DIII-D SHOT #87009 Observes a Plasma Disruption During Neutral Beam Heating At High Plasma Beta...
-
Upload
linda-franklin -
Category
Documents
-
view
219 -
download
3
Transcript of DIII-D SHOT #87009 Observes a Plasma Disruption During Neutral Beam Heating At High Plasma Beta...
DIII-D SHOT #87009 Observes a Plasma Disruption During Neutral Beam Heating At High Plasma Beta
Callen et.al, Phys. Plasmas 6, 2963 (1999)
• Rapid loss of thermal energy ~100 microsecond time scale
• Energy deposited on material wall and divertor. If ablative limit reached, material wall is damaged.
• For ITER, stored energy 100x greater than DIII-D
Control and mitigation of disruptions important for advancement of tokamak concept
Free-Boundary Simulations Based on Equilibrium Reconstruction
• Pressure raised 8.7% above most accurate equilibrium reconstruction (EFIT code)
• Pressure raised ideal MHD marginal stability limit to simplify physics
• Simulation includes:– n = 0, 1, 2– Anisotropic heat conduction
(with no T dependence)parperp
• Ideal modes grow with finite resistivity (S = 105)
First Macroscopic Feature is 2/1 Helical Temperature Perturbation Due to Magnetic Island
• Island result of 1/1 and 3/1 ideal perturbation causing forced reconnection
Magnetic Field Rapidly Goes Stochastic with Field Lines Filling Large Volume of Plasma
• Region near divertor goes stochastic first
• Islands interact and cause stochasticity
• Rapid loss of thermal energy results. Heat flux on divertor rises
Maximum Heat Flux in Calculation Shows Poloidal And Toroidal Localization
• Heat localized to divertor regions and outboard midplane
• Toroidal localization presents engineering challenges - divertors typically designed for steady-state symmetric heat fluxes
• Qualitatively agrees with many observed disruptions on DIII-D
Investigate Topology At Time of Maximum Heat Flux
• Regions of hottest heat flux are connected topologically
• Single field line passes through region of large perpendicular heat flux. Rapid equilibration carries it to divertor
• Complete topology complicated due to differences of open field lines and closed field lines
Initial Simulations Above Ideal Marginal Stability Point Look Promising
• Qualitative agreement with experiment: ~200 microsecond time scale, heat lost preferentially at divertor.
• Plasma current increases due to rapid reconnection events changing internal inductance
• Wall interactions are not a dominant force in obtaining qualitative agreement for these types of disruptions.
Future Directions
• Direct comparison of code against experimental diagnostics
• Increased accuracy of MHD model– Temperature-dependent thermal diffusivities– More aggressive parameters– Resistive wall B.C. and external circuit modeling
• Extension of fluid models– Two-fluid modeling– Electron heat flux using integral closures– Energetic particles
• Simulations of different devices to understand how magnetic configuration affects the wall power loading