Large Hadron Collider Restarts after Three-Year Shutdown

protons accelerating for planned july collisions

By Jonny Lupsha, Wondrium Staff Writer

CERN has resumed operations with the Large Hadron Collider (LHC). The LHC was shut down for three years for repairs and upgrades before starting to fire atoms again in April. It’s the most complicated machine ever built.

View of the LHC tunnel sector 3-4
The 27-kilometer tunnel that houses the Large Hadron Collider (LHC) is filled with the most expensive technology on Earth. Shown is the LHC tunnel sector 3-4. Photo by Maximilien Brice (CERN) / Wikimedia Commons / CC BY-SA 3.0

The European Center for Nuclear Research (CERN) has begun firing protons along its 17-mile underground tunnel. In July, the protons should have acquired enough speed for CERN to begin smashing them together, once more, in the search for the universe’s best-kept secrets. The LHC’s resumed atom smashing will begin almost exactly 10 years after scientists used it to discover the Higgs boson particle, which is said to have been the particle that caused the Big Bang 14 billion years ago.

Conceived in 1993 to replace its predecessor—the Large Electron-Positron collider (LEP)—the Large Hadron Collider is the most complicated machine humankind has ever created. In his video series The Higgs Boson and Beyond, Dr. Sean Carroll, Senior Research Associate in Physics at the California Institute of Technology, explains how it works.

Necessity Is the Mother of Atom-Smashing

An American precursor to the LHC, called the Superconducting Super Collider (SSC), was scrapped by Congress in 1993. Its energy goal was 40 trillion electron volts (TeV) of energy. Thus, Europeans decided to build their own supercollider, the Large Hadron Collider, funded by 21 nations involved with CERN—all of whom were very budget-conscious. For example, the LHC was built in the same underground tunnel in which CERN’s LHC predecessor, the LEP, had lived.

“That means we knew what the size was [and] we knew what the maximum energy we could reach was going to be—it’s going to be 14 TeV,” Dr. Carroll said. “They had a 27-kilometer ring underground beneath the French-Swiss border—part of the LHC is in Switzerland, part of it is in France. It’s 100 meters underground.”

The LHC’s circular, 27-kilometer tunnel is filled with the most expensive technology on Earth. Most of the tunnel holds superconducting magnets that bring beams of protons into parallel lines, focus them to very tiny amounts, and steer them. There are 1,600 of these magnets in the LHC. Each one weighs 27 tons.

How It Works

The actual acceleration of the particles is done in metallic chambers along the tunnel. These chambers have electromagnetic fields in them called radio frequency cavities that give the particles electrical impulses that speed them up. The remainder of the ring is only meant for steering and focusing the proton beams. There are two beams traveling in opposite directions, for a total of about 600 trillion protons, and scientists steer them into each other for collision.

“The trick to making the LHC magnets not heat up is to keep them very, very, very cold,” Dr. Carroll said. “The LHC magnets are less than two degrees above absolute zero—they’re literally colder than interstellar space. Through these magnets, of course, we are zooming protons […] at a speed these days of about 99.99999% the speed of light.”

The beams get focused to a size of about two-thousandths of a centimeter across. When they collide, they produce a billion collisions per second, giving scientists an incredible amount of data to study.

Edited by Angela Shoemaker, Wondrium Daily