Despite assurance by Nima Arkani-Hamed, particle theorist at the Institute for Advanced Study, that collision experiments at the Large Hadron Collider (LHC) would not result in a cataclysmic doomsday scenario, qualms about the possible creation of a planet-swallowing black hole led two “researchers-turned-activists” to a Honolulu courtroom in an attempt to stop CERN from starting up its record-setting particle accelerator in 2008. Thankfully, no black holes were recorded during the $3.5 billion machine’s first run, as was coolly predicted in this report, which was released by CERN to counter these very kinds of fears. Instead, researchers were granted glimpse at the Higgs Boson on July 4, 2012, nearly half a century after its existence was first proposed. It was then that the LHC entered a phase termed Long Shutdown 1 (LS1). Yet, during this ostensibly dormant period, the 27 km tunnel did not fall silent. The months leading up to the LHC’s restart in April of this year were marked once more by conspiracy theories heralding the end of time. Rest assured, the machine still operates within reasonable bounds. The LHC is back and better than ever.
Why were the upgrades performed?
As remarkable as the findings of run 1 are, the true potential of the LHC is understood only when we consider that the machine was previously running at slightly over half of its intended operation energy. Proton beams (and occasionally lead ions) are accelerated through a series of smaller accelerators before they are injected into the LHC’s main ring at an energy of 450 GeV. Here, two counter-rotating beams are created and accelerated until each is at the energy required for a collision with total energy twice that of each beam on its own. The first run had a maximum beam of energy of 4 TeV, which yields a total collision energy of 8 TeV. The LHC was designed for collisions of energy 14 TeV. At this point, the energy in each beam is equivalent to that of a 400-ton train traveling at 150 km/h. At near the speed of light, a proton makes 11,245 trips around the 27 km ring every second. A large number of components must work together in clinically-perfect harmony for the scheme to work without mishaps like the explosive helium spill that occurred in the early days of operation.
What exactly was done?
The LHC relies on large magnets to ensure that particle beams remain tightly packed and narrowly guided as they accelerate around the ring. Powering these magnets is an 11,000 Amp current that must make its way between the approximately 1965 connections that occur along the circumference. Eight of the superconducting dipole magnets responsible for directing beams were replaced due to wear and tear, and over 10,000 shunts were installed to provide an alternative pathway for the enormous current in case something goes wrong. Additionally, the superfluid Helium based cryogenic and vacuum systems responsible for cooling the magnets have been revamped, allowing the LHC to maintain an operation temperature of 1.9 K, making it one of the coldest places in the world – in fact, it’s approximately 182 K colder than the coldest recorded natural temperature in the Antarctic. The cooling system alone is impressive considering Geneva enjoys balmy summer days with temperatures in the mid-to-high 60’s in Fahrenheit.
When did it start back up?
Cooling of the LHC began as early as June 2014, when plans for the second run were first announced. For researchers at CERN, the goal is clear: collision energy of 13 TeV, just shy of the device’s operating limit. In early March of this year, the injection systems responsible for delivering the beams into the LHC ring endured a testing process as detectors underwent calibration. Typically, these tests occur one segment at a time. With beams back whizzing through the LHC for the first time in years, the focus has turned toward ensuring stability before cranking energy up to the 6.5 TeV-per-beam target. Still, the laundry list of instruments and fail-safes to check and double check looms formidably. However, progress is steady – one of the beams successfully circulated at the target energy on April 10th of this year.
The true potential of the LHC is understood only when we consider that the machine was previously running at slightly over half of its intended operation energy.
Why does it matter?
Despite the centuries of work put into the set of theories regarded as the standard model, our understanding of the universe is still incomplete. Questions regarding dark matter and dark energy – which actually comprise a majority of the universe – remain unanswered. Specifics of the Higgs field and the origin of mass are not found in the standard model. Even more crucially, the fundamental forces have not been explained in their entirety. The gaps are daunting, but CERN and the LHC hope to bridge them. Theories will either achieve immortality or suffer condemnation based on the results generated several hundred feet beneath the Franco-Swiss border.