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 field Bθ 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 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 ∼ (Bt1/2Ip3/2)/(nT).
Birkenmeier, G., Cavedon, M., Conway, G., Manz, P., Stroth, U., Fischer, R., et al. (2016). Magnetic structure and frequency scaling of limit-cycle oscillations close to L- to H-mode transitions. NUCLEAR FUSION, 56(8) [10.1088/0029-5515/56/8/086009].
Magnetic structure and frequency scaling of limit-cycle oscillations close to L- to H-mode transitions
Cavedon M.;
2016
Abstract
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 field Bθ 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 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 ∼ (Bt1/2Ip3/2)/(nT).
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