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ITER NEWSLINE 219
The last step in installing a seismic pad consists of pouring highly fluid mortar into the small space that persists between top of the concrete plinth and the bottom of the pad's metal plate after the pouring of second-phase concrete.
An ingenious technique was developed specifically for ITER to avoid the formation of bubbles in the mortar: a thin polyethylene film sealing the bottom of the mortar chute is instantly vaporized by the passage of a strong electric current, thus producing a gush of mortar.
On Wednesday, 18 April, the switch that sent the current into the film was jointly pressed by ITER Director-General Osamu Motojima and Laurent Schmieder, head of the Site, Buildings and Power Supplies Division for the European Domestic Agency F4E.
The 493rd—and final—seismic pad has now been finalized, on time and within budget. The event marked an important milestone for ITER, F4E and NUVIA, the company in charge of installing the seismic pads on the basemat of the Seismic Pit.
Although all the ITER seismic pads are identical, number 493 has special symbolic value: it stands precisely at the centre of the star-like formation of plinths that will directly bear the weight of the Tokamak.
And to celebrate the event, instead of opening lunch boxes or taking a quick trip to the worksite canteen, workers and guests were treated to a traditional méchoui (from the Arabic meaning "roasted") in the large tent standing on the site of the future Hot Cell Facility.
In typical south-Mediterranean fashion, mussels and octopus soup were served first, as two whole sheep finished roasting on a bed of embers outside the tent.
Although no speeding train will ever cross the ITER site, the four-hectare electrical switchyard in the southwest section of the platform will act very much like a railroad junction.
In the same way railroad switches direct trains in this direction or that, open a track here and close another there ... the ITER switchyard will dispatch electricity from the newly built 400kV double power line to seven transformers connected to the installations. Construction of these transformers—four procured by the United-States and three by China—should begin in 2014.
The power that will be supplied to ITER is channelled from a giant switchyard located to the west of Avignon in Tavel (famous for its rosé wine...). From there, electricity travels 125 kilometres to a large substation in the hamlet of Boutre, close to village of Ginasservis some three kilometres south-east of the ITER platform.
The 400 kV "Boutre-Tavel" power line is an essential link in the interconnected European grid. It supplies electricity to a vast area of south-eastern France and, since the construction of a derivation in the late 1980s, also to the CEA-Euratom tokamak Tore Supra.
In terms of instantaneous electricity consumption, tokamaks are gluttonous machines. Tore Supra requires up to 100 MW of power for every plasma shot; as a much larger and more powerful machine, ITER will demand an average of three to four times more.
The anticipated needs of ITER have led to an extension and a reinforcement of the Tore Supra derivation: like "Boutre-Tavel," the new power highway delivers 400kV by way of two distinct and redundant power lines.
ITER of course will not use the power lines' total capacity. Plasma pulses will indeed need hundreds of megawatts, but the daily operation of auxiliary plant systems will require much less.
"The ITER switchyard guarantees maximum flexibility, both for ITER and for the Réseau de Transport d'électricité (RTE) that operates the Boutre-Tavel power line," explains Joël Hourtoule, section leader for ITER's Steady State Electrical Network Section.
Tension variation on a 400kV power line must remain limited to 3 percent. In order to remain within this tolerance, ITER operations must be closely coordinated with RTE dispatching.
"ITER will provide RTE with annual, monthly and weekly planning schedules. Prior to each plasma shot, ITER will send a signal to the RTE Regional Dispatch Centre in Marseille and receive back an authorization to proceed — or not. This procedure needs to be finalized prior to ITER's operational phase."
Installing and financing the ITER switchyard and power-line extension was part of France's commitment to ITER. "Our role," explains Agence Iter-France Head of Technical Projects Jean-Michel Bottereau, "was to bring the 400kV to the foot of ITER. This has been done on time and within budget."
The switchyard, which will be "powered on" in June, will remain under the responsibility of RTE. ITER's jurisdiction will begin right outside the switchyard fence, where seven transformers and several circuit breakers will be installed. The 400 kV will be brought down to 66 and 22 kV before dispatch to the various plant systems of the ITER installation.
On 16 April, Halbe Zijlstra, the Dutch State Secretary for Education, Culture and Science, opened the new FOM Institute DIFFER in Nieuwegein. DIFFER is the Dutch Institute for Fundamental Energy Research, previously known as the FOM Institute for Plasma Physics Rijnhuizen. Rijnhuizen was founded in 1959 to be the Dutch centre for fusion research. In 2011, funding agencies FOM and NWO decided to broaden the institute's mission to fundamental energy research.
DIFFER has as its motto Science for Future Energy and wishes to become a leading institute for fundamental energy research. The institute will continue its strong fusion-related research, and will also start a separate research line into solar fuels, the storage of fluctuating sustainable energy in the form of chemical fuels. To facilitate a closer cooperation with academic researchers in these fields, DIFFER will move to a new laboratory building at the campus of Eindhoven University of Technology in 2015.
The new diagnostic design marks a nationwide effort by researchers in support of US contributions to ITER. Scientists at the University of California at Los Angeles and Oak Ridge National Laboratory developed the prototype instrument, which is being tested on the DIII-D Tokamak in San Diego. "This is a good example of US fusion experts working together to support the conceptual design," said PPPL physicist Dave Johnson, who heads the development of the diagnostic tools for US ITER.
The prototype instrument, called a reflectometer, measures the electron density profile of the plasma gas that fuels fusion reactions. The profile shows changes in density from the volatile edge of the plasma to the centre of the plasma core, and must be maintained at an optimal level for a stable self-sustaining reaction, or burning plasma, to take place.
The prototype represents a sharp departure from standard "bistatic" reflectometers that use dual antenna systems—one to launch radar-like microwaves towards the plasma through waveguides, and a second one to carry back the reflected signal for analysis. By contrast, the new design features a single, or "monostatic," antenna/waveguide system to both deliver and return the microwave signal from the plasma.
"The goal of the DIII-D test is to see whether you can launch and receive the reflected power on the same antenna," said Tony Peebles, head of the UCLA Plasma Diagnostics Group that designed the monostatic system together with ORNL engineer Greg Hanson, who created the waveguides that carry the microwave signal.
The single antenna/waveguide system will capitalize on the vast size of ITER, where the vacuum window for the ITER antenna will be many metres from the plasma. This extended propagation distance "will make it significantly easier to filter out spurious radar images," said Peebles. If the tests on DIII-D are successful, he noted, the prospects for a monostatic system look promising for ITER.
Benefits of the monostatic system could range from increased diagnostic capability to potential cost savings. Six monostatic transmission systems could perform the same measurements as the twelve bistatic systems currently planned for ITER. This "monostatic advantage" would allow a potential cost-savings related to construction, installation and maintenance.
Researchers at DIII-D will be led by UCLA in testing the monostatic prototype on the tokamak starting in May and running throughout the summer. "We hope to learn enough from the DIII-D tests to assess the feasibility of the monostatic design," said Johnson. "Based on these results we will possibly make a recommendation to modify the reflectometer to be monostatic."
Read the full article at www.pppl.gov.