1. Divertor plasma-surface interaction and induced radiation under large ELM impact
Appreciate to have the opportunity
In-vessel view into JET … no more time for promoting fusion…
R. A. Pitts, A. Huber, A. Loarte, M. Stamp, S. Brezinsek, S. Jachmich, J. Marki, M. Maslov, E. de la Luna, H. Leggate, G. F. Matthews E. Solano and JET EFDA Contributors
7 May 2007

2. Motivation
JET experiments in 2003 at 3.0 MA (2 discharges only) identified an apparent threshold for the evolution of plasma radiation above a certain ELM energy drop (WELM) for large ELMs
Suspected link to divertor target surface ablation (bulk or layers?)
Experiment repeated in recent campaign under controlled conditions and with improved diagnostics
A. Loarte et al., Phys. Scripta T128 (2007) 222

3. Configuration (I)
Seek highest possible divertor tile surface temperature
Work at 3.0 MA and max. power, low fuelling  largest ELMs possible, low power folding width
Strike points on Tiles 3 and 7 (CFC fibre plain in the toroidal direction  poloidal spreading minimised)
Improved diagnostics
D1Z_VSFE_LT: Ip = 3.0 MA, Bj = 3.0 T, q95 = 3.2, outer-wall gap: ~ 8 cm, du ~ 0.22, dl ~ 0.28, k = 1.73

4. Extract from session pulse list
Experiment performed on March
Did a little better than previous 2003 discharges in terms of injected energy and power loading
Shot
EIN (MJ)
ENBI,ERF (MJ)
Etile3,7 (MJ)
Gas 1022 el/s
Ttile3,7 @t=0 (ºC)
Ttile3,7 peak avge
Comments
70220
195
174, --
18.4, 66.8
2.1
140, 150
217, 430
no KL7
70221
183
158, 7.1
18.1, 63.7
1.5
153, 182
230, 437
½ gas, lost PINIs, KL7 back (wide angle)
70222
191
163, 10.2
19.5, 66.3
1.2
193, 164
244, 492
Less gas (but not much less), KL7 wide angle
70223
178
149, 11.0
19.7, 63.7
0.9
175, 211
257, 486
Still less gas, lost PINIs, KL7 (wide angle)
70224
159
128, 12.2
19.0, 58.8
179, 212
261, 430
Less gas, lost PINIs, KL7 (wide angle). Outer strike up ~2 cm
70225
194
164, 12.5
23.3, 73.9
158, 167
264, 387
No gas, good, got full NBI. KL7 subarray, upper dump, lower div.
70226
163, 12.8
24.6, 70.1
174, 200
286, 408
Repeat, good – full beams. KL7 subarray as in 70226
70228
172
163, 5.0
23.4, 66.8
171, 191
290, 380
Repeat, lost one PINI, KL7 subarray to outer limiter
62220
166
152, --
19.1, 52.7
0.55
130, 145
203, 341
Ref. DOC-L, March 2003

5. Example: 3.0 MA, fuelled (#70220)
Da inner
PNBI, PRF ne
Wdia
Te,ped
Ggas
174 MJ injected, 88.2 MJ radiated, Erad/Etot = 0.51, Tile 7: 67 MJ, Tile 3: 18.4 MJ

6. Example: 3.0 MA, no fuelling (#70226)
Da inner
PNBI, PRF ne
Wdia
Te,ped
Ggas
177 MJ injected, 82.4 MJ radiated, Erad/Etot = 0.47, Tile 7: 70.9 MJ, Tile 3: 24.6 MJ

7. Large ELMs are (very) often compound
#70226
Da inner
Da inner
Wdia (MJ)
Wdia (MJ)
Prad (MW)
Prad (MW)
Erad (MJ)
Zeff (brems)
Zeff (brems)

8. Extracting ELM induced radiation (I)
Da inner #70222
Wdia (J)
Da inner
Initial drop in Wdia an artefact of measurement – take value ~4 ms after fast drop
Erad (J)

9. Extracting ELM induced radiation (II)
Da inner #70226
Da inner
Wdia (J)
Erad (J)

10. Location in parameter space: ne*(neo)
A. Loarte et al., PPCF 45 (2003) 1549
New data
ITER
Lowest fuelling cases working at ITER relevant pedestal n*
Consistent with earlier findings – increased database population
A. Loarte et al., Phys Plas 11 (2004) 2668

11. Location in parameter space: Te,ped
New data Te,ped from ECE
A. Loarte et al., Phys. Scripta T128 (2007) 222
Da inner
Large ELMs asscoiated with large drop in Teped
New 3.0 MA data populates the scaling beyond DTeELM/Te,ped > 0.4

12. Max. divertor target temperatures
70220, high fuelling, Ein = 195 MJ
70228, no fuelling, Ein = 172 MJ
Da inner
Da inner
TINNER, ºC TOUTER, ºC
TINNER, ºC TOUTER, ºC
NOTE: Preliminary IR data – calibration issues still to be resolved
Clear effect of inner target surface layers
Bulk ablation temperatures not achieved in any of the discharges
Large compound ELMs produce high inner surface (layer) temp.

13. Surface ion fluxes (example 70224)
Da inner
NB: Both LP and IR see the strike points lower than found with EFIT 14
jsat INNER (106 Am-2) 29
jsat OUTER (106 Am-2) 8
jsat LIM (105 Am-2)
Fast Langmuir probe acquisition for a few ELMs only (250 kHz)
Extremely rich structure after first “peak”of compound ELM – not seen on volume averaged Da
Strong far-SOL limiter interaction
Activity dies out faster at outer than inner (in this case)
jsat LIM (105 Am-2) x10

14. ELM radiation distribution: example
Da inner
Wdia (MJ)
Prad (MW)
Erad (MJ)
70225: Ein = 194 MJ, DWELM = ~0.9 MJ ETile3 = 23.3 MJ, Etile7 = 73.9 MJ

15. Total radiated energy vs. DWELM
First ELM spike
Entire ELM (incl. compound phase)
Clean break in radiation above given DWELM not (clearly) seen in new data
Approx. 50% of the ELM energy radiated at lower DWELM due to “first” spike
Similar trend when including whole compound phase

16. In-out ELM radiation asymmetry
First ELM spike, unfuelled shots only
In-out divertor volume, in-out radiation asymmetry during the ELM linearly dependent on DWELM up to ~0.6 MJ
Erad,ELM(IN)/Erad,ELM(OUT) as high as 6
Break in asymmetry for DWELM > 0.6 MJ – not understood
ELM exacerbates the inter-ELM in-out radiation asymmetry
Higher inboard ELM radiation consistent with higher ELM power there

17. Radiation distribn.: large vs. small DWELM
First ELM spike only – reconstruction for 4 ms averaging period
#70225: s
#70225: s
DWELM = MJ Erad,ELM = MJ
DWELM = MJ Erad,ELM = MJ
Radiation “spills over” into outboard X-point region for large ELMs

18. Conclusions
Operation at high Ip and low fuelling has produced a few large ELMs (DWELM <0.9 MJ) at ITER n*ped
Up to ~195 MJ delivered to plasma, in-out divertor energy deposition ratio :1
Surface (layer) temperatures do not exceed ~ 2000ºC at inner target. Max. outer target temperature ~ 800 ºC (no layers)
In the range 0.1 MJ < DWELM < 0.9 MJ, ~50% of DWELM is radiated, but there is considerable scatter
ELM induced radiation always higher at inner than outer divertor: approx. linear increase in asymmetry up to DWELM ~ 0.6 MJ then decrease for higher DWELM
Higher inner divertor induced radiation consistent (but not only due to) higher ELM energy deposition at inboard side (T. Eich et al., PSI 2006)

19. Reserve slides

20. Fast divertor visible spectroscopy
KS3 div. view
KE9 inner div. view
Acquisition at 250 kHz
BeII and CIII react at same time ~300 ms after fall in Wdia
Often secondary peaks in CIII at outer divertor hardly seen at inner

21. 70228 (new experiment) 62220 (DOC-L: old experiment)
Configurations (II)
70228 (new experiment) (DOC-L: old experiment)
Operational restrictions prevented strike point positions as high as had been achieved in DOC-L
Less favourable for high power loading (tile geometry).

22. Divertor target ELM energy asymmetry
ELM resolved target heat flux (IR)
Type I ELM energy deposition strongly favours INNER target for FWD-Bj
For REV-B, some evidence for more balanced deposition,
Consistent with similar analysis from AUG (WELM < 20 kJ) and linked to passage of net current through target plates
Favourable trend for ITER target power loading (since always more energy to OUTER target inter-ELM)
T. Eich et al., PSI 2006

23. 3.0 MA, DOC-L ref. (#62220) PNBI (106 W) ne (1019 m-3) Wdia (106 J)
Da out, in
Wtot, Prad (107 J)
Erad, Pin (108 J)
Ggas (1022 els-1)
152 MJ injected, 74.0 MJ radiated, Erad/Etot = 0.49, Tile 7: 52.7 MJ, Tile 3: 19.1 MJ