15 August 2012
One of the most promising approaches to controlled thermonuclear fusion is a hot plasma magnetically confined in a doughnut-shaped “tokamak” reactor. However, scientists have struggled with the safe dissipation of power exhaust from this hot plasma. Hundreds of megawatts worth of charged particles accumulate in the reactor chamber. An exhaust channel called a divertor can handle this overload, but until now no method has been found to lower the heat and power density to a manageable level.
Recent work at Lawrence Livermore National Laboratory, Livermore, Calif., has produced the Snowflake Divertor for Nuclear Fusion Reactors. This technology can dissipate the 100 MW/m2(more than the Sun’s surface) of power load on future commercial reactors by spreading the heat out over a large area in accordance with the way heat fluxes form. Physicists developed a magnetic configuration in which the shape of the poloidal magnetic field lines, which loop through the hole of the tokamak doughnut, are reminiscent of a snowflake. The divertor is then able to create a large zone of weak poloidal magnetic field, which has the effect of flaring the plasma flow and dramatically decreasing heat fluxes.
Livermore Lab performed this work in conjunction with the Center for Research in Plasma Physics, Lausanne, Switzerland, which were the first to generate the snowflake geometry in an operating tokamak, and Princeton Plasma Physics Laboratory, Princeton, N.J., which demonstrated a dramatic reduction of the divertor heat flux in the tokamak with high power densities.