Engineering news
Visualisation of energy flow in fast ignition experiment
An international team of researchers has taken a step toward achieving controlled nuclear fusion thanks to a new energy imaging technique to monitor a process called ‘fast ignition’.
The team, led by scientists and engineers at the University of California, San Diego and General Atomics, developed the technique to "see" where energy is delivered during 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. The researchers published their findings online in the Jan. 11 issue of the journal Nature Physics.
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 the compressed fuel. Scientists consider fast ignition a promising approach toward controlled nuclear fusion because it requires less energy than other approaches.
However, in order for fast ignition to succeed, scientists must first find a way 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," said Farhat Beg, professor of mechanical and aerospace engineering and 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.
Christopher McGuffey, co-author on the paper, said: "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."
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.
Computer simulations also predicted an energy delivery efficiency as high as 15 per cent if the experimental design was scaled up. The prediction still needs to be tested experimentally. Beg said: “We hope this work opens the door to future attempts to improve fast ignition."