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ITER NEWSLINE 140
The powerful current coursing through the veins of ITER's most powerful magnet systems will be carried along thousands of individual pathways known as strands. Made up of a very precise combination of elements, these superconducting strands measure from 0.73 mm-0.83 mm in diameter, and constitute the essential building materials for ITER's high-performance magnet conductors.
For two of ITER's magnet systems—the toroidal field coils and the central solenoid—the superconducting strands will be made of niobium-tin (Nb3Sn) alloy. Nb3Sn is one of an array of advanced materials capable of superconductivity under high magnetic field. Its performance characteristics and relative market maturity—suppliers capable of producing long lengths of strand now exist—make it the best choice for ITER's high-field magnets.
Nb3Sn is a challenging material to manufacture, however. Once niobium and tin are reacted together to form the alloy, the material becomes as brittle as glass. For ITER's purposes, manufacturers are obliged to work with the materials in their precursor state—one still separate from the other—until the magnet conductor is wound into its final position. Only then is the heat treatment that will diffuse tin into niobium applied.
The manufacture of ITER's fine strands begins with a 40-100 kg metal billet, or cylinder, that contains niobium filaments, a copper matrix and a tin source—typically bronze (copper-tin) or pure tin. The precise design and composition of the billets—and the performance of the resulting strands—were carefully documented through a joint program of research and development involving the six ITER Members that will be procuring Nb3Sn strand for the project. During trials, approximately 0.1 tonne of advanced Nb3Sn strands were produced by each supplier to demonstrate production capacity.
Each manufacturer will pick the design of its billet, and draw it down to strands of less than one millimetre in diameter and 10-30 kilometres in length. Some strand from every billet will undergo tests to assure that ITER's performance metrics are met. The detailed test results of every strand piece and billet will be stored in ITER's Conductor Database.
A length of superconducting cable is made up of both Nb3Sn strands (900 for the toroidal field coils and 576 for the central solenoid coils) and pure copper strands. The copper strands are included in the mix to provide protection in the case of a quench—a situation where superconductivity is lost due to a local temperature rise in the magnets, and the electric current needs supplementary pathways to travel along.
Six of the seven ITER Members will contract with their industries for the manufacture of the tens of thousands of kilometres of Nb3Sn strand required for the toroidal field magnet system (380 tonnes) and central solenoid system (122 tonnes). The first 50 kilos of Nb3Sn strand was produced in December 2008 by the Japanese manufacturer Jastec. Since then, two suppliers in Japan have produced more than 50 tonnes of Nb3Sn strand.
Production has now also begun in Korea, the Russian Federation and the United States, and pre-production in China and Europe. By 2011, worldwide capacity will have expanded five-fold thanks to the requirements of ITER.
Thanks to Matt Jewell, ITER-Monaco Postdoctoral Fellow in the Magnet Division, for his contribution to this article.
In order to define the test procedures and the acceptance criteria for the manufacturing of the ITER poloidal field coil conductor, the ITER Organization commissioned ENEA (Italy), in collaboration with CEA/IRFM, to study, design and produce two prototype samples.
The ITER Organization provided the raw conductor, while the ENEA took care of the "jacketing" operations and manufactured the lower box. IRFM was entrusted with the realization of the terminals and the instrumentation.
Both teams worked in close cooperation. The first sample was successfully tested on the test bench SULTAN at the Institute Paul Scherrer, in Villigen (Switzerland). Testing of the second sample should be complete by the end of the summer.
CEA also participated in the supervision and analysis of the test results. Tests carried out on the first sample indicate good performances that confirm the quality of the poloidal field conductor design, as well as the validity of the work performed by ENEA and IRFM teams in the manufacturing process and instrumentation of the sample.
This constitutes an important and promising step on the critical path to qualify the ITER poloidal field conductors.
South Korea will soon conduct the third operation campaign of the Korea Superconducting Tokamak Advanced Research device (KSTAR) at the National Fusion Research Institute (NFRI).
During the first and second operation campaigns, KSTAR superconducting magnets showed reliable operation characteristics up to the designed value of 3.5 Teslas.
Major experimental goals of the third campaign are to achieve D-shaped and diverted plasma over 500 kA and to study the plasma behaviour during the application of the heating systems, amongst which will be a newly developed neutral beam injector system.
KSTAR was significantly upgraded following the second operation campaign and in preparation for the third. All the plasma-facing components are now installed inside the vacuum vessel, as are the sixteen segmented in-vessel control coils that are positioned behind the plasma-facing components.
During the upcoming campaign, the first of three ion sources in the neutral beam injection system, designed to deliver 8 MW, will be commissioned to provide 1 MW beam power.
The neutral beam injector system has been designed to deliver the deuterium beam for 300 seconds.
Wu Bangguo, who visited ITER on Tuesday 13 July, has chaired the Standing Committee of the National People Congress (NPC) of China for the past seven years. One understands that the energy issue is of particular interest to him.
Under Wu Bangguo's leadership, the NPC ratified the ITER Agreement in August 2007. "Three years ago," said ITER Director-General Kaname Ikeda in his welcome address, "you set this unique science endeavour into motion."
Since then, as ITER Deputy Director-General Shaoqi Wang summarized in his presentation, impressive progress has been made. The ITER Organization is now fully established, the design of ITER is finalized and manufacturing of the various components is in full swing all around the globe.
"I am very impressed by the scale of the project and the scope of the international collaboration," said Wu Bangguo. "ITER," he added "represents our hope in the energy of the future."
"Developing fusion as a reliable source of large-scale energy remains a tremendous challenge," said Kaname Ikeda. "It requires (...) the unfailing political will of the world's leading nations".
Chairman Bangguo's visit to ITER, last Tuesday, was a sure sign of that commitment.
Read the press release in English...
Lire le communiqué de presse en français...
This week, we tune in to Chinese National TV CCTV and more specifically to a selection of programs that have focused on ITER over the past four years.
In 2006, the CCTV talk show Dialogue with policy makers featured an interview with former science minister Xu Guanhua, one of the signatories of the ITER Agreement at the Élysée Palace in Paris on 21 November of that year.
Two years later, CCTV reported on the establishment of the Chinese Domestic Agency.
Last month ITER was featured again as CCTV covered both the sixth meeting of the ITER Council in Suzhou and the "ITER and Nuclear Fusion Exhibition" that the Chinese Domestic Agency had organized in the city's Industrial Park.
Summer days in Provence are filled with the sound of cicadas. As soon as the temperature rises above 28 °C, the air begins to vibrate with their song, one of the loudest any insect can produce. Some cicada songs can reach up to 120 dB, as loud as a power saw or a motorcycle.
Whether you call it noise or music, the cicada song is a love call. It is the eternal story of the male seeking his partner, and not being very discreet about it at that ...
Unlike crickets, who rub their legs together to produce a "stridulation," male cicadas possess a special membrane, called a "timbal," that they contract and relax at very high speed.
Amplified by their abdomen, which is almost hollow, the fast-following clicks create the deafening noise that is characteristic of summers in Provence.
But so much for entomology ...
Besides being a symbol of Provence—one can find kitsch ceramic cicadas in just about every tourist store—the cicada is synonymous in the French language and culture of mindlessness and insouciance. And this is all due to Jean de la Fontaine (1621-1695).
One of the most famous pieces of the French fabulist, called La Cigale et la Fourmi, generally and wrongfully translated in English as "The Cricket and the Ant", features the thrifty, hard-working little ant who spends his summer collecting food for "when the north wind doth blow," and the happy-go-lucky cicada who does nothing but "sing her song all summer long."
When winter comes, the cicada goes begging to her neighbour the ant "for a little grain 'til summer comes back again." The ant in the fable however, being self-righteous and stingy, replies with: "You sang did you?" ... "Well, dance now!"
Every child in France learns this fable by heart at primary school. This is why only foreigners rejoice in the summer song of the cicada. For all former French schoolchildren, it is the sound of an impending drama—the winter starvation of the carefree cicada.