936 research outputs found
Angular momentum transport modeling: achievements of a gyrokinetic quasi-linear approach
QuaLiKiz, a model based on a local gyrokinetic eigenvalue solver is expanded
to include momentum flux modeling in addition to heat and particle fluxes.
Essential for accurate momentum flux predictions, the parallel asymmetrization
of the eigenfunctions is successfully recovered by an analytical fluid model.
This is tested against self-consistent gyrokinetic calculations and allows for
a correct prediction of the ExB shear impact on the saturated potential
amplitude by means of a mixing length rule. Hence, the effect of the ExB shear
is recovered on all the transport channels including the induced residual
stress. Including these additions, QuaLiKiz remains ~10 000 faster than
non-linear gyrokinetic codes allowing for comparisons with experiments without
resorting to high performance computing. The example is given of momentum pinch
calculations in NBI modulation experiments
Comparison between measured and predicted turbulence frequency spectra in ITG and TEM regimes
The observation of distinct peaks in tokamak core reflectometry measurements
- named quasi-coherent-modes (QCMs) - are identified as a signature of
Trapped-Electron-Mode (TEM) turbulence [H. Arnichand et al. 2016 Plasma Phys.
Control. Fusion 58 014037]. This phenomenon is investigated with detailed
linear and nonlinear gyrokinetic simulations using the \gene code. A Tore-Supra
density scan is studied, which traverses through a Linear (LOC) to Saturated
(SOC) Ohmic Confinement transition. The LOC and SOC phases are both simulated
separately. In the LOC phase, where QCMs are observed, TEMs are robustly
predicted unstable in linear studies. In the later SOC phase, where QCMs are no
longer observed, ITG modes are identified. In nonlinear simulations, in the ITG
(SOC) phase, a broadband spectrum is seen. In the TEM (LOC) phase, a clear
emergence of a peak at the TEM frequencies is seen. This is due to reduced
nonlinear frequency broadening of the underlying linear modes in the TEM regime
compared with the ITG regime. A synthetic diagnostic of the nonlinearly
simulated frequency spectra reproduces the features observed in the
reflectometry measurements. These results support the identification of core
QCMs as an experimental marker for TEM turbulenc
Nonlinear stabilization of tokamak microturbulence by fast ions
Nonlinear electromagnetic stabilization by suprathermal pressure gradients
found in specific regimes is shown to be a key factor in reducing tokamak
microturbulence, augmenting significantly the thermal pressure electromagnetic
stabilization. Based on nonlinear gyrokinetic simulations investigating a set
of ion heat transport experiments on the JET tokamak, described by Mantica et
al. [Phys. Rev. Lett. 107 135004 (2011)], this result explains the
experimentally observed ion heat flux and stiffness reduction. These findings
are expected to improve the extrapolation of advanced tokamak scenarios to
reactor relevant regimes.Comment: 5 pages, 5 figure
Real-Time multichannel tokamak plasma profile simulations using the RAPTOR code and the QLKNN first-principle transport model
WEST Physics Basis
With WEST (Tungsten Environment in Steady State Tokamak) (Bucalossi et al 2014 Fusion Eng. Des. 89 907-12), the Tore Supra facility and team expertise (Dumont et al 2014 Plasma Phys. Control. Fusion 56 075020) is used to pave the way towards ITER divertor procurement and operation. It consists in implementing a divertor configuration and installing ITER-like actively cooled tungsten monoblocks in the Tore Supra tokamak, taking full benefit of its unique long-pulse capability. WEST is a user facility platform, open to all ITER partners. This paper describes the physics basis of WEST: the estimated heat flux on the divertor target, the planned heating schemes, the expected behaviour of the L-H threshold and of the pedestal and the potential W sources. A series of operating scenarios has been modelled, showing that ITER-relevant heat fluxes on the divertor can be achieved in WEST long pulse H-mode plasmas.EURATOM 63305
The Problem of Marginality in Model Reductions of Turbulence
Reduced quasilinear (QL) and nonlinear (gradient-driven) models with scale
separations, commonly used to interpret experiments and to forecast turbulent
transport levels in magnetised plasmas are tested against nonlinear models
without scale separations (flux-driven). Two distinct regimes of turbulence --
either far above threshold or near marginal stability -- are investigated with
Boltzmann electrons. The success of reduced models especially hinges on the
reproduction of nonlinear fluxes. Good agreement between models is found above
threshold whilst reduced models would significantly underpredict fluxes near
marginality, overlooking mesoscale flow organisation and turbulence
self-advection. Constructive prescriptions whereby to improve reduced models is
discussed
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