Super-hot water in less than a second

If you are sick of waiting for the kettle to boil for your morning coffee then a new technique to heat water with a powerful X-ray laser could be for you.

Scientists developed the technique at the Linac Coherent Light Source X-ray laser in California, US, and used it to heat water to 100,000 degrees Celsius – in just 75 femtoseconds, or 75 millionths of a billionth of a second.

The techniques overshot the pressure of steam required to produce a good espresso somewhat, and instead turned the water into a dense electrically charged state known as plasma, resembling some extreme cosmic environments.

“It has similar characteristics as some plasmas in the sun and the gas giant Jupiter, but has a lower density. Meanwhile, it is hotter than Earth’s core,” says researcher Olof Jönsson from Uppsala University in Sweden.

The team’s technique, which was written up in the journal Proceedings of the National Academy of Sciences may help scientists use X-rays to study the structure of liquids.

X-ray diffraction is a common technique for looking at the structure of crystals and other solids, but this experiment shows that the approach will need to be altered when applied to liquids.

“Any sample that you put into the X-ray beam will be destroyed in the way that we observed,” says co-author Kenneth Beyerlein from the Centre for Free-Electron Laser Science (CFEL) in Hamburg, Germany.

“If you analyse anything that is not a crystal, you have to consider this.”

The team’s measurements showed that the water molecules barely responded to the X-ray laser for the first 25 femtoseconds, but 50 femtoseconds they were shedding electrons and turning to plasma.

The change to an electrically charged gas is the key to the sudden heating, which is quite different to what happens in the average electric jug, explains Carl Caleman from the Deutsches Elektronen-Synchrotron, also in Hamburg.

“The energetic X-rays punch electrons out of the water molecules, thereby destroying the balance of electric charges,” he says. “So, suddenly the atoms feel a strong repulsive force and start to move violently.”

Despite being common on Earth, water has unusual characteristics that make it interesting to study, says Jönsson.

“Water really is an odd liquid,” he notes, “and if it weren’t for its peculiar characteristics, many things on Earth wouldn’t be as they are, particularly life.”