DIII-D 3D edge physics capabilities: modeling, experiments and physics validationPresented by

T.E. Evans1

I. Joseph2, R.A. Moyer2, M.J. Schaffer1, A. Runov3, R. Schneider3, S.V. Kasilov4, M.E. Fenstermacher5, M. Groth5, J.W. Watkins6

1GA, 2UCSD, 3MPI-Griefswald, 4Kharkov IPT, 5LLNL, 6SNL,

Presented at NCSX Research Forum 2006December 8th, 2006

DIII-D has generated capability in 3D edge physics modeling & interest in validation of physical models• DIII-D’s most successful ELM suppression techniques rely on the

essential 3D physics of non-axisymmetric perturbations – RMP H-mode: externally induced resonant fields– QH-mode: internally generated, nonlinearly saturated EHO hypothesis

• 3D equilibrium reconstructions are critical to validating underlying physics mechanisms– DIII-D plasmas can be used to benchmark 3D equilibrium codes

• VMEC, V3FIT, PIES, EFIT + ideal DCON response, …– Field line tracing used to explore field structure: TRIP3D (GA)

– Braginskii 2-fluid codes used for equilibrium transport• E3D (MPI-Greifswald) thermal transport in stochastic fields

• EMC3-EIRENE (FZ-Jülich) currently used by TEXTOR collaborators

– MHD: NIMROD, M3D, JOREK

Key physics issues for DIII-D are clearly important for NCSX• Can we validate the physics of resonant magnetic field penetration?

– MHD modeling by NIMROD, M3D, JOREK codes can be used to assess physics of forced reconnection at finite toroidal flow

– Extended MHD models can test various neoclassical predictions for viscosity

– Parallel kinetic closures can extend validity to lower collisionality

• ELM peeling-ballooning stability needs to be reassessed in 3D equilibria – Experimental results from DIII-D and JET seem to indicate that the Type-I ELM threshold can be continuously tuned by applying external perturbations

– MHD modeling by NIMROD, M3D, JOREK– ELITE-3D??? will be required for efficient analysis of experimental stability threshold

Magnetic footprint structures predicted by TRIP3D/E3D have been observed on Xpt/IR-TV

Xpt-TV ISP: filtered D123301 2170 ms

TRIP3D ISP: field lines 123301 2170 ms

• Asymmetric footprint observations can be used to validate the magnetic field model

E3D ISP heat flux122342 4650 ms I-coil

only

q95=3.55

Drift Effects?

Detailed OSP footprint can be compared to strike point sweep of Langmuir probe array

LPA: 125912 3200-3800 ms

Jsat at =180o

• Proper in-out asymmetry may require asymmetric Danom• Drift effects? extra bump in private flux zone requires new explanation

E3D: 122342 4650 ms ISP at =150o and OSP at =180o

Paradox: the RMP primarily controls peeling-ballooning stability through particle transport! n decreases, not T

Resolution? pedestal toroidal rotation and Er change promptly when RMP is applied at q95 resonance• H-mode pedestal v spins up and Er well narrows.

Summary

• Experience gained at DIII-D in 3D edge physics may be valuable for NCSX– Validation of 3D edge models

• Equilibrium reconstruction• Field line integration and mapping• Fluid transport (heat, particle and momentum)

• Resonant field screening (flow and pressure)• Divertor footprints• MHD stability (peeling-ballooning, forced reconnection, etc.)

– Availability of experimental data in high power discharges• Developing 3D diagnostic capabilities• Developing 3D boundary control systems and technology

N = 3 perturbations induce edge stochastic layer which destroys axisymmetric flux surfaces

• Color = # toroidal transits for escape (red=201 max, black<10)• Caveat: no plasma response in this model

Detailed OSP footprint can be compared to strike point sweep of Langmuir probe array

E3D heat flux simulation

• E3D heat flux qualitatively matches measured fluxes• Quantitative agreement will require …?

LPA Jsat at DIII-D=180o

125912 3200-3800 ms

q95=3.55

Due to drifts?

E3D simulations show that the tangle also efficiently guides heat flux to the divertor targets

• Private flux region still exists due to short divertor connection length• The field lines cannot sample the lower branches of the tangle

As RMP , predicted tangle structure grows & heats 122342 at 4650 ms BC’s: Te= 1.6

keV, Ti= 2.6 keV at n = 77%

€

D⊥= 0.2m2 / s nsep = 4 ×10

18m−3

Te (eV): 50 100 150 200

I-coil (kA): 0 (2D) 1 2 3

As RMP predicted edge temperature cools122342 at 4650 ms BC’s: Te= 1.6 keV, Ti= 2.6 keV

at n = 77%

• Constant temperature BC’s • Edge stochastic layer cools relative to pedestal

– remains hot compared to SOL

TeTi

Escaping field lines are trapped by the invariant manifolds which exit the X-point

BackwardEscape

Upper“Stable”manifold

Forwardescape

Upper“Unstabl

e”manifold

•The outline of the field line escape pattern traces out the surfaces of the invariant manifold•The homoclinic tangle encodes the structure of chaos

123301 3000msColor = field line

length red<2kmblue<200m

The tangle forms non-axisymmetric magnetic footprints which have been experimentally observed

• Te reflects a superposition of both upper invariant manifolds• Multiple magnetic footprint stripes observed during I-coil operation

123301: filtered D Xpt-TV

123300: filtered CIII Xpt-TV