# Presentation: 193966

## DIII-D 3D edge physics capabilities: modeling, experiments and physics validation

**DIII-D 3D edge physics capabilities: modeling, experiments and physics validation**

**Presented by**** T.E. Evans****1**
**I. Joseph****2****, R.A. Moyer****2****, **
**M.J. Schaffer****1****, **
**A. Runov****3****, R. Schneider****3****, **
**S.V. Kasilov****4****, **
**M.E. Fenstermacher****5****, M. Groth****5****, **
**J.W. Watkins****6**
**1****GA, ****2****UCSD, ****3****MPI-Griefswald, **
**4****Kharkov IPT, ****5****LLNL, ****6****SNL, **
**Presented at **
**NCSX Research Forum 2006**
**December 8****th****, 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

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

**Xpt-TV ISP: filtered D********123301 2170 ms**

**TRIP3D ISP: field lines**** 123301 2170 ms**

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

**E3D ISP heat flux**
**122342 4650 ms I-coil only**

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

- Drift Effects?

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

**LPA:**** 125912 3200-3800 ms**
**J****sat**** at ******** ****=180****o**

- Proper in-out asymmetry may require asymmetric *D**anom*
- Drift effects? extra bump in private flux zone requires new explanation

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

## 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 E****r**** 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

**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 J****sat**** at ********DIII-D****=180****o**
**125912 3200-3800 ms**

## 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

**Notes:**
Ωo 



## As RMP , predicted tangle structure grows & heats  122342 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 cools122342 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

*T**e*

*T**i*

**Notes:**
Ωo 



## Escaping field lines are trapped by the invariant manifolds 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 the invariant 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 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