1 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 2004 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)

2 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 2004 The Tore Supra tokamak at CEA Cadarache

3 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 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

4 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Introduction (1/4) The Tore Supra TF magnet during assembly

5 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Introduction (2/4) Tore Supra TF coil structure Supercritical helium (4.5 K) in thick casing channels Superfluid helium (1.8 K) in thin casing bare conductors in superfluid helium !

6 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Introduction (3/4)  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 Continuous toroidal field on the whole day

7 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Introduction (4/4) 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

8 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Status of the Tore Supra TF system (1/3) coil manufacture and magnet assembly  all coils tested up to nominal current (1 400 A) at Saclay 1988start of operation  short circuit in BT17 during a fast safety discharge 1989replacement 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 1995disparition of defect on BT13  no more temperature increase in BT13 during FSD 2002continuous data acquisition system

9 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Status of the Tore Supra TF system (2/3) Similar behaviour of BT13 compared to the other coils Green light for TF operation 1.87 K No more apparent defect on BT13 Temperature increase in coils during FSD (2003)

10 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 2004 Coil Critical current at 1.8 K (except BT19) Operation point Critical 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 2. Status of the Tore Supra TF system (3/3) BT19

11 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Normal operation (1/4) Tore Supra TF activity Since 1988 Since 1988 :  13 thermal cycles from room to LHe temperature  TF cycles  plasma discharges

12 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Normal operation (2/4) Winding-pack temperature during one day of operation Temperature increase at current ramping-up and down (0.06 K) Green light for TF operation 1.87 K

13 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Normal operation (3/4) Thick casing helium temperature during one day of operation Temperature increase linked to cleaning plasma discharges

14 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Normal operation (4/4) Temperature increase due to a disruption from 1.7 MA Plasma disruption Thick casing : K Winding-pack : K 18/09/03

15 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 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 Since 1989 : 75 Fast Safety Discharges of the TF magnet (on 1090 TF cycles) FSDTF cycles

16 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Fast Safety Discharges (2/3) Origin of Fast Safety Discharges since 1994 No FSD due to a quench !

17 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Fast Safety Discharges (3/3) 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

18 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September The cryogenic system (1/2) Availability Manpower : 12 persons Electric power : 1.1 MW Cost : 0.5 M€/year (excluding staff and energy) 2003 : 97 % 2002 : 92% availability

19 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 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 :

20 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 2004 TF systemTore SupraITER Magnetic energy0.6 GJ40 GJ SuperconductorNbTiNb 3 Sn Conductor typemonolithic bare conductor 2.8 mm x 5.6 mm Cable-in-conduit TFMC (40.7 mm Ø) Conductor current1.4 kA68 kA Discharge voltage0.5 kV10 kV Cooling systemSuperfluid helium bath Supercritical helium forced flow Cryogenic power1.1 MW~ 35 MW 6. Can the TF magnet experience of Tore Supra be useful for ITER ? (1/4)

21 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 2004 NbTi, 1.8 K NbTi, 4.5 K Nb 3 Sn,TFMC -0.65%, 4.5 K Tore Supra ITER 6. Can the TF magnet experience of Tore Supra be useful for ITER ? (2/4) Operation of ITER TF at 11.8 T doesn’t allow NbTi to be used

22 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Can the TF magnet experience of Tore Supra be useful for ITER ? (3/4) 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

23 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September Can the TF magnet experience of Tore Supra be useful for ITER ? (4/4) 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 done Experience in TS can help : Design of protection and monitoring system Impact on cryoplant Detailed magnet operation Impact on scenarios

24 Association Euratom-CEA P. Libeyre Pioneering superconductivity 23rd SOFT, Venice 21 September 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