Projects per year
Abstract
The work presented in this thesis falls into two categories: development of
reduced dynamical models applicable to edge turbulence in magnetically
confined fusion plasmas and numerical simulations of isolated plasma
filaments in the scrapeoff layer region investigating the influence of finite
Larmor radius effects on the radial plasma transport.
The coexistence of lowfrequency fluctuations, having length scales
comparable to the ion gyroradius, steep pressure gradients and strong E × Bflows
in the edge region of fusion plasmas violates the standard gyrokinetic
ordering. In this thesis two models are presented that overcome some of the
difficulties associated with the development of reduced dynamical models
applicable to the edge.
Second order guidingcenter coordinates are derived using the phasespace
Lie transform method. Using a variational principle the corresponding
VlasovMaxwell equations expressed in guidingcenter coordinates are
derived including a local energy theorem. The second order terms describe
lowest order finite Larmor radius effects. This set of equations might be
relevant for edge plasmas due to the capability of capturing strong E ×B 
flows and lowest order finite Larmor radius effects selfconsistently.
Next, an extension of the existing gyrokinetic formalism with strong flows is
presented. In this work the background electric fields is dynamical, whereas
earlier contributions did only incorporate a stationary electric field. In an
ordering relevant for edge plasma turbulence, fully electromagnetic second
order gyrokinetic coordinates and the corresponding gyrokinetic Vlasov
Maxwell equations are derived, including a local energy theorem. By taking
the polarization and magnetization densities in the drift kinetic limit, we
present the gyrokinetic VlasovMaxwell equations in a more tractable form,
which could be relevant for direct numerical simulations of edge plasma
turbulence.
Finally, an investigation of the influence of finite Larmor radius effects on
the radial transport of isolated plasma filaments (blobs) in the scrapeoff
region of fusion plasmas is presented. We employ an isothermal electrostatic
twodimensional gyrofluid model to simulate the blob dynamics. The
numerical simulations show that, to lowest order, the blob center of mass
velocity scales as the acoustic speed times the square root of the ratio of the
structure size to the gradient lengthscale of the magnetic field, in agreement
with earlier results. However, when the ratio of the thermal ion gyroradius to
the structure size exceeds 10 − 20 % the transport is dramatically enhanced.
Having traveled its own initial size 15 times, blobs carry ∼ 80 % of their
initial density above this threshold but only ∼ 20 % below. This observation
demonstrate the importance of finite Larmor radius effects in plasma
transport modeling.
Original language  English 

Place of Publication  Roskilde 

Publisher  Danmarks Tekniske Universitet, Risø Nationallaboratoriet for Bæredygtig Energi 
Number of pages  152 
ISBN (Print)  9788755038448 
Publication status  Published  Sep 2010 
Series  RisøPhD 

Number  65(EN) 
Keywords
 Fusion energy
 RisøPhD65(EN)
 RisøPhD65
 RisøPhD0065
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Projects
 1 Finished

Modelling of Plasma edge turbulence and transport
Madsen, J., Naulin, V., Nielsen, A. H., Hansen, P. C., Heikkinen, J. A., Scott, B. D. & Rasmussen, J. J.
15/04/2007 → 21/12/2010
Project: PhD