Phoenix rises to the ITER challenge

It's not easy containing a plasma at 150

C. Our Sun, fortunately, cannot keep energy to itself, even though it is 10 times cooler but scientists running the

(ITER) require a vessel that must not be breached if their research into nuclear fusion is to succeed.

Phoenix Inspection Systems of Warrington is designing and building ultrasonic non-destructive testing equipment that can be used to check the quality of the welds on the ITER vacuum vessel, where the high temperature fusion plasma will be held.

The doughnut-shaped vessel — 15m high and 25m diameter — will be made of nine segments of an austenitic alloy that will be joined either by tungsten inert gas welding or electron beam welding.

The challenge for Phoenix is to perfect testing equipment that can detect defects in such narrow gap welds and in metals that have coarse grain structure. And the job has to be done from within the finished vessel itself.

To get around inside ITER's doughnut the Phoenix inspection head will hitch a ride on the robot that will have been used to carry the welding equipment. The TIG welds will be typically 10mm wide, and previous work has already shown that the techniques Phoenix propose can detect defects as small as 4mm2.

'Narrow gap welding processes make for more rapid production with less use of filler metals,' said Phoenix special projects manager John Turner. 'But the coarse grain structure in the weld metal makes it difficult for the ultrasound beam to penetrate and detect defects that may be present. We have found that low-frequency waves and the use of ultrasonic phased array devices in conjunction with more established techniques can help overcome these problems.'

The company, which specialises in developing machines for the nuclear and power sectors, has been awarded a €320,000 (£220,000) contract to design and build the prototype.

Managing director Karl Quirk believes there is a good chance that the machine, when finished next summer, will actually be used on the finished ITER vessel when it is constructed at

.