A new technique brings scientists closer than ever to harnessing the power of fusion, the process that fuels the sun. A fusion reactor is still a long way away, but tests bode well for a new way to contain fusion's fuel, hydrogen plasma.
Unlike starting fission reactions, which need only a minor nudge to get going, fusing hydrogen atoms is a very difficult task. Hydrogen nuclei repel each other, so the plasma that contains them must be very dense and very hot for the nuclei to collide strongly enough to fuse. Tokamaks--doughnut-shaped magnetic bottles--have long been the method of choice for maintaining a hot, dense plasma, but even the doughnut's magnetic fields need help in keeping the hydrogen atoms from drifting away and dissipating the plasma.
Now plasma physicists led by Olivier Sauter of the Swiss Federal Institute of Technology in Lausanne have shown that there is a better way to keep hydrogen atoms swarming together than the method currently being used at tokamaks. In a process called electron cyclotron current drive, the researchers point microwave beams at the plasma. The microwaves are tuned to the speed at which electrons in the plasma spin in the vertical plane. By controlling the angle of the microwaves, scientists can give an extra kick to electrons moving in one direction around the magnetic torus, which in turn induces a current around the doughnut and keeps the hydrogen atoms in the plasma from drifting apart, the researchers report in the 10 April issue of Physical Review Letters.
"It's very significant that they actually made it work," says Frank Skiff, a plasma physicist at Iowa State University in Ames. The big hurdles for fusion projects are political, however, as governments around the world have been scaling back their fusion programs in recent years. Compared to confining plasma, mustering political support for fusion research "is a much more difficult task," Sauter says.