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J. Bucalossi 1Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA

Report on Tore Supra activities on Mitigation of disruptions loads for ITER

WP09-PWI-08-01/08-02

J. Bucalossi, F. Saint-Laurent, C. Reux

and Tore Supra team

Institute for Research on Magnetic Fusion

Association Euratom-CEA

Annual meeting of the SEWG Transient Heat LoadsLjubljana, 1st/2nd October 2009

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J. Bucalossi 2Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Outline

•Mitigation of disruption loads with massive gas injection

•Control of runaway electron beams

•Activities in 2010

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J. Bucalossi 3Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Outline

•Mitigation of disruption loads with massive gas injection

•Control of runaway electron beams

•Activities in 2010

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J. Bucalossi 4Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Previously on TS

0 0.2 0.4 0.6 0.8 1 1.2 1.410

2

104

106

108

1010

1012

1014

Neu

tron

s pr

oduc

ed d

urin

g du

ring

disr

uptio

n

Initial plasma current [MA]

Non-mitigated disruptions

Helium

Neon

Argon

Mix He/Ar

• With MGI reduction of dIp/dt for all gases (~50%), mild reduction of eddy current in toroidal pumped limiter (TPL)

• Ne and Ar MGI have no effect on RE production• He (He/Ar) MGI are very efficient at suppressing RE even in small

amount (12-500 Pa.m3, plasma ~25m3, vacuum vessel ~50 m3)

NB: MGI triggered disruptions on stable plasmas

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J. Bucalossi 5Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Fuelling efficiency

• Ne was estimated using fast FIR interferometer and approximate integration of several chords

• He assimilation much higher (measurement not possible up to TQ)

TQ

TQ

TQHe reaches plasma edge

Ar reaches plasma edge

0

0.5

1

1.5

2

x 1021 Electrons added to the plasma

N

e

6 8 10 12 14

0

5%

10%

15%

Time from Massive gas injector trigger [ms]

fuel

ling

eff

icie

ncy He - 270 Pa.m3

He - 90 Pa.m3

Ar - 230 Pa.m3

Ar - 120 Pa.m3

• Ne ~ 2x plasma e content with Ar

• Ne > 6x plasma e content with He

• TQ at higher density with He• Only a fraction of the

injected gas reaches the plasma before TQ

NB: fuelling efficiency estimated assuming single ionization and that all the gas reached the plasma before TQ

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J. Bucalossi 6Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Gas penetration

• Determined using a Fast framing visible camera and interference filters for low ionized species (He II 468.5 nm, Ar II 476.5 nm, He I 706.5 nm)

cold front

poloidal plane parallel to the endoscope lens

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J. Bucalossi 7Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Gas jet dynamics

• Penetration depth nearly independent of nature and amount of gas (5 to 500 Pa.m3 in He)

• Penetration speed higher for higher amount of gas (consistent with density measurement) but smaller than gas sound speed (He~1000m/s and Ar~320m/s)

0 100 200 300 400 500 6000

20

40

60

80

100

120

140

Amount of gas injected [Pa.m3]

Co

ld f

ron

t sp

ee

d in

sid

e t

he

pla

sma

[m

.s-1

]

HeliumArgon

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J. Bucalossi 8Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Safety factor influence

Stopping surface

qρ

• Penetration depth nearly constant in safety factor (stop near q = 2)

• Scan in q profile (Ip / Bt variations)• Same He MGI 25 Pa.m3

• q profile reconstructed with CRONOS

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J. Bucalossi 9Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Thermal energy influence

• Scan in LH power (1 to 3.5 MW)• Same He MGI 25 Pa.m3

• q profile reconstructed with CRONOS

• Penetration depth more sensitive to q profile than thermal energy

LH power [MW]

Energy stored

between plasma edge

and gas stopping

surface [kJ]

ohmic 18

1 21.1

2,5 33.1

3,2 40.8

3,5 34

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J. Bucalossi 10Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Penetration “bounce”

0

50

100

SX

R s

ign

al [

a.u

.]

0

0.5

1

Pla

sma

cu

rre

nt [

MA

]

5 10 15 20 25 30

0.8

0.9

1

Time from MGI trigger [ms]

ga

s fr

on

t po

sitio

n [r

/a]

SXR - coreIp

SXR - edge

gas frontposition

(a)

(a)

(b)

(b)

(c)(c)

(d)

(d)

8.8 ms

15.1 ms

18.8 ms

24.4 ms

TQ

He 25 Pa.m3

PLH = 3.5 MW

• Soft X-ray analysis• Core and edge chords behavior correlated with the movement of the

cold front

• Heat pulse from the core to the edge triggered by the perturbation of the q = 2 rational surface (MHD)

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J. Bucalossi 11Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Outline

•Mitigation of disruption loads with massive gas injection

•Control of runaway electron beams

•Activities in 2010

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J. Bucalossi 12Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA RE creates a cold plasma

0 0.5 1 1.50

1

2

3

4

5

6

7

Time (s)

Plasma currentIp (MA)

Line integratedElectron Density(1019 m-2) for 2chords

TS#33707

Photoneutron (s-1)

1010

1012

1014

( N

tn/s

)

0 0.5 1 1.50

1

2

3

4

5

6

7

Time (s)

Plasma currentIp (x100 kA)

Line integratedElectron Density(1019 m-2) for 2chords

TS#33707

Photoneutron (s-1)

1010

1012

1014

( N

tn/s

)

• Line averaged density recovers after the disruption without any gas puffing (RE density ~ only a few 1017 m-2 from RE current)

• A cold background plasma is generated: RE-neutrals collisions (ionization on C dusts and D atoms)? RE-wall interaction?

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J. Bucalossi 13Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA RE beam in action

450 ms plateauExp: 495 µs

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J. Bucalossi 14Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Interaction with dust

-0.1 0 0.1 0.2 0.3 0.40

1

2

3

4

5

6

7TS#43493

Ip (100 kA)nl (1019 m-2) chord#3

Time (s)

1010

1014

1012

neutron (s-1)

nl (1019 m-2) chord#4

-0.1 0 0.1 0.2 0.3 0.40

1

2

3

4

5

6

7TS#43493

Ip (100 kA)nl (1019 m-2) chord#3

Time (s)

1010

1014

1012

neutron (s-1)

nl (1019 m-2) chord#4

• Many photoneutron peaks, large peaks associated to density rises and radiating events

• Radiating events associated to transverse transport of RE• Filamentary events observed using fast visible camera• Location and radial size of RE beam can be estimated

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J. Bucalossi 15Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Controlling beam position

• Controlling the beam position is an important issue• Active position control on current channel barycentre was

implemented 30 ms after the disruption (no Ip control nor fuelling so far)

• More time to apply mitigation technique on the RE beam

0 0.5 1 1.5

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

Time -tdisr (s)

TS#33707TS#43491

Rb

ary

cen

tre

(m)

disruption

RE plateau

Without

With

0 0.5 1 1.5

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

Time -tdisr (s)

TS#33707TS#43491

Rb

ary

cen

tre

(m)

disruption

RE plateau

Without

With

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J. Bucalossi 16Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Decelerating electric field

• Variation of the central solenoid voltage with RE beam position control

0 500 1000 15000

0.1

0.2

0.3

0.4

0.5

0 200 4000

0.1

0.2

0.3

0.4

0.5

TS#43491

Neutrons (s-1)

Time -tdis(ms)

TS#43493

Ip (MA)

Time -tdis(ms)

ECS = 0 mV/m 35 mV/m

Ntn = 2.5 1012

Ntn = 1.7 1012

1011

1012

1013

1014

1015

Mechanical load (a.u)

0 500 1000 15000

0.1

0.2

0.3

0.4

0.5

0 500 1000 15000

0.1

0.2

0.3

0.4

0.5

0 200 4000

0.1

0.2

0.3

0.4

0.5

0 200 4000

0.1

0.2

0.3

0.4

0.5

TS#43491

Neutrons (s-1)

Time -tdis(ms)

TS#43493

Ip (MA)

Time -tdis(ms)

ECS = 0 mV/m 35 mV/m

Ntn = 2.5 1012

Ntn = 1.7 1012

1011

1012

1013

1014

1015

Mechanical load (a.u)

• Reduction of the plateau duration with a small voltage (~0.5 V/turn)• Photoneutrons reduced (~30%) but still a neutron burst at the end• Further studies required

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J. Bucalossi 17Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Effect of MGI on RE beam

0 0.2 0.40

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.40

0.1

0.2

0.3

0.4

0.5

0.6

TS#33711 TS#43512

He MGI

Ar MGI

Time (s)

Ip (MA) Ip (MA)

Neutron (s-1)

Neutron (s-1)

1011

1012

1013

1014

1015

4 1021 at/m3 6 1020 at/m3

5.5 1012 ntn 1.3 1012 ntn

0 0.2 0.40

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.40

0.1

0.2

0.3

0.4

0.5

0.6

TS#33711 TS#43512

He MGI

Ar MGI

Time (s)

Ip (MA) Ip (MA)

Neutron (s-1)

Neutron (s-1)

1011

1012

1013

1014

1015

4 1021 at/m3 6 1020 at/m3

5.5 1012 ntn 1.3 1012 ntn

Xo Density thickness dE Stop Time Exp.

(g cm-2) (at/m3) 1 turn (g cm-2) (eV) (ms) (ms)

He 94.3 4 1021 2.7 10-5 58 10 150

Ar 19.6 6 1020 4.3 10-5 87 7.5 35

Tabulated using an averaged RE energy E = 10 MeV

• faster decrease of RE current• increase of the photoneutron flux• slowing down by neutrals not

effective

• Increase of the RE transverse transport towards the wall: Multiple Coulomb scattering = stochastic effect larger interacting area lower heat loads

• Beneficial effect for mitigating RE

3/ Heo

Aro 5/ He

ntnArntn

Simple assumption of a free stopping in neutral gas

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J. Bucalossi 18Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Damages on CFC tiles

• large energy deposit leads to vaporization of CFC bulk and fast expulsion of carbon fragments (200-600 m/s)

• Detailed Monte-Carlo simulation of RE-carbon interaction in progress

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J. Bucalossi 19Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Outline

•Mitigation of disruption loads with massive gas injection

•Control of runaway electron beams

•Activities in 2010

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J. Bucalossi 20Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Activities in 2010

•MGI

– radiated power analysis with “faster” bolometers

– better characterization of the gas jet

– modeling effort (CRONOS, JOREK, etc.)

•RE beam control

– improve statistics (reliable RE beam creation)

– study of mitigation of RE beams with MGI

– modeling of RE beam damping

•IR fast camera (from ASDEX Upgrade)

– analysis of SOL widening on the TPL during disruption

– estimation of conducted heat loads on the TPL during TQ

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J. Bucalossi 21Annual meeting SEWG Transient Heat Loads, Ljubljana, 1st/2nd October 2009

TORE SUPRAAssociationEuratom-CEA Summary

•MGI

– Fuelling efficiency estimated

– Data gathered on gas penetration

•Runaway electrons

– Cold background plasma observed

– Interaction with dusts observed

– Active position control achieved

– Mitigation techniques applied to created RE beam

•2010

– More experiments planned

– New diagnostic (fast IR camera)

– Modeling effort