# Presentation: 945981

## Stellarator Boundary Modelling Issues    and Goals

**Stellarator Boundary Modelling Issues    and Goals**

**Peter Mioduszewski for the NCSX Boundary Group**
- PPPL Stellarator Theory Tele-Con Meeting
- June 3, 2004

## Plasma Boundary Modelling

**Machine Design****:**** vacuum vessel, plasma-facing components, divertor plates & baffles, power- and particle fluxes, etc. to provide optimum design of surfaces for ****controlled**** plasma-wall interactions.**
**Predict**** ****plasma edge parameters such power and particle fluxes, densities, temperatures, operating conditions such as “high-recycling” or “detached” etc.**
**Interpret**** experimental parameters and results**
**Development ****of optimum**** plasma boundary scenarios**
**Codes exist for**** 1.)  magnetic configuration; 2.)  neutrals transport, 3.)  plasma transport**

## Machine Design 

**Machine Design **

**  ****Define ****vacuum vessel contour****, i.e. determine the envelope of**
**   ****the field line excursions of the magnetic boundary**
**	****- for day-1 plasma configuration ****  **
**	****- for future upgrades including divertor plates/baffles and ****	****	****  pumping **
**  ****Define location and shape of the ****plasma-facing components**
**- ****accommodate islands, stochastic layers, laminar layers**
**	****- peaking factors of power fluxes on PFCs**
**	****- optimize baffling for neutrals control**
**  ****Configuration flexibility**
** ****	****- vacuum configuration -> finite beta, current, shape               **

## Magnetic Configuration Modelling

_**Presently, we are pursuing  two approaches**_**:**
**VMEC + MFBE + Gourdon Code**
**PIES + Drevlak + Field-line Integrator**
**benchmarking**** between the two approaches is ongoing  **

**output****  ==> poloidal-plane Poicaré plots in various toroidal planes**

## Example of NCSX Poincaré Plot in the  = 0 Plane 

- Poincaré plots, generated with the _MFBE_* and _Gourdon_ codes, at =0 cross-section show flux expansion/ clusters (islands?) which can be used for power and particle control.
- Example shows 1.4m/18-coil configuration. 60 field-lines were started at the outer midplane      (0-4cm) and followed for 20 revolutions (Lc~200m).
- Flexibility studies are underway to explore the boundary for various beta and iota.

- A. Grossman

- *E. Strumberger

**1**

**5**

**4**

**3**

**2**

## Stochasticity in the Near-sol Is Low, As Indicated by the Kolmogorov Length

**Stochasticity in the Near-sol Is Low, As Indicated by the Kolmogorov Length**

**L****k**** ~ 40 m**
**L****c****~ 100-200 m**

## Plasma- and Neutrals Modeling

**   ****	****estimate ****atomic and molecular effects**** in the (narrow) bean-shaped  ****	****cross-section and to provide ****guidance for the design**** of the plasma-****	****facing components**
**   ****So far we have performed **
**	****- ****2-D DEGAS**** (axisymmetric) with fixed plasma background for NCSX**
**	****- ****3-D DEGAS**** modelling for HSX (validated with H******** results)**
**   ****Fully ****3-D DEGAS**** modelling for NCSX is ~underway (resource limited)**
**  ****3-D plasma codes**** are available at IPP Greifswald: the fluid transport  **
**    ****code ****E3D****, the Monte-Carlo code ****EMC3-EIRENE**** (has been applied to  **
**    ****W7-AS, W7-X, TEXTOR, and LHD); the 3-D finite volume ****BoRiS**** code**
**   ****Presently, we don’t have the resources to participate  ****   **

**Plasma- and Neutrals Modeling**

## Example: Neutrals Calculations Show the Effect of Divertor Baffling

- L. Owen

## Example: Magnetic Foot-Print Modelling Is Used For Divertor Plate Design

**Example: Magnetic Foot-Print Modelling Is Used For Divertor Plate Design**

- A. Koniges

**toroidal**

**poloidal**

- outer
- midplane

**still needs**
**flexibility**
**analysis!**
**(beta,iota)**

## Summary

**  ****The plasma boundary in stellarators is ****3-dimensional**** and has ****islands****  ****	****and/or ****stochastic**** layers.**
**   ****Codes are available to calculate the ****magnetic**** configuration in the   ****	****boundary including ****finite beta**** and plasma ****current**** cases.**
**  ****We have used two existing approaches and are presently ****	****	****benchmarking them with each other: ****VMEC+MFBE+Gourdon**** and ****	****PIES+Drevlak+Integrator****.**
**  ****3-D plasma- and neutrals codes for the plasma boundary are ****	****	****available: ****DEGAS, EIRENE****, ****E3D, EMC3-EIRENE****; BoRiS is under ****	****development.**
**  ****So far, we have used the ****DEGAS code with fixed plasma**** for neutrals**
**  ****Coupled 3-D plasma and neutrals**** calculations will have to be done in****	****the future to predict and interpret divertor performance etc. ****	****	****Presently,  no resources are available.         **

## Extras:

## Do we need a divertor?  

- courtesy of P. Grigull

_**Summary of W7-AS Results With Divertor Operation**_**:**
- The new divertor enables access to a new regime with NBI at very high
-  density (up to ne~ 3.5 x 1020 m-3 ) with promising confinement properties:
- 	- ******E**  increases steeply with density,
- 	- ****p  and ****imp decrease with increasing density
- 	   (****imp~ ****E at highest density)
- Record value of <ß> ~ 2.7% achieved (at B = 1.25 T)
- Full density control already without Ti- gettering.
- Quasi-steady state operation also including partial detachment.
- Radiation stays always peaked at the edge.
- Plasma heating at extremely high density by HF (EBW 140 GHz) is
- successfully demonstrated.

## W7-AS Divertor Configuration

- courtesy of P. Grigull

**10 modules**

## The Modified NCSX Vacuum Vessel Can Accomodate Pumped Divertor Hardware 

- 4-cm conformal
- surface