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Modeling of disruption mitigation by massive gas injection (MGI)

Modeling of disruption mitigation by massive gas injection (MGI). A. Fil 1 , E. Nardon 1 , M. Bécoulet 1 , R. Guirlet 1 , M. Hoelzl 2 , G.T.A Huijsmans 3 , M. Lehnen 3 F. Orain 1 , C. Reux 1 , F. Saint-Laurent 1 , P. Tamain 1 and JET EFDA Contributors*.

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Modeling of disruption mitigation by massive gas injection (MGI)

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  1. Modeling of disruption mitigation by massive gas injection (MGI) A. Fil1, E. Nardon1, M. Bécoulet1, R. Guirlet1, M. Hoelzl2, G.T.A Huijsmans3, M. Lehnen3 F. Orain1, C. Reux1, F. Saint-Laurent1, P. Tamain1 and JET EFDA Contributors* 1 CEA, IRFM, F-13108 Saint Paul-lez-Durance, France 2 Max-Planck-Institut fur Plasmaphysik, 85748 Garching, Germany 3 ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France Motivations Results • Unmitigated disruptions are not tolerable in ITER: • Heatloads (expected: 500 MJ.m-2.s-1/2tolerable: 50) • Runawayelectrons (expected: 10 MA, tolerable: < 1 MA) • Large forces on structures • MGI isplanned in ITER in order to mitigatetheseeffects. • However, detailed design remains open: mitigating all effects of disruptions at the same time is a challenge • A modeling effort is needed to make predictions for ITER, extrapolatingfrompresentexperiments • First thermal quench simulation with the JOREK code, triggered by MGI in JET: • Cold front penetrationcreatesunstablecurrentprofile • (2,1) and (3,2) modes coupling leads to TQ • 1D radial simulations with IMAGINE: • Rarefactionwaveprogressing at 3*cs in the vacuum • Cold front penetration in the plasma withVfront = fraction of cs 3D non-linearresistive MHD simulations with the JOREK code [1] Poincare plots Toroidalcurrentdensity Temperature JOREK equations for MGI simulations Thermal quench • Overlappingislands trigger the thermal quench • Thermal quench duration around 1 ms: realistic At t=0s (+ otherequations) Parameters • Initial conditions : JET 77803 experimental profiles • Stable L-mode plasma • Initial q0 adjusted to be just above 1 (to avoid internal kink) • Injection of 1023neutralparticlesper second • Central Lundquistnumber S0 = 2.107 BeforeTQ (t = 50ms) Results, sequence of events AfterTQ (t = 52ms) • Cooling of the plasma edge • Contraction of the current profile • Destabilization of (2,1) tearing mode • Growth of a (3,2) mode Perspectives 1D radial simulations of MGI-plasma interaction Gaspenetrationmechanismsstillunclear;treated as an effective diffusion in JOREK but what about first principles? • For JOREK (3D MHD) : • Detailedcomparisonwithexperiments • JOREK-STARWALL simulations (resistivewall) • ASDEX-U simulations • Improve model (atomicphysics, …) • For IMAGINE (1D Fluid) : • Relax the assumption of ions at rest • Ions can move radially due to ExB drift • But theyundergobrakingeffects • Comparisonwithexperiments (JET, ASDEX-U, Tore Supra) Parameters Equations of the new IMAGINE code • Input: experimental ne, Te profiles • DeuteriumJET MGI simulations • Scan in numberof injectedparticles (ninj) and friction coefficient (αfric) • Rarefactionwave in the vacuum at 3*cs for the first particles: realistic [2] • In the plasma, cold front velocityVfront = fraction of cs • Vfrontdependsweakly on ninj and αfric • Couldbepartly due to neutralsaccumulation at the front Results • Simulateddomain: reservoir, vacuum injection tube and plasma • IMAGINE containskey ingredients for gaspenetrationphysics: • Energetics: completeatomicphysics (ADAS coefficients) • Gasvelocitydynamics: • Euler equations in vacuum • Friction from charge-exchange with ions assumed at rest References: *See the Appendix of F. Romanelli et al., Proceedings of the 24th IAEA Fusion Energy Conference 2012, San Diego, USA

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