Solar Plasma on Earth for over 30 Seconds
Fusion researchers use radio waves to control plasma for a record length of time in the Experimental Advanced Superconducting Tokamak (EAST)
Jülich, 19 November 2013 – Nuclear fusion imitates the processes that occur inside the sun and is regarded as a safe, environmentally friendly, and practically inexhaustible source of energy. One of the core issues in exploiting this technology is how to sustain the fusion reaction – which is unstable and difficult to control – over a prolonged period of time. An international team headed by Jülich fusion researcher Prof. Yunfeng Liang in collaboration with his Chinese partners Prof. Houyang Guo and Prof. Guosheng Xu reports on a new method for confining high-performance hot plasmas for longer in the prestigious journal Nature Physics (DOI 10.1038/nphys2795). Using radio waves, the team confined a high-energy plasma for a record of over 30 seconds in the Chinese fusion experiment EAST.
If it proves possible to utilize the fusion of atomic nuclei to generate energy, this could provide a solution to many of the open issues associated with the future energy supply. The ITER fusion reactor, which is a ‘tokamak’ like many fusion experiments, is considered the next big step in fusion research. It is expected to commence operation in Cadarache in the south of France before 2020 as part of a global cooperation. Scientists hope to demonstrate how nuclear fusion can be used to produce energy on a power-plant scale for the first time in ITER. However, controlling the fusion reaction is extremely challenging from a technical point of view.
No material in the world is capable of withstanding temperatures of over 100 million °C in the hot plasma. The plasma therefore has to be kept enclosed in the doughnut-shaped vacuum vessel by magnetic fields. However, this ‘magnetic cage’ alone is not enough to prevent wall contact over prolonged periods of time. Even within the magnetically confined plasma, many different instabilities can occur. Different waves and modes develop and there is also the high pressure of the constricted, highly energetic plasma flow.
Global collaborations at the large American and European fusion experiments successfully showed that these undesirable instabilities can be dampened or even completely suppressed by applying additional resonant magnetic perturbation fields. Jülich fusion researcher Prof. Yunfeng Liang is one of the pioneers of this method. Following basic tests at the TEXTOR experiment in Jülich, the technology was also applied for the world’s largest fusion experiment JET in the United Kingdom.
Now, in cooperation with Chinese fusion researchers, another promising method has been developed. Using high-frequency radio waves, the international EAST team succeeded in further confining the high-performance hot plasmas at the new superconducting fusion facility EAST in Hefei, China, contributing to the achievement of new record values in high-performance experiments. “We succeeded in generating an over 30-second plasma discharge in ‘H-mode’. This is a plasma state with excellent confinement properties, which is the subject of intensive research for the development of ITER,” explains Liang, who works at the Jülich Institute of Energy and Climate Research.
Experiments have shown that high-frequency radio waves can dampen undesirable instabilities in the plasma edge. Such ‘edge localized modes’ (ELMs for short) cause high transient heat loads on the plasma facing components, and therefore pose a risk – particularly in the steady state operation envisaged for ITER – of exceeding the durability of the walls. “The method described will therefore achieve much more than the results reported and go on to influence the long-term planning of ITER,” says Prof. Ulrich Samm. Together with Prof. Christian Linsmeier, he is head of Plasma Physics at the Jülich Institute of Energy and Climate Research, where the foundation was laid for the development of the new method.
J. Li, H. Y. Guo, B. N. Wan, X. Z. Gong, Y. F. Liang, G. S. Xu, K. F. Gan, J. S. Hu, H. Q. Wang, L. Wang, L. Zeng, Y. P. Zhao, P. Denner, G. L. Jackson, A. Loarte, R. Maingi, J. E. Menard, M. Rack & X. L. Zou
A long-pulse high-confinement plasma regime in the Experimental Advanced Superconducting Tokamak
Nature Physics (published online 17 November 2013), doi:10.1038/nphys2795
Report in Nature News and Views: Magnetically confined plasma: Fusion's Eastern promise?
Prof. Dr. Yunfeng Liang
Institute of Energy and Climate Research – Plasma Physics
Tel: +49 2461 61-6002
Prof. Dr. Ulrich Samm
Head of the Institute of Energy and Climate Research
Tel: +49 2461 61-3085
Tel: +49 02461 61-878