Energy & Power
Is a self-sustained fusion reaction (i.e. massive energy) nearly here?
By Anthony Capkun
September 26, 2013 – The dream of igniting a self-sustained fusion reaction with high yields of energy—a feat likened to creating a miniature star on Earth—is getting closer to becoming reality, according the authors of a new review article in the journal “Physics of Plasmas”.
Researchers at the National Ignition Facility (NIF) engaged in a collaborative project led by the U.S. Department of Energy’s Lawrence Livermore National Laboratory, report that while there is at least one significant obstacle to overcome before achieving the highly stable, precisely directed implosion required for ignition, they have met many of the demanding challenges leading up to that goal since experiments began in 2010.
The project is a multi-institutional effort including partners from the University of Rochester’s Laboratory for Laser Energetics, General Atomics, Los Alamos National Laboratory, Sandia National Laboratory and the Massachusetts Institute of Technology.
To reach ignition (defined as the point at which the fusion reaction produces more energy than is needed to initiate it), the NIF focuses 192 laser beams simultaneously in billionth-of-a-second pulses inside a cryogenically cooled hohlraum (from the German for ‘hollow room’)—a hollow cylinder the size of a pencil eraser.
Within the hohlraum is a ball-bearing-size capsule containing two hydrogen isotopes: deuterium and tritium (D-T). The unified lasers deliver 1.8MJ of energy and 500TW of power to the hohlraum, creating an ‘X-ray oven’ that implodes the D-T capsule to temperatures and pressures similar to those found at the centre of the sun.
“What we want to do is use the X-rays to blast away the outer layer of the capsule in a very controlled manner, so that the D-T pellet is compressed to just the right conditions to initiate the fusion reaction,” explained John Edwards, NIF associate director for inertial confinement fusion and high-energy-density science. “In our new review article, we report that the NIF has met many of the requirements believed necessary to achieve ignition—sufficient X-ray intensity in the hohlraum, accurate energy delivery to the target and desired levels of compression—but that at least one major hurdle remains to be overcome: the premature breaking apart of the capsule.”
Edwards said the team is concentrating its efforts on NIF to define the exact nature of the capsule’s instability and use the knowledge gained to design an improved, sturdier capsule. Achieving that milestone, he said, should clear the path for further advances toward laboratory ignition.