the iter divertor concept: physics and engineering design
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1IDM UID: RF2HCM
@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.
2IDM 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
3IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Recap of basic design features
4IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
5IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
6IDM 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
7IDM 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)
8IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
9IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Global shaping for transientsOVTDOME: protection against strike point
excursions
Outer baffle toroidalchamfering for VDE protection
10IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Vertical target & monoblock shaping
Individualmonoblockshaping
Global target tilt
Worst case expected radial misalignment betweentoroidally neighbouringmonoblocks ± 0.3 mm
0.3 mm
11IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Monoblock shaping
Individualmonoblockshaping
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)
12IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Individualmonoblockshaping
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
13IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Operational physics considerations
14IDM 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) 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
15IDM 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 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
16IDM 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 MWcne (separatrix)
NeonPower handling limit
Detachm
entlimit
17IDM 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: P
SO
L = 100 MW
, cN
e,sep ~1.2%
18IDM 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, 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?
19IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Total PRAD,DIV = 59 MWPRAD,fuel = 17 MW
Radiation distributions (C vs. N)• N very like C (as expected)
N CPSOL = 100 MW
Total PRAD,DIV = 65 MWPRAD,fuel = 12 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)
20IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Total PRAD,DIV = 59 MWPRAD,fuel = 17 MW
Radiation distributions (Ne vs. N)• Ne more distributed (as expected)
N NePSOL = 100 MW
Total PRAD,DIV = 56 MWPRAD,fuel = 13 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)
21IDM 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(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
22IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
23IDM 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
q pk,
targ
et(M
Wm
-2)
PSOL = 100 MW, cNe,sep ~1.2%
24IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Pressure loss
r – rsep (m)
Pla
sma
pres
sure
(Pa)
PSOL = 100 MW, cNe,sep ~1.2%
• Attached to detached solutions depending on target and neutral pressure
#2463 #2476
UpstreamDownstream
25IDM 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%
26IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
PSOL = 100 MW, cNe,sep ~1.2%
27IDM 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
28IDM 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
29IDM 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 on NSTX, DIII-D, AUG results are mixed
30IDM 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
31IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
32IDM 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 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
33IDM 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 ...
Tsurf = 1500ºC105 pulses @ 0.3 MJ.m-2
500 m
Profilometry
Th. Loewenhoff et al., JNM in press
1 mm
34IDM 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 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)
35IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
36IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Heat flux/detachment control: diagnostics
37IDM 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
on the basis of SOLPS simulations
38IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
39IDM 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
40IDM 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
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
41IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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)
42IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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
43IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
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)
44IDM 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?
45IDM UID: RF2HCM
@2015, ITER Organization IAEA TM on Divertor Concepts, Vienna, Austria, 29 September 2015
Reserve
46IDM 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
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