Reverse Field Pinch (RFP) devices rely on a combination of toroidal and poloidal magnetic fields to confine the plasma, just like tokamaks. However, in the case of an RFP device, both fields are of the same magnitude with the toroidal field being much smaller. If this concept succeeds in achieving the power and confinement conditions needed for fusion reaction, it would offer a less elaborate alternative to a tokamak. Even for large devices, it would not require costly superconducting coils to create large toroidal fields. Moreover, it could manage fusion with ohmic heating only, omitting the additional heating techniques. However, RFP experiments have suffered from poor stability, which eventually downgraded the confinement performance as a result of magnetic turbulence.

Scientists of the European Reversed Field Pinch fusion experiment, RFXmod, led by Piero Martin and Maria Ester Puiatti, have now discovered that the plasma spontaneously chooses a more stable state if it is operated at high currents (above approximately 1.5 MA). The newly discovered equilibrium features strong electron transport barriers and improved confinement. Moreover, these conditions and the duration of the equilibrium state improve with the increasing plasma current. From present experiments, the potential of achieving such steady regimes, so called single axis helical states in multi-megaampere RFP devices can be inferred. This result sheds new light on supporting the RFP as a low-external field, nondisruptive, ohmic approach to fusion.

The work of the scientists has drawn wide-spread attention even from outside the fusion research sector thanks to publication on the front page of Nature Physics, one of the world’s leading physics journals.

Thanks to Piero Martin, leader of RFX-mod Padova, for his contribution to this article.

The paper is available on-line at

Full reference: Nature Phys. 5, 570 – 574 (2009)

More information on the RFX-mod device can be found here

ISSN 1818-5355

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editors: Christine Rüth, Örs Benedekfi

layout: dolp & partner

© Jérôme Paméla (EFDA Leader) 2009.

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