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ITER NEWSLINE 157
The lights are dim in Tore Supra's Control Room and the conversations subdued. A plasma shot is imminent and, while the operation has become routine for this 22-year-old machine, the atmosphere in the room is still one of slight tension, expectation and apprehension.
A figure on a small digital panel reads 46,551—this is the number of shots that have been fired since Tore Supra saw First Plasma during the night of 30 March to 1 April 1988. By the end of the work day, the figure will have changed to somewhere around 46,580. Thirty shots is a daily average for an experiment campaign like the one ongoing.
Today's "pilot" is a young engineer, an ELMs-control specialist named Éric Nardon who "learned to drive tokamaks" at MAST, Culham's Mega Ampere Spherical Tokamak. His job is to make sure that all parameters are optimal before pushing the button. Éric works in close coordination with Julien Hillairet and Annika Ekedahl, today's "physicists in charge." As the present three-month campaign is drawing to an end, the Tore Supra team focuses on one objective: "To do the GigaJoule again."
In Tore Supra parlance, "the Gigajoule" is the world-record shot of December 2003, unmatched to this day, which lasted six and a half minutes and produced one Gigajoule of energy.
Seven years after this historical shot, Tore Supra is almost a new machine and its operators have considerably more power at their disposal. The tokamak, still the third largest in the world after JET and JT-60U, was recently fitted with new steady-state klystron amplifiers and more powerful heating antennas that make "ITER-relevant" experiments possible.
"We're getting closer everyday. Compared to 2003, we can now produce significantly longer shots and use more hybrid power," says Éric. The present campaign's experiments aim at realizing "the ideal physics configuration" that will enable shots as long as 15 minutes and an energy release of over one Gigajoule.
The shots also provide for ITER-relevant "side experiments": this morning for instance, a laser beam was used to vaporize part of a small tungsten target into the vacuum vessel and measure the particles' penetration into the plasma. The data collected will contribute to optimizing the ITER divertor which is partly made of tungsten.
What happens inside Tore Supra's vacuum vessel, however, is very different from what will happen in ITER's: the CEA-Euratom machine was not designed to realize deuterium-tritium fusion reactions and no fusion power production was ever expected from its hydrogen, helium or deuterium-only plasmas.
What made Tore Supra unique in its time was its capacity, thanks to a partly superconducting magnet system, to explore the realm of long-duration plasmas. Twenty-two years after it saw First Plasma, its contribution to steady-state operation—and hence to the future of fusion—remains essential.
The 31st annual meeting of the Fusion Power Associates took place in Washington D.C. on 1-2 December. The meeting brings together senior representatives of the US and international fusion communities and US policymakers to review the status of fusion research and consider the way ahead.
This year's meeting reviewed the fusion research landscape in the context of the approaching ignition experiments in the US's National Ignition Facility (NIF) and the progress on construction of ITER. The meeting therefore provided an excellent overview of the progress which is being made in fusion R&D towards the study of burning plasmas.
Many of the presentations from both the magnetic and inertial confinement communities reflected the universal awareness within these communities that future progress on fusion energy development towards the construction of fusion power plants depends heavily on advances in fusion technology. Proposals are being drawn up by the magnetic and inertial confinement communities for devices which can address key issues in the areas of fusion-relevant materials and reactor component testing, while taking the science of fusion energy forward into the burning plasma area.
The presentations made on these concepts provoked a lively discussion on the way ahead amid the recognition that the fusion community will have to work hard to secure the required funding for these ambitious, but necessary, projects in the current global economic situation.
A delegation from the ITER Cooling Water System Section recently visited the Dipartimento di Ingengeria Meccanica, Nucleare e della Produzione (DIMNP) in Pisa, Italy. The University is in close proximity to the famous leaning tower. During the meeting between the Section and DIMNP, the possibility of future collaborations with the University of Pisa was discussed utilizing direct academic experience for the ITER cooling water system design.
The DIMNP is a research structure of the University of Pisa, with more than 50 academic and research staff members and about 30 technical administrative staff. Since its institution, the department has been characterized by a strong orientation towards collaborations with Italian and European industries in applicative research projects with wide scientific and technological significance.
The DIMNP Nuclear Section has long experience in computer code analysis, in particular using the RELAP code for the thermal-hydraulic transient analysis in fission reactors; computational fluid dynamics to evaluate the various regimes of velocity, pressure and temperature; and specific codes such as the Enel Code for analysis of radionuclide transport (ECART) to evaluate the dust re-suspension during a loss of pressure accident in the ITER vacuum vessel (STARDUST campaign, developed in collaboration with ENEA UTFUS Frascati).
Based on this relevant expertise, a future collaboration between DIMNP and the ITER cooling water group would be possible on the steady state and transient thermal-hydraulics analyses to simulate the ITER cooling water system during plasma operations to be performed by Fathom and RELAP codes.
Within the University of Pisa, the Gruppo di Ricerca San Piero a Grado was created in December 2003 to maintain and improve the Italian competencies in the field of the nuclear technology, performing R&D, engineering services and training activities according to the tradition of the Department of Mechanics, Nuclear and Production Engineering (DIMNP) and of the University of Pisa (UNIPI).
In last week's Newsline we reported about the recent workshop on earthing and electromagnetic compatibility (EMC) design for ITER. For the article we interviewed one of the participants, the UK expert on electromagnetic compatibility and functional safety, Keith Armstrong of Cherry Clough Consultants, but unfortunately the recorder failed to record the interview. Welcome to the machine!
So we asked Keith to repeat what he had said about the importance of grounding ITER:
Keith Armstrong: "ITER is much larger than any previous tokamak, so the common technique of using insulation breaks, used by previous tokamaks, would have to handle much higher voltages, making them very much more costly— and significantly increasing the safety problems."
"ITER has to operate in fusion mode for many seconds, even minutes, when previous tokamaks only had to operate for a second or so. So interference with its measurement and control systems needs to be lower. ITER is more like an industrial product, that has to reliably do a job of work, than a scientific experiment that only has to prove or disprove a theory!"
"To deal with these issues whilst also improving safety and reducing the cost—as well as for other more technical reasons that I don't understand—the design of ITER is different than what has gone before. It will be based on a 'low-impedance' tokamak."
"A 'low-impedance' tokamak has a very low-resistance vacuum vessel, and ITER's is nearly 1,000 times less resistive than Tore Supra, for example. It also closely 'meshing-bonds' all of its metalwork—including the reinforcing bars in its concrete walls and floors. This will allow us to avoid using most of the costly insulation breaks, while also reducing the noise in the signals and increasing safety."
"Of course, the metalwork will not be meshed in the area in which the resulting current loops might disturb the plasma! But this area won't have any poeple in it anyway, because it is too close to the vacuum vessel and so too radioactive. The 'mesh-common-bonding' technique proposed for ITER has been widely used for decades in other industrial applications, including those that use high levels of magnetic field that fluctuate as much, if not more, than ITER's will. So it's not a risky or untried technique—in fact IEC good-practice guidelines recommending it for controlling interference were first published in 1997!"
"When we use mesh-bonding in other installations, their users are usually very surprised by how much better their signal quality is! They expected not to have gross interferences, but they hadn't expected to get much better signal quality all the time. So I am confident that ITER's 'low impedance' design will allow researchers to discover new things and achieve better control."
"Hopefully, this new approach to tokamaks will speed the day when fusion power is so common that we no longer have to overheat our world by burning fossil fuels."