kansas annual nsf epscor statewide conference wichita, ksjanuary 12-13, 2012
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Kansas Annual NSF EPSCoR Statewide Conference Wichita, KSJanuary 12-13, 2012. Simulation of pellet ablation in DIII-D Tianshi Lu Patrick Rinker Department of Mathematics Wichita State University In collaboration with Roman Samulyak, Stony Brook University - PowerPoint PPT PresentationTRANSCRIPT
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Kansas Annual NSF EPSCoR Statewide ConferenceWichita, KS January 12-13, 2012
Simulation of pellet ablation in DIII-D
Tianshi Lu
Patrick RinkerDepartment of Mathematics
Wichita State University
In collaboration with
Roman Samulyak, Stony Brook University
Paul Parks, General Atomics
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Model for pellet ablation in tokamak
• MHD system at low ReM
• Explicit discretization• EOS for partially ionized gas• Free surface flow• System size ~ cm, grid size ~ 0.1 mm
Courtesy of Ravi Samtaney, PPPL
Tokamak (ITER) Fueling
• Fuel pellet ablation• Striation instabilities• Killer pellet / gas ball for
plasma disruption mitigation
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Schematic of pellet ablation in a magnetic field
Schematic of processes in the ablation cloud
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Sheath Fluxes
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MHD at low magnetic Reynolds numbers
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Heat deposition of hot electron
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Axisymmetric MHD with low ReM approximation
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Centripetal force
Nonlinear mixedDirichlet-Neumann boundary condition
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Transient radial current approximation
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1.Spherical model• Excellent agreement with NGS model
2.Axisymmetric pure hydro model• Geometric effect found to be minor (Reduction by 18% rather than 50%)
3.Plasma shielding without rotation• Subsonic ablation flow everywhere in the channel• Ablation rate depending on the ramp-up time
4.Cloud charging and rotation• Supersonic rotation causes wider channel and faster ablation• Ablation rate independent of the ramp-up time
Simulation results of pellet ablation
Spherical model Axis. hydro model Plasma shielding
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Plasma shielding without rotation
Mach number distribution
Double transonic flow evolves to subsonic flow
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-.-.- tw = 5 s, ne = 1.6 1013 cm-3
___ tw = 10 s, ne = 1014 cm-3
----- tw = 10 s, ne = 1.6 1013 cm-3
Formation of the ablation channel and ablation rate strongly depends on plasma pedestal properties and pellet velocity.
Plasma shielding without rotation
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Supersonic rotation of the ablation channel
Cloud charging and rotation
Isosurfaces of the rotational Mach number in the pellet ablation flow
Density redistribution in the ablation channel
Steady-state pressure distribution in the widened ablation channel
2TB
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• Gsteady of a rotating cloud is independent of tramp
• G(tramp) < Gsteady
• G(tramp) increases with tramp
• Fast pellet
• Short ramp-up distance
Fixed pellet: effect of ramp up time
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Shrinking pellet: tumbling pellet model
“Pancake” pellet
• Due to anisotropic heating, the pellet would evolve to a pancake shape.
• In reality, the pellet is tumbling as it enters the tokamak, so its shape remains approximately spherical.
• In the simulation, the pellet shrinking velocity is averaged over the surface to maintain the spherical shape.
Tumbling spherical pellet
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Shrinking pellet: DIII-D temperature profile
DIII-D Temperature and Density Profile G from simulation agrees with 0.8 GNGS
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Conclusions and future work
Conclusions
• Supersonic rotation causes wider channel and faster ablation• Good agreement with NGS model for DIII-D profile • Smaller Ablation rate during fast ramp-up
Future work
• Inclusion of grad-B drift in the simulation• Non-transient radial current for smaller B field – finite spin up• Mechanism of striation