Moles for LHC magnet testing
Custom-designed test benches will be used to test the magnetic properties of the dipoles directly in the premises of the assembly firms.
The LHC project teams have one thing on their mind - ramping up the production of the dipoles. Participating in this process are the Industrial Systems Section of AB Division's Control Group (CO/IS), AT Division's Magnets and Superconductors Group (AT/MAS) and, since the beginning of the year, the Magnet Tests and Measurements Group (AT/MTM). These are the teams that have been putting their heads together to come up with a way of automating the magnetic acceptance tests of the LHC dipole magnets. Together, they have developed, assembled and tested a magnetic measurement bench that is now being dispatched to each of the three firms responsible for assembling the 1232 dipole magnets to be installed in the LHC - Alstom in France, Noell in Germany and Ansaldo in Italy. With the help of these new benches it will be possible to test a 15-m dipole entirely automatically in little over two hours. Previously, measurements with a provisional system tokk from 5 to 6 hours.
The bench uses two probes, imaginatively nicknamed "moles", an electronic component and control software. The purpose of the moles is to make parallel measurements of each aperture of the dipole. True to their name, they burrow through the heart of the magnet, measuring its magnetic properties as they go. Each one consists of a series of coils rotated by a small motor. As the magnetic field characteristics are being tested at room temperature only a very low current (less than one thousandth of the nominal value) is needed to power the dipole. Each mole is pulled by a cable, itself connected to a motor on the outside of the dipole. As the measurements are taken, the motor reels in the cable, pulling the mole slowly through the magnet and allowing precise measurements to be taken over its entire length.
The bench is supplied complete with a workstation and bespoke software, custom-developed to configure the measurement equipment for the task in hand and to carry out the tests, analysis and data storage.
Each of the three firms will ultimately be supplied with two of these benches to measure the magnets at two different stages of production - before and after their insertion into the collared coil inside the cold mass. CERN teams are installing the device in the firms' premises and providing staff training and maintenance services, while the staff of the firms are responsible for conducting the series measurements. "The measurement results are forwarded in real time to CERN," explains Hubert Reymond of AB Division's Control Group, "allowing the experts in the AT-MAS Group to make quick checks on the magnetic field quality without interrupting production."
The objective is to do high-precision quality control of the cold-mass assembly process. "Field quality control is crucial to the smooth operation of the LHC," adds project leader Vittorio Remondino (AT-MAS). "On top of that, by detecting manufacturing faults during assembly we are able to minimise the series production costs."
These tests allow the acceptance of each magnet produced by industry. Once delivered to CERN, the magnets will endure a new battery of tests in conditions closer to those of their final use and, hence, their working temperature (1.9 K, or -271°C).
