the iter divertor concept: physics and engineering design · @2015, iter organization iaea tm on...

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@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015

The ITER divertor concept: physics and engineering

designR. 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, France1EIRL 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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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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Recap of basic design features

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Outer verticaltarget

Inner vertical target

Dome

Reflector plates

Pumping slot

Cassette body

54 divertorassemblies ~500 tons total mass~150 m2 W surface4320 actively cooled heat flux elementsBakeable to 350C

The W divertor• ITER will begin

operations with a full-W armoured divertor Must survive to at

least the end of the first full DT campaign

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W divertor: essential characteristicsBaffles to limitneutral escape to the core

Strong outboard shaping for disruption transients

Reflector plates to protect against strikepoint excursions and some measure of diagnostic/cassette protection

Dome – improvepumping lesspumping speed required for givenupstream He concor fuel throughput.Diagnostic/cassette protection Open pathway between divertors for neutral recirculation

– reduction of target heat load asymmetries

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• “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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• 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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Monoblock numbers

tiltin

g axis+

80º

0.74º

0.5o

Tilting

axis

• Totals, for the record (as of June 2014)16 PFUs138 monoblock/PFU119,232 total per divertor48,384 on the straight vertical part

22 PFUs143-146 monoblock/PFU172,962 total per divertor

61,182 on the straight vertical part

292,194 grand total313,838 with 4 spare cassettes

IVTOVT

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Global shaping for transientsOVTDOME: protection against strike point

excursions

Outer baffle toroidalchamfering for VDE protection

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Vertical target & monoblock shaping

Individualmonoblockshaping

Global target tilt

Worst case expected radial misalignment betweentoroidally neighbouringmonoblocks ± 0.3 mm

0.3 mm

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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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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 shapingSimplest solution to hideworst case leading edge: single toroidal chamfer of height 0.5 mm

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Operational physics considerations

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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) 887A. S. Kukushkin et al. Nucl. Fusion 42 (2002) 187A. S. Kukushkin and H. D. Pacher, PPCF 44 (2002) 931A. S. Kukushkin et al. Nucl. Fusion 43 (2003) 716A. S. Kukushkin et al. Fus. Eng. Design 65 (2003) 355 A. S. Kukushkin et al. J. Nucl. Mat. 337-339 (2005) 17A. S. Kukushkin et al. Nucl. Fusion 45 (2005) 608A. S. Kukushkin et al. Nucl. Fusion 47 (2007) 698A. S. Kukushkin et al. J. Nucl. Mat. 363-365 (2007) 308A. S. Kukushkin et al. Nucl. Fusion 49 (2009) 075008A. S. Kukushkin et al. Fus. Eng. Design 86 (2011) 2865A. S. Kukushkin et al., J. Nucl. Mat. 415 (2011) 2011A. S. Kukushkin et al. Nucl. Fusion 53 (2013) 123024A. S. Kukushkin et al. J. Nucl. Mat. 438 (2013) S203H. D. Pacher et al. J. Nucl. Mat. 463 (2015) 591H. D. Pacher et al. J. Nucl. Mat. 415 (2011) S492H. D. Pacher et al. J. Nucl. Mat. 390-391 (2009) 259G. W. Pacher et al. Nucl. Fusion 48 (2008) 105003G. W. Pacher et al. Nucl. Fusion 51 (2011) 083004H. D. Pacher et al. J. Nucl. Mat. 313-316 (2003) 657

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

Now moving to new code version

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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 on 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

0 5 10 15 20

1

e-1

q||,omp (MWm-2)

(r – rsep)omp (mm)

q ~ 3.6 mm

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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 MWcne (separatrix)

NeonPower handling limit

Detachm

entlimit

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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: P

SO

L = 100 MW

, cN

e,sep ~1.2%

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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, N

ucl. Mat.

438(2013) S

203

q,peak, target, (MWm-2)

1

10

1 10 pn [PaDivertor neutral pressure (Pa)

q (mm)~1.3~1.7~3.6

0.1

0.2

0.3

0.40.50.60.70.8

1 10

ne_sep mod [1020m-3]

pn [Pa

ne,sep (1020 m-3)

Divertor neutral pressure (Pa)

Problems likelyhere due to excessive W release?

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

Radiation distributions (C vs. N)• N very like C (as expected)

N CPSOL = 100 MW


#253

3

#157

7qpk,outer = 4 MWm-2

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

cC,sep = 2.0%

(Wm-3)

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Radiation distributions (Ne vs. N)• Ne more distributed (as expected)

N NePSOL = 100 MW


qpk,outer = 4 MWm-2

cN,sep = 0.8%qpk,outer = 5 MWm-2

cNe,sep = 1.2%

#253

3

#246

3

(Wm-3)

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Separatrix Te (C, N, Ne)

Parallel distance along field line (m)

T e(e

V)

#1577 #2463#2533

PSOL = 100 MWqpk ~ 4.5 MWm-2

Extended convective regions

Drop to very low Te (<1 eV) occurs only right in front of targets

X-point

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Contributions to target power loadP

ower

flux

den

sity

(MW

m-2

)• Range from almost fully due to thermal plasma or a

balance between plasma, neutrals and radiationTotalRadiationPlasmaNeutrals

TotalRadiationPlasmaNeutrals

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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Low in-out power asymmetries• No drifts and currents yet asymmetries due mostly to

geometry (target orientation & larger LFS power outflux)Inner Outer

q pk,

targ

et(M

Wm

-2)

PSOL = 100 MW, cNe,sep ~1.2%

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Pressure loss

r – rsep (m)

Pla

sma

pres

sure

(Pa)


• Attached to detached solutions depending on target and neutral pressure

#2463 #2476

UpstreamDownstream

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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)


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Te (eV)

Parallel distance along field line (m)

Dis

tanc

e al

ong

targ

et(m

)

ne (1021m3)

Ionization/recombination• Net particle loss occurs extremely close to the targets


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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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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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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 on NSTX, DIII-D, AUG results are mixed

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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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JET‐CJET‐ILWAUG‐CAUG‐W

qII,regression (MJm-2)

q II,m

easu

red

(MJm

-2)

• From JET and AUG, peak outer 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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Long term ELM effects (1)• Even if ELMs can be mitigated, the frequent thermal

cycling will lead to damage formation over timeJUDITH 2 e-beam

Damage threshold ≤ 3 MJm-2s-1/2

For 106 square wave pulses at ~500 s duration (Wmelt ~50 MJm2s-1/2)Tsurf = 1200C(NB: triangular pulses likely to givehigher damage thresholds (see Yu et al., NF 55 (2015) 093027))

Th. Loewenhoff et al., PFMC 2015

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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 ...

Tsurf = 1500ºC105 pulses @ 0.3 MJ.m-2

500 m

Profilometry

Th. Loewenhoff et al., JNM in press

1 mm

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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 770MJm-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 disruption350 MJ(worst case)

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Disruptions: benefit of vapour shielding

Time (ms)

T sur

f(x

1000

K)

q

(GW

m-2)

Strike pt Adjacent to Strike pt.

S. Pestchanyi, et al., ISFNT 2015 TOKEScode

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, vapourshielding helps but complex, 2D, time dependent

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Heat flux/detachment control: diagnostics

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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

on the basis of SOLPS simulations

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DiagnosticsFoil bolometry

8 bolometers in each of 5 cassettes: 40 LOS / cassette LOS still to be fixed ~5 cm resolution

Usual issue withneutrals 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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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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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

DivertorPort plug

Viewing area of outer divertor

1st relay optics • Distributing optics• Imaging optics• 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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DiagnosticsDivertor 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 neutralpressure (S. Lisgo)

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DiagnosticsDivertor 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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DiagnosticsDivertor 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

Te (eV)ne (m3)

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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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Reserve

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

Recombination rate coefficents

Parallel distance along field line (m)1

the iter divertor concept: physics and engineering design · @2015, iter organization iaea tm on...

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