Abstract
The effect of fast ions on turbulent particle transport, driven by ion temperature gradient (ITG)/trapped electron mode turbulence, is studied. Two neutral beam injection (NBI) heated JET discharges in different regimes are analyzed at the radial position ρt = 0.6, one of them an L-mode and the other one an H-mode discharge. Results obtained from the computationally efficient fluid model EDWM and the gyro-fluid model TGLF are compared to linear and nonlinear gyrokinetic GENE simulations as well as the experimentally obtained density peaking. In these models, the fast ions are treated as a dynamic species with a Maxwellian background distribution. The dependence of the zero particle flux density gradient (peaking factor) on fast ion density, temperature and corresponding gradients, is investigated. The simulations show that the inclusion of a fast ion species has a stabilizing influence on the ITG mode and reduces the peaking of the main ion and electron density profiles in the absence of sources. The models mostly reproduce the experimentally obtained density peaking for the L-mode discharge whereas the H-mode density peaking is significantly underpredicted, indicating the importance of the NBI particle source for the H-mode density profile.
Highlights
The main ion density peaking is crucial for the performance of a fusion reactor
Though much less effort has been devoted to turbulent particle transport compared to heat transport, it is known that the particle pinch driven by ion temperature gradient/trapped electron (ITG/ TE) mode turbulence can support a peaked density profile in the absence of particle sources [2, 3]
In the present paper we studied the effect of fast ions on particle transport due to ITG/TE mode turbulence using the fluid model EDWM, the gyro-fluid model trapped-gyro-Landau-fluid model (TGLF) as well as linear and nonlinear simulations using the gyrokinetic code GENE
Summary
The main ion density peaking is crucial for the performance of a fusion reactor. Obtaining high values of the central density is of particular importance since fusion power scales with the square of the density and the density at the plasma periphery needs to be below the Greenwald limit in order to avoid disruptions. Though much less effort has been devoted to turbulent particle transport compared to heat transport, it is known that the particle pinch driven by ion temperature gradient/trapped electron (ITG/ TE) mode turbulence can support a peaked density profile in the absence of particle sources [2, 3]. Previous modeling efforts show that the inclusion of a fast ion species has a stabilizing influence on ITG driven turbulence through a number of effects [6, 7] including dilution of the main ions [8], Shafranov shift stabilization [9] and electromagnetic stabilization due to the suprathermal pressure gradients [10, 11]. The focus is on interpretative comparison between transport models and the role of the NBI particle source by including a high energy (fast) ion species in the modeling. Following [15], we have expanded the model to contain full FLR effects in the continuity and energy equations for the main and fast ions
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