G. Arnoux (1/19) SEWG on transient heat loads Ljubljana, 02/10/2009 Heat load measurements on JET...

G. Arnoux (1/19) SEWG on transient heat loads Ljubljana, 02/10/2009

Heat load measurements Heat load measurements on JET first wall during on JET first wall during

disruptionsdisruptions

G. Arnoux, M. Lehnen, A. Loarte, V. Riccardo and JET-EFDA Contributors


IntroductionIntroduction

• What we know– 90-50% of the energy during thermal quench goes onto the first wall,

not on the divertor– Transport plays a key role in the heat load deposition (time scale

and distribution) on the first wall– Runaway electron (RE) production and loss is a critical issue for the

design/safety if ITER first wall

• What we can learn from JET measurements– Recent fast IR measurements of heat loads on the first wall and

divertor during thermal quench• What time scales?• What spatial distribution?

– IR measurements of RE impact on first wall• What fraction of RE energy converted into kinetic energy, i.e.

impacts onto the wall?


Fast IR on main chamber PFCs (KL7)Fast IR on main chamber PFCs (KL7)

• Fast time resolution: tIR≃1ms• Reduced IR view (coloured areas)• Region of interest (shot to shot)

– Divertor– Outer limiter– Inner limiter– Upper dump plate

• Data reduction– T(x,y,t) → T(s,t)

• Heat load computation (THEODOR)– T(s,t) → q(s,t)


Fast IR on divertor targets (KL9)Fast IR on divertor targets (KL9)

CFC

W

TIR = 86s


Heat load during thermal Heat load during thermal quench: the case of a quench: the case of a

low q disruption low q disruption


Heat load on inner limiterHeat load on inner limiter

s

+8.7ms+4.7ms+2.7ms


Heat load on inner limiterHeat load on inner limiter

Bottom Top


Heat load on outer limiterHeat load on outer limiter

s

+4.94ms+3.05ms+2.10ms


Heat load on outer limiterHeat load on outer limiter

Bottom Top

Divertor


Wide view onto divertorWide view onto divertor

JPN77663

No obvious broadening out of tile 5


Time scales and plasma movementTime scales and plasma movement

R=-15cm

z=+6cm

Radial position

Inner limiter

Outer limiter

DivertorIR,div=0.9ms

IR,outer=1.2ms

IR,div=4.7ms

15cm inward


Summary part ISummary part I

During thermal quench: Eth = Erad + Ediv + Ewall

with Ewall = Einner+Eouter+Eupper

Pulse Eth Erad Ediv* Einner Eouter

** Etot,meas

77658 2.14MJ 31% 7%-14% ? 40-58%

77660 2-13%

On divertor: 4 ≤ t ≤ 10ms

On outer limiter: 4 ≤ t ≤ 60ms

Timescale almost an order of magnitude larger for outer wall heating


Summary Part ISummary Part I

• Measurements show– Of the 60% of the thermal energy measured “during” thermal

quench, half is radiated– From the conducted energy measured onto the PFCs, half goes onto

the divertor and half on the outer limiter– The time scale of the heat load on the outer limiter, combined with

plasma movement suggest a strong enhancement of perpendicular transport (MHD)

– The time scale of the heat load on the inner wall seems to be dominated by the plasma movement

– Energy on the inner limiters still to be determined, but data are there…


Heat load from RE Heat load from RE generated by massive gas generated by massive gas

injection (DMV experiments)injection (DMV experiments)


RE impact on upper dump plateRE impact on upper dump plate

tIR=1.1ms#76533

#76534

Bt=3.0T

Bt=1.8T


RE impact on upper dump plateRE impact on upper dump platen0

RE=14x1012 ; Bt/Ip = 3.0/2.0

#76541T1T2

T3

T4

#76541, f9018


RE current estimateRE current estimate

Ifit=I0exp{t/}

Imeas

IRE=Imeas-Ifit

T


RE energy on upper dump plateRE energy on upper dump plate


Conclsion/summaryConclsion/summary

• Recent IR measurement on PFCs showed– Runaway electrons energy deposited on first wall

scales with the square of RE current– Transport plays a key role on heating the outer wall

during the thermal quench and remains not understood– The time scale of conducted heat load on the outer wall

is an order of magnitude larger than that on the divertor• These measurements suggest

– Can we model the heat load observed on first wall during the thermal quench?

– Can we model RE impact on dumplate in order to match measurement?

G. Arnoux (1/19) SEWG on transient heat loads Ljubljana, 02/10/2009 Heat load measurements on JET...

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