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ITER NEWSLINE 272
The IFMIF/EVEDA project is advancing. Concurrently with the accomplishment of the Intermediate Engineering Design report of IFMIF, the installation of LIPAC, the Linear IFMIF Prototype Accelerator has now started in Rokkasho, Japan.
The commissioning of LIPAc within the Broader Approach Agreement between Japan and EURATOM aims to demonstrate the technical feasibility of the IFMIF accelerator designed to operate two beams of deuterons at 125 mA with 100 percent duty cycle to obtain a source of fusion-relevant neutrons equivalent in energy and flux to those of a fusion power plant.
IFMIF will be capable of providing >20 dpa/fpy (displacements per atom/full power year) with neutrons with a broad peak at 14 MeV allowing, within a few years of operation, the characterization of suitable materials for the first wall of the reactor vessel, together with the acquisition of data from fusion-relevant neutrons that will help material scientists unravel the underpinning physics.
LIPAc is under design and construction mainly in different labs in Europe under the coordination of the European Domestic Agency (F4E), and will be installed in Japan by a joint team from Europe and Japan. On its own, with 1.125 MW of average beam power, LIPAc will lead the world ranks of high current accelerators. Its commissioning will be the responsibility of IFMIF/EVEDA Project Team, led by Juan Knaster.
After the successful performance during the individual system tests carried out at CEA (Saclay) in November 2012, the ion source and the low energy beam transfer have been delivered to Rokkasho and the installation activities have now started. An upgrade of the survey network in the accelerator hall was deemed necessary following a study by F4E to meet the alignment precision of 0.1 mm of certain components; an essential factor given the unprecedented beam current. The fiducialization upgrade will install 120 new additional fiducials and a permanent pillar, which will allow the placement of the laser tracker anywhere in the accelerator hall within uncertainties below 0.03 mm. This activity will be performed in Rokkasho by a team led by Luigi Semeraro (F4E) and the collaboration of JAEA during the third week of June.
The validation of the accelerator prototype, together with the success of other constructed prototypes related with the Target facility and Test Facility in Europe and Japan within the time allocated for IFMIF/EVEDA will support the start of construction of IFMIF whenever the fusion community demands a fusion-relevant neutron source.
Tungsten is particularly suitable as material for highly stressed parts of the vessel enclosing a hot fusion plasma, as it is the metal with the highest melting point. A disadvantage, however, is its brittleness, which under stress makes it fragile and prone to damage. A novel, more resilient compound material has now been developed by the Max Planck Institute for Plasma Physics (IPP) at Garching. It consists of homogeneous tungsten with embedded coated tungsten wires. A feasibility study has just shown the basic suitability of the new compound.
The objective of the research conducted at IPP is to develop a power plant that, like the sun, derives energy from fusion of atomic nuclei. The fuel used is a low-density hydrogen plasma. To ignite the fusion fire the plasma has to be confined in magnetic fields and heated to a high temperature, up to 100 million degrees in the core. Tungsten, as demonstrated by extensive investigations at IPP, is a highly promising metal as material for components coming into direct contact with the hot plasma. A hitherto unsolved problem, however, has been the brittleness of the material: tungsten loses its toughness under power plant conditions. Local stress—tension, stretching or pressure—cannot be obviated by the material slightly giving way: cracks form instead. Components therefore react very sensitively to local overloading.
That is why IPP looked for structures capable of distributing local tension. Fibre-reinforced ceramics served as models: for example, brittle silicon carbide is made five times as tough when reinforced with silicon carbide fibres. After a few preliminary studies, IPP scientist Johann Riesch was able to investigate whether similar treatment can work with tungsten metal.
The first step was to produce the new material. A tungsten matrix had to be reinforced with long coated fibres consisting of extruded tungsten wire thin as hair. The wires, originally intended as luminous filaments for light bulbs, where supplied by Osram GmbH. Various materials for coating were investigated at IPP, including erbium oxide. The completely coated tungsten fibres were then bunched together, either side by side or braided. To fill out the gaps between the wires with tungsten Johann Riesch and his co-workers then developed a new process in conjunction with English industrial partner Archer Technicoat Ltd.
Whereas tungsten workpieces are usually pressed together from metal powder at high temperature and pressure, a more gentle method of producing the compound was found: the tungsten is deposited on the wires from a gaseous mixture by applying a chemical process at moderate temperatures. This was the first time that tungsten-fibre-reinforced tungsten was successfully produced, with the desired result—the fracture toughness of the new compound had already tripled in relation to fibreless tungsten after the first tests.
The second step was to investigate how this works. The decisive factor proved to be that the fibres bridge cracks in the matrix and can distribute the locally acting energy in the material. Here the interfaces between fibres and the tungsten matrix, on the one hand, have to be weak enough to give way when cracks form and, on the other, be strong enough to transmit the force between the fibres and matrix. In bending tests this could be observed directly by means of X-ray microtomography demonstrating the basic functioning of the material.
Decisive for the material's usefulness, however, is that the enhanced toughness is maintained when it is applied. Johann Riesch checked this by investigating samples that had been embrittled by prior thermal treatment. When the samples were subjected to synchrotron radiation or put under the electron microscope, stretching and bending them also confirmed in this case the improved material properties. If the matrix fails when stressed, the fibres are able to bridge the cracks occurring and stem them.
The principles for understanding and producing the new material are thus settled. As a prerequisite for large-scale production, samples are now to be produced under improved process conditions and with optimized interfaces. The new material might also be of interest beyond the field of fusion research.
In the world of tokamaks ITER will be a giant, weighing some 23,000 tonnes and measuring 30 x 30 metres. Whatever its might, however, the operation of this giant couldn't be successful without such tiny elements as diamond detectors. These small components, only 4 x 4 x 0.5 mm, are an important part of one of ITER's neutron diagnostics, the vertical neutron camera.
The diamond detectors, part of the Russian Domestic Agency's procurement responsibilities for ITER diagnostics, will be manufactured at a dedicated facility at the Troitsk Institute for Innovation and Fusion Research (TRINITI) near Moscow.
Manufacturing is a sophisticated and multi-stage process, according to Nikolay Rodionov who heads the facility: "In ITER, detectors will operate under high neutron flux and high temperature, and it will be our task is to produce diamond detectors that are capable of withstanding such extreme, severe conditions."
At the beginning of detector manufacture, the key elements—electronic-grade, single-crystal diamond plates—arrive at the material analysis laboratory where highly sensitive instruments test quality and identify defects. Next, the plates and associated metal fixings are cut to the required sizes and shapes by laser.
To correct possible defects, the single crystal diamond plates are annealed in a high-temperature vacuum oven at temperatures no less than 1500 degrees Celsius. Rid of their organic impurities by specially mixed acids, the diamond crystals are exposed to additional purification from an ion beam of oxygen or argon.
For such a sensitive component as a neutron detector, even the smallest impurities are inadmissible.
In the next stage of manufacturing a metal layer (gold, titanium, platinum or aluminum) is deposited on the diamond plate and gold or aluminum current conductors are welded on—these conductors, which at 30 micrometres thick can hardly be seen by the naked eye—collect electric charge from metal contacts. Now the detector, placed into a special mounting of thin sapphire plate and attached by two membranes of bronze or copper, is ready for installation on the vertical neutron camera.
By 2018, the specialists at TRINITI will have manufactured approximately 100 diamond detectors for ITER, including test samples, prototypes and spares. Currently, the facility has been equipped with laboratory and technical equipment for the manufacturing of dummies and test samples. For the production of prototypes and the beginning of batch manufacturing of qualified diamond detectors, additional modernization is planned to meet the requirements of the complex manufacturing operations for the diamond detector.
Click here to view a video on the manufacturing of ITER diamond detectors.
On 5 June 2013, ITER Director-General Osamu Motojima was honoured for his long-term achievements as Professor in Plasma Science and education by receiving a degree honoris causa from the Graduate University for Advanced Studies of Japan.
The Graduate University for Advanced Studies (Sokendai) was founded in 1988 as the only university in Japan and throughout the world to offer exclusively doctorate-level training. It is made up of 16 national institutes and organizations such as the National Institute for Fusion Science, the National Astronomical Observatory of Japan, and the High Energy Accelerator Research Organization.
The university has the world's highest level of education, curriculum and syllabus taught by professors who are closely affiliated with research institutes and organizations throughout Japan, providing doctoral students with access to the nation's premier facilities for mathematical, physical and life sciences, as well as cultural and social studies.
Its Department of Fusion Science, established in 1992, is closely associated with the National Institute for Fusion Science (NIFS) which is home to the Large Helical Device (LHD).
Before coming to ITER, Osamu Motojima held a full-time professorship at NIFS from 1989-2003 in the Department of Fusion Science. In 1998, he took over responsibility for the LHD Program; during his time there the device achieved its first high-temperature plasma. Prof. Motojima continued to direct the LHD Program until April 2003, when he became Director-General of NIFS, crowning nearly twenty years spent within the Institute.
During the ceremony, the university's President, Prof. Naoyuki Takahata, congratulated all the awarded honorary professors, and thanked Prof. Motojima for coming all the way from France to attend the ceremony, for his long-time contribution at the highest level of responsibility for education in NIFS, and for having supervised many doctoral students (about 20). Prof. Takahata also stressed that this year is the 25th anniversary of Sokendai.
During his acceptance speech, Prof. Motojima said, "It is my great honour to be awarded honoris causa together with my old colleagues. Sokendai is well known throughout the world and I wish it further progress in its contributions to worldwide post-graduate education. ITER has a scholarship program of post-doctoral fellows supported by His Serene Highness Prince Albert of Monaco and has established a good relationship with several universities. It is the necessary condition for the success of the ITER project to have a high level of research and engineering, in addition to supporting education and training for the next generation. I will contribute towards this from now on too."
For the ITER Director-General, 5 June has become a date that he will always remember.
On maps and in geography books its name is the Mont Ventoux—the "Windy Mountain" of Provence—that towers over the plain of Vaucluse halfway between the Rhône and Durance rivers valleys. However to many people, and especially to Tour de France racers, it is known as the "Beast of Provence."
The climb to the summit at an altitude of nearly 2,000 metres is one the toughest and most gruelling in professional cycling. The 21-kilometre road that leads from the village of Bédoin to the finish line has an average gradient of 7.5 percent, with peaks above 10 percent—meaning that for every kilometre covered, the rise in altitude can be as high as 100 metres.
The Tour de France has ascended the Beast 14 times since 1951. Everyone here, bicycle aficionado or not, remembers the tragic date of 13 July 1967 when British champion Tom Simpson collapsed and died during the climb at age 29.
The mountain, which appears perpetually snow-capped even in the hottest days of summer (bare, white limestone creates the illusion) acts as a magnet for cyclists around the world.
Ascending the Mount Ventoux is a ritual of passage: no one can pretend to be a real cyclist who hasn't suffered through the torments of the climb, preferably in July when temperatures can reach 35 °C.
The first cycling champion to challenge the mountain was a Frenchman named Jacques Gabriel: in July 1908, by way of the Bédoin route, it took him 2 hours and 29 minutes to reach the summit. The present record (55 minutes and 51 seconds ... with a much lighter bicycle) was established in 2004 by Spanish cyclist Iban Mayo Diez.
On Sunday 2 June, after a couple of months of training, six ITER staff members (Hyun-Sik Chang, Russell Eaton, Benoît Giraud, Edward Daly, Joo-Shik Bak and René Raffray) decided they were ready for the trial. Starting from the village of Sault, which makes for a longer 26-kilometre climb but one that is relatively easier, they reached the summit in 2 hours and 45 minutes.
One century ago, they would have been hailed as champions; in 2013, they can be considered impressive climbers ...