As the second-largest accelerator at CERN, the Super Proton Synchrotron (SPS) is an indispensable machine that provides beams not only to the LHC and AWAKE, but also to many fixed-target experiments, including SHINE, NA62, COMPASS, NA64 and NA65, and various R&D programmes, through 6 kilometres of beamlines supplying the North Area's experimental halls .
The first beams from the North Area, which was built in the 1970s, were sent to the experiments in 1978. Initially, the area was dedicated almost exclusively to physics experiments, but over the years many beam lines have also served a very dynamic programme of R&D and tests for experiments at CERN colliders, other labs and even in space. New experiments will also see the light of day in the future, following the Physics Beyond Colliders (PBC) initiative.
The initial design of the North Area (NA) was very sound, allowing for perpetual changing requirements for more than 40 years. However, most of the equipment and infrastructure is just as old, and the time has come to give the NA a fresh look and to prepare the beamlines and infrastructure for the coming decades. New experiments constantly require higher intensities, putting the equipment under strain and necessitating maximum reliability.
Discussions about the refurbishment of the NA began as early as 2013, when Long Shutdown 1 was about to start. As the area has been in operation since 1978, when the SPS was first switched on, the equipment hasn’t really been touched since.
Initial consolidation work on the safety of the installations in the NA took place during Long Shutdown 2 (LS2). However, the daily fixes needed on the power converters in the NA raised reliability questions that needed to be addressed.
As of 2021, a two-phased approach has been endorsed for the consolidation of the NA that will allow the full renovation costs to be staged. Phase 1, approved as of 17 June 2021 through the Medium-Term Plan, has already started and will focus on the replacement of the power converters in BA80 and BA2, covering the first 1.2 kilometres of beamlines upstream of the experimental halls. This replacement will take place during Long Shutdown 3, which is scheduled to end in mid-2027, so as not to hamper Run 3. The first visible result of the consolidation activities will appear in 2023, with the construction of a fifth cooling tower to handle the future cooling needs.
Phase 2, starting in 2027, will be the refurbishment of the experimental halls and of auxiliary technical buildings BA81 and 82. We are talking here of about 60 000 square metres of buildings, facilities including North Experimental Halls 1 and 2 (EHN1 and EHN2) and underground cavern ECN3, which are essential for the searches for rare processes in the framework of the PBC Study.
The NA consolidation project will not result in the same energy savings as the East Area (EA) makeover. The main reason is its major energy consumer. The duty cycle, that is the fraction of the time during which beam is actually delivered, is much larger than in the EA. Moreover, the big experimental magnets run constantly and cannot be pulsed. Nevertheless, the upgrades of the beam equipment and interlock protection will help reduce beam losses, building refurbishments will allow for energy savings and the project will investigate further means to improve energy consumption in several related areas.
The facelift will bring the NA facilities into compliance with modern safety requirements. In addition, the SPS itself has been majorly upgraded during LS2. All beams are now accelerated by a renewed and improved radiofrequency system. While mainly geared to increase the intensity and quality of beams to the LHC, the beam parameters to the NA may also benefit soon. A new beam dump has been installed at Point 5 of the accelerator ring to cope with these higher intensity beams that will be commissioned during Run 3, and then needed as of 2027 for the High-Luminosity Large Hadron Collider.
This article is a part of the series “A quiet revolution is under way at Prévessin”.