ABSTRACT: A 30 kA/23 kV current lead cooled by forced-flow supercritical
helium has been developed at KfK. It allows position independent
installation and well controlled operation which would be advantageous
for operation of all kind of superconducting forced-flow cooled magnets.
The design of the lead is described in this paper. The main feature is
the insertion of Nb<sub>3</sub>Sn wires inside the conductor of the heat
exchanger allowing the operation at minimum mass flow in a wide current
range. Measurement results are presented for steady-state operation up
to 30 kA, for short time operation up to 50 kA, for pulsed operation up
to ±1000 A at 10 Hz, and for simulation of loss of mass flow. A
high-voltage test up to 28 kV DC has been done. The mass flow rate
normalized to current is about 0.055 g/(s-kA) for 15 to 30 kA proving
the effectiveness of the Nb<sub>3</sub>Sn inserts. Comparison to
numerical calculations shows good agreement allowing extrapolation for
the design of leads for currents up to 80 kA for ITER model coil tests
in the TOSKA test facility at KfK
IEEE Transactions on Magnetics 08/1994; · 1.36 Impact Factor
ABSTRACT: Poloidal field coils of Tokamak machines are characterized by
their pulsed operation needed for plasma ramp up and control. They have
to sustain operation faults such as plasma disruptions in their
superconducting state. A low-loss conductor, low-loss structural
reinforcement and a high-voltage insulation system are needed for
fulfilling these requirements. The basis for this technology has been
developed for a superconducting model coil. The fabrication technique
applied for the coil and some high-voltage related components are
IEEE Transactions on Magnetics 02/1992; · 1.36 Impact Factor
ABSTRACT: In this test, the coil reached (in stable operation) a field of 9 T at 140% of rated current. It reached the short-sample values of the strands used in the cable. The coil was operated up to 8 T with and without poloidal field transients in a toroidal configuration. The mass flow rate was reduced by a factor of 5 compared with the design value without any visible impact on stability. Averaged AC losses (winding, 14 W; case, 7 W) were measured under Large Coil Task (LCT)-specified poloidal field pulses, and the findings agreed with those of the short-sample measurements. The coils mechanical properties, which behaved as theoretically predicted, are also reported. All results obtained are thought to demonstrate that the applied technology has achieved reliable engineering standards.
IEEE Transactions on Magnetics 04/1988; · 1.36 Impact Factor
ABSTRACT: The Euratom-LCT-coil was tested as a single coil in the TOSKA facility at KfK Karlsruhe and in IFSMTF at ORNL Oak Ridge. Different mechanical boundary conditions and other operation parameters (mass flow, current) in the IFSMTF led to new set of results which broaden the knowledge about the coil. During cooldown the coil showed excellent heat transfer properties. The design current 11.4 kA with a max. field of 6.63 T could be reached with a ramp rate of 4 A/S without visible instabilities and thermal losses. The coil had at rated current a Stekly parameter α = 2.3 and could safely operated outside the cryogenic stability regime. The coil was 7 times dumped from currents higher than 4 kA with a peak voltage of 2.5 kV. Pressure increase was investigated under different boundary conditions and remained moderate. Dump losses measured were about 2 % of the stored energy. The coil was two times quenched during investigation of the operation limits. The quench detection system specially developed for this coil could be successfully tested with a level setting of 50 mV. For the first time the operation limits of such a coil were determined by current sharing measurement with heated helium slugs. The results are in fair agreement with those extrapolated from single strand measurements.
IEEE Transactions on Magnetics 04/1987; · 1.36 Impact Factor
ABSTRACT: The forced flow cooled European LCT coil was tested successfully as a single coil in the Karlsruhe test facility TOSKA. Operation at design conditions (10 kA, 5.6 T at 4.8 K and 6 bar) was achieved without any problems. Cryogenic, mechanical and electrical performance was in agreement with predictions. Due to the high stability, the coil could be operated close to its critical parameters by heating the supercritical helium up to about 6 K. The coil stayed superconducting even after a fast dump (7 s) from full current. Good performance is also expected for operation in the 6 coil toroidal array of the LCTF.
IEEE Transactions on Magnetics 04/1985; · 1.36 Impact Factor
ABSTRACT: A special quench detection system has been developed for the EURATOM Large Coil Task (LCT) coil. The system is based on a bridge circuit which uses a special ‘two in hand’ winding technique for the pancakes of the EURATOM LCT coil. The electronic circuit was designed in a fail safe way to prevent failure of the quench detector due to failure of one of its components. A method for quick balancing of the quench detection system in a large toroidal magnet system was applied. The quench detection system worked very reliably during the experimental phase of the LCT and was within the quench detection level setting of 50 mV, i.e. the system was not sensitive to poloidal field transients at or below this level. Non-electrical methods for quench detection were also investigated.