Influence of Equilibrium Shear Flow on Peeling-Ballooning Instability and ELM Crash
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1 Lawrence Livermore National Laboratory Influence of Equilibrium Shear Flow on Peeling-Ballooning Instability and ELM Crash Pengwei Xi 1,2 , Xueqiao Xu 2 , Xiaogang Wang 1 , Tianyang Xia 2,3 1 FSC, School of Physics, Peking University, Beijing, China. 2 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 3 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China Presented at 6 th US-PRC Magnetic Fusion Workshop San Diego, CA, USA, July 10-12, 2012 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Security, LLC, Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and is supported by the China Scholarship Committee under contract N0.2011601099. LLNL-PRES-563575 1
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Influence of Equilibrium Shear Flow on Peeling-Ballooning Instability and ELM Crash. Pengwei Xi 1,2 , Xueqiao Xu 2 , Xiaogang Wang 1 , Tianyang Xia 2,3 1 FSC, School of Physics, Peking University, Beijing, China. 2 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA - PowerPoint PPT Presentation
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Influence of Equilibrium Shear Flow on Peeling-Ballooning Instability and ELM CrashPengwei Xi1,2, Xueqiao Xu2, Xiaogang Wang1, Tianyang Xia2,3
1FSC, School of Physics, Peking University, Beijing, China. 2Lawrence Livermore National Laboratory, Livermore, CA 94550, USA3Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China
Presented at 6th US-PRC Magnetic Fusion Workshop San Diego, CA, USA, July 10-12, 2012
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Security, LLC, Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and is supported by the China Scholarship Committee under contract N0.2011601099. LLNL-PRES-563575
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#Lawrence Livermore National Laboratory11Research MotivationSimulation SetupsSimulation ResultsLinear Nonlinear SummaryOutlines
3#Lawrence Livermore National LaboratoryResearch Motivation: Dramatic influence of shear flow on ELM behavior
Fig1. ELM image from MAST(Scannell .R Plasma Phys. Control. Fusion 49 1431)123Fig2. Ideal MHD simulation about shear flow influence on peeling-ballooning mode(H.R.Wilson, Plasma Phys. Control. Fusion 48 (2006) A71A84) Fig3. Experiment shows rotation frequency can change ELM frequency significantly.(N.Oyama, Nucl. Fusion 45 (2005) 871881)4#Lawrence Livermore National LaboratorySimulation Equations: 3-fields reduced MHD equations with equilibrium EXB flow
In our simulation, we assume ion diamagnetic flow is balanced by the first part of EXB flowKelvin-Helmholtz termResistivity/Hyper-resistivityIon diamagnetic effectNet flow5#Lawrence Livermore National LaboratoryTotal Er profiles for EXB flow at H-mode pedestal
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Counter-direction flowCo-direction flowRigid flow#Lawrence Livermore National Laboratory
Simulation Results: Rigid flow only leads to Doppler shift but doesnt change peeling-ballooning mode growth rate10
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7Ideal MHD: Flow shear strongly stabilizes high-n ballooning modes and weakly destabilizes low-n peeling modes
High-n modes are twisted and the radial extension is limited by shear flow, while this effect becomes weaker for modes with lower mode number.N=15N=15N=30N=30#Lawrence Livermore National Laboratory
9Destabilizing effect of Kelvin-Helmholtz term depends on mode number and flow shear, and is different from its role in neutral fluid
Gradient of equilibrium vorticity
Step functionIn neutral fluid, shear flow with step function profile cause strong Kelvin-Helmholtz instability. But in our simulation, the destabilizing effect from Kelvin-Helmholtz term disappear when flow shear is vary large.
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10Nonlinear simulation: shear flow can reduce ELM size and limit the radial extension of profile collapse
Resistivity, hyper-resistivity and ion-diamagnetic effects are included in nonlinear simulation
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11Nonlinear simulation: shear flow can reduce ELM size and limit the radial extension of profile collapse
Without shear flowWith shear flow#Lawrence Livermore National Laboratory
12Nonlinear simulation: Without Kelvin-Helmholtz term
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13Nonlinear simulation: With Kelvin-Helmholtz term
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22Nonlinear simulation: For large flow shear case, Kelvin-Helmholtz term reduces mode number at nonlinear phase
Before ELM crashAfter ELM crashW/O KHWith KHWith KHW/O KHInitial perturbation has mode number n=1514#Lawrence Livermore National Laboratory
15Nonlinear simulation: Kelvin-Helmholtz term becomes dominant for middle flow shear value and leads to larger ELM crash
The competition between flow shear stabilizing effect and Kelvin-Helmholtz destabilizing effect decides the overall influence of shear flow on ELM #Lawrence Livermore National LaboratorySummaryLinear simulation resultsFlow shear has strong stabilizing effect on high n mode and is destabilizing for low n modes for ideal MHD;Kelvin-Helmholtz term is destabilizing and the effects depends on mode number and shear;Nonlinear simulation resultFlow shear can reduce ELM size and limit profile collapse;Kelvin-Helmholtz term is dominant for intermediate flow shear value and leads to larger ELM size;
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Flow shear#Lawrence Livermore National Laboratory
