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


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


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


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


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)


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


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


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)


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


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


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.)


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?


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


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


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


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


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.))


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


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


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


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


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 (!)


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 (%)


Only JET-ILW data

Result for JET-ILW only: Almost linear to the pedestal pressure

B.Sieglin


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)


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


Back Up (GLADIS)

• Results from GLADIS (B.Böswirth & B.Sieglin)

α=333 kW/K/m2


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:


εELM versus pped,e

Assessing ELM mitigation techniques:


To Do, Improvements

Suttrop: AUG B-coils

Jachmich: EFCC Results

Power versus time for AUG


ELM Heat Load

• Good agreement of ILW data with free streaming approach

• No dependence on relative ELM size

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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