A particle accelerator that slams electrons together here on Earth has achieved temperatures colder than those of outer space.

Using the X-ray free-electron laser at the Department of Energy’s SLAC National Accelerator Laboratory  —  part of an upgrade project to the Linac Coherent Light Source (LCLS), called LCLS II  — scientists chilled liquid helium to minus 456 degrees Fahrenheit ( minus 271 degrees Celsius), or 2 kelvins. That is just 2 kelvins above absolute zero, the coldest possible temperature at which all particle movement ceases. That frosty environment is crucial for the accelerator, because at such low temperatures the machine becomes superconducting, meaning it can boost electrons through it with just about zero energy loss.


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