DIII-D 3D edge physics capabilities: modeling,experiments and physics validation
Presented 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 2006
December 8th, 2006
DIII-D has generated capability in 3D edge physicsmodeling & interest in validation of physical models
•DIII-D’s most successful ELM suppression techniques rely on theessential 3D physics of non-axisymmetric perturbations
–RMP H-mode: externally induced resonant fields
–QH-mode: internally generated, nonlinearly saturated EHOhypothesis
•3D equilibrium reconstructions are critical to validating underlyingphysics 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 forNCSX
•Can we validate the physics of resonant magnetic fieldpenetration?
–MHD modeling by NIMROD, M3D, JOREK codes can be used toassess physics of forced reconnection at finite toroidal flow
–Extended MHD models can test various neoclassical predictions forviscosity
–Parallel kinetic closures can extend validity to lower collisionality
•ELM peeling-ballooning stability needs to be reassessed in 3Dequilibria
–Experimental results from DIII-D and JET seem to indicate that theType-I ELM threshold can be continuously tuned by applyingexternal perturbations
–MHD modeling by NIMROD, M3D, JOREK
–ELITE-3D??? will be required for efficient analysis of experimentalstability threshold
Magnetic footprint structures predicted by TRIP3D/E3Dhave been observed on Xpt/IR-TV
Xpt-TV ISP: filtered D123301 2170 ms
TRIP3D ISP: field lines 123301 2170 ms
•Asymmetric footprint observationscan be used to validate themagnetic field model
E3D ISP heat flux
122342 4650 ms I-coil only
q95=3.55
Drift Effects?
Detailed OSP footprint can be compared to strikepoint 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-ballooningstability through particle transport! n decreases, not T
Resolution? pedestal toroidal rotation and Er changepromptly 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 physicsmay 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 powerdischarges
•Developing 3D diagnostic capabilities
•Developing 3D boundary control systems andtechnology
N = 3 perturbations induce edge stochastic layer whichdestroys 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 strikepoint 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 efficientlyguides 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 & heats122342 at 4650 ms BC’s: Te= 1.6 keV, Ti= 2.6 keV at n = 77%
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
Te
Ti
Escaping field lines are trapped by the invariantmanifolds which exit the X-point
Backward
Escape
Upper
“Stable”
manifold
Forward
escape
Upper
“Unstable”
manifold
•The outline of the field line escape pattern traces out the surfaces of theinvariant manifold
•The homoclinic tangle encodes the structure of chaos
123301 3000ms
Color = field line length
red<2km
blue<200m
The tangle forms non-axisymmetric magnetic footprintswhich 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
