Today, 9 March, marks the end of CERN’s annual winter shut down. The Laboratory’s massive accelerator complex will soon begin to lumber out of its winter hibernation and resume accelerating and colliding particles.
But while the Large Hadron Collider (LHC) has not been filled with protons since the Year-End Technical Stop (YETS) began on 4 December 2017, its tunnels and experimental caverns have been packed with people performing maintenance and repairs as well as testing components for future accelerators.
Watch this short overview of activities from around the LHC ring during the YETS (Video: CERN)
Today, CERN’s Engineering department hands the accelerator complex back to the Beams department, who will commence hardware commissioning for 2018. This commissioning will culminate in the restart of the LHC, planned for early April.
This week CERN marks 25 years since the meeting at Evian, where the first ideas for the LHC experimental programme were debuted (Image: Maximilien Brice/CERN)
On Friday 15 December 2017, CERN is celebrating the 25th anniversary of the Large Hadron Collider (LHC) experimental programme. The occasion will be marked with a special scientific symposium looking at the LHC’s history, the physics landscape into which the LHC experiments were born, and the challenging path that led to the very successful LHC programme we know today.
The anniversary is linked to a meeting that took place in 1992, in Evian, entitled Towards the LHC Experimental Programme, marking a crucial milestone in the design and development of the LHC experiments.
The symposium, which will be live webcast, will also include a presentation of the latest results from the four large experiments, ATLAS, CMS, LHCb and ALICE.
Join the live webcast from 11:00-16:00 CET.
The CERN Control Centre in 2017, from where all the Laboratory's accelerators and technical infrastructure are controlled. The accelerator complex and the LHC produced a record amount of data in 2017. (Image: Julien Ordan/CERN)
On Monday, 4 December at 4.00 a.m., the accelerator operators hit the stop button on the accelerator complex and the Large Hadron Collider for their usual winter break. But while the machines are hibernating, there’s no rest for the humans, as CERN teams will be busy with all the maintenance and upgrade work required before the machines are restarted in the spring.
The LHC has ended the year with yet another luminosity record, having produced 50 inverse femtobarns of data, i.e. 5 million billion collisions, in 2017. But the accelerator hasn’t just produced lots of data for the physics programmes.
Before the technical stop, a number of new techniques for increasing the luminosity of the machine were tested. These techniques are mostly being developed for the LHC’s successor, the High-Luminosity LHC. With a planned start-up date of 2026, the High-Luminosity LHC will produce five to ten times as many collisions as the current LHC. To do this, it will be kitted out with new equipment and will use a new optics scheme, based on ATS (Achromatic Telescopic Squeezing), a configuration that was tested this year at the LHC.
Handling beams of particles is a bit like handling beams of light. In an accelerator, dipole magnets act like mirrors, guiding the beams around the bends. Quadrupole magnets act alternately like concave or convex lenses, keeping the beams in line transversally, but mainly focusing them as much as possible at the interaction points of the experiments. Corrector magnets (hexapoles) correct chromatic aberrations (a bit like corrective lenses for astigmatism). Configuring the optics of an accelerator is all about combining the strengths of these different magnets.
One particularly efficient approach to increasing luminosity, and therefore the number of collisions, is to reduce the size of the beam at the interaction points, or in other words to compress the bunches of particles as much as possible. In the High-Luminosity LHC, more powerful quadrupole magnets with larger apertures, installed either side of the experiments, will focus the bunches before collision. However, for these magnets to be as effective as possible, the beam must first be considerably expanded: a bit like a stretching a spring as much as possible so that it retracts as much as possible. And this is where the new configuration comes in. Instead of just using the quadrupole magnets either side of the collision points, the ATS system also makes use of magnets situated further away from the experiments in the machine, transforming seven kilometres of the accelerator into a giant focusing system.
Graph showing the integrated luminosity over the various runs of the LHC. In 2017, the LHC produced 50 inverse femtobarns of data, the equivalent of 5 million billion collisions. (Image: CERN)
These techniques have been used in part this year at the LHC and will be used even more during future runs. “The heart of the High-Luminosity LHC is already beating in the LHC,” explains Stéphane Fartoukh, the physicist who came up with the new concept. “The latest tests, carried out last week, have once again proved the reliability of the scheme and demonstrated other potential applications, sometimes beyond our initial expectations.”
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