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

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. Wykes, 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.
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