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The Tore Supra tokamak at CEA Cadarache

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).

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The Tore Supra tokamak at CEA Cadarache

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  1. 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. The Tore Supra tokamak at CEA Cadarache

  3. Introduction • Status of the Tore Supra Toroidal Field (TF) system • Normal operation • Fast safety discharges • The cryogenic system • Can the magnet experience of Tore Supra be useful for ITER ? • Conclusion

  4. 1. Introduction (1/4) The Tore Supra TF magnet during assembly

  5. bare conductors in superfluid helium ! Superfluid helium (1.8 K) in thin casing Supercritical helium (4.5 K) in thick casing channels 1. Introduction (2/4) Tore Supra TF coil structure

  6. one of the largestsuperconducting system in operation (600 MJ magnetic energy) • Operated daily close to nominal conditions (1250 A) since November 1989. Continuous toroidal field on the whole day  Relying on a refrigerator including for the first time industrial quantities of superfluid helium ( Claudet bath) 1. Introduction (3/4) The Tore Supra TF system is :

  7. The Tore Supra TF system contribution The revolution of superfluid helium 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 path to steady-state operation the continuous toroidal field allows long duration plasma experiments to be performed 1. Introduction (4/4) 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

  8. 1982-1988 coil 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 2. Status of the Tore Supra TF system (1/3)

  9. 2. Status of the Tore Supra TF system (2/3) No more apparent defect on BT13 Similar behaviour of BT13 compared to the other coils Green light for TF operation 1.87 K Temperature increase in coils during FSD (2003)

  10. Load line Coil Critical current at 1.8 K (except BT19) Coil Critical current at 4.2 K (except BT19) BT19 BT19 reduced Large margin (2.4 K) Critical point nominal Operation point Safe operation of the TF magnet since 1989 at 1250 A, 8 T 2. Status of the Tore Supra TF system (3/3)

  11. 3. Normal operation (1/4) Since 1988 :  13 thermal cycles from room to LHe temperature  1 090 TF cycles  20 074 plasma discharges Tore Supra TF activity Since 1988

  12. 3. Normal operation (2/4) Winding-pack temperature during one day of operation Green light for TF operation 1.87 K Temperature increase at current ramping-up and down (0.06 K)

  13. 3. Normal operation (3/4) Thick casing helium temperature during one day of operation Temperature increase linked to cleaning plasma discharges

  14. 3. Normal operation (4/4) 18/09/03 Plasma disruption Winding-pack : + 0.02 K Thick casing : + 0.83 K Temperature increase due to a disruption from 1.7 MA

  15. FSD TF cycles Since 1989 : 75 Fast Safety Discharges of the TF magnet (on 1090 TF cycles) 4. Fast Safety Discharges (1/3) Largest voltage at terminals (320 V at 1400 A) Risk of short circuit (bare conductors) To be avoided ! FSD thermal load on cryogenic system 2h30 to recover

  16. No FSD due to a quench ! 4. Fast Safety Discharges (2/3) Origin of Fast Safety Discharges since 1994

  17.  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 4. Fast Safety Discharges (3/3) Remedies to Fast Safety Discharges

  18. 2003 : 97 % 2002 : 92% availability 5. The cryogenic system (1/2) Availability Manpower : 12 persons Electric power : 1.1 MW Cost : 0.5 M€/year (excluding staff and energy)

  19. 5. The cryogenic system (2/2) The major tendencies of the cryoplant ageing Preventive maintenance of compressor units Good availability of the refrigerator Nevertheless, ageing signs are visible :  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.

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

  21. 6. Can the TF magnet experience of Tore Supra be useful for ITER ? (2/4) Nb3Sn,TFMC -0.65%, 4.5 K NbTi, 4.5 K ITER NbTi, 1.8 K Tore Supra Operation of ITER TF at 11.8 T doesn’t allow NbTi to be used

  22. 6. 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 Very high voltage monitoring Forced flow cooling Tore Supra : no quench Fast safety discharge ITER : quench of all coils

  23. 6. Can the TF magnet experience of Tore Supra be useful for ITER ? (4/4) 16 years of reliable plasma operation with a TF superconducting magnet Decision to build ITER is possible experience of the CEA magnet team in conductor and coil design 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. 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

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