Physicists want to work in a much greener way, because a particle accelerator consumes energy

It saves a lot of kilowatt hours: the Large Hadron Collider is switched off. Administrator CERN is one of the largest energy consumers in France. The particle accelerator organization uses 1.3 terawatt hours of electricity annually, about a third of Amsterdam’s annual power consumption.

CERN is not alone. Virtually all major physics experiments, from particle accelerators to (space) telescopes, consume energy. In recent years, this has received increasing attention from the community itself. This is apparent, among other things, from scientific publications with quantitative analyzes of CO₂footprint of current experiments and of future installations, which are still in the design phase. The CO₂footprint is the total emission of greenhouse gases, converted to CO₂equivalent, where greenhouse gases that do not contain CO₂ are, such as methane, converted to how much CO₂ which would have the same contribution to global warming.

Emission telescopes

The authors argue that the CO₂emissions and the other environmental impact of scientific research as much as possible. “It’s important for scientists to act,” astronomer Annie Hughes said at a press conference on emissions from observatories at the end of March. “If we as scientists do not respond to the reports and warnings of our [klimaatwetenschappelijke] colleagues, then it is like your father telling you not to smoke while he himself lights a cigarette.”

What helps these advocates is the rise in energy prices. This means that keeping energy consumption low also ensures that costs are reduced.

The study by Hughes and her colleagues at the Institute for Research in Astrophysics and Planetology in Toulouse found that all astronomical observatories operating in 2019 collectively produced about 20 million tons of CO₂equivalent during their lifetime. This is comparable to the annual emissions of Estonia or Croatia, for example. For this calculation, that appeared in Nature Astronomythe researchers looked at the CO₂emissions from the construction and use of telescopes on Earth and space missions – which included the launch.

More accurate estimate

To simplify their estimation, the researchers assumed that the CO₂emissions of the installations is in proportion to their cost or weight. The more expensive or heavier a telescope, the more CO₂emissions was charged to him. That provides a rough estimate, the researchers acknowledge. They can be wrong by up to 80 percent. For example, they estimate the emissions from the James Webb space telescope, which was launched last year, to be between 310,000 and 1.2 million tons of CO.₂-equivalent. For a more accurate estimate, the researchers would need much more information than is publicly available.

The researchers therefore call on all research institutions and funding agencies to publish a detailed calculation of the total (intended) CO for each project.₂footprint, from construction to demolition.

Despite the very rough estimate, according to the researchers, the calculation shows that the annual CO₂emissions from astronomical observatories must be reduced by up to twenty times if they want to meet the climate targets.

Unexpected emissions data

A future experiment requiring such a extended CO₂-calculation has been carried out is the Giant Array for Neutrino Detection project (Grand). This experiment will detect cosmic particles with 200,000 antennas from the 1930s.

Three researchers, including two Grand physicists, calculated the CO₂footprint of everything involved: from the construction of the experiment and the software required for the data analysis, to the emissions of the transport of the parts, the travel and the data storage.

They amount to almost 500 tons of CO₂equivalent per year for the first four years, in which the first three hundred antennas are installed. The second phase of more than five years, with ten thousand antennas, is good for more than 1,000 tons of CO₂equivalent per year. In the final phase, in which the experiment will be completed, there will be more than 13,400 tons of CO₂equivalent per year – that is comparable to the production of a thousand cars, the researchers write.

Physicists are already fantasizing about the next particle accelerator

In all phases, digital technology, such as computers, simulation software, data processing and data storage, turned out to be responsible for a large part of the emissions. “We didn’t expect that,” emails physicist Kumiko Kotera of the University of Paris. “We think people are aware of the emissions caused by travel and the production of the measuring equipment, but forget that large amounts of measurement data that must be processed and stored can also lead to enormous CO₂footprint.”

Following the publication of Kotera and her colleagues, a ‘green policy plan’ has been drawn up for Grand. It states, for example, that traveling must be kept to a minimum by having local partners carry out as much work as possible on site. Furthermore, the data will be stored in centers with the lowest possible CO₂footprint. There will also be a recycling plan for the measuring equipment.

A green higgs factory

The particle accelerator physicists are not sitting still either. They are already fantasizing about another billion-dollar, energy-guzzling particle accelerator. With this, they want to produce Higgs particles – which were discovered in 2012 – on an assembly line in order to study them in detail.

There are several designs on the table for such a Higgs factory. Which one you choose turns out to make quite a difference for the CO₂footprint of the machine, discovered two particle physicists who examined five designs in October. Two of them, like the LHC, are circular: the FCC at CERN in Geneva and the CEPC. The three others are linear: Japan’s ILC, CERN’s CLIC, and the US’s C³.

The particle physicists took a special approach to their comparison. They calculated the energy consumption and CO for each design₂footprint per Higgs particle produced. Patrick Janot, particle physicist at CERN explains: “We do this because the ability to do science is directly related to the number of higgs: the more higgs, the better the scientific outcome.”

The FCC does it better

The circular accelerators come out on top in the energy consumption test because they produce Higgs particles faster than the linear accelerators. The FCC comes out on top with 3 megawatt-hours of electricity per Higgs boson. At the bottom is the C³ at 16 megawatt hours – more than five times more than the FCC.

The FCC does even better if you include the origin of the power. At CERN, 90 percent of the electricity comes from CO₂-free sources, such as nuclear energy. As a result, the CO₂footprint of the FCC is only a mere 2 percent of that of the ILC, the least sustainable alternative. That shows that it is best to build your accelerator in a country where the CO₂emissions from electricity production are low.

If it’s up to Janot, the CO₂footprint is one of the most important decision criteria when it comes to the choice, design and optimization of a particle accelerator.

Excessive emissions

“I don’t think the higgs factory design with the smallest CO₂footprint will be built by definition,” says particle physicist Tristan du Pree, from Nikhef and the University of Twente, who is involved in the FCC design. “But those with exorbitant levels of CO₂emissions are excluded. In my opinion, for example, CLIC is a no-go because of the energy consumption.”

“This analysis is a good way to start the conversation about the CO₂footprint of particle accelerators,” says particle physicist Caterina Vernieri, who is involved in the design of C³. “But there are more aspects, which the researchers have not looked at, that we need to take into account in order to make a better estimate of the CO₂footprint.”

The most sustainable scientist is the one who does no research

Vernieri, for example, does not entirely agree with the assumption that more Higgs particles is the best way to achieve better scientific results. “In linear accelerators you can get more information from the Higgs particles you have, even if you make less. That is not included in the calculation.”

Moreover, nowhere is it mentioned that the C³physicists are looking at ways to build a solar park next to it, for example, so that the machine can run entirely on green electricity, says Vernieri. “And we are working on automating a lot so that few people need to be present at the experiment, which saves emissions from travel.”

Janot and his colleague did not include the emissions associated with the travel of the researchers involved, construction, data analysis, data storage and simulations in their estimate. They defend this choice at the end of the paper, where they show that these emissions are small compared to those of the electricity used to run an accelerator. Janot: “The latter dominates the total CO₂footprint and is therefore the most important factor if you want to optimize a machine.”

Cut down on

What these first estimates of the CO₂footprint of experiments and observatories is that they are complex calculations if you want to perform them accurately. This makes it difficult to properly compare different designs. But it is clear that something has to change if physicists and astronomers are to meet climate goals.

A relatively simple way to save the climate, advocated by Hughes and her colleagues, is to slow down the rate at which new astronomical observatories are built. And Vernieri calls it essential to start looking at new techniques for particle physics experiments. “Because building ever larger particle accelerators that work with even higher energies is not tenable or sustainable.”

The physicists emphasize that striving for ever-smaller CO₂footprint should not paralyze research. After all, the most sustainable scientist is the one who does no research. DuPree. “I do hope that another particle accelerator will be built in the near future.”