This year, the Large Hadron Collider was rebooted to run at twice its previous energy, in an effort to redouble particle physics research after the Higgs boson discovery in 2012.
But researchers at CERN, the Geneva-based European Organisation for Nuclear Research, are already looking to much greater possibilities, with a major upgrade officially entering the construction phase this week.
The High-Luminosity Large Hadron Collider (HL-LHC) will see the world's largest particle accelerator given a major tech boost from 2025. CERN claims the High Luminosity upgrade will deliver 10 times more particle collisions than the LHC. And in the simplest terms, more collisions means more discoveries.
The HL-LHC has been in the works for a while, but project leader Lucio Rossi said that meetings this week marked the passage from design studies to the start of construction. "It's not that we are breaking ground tomorrow, but we are passing to a phase where the main technology and the main equipment is entering the prototyping and industrialisation phase," he told Motherboard.
The upgrade is a much bigger technological project than this year's reboot, which took the LHC from energies of 8 TeV to 13 TeV by pushing its existing limits. The HL-LHC will take the LHC beyond its original potential by replacing approximately 1.2 km of the 27 km-circumference accelerator with new technologies.
This will signal a hefty uptick in performance. "Luminosity" is directly related to the number of particle collisions. It's called luminosity, Rossi explained, because the particles generate a kind of light wave, the tiny wavelengths of which are what allow the LHC to "see" at the subatomic level. There's a clear symbolism to the increased luminosity of increased collisions too: Rossi compared the upgrade to going from looking at a room lit by a 50 Watt bulb to discerning the further details illuminated by a 500 Watt bulb.
One goal of the upgrade is to discover more about the Higgs boson, as we still don't know all the details of the peskily uncertain particle. "We know the Higgs boson exists, but to measure the Higgs's properties we need to have many bosons—we need thousands, millions of Higgs bosons to measure the properties," said Rossi.
CERN says the HL-LHC will produce 15 million Higgs bosons per year, compared to the 1.2 million produced from 2011-2012, all because of the increased collisions. In Rossi's words, "If the Higgs boson is a needle in the haystack and we want to have many needles—to study many Higgs bosons—you need to have many haystacks."
Beyond the Higgs boson, the HL-LHC will naturally boost the search for other mysterious particle behaviour and evidence of theories that go beyond the Standard Model.
CERN will achieve the increase in luminosity with several main changes. The physicists will inject more protons into the accelerator but will reduce the size of the proton beam at its collision point, densifying the cloud of particles so that there is a higher probability of them colliding. The whole project requires some completely new technology, so it will also be something of a test case for future accelerators.
Rossi said that the main challenges ahead of getting the HL-LHC up and running in 2025 included the civil engineering feat of digging new tunnels, which must be done during a scheduled LHC shutdown in 2018-2020 so as not to disrupt operations.
But the main hurdles are technical. The team will replace older magnets with new quadrupole magnets to densify the particle cloud. "They will be the most powerful accelerator magnets ever conceived," said Rossi.
These magnets are based on a new superconductor, niobium-3-tin (Nb3Sn), which is more powerful than the niobium-titanium alloy used in the LHC's superconductors. "We are really pushing this new material to its limits, and thanks to this we can build magnets which are 50 percent more powerful than the ones of the LHC," Rossi explained.
Other new features include special superconducting radiofrequency cavities, nicknamed "crab cavities," that will allow operators to manipulate or "tilt" the proton beam, new collimators to prevent damage, and superconducting links that can transfer current with zero energy dissipation. The project budget is around $1 billion Swiss francs (just over $1 billion).
The new phase of the HL-LHC project comes as media reports claim China will start work on its own particle accelerator, which is planned to access higher energies than the current LHC, around 2020.
After the HL-LHC, researchers' attention is fixed on building a whole new collider, rather than further upgrading the older machine. There are already plans proposing a circular accelerator with a whopping 100 km circumference, three times the size of the LHC. Whatever the next step, later collider models will take their lead from the High Luminosity upgrade, particularly its work with the niobium-3-tin magnets.
"It is a technological test bed for the future accelerator, for a further, bigger leap forward," said Rossi.