W dniu 29 września b.r. w LLNL w Kalifornii uzyskano bardzo ważny wynik eksperymentalny w badaniach kontrolowanej syntezy termojądrowej (fuzji) realizowanej za pomocą lasera wielkiej mocy i energii. 

Widok laboratorium NIF w LLNL z lotu ptaka. LLNL Photo Gallery.

W eksperymentach realizowanych ostatnio w LLNL wykorzystany jest największy na świecie 192-wiązkowy laser NIF (National Ignition Facility) generujący impulsy o energii ~1.80 MJ i czasie trwania kilku nanosekund (moc impulsu wynosi do ~400 TW). Wiązki lasera NIF o długość fali 351 nm (nadfiolet) są symetrycznie wprowadzane przez otworki w ”denkach” złotej tarczy-cylinderka (zwanego hohlraum target) o wymiarach: długość ~10 mm średnica – 4-5 mm. Wiązki laserowe wchodzą do cylinderka pod różnymi kątami i oddziałują z jego wewnętrznymi ściankami generując intensywne miękkie promieniowanie rentgenowskie. W centrum cylindra znajduje się cienkościenna kulka o średnicy ~2 mm wykonana z plastiku, albo innych lekkich materiałów. Na wewnętrznej ściance kulki znajduje się warstwa zamrożonej mieszaniny cięższych izotopów wodoru - deuteru (D) i trytu (T). Intensywne promieniowanie rentgenowskie oddziałując z powierzchnią kulki-tarczy powoduje gwałtowną jonizację i odparowanie (ablację) warstwy powierzchniowej kulki skutkujące implozję warstwy wewnętrznej pokrytej „lodem” DT (efekt „rakietowy”). W wyniku kompresji i grzania plazma w centrum kulki DT osiąga setki g/cm³ a temperatura przekracza kilkadziesiąt milionów stopni Kelvina. W tych warunkach zachodzą reakcje syntezy (fuzji) jąder izotopów wodoru, głównie najbardziej prawdopodobna reakcja D+T z emisją wysokoenergetycznych cząstek alfa i neutronów. 

Fragment lasera NIF. LLNL Photo Gallery.

 Schemat oddziaływania wiązek lasera NIF z wewnętrznymi ściankami złotego cylinderka (hohlraum target) z kulką zawierającą paliwo DT. LLNL Photo Gallery.

Wnętrze komory eksperymentalnej przy laserze NIF z urządzeniem do ustawiania tarczy w ognisku wiązek laserowych. LLNL Photo Gallery.

W ostatnio wykonanym w LLNL eksperymencie uzyskano rekordową generację ~5x10¹⁵ neutronów o całkowitej energii ~14 kJ. Stwierdzono, że wydzielona energia termojądrowa była większa od energii pierwotnie dostarczonej przez promieniowanie rentgenowskie do paliwa DT. Bardzo ważnym rezultatem tego eksperymentu było potwierdzenie przewidywań modeli teoretycznych, co stanowiło problem we wcześniejszych badaniach na układzie NIF. Pokazany wynik ostatnich badań wykonanych w LLNL jest bardzo ważnym osiągnięciem na drodze do efektywnej produkcji energii w wyniku fuzji inicjowanej laserem. Następnym krokiem będzie zwiększenie wzmocnienia energetycznego w skomprymowanym, gorącym paliwie DT w wyniku przekazu do tego paliwa energii cząstek alfa produkowanych w reakcji syntezy D+T. Informacje o ostatnim eksperymencie wykonanym w LLNL można znaleźć na stronie internetowej: http://www.bbc.co.uk/news/science-environment-24429621.

Opanowanie kontrolowanej syntezy termojądrowej (fuzji) dla przyszłej produkcji energii elektrycznej jest obecnie jednym z najważniejszych zadań światowej nauki i technologii. Realizacja tego zadania wiąże się z szybkim wzrostem zapotrzebowania na energię elektryczną i koniecznością radykalnego ograniczenia energetyki wykorzystującej paliwa kopalne. Stosowanie odnawialnych źródeł energii jest mało wydajne w skali globalnej i wiąże się z ingerencją w środowisko naturalne. Energetyka termojądrowa w przeciwieństwie do energetyki jądrowej nie łączy się z produkcją dużej ilości długożyciowych odpadów radioaktywnych i z możliwością katastrofalnego rozprzestrzenienia się materiałów radioaktywnych. Do wytwarzania energii w wyniku fuzji izotopów wodoru D i T wykorzystuje się deuter, który znajduje się w dużych ilościach w wodzie, i tryt produkowany w reakcji neutronów z łatwo dostępnym litem. 

Reakcje fuzji w gorącej i bardzo gęstej, krótkożyciowej plazmie wytwarzanej laserem, jak to ma miejsce w układzie NIF, zachodzi bez stosowania zewnętrznych układów do utrzymania plazmy. Reakcja ta zachodzi przy jedynie inercyjnym utrzymaniem paliwa DT. Metoda taka jest nazywana Inertial Confinement Fusion - ICF. Programy dotyczące opracowania fuzji ICF realizowane są także w Europie (projekt HiPER) i w Japonii (projekt FIREX). Inną metodą opanowania efektywnej produkcji energii fuzji, bardziej rozpowszechnioną niż ICF, jest zastosowanie pól magnetycznych w toroidalnych pułapkach typu tokamak albo stellarator służących do odpowiednio długiego utrzymania bardzo gorącej i rzadkiej plazmy. Czas utrzymania plazmy, jej temperatura i gęstość powinny umożliwić uzyskanie energii fuzji przewyższającej energię dostarczaną do tych układów przez zewnętrzne strumienie cząstek i mikrofal. Metoda ta nazywana jest Magnetic Confinement Fusion - MCF). W ramach międzynarodowego projektu ITER w południowej Francji jest obecnie budowany przez Unię Europejską, St. Zjed. Am. Pn., Japonię, Chiny, Republikę Korei, Kanadę i Indie wielki tokamak jako fuzyjny reaktor eksperymentalny.

Instytut Fizyki Plazmy i Laserowej Mikrosyntezy jest wiodącym w Polsce ośrodkiem naukowym realizującym prace dotyczące fuzji w ramach projektów europejskich zarówno w wersji ICF jak i MCF. Informację o badaniach realizowanych w IFPiLM można znaleźć na stronie www.ifpilm.pl.

Fusion for Energy (F4E) has signed its largest contract to date with Cofely Axima, Cofely Ineo, Cofely Endel (GDF Suez Group) and M+W Group. The strong expertise of the Franco-German group of companies will be used to provide the building services for the Tokamak complex, where the ITER Tokamak machine will be located, and the surrounding buildings. The contract is expected to run for six years and its budget is approximately 530 million EUR.

 
Professor Henrik Bindslev, F4E’s Director, stated that “this is an important achievement for Europe not only because of the volume of the contract but also because European companies will be given an unprecedented opportunity to share and acquire new know-how that will generate future business opportunities.” Guy Lacroix, Managing Director of GDF SUEZ Energy Services in charge of Cofely Axima, Cofely Ineo and Cofely Endel confirmed that “being part of the largest international collaboration in the field of fusion energy makes us extremely proud. All the members of the consortium bring together a diversity of skills and expertise which allow us to demonstrate that we can be at the forefront of large scale industrial projects like ITER.”

The ITER site in figures: 
The size of the ITER platform is 42 hectares and Europe is the party responsible for the delivery of the 39 buildings that the ITER platform will host. Currently, the personnel directly involved in construction counts 250 people and by the end of 2014 it is expected to reach 2,000 people. One of the key challenges will be to accommodate the needs of the rapidly growing workforce and to guarantee an optimal use of space to the different companies operating on the ground, in order to carry out the construction of all infrastructures in parallel and on time. 

The scope and key figures of the contract: 
The contract covers the design, supply, installation and commissioning of the mechanical and electrical equipment for the Tokamak complex, which consists of the Tokamak, Diagnostic and Tritium buildings, plus the surrounding buildings which reach a total of 97,200 m3. Thanks to this contract all the necessary works of the ITER Assembly phase will start in order to host ITER’s high tech equipment in compliance with the strict safety requirements and in line with the rigorous qualification tests.

Through this contract a Heating Ventilation Air Conditioning (HVAC) system will be delivered powerful enough to treat the air flow of 1,000,000 m3/hour which corresponds to the volume of air that is inhaled and exhaled by 3,5 million people/hour. Furthermore, Instrumentation and Control (IC) systems, power supplies, interior and exterior lighting, gas and liquid networks will be installed. State of the art fire detection and extinguishing systems, consisting of 2,000 fire detectors, will be supplied, pipe fittings and handling equipment with various interfaces connecting buildings and systems. 

Source: F4E

One of the most fascinating aspects of the ITER project is the technology that is being deployed in order to test the viability of fusion energy at such scale. For an outsider, the project is a leap to the future. For scientists and technical experts who have spent most of their life in the fusion community, ITER is validating and upgrading existing know-how that has been accumulated throughout the years in fusion laboratories around the world. 
There will be some, however, who will be given a once in a lifetime opportunity to push the envelope further and use ITER as a laboratory. They will witness technological breakthroughs and pave the way for DEMO, the fusion demonstration reactor planned to come after ITER. Amongst the fortunate vanguard fusion specialists are those involved in the Test Blanket Modules (TBMs). During the last International Symposium on Fusion Nuclear Technology there was a lot of buzz about the progress made in the area of TBMs. What is this blanket made of that is exposed to plasma reaching 150 million°C and what purpose does it serve? We met with Yves Poitevin, F4E’s Project Team Leader for TBMs and Materials Development, to understand the background, the state of play and potential of this domain.
Apart from deuterium, ITER will require the administration of tritium in order to make the fusion reaction happen. In DEMO, it will need to be bred continuously within the reactor in order to keep the fusion reaction going. How can this be achieved? Tritium can be produced within the reactor once the neutrons of the fusion reaction bounce on lithium, which is contained in the reactor’s blanket. “One of our aims is to test the prototypes of future breeding blankets in real fusion conditions offered by ITER and then export that knowledge to DEMO. In essence, we are generating a new component and qualifying it in unprecedented conditions. Furthermore, through this process, we are licensing a nuclear system based on advanced materials and top fabrication technology” Yves Poitevin explains. “We are writing a new chapter in this field by collecting new data, developing new codes and extrapolating them to DEMO. This is a real opportunity for Europe’s research and industrial communities to collaborate and develop together a vital technology for fusion reactors.”

Work started in the late 90s when the European Fusion Development Agreement (EFDA) conducted research to address the need for the development of new materials and technologies for tritium production. The transition from research to licensing and fabrication is challenging. F4E has been collaborating with specialised engineering companies like IDOM, Atmostat, Iberdrola, AMEC, Empresarios Agrupados to take stock of their expertise. Similarly, for the design and qualification phases the input received by laboratories like KIT, CEA, ENEA, CIEMAT, UJV, KFKI, NRG, etc. has proved extremely valuable. Approximately 30 contracts have already been signed in this domain and the work is gradually increasing in volume.

Europe is standing at the crossroads of two blanket concepts: the Helium-Cooled Pebble-Bed (HCPB) and the Helium-Cooled Lead Lithium (HCLL). The key difference lies in the type of material used for the tritium breeder. In order to choose which way to go for DEMO, it has been decided to test both concepts simultaneously in ITER by placing the TBMs in an equatorial port of the machine. 

In terms of the TBMs structural materials, Europe has set its hopes on EUROFER, a newly developed reduced activation ferritic/martensitic (RAFM) steel developed in Europe, which provides adequate resistance to neutron irradiation, corrosion and with acceptable resistance at high temperatures. “EUROFER is Europe’s choice for ITER’s TBMs because of its properties, its mechanical resistance and its tolerance to neutrons irradiation” explains Yves Poitevin. Part of EUROFER design limits have been recently added to the RCC-MRx nuclear construction code and progress is being made to complete them. Japan, Korea, India and China are also developing their own TBMs for ITER. The potential of developing in parallel different degrees of expertise is there. What is here, however, is the opportunity to invest and test today a technology that will be necessary tomorrow. 

Source: F4E

Scientific advisers to the ITER fusion reactor project have recommended several key changes to its design that could increase technical risks—but also smooth the path to producing excess energy. The recommendations, made last week by ITER’s Science and Technology Advisory Committee (STAC), will have to be approved by the full ITER council in November. But if approved, as expected, “the chance of surprises later is reduced,” says Alberto Loarte, head of ITER’s confinement and modeling section. “The risk will pay off.”

ITER, being built in France by an international collaboration, aims to show that nuclear fusion, the reaction that powers the sun, can be controlled on earth to produce energy. But reaching that goal involves heating hydrogen gas to more than 150 million°C so that hydrogen nuclei slam together with enough force to fuse. To do this, researchers are building a huge doughnut-shaped container called a tokamak to confine the ionized gas—or plasma—using enormously strong magnetic fields. ITER’s goal is to coax the plasma to produce 500 megawatts (MW) of heat, 10 times the 50 MW of power required to heat the plasma; this multiplying effect is known as a gain of 10.

The most significant change decided at the STAC meeting concerns a structure at the base of the tokamak vessel called the divertor. Its main function is to remove the helium that is the “exhaust” gas of the fusion reaction. The divertor is the only part of the vessel where the superhot plasma actually touches a solid surface, so it has to be able to absorb huge quantities of heat, as much as 10 MW per square meter of surface.

Existing plans call for making ITER’s first divertor with an outer layer of carbon. This is the safe option: Carbon is well proven in tokamak interiors; it can easily withstand the temperatures; and if any is blasted off into the plasma, it doesn’t affect the performance very much. The problem with carbon, however, is that it happily reacts with hydrogen, binding atoms into its structure. This wouldn’t be a problem during the early phases of ITER operation when researchers plan to use simple hydrogen or helium in the machine to get the hang of how it works. But a carbon coating could be a huge problem in later phases, when researchers plan to switch to real fusion fuel—a more reactive mixture of the hydrogen isotopes deuterium and tritium. Tritium is radioactive and so needs to be carefully controlled and accounted for. Nuclear regulators would never accept a divertor material that absorbs tritium and so makes it impossible to locate.

To address that problem, planners had proposed running ITER for several years with the carbon-coated divertor, and then switching to one made of tungsten. Tungsten has the highest melting point of any metal: 3422°C. That should be fine for withstanding the heat produced during normal, steady ITER operations. But any unexpected bursts of heat could potentially melt the divertor, and tungsten—unlike carbon—instantly poisons the plasma, bringing fusion to a halt. So ITER’s operators would have to run the reactor much more carefully with a tungsten divertor, not pushing it to limits where the plasma might become unstable.

Despite this drawback of tungsten, STAC has recommended that ITER be built with a tungsten divertor from the start. “It was not an easy decision,” says STAC Chair Joaquín Sánchez, head of Spain’s National Fusion Laboratory in Madrid. The decision was made after years of research at other tokamak laboratories, in particular the Joint European Torus (JET) at Culham in the United Kingdom, which is the closest machine to ITER in size and design. Several years ago, JET researchers refitted the reactor with a tungsten divertor and beryllium lining (as ITER will have). After a year of testing, they confirmed that this “ITER-like wall” worked well enough not to cause problems for ITER.

Although some fusion researchers think that it would be safer to start ITER with a well understood carbon divertor, allowing them to push the reactor to extremes in search of high performance, starting with tungsten has advantages, too. Changing divertors is a complex process that would take many months. In addition, once operation with deuterium-tritium fuel has started, the interior of the vessel becomes radioactive (or “activated”), making it much harder to modify internal components. “If we start with tungsten, we save the cost of the change,” Sánchez says. “We know tungsten will be more difficult, but we will start learning earlier in the nonactivated phase and if there is a problem we can send people inside to fix it.”

The other design changes concern two separate magnetic coils to be inserted inside the reactor vessel to fine-tune control of the plasma. ITER’s main plasma-confining magnets are outside the vessel and act as something of a blunt instrument. About 5 years ago, researchers highlighted the fact that operators would have difficulty keeping the vertical position of the plasma steady, and so proposed some extra magnetic coils on the inside.

In addition to those for vertical stability, researchers proposed installing a second set of internal coils to combat a troubling phenomenon in superhot fusion plasma called edge-localized modes, or ELMs. ELMs occur when energy builds up in the plasma during fusion and then bursts out of the edge unpredictably, potentially damaging the lining or the divertor. The second set of coils deploys a magnetic field to roughen up the surface of the plasma so that it leaks energy at a constant rate rather than in erratic bursts.

Anything inside the vessel is subjected to extreme heat, radioactivity, and magnetic forces, so researchers had to persuade STAC that these two sets of coils could be made resilient enough to survive. “There was some reluctance in STAC and the ITER Organization because of the technical issues of installation,” Loarte says. Experiments at other labs around the world reassured them. “The results obtained were very positive,” he says.

STAC also took a hard look at the delivery schedule of components for ITER. The original plan called for everything—heating systems, instruments, ELM mitigation—to be in place when ITER is completed in 2020. But delays have meant that some items will be arriving later. “We needed to redo the schedule with a logic consistent with [achieving deuterium-tritium operation] faster. It was not consistent before and that led to criticism,” Loarte says. “Now we have to do the organizational part, which is not simple.”

Source: news.sciencemag.org

F4E has signed the contract for the Poloidal Field (PF) coils Engineering Integrator (EI). Awarded to ASG and worth approximately 27.5 million EUR, this contract is the first of a number of work packages, which will cover tooling (equipment necessary in order to manufacture and handle the components) , site and infrastructure, manufacturing and cold testing.These work packages are currently being prepared in order to provide F4E’s contribution of the PF coils 2-6 (PF coils 2-5 will all be manufactured in Europe, while PF coil 6 will be manufactured in China, but cold tested in Europe; the Russian Domestic Agency will procure PF coil 1). The PF coils contribute in generating the magnetic field to control the plasma position, maintaining the plasma's shape and stability inside the tokamak, in order to provide the conditions for the fusion reaction. The Poloidal Field coil system consists of six horizontal, circular coils placed outside the toroidal magnet structure. Due to their very large size making impossible to transport them, manufacture of four of the six PF coils will take place in the PF coil winding building, directly on the ITER site in Cadarache, France.

The ASG Engineering Integrator team is composed of approximately 20 engineers working to issue the manufacturing plan (developing plans in support of rigorous Quality Assurance, control of manufacturing activities, and establishing a production time schedule) to define the manufacturing layout and workflow, as well as to issue the manufacturing drawings and procedures for the production of all four PF coils. ASG will also support F4E in the procurement of the tooling and equipment for component manufacture; in addition, they will supervise the manufacturing and cold test activities (the final acceptance test which involves cooling the coil at low temperature of 80 K in order to reproduce thermal stresses similar to the ones experienced in the operating conditions in the ITER machine). 

Focus will now be on implementing the EI contract and negotiating the next procurement which is for winding tooling (expected to be signed during the first quarter of 2014). The Calls for tender for the other remaining contracts (except the contract for the cold testing facility) are foreseen to be launched during 2014.

Source: F4E