R. A. Pitts et al. 1 49th APS, Orlando, Florida, USA 12 November 2007
Progress in ITER relevant exhaust physics at JETPresented by R. A. PittsCRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederation
on behalf of JET Task Force E and JET EFDA Contributors
49th Annual Meeting of the APS-DPP, Orlando, Florida, US, 12-16 November 2007
R. A. Pitts et al. 2 49th APS, Orlando, Florida, USA 12 November 2007
A. Alonso1, P. Andrew2, G. Arnoux3, S. Brezinsek4, M. Beurskens5, J. P. Coad5, T. Eich6, G. Esser4, W. Fundamenski5, A. Huber4, S. Grünhagen7, B. Gulejova8, S. Jachmich9, M. Jakubowski10, A. Kirschner4, S. Knipe5, A. Kreter4, T. Loarer3, J. Likonen11, A. Loarte12, E. de la Luna1, J. Marki8, M. Maslov8, G. F. Matthews5, V. Philipps4, M. Rubel13, E. Solano1, M. F. Stamp5, J. D. Strachan14, D. Tskhakaya15, A. Widdowson5 and JET EFDA Contributors*
1Associacion Euratom/CIEMAT para Fusion, Madrid, Spain2ITER Organization, Cadarache, France, 3Association EURATOM-CEA, DSM-DRFC, CEA Cadarache, 13108 Saint Paul lez Durance, France4Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Jülich, Germany5Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK6Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, D-85748 Garching, Germany7FZ Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany 8CRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederation9LPP, ERM/KMS, Association Euratom-Belgian State, B-1000, Brussels, Belgium10Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Germany11VTT Technical research Centre of Finland, Association EURATOM-Tekes, Finland12EFDA-Close Support Unit, Garching, Boltzmannstrasse 2, D-85748 Garching bei München, Germany13Association EURATOM-VR, Fusion Plasma Physics, Stockholm, Sweden 14PPPL Princeton University, Princeton, NJ 0854, USA15University of Innsbruck, Institute for Theoretical Physics, Association EURATOM-ÖAW, A-6020 Innsbruck, Austria*See appendix of M. Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Conf. Chengdu, 2006) IAEA Vienna (2006)
with thanks to many co-authors
R. A. Pitts et al. 3 49th APS, Orlando, Florida, USA 12 November 2007
Outline
• Long term Tritium retention– Gas balance and post-mortem analysis
• ELMs– Divertor induced radiation under large ELM
impact
– Filamentary structure and main wall interactions
• Conclusions
R. A. Pitts et al. 4 49th APS, Orlando, Florida, USA 12 November 2007
Tritium retention
R. A. Pitts et al. 5 49th APS, Orlando, Florida, USA 12 November 2007
A major worry for ITER …
T-retention constitutes an outstanding problem for ITER operation
A retention rate of 10% in ITER would lead to the in- vessel mobilisable T-limit (1 kg) being exceeded in ~200 pulses
Retention rates of this order or higher are regularly found using gas balance in tokamaks
Gas balance is difficult to make accurately and is strongly influenced by “history” (previous pulses).
JET has performed dedicated gas balance expts. in sets of repeated, identical discharges
Important aim is to provide best possible reference T-retention measurements in all-C JET before new Be-W ITER-like wall (ILW) expt. planned for 2010
R. A. Pitts et al. 6 49th APS, Orlando, Florida, USA 12 November 2007
Particle balance procedure
Wall retention – short (dynamic) and long term
Calibrated particle injection:Gas, NBI, ….
Divertor cryopump
Regenerate cryopumps before and after expt. collect total pumped gas with ~1.2% accuracy
Repeat sets of identical discharges (no intershot conditioning): L-mode, H-mode (Type III, I)
Injection = Short term ret. + Long term ret. + Pumped
NB: Total recovered from cryo-regeneration = pumped+intershot outgassing over ~800s (assumed equal to short term retention)
R. A. Pitts et al. 7 49th APS, Orlando, Florida, USA 12 November 2007
Example: Type I ELMing H-mode
ne~0.7nGW
PTOT (MW)
D(in) D (out)
Time (s)
Long term retention estimate (from overall gas balance)
Time (s)
Fluxes (1021 elec/s)
Injected
PumpedRetain
ed
#69260 – 5 repeat shots
@16sRetention ~ 51021Ds-1
Short term = 2.21021Ds 1(44%)Long term = 2.81021Ds-1 (56%)
@20sRetention ~ 31021Ds-1
Long term retention totally dominates after ~6s heating
Ip = 2.0 MA, B = 2.0 TWELM ~100 kJNBI+ICRH, fELM ~ 60 HzCryopumps: divertor+1NBI
T. Loarer et al., EPS 2007
R. A. Pitts et al. 8 49th APS, Orlando, Florida, USA 12 November 2007
Particle Balance summary
Pulse type
Heating phase (s)
Divertor phase (s)
Injection(Ds-1)
Long term retention (Ds-1)
ret/inj
L-mode 81 126 ~1.81022 1.741021 ~10%
Type III 221 350 ~0.61022 1.311021 ~20%
Type I 32 50 ~1.71022 2.831021 ~17%
• Long term retention increases from L-mode to H-mode– Increased C erosion and transport due to increased recycling and
effect of ELMs enhanced C erosion enhanced co-deposition and retention
• Recovery between pulses (short term retention) always constant within a factor ~2 – in the range 1-31022D– Independent of discharge type, ELM energy, quantity of injected
particles
R. A. Pitts et al. 9 49th APS, Orlando, Florida, USA 12 November 2007
J. Likonen, J. P. Coad, M. Rubel, to be submitted to PSI 2008
C-erosion/depostion: Campaigns C5-C14, 2001-2004Divertor only – main chamber net erosion dominated
105g
Louvre: 60g (from QMB)
233g
17g
99g
44g
67g
464g
Erosion
No clear erosion or deposition
Negligible
83,000 s divertor plasma (23 hours)Total inner: 625 gTotal outer: 507 g ( = 1.0 gcm-3 taken for deposit, toroidal symmetry assumed tile gaps ignored)
Post-mortem analysis (I)
19g
24g
Deposition
R. A. Pitts et al. 10 49th APS, Orlando, Florida, USA 12 November 2007
J. Likonen, J. P. Coad, M. Rubel, to be submitted to PSI 2008
D/C ratios: Campaigns C5-C14, 2001-2004
0.91 0.25
0.15
0.11
0.42
0.02
0.12
Total D inner: 30 gTotal D outer: 13 g (from Nuclear Reaction Analysis)
Post-mortem analysis (II)
0.08
0.14
0.17 0.79
R. A. Pitts et al. 11 49th APS, Orlando, Florida, USA 12 November 2007
T-retention summaryPost-mortem analysis: total D-retention (inner + outer divertor): 43 gTotal D inlet: 1800 gFuel retention: 2.4%Gas balance: long term retention in the range 10 - 20%
Discrepancy in range 4 – 8Effects of long term outgassing, thermal release (plasma ops.), GDC, disruptions and because campaign averaged power generally very low (~ 4 MW) with variable plasma configs.
Retention requires long range migration from net erosion to net co-deposition areas (e.g.):
main chamber to divertorstrike zones to PFRouter divertor to innerELMs
See poster GP8.00092 (Tuesday) by J. D. Strachan for more on C-migration based on JET 13C puffing experiments
D, C
R. A. Pitts et al. 12 49th APS, Orlando, Florida, USA 12 November 2007
ELMs can move carbon
Non-linear dependence of carbon erosion on ELM energy
thermal decomposition of surface layers and favourable geometry rapidly increases QMB deposition
A. Kreter, H. G. Esser et al., submitted to PRL
1
3
4
LBSRPQM
B
Explains high deposition rates on water-cooled louvres during 1997 JET DT experiments high T-retention
R. A. Pitts et al. 13 49th APS, Orlando, Florida, USA 12 November 2007
ELMs
R. A. Pitts et al. 14 49th APS, Orlando, Florida, USA 12 November 2007
The problem with ELMs
Material damage poses a limit on the maximum ELM size tolerable on ITER
Current estimates indicate that ELM power fluxes (for CFC or W) must remain below ~0.5 MJm-2 at the ITER divertor targets
This implies an ELM energy loss, WELM ~ 1 MJ ~0.3% of stored energy in ITER QDT = 10 burning plasma!
This is lower than any ELM energy so far achieved mitigation strategies required. BUT …
JET Type I ELMs can approach 1 MJ study the effects on first wall surfaces and edge plasma
Important also in preparation for JET ITER-like wall and improved understanding of ELM SOL physics
R. A. Pitts et al. 15 49th APS, Orlando, Florida, USA 12 November 2007
Large ELMs with low fueling
Vertical targets, MarkIIHD div.Specific JET sessionIp = 3.0MA, B = 3.0T, gas scanq95 ~ 3.1, 95 ~ 0.25Input energy ~195 MJEnergy Tile 3,7: 24.6, 70.1 MJ
D (inner)
PTOT (MW)
WDIA (MJ)
Te,ped
(keV)
ne,ped (1019m-3)
H98Y
Zeff (Brems)
Time (s)
#70226 – no gas fuelling
R. A. Pitts et al., ITPA, Garching, 2007
Mostly NBI
R. A. Pitts et al. 16 49th APS, Orlando, Florida, USA 12 November 2007
Large ELMs with low fueling
Lowest fuelling cases at ITER relevant *ped
WELM/Wped ~ 0.2 for largest ELMs
R. A. Pitts et al., ITPA, Garching, 2007
D (inner)
PTOT (MW)
WDIA (MJ)
Te,ped
(keV)
ne,ped (1019m-3)
H98Y
Zeff (Brems)
Time (s)
#70226 – no gas fuelling
ITER
R. A. Pitts et al. 17 49th APS, Orlando, Florida, USA 12 November 2007
Target surface temperatures
D (inner)
Tmax outer (ºC)
Time (s)
#70228 – no gas fuelling
Tmax inner (ºC)
Target surface temperatures from tangential view. Time resolution insufficient for power flux analysis
Total wetted area ~1.0 m2 (cf. ITER ~ 3.5 m2)
Inter-ELM power loads higher at outer than inner as usualClear affect of surface layers on inner target (none on outer)Large ELMs: Tsurf (inner) ~ 600ºCTsurf (outer) ~ 200ºCTsurf far from bulk sublimation
Inner
Outer~600ºC
~200ºC
#70228
J. Marki, T. Eich
R. A. Pitts et al. 18 49th APS, Orlando, Florida, USA 12 November 2007
Radiation during large ELMs
Time (s)
#70225, low fuelling
D(inner)
WDIA (MJ)PRAD (MW)
Erad (MJ)
0.58 MJ1.08 MJ
0.85 MJ1.29 MJ
Strong in-out asymmetry in ELM induced radiation for high WELM probably due to layers on inner targets and preferential inboard deposition of ELM energy
A. Huber et al., EPS 2007
R. A. Pitts et al. 19 49th APS, Orlando, Florida, USA 12 November 2007
In-out ELM radiation asymmetry
WELM = 0.85 MJWELM = 0.45 MJ
First ELM spikeonly
ForWELM 0.6 MJ radiation “spills over” separatrix – in-out radiation asymmetry reduced
>~
ERAD/WELM ~ 0.5 if WELM 0.6 MJ
Evidence for a break at larger WELM
<~
R. A. Pitts, ITPA 2007, A. Huber et al., EPS 2007
Up to 70% WELM radiated
R. A. Pitts et al. 20 49th APS, Orlando, Florida, USA 12 November 2007
Main wall ELM filaments
W. Fundamenski, M. Jakubowski, ITPA Garching May 2007, P. Andrew et al., EPS 2007
#66515
WELM ~ 200 kJt = 7.6 sExp. time 300 sFrame time 7.8 ms
New wide angle IR camera diagnostic (E. Gauthier et al., CEA) using ITER-like front mirrors. 640x512 pixel FPA, max. full frame rate 100 Hz
ELM exposure superimposed on ambient background Difference frame: ELM – previous ELM-free frames
R. A. Pitts et al. 21 49th APS, Orlando, Florida, USA 12 November 2007
Filament footprint field aligned
= 22o ,35o
Filament IR footprint in main chamber closely aligned to pre-ELM field linesMode number (in this case) n ~360/ = 11-16. More cases n = 10 - 50
Field aligned filaments also seen at upper dump plates: crude mode analysis gives n ~ 5 - 20
68193, 57 s
R. A. Pitts et al. 22 49th APS, Orlando, Florida, USA 12 November 2007
How much ELM energy to walls?
Main chamber IR camera too slow to follow single ELMs and filaments very asymmetric toroidally and poloidally
68193, 57 s
Make energy balance for a single outboard poloidal limiter during H-mode phase, assume:Only ELMs can deposit energy on limitersNo energy to upper dump platesNo energy deposited in compound phasesSame energy on 16 limiters
R. A. Pitts et al. 23 49th APS, Orlando, Florida, USA 12 November 2007
D(inner)
Time (s)
Temp. (ºC)
Energy per tile (kJ)
#70226
How much ELM energy to walls?
Main chamber IR camera too slow to follow single ELMs and filaments very asymmetric toroidally and poloidally
68193, 57 s
20.016 s 17.405 s
111213Make energy balance for a
single outboard poloidal limiter during H-mode phase, assume:Only ELMs can deposit energy on limitersNo energy to upper dump platesNo energy deposited in compound phasesSame energy on 16 limiters
∑E
tile (15 tiles)
R. A. Pitts et al. 24 49th APS, Orlando, Florida, USA 12 November 2007
Wall loading and ELM size
68193, 57 s
Pulse No.
gas
(1022e-/s)
No. ELMs (MJ) (MJ) (kJ)
70221 1.47 133 29.7 1.49 224 5.3
70222 1.24 87 23.9 1.02 275 4.3
70223 0.89 50 18.0 0.85 360 4.7
70224 0.38 16 8.34 0.71 521 8.8
70225 0 30 14.9 1.37 497 9.2
70226 0 24 12.7 1.49 528 11.8
Ip = 3.0 MA, B = 3.0 T, gas scan. Separatrix-midplane outer wall gap fixed at ~5.0 cm. WELM estimated for first ELM peak only
(%)ELM
LIM
W
E
ELMW LIME ELMW
Larger ELMs deposit more energy on outboard main chamber surfaces.
How does this compare with theory?
Pulse No.
gas
(1022e-/s)
No. ELMs (MJ) (MJ) (kJ)
70221 1.47 133 29.7 1.49 224 5.3
70222 1.24 87 23.9 1.02 275 4.3
70223 0.89 50 18.0 0.85 360 4.7
70224 0.38 16 8.34 0.71 521 8.8
70225 0 30 14.9 1.37 497 9.2
70226 0 24 12.7 1.49 528 11.8
(%)ELM
LIM
W
E
ELMW LIME ELMW
R. A. Pitts et al. 25 49th APS, Orlando, Florida, USA 12 November 2007
Compare with filament model
Filament parallel energy loss model(W. Fundamenski, R. A. Pitts, PPCF 48 (2006) 109)
W/W0 = 9.4% at limiter radius, cf. Experiment = 8.8%Excellent agreement given inherent approximations ELMs with <WELM> 500 kJ deposit ~10% of their energy on the main chamber limiters (for separatrix-wall gap ~ 5 cm)
>~
Assume mid-pedestal paramsTe,0 = Ti,0 ~ 800 eVne,0 ~ 3.01019 m-3
ped ~ 4 cm
vELM = 600 ms-1
)(2
3~ 0,0,00 ie TTnW
R. A. Pitts et al. 26 49th APS, Orlando, Florida, USA 12 November 2007
Conclusions (I)
• Long term Tritium retention– Dedicated gas balance: 10-20% increasing from L to
H-mode
– Post-mortem analysis: ~2.5%
– Difference due to campaign averaging/conditioning cycles, low campaign averaged power
– Majority of retention attributable to C migration to remote areas followed by co-deposition
– ITER QDT = 10 pulse expecting to use ~50g T at 20% retention, 1 kg in-vessel mobilisable T-limit reached in ~100 pulses!
R. A. Pitts et al. 27 49th APS, Orlando, Florida, USA 12 November 2007
Conclusions (II)
• Large ELMs– JET can access ELM conditions which match new ITER
specifications (WELM ~ 1 MJ) in pulses at Ip = 3.0 MA with upstream p ~ 5 mm and divertor wetted area ~1.0 m2
– Strong in-out divertor radiation asymmetry – up to 70% of the ELM energy drop can be radiated, mostly in the divertor volume.
– Evidence that thermal decomposition of inner divertor surface layers increases radiation but Tsurf provoked by largest ELMs relatively modest (~ few 100 ºC)
– ELM filaments seen clearly at main chamber limiters but only carry ~10% of WELM for largest ELMs (<WELM> > 0.5 MJ with fixed wall gap (~5 cm).
R. A. Pitts et al. 28 49th APS, Orlando, Florida, USA 12 November 2007
Reserve slides
R. A. Pitts et al. 29 49th APS, Orlando, Florida, USA 12 November 2007
Example: L-mode
ne~0.4nGW
PTOT (MW)
D(in) D (out)
Time (s)
Injected
Pumped
Retained
Long term retention
Time (s)
Fluxes (1021 elec/s)#70534 @15sRetention = 6.31021Ds-1
Short term = 4.561021Ds-1 (72%)Long term = 1.741021Ds-1 (28%)
@25sRetention = 4.681021Ds-1
Short term = 2.941021Ds-1 (63%)Long term = 1.741021Ds-1 (37%)
Ip = 2.0 MA, B = 2.0 TICRH only (~1.2 MW)Divertor cryopump only
T. Loarer et al., EPS 2007
R. A. Pitts et al. 30 49th APS, Orlando, Florida, USA 12 November 2007
Large ELMs with low fueling
Large ELMs have large drop in Te,ped
New data populate scaling beyond Te,ELM/Te,ped = 0.4
R. A. Pitts et al., ITPA, Garching, 2007
D (inner)
PTOT (MW)
WDIA (MJ)
Te,ped
(keV)
ne,ped (1019m-3)
H98Y
Zeff (Brems)
Time (s)
#70226 – no gas fuelling
R. A. Pitts et al. 31 49th APS, Orlando, Florida, USA 12 November 2007
Filaments in fast visible light#70228
D(inner)divertor
WDIA (MJ)
Time (s) Frame time 33 s, main chamber view – filament-wall interaction seen during divertor D rise.
Courtesy of J. A. Alonso, CIEMAT
1 2 3
6 5 4
WELM = 804 kJERAD = 537 kJ
R. A. Pitts et al. 32 49th APS, Orlando, Florida, USA 12 November 2007
Parallel ELM transportSignificant progress being made in realistic parallel transport modelling of ELM pulse with the BIT1 PIC code
Treat ELM as a square wave pulse launched upstream over time ELM with specified Tped, nped
WELM ~ ELM3npedTped2LpolRdR
Plasma expelled into 1D SOL with cosine distribution centred on midpoint between targets.B = const., inclined targets (~5º)
D. Tskhakaya et al., EPS 2007
ELM = 200 s Post ELM 150 s
T, n
Nparticles = 0.8 – 5.0 106, Ncells = 6000High resolution, low noiseTped = 0.5 – 5 keVnped = 0.15 – 15 1019 m-3
WELM = 0.025 – 2.5 MJ
2L|| = 80 m
dR
R. A. Pitts et al. 33 49th APS, Orlando, Florida, USA 12 November 2007
Test case: PIC vs. expt.
Clear separation of electron (~2 s) and ion (~100 s) transit times
Assumed “ELM duration” 200 s
Example: WELM = 400 kJTped = 1.5 keVnped = 51019 m-3
e
i
ELM
D. TskhakayaPIC ONLY
R. A. Pitts et al. 34 49th APS, Orlando, Florida, USA 12 November 2007
Test case: PIC vs. expt.D. Tskhakaya, T. Eich, R. A. PittsIR data obtained at outer
target (no layers) from coherent average of 20 similar ELMs with <WELM> ~ 310 ± 66 kJ
Time resolution artifically enhanced to 50 s
Good agreement in shape of pulse rise
Width a question of time and shape of ELM pedestal loss
PIC overestimates expt. by ~ factor 5
Factor ~2 due to known in-out ELM loading asymmetryFactor ~2 due to 1D nature of PICReasonable agreement given how WELM specified in the code
PIC + EXPT.