Modeling of disruption mitigation by massive gas injection (MGI)

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