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)  par  perp   Ideal modes grow with finite resistivity (S = 10 5 )

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