The ITER divertor concept: physics and engineering design R. A. - - PowerPoint PPT Presentation

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The ITER divertor concept: physics and engineering design R. A. - - PowerPoint PPT Presentation

Aug 19, 2022 716 likes •1.21k views

The ITER divertor concept: physics and engineering design R. A. Pitts, X. Bonnin, S. Carpentier 1 , W. Dekeyser, F. Escourbiac, L. Ferrand, T. Hirai, A. S. Kukushkin 2 , A. Loarte, R. Reichle ITER Organization, CS 90 046 - 13067 St Paul Lez

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

The ITER divertor concept: physics and engineering design

  • R. A. Pitts, X. Bonnin, S. Carpentier1, W. Dekeyser, F. Escourbiac,
  • L. Ferrand, T. Hirai, A. S. Kukushkin2, A. Loarte, R. Reichle

ITER Organization, CS 90 046 - 13067 St Paul Lez Durance Cedex, France

1EIRL S. Carpentier-Chouchana, 13650 Meyrargues, France 2Present address: NRC “Kurchatov Institute”, Moscow 123182 and National Research Nuclear

University MEPhI, Moscow 115409, Russia

The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Content

  • Recap of what the ITER W divertor looks like
  • Basic design features
  • Operational physics considerations
  • Baseline operating condition (note most will be

covered in talk I-2, A. S. Kukushkin)

  • Consequence of magnetic perturbations
  • Transients (very brief)
  • Detachment control options (to be dealt with in detail

in talk I-3, B. Lipschultz)

  • Summary of key outstanding R&D areas
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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Recap of basic design features

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Outer vertical target Inner vertical target Dome Reflector plates Pumping slot Cassette body 54 divertor assemblies ~500 tons total mass ~150 m2 W surface 4320 actively cooled heat flux elements Bakeable to 350C

The W divertor

  • ITER will begin
  • perations with a full-

W armoured divertor

  • Must survive to at

least the end of the first full DT campaign

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

W divertor: essential characteristics

Baffles to limit neutral escape to the core Strong outboard shaping for disruption transients Reflector plates to protect against strike point excursions and some measure of diagnostic/cassette protection Dome – improve pumping  less pumping speed required for given upstream He conc

  • r fuel throughput.

Diagnostic/cassette protection Open pathway between divertors for neutral recirculation – reduction of target heat load asymmetries

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

  • “Standard” technology  W blocks

bonded to a CuCrZr cooling tube via a Cu interlayer

W monoblocks

Monoblock Cu interlayer CuCrZr tube

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

  • Still working on the final thickness to cooling tube and

top surface shaping (see later)

W monoblock dimensions

Poloidal gap (0.5 mm) Toroidal gap (0.5 mm) Thickness to cooling pipe (6 – 8 mm)

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Monoblock numbers

tilting axis+80º 0.74º 0.5o Tilting axis

  • Totals, for the record (as of June 2014)

16 PFUs 138 monoblock/PFU 119,232 total per divertor 48,384 on the straight vertical part 22 PFUs 143-146 monoblock/PFU 172,962 total per divertor 61,182 on the straight vertical part

292,194 grand total 313,838 with 4 spare cassettes

IVT OVT

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Global shaping for transients

OVT

DOME: protection against strike point excursions Outer baffle toroidal chamfering for VDE protection

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Vertical target & monoblock shaping

Individual monoblock shaping Global target tilt

Worst case expected radial misalignment between toroidally neighbouring monoblocks ± 0.3 mm

0.3 mm

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Monoblock shaping

Individual monoblock shaping Global target tilt

  • Full scale OVT prototype PFUs from

Japan now just undergoing high heat flux testing (in Russia) and meets the geometrical tolerances (PFU-PFU radial misalignment within ±0.3 mm)

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Individual monoblock shaping Global target tilt

  • Shaping ALWAYS increases plasma heat loads (reduced

projected area)  e.g. for ITER outer vertical target

  • Global target tilt: increase by 19%
  • 0.5 mm toroidal monoblock chamfer: increase by 37%
  • 10 MWm-2 becomes ~15 MWm-2

0.5 mm

Monoblock shaping

Simplest solution to hide worst case leading edge: single toroidal chamfer of height 0.5 mm

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Operational physics considerations

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Baseline operating mode

  • Deep vertical target with partially detached strike regions

maintaining steady state peak load q ≤ 10 MWm-2

  • The physics operating mode for ITER is entirely based on

very extensive set of SOLPS-4.3 simulations conducted over 15 years  talk I-2 by A. S. Kukushkin

  • A. S. Kukushkin et al. J. Nucl. Mat. 290-293 (2001) 887
  • A. S. Kukushkin et al. Nucl. Fusion 42 (2002) 187
  • A. S. Kukushkin and H. D. Pacher, PPCF 44 (2002) 931
  • A. S. Kukushkin et al. Nucl. Fusion 43 (2003) 716
  • A. S. Kukushkin et al. Fus. Eng. Design 65 (2003) 355
  • A. S. Kukushkin et al. J. Nucl. Mat. 337-339 (2005) 17
  • A. S. Kukushkin et al. Nucl. Fusion 45 (2005) 608
  • A. S. Kukushkin et al. Nucl. Fusion 47 (2007) 698
  • A. S. Kukushkin et al. J. Nucl. Mat. 363-365 (2007) 308
  • A. S. Kukushkin et al. Nucl. Fusion 49 (2009) 075008
  • A. S. Kukushkin et al. Fus. Eng. Design 86 (2011) 2865
  • A. S. Kukushkin et al., J. Nucl. Mat. 415 (2011) 2011
  • A. S. Kukushkin et al. Nucl. Fusion 53 (2013) 123024
  • A. S. Kukushkin et al. J. Nucl. Mat. 438 (2013) S203
  • H. D. Pacher et al. J. Nucl. Mat. 463 (2015) 591
  • H. D. Pacher et al. J. Nucl. Mat. 415 (2011) S492
  • H. D. Pacher et al. J. Nucl. Mat. 390-391 (2009) 259
  • G. W. Pacher et al. Nucl. Fusion 48 (2008) 105003
  • G. W. Pacher et al. Nucl. Fusion 51 (2011) 083004
  • H. D. Pacher et al. J. Nucl. Mat. 313-316 (2003) 657

SOLPS-ITER

  • S. Wiesen et al, . J. Nucl. Mat. 463 (2015) 480
  • X. Bonnin et al., 15th PET, 9-11 Sept. 2015

Now moving to new code version

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Baseline operating mode

  • Most work done for C divertor targets but with decision

to go full W, work switched to “carbon-free” (from 2013)

  • Ne and N2 impurity seeding, no W yet  assume that

anything other than trace quantities unacceptable

  • Steady state simulations, ELM power included implicitly

through PSOL, no drifts, currents (yet)

  • High performance (QDT = 10, PSOL~100

MW) of primary interest  sets limits

  • n target heat flux
  • Most simulations fix

D = 0.3 m2s-1, i,e = 1.0 m2s-1  q (omp) = 3 – 4 mm

  • Have studied cases with q ~ 1 mm

1 10 100 5 10 15 20

1 e-1

q||,omp (MWm-2) (r – rsep)omp (mm)

q ~ 3.6 mm

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

  • H. D. Pacher et al., J, Nucl. Mat. 463 (2015) 591

Operating window in target power flux

  • Similar operating window as for

Carbon exists for Ne and N

  • Window up to QDT ~15 for

qpk< 10 MWm-2 at lowest cNe

  • For any reasonable pn, only very

low cNe required to maintain acceptable qpk

  • ~2x core concentration of N gives

same QDT as for Ne

  • Simulations for q ~3.5 mm

qpk,target (MWm-2)

Divertor neutral pressure (Pa)

PSOL = 100 MW cne (separatrix)

Neon

Power handling limit Detachment limit

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Lower limit on operating window

  • W source likely too high at high qpk (low pn)

Distance along target (m) Distance along target (m)

Te (eV) ne (1021m-3) qpk (MWm-2) Ti (eV)

Outer target: PSOL = 100 MW, cNe,sep ~1.2%

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Consequence of reduced transport?

  • Ok if pn high enough, BUT increased ne,sep due to higher

power density

  • Integrated modelling indicates reduced operational window if

q ≤ 10 MWm-2

  • A. S. Kukushkin et al., J, Nucl. Mat.

438 (2013) S203

q,peak, target, (MWm-2)

1 10 1 10

pn [Pa

Divertor neutral pressure (Pa)

q (mm)

~1.3 ~1.7 ~3.6

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1 10

ne_sep mod [1020m-3] pn [Pa

ne,sep (1020 m-3)

Divertor neutral pressure (Pa) Problems likely here due to excessive W release?

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Total PRAD,DIV = 59 MW PRAD,fuel = 17 MW

Radiation distributions (C vs. N)

  • N very like C (as expected)

N C

PSOL = 100 MW Total PRAD,DIV = 65 MW PRAD,fuel = 12 MW

#2533 #1577

qpk,outer = 4 MWm-2 cN,sep = 0.8% qpk,outer = 4.5 MWm-2 cC,sep = 2.0%

(Wm-3)

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Total PRAD,DIV = 59 MW PRAD,fuel = 17 MW

Radiation distributions (Ne vs. N)

  • Ne more distributed (as expected)

N Ne

PSOL = 100 MW Total PRAD,DIV = 56 MW PRAD,fuel = 13 MW qpk,outer = 4 MWm-2 cN,sep = 0.8% qpk,outer = 5 MWm-2 cNe,sep = 1.2%

#2533 #2463

(Wm-3)

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Separatrix Te (C, N, Ne)

Parallel distance along field line (m)

T

e (eV)

#1577 #2463 #2533

PSOL = 100 MW qpk ~ 4.5 MWm-2

  • Extended

convective regions

  • Drop to very low

T

e (<1 eV) occurs

  • nly right in front
  • f targets

X-point

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Contributions to target power load

Power flux density (MWm-2)

  • Range from almost fully due to thermal plasma or a

balance between plasma, neutrals and radiation

Total Radiation Plasma Neutrals Total Radiation Plasma Neutrals

Distance along target (m)

PSOL = 100 MW cNe,sep ~1.2% OUTER target

#2476 #2463

PSOL = 100 MW cNe,sep ~1.2% OUTER target

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Low in-out power asymmetries

  • No drifts and currents yet  asymmetries due mostly to

geometry (target orientation & larger LFS power outflux)

Inner Outer

qpk,target (MWm-2)

PSOL = 100 MW, cNe,sep ~1.2%

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Pressure loss

r – rsep (m) Plasma pressure (Pa) PSOL = 100 MW, cNe,sep ~1.2%

  • Attached to detached solutions depending on target and

neutral pressure

#2463 #2476

Upstream Downstream

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Ionization/recombination

Ionization from D0

(cm-3s-1)

  • Net particle loss occurs extremely close to the targets

Recombination from D+ Net source D+

(cm-3s-1) (cm-3s-1)

PSOL = 100 MW, cNe,sep ~1.2%

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

T

e (eV)

Parallel distance along field line (m)

Distance along target (m)

ne (1021m3)

Ionization/recombination

  • Net particle loss occurs extremely close to the targets

PSOL = 100 MW, cNe,sep ~1.2%

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Global picture

Heat conduction zone Impurity radiation zone H0/D0/T0 ionization zone (Te > 5 eV) Neutral friction zone Recombination zone (Te < 1 eV)

PSOL

  • Simulations consistent with conventional picture of

dissipative divertor

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Effect of ELM control coils

Toroidal angle (deg)

q (MWm-2)  = 0

  • O. Schmitz et al., submitted to NF
  • Not at all accounted for by SOLPS

baseline simulations

  • Potential issues of power overloading if

high qpk in lobes  rotate the perturbation

  • OVT a difficult area  lobes connect

there and target strongly shaped

EMC3-Eirene, outer target, n = 3 perturbation

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Effect of ELM control coils

  • Effect of 3D fields on divertor function still an immature

R&D area

  • Will dissipation be sufficient to stop lobe burn through?
  • If yes, what price to pay in confinement (state too detached)?
  • Push experiments and code development to deal with

realistic detached regimes in the presence of MPs

J.-W. Ahn et al., PPCF 56 (2014) 015005

A few experiments so far

  • n NSTX, DIII-D, AUG

 results are mixed

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Tolerable ELM energy loss

  • Original ELM energy loss spec derived from Russian

plasma gun experiments on melting of W assuming no misalignments and no ELM footprint broadening

  • Fixed at 0.5 MJm-2  translates to WELM ~1.0 MJ
  • A. Zhitlukhin et al., J. Nucl. Mat. 363-365 (2007) 301
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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

JET‐C JET‐ILW AUG‐C AUG‐W

qII,regression (MJm-2) qII,measured (MJm-2)

  • From JET and AUG, peak
  • uter target Type I ELM

energy flux density scales like ~ppedR

  • Nearly independent of ELM

energy drop, WELM

  • e.g.: E,ELM ~ 0.32 MJm-2 for

Ip = 7.5 MA (WELM ~ 4 MJ)

Transients: peak ELM energy fluxes

  • Opens up window for lower power H-mode operation

without need for mitigation

  • Awaiting scaling for INNER targets
  • T. Eich et al., APS 2013
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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Long term ELM effects (1)

  • Even if ELMs can be mitigated, the frequent thermal

cycling will lead to damage formation over time

JUDITH 2 e-beam Damage threshold ≤ 3 MJm-2s-1/2 For 106 square wave pulses at ~500 s duration (Wmelt ~50 MJm2s-1/2) T

surf = 1200C

(NB: triangular pulses likely to give higher damage thresholds (see Yu et al., NF 55 (2015) 093027))

  • Th. Loewenhoff et al., PFMC 2015
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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Long term ELM effects (2)

  • Tungsten surface can be strongly modified if conditions

are not carefully controlled even for sub-melting threshold events

  • 105 ELMs ≡ 24 mins exposure time at fELM = 70 Hz on ITER ...

T

surf = 1500ºC

105 pulses @ 0.3 MJ.m-2 500 m Profilometry

  • Th. Loewenhoff et al., JNM in press

1 mm

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

NB: Be/W melt limit: ~28/50 MJm-2s-1/2

80 - 320 MJm-2s-1/2 130 - 280 MJm-2s-1/2 up to 770 MJm-2s-1/2

Transients: disruptions

  • Traditionally considered the most difficult for PFCs
  • Loss of thermal, magnetic

energy, runaway electrons

  • Can potentially melt up to

several kg per disruption (large scale shallow melt)

  • Runaway electrons: highly

localized, deep deposition (e.g. 10 MJ, IRE = 5 MA, <ERE> = 15 MeV)  no protection possible  avoid

Major disruption 350 MJ (worst case)

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Disruptions: benefit of vapour shielding

Time (ms)

T

surf (x1000 K)

q (GWm-2)

Strike pt Adjacent to Strike pt.

  • S. Pestchanyi, et al., ISFNT 2015

TOKES code

  • Factor 5-10 reduction in heat flux with shielding
  • Need experimental benchmark (plasma guns)
  • NB in case of melting, calculations indicate no splashing for W
  • New simulations show that for a W divertor, vapour

shielding helps  but complex, 2D, time dependent

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Heat flux/detachment control: diagnostics

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Diagnostics

  • ITER will be well diagnosed in the divertor
  • But divertor heat flux control methodology still to be developed
  • Control methods must be as SIMPLE as possible and

ROBUST  next steps after ITER will not be as well diagnosed ….

  • Lifetime of systems not guaranteed, replacement in case of

malfunction not easy

  • NB: almost all divertor diagnostic systems are being designed
  • n the basis of SOLPS simulations
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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Diagnostics

Foil bolometry

  • 8 bolometers in each of

5 cassettes: 40 LOS / cassette

  • LOS still to be fixed
  • ~5 cm resolution

Usual issue with neutrals  hope to use for measure of neutral distribution

  • A. Suarez et al., 1st EPS Conf. on Plasma Diagnostics April 14-17, 2015, Frascati, Italy
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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Diagnostics

  • 6 separate views
  • VIS and VUV
  • 4 directly into the

divertor (through cassette gaps and from under the dome)

  • ~250 LOS
  • < 1 nm resolution
  • ~50 mm spatial

1 ms temporal Divertor impurity monitor

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Diagnostics

  • 4 equatorial (IVT)

and 4 upper port (OVT) views

  • 3-5 m (IR), 2-colour
  • 400-700 nm (VIS)
  • Best spatial

resolution 7.5 mm (IR), 3 mm (vis)

Divertor IR/VIS

Front-End optics Viewing area of inner divertor Divertor Port plug Viewing area of outer divertor 1st relay optics

  • Distributing
  • ptics
  • Imaging
  • ptics
  • Spectroscope
  • Detectors
  • 3 mm spatial resolution
  • 2-colour 3-5 m and 100

spatial points with 30 point spectroscopic resolution in 1.5-5 m ( = 0.17 m)

Single view high resolution IR

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Diagnostics

Divertor pressure gauges

  • ASDEX-type fast gauges
  • 6 gauges per cassette, 4 cassettes instrumented
  • 44 gauges in total (2 in 2 equatorial ports, 16 in lower ports

for pump duct pressure)  only 26 running at any time

Eirene simulation of divertor D2 neutral pressure (S. Lisgo)

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Diagnostics

Divertor Langmuir probes

  • Up to 350 tungsten tip probes (tbd) on 5

cassettes (IVT and OVT)

  • Single, double and fixed biased operation

modes

  • Spatial resolution tbd, but minimum

determined by PFU monoblock attachment (1 probe per 2 monoblocks)  ~2.5 cm

OVT

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Diagnostics

Divertor Thomson Scattering

  • 25 measurement points along

a 0.75 m chord length

  • 20 ms time resolution
  • ne = 1019 – 1022 m-3
  • Te = 0.3 – 1.0 eV & 1 – 200 eV
  • E. Mukhin et al., Nucl. Fusion 54 (2014) 043007

PSOL = 100 MW, SOLPS #1514, qpk ~8 MWm-2

T

e (eV)

ne (m3)

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Key R&D issues (not exhaustive)

  • Are we sure that the SOLPS code is correctly

describing the ITER divertor function?

  • Importance of drifts and currents on baseline solution?
  • What sets the upstream heat flux width at the ITER

scale (q)?

  • Physics of cross-field transport in the divertor
  • Impact of magnetic perturbations on SOL transport

and divertor detachment

  • What is the true minimum required ELM energy

density for divertor lifetime?

  • What are the best divertor heat flux control schemes?
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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

Reserve

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IDM UID: RF2HCM @2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

  • A. S. Kukushkin et al., Nucl. Fusion 45 (2005) 608

Recombination rate coefficents

Parallel distance along field line (m)

1