The Future of Particle Physics: Exploring CERN’s Next Big Collider

CERN are currently running the Future Circular Collider (FCC) study, which is designed to create a higher performing circular collider, following on from the operation and developments of CERNs Large Hadron Collider (LHC). The FCC is planned to have a circumference of 90.7 km, meaning the area enclosed by the FCC could house approximately six Dublin cities (CERN, Future Circular Collider).

Figure 1: Comparison of FCC to LHC size. (Piper, 2019)

The Operation of CERN’s Future Circular Collider

To understand how the FCC will operate, the operation LHC can be delved into, as the FCC is proposed to have a similar basis of operation to the LHC.

The LHC is the world’s largest and most powerful particle accelerator, operating on a circumference of 27 km, creating beam energies of 6.5 TeV, about the same energy that a mosquito will have in flight. This value may seem incredibly small, however, this value is condensed into a proton, which is a trillion times smaller than a mosquito. Considering billions of these protons will collide at once, the total energy produced is enormous. Think of a freight train being compacted into a subatomic bullet, the energy created would (and is) massive! (CERN, The Large Hadron Collider)

Figure 2: What happens when two particles collide. (Dickerson, 2015)

These incredible energies are created withing the beams by accelerating the particles, using superconducting electromagnets, which create a strong magnetic field (8.3 T, which is 100,000 times the Earth’s magnetic field!) in two separate ultrahigh vacuum beam pipes.

Before collision, the particle beams are squeezed to the width of one quarter of a human’s hair, so that the chance of collision is greatly increased. This is at the detector point of one of the four main detectors: ALICE, ATLAS, CMS and LHCb. (CERN, Pulling together: Superconducting electromagnets)

Creation of Large Magnetic Fields

For the LHC to operate at such large magnetic fields, the superconducting magnets need to be cryogenically cooled, to 1.9 K, which is a temperature colder than outer space!

Helium is chosen as the coolant for this cooling process. Gaseous helium will become a liquid at -269 ºC. however, if cooled slightly further, say to -271 ºC, the helium will enter a superfluid state, causing helium to have amazing qualities, meaning that this state of helium is an amazing heat conductor. This makes helium an amazing refrigerator, used for the cooling process in the LHC.

The process of cooling the superconducting magnets is three steps, taking weeks to be completed. During the first stage, 10,000 tonnes of liquid nitrogen is used as heat exchanges, to cool the temperature of the used helium to -193.15 ºC. Internal turbines further cool the helium to -269 ºC, as the second step. The magnets are then filled with this helium, where refrigerator units cool the helium to -271.3 ºC, so the superfluid state has been reached, creating superconducting magnets. (CERN, Cryogenics: Low temperatures, high performance)

Figure 3: Example of cooling process. (Stanford University, 2022)

Why a New Collider

This operation process will be very similar in the FCC, however there are some operational differences. Due to the respective sizes, the FCC is expected to be able to reach particle beam energies up to 100 TeV, which is seven times larger than the energies. The question supposed here is, why?

This comes from the discovery of the Higgs boson, which has proved how other particles obtain their respective masses, being the signature of an invisible field which fills the universe! This has led to many questions within physics, like how the Higgs can evolve the universe and our understanding of physics? The Higgs boson was found in 2012 by CERNs LHC, with the discovery winning the 2013 Nobel Prize in Physics. (CERN, Future Circular Collider)

Figure 4: Example of Higgs Boson interaction. (Higgs Boson)

This discovery has caused the question, are there particular situations where new, heavier particles, which are beyond the reach of CERN’s LHC, lying outside of the Standard Model? This calls for a new, higher energy facility in which these proposed particles can be investigated. Others suggest that it is possible that lighter particles which interact very weakly with standard particles would require more data and greater sensitivity to obtain a signal. Given that the FCC will have enhanced sensitivity, it would also allow these particles to be observed.

Due to the price, approximately 15 billion euro spread over twelve years, a question which arises with the FCC is, is it ethical to create such a particle accelerator? This question is yet to be answered, as there are still many factors and integers that CERN are considering.

CERN have released an FCC feasibility report in 2025, with CERN official holding a dedicated meeting in November to determine the future of the FCC project. CERN and their early partners will make the decision on the project in 2028, with construction beginning in the early 2030’s, given that the go ahead is given. CERN is expected to being the FCC operation in the late 2040’s, first running 15 years of precision measurements, then scheduled to perform 25 years of high energy experiments. This timeline is not definitive; however, it does create an excitation around the future of particle accelerators and CERN.

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