LHC: Delivery of the superconducting cable reaches the half-way point!
Less than half of the superconducting cable needed for the LHC magnet coils now remains to be produced.
A total of seven thousand kilometres of superconducting cable is needed for the twenty kilometres of LHC magnet coils. For the last four years, this cable has been in production in four factories in Europe, one in Japan and one in the United States. A total of four companies are involved, namely Alstom, European Advanced Superconductors, Outokumpu and Furukawa.
About 45 km of cable is delivered to CERN every week and checked before being sent to the factories of the magnet manufacturers for winding. At the end of January and the end of February, respectively, half the outer cable and half the inner cable had been delivered, leaving only 3500 km of cable to be manufactured!
This superconducting cable will be used for the main LHC magnets, i.e. the dipoles that will guide the particles in the LHC ring and the quadrupoles that will focus the particle beam. The dipoles require two kinds of cable, an inner and an outer one, each measuring 15.1 millimetres wide. The inner cable comprises 28 strands, each made of some 8900 7-micron filaments of niobium-titanium (the superconducting alloy) coated with a copper matrix, while the outer cable comprises 36 strands of some 6400 6-micron filaments. The quadrupoles consist exclusively of the outer cable. The insertion quadrupoles - placed either side of the experiments' detectors to help to increase the beam luminosity at the collision point - require special cables measuring about 8 millimetres across.
One of the difficulties involved in producing the cables is the need for strict compliance with the set dimensions. Initial precision measurements of the dimensions and mechanical tests are carried out in the factory during the production phase. The same tests are then repeated on approximately 35% of the cables at CERN, on the cable inspection lines in Building 103. "This control process has enabled us to improve production quality. Today, fewer than 1% of cables are rejected" underlines Lucio Rossi, Head of the Magnets and Superconductors Group.
The cables are then subjected to cryogenic tests at 1.9 K in Building 163, in the course of which almost 8000 measurements are taken every year. These tests involve checking, in particular, the critical current of 13000 amps (and thus zero volts, thanks to superconductivity!), magnetisation and the conductivity of the stabilising copper, in other words all the properties of the cable at cryogenic temperatures. These properties govern the uniformity and quality of the nominal field of 8.33 Tesla that will be produced and thus the quality of the beam. Every step is taken to ensure that the cable does not heat up, which would cause it to lose its superconductivity.
The delivery of the superconducting cable for the LHC magnets is now on schedule (see graph pg.2). Now that the production has reached the half-way stage and is up to cruising speed, there are less than two years to go before the completion date. For Lucio Rossi and his supercondutor team, headed by Luc Oberli, "the battle is still on"!
