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. Even 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 transport are mainly focused on topics related to edge and scrape-off-layer (SOL) regimes of toroidal plasmas. 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. But certainly the coupling to the core plasma dynamics is essential. 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 figure shows a typical result of the simulations of turbulence in the edge/SOL regime. The dynamics is dominated by intermittent burst of hot plasma – so-called plasma “blobs” taking the shape of field-aligned filaments - originating in the edge region and propagating far out into the SOL regime towards the wall of the enclosing vacuum vessel. 

  Evolution of a plasma blob at the edge of the plasma, showing a poloidal cross section at the edge of the plasma.

Evolution of a plasma blob at the edge of the plasma, showing a poloidal cross section at the edge of the plasma. The red color is high plasma pressure, while green is very low pressure. Simulations with parameters from the ASDEX Upgrade Tokamak at IPP Garching bei München, Germany. 

Mission

  • Theoretical and numerical investigations of the plasma edge regime.
  • Theoretical and numerical investigations of the self-regulation of turbulence and the emergence of coherent structures.
  • Edge turbulence is the major ingredient in L-H transition and the entangled ELM dynamics.
  • We are developing first principles two- and three-dimensional advanced numerical codes to simulate low frequency turbulence at the edge of toroidal plasma devices.
  • Parameters relevant to existing or planned fusion experiments.
  • Close collaboration within the European fusion program and with leading plasma and fusion research institutes in China and USA.



 

Contact

Jens Juul Rasmussen
Professor
DTU Physics
+45 25 38 45 37