PROTECTION MEASURES FOR SELECTED ITER MAGNET SYSTEM OFF-NORMAL CONDITIONS

The International Thermonuclear Experimental Reactor (ITER) magnet sys tems provide the magnetic field intensity and held geometry to contain and control plasma during the various phases of pulsed operation. Dur ing these pulses, the toroidal held (TF) coils operate with a constant current. The central solenoid (CS) and poloidal field (PF) coils, on the other hand, are each independently powered. The maximum terminal v oltages during plasma operation and protective discharges are 15 kV fo r CS and IO kV for TF and PF. The energy stored in the 20 TF coil syst em is 103 GJ; in each of the other coils it is approximately 10 GJ or less. This paper describes the protection requirements and selected de sign concepts being considered for the large superconducting coils for the ITER. Ground faults, short circuits and helium leaks are the majo r serious accidents to be prevented in the coils. All coils use a soli d insulation system to avoid ground faults. The electrical circuits in cluding coil and power supply are grounded through resistors that limi t current in the event of a ground fault. In the case of a short circu it within the coil winding, a large energy would be dissipated close t o the small shorted volume. The impact of the short circuit can be red uced by using a potential screen. Inside the cryostat, helium leakage is most likely at the electrical insulating breaks in the cryogenic co oling lines between the coils and helium manifolds. A double containme nt (metallic shield and glass-epoxy) is therefore provided for the ins ulation breaks to allow for the detection of small leaks and to limit the spread of helium to other locations. (C) 1998 Elsevier Science S.A . All rights reserved.