Subscribe options

Select your newsletters:


Please enter your email address:

@

News & Media

Latest ITER Newsline

  • Computer-Aided Design | A new platform with Australia

    In September 2016, the signature of a Cooperation Agreement between the Australian Nuclear Science and Technology Organisation (ANSTO) and the ITER Organization [...]

    Read more

  • ITER Council | Project metrics confirm performance

    The governing body of the ITER Organization, the ITER Council, met for the twenty-first time on 15 and 16 November 2017 under the chairmanship of Won Namkung (K [...]

    Read more

  • COP 23 | Placing ITER on the global scene

    On the western bank of theRhine and not far from the seat of the UN Climate Change Secretariat, world leaders are discussing how to push ahead for international [...]

    Read more

  • Japan's MEXT Minister | Seeing is believing

    On 4 November, ITER received Yoshimasa Hayashi, the Japanese Minister of MEXT—the Ministry of Education, Culture, Sports, Science and Technology with oversight [...]

    Read more

  • Architect Engineer | ENGAGE receives prestigious award

    Since 2006, the French 'Grand Prix de l'Ingénierie' has recognized engineering projects and/or teams that are remarkable in terms of scope, innovation, complexi [...]

    Read more

Of Interest

See archived articles

Turbulent behaviour under radar scrutiny

Robert Arnoux

The DREVE team atop Tore Supra: Pascale Hennequin (LPP), Laure Vermare (LPP) and Jean-Claude Giacalone (IRFM). A fourth member, Roland Sabot, was absent on the day the picture was taken. (Click to view larger version...)
The DREVE team atop Tore Supra: Pascale Hennequin (LPP), Laure Vermare (LPP) and Jean-Claude Giacalone (IRFM). A fourth member, Roland Sabot, was absent on the day the picture was taken.
Fusion plasmas are turbulent. They develop a large variety of instabilities and fluctuations that drain energy out of their core and reduce the overall performance of fusion devices.

The physics that drive turbulent phenomena are now well identified. Finding means to mitigate their consequences however, remains extremely difficult. Detailed measurements of turbulence are in high demand within the fusion community, as they hold the keys to predicting and controlling the quality of fusion plasma confinement in future tokamaks.

Fluctuations and dynamics in a fusion plasma can be probed by way of microwave radar beams, a technique referred to as "doppler reflectometry" that is routinely implemented in tokamaks around the world, among them DIII-D, Asdex Upgrade and, next door to ITER, Tore Supra.

At Tore Supra, collaboration between the Plasma Physics Laboratory (LPP) at the École Polytechnique in Paris and CEA-Cadarache's Institute for Magnetic Fusion Research (IRFM) has led to the development of a reflectometry system called DIFDOP (doppler diffusion) that has been operated extensively since 2003.

By "shooting" microwave beams from different angles, DIFDOP gives access to different sizes of turbulences. Tore Supra's long discharges provide several seconds of "stationary plasma"—a time long enough for operators to perform up to 200 measurements.

"Observing the density fluctuations within the plasma and the dynamics of turbulences at different scales helps us understand how energy is transferred between these different scales," says Laure Vermare, a physicist at École Polytechnique and a member of the LPP-IRFM collaboration. "This understanding will prove very useful in predicting what will happen in ITER."

DIFDOP has also yielded precious information about the rotating speed of the plasma, a yet little-understood phenomenon that has a stabilizing effect on plasma turbulence as well as on the repartition of the energy fluctuations over the different spatial scales.
 
Recently, EFDA issued a call for the development of new, powerful tools to study one specific behaviour of fusion plasma turbulence, possibly linked to an improvement of the plasma confinement. LPP and IRFM answered with a joint proposal to develop an additional diagnostic system, also based on doppler reflectometry and backscattering.

This vertical reflectometry diagnostic (DREVE) was installed at Tore Supra in March 2010. When the installation resumes operation in October, DREVE's data will be combined with that of DIFDOP to provide a much clearer picture of the movements inside Tore Supra's plasmas and, by extension, inside fusion plasmas in general.

Having one eye (DIFDOP) that looks into the equatorial plane of the plasma and another one (DREVE) that peers "from above" in the toroidal direction should provided physicists with a treasure trove of information. 

"Recent observations on the TJ-II Tokamak, in Spain," says Laure Vermare, "suggest that a form of organization of the turbulence occurs in the transition to the H-Mode. How this transition takes place is still a bit of a mystery. What we are doing here, on a machine that does not operate in H-Mode, is testing new tools that will help us understand this crucial transition."

The H-mode, said its "discoverer" Fritz Wagner in an interview with Newsline last year, is what "makes the goals of fusion possible." Hence the importance of unveiling its secrets ...


return to the latest published articles