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F. Nabais - Vilamoura - November 2004 Internal kink mode stability in the presence of ICRH driven fast ions populations F. Nabais, D. Borba, M. Mantsinen, M.F. Nave, S. Sharapov and JET-EFDA contributors
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F. Nabais - Vilamoura - November 2004 Outline Internal kink mode n=1, m=1 Effect of ICRH driven populations on Perturbative method Variational method Quantitative results (F. Porcelli et al. Phys. Plasmas,1 (3), 470 (1994)) Sawteeth Fishbones Sawteeth, (R. White et al. Phys. Fluids B 2, 745 (1990)) Qualitative results MHD energy functional Fast ions energy functional Fast ions Objective : Explain experimental observations in JET
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F. Nabais - Vilamoura - November 2004 Perturbative method eigenfunction perturbation (F. Porcelli et al. Phys. Plasmas,1 (3), 470 (1994)) Relevant equations, which include Finite Orbit Width effects, Adiabatic part - destabilizing
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F. Nabais - Vilamoura - November 2004 Perturbative method CASTOR-K Non-adiabatic part - stabilizing Sawteeth Safety factor on axis Fast ions temperature Location of the ICRH resonant layer Fast ions radial profile
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F. Nabais - Vilamoura - November 2004 Non-adiabatic Adiabatic part of (Preliminar results) Destabilizing increases with T HOT Effect of the ICRH fast ions on sawteeth Blue regions: stabilizing Red regions: destabilizing as function of q 0 and T HOT on-axis heating
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F. Nabais - Vilamoura - November 2004 Experiments with low plasma densities T HOT ~ P ICRH nene Sawteeth destabilization occurred when: ICRH power increases Plasma density decreases Application to experiments Non-adiabatic as function of T HOT
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F. Nabais - Vilamoura - November 2004 The stabilizing effect of the non-adiabatic part of decreases as T HOT increases, so this mechanism for sawtooth stabilization is weakened. The destabilizing effect associated with the adiabatic part of is increased. Numerical results show: Application to experiments The non-adiabatic part of is dominant. Sawteeth destabilization coincides with an increase in T HOT
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F. Nabais - Vilamoura - November 2004 Variational method Solutions of the internal kink dispersion relation: Low frequency High frequency Kink Branch Ion Branch Fishbone Branch Sawteeth Low frequency (diamagnetic) fishbones High frequency (precessional) fishbones (R. White et al. Phys. Fluids B 2, 745 (1990)) (B. Coppi and F. Porcelli P. R.L, 57, 2272 (1986)) ω ≈ ω *i ω ≈ (L. Chen et. al P. R.L, 52, 1122 (1984)) (Ideal limit)
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F. Nabais - Vilamoura - November 2004 Marginal equation ω=real, ideal limit, ICRH population Stability governed mainly by Ideal (MHD) growth rate Diamagnetic frequency Fast particles beta Determination of the regions of stability
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F. Nabais - Vilamoura - November 2004 I I hh Regions of stability
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F. Nabais - Vilamoura - November 2004 Magnetic spectrogram from JET Precessional Fishbones Diamagnetic Fishbones Hybrid Fishbones Sawtooth Crash
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F. Nabais - Vilamoura - November 2004 Increases Decreases during a burst Increases between bursts In between crashes the q=1 surface expands In between crashes the ion bulk profile peaks : 3 kHz20 kHz Variation of the relevant parameters
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F. Nabais - Vilamoura - November 2004 Variation of the regions of stability hh I I
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F. Nabais - Vilamoura - November 2004 Regions of stability I I hh
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F. Nabais - Vilamoura - November 2004 Ion branch Fishbone branch β h decreases during the burst Diamagnetic behaviour Precessional behaviour Coalescent Ion-Fishbone branch hh (R. White et al. Phys. Fluids B 2, 745 (1990)) Solutions of the dispersion relation ω *i2 ω *i1 ω *i1 < ω *i2
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F. Nabais - Vilamoura - November 2004 Time (s) Magnetic perturbation Magnetic perturbation for an hybrid fishbone
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F. Nabais - Vilamoura - November 2004 Ion mode Fishbone mode Coalescent ion-fishbone mode Low frequency fishbones High frequency fishbones Hybrid fishbones Both types of fishbones occuring simultaneously ( Gorolenkov et al. “Fast ions effects on fishbones and n=1 kinks in JET simulated by a non-perturbative NOVA-KN code, this conference) Modes and regimes
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F. Nabais - Vilamoura - November 2004 Summary Perturbative Method - Accurate calculation of HOT for a realistic geometry - Only for the “kink mode” Variational Method - All branches of the dispersion relation - Simplified geometry and fast ions’ distribution function, suitable only for a qualitative approach - Predicts changes in instabilities behaviour knowing the relevant parameters Stabilizing term vanishes for high fast ions temperatures Hybrid fishbones and both types of fishbones occuring simultaneously
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