The ITER divertor is located at the base of the vacuum chamber and its main function is to extract most of the helium from the plasma, while minimizing the impurity influx to the plasma. As the main interface component between the plasma and material surfaces under normal operation, it has to tolerate the highest heat loads of all the plasma-facing components.
The divertor design needs to provide an engineering solution compatible with today's plasma physics expectations but, given the uncertainties in extrapolating the future progress in plasma physics (and thus in component durability), the design also needs to provide the highest flexibility in terms of possible modifications of the plasma-facing component configuration and ways for rapid replacement and refurbishment.
The divertor consists of 54 cassettes (six per vacuum vessel sector) that are inserted radially through three lower level ports and moved toroidally before being locked into position.
The cassette body is reusable and designed to provide neutron shielding for the vessel and to provide a mechanical support for the plasma-facing components and a variety of diagnostics.
The divertor plasma-facing components, together with the toroidal field magnet conductors and the blanket modules, require a qualification by each party prior to the start of the procurement. This means that each party allocated one of these critical procurement packages must first "qualify" by demonstrating its technical capability to carry out the procurement with the required quality, and in an efficient and timely manner. This is achieved via the successful manufacturing and testing of medium-size qualification prototypes.
After manufacturing is completed, the divertor qualification prototypes, which include all the most technically challenging features of the corresponding ITER divertor design, will be subject to performance tests in the TSEFEY-M electron beam facility at the Efremov Institute, Saint Petersburg, Russia, to assess their heat flux load carrying capability.
The European, Russian and Japanese Domestic Agencies are involved in this qualification program, which was first presented to them by the ITER Organization at the ITER Divertor Meeting held in Genova, Italy on 26-28 October 2005. Extensive technical and administrative negotiations followed, which culminated with the approval of the Memorandum of Understanding on the Procurement of the ITER Divertor in July 2006. This document, together with the ITER Divertor Procurement Plan which was agreed at technical level and explicitly recalled in the Memorandum of Understanding, paved the way for the preparation of the detailed technical specification as well as the acceptance criteria of the qualification prototypes. This preparatory work was then formalized in Qualification Task Agreements, which were signed by the ITER Organization and the Domestic Agencies concerned during the first half of 2007.
Each Domestic Agency has to deliver at least two qualification prototypes by mid-2008. The protocol for the performance tests was formalized in a High Heat Flux Testing Task Agreement between ITER Organization and the Russian Domestic Agency on 14 June 2007. More recently, in June 2008, a customs agreement on the temporary admission of the qualification prototypes into Russia was signed to ensure a smooth import and export of the components from Europe and Japan.
The performance tests are due to be completed by the end of 2008, thus allowing the finalization of the three Procurement Arrangements on the divertor plasma-facing components by February 2009, a date which has remained unchanged since it was first proposed to the Domestic Agencies in mid-2005.
In last week's edition of ITER Newsline we reported on the successful tests of the PF Insert Coil conducted in Naka. Last Monday, 23 June, the conductor was successfully taken up to an operating point of 52kA at 6.5T and 4.6K. In this week's issue, Neil Mitchell, Head of ITER's Magnet Division, explains in more detail what exactly is happening in Naka these days.
The PF Insert Coil is currently being tested in Naka. What exactly is the PF Insert Coil and how is it made?
The PF Insert Coil is made from a 40m length of conductor for the ITER Poloidal Field Coils. The conductor is made of 1400 NbTi strands in what is called a cable-in-conduit configuration. The strands are about 0.75mm in diameter and are twisted together inside a steel tube. Helium flows in the gaps between the strands. The 40m of conductor is wound in a spiral and put inside the bore of the Central Solenoid Model Coil facility at Naka.
Can you describe what exactly is being tested, what is the goal of these tests?
The tests last about nine weeks. The first priority has been to measure the superconducting performance of the conductor. All superconductors have a limited range of operation (depending on field, current density and temperature) in which they remain superconducting. If these limits are exceeded, the conductor quenches. This means it becomes normal conducting and the current has to be decreased rapidly as the sudden increase in resistance means that the temperature increases rapidly so that the strands would melt in a few 10s of seconds. The PF Insert Coil thus allows us to measure the limit of the operation range under the same conditions as will be experienced in ITER's six PF coils (in particular the high field PF6).
These tests are performed in a special test facility in Naka. What makes it special?
The Central Solenoid Model Coil, set up in the testing station at JAERI in Naka, Japan, is a large Nb3Sn coil we built about eight years ago in the ITER EDA to test conductors up to 13T. For the PF insert we will test up to about 10T. It is the biggest Nb3Sn coil in the world (it uses about 27t of Nb3Sn material and the coils themselves weigh 110t) and the stored energy is about 700MJ, approximately comparable with the TF system of Tore Supra. It has a large bore into which insert coils can be fitted.
Talking about the latest promising results. What has been achieved and how do we interpret the recent results in regard to ITER operation.
The PFI conductor has performed at the level expected on the basis of the performance of the strands making up the cable. There is no degradation and no unexpected stability limits that have been known to reduce performance in NbTi coils (using different conductor designs). We actually designed the coil with a 1.5K temperature margin to the limiting performance (so that for example at 6.4K the coil operates with a current of 52kA and a temperature of 4.5K, but the limiting temperature at which quench occurs is 6.0K. We had expected that about 0.5K of this may be lost due to degradation and/or stability but actually it has not been, so we have possibly a little larger operation window than we expected. This is important for the operational window of the plasma as the PF6 coil capacity is one of the determining factors.
Chandresh Hansalia took his first steps in fusion at the Indian Institute for Plasma Research. The centre for thermo-nuclear fusion research was founded by the current Chairman of the Science and Technology Advisory Committee, Predhiman Kaw, in 1986. As the institute has now turned into being the Indian Domestic Agency for the ITER Organization, Chandresh Hansalia was in for some international exposure.
Chandresh Hansalia arrived at ITER on 3 March, 2008. He is an Instrumentation & Control Engineer at the Department for CODAC & IT, Heating and CD and Diagnostics (CHD). On his arrival, he found that the CODAC team was still in its formative stage and the CODAC & IT Division Head, Dr.Wolf-Dieter Klotz, had joined ITER on the same day. So, the team coach did arrive and now the team was waiting for its captain to arrive, the new CODAC Responsible Officer, Anders Wallander.
"Working in such a multi-cultural environment as ITER is a totally new and refreshing experience," he says. "Issues at CODAC are quite varied and challenging but the team spirit seems very high. Being a football freak, our captain seems to know the virtue of a good team. And having a coach with a very good sense of humour makes life so much easier, especially when certain issues are bugging our minds to no end!"
Chandresh and his wife Ila found a place to live in Manosque, but their 18 year old son has had to stay back home in Goa, India, where he is going to an engineering college for Electronics & Instrumentation—thus following the footsteps of his father.
"People are very friendly and hospitable in our neighbourhood. In order to be able to socialize with them I am doing my best to learn French as quickly as I can."
For several months now, scrapers, rock-crushers and Caterpillars have been moving tens of thousands of cubic metres of dirt and debris in order to prepare the site for the reactor's foundations. Soon the "first concrete" will be pumped into the ground and in a matter of years the first buildings will be completed.
ITER? No, we are talking about the Reactor Jules Horowitz (RJH), a research facility which is being built at CEA Cadarache, two miles, as the crow flies, from the south of the ITER site.
Jules Horowitz (1921-1995) was a Polish-born French scientist who pioneered the field of "reactor physics" in the 50s. Breaking away from a long-established tradition of poetic acronyms—Osiris, Phebus, Rapsodie, etc—CEA has named this new installation after one of the legendary figures in its history.
Reactor Jules Horowitz will be devoted to studying materials and fuel behaviour under irradiation. It will be able to recreate the physical and chemical environments of all existing and projected power reactors. Its contribution will be essential to the development of the fuels and materials for the new Generation III power plants and for the Generation IV fast neutron reactors of the coming decades.
Since material stress and fatigue in fast neutron and in fusion reactors present similar challenges, ITER and fusion will also benefit from research done at RJH.
"All European Material Testing Reactors were built in the 60s, explains Gilles Bignan, the user's facility interface manager at RJH. By 2015-2020, they will have reached their age limit. We needed at least one facility to cope with the growing needs of our community."
Powerful (100 MW), modular, and highly versatile, RJH will be able to accommodate some 20 simultaneous experiments. "The instrumentation which has been developed will allow us to do real-time analysis. Until now, with the existing installations, we could mainly do 'post-mortems'..."
The Chinese Domestic Agency has been approved by the Chinese government and the formal establishment will take place after the summer. The good news was announced by former Vice-Minister Jinpei Cheng at the recent ITER Council meeting in Japan. In the middle of June, just before the Council meeting, the document applying for the establishment of the China DA was approved by the State Council.
The ITER China Office is located near the Ministry of Science and Technology in Beijing. Currently, there are 20 people working with the prospect of increasing the staff around the end of the year. The ITER China Office will be in charge of Procurement Packages allocated to China according to Common Understanding reached during the ITER negotiations. It will also coordinate domestic fusion research and development.
Last week, the ITER Organization and Jacobs Engineering UK Limited signed a Preliminary Architectural & Engineering Design Services Contract. The contract is focused on developing the preliminary design of the ITER facility buildings and site infrastructure to a level sufficient to support tendering the detailed design (architectural/engineering services) later this year. Invitations for this tender will be issued by the European ITER Domestic Agency "Fusion For Energy" (F4E). The 12-month contract is worth €6.5 million and is the biggest contract placed so far by the ITER Organization.
Download Jacobs' press release here...