Life after discovery: a look at the SPS of 2012

Though no longer the newest kid on the block, the SPS remains as essential to CERN’s research programme as it was when it discovered the W and Z bosons back in 1983. The CERN Bulletin takes a look at how the SPS has kept up with younger CERN accelerators...


Teams changing an SPS magnet during a technical stop. Image courtesy of Franck Bais.

It’s the 1970s and the Super Proton Synchrotron (SPS) is at the top of the charts. It’s accelerating protons at 400 GeV - an unprecedented energy for CERN - and its discoveries will make it the first (and, so far, the only) CERN accelerator to generate a Nobel Prize. Fast-forward to 2012 and the SPS is running at 450 GeV – well beyond its original design parameters – and is an essential part of the LHC accelerator complex. Not bad for a machine heading into its 40s.

While much of the SPS dates back to the original set-up, it has been in constant evolution over the years. Except for a long shutdown in 2005 during the construction of the LHC, the SPS has not had much of a “break” in recent years. “The SPS has a lot of responsibilities: not just to the LHC but also to the North Area experiments and CNGS,” explains David McFarlane, the SPS technical coordinator in the Engineering Department. “So even when the LHC is offline, we still have to operate.”

Since the LHC first started up in 2008, the SPS has had only short shutdowns – ranging from a single day to a few weeks. The last winter stop, for example, was nearly 4 months for the LHC – but that's the time between the LHC stopping the beam and receiving beam. The SPS cannot be offline that long, as it takes time to restart the chain to provide the LHC with beam. “The last winter stop was only 5 weeks long for the SPS,” says David. “Although this timeframe does not allow us to carry out major upgrades, we are able to ensure essential maintenance is carried out.”

But, for the SPS, “essential maintenance” often means more than checking a few cables. Every technical stop sees the change of at least one magnet in the SPS, often carried out in a single day. “Once we actually changed 4 magnets over a 2-day technical stop, with one team moving a magnet out while another brought one in,” says David. “It seems rather extraordinary, but the teams have got the process down to an art.”

The long accelerator shutdown planned for 2013/2014 (LS1) will be an opportunity for the SPS teams to get significant work done on the accelerator, preparing it for the LHC’s 14 TeV run. One major upgrade will combat current problems caused by electron clouds. A beam pipe coating has been developed to counteract these unwanted effects, and new magnets with coated chambers will be installed across one entire arc of the SPS. Another major upgrade, which will start during LS1 but will not be completed until LS2 in 2018, is the upgrade of the radio-frequency cavities in the SPS. These cavities have to be replaced in order to meet the new beam intensity requirements of the High Luminosity LHC programme.

These upgrades will be just another impressive chapter in the life of a machine that has, over the past 36 years, exceeded every possible expectation. The SPS established CERN as a laboratory of discovery: accelerating everything from sulphur ions to positrons, acting as a proton-antiproton collider at 315 GeV, and injecting particles into LEP and the LHC. 

by Katarina Anthony