mercredi 20 septembre 2017

Detectors: unique superconducting magnets

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20 Sep 2017

Image above: The enormous toroidal superconducting magnet of ATLAS during its installation. Each of its eight coils, the last of which is being assembled in this photo, is 25 metres long. (Image: ATLAS/CERN).

Even before they were used widely in particle accelerators, superconducting magnets were adopted for the detectors used to analyse collisions. A magnetic field is essential for identifying the particles emerging from collisions: it curves their trajectory allowing physicists to calculate their momentum and to establish whether they have a positive or negative charge. The stronger the field and the larger the volume on which it acts, the higher the resolution of the detector.

As early as the 1960s, physicists saw the potential benefits of using superconducting magnets in their detectors. In the early 1970s, experiments in the United States and at CERN were developing large superconducting magnets capable of generating fields of up to 3.5 Tesla. This development work was all the more daring since the technology was still in its infancy. But contrary to the magnets for accelerators, which need to be produced in their dozens, the magnets in detectors are unique.

One of the trailblazers of these detectors was CERN’s Big European Bubble Chamber (BEBC), which entered service in 1973 and in which the superconducting magnet generated a field of 3.5 Tesla. Its stored energy was almost 800 megajoules, a level of performance that wouldn’t be bettered until the late 1990s.

Image above: The superconducting coil of CMS, the biggest superconducting solenoid magnet ever built, being inserted in its cryostat. (Image: Maximilien Brice/CERN).

In the 1980s, significant progress was made on improving the magnets’ performance and making them more “transparent”, so that they didn’t interact with the particles and change their characteristics. Increasingly larger magnets were constructed and the work culminated in the 2000s with the giant superconducting magnets of the landmark CMS and ATLAS experiments at the Large Hadron Collider (LHC). The first of these is a huge solenoid that generates a field of 4 Tesla and is able to store 2.7 gigajoules, enough energy to melt 18 tonnes of gold. The second is an enormous and completely novel toroidal magnet formed of eight superconducting coils, which also generate a magnetic field of 4 Tesla, surrounding a smaller solenoid.

The next generation of superconducting magnets for detectors, which will be even bigger and more powerful, is being developed in the context of preparations for major accelerator projects at CERN and elsewhere.

This text is published on the occasion of the conference EUCAS 2017 on superconductors and their applications​. It is based on the article entitled “Unique magnets”, which appeared in the September issue of the CERN Courier:


CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.

Related links:

Superconducting magnets:

Large Hadron Collider (LHC):



EUCAS 2017:

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Images (mentioned), Text, Credits: CERN/Corinne Pralavorio.


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