LHC and the environment
Our machines in the underground of a beautiful environment
- What is the LHC power consumption?
- Are the LHC collisions dangerous?
- What are the rules regarding access to the LHC?
- What is the helium consumption at the LHC?
- What happens if the beam becomes unstable?
It is around 120 MW (230 MW for all CERN), which corresponds more
or less to the power consumption for households in the Canton
(State) of Geneva. Assuming an average of 270 working days for the
accelerator (the machine will not work in the winter period), the
estimated yearly energy consumption of the LHC in 2009 is about
800 000 MWh. This includes site base load and the experiments.
The total yearly cost for running the LHC is therefore, about 19
million Euros. CERN is supplied mainly by the French company EDF
(Swiss companies EOS and SIG are used only in case of shortage
A large fraction of the LHC electrical consumption will be to keep the superconducting magnet system at the operating temperatures (1.8 and 4.2 K) depending on the magnets. Thanks to the superconducting technology employed for its magnets, the nominal consumption of the LHC is not much higher than that of the Super Proton Synchrotron (SPS), even though the LHC is much larger and higher in energy.
The Large Hadron Collider (LHC) can achieve an energy that no other particle accelerators have reached before, but Nature routinely produces higher energies in cosmic-ray collisions. Concerns about the safety of whatever may be created in such high-energy particle collisions have been addressed for many years. In the light of new experimental data and theoretical understanding, the LHC Safety Assessment Group (LSAG) has updated a review of the analysis made in 2003 by the LHC Safety Study Group, a group of independent scientists.
LSAG reaffirms and extends the conclusions of the 2003 report that LHC collisions present no danger and that there are no reasons for concern. Whatever the LHC will do, Nature has already done many times over during the lifetime of the Earth and other astronomical bodies. The LSAG report has been reviewed and endorsed by CERN’s Scientific Policy Committee, a group of external scientists that advises CERN’s governing body, its Council.
The following summarizes the main arguments given in the LSAG report. Anyone interested in more details is encouraged to consult it directly, and the technical scientific papers to which it refers.
} Unprecedented energy collisions? On Earth only! Accelerators only recreate the natural phenomena of cosmic rays under controlled laboratory conditions. Cosmic rays are particles produced in outer space in events such as supernovae or the formation of black holes, during which they can be accelerated to energies far exceeding those of the LHC. Cosmic rays travel throughout the Universe, and have been bombarding the Earth’s atmosphere continually since its formation 4.5 billion years ago. Despite the impressive power of the LHC in comparison with other accelerators, the energies produced in its collisions are greatly exceeded by those found in some cosmic rays. Since the much higher-energy collisions provided by Nature for billions of years have not harmed the Earth, there is no reason to think that any phenomenon produced by the LHC will do so. Cosmic rays also collide with the Moon, Jupiter, the Sun and other astronomical bodies. The total number of these collisions is huge compared to what is expected at the LHC. The fact that planets and stars remain intact strengthens our confidence that LHC collisions are safe. The LHC’s energy, although powerful for an accelerator, is modest by Nature’s standards.
} Cosmic rays The LHC, like other particle accelerators, recreates the natural phenomena of cosmic rays under controlled laboratory conditions, enabling them to be studied in more detail. Cosmic rays are particles produced in outer space, some of which are accelerated to energies far exceeding those of the LHC. The energy and the rate at which they reach the Earth’s atmosphere have been measured in experiments for some 70 years. Over the past billions of years, Nature has already generated on Earth as many collisions as about a million LHC experiments – and the planet still exists. Astronomers observe an enormous number of larger astronomical bodies throughout the Universe, all of which are also struck by cosmic rays. The Universe as a whole conducts more than 10 million million LHC-like experiments per second. The possibility of any dangerous consequences contradicts what astronomers see - stars and galaxies still exist.
} Microscopic black holes Nature forms black holes when certain stars, much larger than our Sun, collapse on themselves at the end of their lives. They concentrate a very large amount of matter in a very small space. Speculations about microscopic black holes at the LHC refer to particles produced in the collisions of pairs of protons, each of which has an energy comparable to that of a mosquito in flight. Astronomical black holes are much heavier than anything that could be produced at the LHC.
According to the well-established properties of gravity, described by Einstein’s relativity, it is impossible for microscopic black holes to be produced at the LHC. There are, however, some speculative theories that predict the production of such particles at the LHC. All these theories predict that these particles would disintegrate immediately. Black holes, therefore, would have no time to start accreting matter and to cause macroscopic effects.
Although stable microscopic black holes are not expected in theory, study of the consequences of their production by cosmic rays shows that they would be harmless. Collisions at the LHC differ from cosmic-ray collisions with astronomical bodies like the Earth in that new particles produced in LHC collisions tend to move more slowly than those produced by cosmic rays. Stable black holes could be either electrically charged or neutral. If they had electric charge, they would interact with ordinary matter and be stopped while traversing the Earth, whether produced by cosmic rays or the LHC. The fact that the Earth is still here rules out this possibility for cosmic rays and therefore for the LHC. If stable microscopic black holes had no electric charge, their interactions with the Earth would be very weak. Those produced by cosmic rays would pass harmlessly through the Earth into space, whereas those produced by the LHC could remain on Earth. However, there are much larger and denser astronomical bodies than the Earth in the Universe. Black holes produced in cosmic-ray collisions with bodies such as neutron stars and white dwarf stars would be brought to rest. The continued existence of such dense bodies, as well as the Earth, rules out the possibility of the LHC producing any dangerous black holes.
} Strangelets Strangelet is the term given to a hypothetical microscopic lump of ‘strange matter’ containing almost equal numbers of particles called up, down and strange quarks. According to most theoretical work, strangelets should change to ordinary matter within a thousand-millionth of a second. But could strangelets coalesce with ordinary matter and change it to strange matter? This question was first raised before the start up of the Relativistic Heavy Ion Collider, RHIC, in 2000 in the United States. A study at the time showed that there was no cause for concern, and RHIC has now run for eight years, searching for strangelets without detecting any. At times, the LHC will run with beams of heavy nuclei, just as RHIC does. The LHC’s beams will have more energy than RHIC, but this makes it even less likely that strangelets could form. It is difficult for strange matter to stick together in the high temperatures produced by such colliders, rather as ice does not form in hot water. In addition, quarks will be more dilute at the LHC than at RHIC, making it more difficult to assemble strange matter. Strangelet production at the LHC is therefore less likely than at RHIC, and experience there has already validated the arguments that strangelets cannot be produced.
} Vacuum bubbles There have been speculations that the Universe is not in its most stable configuration, and that perturbations caused by the LHC could tip it into a more stable state, called a vacuum bubble, in which we could not exist. If the LHC could do this, then so could cosmic-ray collisions. Since such vacuum bubbles have not been produced anywhere in the visible Universe, they will not be made by the LHC.
Magnetic monopoles are hypothetical particles with a single magnetic charge, either a north pole or a south pole. Some speculative theories suggest that, if they do exist, magnetic monopoles could cause protons to decay. These theories also say that such monopoles would be too heavy to be produced at the LHC. Nevertheless, if the magnetic monopoles were light enough to appear at the LHC, cosmic rays striking the Earth’s atmosphere would already be making them, and the Earth would very effectively stop and trap them. The continued existence of the Earth and other astronomical bodies therefore rules out dangerous proton-eating magnetic monopoles light enough to be produced at the LHC.
} Reports and reviews Studies into the safety of high-energy collisions inside particle accelerators have been conducted in both Europe and the United States by physicists who are not themselves involved in experiments at the LHC. Their analyses have been reviewed by the expert scientific community, which agrees with their conclusion that particle collisions in accelerators are safe. CERN has mandated a group of particle physicists, also not involved in the LHC experiments, to monitor the latest speculations about LHC collisions.
* Download this summary of the LSAG report. Translations are available in the following languages : fr de it.
* Download the LSAG report (2008)
* Download the specialist report published in the United States (1999)
* Download the specialist report published in Europe (2003)
} Radiation? Radiation is unavoidable at particle accelerators like the LHC. The particle collisions that allow us to study the origin of matter also generate radiation. CERN uses active and passive protection means, radiation monitors and various procedures to ensure that radiation exposure to the staff and the surrounding population is as low as possible and well below the international regulatory limits. For comparison, note that natural radioactivity – due to cosmic rays and environmental natural radioactivity – is about 2400 μSv/year and a round trip Europe-Los Angeles accounts for about 100 μSv. The LHC tunnel is housed 100 m underground, so deep that both stray radiation generated during operation and residual radioactivity will not be detected at the surface. Air will be pumped out of the tunnel and filtered. Studies have shown that radioactivity released in the air will contribute to a doses to members of the public of no more than 10 μSv/year.
CERN’s guidelines for the protection of the environment and personnel comply with the Swiss and the French National Legislations and with the European Council Directive 96/29/EURATOM. In both the Swiss and French legislations under no circumstances can professional activities lead to an effective dose of more than 20 mSv per year for occupationally exposed persons and more than 1 mSv per year for persons not occupationally exposed and for members of the public
Outside beam operation, the large part of the LHC tunnel will be only weakly radioactive, the majority of the residual dose rates being concentrated in specific parts of the machine such as the dump caverns – where the full beam is absorbed at the end of each physics period – and the regions where beams are collimated.
Only a selection of authorized technical people will be able to access the LHC tunnel. A specialized radiation protection technician will access it first and measure the dose rate at the requested intervention place, to assess when, and for how long, the intervention can take place.
The exact amount of helium loss during operation of the LHC is not yet known. The actual value will depend on many factors, such as how often there are magnet quenches, power cuts and other problems. What is well known is the amount of helium that will be needed to cool down the LHC and fill it for first operation. This amount is around 120t.
The energy stored in the LHC beams is unprecedented, threatening to damage accelerator equipment in case of uncontrolled beam loss, so everything is done to ensure that this never happens. Safe operation of the LHC requires correct operation of several systems: collimators and beam absorbers, a beam dumping system, beam monitoring, beam interlocks, and quench protection systems. If the beam becomes unstable the beam loss sensors will detect it and within three revolutions (<0.3ms) a set of magnets will extract the beam from the LHC. The beam will then travel through a special tunnel to the beam stop block, which is the only item in the LHC that can withstand the impact of the full beam. The core of the stop block is made of a stack of various graphite plates with different densities.
The total energy in each beam at maximum energy is about
350 MJ, which is about as energetic as a 400 t train, like the French TGV, travelling at 150 km/h. This is enough energy to melt around 500 kg of copper. The total energy stored in the LHC magnets is some 30 times higher (11 GJ).
For more information, visit the LHC Environment website