Nonlinear dynamics of turbulence driven magnetic islands. I. Theoretical aspects

Abstract

The nonlinear properties of a turbulence driven magnetic island (TDMI) are investigated. Starting from a minimal magnetohydrodynamic fluid model that provides for the generation of a TDMI and using scale separation arguments along with numerical simulation findings, we elucidate the links between the nonlinear transport properties of such magnetic islands and the characteristic features of the small scale turbulence. We also explain the phenomenon of partial pressure flattening inside the TDMI. Published by AIP Publishing. [http://dx

Nonlinear dynamics of turbulence driven magnetic islands. II. Numerical simulations

“…In Ref. 5, a model has been developed to evaluate the role of the turbulence in the generation of magnetic islands. The issue is both to obtain a better understanding of the impact of the interchange scales on the transport properties of TDMIs and to infer some signatures of TDMIs.…”

A reduced MHD model for ITG-NTM interplay

“…In our 6field model, adiabaticity is only ensured if the parallel electron heat flux is sufficiently large so that ∇ T e ≈ 0. Together with the condition ∇ φ ≈ ∇ p e from Ohm's law equation (18), this results in ∇ φ ≈ ∇ n. However, we should not assume perfect equilibration of the ion temperature. This necessity to decouple electron and ion temperature is the reason why we chose to maintain separate ion and electron pressure evolution equations rather than assuming p i ∝ p e .…”

“…The variations of these energy contributions are readily obtained from the evolution equations (18) to (23) by partial integration. For all our fieldsf we use periodic boundary conditions in y-direction and Dirichlet boundary conditions f = 0 in the x-direction.…”

“…Since we assume u 2 s = 0, only the perpendicular heat flux component is finally retained. Inserting the results (43) to (45) into the equation set (39) yields, after normalisation, the neoclassical terms that we included in our set of final equations (18) to (23).…”

“…The interaction between turbulence and MHD phenomena in fusion device plasmas has received growing attention in the last decade, both in experimental 1-10 and theoretical context [11][12][13][14][15][16][17][18][19][20][21][22][23] . Basically, core MHD activity is dominated by sawteeth and neoclassical tearing modes (NTMs).…”