The Vacuum Vessel (VV) Final Design Review was held on July 21-23. This review was critically important to the project because the vessel is a safety class component that forms part of the first containment barrier. Also it is on the project critical path, and it interfaces with many different systems so its design has far-reaching effects.
The review was chaired by Brad Nelson from the US Domestic Agency (DA) and consisted of committee members, DA members as well as independent experts, from the EU, Korea, the Russian Federation and India. The scope of the review included the main Vacuum Vessel and its ports — including the ELM coil interfaces — which are included in the first VV Procurement Arrangements (PAs). Systems which will be included in these PAs later or in later PAs (such as the in wall shielding, blanket manifolds, and VV supports) were not included in the review but their interfaces were discussed.
Major topics discussed at the review included requirements (including safety and regulatory requirements), analyses, the design, interfaces, manufacturability, assembly plans, risk assessment, the schedule, and the annex B of the PA's describing the manufacturing requirements, drawings, welding and documentation and acceptance requirements. All of these topics are important but the analyses, interfaces, and topics related to tolerances (both manufacturing and assembly) were of particular interest to the committee.
After the intensive three day meeting, Brad Nelson took a positive view of the review had achieved. The functional requirements for the System Documentation appear to be met, the critical analyses have been done. Out of the 67 interface documents 23 have been signed. Also, the main interfaces between the ELM Coils and the Vessel are being defined. Thus the design and analyses are now sufficiently defined to allow the PA to be finalized — jointly with the DA's — so procurement can proceed.
Clearly, much work remains to be done particularly related to finalizing analyses, interfaces, and the incorporation of the ELM coils. But this review confirmed that the design meets the requirements and will help focus our efforts over the coming weeks as we move toward the completion of the PA. Completing the resulting action items from the review is critically important in order to proceed with the PA and thus it is one of the highest priorities for the project. As has been in the past, it will take a collaborative effort with all ITER technical departments to resolve these issues efficiently and rapidly so we can move forward.
On 24 July 2008, the ITER Organization formally accepted the two Qualification Prototypes supplied by the EU Domestic Agency within the Divertor Qualification Program. "These components have successfully completed all the required non-destructive tests and qualification procedures of the manufacturing process," said Mario Merola, Divertor Section Leader in the ITER Organization, "and I am very pleased to sign today their final acceptance. This event culminates several months of dedicated efforts and hard work, which was coordinated by the EU Divertor Responsible Officer Bruno Riccardi. The EU Domestic Agency is, since today, just a step away from its formal qualification, which is a prerequisite to start the procurement of the divertor, planned in February 2009."
The divertor plasma-facing components, together with the toroidal field magnet conductors and the blanket modules, require the qualification of the Member prior to the start of the procurement. This means that each Member allocated one of these critical procurement packages must first "qualify" by demonstrating its technical capability. In regards to the divertor, this is achieved in two steps: first, at least two medium-size "Qualification Prototypes" have to be manufactured and meet all the prescribed acceptance criteria, then at least one of them must withstand the high heat flux performance tests.
The two delivered prototypes were manufactured by the Austrian company Plansee and will be soon followed by a third prototype, supplied by the Italian Ansaldo Ricerche. These components will be shipped to the Efremov Institute in St Petersburg, Russian Federation, where they will be subject to high heat flux performance tests planned for September 2008.
The levelling of the ITER site is making progress — though a little more slowly than expected due to the stronger-than-expected sub-surface rock structure. Nevertheless, the first 1 million cubic meters of earth has been moved. Also, the five gates giving access to the ITER site are in place, the area for the contractors is almost completed and the work on the new temporary offices (JWS-2) is also progressing. It looks as if the first staff will be able to move into their offices later in October this year. Apart from participation in ITER and the Test Blanket Program, India is also proactively pursuing its own domestic fusion research program which includes the development of a prototype vacuum vessel, superconducting coils, divertor cassettes etc. To address the requirement of special steel fabrication techniques in all these activities, the Institute for Plasma Research in Gandhinagar organized a workshop on steels and fabrication technologies for fusion 21-22 July. The major objective of the workshop was to bring together experts in various Indian R&D organizations involved in developing special steels, materials modelling and materials processing such as Hot Isostatic Pressing (HIP) and welding technologies and to initiate joint activity to meet the requirements for immediate and long-term fusion programs. It's been 30 years, but Andre Junca, who was CEA-Cadarache director from 1974 to 1983, is still a very angry man. "What this guy wrote about Cadarache is a disgrace! We all fell into his trap..."
The "guy" in question was Dominique Lapierre, of the famous Franco-American duo "Lapierre and Collins", the acclaimed authors of such blockbusters as "O Jerusalem", "Is Paris Burning?" and "Freedom at Midnight". In 1978 they were researching a book about international terrorism and nuclear blackmail and asked to visit Cadarache's installations — "The Fifth Horseman", a reference to the Four Riders of the Apocalypse, was eventually published in 1980 in two slightly different versions, one in French, and one in English.
The cast of characters featured the President of the United States, "sad blue eyes" and "deep auburn hair"; Libyan leader Muammar Al Qadafi, a "son of the desert" then in his late thirties; a Palestinian terrorist named Kamal and his brother Whalid, a plutonium expert to whom the French had offered "a key position in the Phoenix programme", the breeder reactor CEA had developed in the late 60's.
In the terrorists' scheme, plutonium was to be stolen from Cadarache, where, in the French version of the book, "the largest plutonium stock in Europe, probably in the world" was stored. Dominique Lapierre, pretending to be researching for a sweeping historical epic on nuclear energy was granted a VIP tour of the installations. "I showed him everything, remembers Andre Junca, Rapsodie, Phebus, even the ATPu plant, and look what he came up with!"
According to Lapierre (p.77 of the French hardback edition), "getting in and out of Cadarache was child's play", the plutonium storage location was "clearly indicated by a pointing arrow on a road sign" and, should the terrorists seize the 200 drums it contained, the alarm would only be raised hours after the plutonium had been stolen: "The Gendarmerie in Peyrolles (7 gendarmes), in charge of protecting the installations, had only one telephone line. A five-year old wouldn't even need a stepladder to cut through it".
The book was to be a huge bestseller, selling millions of copies in more than 30 languages. "When it came out, I raised hell at CEA head offices, says Junca, now 83. Maybe we should have sued. But what could we expect? This guy was like all journalists..."
Princeton University has named Stewart Prager, the director of a fusion research project at the University of Wisconsin as the new director of the Princeton Plasma Physics Laboratory (PPPL), starting this fall.
Today, the independent assessment of the resource estimates for ITER construction started in the Chateau of Cadarache. The review is led by Dr. Frank Briscoe, the committee has two representatives from each party. This first meeting will last until this Thursday, a second meeting is scheduled for mid September. Frank Briscoe will then report the outcome to the ITER Management Advisory Council.
For more information on the "Briscoe Review" read ITER Newsline #40, published 17 July.
During plasma disruptions in tokamaks, the fast current quench generates substantial electromagnetic forces on the vacuum vessel and can also produce a significant current of runaway electrons (REs). The REs are accelerated in the high electric field associated with the current quench and resemble an electron beam with velocities close to that of light. Model predictions indicate that in ITER a runaway electron current of up 70% of the initial plasma current could be generated due to a "secondary avalanche" process. REs are eventually lost to the first wall and this can result in significant local energy deposition, which can potentially cause damage such as localized melting of the first wall surface. Assessment of the severity of such events requires an accurate quantitative specification of the characteristics of the energy deposition of REs, e.g., probable locations of deposition, time duration of loss process and incident angle of electrons, is of primary importance.
To eliminate the potential for such damage, development of techniques for mitigation of REs (i.e. avoidance of their generation and/or suppression of generated REs) is a key issue for ITER. To date, two potential methods, massive gas injection (MGI) and stochastic magnetic field application, have been investigated in current tokamaks. Both methods would require design changes or some upgrading of foreseen systems to be implemented. Therefore, their suitability for ITER must be assessed and the relevant physics guidelines must be specified in the near future.
To this end, a three-day workshop was held in Cadarache during 15-17 July under the leadership of Masayoshi Sugihara from the ITER Fusion Science & Technology Division, to review the latest information on the experimental characteristics of REs and the results of mitigation experiments, to update the ITER specifications in this area and to promote R&D studies in support of the design of the ITER RE mitigation system. 25 scientists and engineers from laboratories around the world and about 20 IO members participated in the workshop, listening to a series of presentations which revealed considerable progress in this area in recent years and contributing to several lively and productive discussion sessions on the implications of the results for ITER and for future R&D activities in response to ITER's needs.
Sugihara summarizes the main outcome of the workshop as follows:
Many devices observe a threshold in toroidal magnetic field (remarkably uniform at ~2T) and/or safety factor (qeff ~2) for the generation of REs at disruptions. Larger RE currents are generated for higher current quench rates. These data suggest that the present specifications of the frequency with which REs occur in ITER (i.e. it is assumed that REs are generated at every major disruption) and of anticipated RE current fractions may be pessimistic.
The possibility of controlling the vertical position of the RE beam using the proposed in-vessel coils was considered in relation to the fact that the spatial profile of the RE current will probably be more peaked than that of typical ITER plasmas. Nevertheless, if the position of the RE-dominated plasma could be controlled for sufficiently long, several possible RE suppression schemes could be applied, e.g., impurity gas injection, application of reverse one-turn voltage, interception by a dedicated sacrificial wall element, or application of a stochastic magnetic field.
Understanding of the mechanism by which massive gas injection mitigates RE generation has steadily progressed. The figure shows the penetration of injected gas into the TEXTOR plasma. All tokamaks demonstrate that REs are suppressed, even when density is below the predicted threshold density for suppression (commonly referred to as the "Rosenbluth" density). According to numerical studies, this can be explained by the induced stochastic magnetic perturbation in the plasma which occurs at the disruption.
The suppression of REs by an external magnetic perturbation has been demonstrated. The required magnetic perturbation is estimated as ~0.1% of the toroidal field in the spatial region in which REs are most likely to be generated (usually close to the pre-disruptive plasma centre).
Helium has been recommended as the optimum gas species for MGI. Pumping down the torus down to the required operating pressure after the injection of ~5 x 10^5 Pam3 of gas appears possible in a time of 3-4 hours with some additional investment, allowing an acceptable recovery time for plasma operation.
Building on the results of the workshop, the specification of possible mitigation schemes (including combinations of several techniques) will be updated and a programme of studies will be developed between the IO and Members' fusion communities to support further improvements in the understanding of RE characteristics and the processes contributing to their mitigation. This will provide important input for the design of the ITER disruption mitigation system.
ITER is an international organization — meaning it is a melting pot for fusion scientists and engineers from all over the world — east and west. But even Beijing or San Francisco, on the other side of the planet, seem to be more familiar to us than Vladivostok, Russia's biggest port situated on the Pacific Ocean, seven time zones away from Moscow. A few miles further out lies Kraskino, the hometown of Denis Stepanov. The young man with distinctive red curls and a charming smile has been a member of the ITER CODAC group since October last year and is in charge of the data management.
Denis obtained a degree in physics automation from the Novosibirsk State University in Siberia. After his graduation he worked on plasma traps at the Budker Institute of Nuclear Physics, one of the major centres for advanced study of nuclear physics in Russia. It is located in the Siberian town of Akademgorodok.
So, when Denis says that "moving to France and working for ITER is a big step for me" we know what he means. "This for sure is a big change to my life: a new country, a new environment, a new job and a new language." But the new territory doesn't scare Denis. He is willing to take the opportunity. So he is busy learning French and exploring French culture. And, by the way, he is going to get married soon.
The ITER-India personnel, presently 35 in number, has moved to the new office which is located in Gandhinagar, about 20 kilometres away from the official Domestic Agency Office at the Institute for Plasma Research. Also, about 12 CAD designers from contracted Engineering Services industries are presently working in the ITER-India Office. Most of the infrastructure, including a new Internet connection is in place and a separate 45 Mbps leased line linked directly to ITER, Cadarache is presently being commissioned. This allows the installation of the so-called ITER collaborative network connecting the two Design Offices in India and Cadarache along with the other DA offices and thus enables the safe and real-time exchange of data.