Turbulence and Transport in Plasmas

 

Turbulence is a ubiquitous phenomenon appearing in many different contexts ranging from turbulence in galaxies and the solar wind to energy transport in the convective layer of the sun, further including geophysical flows, weather and climate simulations and more mundane areas such as pipe flows. Turbulence remains a key problem for physics and engineering, and has been a grand challenge for both theoretical and computational techniques.  One of the key aspects of turbulence is the ability for increased mixing of particles and energy in physical systems, and it is well established that turbulence increases the abilities to even out gradients through mixing and transport.

The transport of heat, particles, and momentum across the confining magnetic field in hot plasmas is one of the most important, but also most difficult areas of contemporary plasma research specifically in relation with fusion energy research. It is well established that the “anomalous” transport component due to low frequency turbulence is usually far larger than the classical collisional transport, particularly in the edge region of the confined plasma. It is, therefore, of highest priority to achieve a detailed understanding of anomalous transport and the underlying turbulence for the design of an economical viable fusion reactor based on magnetic confinement schemes. In spite of the dramatic progress in experiment, theory and computations during recent years, the quantitative understanding is still sparse and lacking predictive capability. Fundamental phenomena such as transitions from low confinement regime (L-mode) to high confinement regime (H-mode), the profile resilience, and the particle pinch that are routinely observed and classified experimentally have no generally accepted explanations.

The activities within plasma turbulence and fluctuation driven transport are mainly focused on topics related to the plasma periphery of toroidal plasmas comprising the coupling from the edge confinement region to the Scrape-Off-Layer (SOL) with open magnetic field lines. The investigations contribute significantly to the highly prioritized topics of understanding the plasma exhaust dynamics and quantifying the heat loads on plasma facing components.. Generally, it is acknowledged that the conditions near the edge of the plasma are dictating the global performance, which seems natural since all transport has to go through the edge region. Thus, a detailed understanding and modelling of the plasma periphery is essential for the  coupling to the core plasma dynamics. Theoretical and numerical investigations of first principle models form the majority of the work performed. We emphasize benchmarking of results and performance, both with other codes and analytic results (verification) and then also with experimental observations (validation).

Besides the specific activities within turbulence and transport in magnetically confined plasmas our results are also of relevance for the general understanding of turbulence.

The present activities and our suit of modelling tools are described here Recent-activities-and-suits-of-modelling-tools.

Mission

  • Theoretical and numerical investigations of the plasma periphery of toroidal magnetically confined plasmas.
  • Theoretical and numerical investigations of the self-regulation of turbulence and the emergence of coherent structures.
  • We are developing first principles two- and three-dimensional advanced numerical codes to simulate low frequency turbulence at the edge of toroidal plasma devices.
  • The models aim at predictive capabilities
  • General issues of anomalous plasma transport – non-locality and turbulence spreading
  • Close collaboration within the EUROfusion consortium and with leading plasma and fusion research institutes in China, Korea and USA.

Contact

Jens Juul Rasmussen
Professor
DTU Physics
+45 25 38 45 37
http://www.fysik.dtu.dk/english/Research/PPFE/Research-at-PPFE/Turbulence_and_Transport
22 OCTOBER 2018