Speaker
Description
The tokamak H-mode regime of confinement relies on the formation of an edge transport barrier, resulting in the appearance of the so-called “pedestal” in the plasma profiles. Understanding the mechanisms responsible for the pedestal evolution and features is crucial for optimizing fusion performance in the next-generation devices, such as ITER. However, a complete understanding of the role of turbulent transport in the pedestal region is lacking.
In this study, we focus on characterizing turbulent transport at the top of the pedestal in JET discharges in different regimes: a type-I edge-localized modes (ELM), and two baseline small-ELM (BSE) regimes [1]. To achieve this goal, we performed gyrokinetic stability analysis using the local versions of the GENE and GKW codes.
A detailed characterization of the most unstable modes around the pedestal top positions of the three discharges has been carried out. At the ion-scale, we found that kinetic-ballooning modes are dominant in the type-I ELM regime, while the BSE regimes are characterized by a hybrid TEM/ITG branch. At the electron-scale, both regimes are dominated by the toroidal and slab ETG branches [2]. Moreover, the sub-dominant modes spectra have been obtained by performing gyrokinetic eigenvalue computation, revealing that a rich variety of modes of different nature are destabilized. Starting from linear results, a quasi-linear (QL) model is applied to get an estimate of the turbulent fluxes to be compared with experimental values. Moreover, the impact of the electron scales modes in the QL estimates will be assessed.
Finally, to gain physical insights on magnetized plasma turbulence in regimes with sub-dominant modes, a mode decomposition technique is being developed. Firstly, we selected as reference case the Waltz standard case, linearly characterized by unstable ITG and TEM branches. Preliminary results on the decomposition of turbulent field structures will be shown. After its validation, the modal decomposition will be applied to non-linear gyrokinetic simulations with pedestal-like parameters.
