Scientific News

Does particle physics have its head in the clouds?

July 2010 - While the LHC is delivering its first beams for experiments, the 50-year-old Proton Synchrotron is being used to investigate Earth’s climate.

Although many experiments worldwide are investigating what affects the planet’s climate, the CLOUD experiment at CERN is the only one that makes use of a particle accelerator. In the experiment, a beam of protons is used to simulate the difference of particle flux in the atmosphere, which varies by a factor of 100 from ground level to the outermost layers of the stratosphere.

From the Proton Synchrotron, protons enter the experiment’s 3 m diameter aerosol/cloud chamber, which accurately recreates various conditions in the atmosphere. The chamber is fitted with an array of sensitive analytical instruments to follow the processes involved: the birth of embryonic aerosols, and their growth to become the seeds for cloud droplets and ice particles. CLOUD will also study the effect of cosmic rays on the cloud droplets and ice particles.

CLOUD is unique in that the parameters that are likely to affect cloud formation can be controlled in the laboratory. CLOUD scientists can vary the chemicals involved and the temperatures of the gas in the chamber. The temperature in the cloud chamber can be varied from -90 °C to +40 °C, which essentially covers the range of atmospheric temperature from the coldest part of the stratosphere to the warmest part of the troposphere.

Ultimately, by modelling how cloud processes affect climate, the CERN scientists and their collaborators hope to be able to investigate possible additional causes of climate change.

For more information, visit the CLOUD website, and an online lecture about the CLOUD experiment.