progress in iter relevant exhaust physics at jet

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


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


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


Tritium retention


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


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)


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


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


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


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


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


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


ELMs


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


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



Lowest fuelling cases at ITER relevant *ped

WELM/Wped ~ 0.2 for largest ELMs


D (inner)

PTOT (MW)

WDIA (MJ)

Te,ped

(keV)

ne,ped (1019m-3)

H98Y

Zeff (Brems)

Time (s)


ITER


Target surface temperatures

D (inner)

Tmax outer (ºC)

Time (s)


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


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


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


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


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


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


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)


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


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


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!


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).


Reserve slides


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



Large ELMs have large drop in Te,ped

New data populate scaling beyond Te,ELM/Te,ped = 0.4


D (inner)

PTOT (MW)

WDIA (MJ)

Te,ped

(keV)

ne,ped (1019m-3)

H98Y

Zeff (Brems)

Time (s)



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


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


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


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.

progress in iter relevant exhaust physics at jet

Documents