An international team has installed the Large Hadron Collider at CERN in a 27-kilometer ring buried deep below the countryside on the outskirts of Geneva, Switzerland. The LHC is the world’s most powerful particle accelerator. Its very-high-energy proton collisions are yielding extraordinary discoveries about the nature of the physical universe. Beyond revealing a new world of unknown particles, the LHC experiments could explain why those particles exist and behave as they do. The LHC experiments could reveal the origins of mass, shed light on dark matter, uncover hidden symmetries of the universe, and possibly find extra dimensions of space.
Billions of protons in the LHC’s two counter-rotating particle beams smash together at an energy of 14 trillion electron volts. After injection into the accelerator, the hair-thin proton beams accelerate to a whisker below the speed of light. They circulate inside for hours, guided around the LHC ring by thousands of powerful superconducting magnets. For most of their split-second journey around the ring, the beams travel in two separate vacuum pipes, but at four points they collide in the hearts of the main experiments, known by their acronyms: ALICE, ATLAS, CMS and LHCb.
The experiments’ complex detectors will eventually see up to 600 million collisions per second, as the energy of colliding protons transforms fleetingly into a plethora of exotic particles. In the data from these ultrahigh-energy collisions scientists from universities and laboratories around the world search for the tracks of particles whose existence could transform humankind’s understanding of the universe we live in.
What is the Large Hadron Collider?
The LHC at CERN, the European Organization for Nuclear Research, is the largest, most complex and most powerful particle accelerator ever built. It operates in a circular 27-kilometer tunnel about 100 meters underground, between Switzerland’s Lake Geneva and France’s Jura mountains. The LHC will create almost a billion proton-proton collisions per second at an energy of 14 trillion electron volts, seven times higher than any accelerator has previously achieved.
At the heart of the LHC are superconducting magnets made of niobium-titanium. Cooled to nearly absolute zero by superfluid helium, the coils of these magnets conduct electricity without resistance. The LHC’s 1,232 dipole magnets guide the opposing beams of speeding protons in their circular orbits. Several thousand additional magnets fine-tune the beams’ orbits, and some 400 quadrupole magnets focus the protons into hair-thin beams that collide within the LHC experiments. Cryogenic, electronic and information systems of unprecedented scope and complexity support the LHC’s ’round-the-clock operation.
The US and the LHC Accelerator
The US LHC Accelerator Construction Project, a $200 million project funded by the US Department of Energy Office of Science, managed US participation in the design and building of the LHC accelerator. This project, now complete, included scientists from Brookhaven National Laboratory in New York; Fermi National Accelerator Laboratory in Illinois; and Lawrence Berkeley National Laboratory in California.
Fermilab, in collaboration with CERN and the KEK laboratory in Japan, designed and constructed final-focus magnet systems used to focus the beams before collision in the center of each of the four main LHC experiments. The systems contain superconducting quadrupole magnets, built by Fermilab and KEK, and CERN-provided correction magnets.
Lawrence Berkeley National Laboratory and Fermilab designed and constructed eight cryogenic and power feed boxes that support these final-focus systems. LBNL also designed and constructed eight specialized absorbers that protect the US-provided superconducting magnets from the secondary particles produced in proton collisions at the center of the LHC experiments. The laboratory also participated in the technical production of superconducting cable.
Brookhaven National Laboratory designed and constructed 20 superconducting “beam separation” dipole magnets of four different designs and production tested superconducting wire and cable.
Scientists from all three laboratories carried out accelerator physics calculations in support of the design of the LHC, including the final-focus magnet systems.
Industry and the LHC
US industries also had a hand in building the LHC machine, supplying $88.5 million in specialized materials and components. These materials included niobium-titanium alloy niobium sheets for use in manufacturing the superconductor for LHC magnets; superconducting cable; high-temperature superconducting tape for use in power leads; insulation for LHC magnets; and cryogenic and beam instrumentation components.
The US LHC Accelerator Research Program (LARP)
LARP coordinates research and development in the US related to the LHC accelerator. The program supports activities at Brookhaven National Laboratory , Fermi National Accelerator Laboratory, Lawrence Berkeley National Laboratory , and the SLAC National Accelerator Laboratory . LARP has also supported some work at the University of Texas at Austin.
LARP began in 2002 and currently operates with an annual budget of approximately $12.5 million. Over 100 scientists, engineers, and graduate students are involved in LARP-related activities.
Approximately half of LARP’s resources are committed to the study of superconducting quadrupole magnets based on Niobium 3 tin (Nb3Sn) technology, so that these magnets can be used in a future Phase II upgrade to the LHC. These magnets could enhance the accelerator’s capabilities compared to traditional Niobium tin magnets.
In the area of accelerator system research and development, LARP scientists provided several types of monitors and a tune feedback system for the LHC. These technologies allow accelerator physicists to monitor and diagnose the LHC particle beams. LARP is also developing a rotatable collimater, which would allow higher LHC beam intensity. Research and development for future upgrades include an electron cloud feedback system for the SPS, crab cavities for the Phase II upgrade, and significant involvement in the proposed PS2 project. The PS2 will replace the current PS accelerator in the injector line that brings an energized beam into the LHC.
LARP also funds two programs to support US personnel working on the LHC. The first is the Toohig Fellowship, open to recent PhD recipients. Successful candidates divide their time between CERN and the LARP laboratory of their choice. The Long Term Visitor program supports senior personnel wishing to relocate to CERN for extended periods. In this case, their home institutions will contribute to pay their salaries, while LARP pays transportation and cost of living expenses.
Accelerator Project for the Upgrade of the LHC (APUL)
While LARP scientists research and develop new techniques and materials, APUL (Accelerator Project for the Upgrade of the LHC) provides an opportunity for US scientists and engineers to become involved in upgrading the LHC with tested technologies.
Both APUL and CERN will build components for a near-term upgrade of LHC luminosity, which will increase the number of proton-proton collisions. The components will improve the LHC magnets’ ability to steer beams into collision. APUL will build superconducting magnets with larger apertures than current magnets, as well as a cold powering system that will bring power to the magnets from supplies more than 100 meters away.
APUL began receiving funding in 2008 and is a collaboration of about twelve scientists and engineers from Brookhaven National Laboratory and Fermi National Accelerator Laboratory.
To date, APUL has completed its conceptual design report and is now preparing a technical design report with CERN. The components being designed are scheduled to be installed in 2014.