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On the road to Geneva...once more

-Sabina Griffith

This week, starting today, the world's fusion community will gather once again in the Palais des Nations in Geneva for the 22nd Fusion Energy Conference organized by the International Atomic Energy Agency (IAEA). This year, the conference will not only bear witness to the most recent progress in fusion research and technology - more than 60 papers and presentation will deal with ITER relevant research and development alone - it will also take time to celebrate a very special moment in the history of nuclear science.

50 years ago, from 1-13 September 1958, about 5000 scientists, government officials and observers from both East and West had come to the old League of Nations building in Geneva - and the nearby exhibition hall that had been constructed especially for this first nuclear world "fair" - to bear witness to the revelation of nuclear research.

Sponsored by the United Nations, the "Second United Nations International Conference on the Peaceful Uses of Atomic Energy", better known as the "Atoms for Peace" conference, was the largest international gathering ever to focus on the potential of taming nuclear energy for peaceful purposes.

50 years later, it is time to celebrate this event: "Fifty years of fusion... entering into the burning plasma era" is the title of this year' s anniversary fusion summit meeting. Newsline took this as a reason to talk to Valery Chuyanov and David Campbell, the Heads of the ITER Fusion Science and Technology Department, about the progress made in fusion over the past years and decades.

Newsline: Looking towards Geneva, where would you say do we stand today?

Chuyanov: Talking about the physics development in fusion science, I would say that considerable progress has been achieved over the past decades. Just look at this graph that shows the progress in Plasma Confinement Quality expressed by the fusion triple product (neTτE), which is closely related to the Lawson Criterion. The first tokamaks developed about 50 years ago achieved a density of 1019 m-3, a temperature of around 102 eV and confinement time in the order of half a millisecond. This resulted in an neTτE of about 5 x 1014 keVsm-3.

Up until now we have achieved a plasma density of up to 1020 m-3, a temperature of around 5 keV and a confinement time in the order of a second, leading to neTτE of over 1020 keVsm-3. So, we made progress of at least 100,000 times, meaning that every ten years, plasma confinement performance increases by a factor of about ten. The rate of progress in magnetic fusion is thus comparable to that of other advanced technologies such as accelerators or computer memory (Moore's Law).

Campbell: As you can see, the plot, limited by the current technology, has sort of saturated. That is in fact why we are building ITER. Our goal with ITER is to achieve a temperature of about 20 keV and a Lawson product of about 3 x 1020 sm-3.

Progress in plasma confinement performance compared to that of other advanced technologies

Newsline: So, what are the chances that we will achieve this goal?

Chuyanov: In the beginning of this year we were handed a list of questions by the scientific community resulting from the comprehensive review of the ITER design carried out last year. I am very glad to say today that all the questions on that list are solved, the baseline document is finalized. We are ready to build a machine that will satisfy all the necessary requirements. We are thus coming to the IAEA conference with conceptual solutions to all the problems addressed by the Scientific and Technology Advisory Committee (STAC) based on direct modeling and experiments. Direct modelling of ITER discharges confirm our expectations in the best possible way that we will gain Q~10 and perhaps even more. We now have to find a way how to implement the resulting design changes in a most cost effective way.

Newsline: What were the main issues on the list to solve?

Campbell: One of the most important issues certainly was disruption control. Not for ITER, as ITER is designed to survive disruptions up to very high levels. Nevertheless we have to solve the problem if we want to develop fusion power plants. We know that a fusion reactor will never operate with Edge Localized Modes (ELMs), high energetic disruptions at the plasma edge. They would erode so much material from the divertor that the plasma could not be maintained. But this is the mission of ITER: to find out what is the best mean to operate a fusion reactor. What is the best way to deal with ELMs? Special control coils or pellet injection? But again, we have another ten years to go before starting ITER operation and in the beginning of this conversation we have discussed what a lot can happen within ten years. Maybe we will see other ideas arising.


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