Magnetic structure and frequency scaling of limit-cycle oscillations close to L- to H-mode transitions

G. Birkenmeier, M. Cavedon, G.D. Conway, P. Manz, U. Stroth, R. Fischer, G. Fuchert, T. Happel, F.M. Laggner, M. Maraschek, A. Medvedeva, V. Nikolaeva (+7 others)
2016 Nuclear Fusion  
Limit-cycle oscillations (LCOs) close to the power threshold of L-to H-mode transitions are investigated in plasmas of ASDEX Upgrade. During this phase, referred to as I-phase, a strong magnetic activity in the poloidal magnetic fieldḂ θ with an up-down asymmetry is found. In some cases, the regular LCOs during I-phase transition smoothly into a phase with intermittent bursts which have similar properties to type-III edge localised modes (ELMs). Indications of precursors during the intermittent
more » ... phase as well as in the regular LCO phase point to a common nature of the I-phase and type-III ELMs. The LCO frequency measured in a set of discharges with different plasma currents and magnetic fields scales as f ∼ (B 1/2 t I 3/2 p )/(nT ).
doi:10.1088/0029-5515/56/8/086009 fatcat:xdmjzt7znbajbfpq6cm2mj34kq