Preparation for Plasma Boundary Research on NCSX

1
Preparation for Plasma Boundary Research on NCSX

• presented
• for the NCSX Plasma Boundary Group
• by
• Peter Mioduszewski
• ORNL
• NCSX PAC-7 Meeting
• July 13-14, 2004

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Mission of the Plasma Boundary Program
1. Develop power- and particle exhaust methods
compatible with high beta, high confinement
operation of NCSX 2. Generate the knowledge
base for plasma boundary operation in compact
stellarators
Evolution of the boundary program
IV
III
V

• Initial Experiments
• 1.5 MW NBI,
• partial PFCs
• plasma-wall contact
• boundary structure

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

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

FY 2008 - 2010
gt FY 2010
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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
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Status and Preparation of Boundary Modeling
Magnetic field topology 1. VMEC-MFBE-Gourdon
codes (A. Grossman, A. Koniges) 2.
PIES-Drevlac-Integrator (T. Kaiser) --gt
generated Poincaré plots of edge fields and
footprints on wall status both approaches
work and are presently being benchmarked
against each other needs 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
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Status and Preparation of Boundary Modeling
contd
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) !
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Boundary Diagnostics Preparation
Phase III Initial Experiments
plasma-wall interactions visible cameras
impurity identification visible spectrometer
Ha 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
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Investigation of Plasma-Wall Contact (Phase III)
1.5 MW, Partial PFC GDC
Preparatory work modeling of intercepts with
first wall and peaking factors of power fluxes
Interaction locations 1. divertor helical
ridges 2. NBI-wall shine-through 3. fast particle
intercepts
Diagnostics fast visible camera visible
spectrometer visible filterscopes compact IR
camera movable Langmuir probe fast pressure gauges
In conjunction with modeling these measurements
will provide the input for the divertor design.
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Plasma-Wall Contact Modeling
Foot-Prints Used For Divertor and Baffle Design
A. Koniges
toroidal
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Structure of the Plasma Boundary NCSX vs.W7-AS

• 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.

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Structure of the Plasma Boundary contd
NCSX
connection lengths are similar
W7-AS

field-lines wind around main plasma pitch angle
is large (10-1)
island
field-line pitch angle is very small
(10-3) (getting smaller with increasing
connection length)
divertor plates
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Auxiliary Heating Experiments (Phase IV)
3 MW NBI PFC liner 350 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

Diagnostics fast visible camera visible
spectrometer visible filterscopes compact IR
camera movable Langmuir probe fast pressure
gauges fast ion loss probe
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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)