Physicists planning to build the successor to the Large Hadron Collider (LHC) have started looking at the climate impact of a massive particle smasher, with plans to make it as energy efficient as possible.
The LHC discovered the Higgs boson, a particle that gives mass to all the others. Now particle physicists want to study it in more detail with a new kind of collider, known as a Higgs factory, to produce large numbers of the particle by smashing together electrons and their antiparticles, positrons.
Such a factory would use vast amounts of energy, so at the CERN particle physics lab in Switzerland and at the University of Geneva, also in Switzerland, have compared the carbon footprint of five of the most popular collider designs to see which might have the smallest environmental impact.
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鈥淚n our times of measurable climate change due to a global warming of unprecedented proportions, resulting from the emission of greenhouse gases, the most important criterion is that the scientific outcome for a given carbon footprint be maximised,鈥� says Janot.
The pair calculated the energy required per Higgs boson created for each collider design and found that the most energy hungry proposal, the Cool Copper Collider (CCC) in the US, would consume 18 megawatt-hours (MWh) per Higgs over a year.
By contrast, the proposed Future Circular Collider (FCC) at CERN would use only 3 MWh, and this could be reduced to 1.8 MWh per Higgs with some upgrades to the design, a tenth that of the CCC. A collider in Switzerland could also benefit from the carbon-free nuclear power produced in nearby France, unlike other designs, they add.
Evaluating new collider designs in this way is a good idea, says at Royal Holloway, University of London.
鈥淏enchmarks such as energy or emissions per Higgs boson, or some other physics-motivated criteria, are more relevant than, say, the energy or emissions used by the facilities per year,鈥� she says.
But the pair fail to take into account some other significant sources of carbon that result from a collider, says Boisvert, such as gases used in the detectors or concrete used to build the facility鈥檚 tunnels, which can vary between designs. Janot and Blondel say they plan to update the work to address concrete emissions.
Uncertainties in predicting future carbon emissions based on countries鈥� current electricity supplies also muddy the waters, says at the University of Sheffield, UK. Many of the countries under consideration for other Higgs factories, such as the US and China, will probably be using far more renewable energy by the time such a facility might get built in the 2030s or 2040s, which would undermine some of the pair鈥檚 arguments around France鈥檚 nuclear power.
The proposed design upgrades to the FCC could also be applied to other colliders, such as the Circular Electron Positron Collider (CEPC) proposal in China, says Lohwasser, but the pair didn鈥檛 consider this in their analysis of the CEPC. Ultimately, how seriously climate considerations will be taken in commissioning a future Higgs factory might depend on the reality of the day.
鈥淐limate considerations have consistently climbed up the list of things that need to be considered,鈥� says Lohwasser. 鈥淚 cannot project whether it will be higher than the physics goals, or vice versa, at the time that this decision will be taken, as this also depends on climate scenarios.鈥�
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