What will the LHC successor look like?

The collider is still called FCC (Future circular collider). According to the project, the length of its ring should be nearly 100 km. The LHC will act as an accelerator for it.


A diagram of the 98 km FCC tunnel (left) and its proposed location (right).

There are two main project implementations: as an electron-positron collider FCC-ee or as a hadron collider FCC-hh. These implementations are mutually exclusive, but the working idea is to implement the first one first, and then implement the second in its place.

The electrons and positrons of a particle are light; therefore, their maximum energy in a cyclic collider is rather strongly limited by the deceleration effect from synchrotron radiation. Therefore, the FCC-ee is designed for collision energies up to 360 GeV. This is enough to produce vector bosons, Higgs bosons, and pairs of poorly understood top and anti-top quarks.

In the FCC-hh, the energy of proton collisions can reach 100 TeV, which is 7 times more than at the LHC. Plus the number of collisions will be increased.

According to the proposed plan, the FCC-ee will be built for 18 years, and then 15 years will operate in various modes. This is, roughly speaking, the program until the 2050s. The dismantling of the FCC-ee and the installation of the FCC-hh will take about 10 years, and for another 25 years it will work, gradually increasing both the energy of the particles and the brightness of the beams. This, it turns out, is a program until somewhere in the 2090s.


  Estimated time of different stages of construction and operation of the new collider.

Estimated time of different stages of construction and operation of the new collider.

The estimated cost of the entire project is large, but not prohibitive – about 10 billion Swiss francs for the FCC-ee and another 17 billion for the FCC-hh. 27 billion is twice as much as, for example, the cost of ITER, but on the other hand, the spending is stretched over decades.

The main problem, in my opinion, is the lack of sufficient confidence that this will be enough for really major discoveries. Everyone wants physics beyond the Standard Model, but simple models have already been effectively disproven, and the chances of finding something on the FCC seem small.

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