'Seeing' where energy goes can make n-fusion possible

A new technology that "sees" where energy goes may bring scientists closer to realising nuclear fusion - a process that powers the Sun and other stars and has the potential to supply the world with limitless, clean energy.

Scientists and engineers from University of California (UC)-San Diego and defence consulting firm General Atomics have developed a novel technique to "see" where energy is delivered during a process called fast ignition, which is an approach to initiate nuclear fusion reactions using a high-intensity laser.

Visualising the energy flow enabled researchers to test different ways to improve energy delivery to the fuel target in their experiments.

"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," explained Christopher McGuffey, assistant project scientist and co-author on the paper published in the journal Nature Physics.

Scientists consider fast ignition a promising approach toward controlled nuclear fusion because it requires less energy than other approaches.

But 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.

"This has been a major research challenge since the idea of fast ignition was proposed," added Farhat Beg, director of the Center for Energy Research at UC San Diego.

To tackle this problem, the team 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 seven percent) efficiency of energy delivery from the high-intensity laser to the fuel.

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

"We hope this work opens the door to future attempts to improve fast ignition," Beg noted.