the tore supra tokamak at cea cadarache

P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 2004 1

AssociationEuratom-CEA

PIONEERING SUPERCONDUCTING MAGNETS IN LARGE TOKAMAKS : EVALUATION AFTER 16

YEARS OF OPERATING EXPERIENCE IN TORE SUPRA

P. Libeyre, J.-L. Duchateau, B. Gravil,

D. Henry, J.Y. Journeaux, M. Tena, D. van Houtte

Association EURATOM-CEA, CEA/DSM/DRFC

CEA Cadarache (France)



•The Tore Supra tokamak at CEA Cadarache



1. Introduction

2. Status of the Tore Supra Toroidal Field (TF) system

3. Normal operation

4. Fast safety discharges

5. The cryogenic system

6. Can the magnet experience of Tore Supra be useful for ITER ?

7. Conclusion



1. Introduction (1/4)

The Tore Supra TF magnet during assembly




Tore Supra TF coil structure

Supercritical helium (4.5 K) in thick casing channels

Superfluid helium (1.8 K) in thin casing

bare conductorsin superfluid helium !




one of the largest superconducting system in operation (600 MJ magnetic energy)

Relying on a refrigerator including for the first time industrial quantities of superfluid helium ( Claudet bath)

The Tore Supra TF system is :

Operated daily close to nominal conditions (1250 A)since November 1989.

Continuous toroidal field on the whole day




The path to steady-state operation

Introduction of a new type of refrigeration for superconducting magnets on an industrial level :

Thousands of litres in TS (1988)Hundreds of thousands litres in LHC

(2007) !

the continuous toroidal field allows long duration plasma experiments to be performed

The revolution of

superfluid helium

The Tore Supra TF system contribution

J.L Duchateau et al. “Monitoring and controlling Tore Supra toroidal field system: status after a year of operating experience at nominal current“ 1991 IEEE Trans. On Magn. 27 2053



2. Status of the Tore Supra TF system (1/3)

1982-1988coil manufacture and magnet assembly

all coils tested up to nominal current (1 400 A) at Saclay

1988 start of operation

short circuit in BT17 during a fast safety discharge

1989 replacement of BT17 by spare coil BT19

acceptance tests of TF coils up to 1450 A (9.3 T)

quench of BT13 during fast safety discharge (FSD)

limitation of operating current to 1250 A

temperature increase observed in BT13 during FSD

1995 disparition of defect on BT13

no more temperature increase in BT13 during FSD

2002 continuous data acquisition system




Similar behaviour ofBT13 compared to

the other coils

1.65

1.70

1.75

1.80

1.85

1.90

1.95

2.00

2.05

2.10

2.15

-500 1500 3500 5500 7500 9500

Time (s)

Co

il te

mp

era

ture

(K

)

4.4

4.6

4.8

5

5.2

5.4

5.6

5.8

6

6.2

6.4

Th

ick

ca

sin

g h

eliu

m t

em

pe

ratu

re (

K)

BT13 Temperature

BT16, BT17 Temperatures

Thick casing coil helium temperature

Green light for TF operation1.87 K

No more apparent defect on BT13

Temperature increase in coils during FSD (2003)



1000

1100

1200

1300

1400

1500

1600

1700

1800

6 7 8 9 10 11 12 13Magnetic Field [T]

Cu

rre

nt

[A]

Coil Critical current at 1.8 K (except BT19)

Operation pointCritical point Large margin

(2.4 K)

reduced

nominal

Load line

Coil Critical current at 4.2 K (except BT19)

Safe operation of the TF magnet since 1989 at 1250 A, 8 T


BT19

BT19



3. Normal operation (1/4)

Tore SupraTF activitySince 1988

0

100

200

300

400

500

600

700

800

120/600 600/900 900/1200 >1200

Range of TF current (A)

Nu

mb

er o

f T

F c

ycle

sSince 1988 :

13 thermal cycles from room to LHe temperature

1 090 TF cycles

20 074 plasma discharges




Winding-pack temperature during one day of operation

0

0.2

0.4

0.6

0.8

1

1.2

5 7 9 11 13 15 17 19 21 23

Time ( h )

Pla

sm

a c

urr

en

t (M

A)

an

d

TF

cu

rre

nt

(kA

)

1.60

1.62

1.64

1.66

1.68

1.70

1.72

1.74

1.76

1.78

1.80

BT

15

co

il t

em

pe

ratu

re (

K)

TF system current

BT15 Temperature

Plasma discharges Long Plasma

discharges

Cleaning Plasma discharges

Temperature increase at current ramping-up and down (0.06 K)

Green light for TF operation1.87 K




0

0.2

0.4

0.6

0.8

1

1.2

5 7 9 11 13 15 17 19 21 23

Time ( h )

Pla

sm

a c

urr

en

t (M

A)

an

d

TF

c

urr

en

t(k

A)

4.40

4.50

4.60

4.70

4.80

4.90

5.00

Th

ick

ca

sin

g h

eli

um

te

mp

era

ture

(K

)

TF system current

Thick casinghelium temperature

Plasma discharges

Long Plasma discharges

Cleaning Plasma discharges

Thick casing helium temperature during one day of operation

Temperature increase linked to cleaning plasma discharges




Temperature increase due to a disruption from 1.7 MA

2.69 2.70 2.71 2.72 2.73 2.74 s

-400

-200

0

200

400

600

800

1000

1200

1400

1600 TS#31828

dIP/dt (MA/s)

IP (kA)

Plasma disruption

Thick casing : + 0.83 K4.5

4.6

4.7

4.8

4.9

5

5.1

5.2

5.3

5.4

5.5

-50 50 150 250 350 450

time (s)

Th

ick

ca

sin

g h

eli

um

te

mp

era

ture

(K

)

1.695

1.7

1.705

1.71

1.715

1.72

1.725

Co

il t

em

pe

ratu

re (

K)

Coil temperature

Thick casing helium temperature

Winding-pack : + 0.02 K

18/09/03



4. Fast Safety Discharges (1/3)

FSD

Largest voltage at terminals (320 V at 1400 A)

Risk of short circuit

(bare conductors)To be

avoided !

thermal load on cryogenic system 2h30 to recover

0

2

4

6

8

10

12N

umbe

r of

Fas

t saf

ety

disc

harg

es

Since 1989 : 75 Fast Safety Discharges of the TF magnet (on 1090 TF cycles)

0

20

40

60

80

100

120

140

160

Num

ber o

f TF

curr

ent c

ycle

s

FSD TF cycles




0 2 4 6 8 10 12 14 16

electric interference

cryogenic system

detection system

power supply

control software

quench

Origin of Fast Safety Discharges since 1994

No FSD due to a quench !




Remedies to Fast Safety Discharges

Increase of trigger delays on alarms as much as possible without affecting the protection of the coil in case of a real quench

Sensor conditioning to decrease sensitivity to electric interference

Optimisation of the protection



5. The cryogenic system (1/2)

Availability

sources of unavailability

0 20 40 60 80 100

2002

2003

% of time

control

magnet safetysystemHeII coldcompressor

Manpower : 12 persons

Electric power : 1.1 MW

Cost : 0.5 M€/year

(excluding staff and energy)

92

97

0 10 20 30 40 50 60 70 80 90 100

2003 : 97 %

2002 : 92%

availability



5. The cryogenic system (2/2)

The major tendencies of the cryoplant ageing

loss of electrical insulation of many temperature sensors located in the depth of the cryostats.

drift of adjustment of the electronic components dedicated to the magnetic bearings of the cold compressors.

Preventive maintenance of compressor units

Good availability of the refrigerator

Nevertheless, ageing signs are visible :



TF system Tore Supra ITER

Magnetic energy 0.6 GJ 40 GJ

Superconductor NbTi Nb3Sn

Conductor type monolithic bare conductor

2.8 mm x 5.6 mm

Cable-in-conduit

TFMC (40.7 mm Ø)

Conductor current 1.4 kA 68 kA

Discharge voltage 0.5 kV 10 kV

Cooling system Superfluid helium bath

Supercritical helium forced flow

Cryogenic power 1.1 MW ~ 35 MW

6. Can the TF magnet experience of Tore Supra be useful for ITER ? (1/4)



0

10

20

30

40

50

60

70

80

90

100

6 7 8 9 10 11 12 13 14 15 16

Magnetic Field (T)

Cri

tica

l ca

ble

cu

rren

t d

ensi

ty

(A/m

m2)

NbTi, 1.8 K

NbTi, 4.5 K

Nb3Sn,TFMC

-0.65%, 4.5 K

Tore SupraITER


Operation of ITER TF at 11.8 T doesn’t allow NbTi to be used




Extrapolation of the operation of the TF magnet

from Tore Supra to ITER is not straightforward

Forced flow cooling Very high voltage monitoring

Fast safety discharge

Tore Supra : no quench

ITER : quench of all coils




experience of the CEA magnet team in conductor and coil design

16 years of reliable plasma operation with a TF superconducting magnet

Decision to build ITER is possible

ITER magnet R&D programme

Still to be doneExperience in TS can help :

Design of protection and monitoring system Impact on cryoplant

Detailed magnet operation

Impact on scenarios



7. Conclusion

The Tore Supra tokamak is the first important meeting between Superconductivity and Plasma Physics.

Superconducting magnets can be operated successfully with plasma physics on the long term

Continuous operation of the toroidal field simplifies plasma discharge preparation

No significant heat load is associated to long shots

Continuous operation limits fatigue degradation

The Tore Supra TF magnet is a useful tool to prepare ITER construction and operation

the tore supra tokamak at cea cadarache

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