Differences in temperature reinforce perturbation in fusion plasma
In a fusion reactor the fuel being a very warm gas, the so-called plasma, is confined in a magnetic field. Chaotic processes in the plasma may perturb that field. Because of this, the heat can leak out of the plasma and the fusion process becomes less efficient. Researchers at the FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein (The Netherlands), have now found out, theoretically, that a difference in temperature is able to reinforce the perturbation of the field. This fresh understanding enables scientists to find ways in order to monitor the magnetic field better, to stabilize the plasma and to have the fusion in the nuclear reactor working better. The reserachers had their findings published in the Physical Review Letters of 29 June 2007.
A fusion reactor is based on the confinement of plasma with temperatures over one hundred million degrees by using a strong magnetic field. In present-day scientific experiments this succeeds within certain limits: if you increase the plasma temperature or if you reduce the magnetic field, then the volatile plasma is able to struggle out of the grasp of the magnetic field. This causes losses of energy, as a result of which the plasma is cooling down. Theoretically, and by experiment, this process has been investigated elaborately and it has been known for quite a long time that extreme differences in temperature between the core and the edge of a fusion plasma are able to break the confining magnetic field.
Now, fresh insight has been gained that due to differences in temperature during the break-up the magnetic field may generate electric currents that will perturb the field even more and determine the final amount of heat loss. This effect arises, because electrons move faster along magnetic field lines in the warmest part of the plasma than electrons in a less warmer area. When these electrons assemble, an electric current arises.
Such insights may lead to a better monitoring of the magnetic field in a future fusion reactor, which will then be able to operate more efficiently.
For more information, please contact Emiel van der Plas, phone +31 (0)30 609 68 30, Hugo de Blank, phone +31 (0)30 609 68 34, or Erik Min (scientific public information officer), phone +31 (0)30 609 68 36 or 06 13 52 15 01.
Reference:
Temperature gradients in fast collisionless magnetic reconnection,
Emiel V. van der Plas and Hugo J. de Blank, Phyiscal Review Letters, vol. 98 (2007), p. 265002
(http://link.aps.org/abstract/PRL/v98/e265002).