07-06.2004.pkm 1NCSX

Preparation for Plasma Boundary Research on NCSX

presented for the NCSX Plasma Boundary Group

by

Peter MioduszewskiORNL

NCSX PAC-7 MeetingJuly 13-14, 2004

07-06.2004.pkm 2NCSX

Mission of the Plasma Boundary Program

1.1. Develop power- and particle exhaust methods compatible with high Develop power- and particle exhaust methods compatible with high beta, high confinement operation of NCSX beta, high confinement operation of NCSX

2.2. Generate the knowledge base for plasma boundary operation in Generate the knowledge base for plasma boundary operation in compact stellaratorscompact stellarators

Confinement and High Beta:• 6 MW,• divertor• power handling • neutrals control• impurity control

Long-pulse pumpeddivertor operation:• 6 MW• divertor pumping• 6 MW; several secs• 20 Pa m3/s exhaust• active density control

VIVIVIII

Auxiliary Heating:• 3 MW NBI, • PFC liner• 350ºC bake• edge parameters• power/particle control

Initial Experiments:• 1.5 MW NBI, • partial PFCs

• plasma-wall contact• boundary structure

FY 2008 - 2010

Evolution of the boundary program:

> FY 2010

07-06.2004.pkm 3NCSX

Boundary Schedule and Tasks

FY 2005 - 2008: Research Preparation Start

Boundary Modeling

- magnetic topology FY 2005 (ongoing)

- plasma: 3-D FY 2005 (mid ‘05)

- neutrals transport: 3-D FY 2006 (2D ongoing)

Diagnostics

- choice of diagnostics FY 2005 (done)

- views and port allocation FY 2005 and FY 2007

FY 2008-2010: Experimental Program

- investigation of plasma-wall contacts FY 2008 ff.

- boundary configurations FY 2008

- particle/impurity control (coatings) FY 2009

- edge parameters FY 2009

- power handling FY 2009

07-06.2004.pkm 4NCSX

Status and Preparation of Boundary Modeling

Magnetic field topology:

1. VMEC-MFBE*-Gourdon codes (A. Grossman, A. Koniges)2. PIES-Drevlac-Integrator (T. Kaiser)--> generated Poincaré plots of edge fields and footprints on wall

status: both approaches work and are presently being benchmarked against each otherneeds: foot prints on wall panels and peaking factors of power fluxes

Neutrals:

we have carried out investigations of neutrals penetration in the “bean” cross-section (for PVR); DEGAS 2-D axisymm.; 3-D for HSX

Fast particles:

have separatrix exits; need to couple with a field-line code for wall intercepts

*E. Strumberger

07-06.2004.pkm 5NCSX

Status and Preparation of Boundary Modeling cont’d

3-D plasma boundary codes:

1. Started collaboration (LLNL) with Greifswald group on the development of the BoRiS code (no funding at this time)

2. The EMC3-EIRENE code (Feng, Sardei) solves self-consistently plasma, neutrals, and impurity behaviour.

It has correctly predicted major parameters of W7-AS, it can treat 3-D structures, islands, stochastic areas.

It has been tested on W7-AS, W7-X, LHD, and TEXTOR DED.

Bottom line: F. Sardei says it is fully parallelized and it works. Wendelstein group will be happy to train a post-doc… We need to get on board as soon as we have the resources (no later than mid ‘05) !

07-06.2004.pkm 6NCSX

Boundary Diagnostics Preparation

Flared ports

Phase III: Initial Experiments

plasma-wall interactions visible cameras

impurity identification visible spectrometer

H and carbon line emission visible filterscopes

PFC temperatures compact IR camera

SOL ne and Te movable Langmuir probe

edge neutral pressure fast pressure gauges

Phase IV: Auxiliary Heating (additional)

energetic particles fast ion loss probe

The most likely location for a divertor has excellent diagnostics access.

adequate set of initial diagnostics has been identified; views are being defined

07-06.2004.pkm 7NCSX

Investigation of Plasma-Wall Contact (Phase III)

Interaction locations:1. divertor: helical ridges2. NBI-wall shine-through3. fast particle intercepts

In conjunction with modeling these measurements will provide the input for the divertor design.

Preparatory work:modeling of intercepts with first wall and peaking factors of power fluxes

1.5 MW, Partial PFC GDC

Diagnostics:fast visible cameravisible spectrometervisible filterscopescompact IR cameramovable Langmuir probefast pressure gauges

07-06.2004.pkm 8NCSX

Plasma-Wall Contact Modeling : Foot-Prints Used For Divertor and Baffle Design

A. KonigesA. Koniges

toroidaltoroidal

poloidalpoloidal

outeroutermidplanemidplane

07-06.2004.pkm 9NCSX

So far, we are learning from the W7-AS and W7-X experience, focused on the island divertor concept:

the divertor intercepts islands, formed by field-lines with very small pitch

angles (10-3) which scale with 1/Lc, leading to very specific effects:

cross-field transport may dominate (control coils) 2-point divertor model does not apply observed momentum loss along the field line of factors 4 - 5, in contrast

to the usual factor of 2 (detachment!)

ndownstream ≤ nupstream

In NCSX the field-lines wind around the main plasma. The pitch

angles (and divertor config.) are more tokamak-like (0.1).

Long connection lengths are favorable for achieving parallel temperature gradients only with sufficiently large pitch angle.

Structure of the Plasma Boundary: NCSX vs.W7-AS

07-06.2004.pkm 10NCSX

Structure of the Plasma Boundary cont’d

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fort._0deg_9_in_kg 1:12:27 PM 6/25/04

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field-lineswind around main plasma

pitch angle islarge (10-1)

NCSXconnection lengths are similar

divertor plates

island

W7-AS

field-line pitchangle is very small (10-3)

(getting smaller with increasing connection length)

07-06.2004.pkm 11NCSX

Auxiliary Heating Experiments (Phase IV)

Diagnostics:fast visible cameravisible spectrometervisible filterscopescompact IR cameramovable Langmuir probefast pressure gauges

fast ion loss probe

3 MW NBIPFC liner350 ºC baking

Along with 3 MW of NBI, there will be new capabilities for particle and impurity control:

• graphite PFC liner, • baking at 350ºC,• wall coatings

During this phase we will investigate:

• more details of the plasma-wall contact areas

• power fluxes and wall temperatures

• temperatures and densities of the boundary plasma

• neutral pressure and particle fluxes during the discharge

• the control of neutrals with wall coatings

• impurity sources as a function of wall conditions

• energetic particles interactions with wall locations

• predictive and interpretive modeling

07-06.2004.pkm 12NCSX

Summary

Preparations for the plasma boundary program are underway.

Highest priority so far has been modeling of the magnetic boundary topology and defining the boundary diagnostics set.

The most important tasks for FY 2005 are:

develop and finalize the diagnostics views

continued modeling of the magnetic topology (benchmarking)

calculation of foot prints and peaking factors on the wall

conceptual design of the partial PFCs

Other priority tasks are:

plasma and neutrals modeling (EMC3-EIRENE)

energetic particle modeling (wall intercepts)