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

2. JET 13C methane injection into 1.4 MA, type I ELMy H-Mode

3. EDGE2D based modeling of 13C deposition indicated a complex pattern, of possible ITER relevance is the PFR deposit

4. Sightlines of shadowed regions created by the tile structure for sources originating at the strike points
Outer target shadowed
Inner target shadowed

5. 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 6 4
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.

6. 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

7. 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

8. Commonly carbon modeling does not feature recycling effects such as this “walking”, but it is in the literature:
David Elder (DIVIMP) described the 13C peaking at the DIII-D corner as due to “walking”- his term
Kirschner (ERO) discussed this mechanism as responsible for the JET C/T deposits on the inner Louvre

9. 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

10. 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
75 MW, nsep= /m3, intra-ELM carbon deposition

11. 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
Fully stripped C density
Source near OSP
Source near X-Point

12. 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

13. 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= /m3, 10 Hz .5 MJ ELMs, L-Mode transport coefficients

14. 1 msec of He injection at 1021/s with calc at 0, 0. 1, 0. 2, and 0
0.1 msec of He injection at 1021/s with calc at 0, 0.1, 0.2, and 0.5 msec afterwards
walking
Corner recycling
Strike point on vertical target
Strike point on dome

15. 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

16. 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
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

17. He pumping with dome operation should be in the corner
Decay of he flux to target and he pressure in the PFR after 0.1 msec of He injection at the outer target

18. 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
Dome target
Vertical target
Suggests he pumping should be in corner

19. 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

20. 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 re-discovers 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.