Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

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JUNE 27 TUESDAY AFTERNOON WS-18-TuA-INV.7 THE DESIGN AND OPERATION OF THE JET VAC- UUM AND FUELLING SYSTEMS AND THEIR RELEVANCE TO ITER. R J H Pearce, Euratom-UKAEA Association, Culham Science Centre, Oxon, OX14 3DB. UK . M. <strong>Wykes</strong>, ITER IT, IPP, Boltzmannstr. 2, 85748 Garching, Germany. JET is the world largest magnetic confinement fusion device and the only device with the capability to operate with tritium. JET first operated in 1983 and since this time it has been regularly enhanced and upgraded. Agreement is now well advanced for building ITER at Caderache in France. JET has played a key role in the ITER design, in particular by operating in deuterium/tritium, by testing divertor designs, in developing first wall technology, by operating with high power heating systems and in consolidating ITER operating scenarios. The JET main vacuum vessel is of doubled walled construction of volume ~200m 3 and is capable of being baked to 320 o C. It is pumped by turbo-molecular pumps in addition to a high pumping speed cryogenic pump in the divertor region. Typically JET now operates at 200 o C with a base pressure in the 10 -8 mbar region. The total pressure is dominated by deuterium outgassing and by the vapour pressure of deuterium held on the supper critical helium cryogenic pumps. Impurity partial pressures are in the 10 -10 mbar region. The JET vacuum vessel and other vacuum containment system also act as the primary containment system for tritium injected or stored in the JET. This necessitates the need for high integrity on all boundary components and double containment on delicate components. The vacuum characteristic of JET are significantly affected by plasma facing components. These have been an important area of development and change in magnetic confinement fusion devices. On JET the vacuum vessel’s first wall has been regularly changed, progressing from inconel, to graphite, to the current carbon fibre composite (CFC). In addition various experiments with partial beryllium coverage have been performed. A full beryllium wall with a tungsten coated, CFC divertor is planned for the future as a reference for ITER. The physics programme on JET has lead to demanding requirements for the supply of gas to the torus. In particular the pumped divertor necessitates scenarios with high fuelling rates. In total 12 fuelling points are used. It is required to deal with large numbers of gas species, expensive gas species, reactive gas species as well as tritium gas. An automated system is used for introducing gas into JET. The system gives the flexibility for gases to be changed frequently without compromising gas purity. Three successful experimental tritium campaigns have been performed on JET. An initial tritium inventory of 20g has been used for a total injection, to date, of ~36g. The experiments have provided very valuable experience in complex systems on, tritium handling, retention and accounting. New challenges will however be encountered within the ITER fuel cycle with ~3Kg of tritium proposed to be on site and ~850Kg to be injected through the life of ITER. The design and operation main JET vacuum and fuelling systems are described. These are compared with the proposed systems for ITER. Where there is particular ITER relevant experience, in the design, manufacturing, and operation of vacuum and fuelling systems, this is highlighted. <strong>82</strong>
JUNE 27 TUESDAY AFTERNOON WS-18-TuA-INV.6 QUALITY CONTROL AND LEAK DETECTION IN LARGE VAC- UUM SYSTEMS. P. Chiggiato. CERN, European Organization for Nuclear Research. CH-1211 Geneva 23, Switzerland. Large ultra-high vacuum systems can be jeopardized by the failure of a single vacuum component. As a consequence, a careful choice of materials, assembling techniques and surface treatments is mandatory in order to avoid leaks (both real and virtual) and excessive outgassing that could spoil the efficiency of the pumping system. However, even if the suitable choice of the production procedure is taken, a dedicated quality control plan is essential to avoid the result of clumsy operations and drifts in the production parameters. For the Large Hadron Collider (LHC), which is under construction at CERN and expected to run at the end of 2007, thousands of vacuum components are being produced and different quality control programs are applied. For the particular case of the about 1200 long straight section (LSS) vacuum chambers, the quality insurance program will be reviewed by taking into account the most critical steps of the production procedure, namely extrusion of the OFS tubes, vacuum brazing of the flanges, TIG welding, chemical treatment of the inner surface, and deposition of the Ti-Zr-V nonevaporable getter (NEG) thin film. Several characterization techniques are involved, for example X- ray radiography, optical and metallurgical analysis, leak detection, surface sensitive inspection (XPS and AES) and non-traditional vacuum measurements. The quality control plan continues also after the installation of the components in the accelerator ring or into complex devices like superconducting magnets and distributing field boxes. In this context, the validation criteria for the NEG film activation process in the LSS will be presented. In addition, an alternative method for detecting leaks in the complex cryogenic lines of the superconductive quadrupoles of the LHC will be described. In order to save and to simply retrieve the massive quantity of data coming from the different controls, a dedicated software has bee developed at CERN; for most of the components installed in the main ring, it allows the tracking of all the production and control reports together with the actual position in the accelerator. 81
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AUTHOR’S INDEX Aouabdia Y. 46 Aba
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PARALLEL SESSIONS 7
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Sigilum Universitatis Studii Salama
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