H. D. Pacher 1, A. S. Kukushkin 2, G. W. Pacher 3, V. Kotov 4, G. Janeschitz 5, D. Reiter 4, D....
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Transcript of H. D. Pacher 1, A. S. Kukushkin 2, G. W. Pacher 3, V. Kotov 4, G. Janeschitz 5, D. Reiter 4, D....
H. D. Pacher1, A. S. Kukushkin2, G. W. Pacher3, V. Kotov4, G. Janeschitz5, D. Reiter4, D. Coster6
1INRS-EMT, Varennes, Canada; 2ITER Organization, Cadarache, France; 3Hydro-Québec, Varennes, Canada; 4FZ Jülich, Germany;
5Forschungszentrum Karlsruhe, Germany; 6Max-Planck IPP, Garching, Germany
presented at PSI200818th Int. Conf. on Plasma-Surface Interactions
Toledo, SpainMay 2008
Impurity seeding and scaling of edge parameters in ITER
Outline
1. Results for nonlinear neutral model with carbon
Update scaling (PSI2006, IAEA 2006)
2. Edge/divertor simulation: Impurity-seeded carbon-free divertor
3. Core simulations: Effect of impurity seeding on ITER operating diagram
Conclusions
1
Edge/Divertor ModelB2-Eirene (SOLPS4.3)
Now routinely nonlinear neutral modelneutral-neutral collisionsD2 molecular kineticsParallelized
2 domes
2
1. Full carbon wallC sputtering: phys. + const. Ych
2. Carbon-free wall with neon: (wall same as 1. but no C erosion)
3. Variant: Full Be wall with neon:(=> with Ne small difference from 2., Be concentration small, Be radiation small)
Edge density limit Density analogue of from n scaling
Scaling Update3
Scaling results PSI2006:Key parameter is normalised pressure
0.4
0.60.8
1
3
5
7
0.2 0.4 0.6 0.8 1
352_c4_z2_5
JETMk2 16JETMk2 24ITER 86
ITER 100ITER 130Demo 200
Demo 400Demo 500fit
qpk norm.
μ
=-1.17m€
μ ≡pDT # P #−0.87 f f
−0.8 fw−1 q95 #
−0.27 fnn−1R#
-1.21
is at detachment of either divertorSame curve for qpk from
JET at 16 MWto DEMO at 500 MW(2006)€
μ =1
€
fsat_n ≡ μ 0.43 : f sat_n = 0.9 same as μ = 0.78
Previous was linear neutral model except for some points=> Update required.
€
μ
PowerDT pressureat PFR(Throughput)
Factors Size
DT flux - Scaling with μ and S4
With nonlinear neutral model
Both domes, both S: DT neutral influx to core:
linear model was:
i.e. stronger variation
Value at is 2.4 times that previously
Total influx is still small:
i.e gas puffing provides little core fuelling (opacity to neutrals)
56789
10
20
30
0.4 0.6 0.8 1
409_iPubB_z1_2
Γ _ _DT n sep [ -Pa m3s-1]
=0.7 m μ
F12 Se=60
F47 Se=56
F47 Se=28
fitfitfit
€
ΓDT _ n _ sep ~ S#0.5μ 0.7
€
ΓDT _ n _ sep ~ S#0.3μ 0.36
€
μ =1
€
ΓDT _ n _ sep < 15 − 25 Pa - m3s−1 for μ <1
Value at is about 1/3 previous (linear)
Helium small, rises less strongly toward lower pressures
helium does not constrain operation unless pumping reduced strongly or dome removed
linear model was:
0.1
0.2
0.3
0.4
0.5
0.4 0.6 0.8 1
409_iPubD_z1_4
Γ _ _He n sep [ -Pa m3s-1]
= -0.86 m μ
Helium - Scaling with μ and S5
0.001
0.002
0.003
0.004
0.0050.006
0.4 0.6 0.8 1
409_iPubD_z1_2
nHe_sep [1020m-3]
m= -1 μ
F12 Se=60 F47 Se=56 F47 Se=28 fit fit fit
With nonlinear neutral model
Helium : slight difference between domes"bump" at related to detachmentScaling:
€
nHe _ sep ~ S#−0.7μ -1 for μ < 0.65
€
ΓHe _ n _ sep ~ S#−0.7μ
−0.86 for μ < 0.65
€
~ S#−1μ -2
€
μ =1
€
μ =1
But:
Impurity radiation in inner divertor volume is smaller than with C:
CarbonNe 3%
Ne 2%Ne 1.5%
Ne 1%Ne 0.5%
Ne 0.25%Ne 0.1%
0
20
40
60
80
100
0.2 0.4 0.6 1 3
409_iPubNe3_z02_1
Prad [MW]
μ
0
5
10
15
20
25
30
35
40
0.2 0.4 0.6 1 3
409_iPubNe3_z02_2
Pimp_rad_divin [MW]
μ
Neon seeding without carbon - power6
With neon seeding:
Impurity radiation for
similar to but smaller than for Cvaries little with
(self-consistent carbon is):
€
0.01 < cNe < 0.03
€
cC ~ 0.025 − 0.03
€
2 /3 at μ =1, 1/3 at μ = 0.4
€
cNe
Ne - T7
With neon:
Temperature at inner target higher ( C chemical erosion,low Ne radiation at < 10 eV)
No additional factor in for detachment
With carbon-free and neon at inner target compared to C:plasma power higherradiation lower,total power a bit higherpower load higher (peaking)
1
10
0.2 0.4 0.6 1 3
409_iPubNe3_z03_3
Te_div_inner_max [eV]
μ
CarbonNe 3%Ne 2%Ne 1.5%
Ne 1%Ne 0.5%Ne 0.25%Ne 0.1%
€
μ
=> peak power load shifts from outer to inner target (see next)
1
10
0.2 0.4 0.6 1 3
409_iPubNe3_z05_3
qpk_inner [MW/m2]
μ
1
10
0.2 0.4 0.6 1 3
409_iPubNe3_z05_4
qpk_outer [MW/m2]
μ
Ne - peak power8
With neon:
Peak power shifts to inner target
1
10
0.2 0.4 0.6 1 3
409_iPubNe3_z05_6
qpk [MW/m2]
μ
€
inner larger μ <1
€
outer larger μ <1
Only points for which larger load is at divertor plotted below
€
for 0.01 < cNe < 0.03
€
qpk |Ne = 0.7qpk |C ~ μ−1.2
Peak powerhas same scaling but is 30% lower
than with C(but flux expansion and angle are
not same)
Ne - nDT and ne 9
The strongest effect of neon is:
As neon density increases, => DT density decreases strongly
CarbonNe 3%Ne 2%Ne 1.5%
Ne 1%Ne 0.5%Ne 0.25%Ne 0.1%
0.1
0.2
0.3
0.4
0.50.6
0.2 0.4 0.6 1 3
409_iPubNe3_z03_4
nDT_sep [1020m-3]
μ
0.1
0.2
0.3
0.4
0.50.6
0.2 0.4 0.6 1 3
409_iPubNe3_z03_6
nDT_sep+40*nNe_sep [1020m-3]
μ
0.001
0.01
0.2 0.4 0.6 1 3
409_iPubNe3D_z1_5
nNe_sep [1020m-3]
μ
=> ne decrease ~80% of nDT decrease over range
varies little=> explains why neon radiation varies little with concentration
€
nDT_sep |Ne + 40 • nNe_sep |Ne =1.45nDT_sep |C μ−0.34 for cNe ≤ 0.01
Factor 40 broadly consistent with ratio of ionisation energy ~100 for 8<Z<9 -
Less power available for DT recycling
€
ne • nNe
Ne - helium10
As neon increases to
relative to carbon
helium density at separatrix progressively decreases by 2.2
helium neutral influx to core progressively decreases by 7.5
CarbonNe 3%
Ne 2%Ne 1.5%
Ne 1%Ne 0.5%
Ne 0.25%Ne 0.1%
fit Cfit high cNe
€
cNe = 0.03
0.1
1
10
0.2 0.4 0.60.81 3
409_iPubNe3_z13_2
nHe_sep norm.
m=-1 μ
0.1
1
0.2 0.4 0.6 1 3
409_iPubNe3_z13_3
Γ _ _He n sep . norm
=-0.86 m μ
Tentatively attribute to:lower DT and electron densities in divertor plasma
=> lower opacity of inner divertor plasma to neutrals=> more efficient pumping=> lower He densities and fluxes upstream
Details to be worked out
(He reduction stronger in inner divertor)
Core/edge model11
Core transport in Astra MMM, stabilised by ExB and magnetic shear,time-average ELMs, sawteeth, fitted to JET and AUG, also fits Sugihara pedestal scaling (EPS2008)
Because of the opacity of the ITER SOL, core fuelling controls mostly the core density, gas puffing controls mostly the edge (including peak power load via μ)
profiles, self-consistent pedestal width and height operating window
cf e.g IAEA2006, also paper submitted to Nucl. Fusion
linked to edge via scaling relations from B2-EIRENE
At constant alpha particle power has maximum as n increases
=>Low temperature limit of alphapower from fusion cross-section
Operating diagram12
€
Plane Paux (inverted) − ne
€
Paux
Peak power load set given value across window by varying gas puffing (throughput and
€
Plane Q − Palpha
€
≤
Operating diagram limits13
For qpk always within limit, a point lies within the operational window if for that point:
Max. attainable alpha power (roll-over of P with <ne>
min Q for ITER mission(5 for ITER)
Edge density limit (full detachment)
H-L transition
Available heating power (73MW)
€
fsat _ n = μ 0.43 < 0.9
Operation at qpk= 5 MW/m2; C vs. C-free+Ne14
If very low peak power load required:
With carbon:Excessive gas puff (up to 300 Pa-m3/s)
would be requiredbut density limit dominates,
=>limiting the actual throughput used=>limiting alpha power
With carbon-free and neon:Q is lower
less gas puff needed=> alpha power is higher
Operation at qpk= 10 MW/m2; C vs. C-free+Ne15
The operating window is smaller in both Q and alpha power with neon Core fuelling:a bit higher at the same alpha power with neon because of increased core radiation (lower T)Gas puffing:much lower with neon (60 vs 120 Pa-m3/s) since favourable scaling of peak power in previous
section demands less gas puffing in addition.
If moderate peak power load required:
Operating diagram summary16
Superposition shows:
For Ne relative to C:
low peak power:advantage with neon in alpha power,
disadvantage in Qsame throughput at limit
moderate peak power: disadvantage both in Q and alpha power throughput lower by a factor 2
(but lower S would do the samething)
edge density limit plays strong role with C, less so with neon
Conclusions17
1. Scaling from edge modelling with nonlinear neutral model updated:- DT neutral influx to core higher than previous but remains small
-> gas puffing ineffective for core fuelling- more benign helium scaling toward lower pressure
-> helium is not strong constraint for ITER unless pumping strongly reduced
2. Edge: carbon-free+neon relative to carbon:- radiated power similar, peak power load 30% lower, but with same scaling- peak power load shifted to inner divertor- helium density and helium influx to core even lower- DT density decreases as neon density increases because less power is available
for DT3. Operating window: carbon-free+neon relative to carbon:
- Operating window increases relative to carbon only when stringent low peak power is specified, which would require excessive gas puffing
- For moderate specified peak power loading:- neon reduces operating window- but also reduces throughput
(as does reducing pumping speed, with less impact)
=>Mutually consistent modelling of edge and core shows that for ITER operation carbon-free operation with neon seeding offers only limited advantage over carbon operation
Carbon-free operation at low seeded impurity levels needs to be examined further, as does W