DEVELOPMENTS TOWARDS REMOTE METROLOGY FOR COMPONENT ALIGNMENT UNDER CONDITIONS 
OF RESTRICTED ACCESS IN JET'S TOROIDAL VACUUM VESSEL 
B. Macklin, R. Brade, G. Celentano, J. Tait, E. van Lente 
JET Joint Undertaking, Abingdon, Oxon, OX14 3EA, UK 
Commission V, Working Group 3 
KEY WORDS: Fusion, Photogrammetry, Electronic Theodolite, Radiation, Laser Scanning 
ABSTRACT 
The JET Joint Undertaking was established in 1978 to construct and operate the Joint European Torus (JET) at Culham in the UK. 
JET is the world's largest fusion experiment funded and staffed by the EU member states and Switzerland. Its aim is to prove the 
scientific feasibility of nuclear fusion as a new energy source. 
A major component of the JET machine is a large (200m?) toroidal vacuum vessel whose interior is subject to regular modifications 
and upgrades. The installed equipment has increased in quantity and complexity while the working environment has deteriorated 
due to increasing radiation levels and the presence of highly toxic beryllium dust. Progress in plasma physics has led to a 
requirement for much improved alignment accuracy. This paper describes the evolution of the survey and alignment methods used 
to accomodate the requirements of increased accuracy and complexity and the wearing of full pressurised suits. The ultimate aim is 
to carry out checking surveys remotely to an acceptable tolerance. 
1. INTRODUCTION 
1.1 Nuclear Fusion 
Nuclear fusion is the energy producing process which takes 
place in the sun and stars. Energy is released when the nuclei 
of light elements fuse together to form heavier ones. The 
easiest fusion reaction to achieve is between the two heavy 
isotopes of hydrogen (tritium and deuterium). In a fusion 
reactor the heat generated from this reaction could be extracted 
to raise steam for conventional electricity generation. The aim 
of the JET project is to prove the scientific feasibility of fusion. 
Nuclear fusion is likely to be Europe's best long-term solution 
to the energy problem. The JET machine is used for advanced 
research into plasma cofinements, boundary interactions, 
heating and fuelling of plasma. To monitor these experiments 
there are numerous diagnostic instruments and systems. 
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l'igure 1. Diagram of the JET Machine 
2. THE JET MACHINE 
2.1 The JET Machine 
The JET device (figure 1) consists of a vacuum vessel in which 
the plasma is created and confined, the magnetic field 
components (the coils) which position the plasma and the 
mechanical structure which encloses the central components of 
the machine and resists the large forces produced due to 
interactions between the currents and the magnetic fields. 
The double walled toroidal vacuum vessel is suspended within 
the cast iron mechanical structure shell. This shell is mounted 
within the large transformer limbs for which the plasma forms 
the secondary winding. Between the mechanical shell and the 
vacuum vessel there are 32 large D-shaped toroidal field coils. 
The vacuum vessel, which is manufactured from inconel, has 
major and minor radii of 2960 and 1315mm, with an internal 
height of 4300mm. It has a volume of 200m’, weighs 108 
tonnes and is designed to operate at a vacuum of 10? mbar. 
JET requires 700MW of power for each pulse of up to one 
minute. This is supplied by the National Grid and two large 
flywheel generators. 
JET uses the Tokamak magnetic field configuration to maintain 
isolation between the hot plasma (up to 300 million degrees 
celcius) and the vessel walls. The primary winding of the 
transformer, situated at the centre of the machine, is used to 
induce the plasma current. The toroidal plasma acts as the 
single turn secondary winding of the transformer. The toroidal 
stabilizing field is generated by the 32 toroidal D-shaped coils. 
Around the outside of the mechanical structure but within the 
confines of the transformer limbs are six poloidal field coils 
which are used for shaping and positioning the plasma. 
330 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996 
  
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