Abstract
The impact on turbulent transport of geodesic acoustic modes excited by energetic particles is evidenced for the first time in flux-driven 5D gyrokinetic simulations using the Gysela code. Energetic geodesic acoustic modes (EGAMs) are excited in a regime with a transport barrier in the outer radial region. The interaction between EGAMs and turbulence is such that turbulent transport can be enhanced in the presence of EGAMs, with the subsequent destruction of the transport barrier. This scenario could be particularly critical in those plasmas, such as burning plasmas, exhibiting a rich population of suprathermal particles capable of exciting energetic modes.
Highlights
The impact on turbulent transport of geodesic acoustic modes excited by energetic particles is evidenced for the first time in flux-driven 5D gyrokinetic simulations using the Gysela code
We provide first numerical evidence of the excitation of Energetic geodesic acoustic modes (EGAMs) in a fully developed ion temperature gradient (ITG) turbulence as well as the impact of these EGAMs on the turbulent transport
The EGAM instability belongs to the more general class of bump-on-tail instabilities, where the drive comes from a positive slope of the distribution function in velocity space
Summary
D Zarzoso,, a) Y Sarazin, X Garbet, R Dumont, A Strugarek, J Abiteboul, T Cartier-Michaud, G Dif-Pradalier, Ph Ghendrih, V Grandgirard, G Latu, C Passeron, and O Thomine1 1)CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 2)Laboratoire AIM Paris-Saclay, CEA/Irfu Universite Paris-Diderot CNRS/INSU, 91191 Gif-sur-Yvette, France (Dated: 8 February 2013). In the simulation with EPs, the depletion around Eω occurs mainly in the outer region (ρ > 0.5) This is illustrated, where we plot the time evolution of the distribution function at v = v0 normalized to its value at t = tinit. After the introduction of SEP, the slope is clearly inverted, mainly in the region ρ > 0.5 It is the positiveness of ∂v Feq at the resonant velocity vres in the simulation with EPs which drives EGAMs. It is the positiveness of ∂v Feq at the resonant velocity vres in the simulation with EPs which drives EGAMs This is evidenced by analyzing the contribution of the up-down poloidally asymmetric components, i.e. sin θ, to the axisymmetric modes, i.e. n = 0, of the electrostatic potential. Analytical predictions of the effect of EGAMs on turbulence is not straightforward and the gyrokinetic simulations presented in this letter prove especially useful
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