J.R. Hale

Progress in the manufacture of the US-DPC test coil

A superconducting ohmic heating coil is being built by MIT to be tested in early 1990 at the Japan Atomic Energy Research Institute (JAERI). This 2-m-diameter coil will be wound from Nb/sub 3/Sn cable-in-conduit conductor. The coil and conductor are briefly described. Manufacturing procedures and problems encountered in the fabrication of the conductor up to August 1988 are considered. Included are descriptions of wire chrome plating, cable manufacture, and conduit fabrication. >

The US-DPC, a poloidal coil test insert for the Japanese Demonstration Poloidal Coil Test Facility

A superconducting pulsed poloidal coil being built by MIT will consist of three double pancakes of Nb/sub 3/Sn cable-in-conduit conductor operating at a maximum coil-envelope current density of 50 A/mm/sup 2/ at 4.2 K in a peak field of approximately 10 T. Peak current and peak ramped field will be 30 kA and approximately 10 T/s, respectively. The coil, conductor, proposed experiment, and supporting research and development efforts are discussed. >

PTF, a new facility for pulse field testing of large scale superconducting cables and joints

A magnetic Pulse Test Facility (PTF), in which samples of CICC electrical joints from each ITER home team will be tested, has been fabricated at the MIT Plasma Fusion Center under an ITER task agreement. Construction of this facility has recently been completed, and an initial test phase on the first CICC joint sample has begun. PTF includes capabilities for sample currents up to 50 kA from a superconducting transformer developed by the University of Twente, magnetic fields up to 6.6 T with ramp rates to +1.5 T/s and -20 T/s, and a cryogenic interface, supplying supercritical helium with flow rates to 20 g/s through each CICC leg at controlled temperatures to 10 K and pressures to 10 atmospheres. A sophisticated, multiple-channel data acquisition system is provided to processed, digitally recorded sensor signals from both the sample and the facility. The facility is totally remote-controlled from a control room through a fiber optic link, and qualified users worldwide are afforded secured access to test data on a 24-hour basis via the Internet. The facility has successfully exercised the first joint sample over the ITER test spectrum with positive results.

Medical applications of magnet devices

The use of magnetic devices in medically-related applications has often been frustrated by insufficient magnetic force, or by an inappropriately designed device. This paper describes magnetic treatment systems which were designed with the benefit of the cooperation of hospital personnel at all levels. Two systems are described in detail. First, a superconducting magnet, with integral orientation system, intended for use in intravascular catheter guidance. The maximum field and gradient produced by this solenoid are 20,000 Oe, and 2250 Oe/cm, respectively. The system is both powerful, and easy to use, by virtue of its completely portable design. The second is a magnetic traction device which has been successfully employed in the treatment of esophageal atresia.

Critical currents of Nb/sub 3/Sn wires for the US-DPC coil

The critical current of titanium-alloyed internal-tin, jelly-roll Nb/sub 3/Sn wire for use in the US Demonstration Poloidal Coil (US-DPC) was evaluated. It was confirmed from 14 randomly-selected samples that the critical-current values were uniform and consistent: the noncopper critical-current density was approximately 700 A/mm/sup 2/ at 10 T and 4.2 K, in agreement with expectations. A 27-strand cable-in-conduit conductor (CICC) using the low-thermal-coefficient-of-expansion superalloy Incoloy 905 yielded a critical current 5-7% below the average value of the single-strand data.

Design of an opposing pair magnet system for ASTROMAG

A magnet system comprising a pair of self-supporting disk-shaped coils has been designed for the ASTROMAG facility on the space station Freedom. The coils are connected in a quadrupole configuration in order to eliminate their dipole moment. One of the primary requirements of this design is that the magnet coils must have near-perfect structural integrity. To this end, each coil would be manufactured as a monolithic composite in which the superconducting wire is incorporated as one of the components. By utilizing a precision X-Y numerically controlled wiring machine, the coil can be built up in pancake layers by alternating prepreg sheets of fiber/epoxy (e.g. carbon or Kevlar fiber) with a layer of NbTi wire that spirals from OD to ID in one layer, from ID to OD in the next. and so on. Each disk magnet will have an ID of 0.4 m and an OD of 1.7 m. The peak field at the winding will be 7.2 T. The system is to operate at 1.8 K. and I/sub op//I/sub c/=0.5. Results of magnetic field and force calculations are presented, and the structural characteristics of the system are described.

A pulsed magnetic field test facility for conductors and joints

A pulsed magnetic field test facility is under construction at Massachusetts Institute of Technology for testing large scale cable-in-conduit superconductor and joint samples. Separate, demountable split-pair solenoid and saddle coils provide a combination of fields which can be either transverse or parallel to the sample axis. The solenoid and saddle magnets together can provide transverse peak fields as high as 8.4 T. Peak parallel fields of 6.6 T can be generated with the solenoid alone. Ramp-up rates of 1.5 T/s and ramp-down rates of 20 T/s are possible. Sample currents up to 50 kA are provided by a superconducting current transformer. The sample is connected to the transformer secondary through a pair of low resistance joints. Supercritical helium is provided to the sample at flow rates up to 20 g/s, pressures up to 1 MPa, and temperatures from 4.7 to 10 K. Programmable logic controllers provide coordination of the magnetic field, sample current, and helium flow rate and temperature in the sample. Sample and facility instrumentation signals are processed and data is stored on a workstation-based data acquisition system with comprehensive data reduction capability. Facility details and status are described.

Design of a retrofit magnet using advanced cable-in-conduit conductor

The excellent properties of the new MIT cable-in-conduit conductor have made possible the design of a retrofit-scale superconducting MHD (magnetohydrodynamic) magnet using a momentless force containment structure. The authors describe the magnet design and compare its weight, cost, and manufacturing logistics with the prior art pool-cooled designs. The magnet system has a peak on-axis field of 4.5 T, has an aperture of 0.8*1.0 m at the inlet end of the magnet and 1.3*1.6 m at the outlet end, and has stored energy of approximately 490 MJ. >

Simulations of quench and recovery in CICC conductors

The authors discuss R. Wongs (1989) CICC, a 1-1/2-D code that models thermal conduction through the insulation of an individual conduit. It is noted that, until recently, the calibration of CICC was restricted to measurements of helium expulsion in normal conductor. No actual quenches in ICCS (internally cooled cable-in-conduit superconductor) coils had been simulated. Recently, several experiments on ICCS conductors of different topology have been performed and compared with CICC simulations, with varying success. The authors report on the capability of CICC to predict and analyze ICCS recovery and quench, and on the codes limitations and the need for further improvements. >

Comparison of two ICCS conductors for MHD application

Two subscale, internally cooled, cabled superconductors (ICCSs) have been examined as candidates for use in a retrofit MHD (magnetohydrodynamic) topping cycle magnet. One of these was a 3*3*3 cable in which all the strands were multifilamentary NbTi stabilized with copper. The other was a 3*3*3 cable in which two strands in each of the nine triplets wa OFHC copper and one was multifilamentary NbTi. The overall copper-to-superconductor ratio for each of the two 27-strand cables was approximately the same. The two conductors were cowound onto a grooved mandrel in such a way that they could be tested alternately. Each sample was instrumented with a heater at the center of the conductor length and with a pressure transducer, four pairs of voltage taps, and one iron-doped gold/constantan thermocouple. Performance tests of the conductors were made at 6-, 7-, and 7.8-T background magnetic fields and at heater input energies ranging from 60 mJ/cm/sup 3/ to 1758 mJ/cm/sup 3/ of conductor. The results of these tests and their significance for MHD magnet design and economics are discussed. >