Sector 7-8 powered up

A first sector of the LHC has been powered up. Sector 7-8 has been cooled down for several weeks and has just passed a series of electrical tests.

Frédéric Gicquel from the Cryogenics for Accelerators Group (AT/ACR) and Anupama Kulkarni from the Magnets and Electrical Systems Group (AT/MEL) at the CERN Control Centre during the powering-up of Sector 7-8.

Frédérick Bordry, leader of the Power Converter Group (AB/PO), and Roberto Saban, responsible for coordinating the LHC commissioning (TS/HDO), celebrate the end of the first powering-up of an entire LHC sector: the sector 7-8.

When the current was increased to 6500 amps on 20 June at 6.30 p.m., the atmosphere was as charged as the magnets. In the CERN Control Centre, the teams responsible for powering up Sector 7-8, the first sector of the LHC to be commissioned, had their eyes glued to the monitor screens. The quadrupole circuits were powered up to 6500 amps (6.5 kA) without problems, just as the dipole circuits had been successfully powered up to several thousand amps on 25 May. Although these are very high intensities, the nominal current for these circuits (12 kA) has not yet been reached.

Once the temperature of 1.9 K (-271°C, see Bulletin No. 16/2007) had been stabilised in most of Sector 7-8, with a small part operating at 4.5 K, current could then be supplied to the magnets in the sector. Depending on the type of superconducting magnet, the nominal current of the electrical circuits varies between 60 A and 12 kA. During the tests, some of the circuits were powered up to the nominal current. Quenches were triggered to test the protection system and the system for extracting the stored energy in the magnets. A quench is when a magnet loses its superconductivity, resistance occurs, the circuit warms up and the energy thereby generated must be dissipated.

These spectacular power tests are the culmination of many electrical tests which have been conducted in Sector 7-8 over the last few weeks. These tests provided the opportunity to test the electrical quality of each circuit, namely its continuity, its earthing system and the intra-circuit insulation. Once the magnet protection systems had been checked, the circuits were powered up. The power converters, which had already been short-circuit tested, were thus connected to the magnets for the first time. During this round of tests, over a hundred superconducting-magnet electrical circuits were checked one by one.

An overall test, during which all the circuits were powered up overnight, was also performed. "This allows us to check that the circuits are performing properly over a prolonged period representing an LHC run. It can also highlight any weaknesses or breakdowns," explains Roberto Saban, who is responsible for coordinating the LHC commissioning. Finally, a power cut was simulated at Point 8. The teams were thereby able to check that all the systems were being supplied with power from the scheduled source, namely the normal or back-up power supply. The tests also provided an opportunity to check that post-mortem data were being generated by each system. These data make it possible to ensure that all the safety systems have operated successfully during a power cut.

This first round of tests is also aimed at verifying the test procedures and their automation as well as a whole range of tools that are used to record and analyse the test data. It also provides vital training for the commissioning of the other sectors. Sector 7-8 will now be warmed up again so that the triplet magnets to the left of Point 8 can be connected up and some consolidation work can be carried out. The next round of power tests will take place in Sector 4-5, which is currently being cooled down.