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Of Interest

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The JET project team in 1977: Paul-Henri Rebut (centre) and colleagues  Alan Gibson (UK), Giulio Celentano (Italy), Ettore Salpietro (Italy), John Last (UK), Barry Green (Australia), Peter Noll (Germany) et Jean-Pierre Poffé (Belgium), Ingevar Selin (Sweden), Dieter Eckhart (Germany). © EFDA
Had Paul-Henri Rebut allowed himself a bit of lyricism, he could have said that 500,000 years after harnessing fire, man was "discovering" it for the second time.

The fire that was lit on 9 November 1991 in Culham, UK, however, was of a different kind: it was a controlled thermonuclear fire confined in a magnetic cage and feeding on the fusion of deuterium and tritium nuclei.

Rebut had been waiting for this moment for most of his adult life. He had designed the Joint European Torus (JET) in that perspective. Twenty years later to the day, the memory was still vivid and the emotion intact. "What happened at JET on 9 November 1991 made ITER possible," he confided in a telephone interview from his home in Paris. "Without it, I doubt there would be any significant fusion research today."

In 1991, JET had been producing deuterium-only plasmas for more than eight years and the installation's performance had progressively approached reactor conditions. In conformity with the project's scientific program, it was time to begin feeding the machine with the actual fusion mix — deuterium and tritium.

On that day twenty years ago, the proportion of tritium was deliberately kept low — no more than 10 to 20 percent, recalls Rebut; the "correct fuel" is an equal proportion of both elements. Still, as the pulse was shot, a peak fusion power of 1 MW was obtained for two seconds. It was precisely 7:44 p.m. at Culham and controlled fusion power, which three generations of physicist had pursued, was at last becoming reality.

"I must say we took a serious risk that day," admits the former director of JET (1985-1992) and later of ITER (1992-1994). "The media had heard about our preparations for tritium operation and insisted on being present in the control room. It was a serious dilemma for me, because many things could have gone wrong. But I decided to accept their presence because the public, who pays for our research, is entitled to be informed. And the following day, every major newspaper in the world carried trumpeting headlines about the breakthrough that had occurred in JET."

"The achievement," wrote the New York Times, "is a major step in harnessing for constructive human use the kind of thermonuclear fire that lights the sun and produces the awesome blast of the hydrogen bomb." In France, Le Monde hailed the "event that the world physics community had long expected." And, as could be anticipated, the expression "Sun in a bottle" was everywhere...

There were, of course, more important rewards than headlines, however large and enthusiastic. "By demonstrating that fusion was feasible" read the official press release, the European JET had "laid a firm foundation for the proposed experimental reactor ITER, which is planned to be carried out as a worldwide collaboration."

Rebut, as always, was already one step ahead. "JET in itself was of no use," he explains, "if it didn't open the path for a new machine." Indeed, the ITER Project entered Engineering Design Activities the following year and Joint Work Sites were set up in three locations, San Diego (US), Garching (Germany) and Naka (Japan).

From Culham, the thermonuclear torch passed to Princeton, New Jersey: on 9 December 1993 it was TFTR's turn to make headlines. Using a 50/50 mix of deuterium and tritium, the US tokamak achieved 6.2 MW of fusion power and crossed the symbolic 10 MW threshold at the end of the following year.

In the "friendly competition" between the two tokamaks, the final goal was scored by JET in 1997 with a triple record-breaking achievement: 22 MJ of fusion energy in one pulse, 16 MW of peak fusion power, and a 65 percent ratio ("Q") of fusion power produced to total input power.

As for Paul-Henri Rebut, the fusion adventure that he had joined in 1958 continues. On leaving JET in 1992, he was appointed director of ITER, which he led until 1994. At age 76, his passion for fusion machines is undiminished. Always "a heretic" he is now dreaming of hybrid reactors that would combine the energy of fusion neutrons to the power of fission reactions.

During "The eyes and ears of ITER," Diagnostic Head Michael Walsh acknowledged all those who have contributed to the knowledge base for ITER diagnostics: whom he named the "many patient people past and present."
Surrounded by lengths of metal pipe, batteries, a water kettle, and a few small magnets, Diagnostic Division Head Michael Walsh undertook to explain, in lay terms, the diagnostics planned for ITER during an Inside ITER seminar on Thursday, 10 November.

He used his props to illustrate the ways in which ITER's 45 diagnostic systems will provide precious feedback for the control of the plasma, for machine protection, and for an understanding of the physics during operation.

"Not having diagnostics in the machine would be like flying in the dark," Michael said. "We couldn't 'see' what was happening on the inside. In fact, we couldn't even start the machine without the information that diagnostics will provide to manage operational parameters like coil current."

A basic set of diagnostics will be required from day one in ITER to provide the measurements that will give the green light—a sort of "bill of clean health"—for operation to begin. "But from day two forward, explains Michael, "we'll need much more information than that." ITER's size and scale will create special challenges for the diagnostic systems: ITER's plasma volume is ten times that of the largest operating tokamak JET, its plasma current up to three times greater, its pulse ten to one hundred times longer, and its neutron environment much harsher.

"Challenge is just an opportunity," says Michael. "We are tackling the challenges in a coordinated way, with a capable team within the ITER community and support from many places around the world."

ITER-India started off with 50 scientists and engineers who initially joined from the Institute for Plasma Research (IPR) at Gandhinagar. Now the team has grown to 120 permanent staff. In addition, about 95 contract personnel from engineering and other service providers also work at ITER-India, bringing total staff to 215 people-strong. In additon, the ITER-India laboratory for various ITER R&D and prototype activities has been completed and is now ready for equipment.

When the United Nations comes together in Durban, South Africa, at the end of this month for the next Climate Change Conference, representatives will be faced with some really bad news: The preliminary report from the Carbon Dioxide Information Analysis Center, based at the Oak Ridge National Laboratory in Tennessee, indicates that the global output of heat-trapping carbon dioxide jumped by the biggest amount on record.

The figures for 2010 mean that levels of greenhouse gases are even higher than the worst case scenario outlined by climate experts just four years ago. "It's a big jump," the Associated Press quotes Tom Boden, director of the Energy Department's Carbon Dioxide Information Analysis Center, as saying. "From an emissions standpoint, the global financial crisis seems to be over."

For further reading we recommend the following articles on this issue:

The upper graph illustrates the D-alpha signal and coil current with ELM control by non-axisymmetric field perturbation; the experiments were supported by advanced diagnostics such as electron cyclotron emission imaging (ECEI) (shown in lower images).
There is further promising news with regard to ELM control in ITER: on 3 November, the Korean National Fusion Research Institute (NFRI) announced that the Korean tokamak KSTAR has achieved full ELM suppression by applying non-axisymmetric magnetic perturbations. With this announcement, KSTAR joins the selective club of tokamaks which have achieved elimination of the large impulsive loads on in-vessel components created by Type I ELMs. These ELM-related power fluxes could potentially cause excessive erosion of the plasma-facing components and increase the maintenance requirements for such components, reducing the availability of ITER.

The ELM-suppression technique demonstrated in KSTAR was originally developed at DIII-D (General Atomics, USA) and later demonstrated at ASDEX-Upgrade (IPP-Germany); this research led to the inclusion of a dedicated set of in-vessel coils for ELM control in the ITER design. For the first time, however, the experiments in KSTAR achieved ELM suppression with a perturbation with the lowest toroidal periodicity (n=1); compared to results in DIII-D (n=2 and n=3) and ASDEX-Upgrade (n=2). The n of the toroidal perturbation describes the type of deformation that the perturbation causes to the plasma along its toroidal length, which is a perfect circle around the central solenoid in its unperturbed condition (seen from above).

The n=1 perturbation causes a shift of this circle in the radial direction; the n=2 perturbation causes a squeeze of the circle towards a shape similar to that of the number 8 and the n=3 perturbation deforms the circle into a clover shape. Increasing the n of the perturbation applied to the plasma requires, in general, a more complex system of coils, and the coils themselves have to be located closer to the plasma, which poses significant engineering challenges in fusion devices. On the other hand, higher n perturbations affect the confinement and stability of the plasma less, thus allowing a larger operational range of parameters for a given strength of edge perturbation. 
While KSTAR's third experimental campaign focused on the achievement of the enhanced confinement plasma regime known as H-mode (which is the ITER reference regime for fusion power production), the fourth campaign performed this year focused on active ELM control by various methods such as non-axisymmetric (NA) magnetic perturbation; injection of short and fast pulses of fuelling gas by supersonic molecular beam injection (SMBI); vertical jogs of the plasma column and edge electron heating by electron cyclotron resonance heating (ECRH).

By applying a n=1 non-axisymmetric field, KSTAR researchers observed different effects on the ELMs—going from an increase of their frequency and decrease of size (ELM control) to full ELM suppression—depending on the details of the perturbation applied. These ELM control experiments were supported by advanced diagnostics such as electron cyclotron emission imaging (ECEI), which can provide measurements of the plasma electron temperature with high spatial and time resolution at the edge, showing significant differences between the various ELM regimes studied (uncontrolled ELMs, controlled ELMs and suppressed ELMs), which are being presently analyzed.

While ELM control with n=1 non-axisymmetric perturbations had been observed previously in other tokamaks (such as JET with external coils), it is the first time that ELM suppression has been achieved with n=1 perturbation. While the implications of this finding for ITER remain to be analyzed in detail, it corroborates the reproducibility of the achievement of ELM suppression in tokamaks by the application of non-axisymmetric perturbations as planned for ITER, and may potentially lead to a simplification of the operation of the ELM control coil system in ITER and of its robustness to individual failure of coils.

Besides this major result on ELM control, KSTAR has also explored other schemes of ELM control which could be potentially applied in ITER (for the burning plasmas or ramp-up/down phases)—including injection of fast-gas pulses with SMBI (mimicking pellet pacing in ITER), edge heating and current drive with ECRH and electron cyclotron current drive (ECCD), and vertical plasma position oscillations—with positive results that need to be evaluated in detail.

We'd also like to thank Alberto Loarte, ITER Senior Scientific Officer, for his contribution to this article.

The visitors were accompanied on the ITER worksite by Jin Ju, Director of the General Administration Directorate for ITER, Su Mingxing from the Office of the Director-General, and Ivone Benfatto, Hao Tan and Joel Hourtoule from the Electrical Engineering Division.
On Monday 7 November, a delegation of 20 visitors from China Southern Power Grid Co., Ltd (CSG) were welcomed to the ITER worksite, invited by Schneider Electric Pacific and France.

CSG invests, constructs and operates power networks in five southern provinces of China over an area of one million square kilometres. Part of a two-week visit to France, the visit to ITER was a highlight, according to delegation members. They were greatly interested by ITER's power transmission and distribution, including the Chinese contribution in terms of design and equipment.