°ÄÃÅÁùºÏ²Ê¸ßÊÖ

If one excludes such monsters as the Taisun crane at the Yantai Raffles Shipyard, in Yantai China, capable of lifting 20,000 tonnes, the °ÄÃÅÁùºÏ²Ê¸ßÊÖ assembly crane, with a lifting capacity of 1,500 tonnes, can be counted among the strongest in the world.   The °ÄÃÅÁùºÏ²Ê¸ßÊÖ assembly crane—actually two 750-tonne cranes working in tandem—will provide synchronized lift and millimetre-scale positioning for the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Tokamak components. The system will be complemented by two smaller 50-tonne auxiliary cranes.   In July, the European Domestic Agency Fusion for Energy awarded the contract for the design, certification, manufacturing, testing, installation and commissioning of the four cranes to a German-French consortium, NKMNOELL-REEL, formed by NKMNoell Special Cranes GmbH, Germany and REEL S.A.S., France. The contract, worth approximately EUR 31 million, also includes the 120-tonne capacity Tokamak cargo lift that will move activated components from the Tokamak to the Hot Cell facility during the Operation Phase.   The Final Design Review for the assembly cranes, which started off at °ÄÃÅÁùºÏ²Ê¸ßÊÖ on Monday 30 September with the presentation of the design, generated only minor comments.   The design of the cranes must integrate the wider context, taking decommissioning requirements into consideration and also integrating the crane system into the structures of both the Assembly Building and the Tokamak Complex. However the review, chaired by °ÄÃÅÁùºÏ²Ê¸ßÊÖ's Central Engineering and Plant Directorate head Sergio Orlandi, strongly stressed the necessity of integrating the cranes in respect to the wider context—a "double" integration taking decommissioning requirements into consideration in the crane system design, and integrating the crane system into the structures of both the Assembly Building and the Tokamak Complex Building (two constructions that differ in almost all aspects).   "Decommissioning the installation once the °ÄÃÅÁùºÏ²Ê¸ßÊÖ scientific program is completed some thirty years from now is the responsibility of France," explains Sergio. "However, it is rational for the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization to design a system that will be used for both the assembling of the machine and for its dismantling. To me, integration for both phases is the key point. And this, as the design review pointed out, can be done with later minor refurbishing"   The assembly cranes will move along rails from the Assembly Building to the Tokamak Complex and back to position the components: the design review stressed the "critical point" of connexion between the two structures that must be addressed. The design review also addressed what Sergio calls "a critical point": the connexion between the Assembly Building and the Tokamak Complex whose combined length will be travelled by the cranes as they move from one building to the other to position the pre-assembled components of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Tokamak.   Central to the connexion challenge are the seismic joints that must allow for the progressive settlement of the 360,000-tonne Tokamak Complex. "After five or six years," explains Orlandi, "the building will have 'sunk' some 7 to 10 millimetres relatively to the Assembly Building which is much lighter. This is normal but it is something we have to take into consideration."   We are still two years away from the beginning of assembly operations. "The crane is a very good crane. We have absolutely no worry about it. But integration has to get deep into our culture. Integration will insure that we have a safe and functional behaviour of the whole system in all conditions."

After an intensive effort to improve the capability of °ÄÃÅÁùºÏ²Ê¸ßÊÖ's central solenoid conductor, the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization has concluded that a technically reliable and economically viable solution has been found. This successful result was obtained through a concerted collaborative effort on the part of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization, especially with the Domestic Agencies of Japan and the US, and the international superconductivity research community. The key element of the solution was designing the conductor using a "short twist pitch."  The Japanese strands using this technology confirmed the excellent results obtained during a preceding R&D phase and even enabled the qualification of two additional Japanese strand suppliers for the central solenoid conductor production.   The °ÄÃÅÁùºÏ²Ê¸ßÊÖ central solenoid is one of the most challenging superconducting magnets ever designed. It is made up of a stack of six, independently powered coil modules. The coil stack has a total height of 13.5 metres and an outer diameter of 4.1 metres. One particularity of the central solenoid is that it will be used to inductively drive 30,000 plasma pulses of 15 MA with a burn duration of 400 s.   During their life time, the central solenoid coil modules will have to sustain severe and repeated electromagnetic cycles to high current and field conditions. The most solicited modules are the middle modules in the stack, which will experience up to 60,000 cycles to a maximum peak field of 13 T. This is way beyond anything a large superconducting magnet of this kind has ever experienced. Another challenge is that the °ÄÃÅÁùºÏ²Ê¸ßÊÖ central solenoid is a joint in-kind procurement: the US Domestic Agency is responsible for the central solenoid coil stack, while the Japanese Domestic Agency is responsible for the central solenoid conductor.   A cross section of °ÄÃÅÁùºÏ²Ê¸ßÊÖ's solenoid Cable-in-Conduit-Conductor. Copyright: °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization Like all other °ÄÃÅÁùºÏ²Ê¸ßÊÖ magnets, the central solenoid relies on a Cable-in-Conduit Conductor (CICC) made up of a rope-type cable that is inserted into a stainless steel conduit where a forced flow of supercritical helium circulates. For the central solenoid, the cable relies on 576 superconducting strands mixed with 288 pure copper strands and assembled in five stages around a central cooling spiral. The conduit has a circle-in-square shape and relies on a special high manganese austenitic steel with excellent low fatigue crack growth rate properties at cryogenic temperatures. To achieve the required high field, the superconducting strands are made out of a special alloy made of niobium and tin (Nb3Sn), a material with good current transport properties but that, once formed, becomes brittle and strain-sensitive and which must be handled with care.   The first performance qualification samples of °ÄÃÅÁùºÏ²Ê¸ßÊÖ central solenoid conductors that were tested in the SULTAN facility in Villigen, Switzerland, exhibited excessive degradation as a function of electromagnetic and thermal cycling and did not meet the performance criteria under the SULTAN configuration, which is defined for stable operation of the central solenoid during the life cycle of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ machine.    Following these unexpected results, the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization in early 2010 launched a comprehensive R&D program, with the support of the US °ÄÃÅÁùºÏ²Ê¸ßÊÖ Domestic Agency and Oxford Superconducting Technology (US), to investigate alternative conductor configurations that could potentially achieve more stable performances. This EUR 1.1 million program was successfully completed in May 2012 and a clear solution emerged: among the four variants that were tested, the conductor with the so-called "short twist pitch" configuration behaved as required.    In the "short-twist pitch" set-up, the strands are mechanically better supported and have little room for deleterious bending resulting in almost non-existing degradation as a function of electromagnetic and thermal cycling. The test results even show a slight increase in performance, likely due to compressive strain relaxations that may not be representative of in-coil operation.   The results of the R&D demonstrated that cycling degradation was not inherent to Nb3Sn CICCs and that a technical and economically viable solution could be found to this challenging issue. It remained for the Japanese manufacturers to demonstrate that the short twist pitch configuration could result in the same performance on their strands. In order to do so, the Japanese Atomic Energy Agency (JAEA) prepared a number of samples that were meant to match or even surpass the performances of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization samples. The first of these samples (referred to as CSJA3) was tested in November-December 2012. The tests in SULTAN confirmed the excellent results obtained with the short twist pitch sequence, which demonstrated the best performance. It also enabled the qualification of two additional Japanese strand suppliers for central solenoid conductor production.   The story of central solenoid conductor development is a good example of how scientific collaboration across many borders can lead to solutions for even the most extraordinary challenges of building the °ÄÃÅÁùºÏ²Ê¸ßÊÖ machine—a device that pushes most technologies to their limits and calls for innovative solutions.   Special thanks to Arnaud Devred, °ÄÃÅÁùºÏ²Ê¸ßÊÖ Superconductor Section Leader, for his contribution to this article. 

​In order to improve project performance and in light of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Project's specific managerial and cultural complexities, an External Management Advisory Board (EMAB) was established earlier this year. This week, the members of the EMAB convened for their first meeting at °ÄÃÅÁùºÏ²Ê¸ßÊÖ Headquarters. The objective of the EMAB is to advise the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization's senior managers and the Director-General on enhancing project and safety culture, a challenging activity in the context of a mega international project with seven Members. Also, the Board is charged with assessing the practical implementation of the set of actions that was decided in response to the Management Assessment carried out in 2013. The Chair of this new entity is Jean Jacquinot, who also serves as scientific advisor to the Chairman of the French Alternative Energies and Atomic Energy Commission (CEA), Bernard Bigot. Other Board members are Michael Tendler, professor at Sweden's Alfvén Laboratory (Royal Institute of Technology); Richard Hawryluk, head of the department of °ÄÃÅÁùºÏ²Ê¸ßÊÖ and Tokamaks at the Princeton Plasma Physics Laboratory (US); Dhiraj Bora, director of the Institute for Plasma Research, IPR (India); and Yuanxi Wan, Academician of the Chinese Academy of Sciences and former Chairman of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Science and Technology Advisory Committee (STAC). °ÄÃÅÁùºÏ²Ê¸ßÊÖ's Colette Ricketts, of the System Management Section, is in charge of the secretariat. "During our first meeting held on 20-21 October, we had a very fruitful discussion," the Board members reported after the first meeting. "We openly addressed issues such as the project's nuclear and safety culture, options for improved alignment between the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Organization and the Domestic Agencies, and last but not least the creation of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Chief Executive Team, (ICET), formed to improve collaboration between all actors of the °ÄÃÅÁùºÏ²Ê¸ßÊÖ Project." The Board will continue to address key °ÄÃÅÁùºÏ²Ê¸ßÊÖ management issues at its next meeting, scheduled for 11-12 December 2014.

​Princeton Plasma Physics Laboratory is organizing a colloquium on TFTR  record fusion power shot of December 1993. More information here.