Nuclear powerOne step closer to controlling nuclear fusion

Published 17 January 2012

Nuclear fusion – heating gas to several million degrees so it becomes plasma — holds the promise of abundant energy, but controlling the fusion process inside a nuclear reactor is exceedingly difficult; scientists achieve a breakthrough in controlling instability in the plasma

Scientists have achieved a nuclear power milestone by managing to stop the growth of instabilities inside a nuclear fusion reactor. This may well be a breakthrough for nuclear power because nuclear fusion, while being challenging to control, is nevertheless extremely promising.

Nuclear fusion is an attempt to reproduce the energy of the Sun in an Earth-based reactor system. When gas is heated to several million degrees it becomes plasma. Sometimes an instability will appear in the plasma and grow large enough to perturb the plasma, making it vibrate despite the presence of the magnetic field in which it is contained. If the plasma touches the walls of the reactor, it will cool rapidly and create large electromagnetic forces within the structure of the machine.

An Ecole Polytechnique Fédérale de Lausanne (EPFL) release reports that the challenge is to reduce the instabilities deep within in the interior of the plasma so that they do not amplify, while at the same time allowing the reactor to continue to function normally.

It is thus necessary to work within the specific configuration of these fusion reactors, where the plasma is strongly confined by a magnetic field. By adjusting an antenna that emits electromagnetic radiation, Jonathan Graves and his colleagues from EPFL’s Center for Research in Plasma Physics were able to quench the instabilities, when they appear, in the precise region where they are forming and without perturbing the rest of the installation.

The release notes that the physicists first conducted simulations to verify the extent to which specific radiation frequencies and locations of application would suppress the growth of instabilities. Then they carried out tests to confirm their calculations. The beauty of their approach is that they were able to use antennas which are used as part of the system to heat the plasma and which are already present in the Joint European Torus (JET), the largest reactor currently in use.

The release also points out that, surprisingly, the simulations and the tests showed that heating and instability suppression can be combined, by aiming the radiation slightly off-center in the plasma.

The next step will be to add a detector system that will make it possible to neutralize instabilities in real time over longer time periods. These improvements can then be implemented in the ITER fusion reactor, currently in development in Southern France.

— Read more in J. P. Graves et al., “Control of magnetohydrodynamic stability by phase space engineering of energetic ions in tokamak plasmas,” Nature Communications 3 (10 January 2012), article no. 624 (doi:10.1038/ncomms1622)

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