DIIID RMP simulations enhanced density transport and rotation

DIII-D RMP simulations: enhanced density transport and rotation screening V. A. Izzo, I. Joseph NIMROD meeting: 4 -21 -07

Introduction • Purpose of the simulations is to better understand ELM suppression by n=3 I-coil fields • In particular, why is the drop in pedestal pressure (responsible for ELM stabilization) primarily due to enhanced particle transport as opposed to enhanced thermal transport? • Simulations begin with EFIT from shot 113317 with vacuum RMP fields superimposed • These simulations are not directly comparable with RMP ELM suppression experiments. Shot is much lower temperature. Purpose is for eventual comparison with previous and ongoing ELM simulations done with 113317. • Shot from ELM suppression experiments with realistic rotation profile will be a next step

DIII-D I-Coils

Initial condition • Vacuum fields have : 3 k. A-turns of I-Coil current with even parity + 4 k. A-turns of C-Coil current + intrinsic error fields • n=1, 2, and 3 components are extracted from the vacuum field solution • fields are superimposed directly on EFIT equilibrium as NIMROD initial condition • direct superposition of fields without plasma response destroys outer flux surfaces DIII-D discharge 113317 from EFIT reconstruction (T. Osborne) with n=1 -3 vacuum fields superimposed

No-I-coil comparison Before plasma response Energy spectrum evolution After plasma response

I-coil cases with three rotation profiles • Simulations with: - no rotation - core rotation ~100 km/s, edge rotation < 2 km/s - core rotation ~100 km/s, edge rotation ~30 km/s • Fourth simulation to test sensitivity to initial condition

Screening effect of rotation • with no rotation, stochastic region encroaches further in • some shielding with low edge rotation • very strong shielding with high edge rotation

Energy spectra • Low edge rotation has different 1/1 mode behavior • significant growth of n=3 and n=0 kinetic energies • High edge rotation case has no significant n=3 growth • n=5 growth numerical?

Pedestal density drop without large edge rotation Low edge rotation No rotation High edge rotation

n=3 convection cells responsible for particle transport Strongest radial transport

Comparison of n=3 velocities

Why does factor of 2 reduction in amplitude completely eliminate transport?

Temperature profiles for all three rotation profiles • present transport model yields temperature drop at pedestal • low edge rotation case differs from other two • possible effect of rotation shear on 1/1 mode?

How important is the initial condition? • These simulations began with fully penetrated vacuum RMP fields, rather than ramping the RMP fields with plasma already present • This is done primarily because time dependent boundary conditions in NIMROD are considerably more complicated than static boundary conditions • Could build up RMP fields in a series of steps • A simple approach to generating a different initial condition – use final state from high edge rotation case with RMP fields well screened, then turn off toroidal rotation, so that fields re-penetrate

Fields re-penetrate when rotation turned off t=0. 5 ms

n=3 amplitude, particle transport increase

Conclusions • RMPs can enhance particle transport by n=3 convection across the separatrix associated with resonant mode • Rotation screens RMP fields and a sufficient value at the edge can suppress associated transport • Screened fields re-penetrate when rotation is turned off, transport effects are not strongly dependent on initial condition Future Work: Begin simulations that can compare closely with experiment…