Understanding and modelling kinetic turbulence in magnetized plasmas

Lead Research Organisation: Coventry University
Department Name: Ctr for Fluid and Complex Systems

Abstract

Plasma physics is at the core of the UK Magnetic Fusion Research Program, an important pillar of the EPSRC's Energy theme. The generation of electrical power via magnetic confinement fusion represents a promising endeavour: aiming to provide an abundant, inexpensive, clean, safe and reliable source of energy that can support a thriving economy, while at the same time offering a viable alternative to fossil fuels as a way to tackle global environmental challenges. Magnetic confinement fusion makes use of strong magnetic fields to confine the fusion plasma fuel in a series of nested torus shaped magnetic surfaces, in a device known as a tokamak. Turbulence in plasma represents a key impediment to this objective, as turbulent mixing is known to enhance the transport of particles and heat across magnetic surfaces, leading to the eventual loss of plasma confinement that stops the fusion reaction.

Understanding the proper interactions in plasma turbulence, interactions that occur at physical scales captured only by kinetic theories in a six dimensional phase space, allows for correct implementation of turbulence models. These models can be employed for tokamak transport studies, which in turn can determine the most efficient operational regime of current machines and directly impact the design of future tokamak reactors.

As plasma turbulence at kinetic levels is poorly understood to this day, while adequate kinetic turbulence models are yet to be developed, we turn towards space plasma configurations to offer simpler environments for isolating fundamental turbulence dynamics. This project will tackle plasma turbulence from a kinetic perspective, addressing fundamental questions pursued in the solar wind academic community, such as the identification of the dynamical route used for the dissipation of small scale turbulence energy and, at the same time, develop practical solutions in the form of new knowledge-based turbulence modes that will directly aid fusion research (a promising long term industrial goal).

The work will unite collaborators from national (Culham Centre for Fusion Energy) and international (Max-Planck Institute for Plasma Physics, Germany and University of California, Los Angeles, US) institutions, while being led by a researcher based at Coventry University.

Planned Impact

The development of fusion energy has a clear economical and social impact in the UK. While the proposed work is part of this overarching effort, the current research proposal has a series of immediate institutional, cross-disciplinary, professional and public beneficiaries.

Institutional beneficiaries: The UK Magnetic Fusion Research Program will be the main beneficiary of this research program, through the CCFE and industrial partners. LES kinetic models coupled to reduced nonlinear simulations offer an efficient way to account for plasma turbulence in fusion devices. As such, more computational resources can be allocated to the description of other complex large-scale geometric effects that impacts fusion development. This is important in minimising the R&D costs of the next generation tokamak machines. The UK National Supercomputing Service ARCHER lists the cost of typical foreseen LES runs at 50 to 80 times less than that of their full nonlinear counterparts, bringing the cost per run down to a few hundred pounds from the tens of thousands. This represents an important cost saving measure, allowing resources to be better allocated elsewhere.

Cross-disciplinary beneficiaries: In the process of building LES models that account for kinetic plasma dynamics, we answer a series of critical questions pursued in the solar wind community. Identifying the correct route for the energy dissipation in the solar wind represents a current endeavour for the astrophysical community. This is the goal for the THOR satellite project (B. Teaca is a member of the science team) a European Space Agency (ESA) M4 mission candidate, with a foreseen cost in excess of 400 million Euros. The investigation of fundamental aspects of plasma turbulence proposed here and the possibility to employ LES models in the solar wind to identify different turbulent transport regimes has a direct bearing on the mission policy making of ESA and impacts directly the mission selection process.

Professional and public beneficiaries: Towards the end of the program we aim to organise a one-day workshop on LES methods in plasmas. The workshop will be opened to scientific partners, guests from industry and will feature a general introductory session to fusion in magnetised plasma. This session will be open to the general public, free of charge, and feature a Q&A portion. This will permit to present current scientific advances to the generic public and help popularise natural science from the perspective of real life applications.

Publications

10 25 50
 
Description While the work is ongoing, it is now clear that the spatial localization of turbulence impacts greatly the further development of Sub-Grid Scale (SGS) models in kinetic plasma applicable to the generation of fusion energy in tokamaks. The localization and the coherence level of these structures play an important role in the activation of Landau damping, as stable structures allow the energy in the system to move towards smaller and smaller scales in velocity space, while transient structures leads kinetic turbulence to behave in good part as classical fluid turbulence (this is a novel idea introduced in the community in the last years, which we incorporated into our ongoing work). An a-priory analysis of the SGS flux (the energy channel that links the part of turbulence that we solve numerically and the part that we account through models) shows the importance of its spatial density in the application of the SGS models at the location of the spatial structures. This work continues in collaboration with researchers from Max Plank IPP (Germay) and The Institute for Fusion Studies (Texas, USA).

Making use of sub-critical plasma configurations relevant to tokamaks allows us to control the type of structures that we see in real space, from simple coherent traveling wave structures to volume filling turbulence that exhibits transient structures. This line of work borrows concepts matured in the study of fluid dynamics to find novel and non-intuitive dynamical properties in a plasma medium and is done together with colleagues from Coventry University and the University of Warwick. Sub-critical plasma configurations promise to serve as an important test bed for understanding and modeling kinetic plasma turbulence.
Exploitation Route The new SGS models will be used in the fusion research community. Also, the approach taken for the investigation of a sub-critical plasma allows for a systematic understanding of the problem and can lead to a way to control the development of structures in a tokamak.
Sectors Energy,Other