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Boffins gently wake the Large Hadron Collider from annual hibernation

Winter upgrade boosted 'inverse femtobarns' for more accurate stuff-spotting

By Richard Chirgwin, 2 May 2017

CERN says the restart process for the Large Hadron Collider is complete and the proton-smasher is ready to start its 2017 science program.

Alas, Vulture South's favourite mental image of an Igor saying “Yeth, marthter” and hauling on suitably Big Red Switch doesn't match reality: the restart process is a carefully-managed power-up of each part of the accelerator chain “until it gets to the final, biggest machine”, CERN explains (so we'll just think operations leader Rende Steerenberg as “Igor in chief” and move on).

The LHC layoff for maintenance and upgrades included a “massive” cable removal project, replacing a superconducting magnet, and installing a new beam dump in the Super Proton Synchrotron.

Among other things, the upgrades increase the LHC's “integrated luminousity”, consequently increasing the amount of data collected, and here, we get to mention a unit of measurement so exotic it hasn't yet found an place in The Register's famous Online Standards Converter: the inverse femtobarn.

This measures the number of particle collisions observed per 100 femto metres squared of the target's cross-section.

With the upgrade, the boffins hope for a 12.5 percent improvement in integrated luminosity, to 45 fb-1.

Getting his moment of nominative determinism, Igor-in-chief Steerenberg explains here that the best way to increase luminousity is to steer the beams more accurately.

“The big challenge is that, while you can increase luminosity in different ways – you can put more bunches in the machine, you can increase the intensity per bunch and you can also increase the density of the beam – the main factor is actually the amount of time you stay in stable beams”, he said.

Back in 2015, CERN explains, the beams were stable 35 percent of the time (and that was after the machine had spotted the Higgs boson – that was announced in 2014). In 2016, it delivered stable beams 49 percent of the time.

As well as improving beam stability, the team will test new optics settings this year to try and capture more collisions.

Steerenberg again: “With the new SPS beam dump and the improvements to the LHC injector kickers, we can inject more particles per bunch and more bunches, hence more collisions”. ®

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