Laser Method Would Heat Fusion Materials Faster

Directly targeting ions with lasers could heat certain materials to 1 KeV — equivalent to more than 10 million °F — in 20 fs, or 100 times faster than previously demonstrated.

The method, proposed by researchers from Imperial College London, could advance the study of thermonuclear fusion, which seeks to replicate the sun's ability to produce energy. Other potential applications include proton imaging, cancer therapies and materials science.

When lasers are used to heat most materials, ions, which make up the bulk of matter, are only indirectly heated via electrons through electron-ion thermal equilibration or electron-ion instabilities.

The researchers used supercomputer modeling to demonstrate a method wherein a high-intensity laser was fired at a solid material containing two ion species — such as plastics — to create an electrostatic shockwave that heated ions directly, reducing the overall time to heat the material.

Normally, laser-induced electrostatic shockwaves push ions ahead of them, causing ions to accelerate away from the shockwave but not heat up. In a two-ion material used in the computer model, the shockwave instead created friction between ions, causing them to heat rapidly.

"That the actual material used as a target mattered so much was a surprise in itself," said professor Steven Rose. "In materials with only one ion type, the effect completely disappears."

In the simulation, heating was so fast in part because the material targeted was very dense. Ions were squeezed together to almost 10 times the usual density of a solid material as the electrostatic shockwave passed, causing the frictional effect to be much stronger than it would be in a less dense material, such as a gas.

While faster rates of temperature changes have been observed through the smashing of atoms, as with the Large Hadron Collider, those collisions occur between single pairs of particles only.

The laser-heating technique, if proven experimentally, could be the fastest heating rate ever demonstrated in a lab for a significant number of particles. The current record is held by the Lawrence Livermore National Laboratory in California, home to the world’s most energetic laser system.

The research was published in Nature Communications (doi: 10.1038/ncomms9905).