Worldwide efforts to harness fusion—the power source of the sun and stars—for energy on Earth currently focus on two multibillion dollar facilities: the ITER fusion reactor in France and the National Ignition Facility (NIF) in California. But other, cheaper approaches exist—and one of them may have a chance to be the first to reach “break-even,” a key milestone in which a process produces more energy than needed to trigger the fusion reaction.
Researchers at the Sandia National Laboratory in Albuquerque, New Mexico, will announce in a Physical Review Letters (PRL) paper accepted for publication that their process, known as magnetized liner inertial fusion (MagLIF) and first proposed 2 years ago, has passed the first of three tests, putting it on track for an attempt at the coveted break-even. Tests of the remaining components of the process will continue next year, and the team expects to take its first shot at fusion before the end of 2013.
Fusion reactors heat and squeeze a plasma—an ionized gas—composed of the hydrogen isotopes deuterium and tritium, compressing the isotopes until their nuclei overcome their mutual repulsion and fuse together. Out of this pressure-cooker emerge helium nuclei, neutrons, and a lot of energy. The temperature required for fusion is more than 100 million°C—so you have to put a lot of energy in before you start to get anything out. ITER and NIF are planning to attack this problem in different ways. ITER, which will be finished in 2019 or 2020, will attempt fusion by containing a plasma with enormous magnetic fields and heating it with particle beams and radio waves. NIF, in contrast, takes a tiny capsule filled with hydrogen fuel and crushes it with a powerful laser pulse. NIF has been operating for a few years but has yet to achieve break-even.
Sandia’s MagLIF technique is similar to NIF’s in that it rapidly crushes its fuel—a process known as inertial confinement fusion. But to do it, MagLIF uses a magnetic pulse rather than lasers. The target in MagLIF is a tiny cylinder about 7 millimeters in diameter; it’s made of beryllium and filled with deuterium and tritium. The cylinder, known as a liner, is connected to Sandia’s vast electrical pulse generator (called the Z machine), which can deliver 26 million amps in a pulse lasting milliseconds or less. That much current passing down the walls of the cylinder creates a magnetic field that exerts an inward force on the liner’s walls, instantly crushing it—and compressing and heating the fusion fuel.
Researchers have known about this technique of crushing a liner to heat the fusion fuel for some time. But the MagLIF-Z machine setup on its own didn’t produce quite enough heat; something extra was needed to make the process capable of reaching break-even. Sandia researcher Steve Slutz led a team that investigated various enhancements through computer simulations of the process. In a paper published in Physics of Plasmas in 2010, the team predicted that break-even could be reached with three enhancements.