Notes from the Fusion Energy Conference

The International Atomic Energy Agency (IAEA) held its 23rd biennial Fusion Energy Conference (FEC), often called “the Olympics of fusion” in Daejeon, in the Republic of Korea, between 11th and 16th October. The Korean Prime Minister Hwang-sik Kim and IAEA Deputy Director General Werner Burkart, Head of the Department of Nuclear Sciences and Applications, opened the event which drew more than 1500 participants from 39 countries, who in turn contributed 100
oral and 800 poster presentations. The high quality of the scientific programme reflected the vitality of the fusion programme around the world. Socio-economics studies presented at the meeting highlighted, once again, the potential competitiveness of fusion energy with low proliferation risks and the potential to contribute to a significant proportion of the electricity market by 2100. In the closing ceremony speech, the International Fusion Research Council Chairman Gyung-Su Lee reiterated the commitment made by Korea in participating in the development of fusion energy.

The vast majority of papers addressed key physics and technologies issues in preparation for ITER exploitation. Newly appointed ITER Director Osamu Motojima presented one of the overview papers on the ITER status and progress. This was complemented by a number of papers related to ITER construction in the ITER session.

A number of other highlights and novel ideas in the field of magnetic confinement covered key areas of research such as: new divertor concepts, energy and particle confinement, plasma flows and electric fields, good plasma confinement (H-mode) access and related instabilities (ELMs), fast particles and tokamak disruptions. Some of these discussions are summarised below.

Divertor designs that reduce the heat loads to the plasma facing components are key for future fusion power plants. Concepts with elongated connection length, such as the “snow flake” divertor at TCV tokamak in Lausanne, show promising results in this respect. These ideas will be further investigated at the spherical tokamak MAST at CCFE with the so called super-x divertor concept.

Reaching high confinement H-mode regimes closest to ITER parameters is another important aspect. Capitalising on its unique capability of operating at high current, JET experiments achieved good confinement H-modes at a plasma
current of 4 megaamperes. They established that the auxiliary power needs to exceed 1.7 times the H-mode threshold, in order to maintain the good confinement properties in a steady state. Studies of the H-mode access dependence on the plasma composition have indicated little difference between helium and deuterium plasmas. This is another important result since ITER will need to access the H-mode during the initial non-activated phase in helium in order to qualify a number of systems and techniques ahead of nuclear operation.

Good plasma confinement must be maintained in conditions compatible with a tokamak with all-metal plasmafacing components. Here, several experiments (i.e. at C-MOD and ASDEX Upgrade) indicate that plasma edge seeding with neon and nitrogen mitigates the heat loads at the metal divertor components. Seeding the plasma edge with nitrogen yields also improved plasma confinement, as the ASDEX Upgrade results show. Other experiments indicate that lithium coated  walls might increase the operating space and improve confinement.

A fundamental understanding of the mechanisms involved in the improved confinement of the Hmode regimes has always been a challenge. Improved diagnostics techniques and better theoretical understanding has resulted into new ideas and insights into these complex processes. The TJ-II stellarator showed correlations between the mean and fluctuating plasma flows and the transitions to H-mode. Fine scans of the twisting of the magnetic field lines also highlighted the role of resonant magnetic surfaces in the quality of the H-mode. ASDEX-Upgrade showed an intermediate phase prior to the transition to Hmode, indicating interplay between long wave length fluctuations and the decorrelation of the turbulence structures at the edge. A new mode of operation with similar characteristics was reported by C-MOD, the so called I-mode. It shows L-mode like particle confinement with an energy confinement that is similar to that of H-mode.

Duarte Borba, EFDA