Transcript Folie 1 - mpg.de

Max-Planck-Institut für Plasmaphysik
Prediction of wall fluxes and implications for ITER limiters
Arne Kallenbach,
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
ASDEX Upgrade Team
Arne Kallenbach
1/15
Topics of this talk: guidelines on load specifications
 steady state particle main chamber fluxes from spectroscopy
 estimates of connected power fluxes and decay lengths
 contribution due to ELMs (enhancement factor)
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
2/15
Current ITER Guidelines (PID V3.0):
Only radiation and CX load to first wall, 0.5 MW/m2
transport and drifts lead to
parallel heat fluxes in far SOL
diffusive transport between ELMs
blobby transport between ELMs
(radial outward convection)
ELM SOL transport (like large blobs)
additional players in particle transport:
- parallel drift towards high-field side
- strong recycling around inner X-point
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
3/15
Main chamber spectroscopy at ASDEX Upgrade
Ralph Dux
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
4/15
Innner and outer wall plasma-surface interaction in AUG
from CII spectroscopy: very sensitive on in-out alignment
R lim
8 m2
0.3 m2
 inner heat shield major recycling region except plasma close to outer limiter
 lower inner wall flux dominated from inner divertor
 upper inner wall flux has radial e-folding length ~ 2-3 cm
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
5/15
How to estimate the stationary power flows on the limiters
1) estimate the total radial ion outflux*
average value from different models,
be conservative and use upper end
2) estimate the deposited energy per electron-ion pair
3) estimate the effective wetted area
or peak load and decay length
 limiter power flux density
*IO calculates in terms of parallel power fluxes and decay lengths
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
6/15
1) Total radial ion wall flux in ITER
[i] scaling like diffusive transport
H-mode
recycling
rises
Radial SOL particle flux in ITER
ansatz with effective D:
 = D dn/dr
D = 3 m2/s this value typical for
SOL wing in many devices
conservative,
can be larger
dn/dr = 21019 m-3 / 0.05 m
 = 1.21021 m-2 s-1
AUG edge density profiles from Li-beam
Transport balloons around outer midplane:
total main chamber ion influx: multiply  with 1/3 of plasma surface area
F ITER = 680 m2 1/3   ~ 31023 s-1
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
7/15
1) Total radial ion wall flux in ITER
[ii] some alternative ways of estimation
a) Same flux density as in AUG discharge with high similar fGreen, P/R,
and absolute density, scaled with area
ITER: 100 MW/6 m, not possible in AUG, scale P0.24
[NF 42 (2002) 1184]
AUG 21015/17, 7.5 MW, ne=1020 m-3, =21022 1/s, drXP=3 cm
4.41023 s-1
b) Same flux density as in AUG discharge with high similar fGreen, P/R2
and absolute density, scaled with area  16
ITER: 100 MW/36 m2, 7.5 MW in AUG, AUG # as above
3.21023 s-1
c) Same flux density as in JET discharge with high similar fGreen, P/R2
and absolute density, scaled with area (best use 4 MA, 25 MW discharge)
JET 70054, 3.5 MA, 24 MW, 1e20, midplane H2072 m2  main=7.21022 s-1
2.91023 s-1
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
Over all, 3(1-5)1023 s-1
seems reasonable estimate
8/15
2) Energy per electron ion pair
Te in the SOL wing of a high density H-mode discharge is typically 5-10 eV,
Ti tends to be moderately higher
We assume for ITER Te= 10 eV, Ti= 20 eV
standard model for sheath power deposition (negl. secondary el. emission)
P= ei (2Ti + 3Te + Erec) + ee 2Te
100 eV per e-i pair  1.6 MW
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
 100 e
per 11023 part/s
Arne Kallenbach
9/15
3) effective wetted area and resulting loads
The wetted area depends on actual wall design !
wetted width depends on decay length in limiter shadow
ITER quick guess: 18 protruding ribs, height 5 m, 0.05 m wetted width
 4.5 m2 for HFS and LFS each (good alignment required !)
3 1023 ions/s  4.8 MW
 charge exchange is expected to increase this number by 10-20 %
 ELMs contribute to recycling fux by factor 1.5
 radiation is expected to contribute < 0.2 MW/m2
 some contrib. by fast ion losses on LFS
overall, expected peak loads about 1 MW/m2
not problematic, but safely  1 MW/m2 would allow to avoid active cooling
Of course, the upper X-point region takes more power and must be strengthened
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
10/15
ELM contributions to average particle influxes:
small for D, C, dominnat for W
Outer limiter
ELM-cycle averaged,
D and C fluxes increased
by ~ 1.5
but: 70 % of the W influx
due to ELMs
(increased yield)
R. Dux
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
11/15
Decay length depends on connection length to limiters
Increasing the number of limiters can reduce the power load.
However: the decay length shortens with reduced connection length
and more precise alignment will be required
measurements in
AUG limiter shadow
by H.W. Müller
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
12/15
ITER expects negligible loads on inner wall
- does the existence of a 2nd sep. shield the inner wall ?
No !
further investigations needed on inner wall load close DN
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
dRXP= 3 mm
13/15
Comparison to previous estimate based on JET-AUG
Recycling scaling (Tarragona meeting, July 2005)
new insight: predominantly HFS recycling  multiply with S/4 only: Rtot= 1024 s1
(ne,sol= 4.7 1019)
Strong dependence of total recycling on ne,line-av (power 4) 
If pellets are needed to reach 1020 m-3 in ITER, this number comes down:
19 2008
ITPA meeting
on SOL & divertor physics,
Spain,10
Jan 7-10,
Arne Kallenbach
If 10th
ITER
produces
ne=Avila,7.5
by recycling
only, Rtot= 3 1023, ne,sol= 2.6 1019 14/15
Conclusions
 Main chamber recycling occurs predominantly on the high field side
and on wall structures touching the innermost flux surfaces
 Effect supposed to be connected to strong drifts towards HFS
 Strong plasma wall interaction with the inner wall close to DN
operation is not understood:
fluxes close to the separatrix or ExB drifts around upper X-point ?
 Expected total particle fluxes 3 2 1023 part/s, power fluxes ~ 5 MW
How will the ITER FW will look like ?
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
15/15
ELMs:
Simple size scaling and effect to wall materials
Size scaling based on empirical findings:
natural type-I ELM size ~ 10 % of pedestal energy, 3.5 % of plasma energy
ELMs carry 30 % of the power flux
simple algebra: PELM= 0.3 Ploss = 0.3 Wtot/tE = 0.035 fELM Wtot = fELMWELM
 fELM = 8.6/tE
ITER Sc. 1: Wtot = 353 MJ, tE=3.4 s
 fELM = 2.5 Hz, WELM= 12 MJ
AUG typ.: 0.8 MJ, 0.1 s
80 Hz, 28 kJ
controlled ELMs: if fELM is changed, WELM scales ~ 1/fELM
ITER PID:
uncontrolled ELMs fELM = 1 Hz, WELM= 15-20 MJ
controlled ELMs fELM = 5 Hz, WELM= 3-4 MJ
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
o.k.
16/15
ELMs:
Simple size scaling and effect to wall materials
Material properties:
1556 K 3683 K 3640 K (subl.)
melting/ablation limits: Be 20, W 60, CFC 60-70 [MJ m-2s-0.5]
example: ELM 1 MJ/m2, 0.5 ms duration  45 MJ m-2s-0.5
recent lab exps. (Russian-EU collab.) suggest limit below
0.7 MJ/m2 both for W and CFC (fatigue, crack formation)
 reduce peak load by factor 0.5
Divertor peak power load:
ITER PID assumed effective wetted divertor area of 7.5 m2 (w= 0.1 m along targets)
resulting maximum loads were 2.7 MJ/m2 (uncontr.), 0.5 MJ/m2 (contr.)
the maximum allowed ELM was controlled to 4 MJ
latest changes: no ELM power broadening lp  5 mm (fact 2/3)
in-out asymmetry 2:1 – (fact ¾), recover factor 2 safety margin 0.5  0.25 MJ/m2 ?
 maximum “ELM” ~ 1 MJ
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
too pessimistic – ignores large lp inner div
Arne Kallenbach
17/15
Open points = possible AUG contributions
1) midplane inter-ELM power width
midplane Te decay length scales ~ machine size
A. Kallenbach et al.,
ITPA SOL&Div Topical Group,
PSI 2004
AUG: 1.3 mm omp
expected power width 2/7  lTe
considerably broader widths observed in divertor (mapped to omp)
good topic for future AUG / inter-machine exps (L. Horton)
10th ITPA meeting on SOL & divertor physics, Avila, Spain, Jan 7-10, 2008
Arne Kallenbach
18/15