ATLAS Experiment CERN


Barrel toroid magnet fully charged to nominal field, and it works!

After a few weeks of testing up to intermediate currents, finally, on Thursday evening November 9, the current in the Barrel Toroid was pushed up to its nominal value of 20500 A and even 500 A beyond this value to prove that we have some margin. It went surprisingly well. Of course, the 8 coils forming the toroid were already tested individually at the surface but still, some surprise may have come from those parts added to the toroid in the cavern for the first time like the 8 cryoring sections linking the coils as well as the valve box at the bottom in sector 13 regulating the helium flow or the current lead cryostat on the top in sector 5. No training quenches, nothing to worry about, and the test was concluded with a fast dump triggered at 00:40 in the very early morning of November 10.

barrel toroid full current
The test crew oscillated between fear and hope while looking at the control panels as the current approached 21kA.

Big relief was in the air, making people thirsty and after some moments of disbelief, many bottles of champagne showed up. By far the nicest one was offered by our magnetic field user Laurent Chevalier who was well prepared and apparently confident about the result. His ATLAS champagne specially bottled for this event tasted best.

barrel toroid full current
Laurent Chevalier and his ATLAS Barrel Toroid champagne.

After this successful first test at full current and recovery from the fast dump, which means cooling down again from 58 down to 4 K, the toroid was charged again in the weekend of 18-19 November. A duration test of the toroid during 35 hours (18 hours at full field) was completed by which the long term stability of power supply, cryogenics and controls were checked. On this occasion several detector groups tested their response to the magnetic field as well and the first beautiful curved traces were shown to us by the muon team working one floor below us to master their system as well. (see their report under the Muon Spectrometer section).

barrel toroid full current
The 21000 A test team on top of the toroid.

barrel toroid full current
The toroid current during the evening and night of November 9.

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