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Uppsala researchers create world’s fastest water heater

5 June 2018

The picture shows how the water is rapidly broken down and changes structure. (The picture is cropped.)

In an international collaboration, Uppsala researchers have successfully heated water from room temperature to 100,000 degrees Celsius in less than a millionth of a millionth of a second using an X-ray laser that can be regarded as the world’s fastest water heater.

In the experiment, a micrometre-thin jet of water was shot with extremely intense and ultrashort flashes of X-rays using the Linac Coherent Light Source (LCLS) X-ray free-electron laser at the SLAC National Accelerator Laboratory in the United States. The energetic X-rays punch electrons out of the water molecules, thereby destroying the balance of hydrogen and oxygen in the  water. This causes the atoms to feel a strong repulsive force and start to move violently, while the temperature of the water rises extremely rapidly.

­“It is not the usual way to boil your water,” said Carl Caleman of Uppsala University and the Center for Free-Electron Laser Science (CEFL) at Deutsches Elektronen-Synchrotron (DESY). “Normally, when you heat water, the molecules will just be shaken stronger and stronger. The hotter the temperature, the faster the motion of the molecules.”

In less than 75 femtoseconds (0.000000000000075 seconds), the water goes through a phase transition from liquid to plasma – a state of matter where the electrons have been removed from the atom, leading to a sort of electrically charged gas.

“But while the water transforms from liquid to plasma, it still remains at the density of liquid water, as the atoms didn't have time to move significantly yet,” said Olof Jönsson from the Department of Physics and Astronomy, Molecular and Condensed Matter Physics, at Uppsala University. “This exotic state of matter is nothing that can be found naturally on Earth. It has similar characteristics as some plasmas in the sun and in the gas giant Jupiter, but has a lower density. Meanwhile, it is hotter than Earth's core.”

The researchers used theoretical measurement models to explain the experimental results of the study, which may also be used for purposes including examining biological samples using X-ray lasers.

­“The observations from the study are also important to consider for the development of techniques to image single molecules or other tiny particles with X-ray lasers,” says Nicusor Timneanu, one of the key scientists developing the theoretical model used in the study.

The study is a result of a collaboration among nine research teams in Germany, the United States and Sweden. The Swedish part of the collaborative research project was led by Carl Caleman at Uppsala University. The German team was led by Professor Henry Chapman, who since January 2018 also works at Uppsala University.

The research results were published in the scientific journal Proceedings of the National Academy of Sciences, PNAS: Ultrafast non-thermal heating of water initiated by an X-ray Free-Electron Laser.