'Seeing' where energy goes may make N-fusion possible: study

A new technique to 'see' where energy is delivered in a reactor has brought researchers a step closer towards achieving controlled nuclear fusion - a process that powers the Sun and other stars, and has the potential to supply the world with limitless, clean energy.

The method was developed to see where energy is delivered during a process called fast ignition, an approach to initiate nuclear fusion reactions using a high-intensity laser.

"Before we developed this technique, it was as if we were looking in the dark. Now, we can better understand where energy is being deposited so we can investigate new experimental designs to improve delivery of energy to the fuel," said Christopher McGuffey from the University of California.

Fast ignition involves two stages to start nuclear fusion. First, hundreds of lasers compress the fusion fuel (typically a mix of deuterium and tritium contained in a spherical plastic fuel capsule) to high density.

Then, a high-intensity laser delivers energy to rapidly heat (ignite) the compressed fuel. Scientists consider fast ignition a promising approach towards controlled nuclear fusion because it requires less energy than other approaches.

In order for fast ignition to succeed, scientists need to overcome a big hurdle - how to direct energy from the high-intensity laser into the densest region of the fuel.

To tackle this problem, researchers devised a way to see, for the first time, where energy travels when the high-intensity laser hits the fuel target.

The technique relies on the use of copper tracers inside the fuel capsule. When the high-intensity laser beam is directed at the compressed fuel target, it generates high-energy electrons that hit the copper tracers and cause them to emit X-rays that scientists can image.

After experimenting with different fuel target designs and laser configurations, researchers eventually achieved a record high (up to 7 per cent) efficiency of energy delivery from the high-intensity laser to the fuel.

This result demonstrates an improvement on efficiency by about a factor of four compared to previous fast ignition experiments, researchers said.

The findings were published in the journal Nature Physics.