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Researchers from the Dutch Plasma Physics Institute Rijnhuizen, together with colleagues from Denmark and Germany, have discovered that so-called magnetic islands in fusion reactors can reflect microwaves. Their result was published in Physical Review Letters of 15 September 2009.

Magnetically-confined plasmas for nuclear fusion research exhibit a number of instabilities. One class of these are the so-called magnetic islands, which can destroy the confinement. One way of controlling these islands is by heating them at exactly the right spot with a beam of microwaves. During experiments on the German TEXTOR fusion experiment, the Rijnhuizen researchers discovered a previously unknown phenomenon: under certain conditions, the islands reflect part of the microwaves.

With a clever use of limited resources, a dedicated diagnostic system was designed and built to characterize the effect. The details of this system will soon be published in a Review of Scientific Instruments paper.

According to the measurements, the reflection of microwaves strongly depends on the heating power and the density of the plasma. To get a better understanding of the phenomenon, further experiments on the German Asdex Upgrade tokamak are planned. These experiments will indicate whether or not designers for the international °ÄÃÅÁùºÏ²Ê¸ßÊÖ experiment should take the reflections into account. It is possible, though not expected, that the reflected beams blind delicate diagnostics installed on °ÄÃÅÁùºÏ²Ê¸ßÊÖ.

Reference Strong Scattering of High Power Millimeter Waves in Tokamak Plasmas with Tearing Modes, Phys. Rev. Lett. 103, 125001 (2009) Click here: