T.Eich 1 / 26 rehearsal for PFMC, Jülich 02.05.2013 ELM divertor heat loads in JET- ILW and full-W...
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Transcript of T.Eich 1 / 26 rehearsal for PFMC, Jülich 02.05.2013 ELM divertor heat loads in JET- ILW and full-W...
T.Eich 1 / 26 rehearsal for PFMC, Jülich 02.05.2013
ELM divertor heat loads in JET-ELM divertor heat loads in JET-ILW and full-W ASDEX Upgrade ILW and full-W ASDEX Upgrade
T.EichT.Eich, R.Scannel, B.Sieglin, G.Arnoux, S.Devaux, I.Balboa, , R.Scannel, B.Sieglin, G.Arnoux, S.Devaux, I.Balboa, A.Scarabosio, M.Leyland, S.Brezinsek, G.F.Matthews, A.Scarabosio, M.Leyland, S.Brezinsek, G.F.Matthews, S.Jachmich, H.Thomsen, A.Herrmann, P.DeMarne, S.Jachmich, H.Thomsen, A.Herrmann, P.DeMarne, M.Beurskens, W.Fundamenski, G.HuysmansM.Beurskens, W.Fundamenski, G.Huysmans
PFMC Jülich Germany, 16.05.13PFMC Jülich Germany, 16.05.13
T.Eich 2 / 26 rehearsal for PFMC, Jülich 02.05.2013
Outline
Combining type-I ELM heat load from various experimental campaigns in JET and ASDEX Upgrade (both C and W)
• The story so far: Results from JET and AUG ‘carbon’ operation
• Comparison of ‘W’ and ‘C’ ELM heat loads
• A pedestal pressure based ELM divertor heat load scaling
• Outlook & Summary and Conclusions
• Not covered: Access to small ELM regimes
T.Eich 3 / 26 rehearsal for PFMC, Jülich 02.05.2013
ELMs: transient heat loads
The transient heat flux factor has a simple relation to Energy (E), depositon Area (Adep) and characteristic time scale (tc):
Mitigation of transient events needs to reduce either the energy, increase the area or the characteristic time scale
heat flux factor
J. Linke
0.5MJ/m2
T.Eich 4 / 26 rehearsal for PFMC, Jülich 02.05.2013
Time scales: initial comparison of W and C
• Comparison of ELM power fluxes by IR derived from CFC and W surfaces in JET-C gave fair agreement
#74380
• ELM outer divertor target energy ~ 0.35 of ELM loss energy (same for W and C)
Ref
eren
ce c
ase
CFC
W
T.Eich 5 / 26 rehearsal for PFMC, Jülich 02.05.2013
ELM time scales in ‘Carbon’
ITER assumes :
ELM decay time : 500us
ELM rise time: 200us
This temporal shape was used for material studies
Lc(m) Te(eV) q95 cs(km/s) Lc / cs
AUG 47 600 4.4 241 195us
JET 64 1000 3.4 308 208us
ITER 120 4000 3.0 616 194us
Temporal shape and time scales of ELM heat fluxes in JET and
ITER are expected to be similar, since they scale with τII = Lc/cs
D
ies
c
mTTc
RqL
)(
2 95
t rise
(μ
s)τ|| =Lc / cs (μs)
4401 ELMs, 25 discharges
maxTTpeak tt
maxqqpeak tt
Triniti Plasma Gun (normalized)
Measured ELM power load (JET)
(us)
(MW),(MW/m2)
T.Eich 6 / 26 rehearsal for PFMC, Jülich 02.05.2013
Relaxation of a Maxwell distribution
T.Eich at al, JNM 2009 W.Fundamenski, PPCF 2006
• ELM energy release time into
the SOL, τMHD << τII
• ELM duration time x 2.4 ELM rise time
A.Kirk, PPCF 2006
AS
DE
X U
pg
rad
e
T.Eich 7 / 26 rehearsal for PFMC, Jülich 02.05.2013
ELM time scales by AXUV studies
• Near target ELM induced radation (low density) shows also fair agreement and is in line with Maxwellian velocity
full-W ASDEX Upgrade operation
T.Eich 8 / 26 rehearsal for PFMC, Jülich 02.05.2013
ELM heat loads in ripple experiments
Natural ELMs
Vertical ‘kicks’
For TF ripple studies, an increase of ELM frequencies is found (22Hz, 30Hz, 52Hz) ELM peak heat fluxes are not reduced
JET-C BT=0.08%BT=0.5%BT=0.75%
22Hz30Hz50Hz
EELM(kJ)
T.Eich 9 / 26 rehearsal for PFMC, Jülich 02.05.2013
Divertor peak heat flux vs EELM
ELM wetted area increases with ELM loss energy
peak
hea
t flu
x (M
Wm
-2)
EELM(kJ)
Wet
ted
area
(m
2 )
JET: 2.5MA/2.5T
ELM frequency (Hz)
B=2.2 T, 2 MA, (q95~3.6)δav=0.45, PNBI=10-14 MW
T.Eich 10 / 26 rehearsal for PFMC, Jülich 02.05.2013
ELM wetted area• Observed trend: ELM wetted area increases with ELM
loss size, result seen in JET, DIII-D and ASDEX Upgrade
H.Thomsen et al, NF (2011) M.Jakubowski et al, Nucl.Fusion (2009)
JET
DIII-D
ITER: For minimum sized ELMs broadening (λq,ELM =5mm)
λq,ELM = 20mm
λq,ELM = 5mm
JET-ILW
T.Eich 11 / 26 rehearsal for PFMC, Jülich 02.05.2013
ELM ergodisation & filaments: complex deposition pattern
• No obvious differences found between W and C operation w.r.t. ELM ergodisation or filamentary substructure
• However, detailed studies are in progress,aiming at– (quasi-) toroidal mode numbers– energy distribution beweetn (radially moving) filaments and parallel
losses due to ergodization of field lines
Δt = -215 µsΔt = -129 µsΔt = -43 µsΔt = 43 µsΔt = 129 µsΔt = 215 µs
JET-C JOREK (ITER)
4.0MJ (cond.)1.6MJ (conv.)
T.Eich 12 / 26 rehearsal for PFMC, Jülich 02.05.2013
Tolerable ELM size in ITER
• AELM = 2 π Rdiv * λELM * fx = 0.90m2 (λELM=5mm, fx=6.5, Rdiv,inner=4.4m)
• No Radiation, 100% in deposited in divertor, In/Out Asymmetry 2:1 (favouring the inner)
• Result: Etol = 0.5MJ/m2 * 1.5 * 0.90m2 = 0.7MJ
As AELM increases with ELM loss, how scales effectively the ELM energy density?
T.Eich 13 / 26 rehearsal for PFMC, Jülich 02.05.2013
Comparing W- and C- ELMs
NB: Experimental execution of discharges of JET-ILW and JET-C (slightly) different for dedicated ELM heat load studies
• Shaping, Triangularity, strike lines on target: identical
• Larger NBI heating power required for similar pedestal ne, Te
• Bt / Ip scan executed first at identical PNBI for C/W and with much increased PNBI for W (up to 26MW)
• H98y about 1 for best discharges in JET-ILW
PNBI<13MW
PNBI>20MW
T.Eich 14 / 26 rehearsal for PFMC, Jülich 02.05.2013
W versus C: time scales (1)
• Type-I ELMs in JET-ILW do not follow the simple scaling found for JET-C
• Interpretation: ELM energy release time (ELM MHD time?) is larger than parallel transport time
JET-ILW
JET-C
τMHD << τII ?τMHD >= τII
T.Eich 15 / 26 rehearsal for PFMC, Jülich 02.05.2013
W versus C: time scales (2)
• Also the temporal shape of the ELM power fluxes approaches the shape observed for type-I ELMs in JET-C when τII is
shortest in DB
• Reminder: τII ≈ Te-0.5
• Same holds true for type-I ELMs full-W ASDEX Upgrade operation with good confinement (e.g. with N2 seeding)
JET-ILW
JET-C
T.Eich 16 / 26 rehearsal for PFMC, Jülich 02.05.2013
example plots
A couple of examples showing the increase of the ELM power deposition length, W-ELMs appear to be stretched for low Te
JET-ILWfull-W ASDEX Upgrade
(2.0 & 2.4MA) / 2.5T
PNI= 9MW, Te,ped = 480 eVPNI=10MW, Te,ped = 600 eVPNI=22MW, Te,ped = 1100eV
JPN 82644JPN 83438
Plot needed
JPN 82630
T.Eich 17 / 26 rehearsal for PFMC, Jülich 02.05.2013
H98y vs time scales
• In summary we find, for good confinement conditions (at high pedestal temperature) there is almost no difference between W-ELMs and C-Elms w.r.t time scales
• Such ‘good’ conditions are achieved in JET-ILW at higher heating power or with e.g. N2 seeding
• (In line with ASDEX Upgrade N2 seeded experiments (t.b.c.))
T.Eich 18 / 26 rehearsal for PFMC, Jülich 02.05.2013
A note on ‘long’ ELMs
• ‘Longish’ time scales for pedestal collapse are observed e.g. by Thomson-Scattering or ECE measurements confirming previous assumption of τMHD >= τII
• Such conditions were rarely observed in JET-C, but e.g. in Helium discharges
• For conditions with ‘good’ confinement and high pedestal temperatures, short time scales are recovered (for AUG, PC: A.Burckhardt)
Private communication, JET: L.Frassinetti, D.Dodt & AUG: A.Burckhardt
T.Eich 19 / 26 rehearsal for PFMC, Jülich 02.05.2013
JET-C ILW (no seeding) ILW with N2 seeding
t≈0.3-0.5ms t≈2-3ms
t≈10ms
t≈1ms
Behaviour relatively similar for each ELM Time interval to reach the minimum: t≈0.3-0.5ms
Two different behaviours Time interval to reach the minimum: tfast≈2-3mstslow≈10ms
Behaviour relatively similar for each ELM Time interval to reach the minimum: t≈1ms
at pol=0.9
79501
at pol=0.9 at pol=0.9
8281782537
Duration of T e,ped drop: 0.3-3ms
Courtesy of L.Frassinetti
T.Eich 20 / 26 rehearsal for PFMC, Jülich 02.05.2013
TIME SCALES: DISTRIBUTIONSTIME SCALES: DISTRIBUTIONS
Ip2.5MA only
ILW w/o N2
JET-C
ILW with N2
Shots considered: Ip=2.5MA and Pnet≈15-19MW
5 CFC plasmas
6 ILW plasmas (not seeded)
11 ILW shots (with N2 seeding) - 6 with Wth comparable to CFC
- 5 with low Wth
Wth (
MJ)
CFC
ILW (not seeded)
ILW (seeded) with high Wth
ILW (seeded) with low Wth
CFC and ILW (not seeded) have clearly two different time scales
CFC and seeded ILW are comparable if the stored energy is similar
Seeded ILW are comparable to not seeded ILW if the stored energy is low
The ELM time scale seems to be related more to the stored energy than to the wall
T.Eich 21 / 26 rehearsal for PFMC, Jülich 02.05.2013
Definition of ELM energy fluency
• The ELM energy fluency is the peak of the time integrated heat flux profile (energy / area)
εmax
inter-ELM for reference (5ms)
Typical numbers for large ELMs at JET:
150 kJ/m2
T.Eich 22 / 26 rehearsal for PFMC, Jülich 02.05.2013
W/C: ELM energy fluencyA jump ahead: Attempt to scale or order the ELM energy fluency
NB: Data are mapped to parallel field lines in order to compare the different divertor geometries
JET-C :εtarget x 20 = εII
JET-ILW:εtarget x 12 = εII
Important conclusion: Though distributed on a longer time scale, deposited energy / area is the same (!)
T.Eich 23 / 26 rehearsal for PFMC, Jülich 02.05.2013
W/C: ELM energy fluencyRegression result for JET-C and JET-ILW ELM energy fluency (combined DB)
Worth notifying: Very weak dependency on the relative ELM loss size (!)
v*
EELM/Wplasma (%)
T.Eich 24 / 26 rehearsal for PFMC, Jülich 02.05.2013
Only JET-ILW data
Result for JET-ILW only: Almost linear to the pedestal pressure
B.Sieglin
T.Eich 25 / 26 rehearsal for PFMC, Jülich 02.05.2013
Outlook
• The ultimate goal of this study is to provide a Multi-Machine Scaling for ELM energy fluency and the power deposition ELM time scales by combining JET, DIII-D and ASDEX Upgrade divertor ELM heat load data
• The next step is the inclusion of ASDEX Upgrade data and to provide (i) major R scaling (ii) extrapolation to ITER and (iii) case to compare with ELM models and ELM modelling (JOREK)
• For this endeavour we have run test pulses in GLADIS with JET lamellae, W-coated CFC target and AUG Div-III solid W target plates, in order to cross check JET and ASDEX Upgrade heat load data
• Latter experiments in GLADIS are presented in the poster of Bernd Böswirth (Date, Poster ID)
T.Eich 26 / 26 rehearsal for PFMC, Jülich 02.05.2013
Summary & Conclusions
• Pedestal top pressure and temperature is reduced for the reference pulses with same Ip / Btor and heating power in JET-ILW
• At identical pedestal top densities and temperatures, ELM heat load time scales in JET-ILW and full-W AUG w.r.t ‘carbon’ similar
• ELM peak energy fluency (J/m2) for JET-C and JET-ILW at given pedestal top pressure is very similar
• Simple regression reveals weak dependency of divertor peak energy fluency on relative ELM loss for JET data base
• Latter explains the observed absence of a mitigation of divertor peak heat fluxes with increased ELM frequencies at constant pressure, e.g. by kicks, in ripple discharges, ELM pellet pacing or simple gas puffing
• However, exceptions are e.g. B-coils in AUG or pellets in DIII-D
T.Eich 27 / 26 rehearsal for PFMC, Jülich 02.05.2013
Back Up (GLADIS)
• Results from GLADIS (B.Böswirth & B.Sieglin)
α=333 kW/K/m2
T.Eich 28 / 26 rehearsal for PFMC, Jülich 02.05.2013
EFCC & kicks for ELM mitigation
ne,ped (1019 m-3)
rot(krad/sec) (pedestal)
Wthermal(MJ)
Te,ped (keV)
fELMs up ~3 (in this example)
ELM size reduced ΔWELM by a
factor of ~2.5
W~10%
kicksEFCCs
~15 Hz45 Hz+/-0.4
40 Hz+/-15 14 16 18 20 22
Time (sec)
6
5
4
1.41.2
1.0
5
4
3
20100
30
40
0
80
40
0
80
Courtesy of E. de la Luna
δav=0.45, 2.2T/2.0MA (q95=3.6)
Moderate reduction in Wth<10%
ne reduction (edge & core) ~ 30% :
slightly higher for kicks (higher fELM)
Te,ped, (and Ti,ped) up by ~ 25%
Details:
T.Eich 29 / 26 rehearsal for PFMC, Jülich 02.05.2013
εELM versus pped,e
Assessing ELM mitigation techniques:
T.Eich 30 / 26 rehearsal for PFMC, Jülich 02.05.2013
To Do, Improvements
Suttrop: AUG B-coils
Jachmich: EFCC Results
Power versus time for AUG
T.Eich 31 / 26 rehearsal for PFMC, Jülich 02.05.2013
ELM Heat Load
• Good agreement of ILW data with free streaming approach
• No dependence on relative ELM size