Gyrokinetic study of ASDEX Upgrade inter-ELM pedestal profile evolution

• Published in: Nuclear fusion 2015-06, Vol.55 (6), p.63028-14
• Main Authors: Hatch, D.R., Told, D., Jenko, F., Doerk, H., Dunne, M.G., Wolfrum, E., Viezzer, E., Pueschel, M.J.
• Format: Article
• Language: English
• Subjects: Constants; Density; Electron temperature; Evolution; gyrokinetics; H-mode pedestal; Instability; Nonlinear dynamics; Nonlinearity; Simulation; turbulent transport
• ISSN: 0029-5515; 1741-4326
• DOI: 10.1088/0029-5515/55/6/063028

The gyrokinetic GENE code is used to study the inter-ELM H-mode pedestal profile evolution for an ASDEX Upgrade discharge. Density gradient driven trapped electron modes are the dominant pedestal instability during the early density-buildup phase. Nonlinear simulations produce particle transport levels consistent with experimental expectations. Later inter-ELM phases appear to be simultaneously constrained by electron temperature gradient (ETG) and kinetic ballooning mode (KBM) turbulence. The electron temperature gradient achieves a critical value early in the ELM cycle, concurrent with the appearance of both microtearing modes and ETG modes. Nonlinear ETG simulations demonstrate that the profiles lie at a nonlinear critical gradient. The nominal profiles are stable to KBM, but moderate increases in β are sufficient to surpass the KBM threshold. Certain aspects of the dynamics support the premise of KBM-constrained pedestal evolution; the density and temperature profiles separately undergo large changes, but in a manner that keeps the pressure profile constant and near the KBM limit.