Power Exhaust Walls Materials for Tokamaks Marco Wischmeier - - PowerPoint PPT Presentation

▶
power exhaust walls materials for tokamaks
SMART_READER_LITE
LIVE PREVIEW

Power Exhaust Walls Materials for Tokamaks Marco Wischmeier - - PowerPoint PPT Presentation

Nov 16, 2023 146 likes •786 views

Power Exhaust Walls Materials for Tokamaks Marco Wischmeier Max-Planck-Institut fr Plasmaphysik 85748 Garching marco.wischmeier at ipp.mpg.de Joint ICTP-IAEA College on Advanced Plasma Physics, Triest, Italy, 2016 ICTP Trieste

slide-1
SLIDE 1

1

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Power Exhaust – Walls – Materials for Tokamaks

Marco Wischmeier Max-Planck-Institut für Plasmaphysik 85748 Garching marco.wischmeier at ipp.mpg.de

Joint ICTP-IAEA College on Advanced Plasma Physics, Triest, Italy, 2016

slide-2
SLIDE 2

2

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

slide-3
SLIDE 3

3

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Goal of magnetic confinement research Goal of magnetic confinement research

D + T → He + n + 17.6 MeV

14.1MeV

Neutrons leave plasma into power conversion system è will be used for net energy production

slide-4
SLIDE 4

4

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Goal of magnetic confinement research

D + T → He + n + 17.6 MeV

3.5MeV 14.1MeV

Used for net energy production

He heats plasma è needs to be exhausted

slide-5
SLIDE 5

5

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Losses perpendicular to magnetic field Losses perpendicular to magnetic field

Turbulence Device of R>7m should ignite

From DIII-D

Device of R>7m should ignite

Turbulent transport dominates

Gene code www.ipp.mpg.de /~fsj/gene/

slide-6
SLIDE 6

6

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Fusion exhaust must… Fusion exhaust must…

v Maximize pumping of He ash v Provide sufficient pumping of hydrogen fuel v Minimize damages to the wall (erosion, melting)

slide-7
SLIDE 7

7

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor concept Divertor concept

Confined plasma Scrape-Off Layer plasma Maximize pumping of He ash and minimize erosion

slide-8
SLIDE 8

8

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor concept Divertor concept

TARGET UPSTREAM Confined plasma Scrape-Off Layer plasma

slide-9
SLIDE 9

9

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor & Plasma Divertor & Plasma

From JET

Pheat in centre

slide-10
SLIDE 10

10

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor & Plasma Divertor & Plasma

From JET

Distributed Recycling particles

slide-11
SLIDE 11

11

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor & Plasma Divertor & Plasma

From JET

108 K 10keV

slide-12
SLIDE 12

12

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor & Plasma Divertor & Plasma

From JET

108 K 10 keV 10000 K 1 eV Thin Scrape Off Layer

slide-13
SLIDE 13

13

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Width of Scrape-Off Layer? What is the power flux?

slide-14
SLIDE 14

14

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Measuring power deposition profile Measuring power deposition profile

Infrared image of target

  • T. Eich PSI 2012
slide-15
SLIDE 15

15

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

The power decay length The power decay length λq

  • T. Eich PRL (2011), T. Eich IAEA FEC 2012, A. Scarabosio PSI 2012

H-mode (reduced turbulent transport)

No dependence on machine size R

slide-16
SLIDE 16

16

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

What is the power flux density in the SOL?

slide-17
SLIDE 17

17

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Importance of Importance of tokamak tokamak size R size R

3 m ~ 38 MW 6.2 m ~ 100 MW Major Radius Pheat 1.65 m 23 MW >7 m ~ 600 MW

Good energy confinement è large R (Pfus ~R3 – see yesterday)

ASDEX Upgrade (IPP) JET (EU) ITER DEMO

slide-18
SLIDE 18

18

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

P/R as figure of merit P/R as figure of merit

A measure of the severity of the heat flux is

  • Pheat/R

Device Pheat/R q|| upstream JET 7 20 GW/m2 ASDEX Upgrade 14 35 GW/m2 ITER 20 50 GW/m2 DEMO 80-100 >300 GW/m2

  • M. Kotschenreuter et al. NF 50 2010
  • K. Lackner Comm. PPCFusion 15 1994
slide-19
SLIDE 19

19

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

What are the limitations imposed by wall materials?

slide-20
SLIDE 20

20

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Erosion limits maximum Temperature Erosion limits maximum Temperature

Erosion yields

Ions accelerated to energies ~ Z x 3.5 x Te in electrical field by sheath potential W has low Yield

slide-21
SLIDE 21

21

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Tritium retention Tritium retention

  • J. Roth, K. Schmid, Phys Scripta 2011
slide-22
SLIDE 22

22

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

All tungsten plasma facing components All tungsten plasma facing components in ASDEX Upgrade in ASDEX Upgrade 2012

  • R. Neu PSI 2012
slide-23
SLIDE 23

23

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Technological limits under neutron Technological limits under neutron irradiation irradiation

E.U. protoype monoblock

Integrated approach: Combination of coolant, structural material of coolant pipe and armour material?

10MW/m2 to 5MW/m2 is the technological limit

Water cooled divertor segment

slide-24
SLIDE 24

24

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

slide-25
SLIDE 25

25

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

slide-26
SLIDE 26

26

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

  • D. N. Ruzic et al. NF 2011

Liquid metals as Plasma Facing Components

  • V. A. Evtikhin et al. PPCF 2002

NSTX

  • H. W. Kugel et al. Fusion Eng. and Des. 2012
  • A. G. McLean et al. JNM 2013

Risk mitigation: Liquid metals as PFC

slide-27
SLIDE 27

27

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

  • D. N. Ruzic et al. NF 2011

Liquid metals as Plasma Facing Components

  • V. A. Evtikhin et al. PPCF 2002

NSTX

  • H. W. Kugel et al. Fusion Eng. and Des. 2012
  • A. G. McLean et al. JNM 2013

Risk mitigation: Liquid metals as PFC

slide-28
SLIDE 28

28

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

How can we reduce the power load onto the divertor target plates to match the technological limit?

slide-29
SLIDE 29

29

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

How can we reduce the power load onto the divertor target plates to match the technological limit?

  • 1. GEOMETRY
slide-30
SLIDE 30

30

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Magnetic Flux Expansion Magnetic Flux Expansion

  • R. Pitts et al., TCV, (CH), PSI 2000
slide-31
SLIDE 31

31

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Target inclination Target inclination

Courtesy H. Meyer, MAST

  • R. Chodura 1984

Impact angles of 1.5 – 3.5 degrees

slide-32
SLIDE 32

32

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Power load reduced by geometry Power load reduced by geometry

Device Pheat/R q|| upstream q target (geometry) JET 7 20 GW/m2 20 MW/m2 ASDEX Upgrade 14 35 GW/m2 35 MW/m2 ITER 20 50 GW/m2 50 MW/m2 DEMO 80-100 >300 GW/m2 300 MW/m2

slide-33
SLIDE 33

33

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Increase of divertor major R

  • N. Asakura et al. NF 2014

Numerical simulations of DEMO device: SONIC

  • N. Asakura et al. P1-103 at PSI2014

Ø With long leg – Target at larger R: Ø Lower q|| and larger Awet (here compensated by lower f) Ø Lower core radiation required Ø Lower core dilution

slide-34
SLIDE 34

34

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Risk mitigation: Risk mitigation: Advanced divertor configurations (I) Advanced divertor configurations (I)

NSTX (USA): Snowflake TCV (CH): Snowflake

slide-35
SLIDE 35

35

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Risk mitigation (II): a (Super-) X divertor

Second X-point è low poloidal B

  • M. Kotschenreuther et al. arXiv:1309.5289

Caveat of high flux expansion and thus potentially too low impact angles on target plate à but Super-X may reduce issue

Super-X concept: Valanju et al. Phys. Plasmas 16, 056110 (2009)

slide-36
SLIDE 36

36

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Advanced divertor configurations (III) Advanced divertor configurations (III)

  • E. Havlickova et al., JNM 2013
  • E. Havlickova et al., PET 2013

MAST Super-X (UK)

slide-37
SLIDE 37

37

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

How can we reduce the power load onto the divertor target plates to match the technological limit?

  • 2. Basic SOL Physics
slide-38
SLIDE 38

38

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor Regimes: high recycling Divertor Regimes: high recycling

PSOL ≈conducted ΓSOL è High recycling regime: low Te (< 5eV), high ne è Satisfactory for existing tokamaks è VERY HIGH PARTICLE FLUXES

Total plasma pressure is constant along magnetic field line Pe+ Pi + dynamic pressure = constant

Temperature gradient

upstream target

slide-39
SLIDE 39

39

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Do we need to limit the particle flux? Do we need to limit the particle flux?

Neglecting power loads on PFCs from radiation è Total power = (8T + 15.8 ) 1.602 10-19Γ [W] ; Te= Ti= T [eV]

Power across sheath Surface recombination of D+ to D2

slide-40
SLIDE 40

40

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

What does < 5 -10 MW/m What does < 5 -10 MW/m2 imply for imply for particle flux? particle flux?

Neglecting power loads on PFCs from radiation è Total power = (8T + 15.8 ) 1.602 10-19Γ [W] ; Te= Ti= T [eV]

v For Te < 2.5 eV à heat flux similar to power deposited by surface recombination processes v Power load via radiation to ~2 MW/m2

Power across sheath Surface recombination of D+ to D2

slide-41
SLIDE 41

41

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

What does limit of < 5 -10 MW/m2 mean for the particle flux?

Neglecting power loads on PFCs from radiation è Total power = (8T + 15.8 ) 1.602 10-19 Γ [W] ; Te= Ti= T [eV]

v For Te < 2.5 eV à heat flux similar to power deposited by surface recombination processes v Power load via radiation of ~2 MW/m2 v 5 MW/m2 with T = 1.5 eV è Γ < 5e23 m-2s-1

Power across sheath Surface recombination of D+ to D2

slide-42
SLIDE 42

42

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

What does limit of < 5 -10 MW/m2 mean for the particle flux? Target power flux < 5 MW/m2 à ~1GW/m2 upstream For DEMO: > 95% of power need to be radiated + Ion flux to target reduced to 5 1023m-2s-1 For ITER (10 MW/m2 target limit): ~60-80% of power needs to be radiated + Ion flux to target reduced to ~1024m-2s-1

slide-43
SLIDE 43

43

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Can we achieve these 5MW/m2 in existing tokamaks with high P/R?

slide-44
SLIDE 44

44

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Impurity seeding (I) Impurity seeding (I)

  • F. Reimold et al. DPG 2012
slide-45
SLIDE 45

45

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Impurity seeding (I)

ASDEX Upgrade with all W PFCs

slide-46
SLIDE 46

46

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Impurity Seeding (II) Impurity Seeding (II)

slide-47
SLIDE 47

47

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Highly Radiating Plasma (ASDEX Upgrade) Highly Radiating Plasma (ASDEX Upgrade)

v Pheat= 23 MW v Pheat/R=14 (world record) v Seeding of Ar and N2 v Reduction to <5MW/m2

  • A. Kallenbach et al. NF 2012

t/s

slide-48
SLIDE 48

48

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Power flux can be dropped to < 5MW/m2 in existing devices with high P/R How is the particle flux limited?

slide-49
SLIDE 49

49

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Corrected two point model as a useful guide

fpow: power loss factor (0 – 1 ) à What is the maximum value? fconv : 0=no convection; 1= only convection à What is the interplay? fmom: momentum loss factor (0 – 1) à What is the maximum?

Ø Value of the loss factors and what interdependence?

Ø System codes will require scaling laws to define operational regime of DEMO type device

Particle flux

“Modified” two point model as guidance

slide-50
SLIDE 50

50

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor Regimes: detachment Divertor Regimes: detachment

PSOL ≈conducted ΓSOL

Prerequisite: Loss of plasma pressure a) Radiation in the edge of the plasma core è Reduction of upstream plasma pressure è Reduced recycling

upstream target

slide-51
SLIDE 51

51

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

At low At low Te Te large Complexity of large Complexity of volumetric and surface processes volumetric and surface processes

+ seeded processes for impurities… + surface interaction physics (reflection, recycling)

slide-52
SLIDE 52

52

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor Regimes: detachment Divertor Regimes: detachment

b) Pressure loss along field line v perpendicular transport (independent of Te) v CX reaction losses (Te<5eV)

D + D+ à D+ + D D+ + D2 à D2+ D+

0.01

2 4 6 8

0.1

2 4 6 8

1

2 4

fm (2neTe,plate/neTe,SOL)

5 6 7 8 9

1

2 3 4 5 6 7 8 9

10

2 3 4

Te,plate(eV) Winter 1995 campaign ρ = 1 mm ρ = 2 mm ρ = 4 mm ρ = 6 mm

  • B. Lipschultz et al., FST 51 (2007)

Ratio of target plasma pressure to upstream pressure for C-Mod

Competes with ionization

slide-53
SLIDE 53

53

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Divertor Regimes: detachment Divertor Regimes: detachment

PSOL ≈conducted ΓSOL Γsink

Prerequisite: Loss of plasma pressure on a field line b) Pressure loss along field line v perpendicular transport (independent of Te) v CX reaction losses (Te<5eV)

upstream target

slide-54
SLIDE 54

54

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Density ramp experiments in ASDEX Upgrade Density ramp experiments in ASDEX Upgrade

Total ion flux to inner and outer divertor

Forward field

  • Asymmetry of particle fluxes
  • Integral ‘roll over’ at similar time/density for inner and outer

Time /s = increase of density à

  • S. Potzel, PSI2012

Signature of detachment:

  • Volumetric recombination

processes (visible in Balmer series)

  • reduction of ion flux density
  • n target plates
  • S. Potzel et al. NF 2014
slide-55
SLIDE 55

55

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

How to extrapolate from exiting devices How to extrapolate from exiting devices to future tokamaks? to future tokamaks?

…but requires well established understanding of existing devices …but requires well established understanding of existing devices first.. first..

slide-56
SLIDE 56

56

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Numerical tool Numerical tool

  • Multi fluid code B2.5 (2D)

– Solves modified fluid equations in 2D (Braginskii) – Includes fluid treatment of neutrals – Kinetic limits

ne Interface Fluxes Sources Sinks

Can be time dependent

  • EIRENE (’96, ’99), 3D
  • Solves time dependant linear

transport equations for test particles (photons, neutrals, test ions)

slide-57
SLIDE 57

57

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Role of drift terms in simulations for JET

Exp. No drifts Drifts/Drifts L-mode experiments with semi-horizontal configuration at low density Inner target Outer target

slide-58
SLIDE 58

58

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Perpendicular SOL transport: Intermittent transport and main chamber wall interaction

Effective collisionality in divertor determines filamentary perpendicular transport in midplane

Normalized L-mode SOL density profiles

See also:

  • M. Kocan et al. P3-093 at PSI14
  • T. Lunt et al. O-23 at PSI14
  • K. Schmid et al. I-6 at PSI14
  • D. Carralero et al. I-16 at PSI14
  • B. LaBombard et al. PoP 2001, J. R. Myra et al. PoP 2006
slide-59
SLIDE 59

59

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Modeling ASDEX Upgrade and the high field side high density

slide-60
SLIDE 60

60

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Modeling ASDEX Upgrade and the high field side high density

Combination of activating drift terms and enhanced perpendicular transport

  • f heat in the far SOL
slide-61
SLIDE 61

61

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Impact of drifts and transport

slide-62
SLIDE 62

62

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

slide-63
SLIDE 63

63

ICTP Trieste College on Advanced Plasma Physics M. Wischmeier

Summary Summary

v Power exhaust works in existing devices v Identification of missing physics elements

  • ngoing

v A method for ELM mitigation has been found and fits well with required conditions by power exhaust v Challenge of power exhaust is increasingly demanding è will determine minimum size of fusion reactor