Melting of Tungsten by ELM Heat Loads in the JET Divertor Guy - - PowerPoint PPT Presentation

▶
melting of tungsten by elm heat loads in the jet divertor
SMART_READER_LITE
LIVE PREVIEW

Melting of Tungsten by ELM Heat Loads in the JET Divertor Guy - - PowerPoint PPT Presentation

Feb 25, 2023 228 likes •545 views

Melting of Tungsten by ELM Heat Loads in the JET Divertor Guy Matthews, Gilles Arnoux, Boris Basylev, Jan Coenen,. and JET Contributors G.F.Matthews a , G.Arnoux a , B.Bazylev g , J.W.Coenen b , A.Autrique f , I.Balboa a , M.Clever b ,

slide-1
SLIDE 1

1

Melting of Tungsten by ELM Heat Loads in the JET Divertor

Guy Matthews, Gilles Arnoux, Boris Basylev, Jan Coenen,…. …and JET Contributors EX/4-1, Fusion Energy Conference 2014, St. Petersburg

G.F.Matthewsa, G.Arnouxa, B.Bazylevg, J.W.Coenenb, A.Autriquef, I.Balboaa, M.Cleverb, Ph.Mertensb, R.Dejarnaci, I.Coffeya, Y.Correi, S.Devauxc, L.Frassinettij, E.Gauthieri, J.Horacekd, S.Jachmichh, M.Knaupb, M.Kommd, K.Kriegerc, S.Marsene, A.Meigsa, R.A.Pittsk, T.Puetterichc, M.Rackb, G.Sergienkob, M. Stampa, P. Tamaini, V. Thompsona and JET Contributorsl JET EFDA, Culham Science Centre, Abingdon, OX14 3DB, UK

a CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK b Forschungszentrum Jülich, Jülich, Germany c Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany d Association EURATOM-IPP.CR, AS CR, Za Slovankou 3, 18221 Praha 8, Czech

Republic

e Max-Planck-Institut für Plasmaphysik, D-17491 Greifswald, Germany f Ecole Central Lyon, Lyon, France g Karlsruhe Institute of Technology, P.O.Box 3640, D-76021 Karlsruhe, Germany h Laboratory for Plasma Physics, Ecole Royale Militaire/Koninklijke Militaire School i CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France j Division of Fusion Plasma Physics, KTH, SE-10044 Stockholm, Sweden kITER Organisation, Route de Vinon sur Verdon, 13115 Sain-Paul-lez Durance,

France

l See the Appendix of Romanelli F et al 2014, Proceedings of the 25th IAEA Fusion

Energy Conference, St. Petersburg, Russia

slide-2
SLIDE 2

Outline

  • 1. Background
  • 2. The JET melt experiment
  • 3. Simulation of the results
  • 4. Conclusions and future plans
slide-3
SLIDE 3

3

Decision on material for ITER first divertor Risks for tungsten melting in early ITER

  • peration had to be reviewed by IO
slide-4
SLIDE 4

Bulk W melting well studied in medium sized tokamaks

ASDEX-Upgrade divertor manipulator

Bulk melting can cause disruptions = dangerous for ITER Bulk melting risk was considered low for ITER divertor due to tile shaping & protection systems

slide-5
SLIDE 5

5

Looking down into the tungsten divertor - after

2011 As installed 2012 After ~3500 pulses ~20Hrs plasma

The JET tungsten divertor Tungsten lamella shaping and divertor protection systems in JET at ITER relevant inter-ELM heat fluxes

slide-6
SLIDE 6

W melting by ELMs

6

QSPA-T W target

  • N. Klimov et al., JNM 390-391 (2009)

721

Plasma flow direction q > 2.2 MJm-2, t ~0.5 ms  3.8 MJm-2 for a 1.5 ms pulse (ITER minimum tTQ)

QSPA ELM simulations looked worrying for ITER Extrapolation to ITER requires a benchmark for the MEMOS code JET is capable of achieving a similar transient heat-flux at normal incidence …but plasma pressure lower and B higher in ITER (and JET)  stabilises surface waves

slide-7
SLIDE 7

7 7

Typical temperature rise due to ELMs in JET ITER ~105 Pa

Pedestal pressure (Pa)

Geometric factor for a vertical edge ~ ×20

[T.Eich]

Surface T depends mainly on pedestal pressure not ELM size! So increase heating power or Ip to raise T

Existing data – normal lamellas T during ELMs Temperature rise (C)

slide-8
SLIDE 8

Outline

  • 1. Background
  • 2. The JET melt experiment
  • 3. Simulation of the results
  • 4. Conclusions and future plans
slide-9
SLIDE 9

Exposing a tungsten edge in JET

9

A B

A B

q|| JET pulse 84779

slide-10
SLIDE 10

q|| Typical JET W melt pulse 3MA/2.9T 23MW

~3GWm-2 ~0.5GWm-2 300kJ ELMs

slide-11
SLIDE 11

Limitations of the top IR viewing

slide-12
SLIDE 12

Temperature from IR (C) Special lamella Standard (Ref.) lamella Time (s)

Melt pulses are reproducible and no disruptions

slide-13
SLIDE 13

84686 – Before melting

13

Special lamella 5.5mm LFS HFS Special lamella 5.5mm LFS Special lamella 5.5mm HFS LFS Special lamella 5.5mm

q|| q||

slide-14
SLIDE 14

After 84724

14

Special lamella LFS HFS

slide-15
SLIDE 15

After 84778

15

Special lamella LFS HFS

slide-16
SLIDE 16

After 84779

16

Special lamella LFS HFS

slide-17
SLIDE 17

After 84781

17

Special lamella LFS HFS

slide-18
SLIDE 18

After 84782

18

Special lamella LFS HFS

slide-19
SLIDE 19

After 84783

19

B

 Jthermionic

JxB

Erosion: 150-300m per pulse, 5-10m per ELM (frequency 30Hz) Total volume moved: ~6mm3 HFS LFS 5.5mm

slide-20
SLIDE 20

Tref(C)

Erosion centres on the ELM footprint

20

slide-21
SLIDE 21

Indirect evidence for W droplet expulsion

Laser blow off with W target W droplet event during melt pulse

A few droplets reach the main plasma with diameters ~ 100m

  • Small perturbations only and no disruptions

21

slide-22
SLIDE 22

Outline

  • 1. Background
  • 2. The JET melt experiment
  • 3. Simulation of the results

MEMOS = key tool used for ITER predictions Stefan problem in 3D geometry accounting surface evaporation, melting and re-solidification solved by implicit method

  • Surface power density vs time from IR is the input
  • Vapour shielding
  • Temperature dependent thermophysical data applied
  • Moving boundaries are attached to melt layers
  • All forces: Gradient of plasma pressure, gradient of surface

tension, JxB, tangential friction force [Bazylev TH/P3-40]

22

slide-23
SLIDE 23

Power density q|| from reference lamellas

23

Reference lamellas qn (MWm-2) T(t) Theodor 2D inverse code IR camera  q|| = qn / sin 

MEMOS 3D B

slide-24
SLIDE 24

Power density on the special lamella

24

qs qs = fs q|| cos  MEMOS input = qn from IR (Theodor) fs iterated to match: evaporation rate, synthetic IR image and Planck radiation

Special lamella

qn= q|| sin  qs = fs q|| cos  PIC model says: fs >0.6 during ELMs fs~1 inter-ELM and L-mode q|| from reference lamellas

slide-25
SLIDE 25

fs chosen to fit evaporation rate and Planck radiation

25

IR

Temperature #84779 – IR (unresolved) and peak (MEMOS)

Melting

W evaporation rate from WI (400.88nm)

MEMOS fs=1 MEMOS fs=0.4

Best fit to all data with fs=0.4

slide-26
SLIDE 26

W melt evolution #84779 – MEMOS [Bazylev TH/P3-40]

26

fs=0.4

slide-27
SLIDE 27

Melt depth and motion match JET data Hierarchy of forces – MEMOS [Bazylev TH/P3-40]

27

Plasma pressure (6kPa) + surface tension gradients

Surface: -40 to +10m HFS LFS Shadow

2.5mm 60mm

m Surface: -200 to +400m

Plasma pressure (6kPa) + surface tension gradients + thermionic emission (JxB)

B J JxB

m

JET pulse #84779 - MEMOS

slide-28
SLIDE 28

Conclusions

W melting by ELMs in JET provided important inputs to ITER:

  • Shallow melts with a few small droplets ejected but no disruptions
  • JET melt results are consistent with MEMOS assuming J×B dominant
  • Unexpectedly large power mitigation factor found for exposed W edge

New lamella at 15:

  • Fully resolved IR temperature
  • Grazing field angle / more ITER-like
  • Simpler geometry

Future JET plans

28

slide-29
SLIDE 29

29

Thermionic emission during ELM - MEMOS

[Bazylev TH/P3-40]

JET pulse #84779 - MEMOS

Unlike JET experiment, suppression of thermo electron emission is predicted in ITER due to grazing field angles

slide-30
SLIDE 30

Larmor radius smoothing - PIC code [Dejarnac NF]

  • Calculated for ELMs only - insufficient to explain fs=0.4 in H-mode
  • No effect expected in L-mode where we find fs=0.2

30

Equivalent to fs~0.8

slide-31
SLIDE 31

MEMOS suggests significant vapour shielding

31

#84779 …..but we are not able to prove it experimentally due to lack of a consistent physics model for fs=0.4 in H-mode and fs=0.2 in L-mode