Transcript Slide 1

ITER consequences of JET 13C
migration experiments
Jim Strachan, PPPL
Jan. 7, 2008
• Modeled JET 13C migration for last 2 years- EPS
07 and NF paper in prep
– Found neutral C transport causing PFR deposit
• ITER cases, reported in APS 07
– Suggested a modification of the OSP location to
reduce tritium co-dep, but criticized by Kukushkin due
to Helium pumping
• Since then switched to studying He
– Suggesting a change in the pump location
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JET 13C methane injection into 1.4 MA, type I ELMy H-Mode
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-4
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SIM S
IBA
SIM S -2nd toroidal location
model
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10
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C deposited / cm /
2 13
C injected
EDGE2D based modeling of 13C deposition indicated a
complex pattern, of possible ITER relevance is the PFR deposit
OSP
ISP
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10
0
3
4
500
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1000
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7
8
1500
2000
poloidal distance around divertor (mm) 13CH 4
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Sightlines of shadowed regions created by the tile structure for
sources originating at the strike points
Outer target
shadowed
Inner target
shadowed
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The deposits in the PFR show the shadowing of inner
and outer strike point sources indicating 15-20% of 13C
exited the strike points as neutrals
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13
2.0E-6
1.5E-6
2 13
1.5E-6
/
SIMS
IBA
assumed neutral migration
1.0E-6
5.0E-7
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5.0E-7
C deposited / cm
/
1.0E-6
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C deposited / cm
JET H-Mode with C injected near outer strike point
Migration due to 25% neutrals at OSP and 18% at ISP
C injected
2.0E-6
2 13
C injected
JET H-Mode with C injected near outer strike point
Migration due to 25% neutrals at OSP and 18% at ISP
0.0E0
0.0E0
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4
-5.0E-7
0.550
0.600
0.650
0.700
distance around the divertor (m)
0.750
-5.0E-7
1.10
1.15
1.20
1.25
1.30
distance around the divertor (m)
While motivated by Stangeby’s talk at Toronto ITPA, the mechanism must be
different than the neutral transport on DIII-D since those were detached
plasmas and JET was attached at both inner and outer target.
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EDGE2D indicates that the carbon source must be within a
cm of the separatrix in order to have a reasonable probability
of crossing into the PFR as a neutral
fraction crossing separatrix
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0
neutrals during intra-ELM
ions during intra-ELM
neutrals during ELM
ions during ELM
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0
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strike point to injection distance (cm)
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Propose a multi-step recycling process which “walks” the eroded
carbon along the target until it crosses the separatrix either as an
ion or neutral, which should also occur on ITER targets
JET
ITER
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Commonly carbon modeling does not feature
recycling effects such as this “walking”, but
it is in the literature:
Kirschner (ERO) discussed this
mechanism as responsible for the
JET C/T deposits on the inner Louvre
David Elder (DIVIMP)
described the 13C peaking
at the DIII-D corner as due
to “walking”- his term
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Walking does impact ITER by transporting sputtered C into the PFR, that
C will deposit (with T) in the dome interior, and some will re-ionize below
the X-Point where some will transport back into the divertor SOL where it
can be pulled effectively into the main chamber, dominating the core
contamination and the C sputtering of W
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My initial calc of the C deposit assumed long mfp (like the JET
experiments), but Kukushkin’s calc indicate that the mfp is short, so
the same amount is deposited but diffusively transported in the PFR.
Re-erosion
clearly occurred in JET PFR, I am not certain about ITER
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initial
after erosion in PFR
ISP
OSP
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75 MW, nsep=1.5
1019/m3, intra-ELM
carbon deposition
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C deposited / cm / sputtered C
Neutral C deposition
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carbon
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0
200
pump gaps
400
600
800
carbon
1000
1200
poloidal dist ance around divertor (cm)
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EDGE2D calculations indicate migration pathway to W surfaces are
dominated (3-5X) by C ionized below the X-Point, 3-5X W sputtering/m2
as AUG during ICRF and ELMs (Dux, IAEA meeting)
C++++ density
C0 density
Fully stripped C density
Source near OSP
Fully stripped C density
Source near X-Point
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Want to consider if we could change the angle between the target and
the field lines to walk the recycled material away from the separatrix
Proposed separatrix
location
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EDGE2D calculations with a steep target that “walks” recycled particles
towards the corner, (where they can be pumped or collected) indicate that
10-3 to 10-4 less carbon reaches the PFR and core contamination and C
bombardment of W are reduced factors of 3-5.
Run EDGE2D with 150 MW, nsep=1.5
1019 /m3, 10 Hz .5 MJ ELMs, L-Mode
transport coefficients
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0.1 msec of He injection at 1021/s with calc at 0,
0.1, 0.2, and 0.5 msec afterwards
walking
Strike point on vertical target
Corner
recycling
Strike point on dome
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Helium and other recycling particles (D, eroding C) have greater
connection between the outer divertor Sol and the PFR for the vertical
targets. Also greater flow to the main SOL
He particle flow, vertical target
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6x10
total particles/ sec
6x10
total particles/ sec
He particle flow, dome target
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from outer div SOL
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5x10
ions to main SOL
ions to PFR
neutrals to PFR
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4x10
+19
3x10
+19
2x10
+19
1x10
from outer div SOL
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5x10
ions to main SOL
ions to PFR
neutrals to PFR
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4x10
+19
3x10
+19
2x10
+19
1x10
0
0
0x10
0x10
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+19
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-1
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0
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time after 0.1 ms He injection (ms)
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0
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1
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time after 0.1 ms He injection (ms)
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Helium and other recycling particles (D, eroding C) have greater
connection between the outer divertor Sol and the PFR for the vertical
targets. Also greater flow to the main SOL
He particle flow, dome target
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6x10
total particles/ sec
total particles/ sec
He particle flow, dome target
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6x10
from outer div SOL
+19
5x10
ions to main SOL
ions to PFR
neutrals to PFR
+19
4x10
+19
3x10
+19
2x10
+19
1x10
from outer div SOL
+19
5x10
ions to main SOL
ions to PFR
neutrals to PFR
+19
4x10
+19
3x10
+19
2x10
+19
1x10
0
0
0x10
0x10
+19
+19
-1x10
-1x10
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-1
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0
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time after 0.1 ms He injection (ms)
1
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-2
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-1
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0
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1
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time after 0.1 ms He injection (ms)
If the re-eroding carbon is like recycling He, then dome operation
would have approx 15X less C deposits in the PFR and 3X less
carbon core contamination and 3X less carbon ablation of W
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OSP location
vertical
dome
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-1
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0
time since end of He injection (ms)
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1
neutral He pressure in PFR (MB)
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He flux to outer target (/m /s)
He pumping with dome operation should be in the corner
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target location
vertical
Dome
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0
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1
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time after He injected (ms)
Decay of he flux to target and he pressure in the PFR after 0.1 msec of He
injection at the outer target
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100 msec of He injection, then wait for 100 msec to observe
stationary behavior, for vertical target most of recycling is in main
chamber, while for dome target, recycling equal in outer target and
main chamber
Vertical target
Dome target
Suggests he pumping should be in corner
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OSP ops on dome requires D2 gas puffing near the OSP to recover
the ionization/radiation/dissociation losses which reduce the
temperatures along the outer target (Loarte PPCF 2001)
Dome target
Vertical target
Attractive idea: inject Ne at OSP, let it walk to the corner where pumped 19
Conclusions
• JET 13C experiments indicate PFR deposits, proposed
due to walking along OT, which, if occurring in ITER,
may cause inconvenient T co-deposition in the dome, C
core contamination, and C bombardment of W
• Moving the OSP to the dome could walk the C, He, and
Ne/Ar into the corner, where it may be pumped or
removed
• Changing the vertical target to a dome target rediscovers power handling problems and high target
temperatures (Loarte PPCF vert vs horiz targets)
• D2 and Ne gas injection at the OSP can replace the
recycled (ionization/radiation/dissociation) losses and
cause near detachment at the OSP, walking these
particles into the corner. A pump should be located in the
corner.
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