The Impact of large
This presentation is the property of its rightful owner.
Sponsored Links
1 / 21

The Impact of large ELMs on JET PowerPoint PPT Presentation


  • 49 Views
  • Uploaded on
  • Presentation posted in: General

The Impact of large ELMs on JET. Presented by R. A. Pitts CRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederation on behalf of JET Task Force E and JET EFDA Contributors 18 th International Conference on Plasma-Surface Interactions, Toledo, Spain, 23-26 May 2008.

Download Presentation

The Impact of large ELMs on JET

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


The impact of large elms on jet

The Impact of large ELMs on JET

Presented byR. A. PittsCRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederationon behalf of JET Task Force E and JET EFDA Contributors18th International Conference on Plasma-Surface Interactions, Toledo, Spain, 23-26 May 2008


The impact of large elms on jet

with thanks to many co-authors

G. Arnoux1, S. Brezinsek2, M. Beurskens1, T. Eich3, H. G. Esser2, W. Fundamenski1, A. Huber2, B. Gulejova4, S. Jachmich5, A. Kreter2, A. Loarte6, E. de la Luna7, J. Marki4, G. F. Matthews1, V. Philipps2, E. Solano7, M. F. Stamp1 and JET EFDA Contributors*

1Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK

2Institut für Energieforschung-Plasmaphysik, Forschungszentrum Jülich, Association EURATOM-FZJ, Germany

3Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, D-85748 Garching, Germany

4CRPP-EPFL, Switzerland, Association EURATOM-Swiss Confederation

5LPP, ERM/KMS, Association Euratom-Belgian State, B-1000, Brussels, Belgium

6ITER Organization, Cadarache, France

7Associacion Euratom/CIEMAT para Fusion, Madrid, Spain

*See appendix of M. Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Conf. Chengdu, 2006) IAEA Vienna (2006)


Outline

Outline

  • Introduction

  • Experiment

  • Impact on the divetor

    • Radiation

    • Surface temperatures

  • ELM-wall interactions

    • Energy deposition

    • Comparison with theory

  • Conclusions


Introduction elm size limit

Introduction - ELM size limit

Important also in preparation for JET ITER-like wall and improved understanding of ELM SOL physics

Material damage poses a limit on the maximum ELM size tolerable on ITER

Current estimates indicate that ELM power fluxes must remain below ~0.5 MJm-2 at the ITER divertor targets (see J. Roth, paper R-1)

JET Type I ELMs can approach 1 MJ  study the effects on first wall surfaces and edge plasma

This implies an ELM energy loss, DWELM~ 1 MJ ~0.3% of stored energy in an ITER QDT = 10 burning plasma!

This is lower than any Type I ELM energy so far achieved  mitigation strategies required. BUT …


Experiment

Experiment

Fuelling scan producing ELMs with range of frequencies and amplitudes

Vertical targets, MarkIIHD div.Ip = 3.0MA, Bj = 3.0Tq95 = 3.1, d ~ 0.25, k ~ 1.72


Large elms at zero fueling

Large ELMs at zero fueling

#70226 – no gas fuelling

Da (inner)

PTOT(MW)

WDIA(MJ)

Te,ped (keV)

ne,ped(1019m-3)

H98Y

Zeff(Brems)

Time (s)

Mostly NBI

Input energy ~195 MJEnergy Tile 3,7: 24.6, 70.1 MJRadiated energy: ~82 MJn/nGreenwald ~ 0.4

R. A. Pitts et al., ITPA, Garching, 2007


Large elms at zero fueling1

Large ELMs at zero fueling

#70226 – no gas fuelling

Da (inner)

PTOT(MW)

WDIA(MJ)

Te,ped (keV)

ne,ped(1019m-3)

H98Y

Zeff(Brems)

Time (s)

Mostly NBI

ITER

Lowest fuelling cases at ITER relevant n*ped

DWELM/Wped ~ 0.2 for largest ELMs

R. A. Pitts et al., ITPA, Garching, 2007


Radiation during large elms

Radiation during large ELMs

0.85 MJ

1.29 MJ

1.08 MJ

0.58 MJ

#70225, low fuelling

More details: A. Huber et al, P2-24

Da(inner)

WDIA (MJ)

PRAD (MW)

Erad (MJ)

Strong in-out asymmetry in ELM induced radiation for high DWELM  probably due to layers on inner targets and preferential inboard deposition of ELM energy

Time (s)


In out elm radiation asymmetry

In-out ELM radiation asymmetry

DERAD/DWELM ~ 0.5 if DWELM 0.6 MJ

Evidence for a break at largerDWELM

>

~

For DWELM 0.6 MJ radiation “spills over” separatrix – in-out radiation asymmetry reduced

<

~

First ELM spikeonly

Up to 70% DWELM radiated

WELM = 0.61 MJ

WELM = 0.85 MJ

More details: A. Huber et al, P2-24


Target surface temperatures

Target surface temperatures?

Target IR data not of high enough quality in this more recent experiment to quantify tile surface temperatures

Vertical targets, MarkIISRP divertorIp = 1 – 3 MA, Bj = 1 - 3Tq95 ~ 3.1, d ~ 0.253.0 MA discharge #62218 similar in parameters to more recent shot #70226

Return to shots from 2003

Slightly raised strike pts. compared with recent pulses

Slightly lower DWELM


Target surface temperatures1

Target surface temperatures?

Da (inner)

PTOT(MW)

WDIA(MJ)

Te,ped (keV)

ELM averaging period

ne,ped(1019m-3)

H98Y

Zeff(Brems)

#62218

Vertical targets, MarkSRP div.Ip = 1 – 3 MA, Bj = 1 - 3Tq95 ~ 3.1, d ~ 0.253 MA discharge #62218 similar in parameters to more recent shot #70226

Time (s)


Target surface temperatures2

Target surface temperatures?

Inter-ELM power loads higher at outer than inner as usual

Clear affect of surface layers on inner target

For largest ELM (~0.7 MJ):Max Tsurf (outer) ~ 1150ºCMax Tsurf (inner) ~ 875ºC

T. Eich

Max. Tsurf far from sublimationSuggest thermal decomposition and ablation of inner target layers accounts for strong radiation asymmetry

See also talks by A. Kreter, I-3 and T. Eich, O-17


How much elm energy to walls

How much ELM energy to walls?

Main chamber IR camera too slow to follow single ELMs and filaments very asymmetric toroidally and poloidally

For more on ELM filament wall interactions see posters by: A. Alonso, P1-39M. Jakubowski, P1-24D. Moulton, P2-35

Make energy balance for a single outboard poloidal limiter during H-mode phase, assume:Only ELM filaments can deposit energy on limitersNo energy to upper dump platesNo energy deposited in compound phasesSame energy on 16 limiters

68193, 57 s


How much elm energy to walls1

How much ELM energy to walls?

17.405 s

20.016 s

13

12

11

∑Etile (15 tiles)

Main chamber IR camera too slow to follow single ELMs and filaments very asymmetric toroidally and poloidally

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

68193, 57 s


Wall loading and elm size

Wall loading and ELM size

Ip = 3.0 MA, Bj = 3.0 T, gas scan. Separatrix-midplane outer wall gap fixed at ~5.0 cm. DWELM estimated for first ELM peak only

68193, 57 s

For fixed wall gap, on average, larger ELMs deposit more energy on limiters.

How does wall energy fraction compare with theory?


Pedestal profiles 70224

Pedestal profiles (#70224)

Pedestal width ~4 cm

Filament parallel energy loss model(W. Fundamenski, R. A. Pitts, PPCF 48 (2006) 109)

Assume ELM filament released in pedestal region with constant radial speed.

Propagate to walls and track power exhaust due to parallel energy loss

Reasonable assumption: filament is born in the mid-pedestal region


Compare with filament model

Compare with filament model

Mid-pedestal:Te,0 = Ti,0 ~ 800 eVne,0 ~ 3.01019 m-3Dped ~ 4 cmvELM = 600 ms-1 from previous JET studies

W’ = 0.094(model) W’ = 0.088(experiment)

Very good agreement given the approximations!


Compare with filament model1

Compare with filament model

Pedestal top:Te,0 = Ti,0 ~ 1500 eVne,0 ~ 5.01019 m-3

Separatrix:Te,0 = Ti,0 ~ 200 eVne,0 ~ 1.01019 m-3

vELM = 600 ms-1

0.394

0.094

0.037


Compare with filament model2

Compare with filament model

Mid-pedestalPedestal topSeparatrix

vELM = 600 ms-1vELM = 1200 ms-1

A filament starting at the pedestal top with 2x higher vELM deposits the same energy at the limiter

Filaments starting at the separatrix must travel much more slowly (~180 ms-1)


How to extrapolate to iter

How to extrapolate to ITER?

Natural ELM (~20 MJ) vELM = 1000 ms-1

Use previous scaling from JET H-modes2 (vELM = 600 ms-1 for DWELM/Wped ~ 0.12):

Desired ELM (~1 MJ) vELM ~220 ms-1

20%

2.5%

Results indicate that larger ELMs travel faster  consistent with interchange drive and sheath dissipation as mechanism for filament motion1

1 MJ (mitigated) ELMs on ITER deposit negligible energy fraction at wall

1O. E. Garcia et al., Phys. Plasmas 13 (2006), 2W. Fundamenski, JNM 363-365 (2007)


Conclusions

Conclusions

  • JET can access ELMs with DWELM approaching 1 MJ at ITER relevant pedestal collisionality (but low n/nGW)

  • Strong in-out divertor radiation asymmetry – up to 70% of the ELM energy drop can be radiated, mostly in the inner divertor volume

  • Divertor surface temperatures too low for sublimation  thermal decomposition and ablation of inner target co-deposited layers

  • ELM filaments seen clearly at main chamber limiters

  • Deposited energy fraction increases with ELM size

  • Wwall/<DWELM> = 9-12% for <DWELM> ~ 0.5 MJ

  • 1 MJ ELMs on ITER will deposit very small energy fraction at first wall if interchange driven filament velocity scaling applies


  • Login