1 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Physics basis and design of the ITER full-tungsten
divertor R. A. Pitts
ITER Organization, Plasma Operation Directorate, Cadarache, France
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
With contributions gratefully acknowledged from:
B. Bazylev1, S. Carpentier-Chouchana, F. Escourbiac, J. P. Gunn2, T. Hirai, M. Kocan, A. Loarte, M. Lehnen, A. S. Kukushkin
1Karlsruhe Institute of Technology, IHM, Karlsruhe, Germany
2IRFM, CEA Cadarache, St. Paul Lez Durance, France
2 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Content • Introduction § Historical perspective on the ITER Organization
proposal to begin operation with a full-W divertor • Physics basis for a W divertor § Expected lifetime, stationary and transient loads,
technology qualification • Potential issues, design § W melting, accumulation, material evolution/erosion § Component tilting, shaping
• Summary
3 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Reminder: main divertor characteristics
4 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Reminder: main divertor characteristics
Outer vertical target (JA)
Inner vertical target (EU)
Dome (RF)
Reflector plates (RF)
Pumping slot
Cassette body (EU)
5 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Outer vertical target (JA)
Inner vertical target (EU)
Dome (RF)
Reflector plates (RF)
Pumping slot
Cassette body (EU)
Reminder: main divertor characteristics 54 divertor assemblies (~9 tonnes each)
4320 actively cooled heat flux elements
Bakeable to 350°C
NB: technology limit for steady state power handling on HHF areas: 10 MWm-2
6 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
H/He D/DT
BA
SELI
NE
New divertor strategy
H/He D/DT
~10 years
PRO
POSA
L
• IO proposed in 2011 to eliminate first CFC/W divertor and begin operations with a full-W variant which should survive to the end of the first DT campaign
7 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
• Spend ~2 years to: (a) develop a full-W divertor design
à Final Design Review, June 2013 (b) advance tungsten technology R&D
à excellent progress (c) assess the physics/operational risks of starting ITER
with a full-W divertor à IO, ITPA, dedicated experiments on tokamaks
IC recommendation (Nov. 2011)
• Decision on whether or not to start with full-W to be made by late 2013
• STAC-15 (14-16/10) and IC-13 meeting (20-21/11) • IO requested STAC-15 to recommend to IC-13 that a
full W-divertor be used from the start of operations
8 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Operational campaigns • Analysis of what the full-W divertor will be required to
survive has been performed on the basis of the ITER Research Plan (approximate numbers and types of pulse) à grand total of ~25,000 pulses à Provide rough assessment of risks of starting with full-W and
guidance for sustained operation at high power in DT
• Independent of schedule scenarios, always 3 main “operation phases” to first DT burn: He/H, DD, DT § At most ~25% at the highest power/stored energy § Perhaps ~20% in pure He § More than 50% at relatively low flattop duration and low
power
9 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Stationary and slow transient load cycles
~5000 cycles to 10 MWm-2 ~300 cycles to 20 MWm-2
• Derived on the basis of the Research Plan and SOLPS divertor performance simulations
• Defines technology qualification requirement
• Peak heat fluxes to >20 MWm-2 during reattachment if λq is narrower than we think à most important in DT phase § see R. J. Goldston, Y12.000001 for more on narrow λq
10 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Divertor monoblock qualification • Good results now from both JA and
EU Domestic Agencies – tungsten monoblocks tested in ITER Divertor Test Facility (electron beam) § Technology meets design loading:
20 MWm-2 (300 cycles, 10 sec) § Survived 1000 cycles at 20 MWm-2
KHI-MMC KHI-ALMT KHI-ATM
Ansaldo, Plansee
MHI-ALMT MHI-ALMT KHI-MMC
Mitsubishi and Kawasaki heavy Industry
IDTF, St. Pertersburg, RF
11 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Steady state loading – “carbon free”
“Non-active” “Active”
A. S. Kukushkin, et al., EPS 2013 A. S. Kukushkin
10 MWm-2 limit for steady state power handling
• New SOLPS simulation databases under construction for carbon-free divertor performance + impurity seeding § Technology limits can be attained in He, H-mode at low Ip § Simulations typically have λq ~4.5 mm (DT), λq ~ 3.5 mm (He)
PSOL = 60 MW
PSOL = 100 MW
12 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Transient loads: ELMs
Ip (MA)
PIN (MW)
Wplasma (MJ)
Etransient (MJ)
λq||omp (m)
q⊥target (MJ m-2)
FHF (MJ m-2s-1/2)
7.5 40 75 6.4 à 8.0 0.01 1.39 à 1.74 77 à 123
• Example: low power H-mode (likely in Helium)
NB: FHF,melt ~ 50 MJm-2s-1/2 for W
13 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Transient loads: ELMs
Ip (MA)
PIN (MW)
Wplasma (MJ)
Etransient (MJ)
λq||omp (m)
q⊥target (MJ m-2)
FHF (MJ m-2s-1/2)
7.5 40 75 6.4 à 8.0 0.01 1.39 à 1.74 77 à 123
• Example: low power H-mode (likely in Helium)
R. A. Pitts et al., J. Nucl. Mater. 438 (2012) S48 • Uncontrolled ELMs in He/H phase unlikely to melt if ELM footprint broadens
• Unless broadening very large at high current/power, or ELM-free regimes found, ELM control clearly required in the DT phases
• Need to improve physics basis for broadening
14 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
ELMs and W accumulation
Lines to guide the eye only
ΔWELM (MJ)
Peak post ELM W radiation (MW)
DT high Q DT low Q He
Time dependent SOLPS for W source with ASTRA+STRAHL for core transport
• ELM control with W divertor required as much for W impurity control as for material damage avoidance § fELM > 20 – 30 Hz sufficient to
control W accumulation and post-ELM radiation spike for 7.5–15 MA D, DT H-modes
§ NB: fELM uncontrolled ~2-3 Hz § He plasmas require higher fELM
due to higher sputtering and more unfavourable pedestal transport (if Ti,sep ~100 eV)
15 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Transient loads: disruptions
Plasma stored
ene
rgy
[MJ]
No. of p
ulses
Flat to
p success rate
Stored
Ene
rgy achieve
rate
Major DisrupA
on ra
te
MD MiAgaAo
n success
rate
No. of m
iAgated MDs
MiAgated MD pa
rallel
energy flux at LCFS at
inne
r (ou
ter) ta
rget [M
J m
-‐2]
No. of u
nmiAgated MDs
Unm
iAgated MD pa
rallel
energy flux at LCFS at
inne
r (ou
ter)
target [M
J m-‐2]
He-‐H I 30
4200 0.8 0.5 0.2 0.75 252 6 (2) 84 49 (19)
90 0.5 0.2 0.75 252 18 (7) 84 146 (56)
He-‐H II 90
9800 0.9 0.5 0.12 0.85 450 18 (7) 79 146 (56)
150 0.5 0.12 0.85 450 30 (12) 79 243 (93)
DD 150
4950 0.9 0.5 0.08 0.92 164 30 (12) 14 243 (93)
210 0.5 0.08 0.92 164 43 (16) 14 341 (130)
Full Power DT QDT =10
210 5600 0.9
0.5 0.05 0.95 120 43 (16) 6 341 (130)
350 0.5 0.05 0.95 120 71 (27) 6 568 (216)
Plasma stored
ene
rgy
[MJ]
No. of p
ulses
Flat to
p success rate
Stored
Ene
rgy achieve
rate
DW VDE
rate
DW VDE
MiAgaAo
n success rate
No. of m
iAgated DW
VD
Es
MiAgated DW
VDE
pa
rallel ene
rgy flu
x at
LCFS at inn
er (o
uter)
target [M
J m-‐2]
No. of u
nmiAgated DW
VD
Es
Unm
iAgated DW
VDE
pa
rallel ene
rgy flu
x at
LCFS (o
uter baffl
e)
[MJ m
-‐2]
He-‐H I 30
4200 0.8 0.5 0.05 0.8 67 6 (2) 17 34
90 0.5 0.05 0.8 67 18 (7) 17 102
He-‐H II 90
9800 0.9 0.5 0.02 0.9 79 18 (7) 9 102
150 0.5 0.02 0.9 79 30 (12) 9 169
DD 150
4950 0.9 0.5 0.01 0.95 21 30 (12)
16 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Disruption TQ transient loads
Rise times for TQ heat pulse: 1.5 – 3.0 ms (MD), 0.75 - 1.5 ms (VDE) Assumed broadening of heat flux footprint: 3 – 10λq|| Maximum in/out divertor asymmetry = 2
MD E||TQ (MJm-2) VDE E||TQ (MJm-2)
Unmitigated ~325 19 - 243 ~50 34 - 169 Mitigated ~1400 2 - 30 ~300 2 - 30
Unmitigated ~70 93 - 568
17 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
TQ transient heat flux factors MD FHF (MJm-2s-1/2) VDE FHF (MJm-2s-1/2)
Unmitigated ~325 26 - 328 ~50 65 - 321 Mitigated ~1400 3 - 41 ~300 4 - 57
Unmitigated ~70 126 – 768
18 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Disruptions: transient heat flux variants VDE quenching on outer baffle or dome vicinity in limiter config. Current quench halo currents to baffles. Dome or baffle runaway electron impact
Mitigated downward VDE and mitigated+unmitigated in-place major disruptions
DINA simulations
19 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Design: target tilting for steady loads • All main plasma-facing components are tilted when
assembled onto the cassette body to ensure no leading edges from PFC to PFC
plasma flux
20 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Design: target tilting for steady loads
0l0n
g axis+
80º
0.74º
0.5o
Til0ng axis
IVT OVT
Dome 0.7o
Til0ng axis 0.6
o
Til0ng axis
• All main plasma-facing components are tilted when assembled onto the cassette body to ensure no leading edges from PFC to PFC
21 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Design: shaping for transients
Monoblock chamfering to hide all edges in HHF areas
Outer baffle toroidal chamfering for VDE protection
Dome: no shaping à assess consequences
e.g. 0.5 mm
22 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Melt estimates
*see e.g.: B. Bazylev, H. Wuerz, J. Nucl. Mater. 307-311 (2002) 69 B. Bazylev et al., J. Nucl. Mater. 390-391 (2009) 810
Monoblock surfaces: 2D (assuming edge protection) Mitigated and unmitigated Major Disruption Mitigated VDE Outer baffle and dome edges: 2D and 3D Unmitigated VDE (baffle, dome) Runaway electron impact (dome)
• Use 2D and 3D MEMOS code* to assess PFC damage for surface and edge loading
• Heating, melting, evaporation, vapour shielding, heat transport in liquid and solid, viscosity and melt motion (due to surface tension, external pressure and Lorentz forces)
23 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Melt estimates: monoblocks
Assume simple chamfer, depth 0.5 mm, 3.5º total impact angle, monoblock width = 30 mm, gap = 0.5 mm ne = 1020 m-3, Te = 1 keV, M = 1 à p ~0.8 bar, cs ~5 x 105 ms-1 tdecay = 2trise, triangular heat pulse
Event E||TQ (MJm-2) Number trise (ms)
Unmit. MD 340, 570 6,6 1.5 - 3 Mit. MD 45, 70 120, 120 1.5 - 3 Mit. VDE 45, 70 12, 12 0.75 - 1.5
Plasma stream
24 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Melt estimates: monoblocks • E.g.: mitigated MD, E||TQ = 70 MJm-2, trise+tdecay = 4.5 ms • 2D MEMOS à tangential pressure force only, no currents
1 pulse 120 pulses
(cm) (cm)
• For all ttotal < 9 ms, Tsurf > Tmelt, evaporation < 0.1 µm/pulse max. melt pool depth ~70 µm, melt motion 10-40 cms-1
• Overall surface roughness (after 120 pulses) ~800 µm
25 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Melt splashing
1: Melt splashing at monoblock edges: Macrocopic W droplet release and bridging of castellation gaps Cause: Rayleigh-Taylor instability or melt separation
2: Kelvin-Helmholtz instability Droplet breakaway
3: Disruption induced Eddy currents J×B forces perpendicular to melt layer at the TQ
1: vmelt too low for computed hmelt for melt layer separation vmelt too low and λR-T too large cf. hmelt for fast R-T instability
2: Density of impacting plasma too low to generate K-H instability
J×B
B J
hmelt vmelt • 3 main areas of concern:
• Use MEMOS calculations (hmelt, τresolid, etc.) to conclude:
26 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Melt estimates: RE dome impact
Dome tile Dome
tile
RE 2 mm
~10 cm
• RE damage a potential problem in all phases of operation
• Use ENDEP and 2D MEMOS for RE on inter-cassette dome misalignment (max ~3 mm)
• Difficulty is specifying § Total wetted area for RE impact § Total energy carried by RE (e.g.
conversion of poloidal magnetic field energy to RE kinetic energy)
§ Energy deposition time
27 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Melt estimates: RE dome impact
Y
ENDEP MEMOS
RE Dome
tile
T > 7000 K will
convert into
plasma
Melted W
• Example: fast RE loss: tloss = 100 µs WRE = 20 MJ, ERE = 12.5 MeV
• Very serious damage to be expected à no gain from shaping. NB: problem just as bad for main Be first wall
28 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Material issues (active phases) • The most outstanding long term “risk” for high power
operation on a W-divertor in ITER § Will transient melting really occur according to
calculations? à recent JET melting experiment § High fluence, high power operation (including sub-melting
threshold transients) on melt damaged W § Erosion/evolution of recrystallized surfaces under plasma
impact (cracking, roughening) § Surface modification due to He plasma impact (e.g. nano-
structures (W-fuzz)) § Possible Be-W alloying
29 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Example: operation on damaged W • Create melt-damaged
area (Pilot-PSI) using high Tsurf and small transients to take surface above Tmelt
• Expose to high fluence plasma + transients (Magnum-PSI) § Study surface response with
high resolution IR § Examine post-mortem with
microscopy and metallurgy
Courtesy of G. De Temmerman, DIFFER
After 72 shots, ~4100 ELM-like transients
30 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Material issues (non-active phases) • For non-active phases risk of starting full-W appear to
be low* with some caveats: § Concern that pure He operation at lower power (e.g.
H-modes at 7.5 MA) may lead to enhanced erosion through bubble formation driving reduced surface thermal conductivity à more R&D required here
§ Adequate disruption mitigation, ELM control and diagnostics must be in place at appropriate stages in the experimental campaigns
*see R. A. Pitts et al., J. Nucl. Mater. 438 (2013) S48
• A vigorous long term R&D programme required to study W material issues during ITER construction
31 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Concluding remarks • After a crash programme beginning in late 2011:
§ A mature full-W divertor design is in place with key supporting analysis nearly complete
§ Technology in all the supplying Domestic Agencies meets and even largely exceeds the cyclic load specs
32 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Concluding remarks • Key identified risks from the plasma operation side are
W melting, material surface evolution and core plasma contamination § Melt splashing not expected, but surface topology
modifications likely à possibly on mm scales § ELM control required for PFC damage avoidance (high
power) and W accumulation control (all H-modes) § Long term material surface evolution under high power,
high fluence plasma impact in the presence of transients still an area requiring much R&D à was always the case, even in previous ITER divertor strategy
33 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Concluding remarks • Recommendation from ITER STAC after their 15th
meeting (14-16 October 2013): § The ITER Council adopt the IO proposal to implement in
the Baseline the option of choosing W targets for the first ITER divertor
• ITER Council to decide at the next meeting (IC-13, 20-21 November 2013)
34 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Reserve material
35 @2013, ITER Organization
55th Annual Meeting of APS Division of Plasma Physics, Denver, USA, 11-15 November 2013 IDM UID: KXGBBF
Outer target loading profiles B2-Eirene, A. Kukushkin
~10 MWm-2"
All-metal, PSOL = 100 MW, 0.4% Ne Carbon, PSOL = 100 MW
• Baseline” cases retrieved for Ne seeded no carbon operating point at qpk ~10 MWm-2 § But often large differences in contributions to target loads à
Ne and C do not radiate from same location