The new heart of the PS is beating strongly

The PS has resumed operation with a brand new electrical power system called POPS; this enormous system comprising power electronics and capacitors is crucial because if it broke down practically no particles would be able to circulate at CERN. As soon as it started, POPS passed all the tests with flying colours and is now pulsing at full power.


The new PS power system is made up of 6 containers, each with 60 tonnes of capacitors and 8 power converters.

The date 11/02/11 will always be remembered with affection by the engineers in the Electrical Power Converters Group. At 11:11 in the morning (no joke), the first beams powered by the new system began to circulate in the PS. The cutely-named POPS (POwer for PS) took over from the old rotating machine that had been working since 1968. From now on it will be POPS that supplies the PS main magnets with the electrical pulses needed to accelerate the beams for the LHC and all CERN's other facilities. The system is crucial as the PS is one of the lynchpins of CERN's accelerator complex and any failure in the electrical system would practically paralyse all the experiments. Indeed an incident like that did occur in 2006 and was the reason why the campaign to replace the old machine was stepped up (see Bulletin 21/2010).

The solution developed since then is entirely innovative. The fact is that the PS power supply must be capable of delivering extremely high-power – 60 MW – electrical pulses to the magnets and then of reabsorbing the energy at each accelerator cycle, less than two seconds later ! So the rotating machine was replaced by an enormous system of power converters and capacitors. "In terms of its architecture and the energy levels delivered, this power electronics system is the first of its kind," explains Technology Department Head Frédérick Bordry, who initiated the project before handing over to Jean-Paul Burnet, the current leader of the Electrical Power Converters Group (TE/EPC).

POPS was inaugurated and tested on ten SPS test magnets in 2010 and was then hooked up to the 101 PS main magnets for testing on 31 January this year. This system was tested with gradually increasing intensities, right up to 6000 amps. It then took a few days to pass the operation of POPS from the specialist controlling it locally to the CERN Control Centre prior to the crucial beam test on 11 February.

Inside one of the PS containers with Jean-Paul Burnet, the current leader of the TE/EPC Group.

Start-up went so well that the commissioning process - which was supposed to take several months - only took a matter of weeks. "We had planned for POPS to run in parallel with the old rotating machine, but that wasn't necessary in the end," observes Rende Steerenberg, Head of the OP-PS Section in the Beams Department (BE/OP-PS), which operates the PS and its brand new power system.

Of course, such achievements don't just happen at the click of a finger. The teams from the TE/EPC Group did a lot of fine-tuning work with the PS operators. "But we were pleasantly surprised by the system's excellent stability," Rende Steerenberg adds. The PS needs to ramp up very quickly and then maintain a very stable magnetic field on the flattop. POPS is ideally suited for this purpose as it can deliver the electrical intensities required to produce magnetic fields exceeding 1.2 Tesla with close to 0.01 millitesla precision. "We couldn't want for more. In addition to these performance levels we have also achieved excellent reproducibility, which is very important for us," explains Rende Steerenberg.

So the whole project is a real success with potential applications for accelerators in other laboratories where very fast and very high power conversions are needed. The final word goes to Frédérick Bordry: "It's immensely satisfying to have achieved this result, especially as many people thought at the start of the project that it would not be possible. I'd like to take my hat off to all the engineers and technicians who collaborated on this unique project."


by Corinne Pralavorio