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ALEPH coil hits the road

1 July 1987

The giant 1.5 T superconducting solenoid for the ALEPH experiment at LEP demanded special tooling for winding, impregnation, fitting and transport, as the July 1987 issue reported.

Convoy carrying the superconducting magnet for the ALEPH experiment

The size and precision of compo­nents for the four big experiments being prepared for CERN’s new LEP electron–positron collider make special demands on designers and manufacturers.

An example is the superconducting solenoid for the ALEPH experiment at CERN’s LEP electron–positron collider, contracted to the lnstitut de recherche fondamentale of the French Atomic Energy Commission (CEA) in 1983.

It was designed and built by engineers and technicians of the Department of Elementary Particle Physics of the CEN’s Saclay Laboratory. Recent tests at Saclay were highly successful, with current attaining 60 per cent of its design value, the (temporary) absence of shielding not permitting it to go any higher.

Weighing 60 tons, 5 metres across and 7 metres long, the ALEPH solenoid produces a magnetic field of 15 kilogauss (1.5 tesla) in a volume of 130 m3. The use of a superconducting coil reduces electric power requirements by a factor of 40 and overall weight by a factor of four. Producing the required field involves 9 million ampere-turns and a stored magnetic energy of 130 million joules.

Special technology had to be developed for its manufacture in view of the dimensions of the coil and the constraints imposed by the detector design – minimum weight and a minimum of material to be traversed by the particles produced by LEP.

Applying this technology on the required scale called for special tooling for winding, impregnation, fitting and transport. Tests at Saclay checked that the adopted solutions could reach the required performance levels.

Special features of the coil also include: almost exclusive use of aluminium; superconducting niobium-titanium cable coextruded in a pure aluminium sheath (30 kilometres to handle a current of 5000 amperes); the collar constraining the magnetic forces being used as the winding mandrel – the conductor being wound inside the collar; vacuum impregnation of the coil; and indirect coil cooling through tubes welded on the collar.

Meanwhile the barrel yoke for the ALEPH magnet has been reassembled at CERN after initial assembly by Ferriera-Cattaneo and INNSE in Milan.

The coil for the other superconducting coil for a LEP experiment, that for DELPHI, is undergoing tests at Rutherford Appleton Lab­oratory, UK, while the barrel yoke using Soviet steel is being assembled at CERN. 

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