of steel representing the ITER cryostat.
The ceremony marked an important milestone in the fabrication of this strategic component: two sections—the base and lower cylinder—are now completed and fully accepted by the ITER Organization, the upper cylinder is being assembled and aligned prior to welding, and half a world away, in the manufacturer's facility, the last segment of the "top lid" is being finalized.
The ITER cryostat is essential to the ITER machine, providing structural support and also acting as a thermos to insulate the Tokamak's magnetic system, at cryogenic temperature, from the warmth of the outside environment.
It is the largest vacuum vessel ever built—30 metres high, 30 metres in diameter, for a pump volume of 8,500 cubic metres. It is also a highly complex structure which must remain absolutely leak tight despite hundreds of "penetrations" that give passage to thousands of feedthroughs and lines for cryogenics, water, electrical power, diagnostics systems, and more.
In his address to the assembled guests, ITER Director-General Bernard Bigot retraced the "formidable technological, industrial and human venture" that the manufacturing of such a unique object represents. "Designing, manufacturing, delivering, assembling and welding this one-of-a kind component has proved a huge challenge for everyone involved."
And everyone involved was there, either in person or through video conference from India: the ITER cryostat team; representatives of ITER India, which is responsible for the procurement of the cryostat; industrial giant Larsen & Toubro Ltd, in charge of forging and machining the elements of the cryostat at its Hazira facility and assembling them on site; and finally the German company MAN Energy Solutions, subcontractor to Larsen & Toubro for on-site welding.
The fabrication of the ITER cryostat, said Vinay Mohan Kwatra, Indian Ambassador to France, represents "a major achievement for Indian manufacturing—whose capabilities are not always acknowledged as they should be." The Ambassador also stressed the unique nature of ITER, a project that is "not for the benefit of one partner or one country, but for the whole of humankind."
For Ujjwal Baruah, who recently succeeded Shishir Deshpande as Head of ITER India, the ceremony was "a magic moment," the culmination of a "long march" which began in 2012 with the signature of the Cryostat Procurement Arrangement with the ITER Organization.
"Through the innumerable challenges we have faced in the manufacturing of the ITER cryostat, we have learned and grown at every step," said Larsen & Toubro Heavy Engineering Joint General Manager Praveen Bhatt, speaking on behalf of the company's Senior Vice-President Anil Parab.
This "learning process" was also stressed by Rolf Bank, MAN Energy Solutions Head of Site for Deggendorf. The assembly and welding of the cryostat, he said, has made his company take "big steps forward in a whole new area of expertise."
In his opening address, ITER Director-General Bernard Bigot had resituated the fabrication of the cryostat in the broader picture of the ITER Project, which he characterized as "men and women working to the best of their ability in different parts of the world to achieve an utterly ambitious and difficult task—one that is essential for the future of our civilization."
Anil Kakodkar's keynote speech developed along the same lines. For the "father" of the Indian nuclear program, ITER "is our hope for the energy freedom of the world at large and for the development of the large part of humanity that is still undeveloped." The massive international effort that ITER represents is also "the new paradigm that humanity is desperately looking for."
One of the most respected scientific and moral figures in his country, the former chairman of the Indian Atomic Energy Commission and former Secretary to the Indian Government hailed "the stupendous task in which you are engaged." But as he touched on climate change, he also warned: "Fusion must be available before the world reaches the cliff's edge."
For more information about the ITER cryostat, see this page on the ITER website.

F4E signs Diagnostics Engineering Services contract

F4E News - vr, 19/07/2019 - 02:00
The engineering company AVS will assess F4E's on-going Diagnostics design works in terms of manufacturing feasibility, cost and risks.

Space propulsion | Have fusion, will travel

ITER - di, 16/07/2019 - 09:56

The idea of propelling rockets and spaceships using the power of the atom is nothing new: the Manhattan Project in the mid-1940s as well as countless endeavours by NASA in the following decades all explored the possibility of using fission-based reactions to provide lift-off thrust. Today, progress made in controlled nuclear fusion has opened a new world of possibilities.
Fusion, which aims at "bringing the power of the stars to Earth," could also in a not-so-distant future help humans reach the stars from Earth.
At space agencies worldwide, in university labs, and at start-up companies, nuclear fusion propulsion is on the agenda. In the United States, Congress approved USD 125 million in funding in May for the development of nuclear propulsion rockets and called upon NASA "to develop a multi-year plan that enables a nuclear thermal propulsion demonstration" from both fission and fusion. The Russian space agency Roscosmos is working on a "plasma rocket engine" in collaboration with the Kurchatov Institute—a project "made possible by advances made in the study of plasma fusion processes. The Advanced Concept Team at the European Space Agency (ESA), in collaboration with European universities, is conducting a study on the feasibility of open magnetic confinement fusion propulsion. And China intends to develop a whole "fleet" of nuclear carrier rockets by the mid-2040s (without specifying whether they will be fission or fusion-propelled).
Rockets lift from their launchpad and vessels are propelled through deep space by the simple principle of action and reaction: heated exhaust gas is expelled at high speed through a nozzle and, in reaction, a thrust force is exerted on the vessel.
Conventional rockets are propelled by chemical combustion, which requires considerable amounts of fuel—liquid hydrogen and liquid oxygen, or kerosene-like propellant—that are ignited at different stages of the ascent into space.
Expelling hot gas is not the only way to provide thrust however: the father of modern rocketry Robert Goddard (who NASA's Goddard Space Center was named after) suggested in the 1900s that rockets could use electricity to eject electrons or charged ions with a velocity in the range of ~10 kilometres per second, twice as high as that of conventional exhaust gases.
Propelling rockets by atomic bombs, detonated at very short intervals at the rear end of a rocket, was at one point contemplated. From 1958 to 1963 Project Orion, funded by the US Advanced Research Projects Agency (ARPA, today DARPA), the US Air Force, the Atomic Energy Commission and to a lesser extent NASA, aimed at precisely that.
The ban on atmospheric nuclear tests in 1963 put an end to the project. Five years later however, in a Physics Today article titled "Interstellar transport," Project Orion's chief scientist Freeman Dyson suggested that "deuterium fusion explosions" would provide even more thrust and velocity to the bomb-powered rocket and spaceship.
Fifty years later, fusion is still a serious contender for space propulsion although not in its "explosive" applications. Fusion reactors are now contemplated as a heat source that would bring propellant to extremely high temperature (and hence high-velocity exhaust), or expel ultra-hot plasma to provide thrust.
Depending on the concept, the exhaust velocity of a fusion-propelled rocket would be in the range of 150-350 kilometres per second. Planet Mars could be reached in 90 days or even less, as compared to eight months with a conventional propulsion system. The intriguing moons of Jupiter and Saturn would be reachable in reasonable time and the way to exoplanets would open for exploration.
Using the power of fusion to propel rockets to speeds otherwise unattainable, and hence dramatically shortening the duration of space travel, may sound like the stuff of science fiction. And literally, it is: in the 2014 blockbuster Interstellar, the spaceship that carries passengers on a quest for inhabitable planets is fuelled by "compact tokamaks" which also provide the vessel's electricity.
One of the problems is that tokamaks, the most promising of fusion devices in the present state of fusion technology, are all but compact: at 23,000 tonnes (not counting the mass of plant systems), ITER would be difficult to put into orbit.
A fusion reactor, however, is not necessarily a tokamak.
A NASA-funded joint venture between the University of Washington in Seattle and a small company named MSNW LLC focused on the development of advanced space propulsion systems has developed a small field-reversed pulsed-fusion device  (akin to the spheromak concept of 1980s-1990s) to be extrapolated into a "fusion drive engine." Promoters of the project say that they are at work building the components of "a fusion-powered rocket aimed to clear many of the hurdles that block deep space travel, including long times in transit, exorbitant costs and health risks."
In a similar move, the Princeton Plasma Physics Laboratory (PPPL) has entered into a collaboration with a company called Princeton Satellite Systems to work on a direct fusion drive engine for space exploration. Two years ago, NASA awarded a half-a-million dollar grant to the venture, which was also distinguished by a US Federal Laboratory Consortium award in October last year.
In the projected direct fusion drive engine, fusion power would not be produced by the deuterium/tritium (DT) reactions of ITER or future electricity-generating plants. While the DT reaction is the most accessible in today's state of technology, it has two significant drawbacks, particularly for manned space exploration. Tritium is a radioactive element, and the fusion reactions produce a flux of highly energetic neutrons from which humans and electronic equipment must be heavily shielded.
The deuterium/helium-3 reaction that is planned for the direct fusion drive engine has neither of these limitations: both elements are stable and so are the reaction products, hydrogen and helium. As the reaction is "aneutronic," no heavy shielding would be required for protection.
There is, however, one big catch: the temperature required to fuse deuterium and helium-3 nuclei is about ten times higher than that required for DT fusion and no device has yet achieved this level of energy. (The present record is held by the Japanese tokamak JT-60U, which reached an ion temperature of half-a-billion degrees.)
The developers of the direct fusion drive claim that their engine could be operational as early as 2028, which might appear to be a wildly optimistic projection. It might take decades before fusion propulsion quits the realm of science fiction and enters the reality of space travel.
But among space-faring nations there is now a consensus, which the Department of Aeronautics and Astronautics at Washington University, one of the top aerospace schools in the United States, has clearly formulated: "Fusion energy is, in principle, the only conceivable source of energy for rapid, efficient, rocket space travel to Mars, the outer planets, and nearby stars."

EUROfusion TBM secondees take up duties at F4E Cadarache

F4E News - di, 16/07/2019 - 02:00
To rationalise the use of personnel and budget resources for fusion research, F4E welcomes four new EUROfusion secondees to work on TBM.

Europe, Russia, China, Korea and ITER Organization discuss the progress of Blanket components

F4E Events - di, 09/07/2019 - 02:00
Engineers exchange views on prototypes and first factory acceptance tests.

Construction | The stage is now set for the next act

ITER - ma, 08/07/2019 - 18:57

Nine years and 382 Newsline issues ago, a lone power shovel began removing the top soil from the area on the ITER platform where the Tokamak Complex now stands. Following two years of clearing and levelling work by France, construction of the ITER installation was beginning in earnest. 
It may be hard to believe, but this is what the 42-hectare ITER platform looked like in the early months of 2010, just before being transferred from Agence Iter France to the European Domestic Agency, responsible for construction. A vast, featureless, moon-like expanse that—being located in Provence—some described as the largest pétanque court ever created.
One by one, the now-familiar buildings and structures have sprung from the earth: nine years into construction civil works are 73 percent complete, concrete has reached its final level in the Tokamak Building, and a massive machine component—the cryostat lower cylinder—is visible, carefully encased in its protective cocoon, waiting to be installed into the Assembly Pit.
As conveyed by the images from this latest drone survey (June 2019), the stage is now set for the next act in the project's history: the machine assembly phase, set to begin in May 2020.

F4E strengthens cooperation with FAIR Scientific Research facility

F4E News - vr, 05/07/2019 - 02:00
Memorandum of Understanding signed in July 2019

ITER Organization is recruiting - Head of Domain Positions now open

F4E News - do, 04/07/2019 - 02:00
ITER Organization is currently recruiting a Head of Construction Domain, a Head of Engineering Domain, and a Head of Corporate Domain.

Sustained nuclear fusion? Not without control engineering

ITER - ma, 01/07/2019 - 21:43

Without a system to counteract the different sources of variability, the plasma in the ITER Tokamak would cease to produce power. Fortunately, scientists can take what has been learned in the discipline of control engineering—principles and techniques that keep a fighter jet in the air—and apply that same know-how to design the robust plasma control system required by ITER.
"With the development of driverless cars and control systems for airplanes, the control community has put a lot of thought into controlling critical systems in a holistic and robust way that didn't exist ten or twenty years ago," says Tim Luce.
Two years ago, ITER brought in Luce to head the Science & Operations Department. A physicist with 37 years experience working with fusion, he heads the department responsible for both the software and the hardware of ITER's plasma control system. "Now, with advances in computer and communications technologies, we have the capacity to apply new principles and techniques in real time and not just in an offline, theoretical sense," says Luce.
In the past, most systems had simple input and simple output. But control problems have become more complex, requiring a new generation of algorithms that model much more than just a set of independent sensors and actuators. Changes in one component affect the behaviour of other components. Not only do the new systems have to model the dependencies among the different components, but they also have to model the system as a whole.
Because of this interplay among the different inputs and among the different outputs, the matrix models that work so well for control of single-input and single-output (SISO) systems cannot be applied to the control of a fusion reactor, a multiple-input and multiple-output (MIMO) system. Furthermore, to overcome delays in both measurement times and reaction times, the control system has to employ feedforward methods in addition to the more traditional feedback loops.
A multidimensional control problem and a multitude of unknowns
A fundamental part of the control, data access and communication (CODAC) system, ITER's plasma control system is responsible for ensuring that each pulse is executed correctly. It does this by taking data from sensors and applying sophisticated algorithms to generate commands that it sends to actuators to control plasma parameters, such as position, shape or stability.
"We're starting from a point where we do have experience," says Alberto Loarte, head of the Science Division. "If we compare smaller tokamaks operating at highest power and current to large tokamaks operating at lowest power and current, they run the same. So other than a little tuning, we expect our initial models to be based on the behaviour of known systems such as the JET and JT-60SA tokamaks, which have half the linear dimensions of ITER."
"As we move beyond the first stages of operation, we will get into areas where there are more unknowns," says Loarte. "Running our models through simulations, we've found that sometimes when you apply an actuator and expect a certain reaction, the result turns out to be the opposite of what you expected. That's because of the interplay of other factors that are specific to ITER fusion-power-producing plasmas. It's as if you pressed on the accelerator with your foot, and instead of accelerating, the car stops."
There is still a lot to learn about system behaviour at later stages of operation, when fusion reactions in the plasma will cause the plasma to self-heat. In these later stages, the control system will apply heat to the plasma, thereby causing fusion—and the fusion will produce heat, thereby raising the temperature of the plasma even more. The relationship between external heat and plasma temperature will no longer be direct, as it is in present tokamak experiments. This makes the job of the plasma control system much more complicated.
The stakes are high. Once fusion starts to heat the plasma, if the system fails to adjust exactly as required, the plasma can get too hot for fusion to be efficiently produced. The plasma can even become unstable, causing the plant to stop producing power.
Peter de Vries, Scientific Coordinator in the Stability & Control Section led by Joe Snipes, compares the problem to playing mini golf and trying to putt the ball up to a hole on top of a mound. "If you apply too much force you go over the hole and down the other side of the mound. If you apply too little force, the ball doesn't reach the top of the mound and rolls back down. This analogy gives you an idea of how delicate it is for the plasma control system to adjust the external heat."
Temperature and density are major concerns—and so is the shape of the plasma, which also determines the behaviour of the reactor. To monitor plasma shape, the tokamak contains hundreds of tiny sensors, which measure the magnetic fields at different locations. All that information is fed into the control system, which then models the plasma shape, and compares that with a reference.
"It might find that the plasma wants to bulge out a little here," says de Vries. "So then it calculates what voltages it needs to put on the power supplies to change the currents in all the coils that we have around the machine to push the plasma back into shape. Hundreds of measurements go into a complicated calculation—and out of it go dozens of response requests to make sure everything is kept in the right place, with the right plasma density and temperature."
Future-proofing ITER's plasma control system
Employing some of the latest advances in control engineering, ITER's plasma control system is architected to handle both the basic control functions for early commissioning and the advanced control functions that will be needed for future high performance operation. In preparation for each stage of operation, new functions will be added and existing functions will be adapted to new types of plasmas. All modifications will be integrated into the existing system.
In May 2019 the design team reached the halfway point for the final design of the plasma control system for First Plasma operation, the first fully integrated use of all basic tokamak functions. Halfway through scheduled project duration, many of the controllers have been designed and the framework in which the controllers will work is nearly completed.
As for the next steps, Peter de Vries says, "After this summer we will begin several months of intensive assessment—testing and correcting—and documentation of the design. If all goes well, we should be finished with system design for First Plasma by this time next year."
As holistic and robust control engineering is essential to sustained nuclear fusion, any milestone in the design of the plasma control system is a step forward for ITER.

ITER captivates audiences at EU Sustainable Energy Week (EUSEW)

F4E Events - ma, 01/07/2019 - 02:00
Panel makes the case for fusion.

ITER captivates audiences at EU Sustainable Energy Week (EUSEW)

F4E Events - ma, 01/07/2019 - 02:00
Panel makes the case for fusion.

SPIDER experiment delivers its first hydrogen beam

F4E News - do, 27/06/2019 - 02:00
ITER Neutral Beam Test Facility celebrates a year in operation.