Back to work for the PS

On 22 June, the PS's rotating machine started turning again for the first time since its enforced shutdown one month ago (see Bulletin No. 23-24/2006) - and the PS was back in operation the very next day!

A team from Siemens worked their socks off, 6 days a week for one month (including public holidays), to repair the electrical power supply in collaboration with the AB/PO Group's Main Power Converters (MPC) Section. The generator's faulty rotor was dismantled and replaced by the renovated spare rotor. The multitude of electrical and mechanical connections together with the sheer weight of the rotor (80 tonnes) made this an extremely complex job.

The AB/PO Group used the shutdown to test a back-up solution for the PS power supply. The accelerator was directly wired up to the 18 kV electrical network via a 13 MVA transformer, installed at the end of the 1970s but never used. This solution succeeded in bringing the PS back into operation but at limited energy and frequency. Just 14 GeV could be achieved, which is lower than the energy required by the Antiproton Decelerator (AD). For the LHC, the PS will need to produce beams with an energy of 26 GeV. Similarly, the operating frequency was just two cycles of 1.2 seconds per super-cycle of 16.8 seconds.

This run in degraded mode still made it possible to inject a beam into the SPS, which has not had a whiff of a particle in 18 months. SPS commissioning was thus able to proceed and beams were accelerated up to 400 GeV. 'It's a useful fall-back solution and we shall have to keep it up our sleeves,'explains Frédérick Bordry, Head of the AB Department's Power Converters Group.