Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 1

Update on Thermal Loads during

disruptions and VDEsA. Loarte

with contributions from M. Sugihara, A. Herrmann,

G. Arnoux, T. Eich, G. Counsell, G. Pautasso,

V. Riccardo, etc.

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 2

Specification of ITER disruption/VDE Thermal Loads

New ITER specifications for disruptions and VDEs take into account latest physics findings

Pre-disruptive confinement degradation for H-mode disruptions

Footprint broadening at thermal quench qdiv(t) at thermal quench Radiation asymmetries in current quench Plasma evolution to thermal quench in VDEs and broadening of footprint Impact geometry of runaway electrons etc.

Some issues still poorly understood or restricted database : asymmetries, runaway power fluxes, thermal quench limiter

disruptions ,etc. Advice from ITPA required

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 3

Energy Fluxes during disruptions (I)

Energy degradation before thermal quench for resistive MHD disruptions (not for ITBs)

Large broadening of footprint for diverted discharges but small for limiter discharges (?)

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 4

Effect of background radiation

J. Paley, P. AndrewA. Herrmann

More systematic studies of power flux broadening required

JET- G. Arnoux Energy to upper X-point

(Rmp ~ 3.5 cm )

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 5

Energy Fluxes during disruptions (II)

Timescale (~ R) but large variability (1.0-3.0 ms for ITER) Longer timescales in decay phase (> 2 rise phase)

Toroidal asymmetries (~2) seen in some cases but poor documentation/statistics

Systematic study of in/out asymmetries required

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 6

Proposed ITER specifications (M. Sugihara/M. Shimada)Scenario 2 : unit (MJ/m2)

Energy release at TQ (1/2-1/3)Wpeak Wpeak

E// near separatrix at outer midplane

200 - 70 400 - 200

E// near upper ceiling region(6 cm from 1st separatrix)

20 - 50 60 - 100

E// near lower baffle region(6 cm from 1st separatrix)

16 - 40 48 - 80

E// to divertor plate near 1st separatrix

280 – 90 (out)375 – 120 (in)

560 – 280 (out)750 – 380 (in)

=2.5 cm (left), 5 cm (right) Total energy deposition time duration = 3-9 ms

Energy Fluxes during disruptions (III)

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 7

Energy release at TQ Wpeak (325 MJ)

E// near separatrix at outer midplane 510 - 255

E// near upper ceiling region(5 cm from 1st separatrix)

120 - 160

E// near lower baffle region(5 cm from 1st separatrix)

95 - 130

E// to divertor plate near 1st separatrix 730 – 365 (out)375 – 120 (in)

=2.5 cm (left), 5 cm (right) Total energy deposition time duration = 3-9 ms

Proposed ITER specifications (M. Sugihara/M. Shimada)Scenario 4 : unit (MJ/m2)

Energy Fluxes during disruptions (IV)

Plasma shift caused by beta collapse does not cause IW contact in ITER unlike JET

experiments (P. Andrew)

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 8

Wpeak

Start of limiter config.

H-L transition

Fast energy loss phaseafter transition

TQ at q= 1.5

Energy loss phaseduring q decrease

1

2

3

W2

W3

WTQ

Energy Fluxes during VDEs (I)

JET

ITER

Presently proposed ITER specifications based on JET based extrapolations input from other tokamaks needed

W2 = 20-55 MJ

2 = JET/L-modeJET (0.03-0.09)*L-mode

ITER

W3 = W(2)-dW/dt|L-mode*3

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 9

Downward VDE with fast CQ - EM load on BM / DIV by eddy (+halo) current

- Heat load on lower Be wall & W baffle

Upward VDE with fast CQ - EM load on BM by eddy (+halo)

- Heat load on upper Be wall during VDE and TQ

0

5

10

15

20

-6

-4

-2

0

2

640 650 660 670 680 690C

urr

ent

(MA

)Z

(m)

Time (ms)

Z

Ip

Ihalopol

(a)

(b)

(c)

(d)

VDE_downward

-500

-400

-300

-200

-100

0

100

300 400 500 600 700 800 900

Z (

cm)

R (cm)

(d)

(c)

(b)

(a)

1

2

3

4

18

17

16

15

14

0

100

200

300

400

500

300 400 500 600 700 800Z

(cm

)R (cm)

(d)

(c)

(b)

(a)

5

6

3

4

7

8 9

11

10

12

0

5

10

15

20

0

2

4

6

8

860 880 900 920 940

Cu

rren

t (M

A)

Z (m

)

Time (ms)

ZIp

Ihalo

pol

(a)

(b)

(c)

(d)

VDE_upward

Energy Fluxes during VDEs (II)

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 10

Energy Fluxes during VDEs (III)

Indications of broadening of power footprint at VDE thermal quench

AUG-Herrmann

Power width = ∫q(romp)dr

qmax

JET-Arnoux

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 11

Energy Fluxes during current quench (I)

During current quench plasma magnetic energy is lost

Part of Wmag transferred to conductors Wohmic = Wmag-Wconductors plasma heating

Most tokamaks/disruptions Wohmic lost by Prad (except high Bhigh Z Alcator C-mod)

JET-Paley-PhD Thesis 2006JET-P. Andrew JNM 2007

JET-Pulse No. 69787

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 12

#69787

During current quench the radiation distribution is poloidally asymmetric

JET (A. Huber)

Energy Fluxes during current quench (II)

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 13

0.5

1.0

1.5

2.0

2.5

3.0

3.5t=66.861s

t=66.869s

t=66.872s

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 2 4 6 8 10

t=66.869s

t=66.872s

Pwall(MW/m2) Power deposited on the Wall

Poloidal distance along wall (m)

Rad

iati

on

pea

kin

g

Radiation during current quench (II)

JET (A. Huber)

But deposited power on the wall has a peaking factor of only 2

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 14

Predicted runaway current 10 (MA)Energy spectrum of electrons (E0 for exp(-E/E0)) 12.5 MeVInclined angle 1 - 1.5Total energy deposition due to runaway current 20 MJAverage energy density deposition 1.5 MJ/m2

Duration of the average energy density deposition 100 msMaximum energy density deposition (end of the plasma termination) 25 MJ/m2

Duration of the maximum energy deposition 10 msNumber of event Every major

disruption

These specifications are generally reasonable but physics basis is weak (very poor experimental input)

Largest concern energy load by drifted electrons due to formation of X-point

Runaway electron fluxes on PFCs (I)

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 15

Current profile during runaway discharge peaks (seen at JET) X-point formation in Scenario 2

Runaway electron fluxes on PFCs (II)

Smith PoP 2006

EFIT reconstruction by S. Gerasimov

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 16

Runaway electron fluxes on PFCs (III)

Significant drift of runaways near upper X-point due to poloidal field null [f(E) = 1/E0exp(-E/E0) with E0 = 12.5 MeV]

Angle of impact of runaways on drift orbits at upper X-point < 1.5o but impact direction mainly toroidal

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 17

Conclusions

PID specifications for PFC loads during disruptions and VDEs

in ITER being updated following ITER Design Review

Process Key issues for further refinement of disruption thermal quench

loads are timescales, broadening, asymmetries and

dependence on pre-disruptive plasma conditionsFor current quench level distribution of radiative and

conducted loads to be studied systematically Specifications for VDEs are now based on real H-mode plasma

observations but more multi-machine data is required Dedicated studies on runaway loads during disruptions are

required to provide a firmer base of ITER specifications

Alberto Loarte 10th ITPA Divertor and SOL Physics Group Avila – Spain 7/10 – 1 – 2007 18

Major disruptions during limiter phase :(M. Sugihara/M. Shimada)

Ip (MA) 4.5 6.5

Wpeak (MJ) 10 20

P ; peak energy density (MJ/m2)

7.7 15

Most severe assumption :No broadening of deposition width

(Kobayashi NF 07)2 limiter case

Energy Fluxes during disruptions (V)

If there is no broadening energy fluxes on limiter for disruptions can be similar or larger than for the divertor disruptions in scenario 2