Stark choice for tokamaks

The tokamak has proved itself to be the most successful device for magnetically confining the heat in fusion-grade plasmas. However, the fusion community is always seeking ways to improve the performance of tokamaks, and recent work has shown that radial variations in both the magnetic and electric fields inside the plasma can influence the confinement. Now, for the first time, a team at General Atomics in San Diego, California, has measured these key quantities at the same time. This new diagnostic is based on the so-called motional Stark effect. In the traditional Stark effect the energy levels in an atom -- and hence any radiation emitted by the atom -- are split by a strong electric field. And by measuring the polarization of this light as well, it is possible to find out about the magnetic field inside the plasma. The technique is now being investigated at other fusion laboratories. (UK)