S.D. Peck

Thermal-hydraulic simulation of helium expulsion from a cable-in-conduit conductor

The authors present simulation results for a quenching cable-in-conduit conductor (CICC) for application in superconducting magnetic energy storage (SMES). The details of the model and its computational implementation (the code HEDUMP) are discussed. An extensive verification process shows that HEDUMP can accurately model a quenching CICC. Preliminary results of the simulation are given and discussed. In particular, the normal zone propagation is studied. It is shown that CICCs exhibit a thermohydraulic quench-back behavior whereby superconducting regions ahead of the normals front are suddenly driven normal by frictional dissipation and/or compression heating of the fluid. >

Test results from the 200 kA SMES/ETM conductor

The critical current and stability margin of a 200-kA, copper-stabilized, cable-in-conduit conductor cooled with helium-II have been measured. The test specimen was 3 m long, inserted in a uniform background dipole field of up to 5 T with an effective length of 0.9 m. The critical current of the conductor was measured at 1.8 K and found to be 280 kA at a total field of 5.8 T, 260 kA at 6.4 T, and 215 kA at 7.4 T. Normal zones of 2-cm initial length were initiated by inductive heaters, and the voltage and temperature of the conductor in the heated zone were monitored for recovery of propagation. The stability margin is reported as a function of the current density over the cable space at various background fields, bath temperatures, heated lengths, heater pulse durations, and numbers of cumulative load cycles. The test results demonstrated that the conductor can operate at 200 kA in the Engineering Test Model for SMES where the peak total field is 4.13 T.

SMES conductor design

The authors report the current status of the 200-kA SMES (superconducting magnetic energy storage) conductor design and the future test and development plans. The basis is given for selecting the design criteria for each requirement used in the conductor tradeoff study. A CICC (cable-in-conduit conductor) concept has been selected for the SMES system because it represents the most appropriate route for current scale-up to 200 kA (or more) as required by SMES. A CICC has a high stability margin, utilizes proven manufacturing processes, eliminates the need for a high-risk helium vessel and complex helium dump system, and is cost-effective. The results of thermal and stress analyses are given for stability and thermal and magnetic loadings. Finally, a preliminary manufacturing plan is described. >

SMES conductor selection: an engineering perspective

The authors discuss the engineering considerations driving the selection of a conductor concept for large-scale SMES (superconducting magnetic energy storage). There are five areas that require special attention: current diffusion effects, stability margin, AC losses, cooldown stress sustained by the conductor, and helium containment. From a magnet design perspective, there is a strong premium in SMES on utilizing conductors with as high a current as possible. It is difficult to scale up a particular monolithic design to achieve higher current. Overall magnet design issues are also more difficult to tackle with monolithic conductors. It is concluded that cable-in-conduit conductors are more attractive for large-scale SMES.<<ETX>>

Lightweight magnet for space applications

The use of cryogenic and superconducting magnets in space is being investigated for pulsed power generation, power conditioning and energy storage and could play a major role in the Strategic Defense Initative (SDI) program. Potential space magnet applications, current technological limits and areas where additional development is required have been identified. A short history of superconducting magnets in space is included. Technology study results, including consideration of zero-gravity conditions for magnet cooling, space-based refrigerator/liquefiers, advanced composites to reduce magnet weight and structures that satisfy launch and space environmental requirements are presented. Computer programs have been developed to optimize spaceborne magnet system weight with respect to the power supply, magnet operating current density, cooling scenario, charge and discharge rates, load characteristics and magnet configuration. Ground-based magnets built to date have stored energy to mass ratios (specific energies) of less than 3 J/gm ; it is expected that space-based magnets with specific energies of more than 50 J/gm can be designed and built in the near future.

Design of a 200kA Conductor for Superconducting Magnetic Energy Storage (SMES)

This paper reports the status of the design of a 200kA conductor for a Superconducting Magnetic Energy Storage (SMES) system. The reasons for adopting the Cable-In-Conduit-Conductor concept were reported previously. A brief review of these reasons together with the conductor design requirements will precede a description of the method used to establish the detailed design of the conductor. This method utilized manufacturing development test and evaluation techniques to provide discriminators between several CICC configurations. The rationale for selecting the detailed design configuration is given together with a brief overview of conductor testing.

Analysis of SSC dipole quench behavior as a function of quench protection heater configuration

Analytic modeling tools have been developed to predict the quench behavior of the Superconducting Super Collider (SSC) dipole coils for a wide range of quench protection heater designs and configurations. Computer modeling tools have been developed to predict the time between heater firing and the initiation of conductor normal zones, and the maximum heater temperature for parametric variations in the heater strip geometry, resistance, material, protection circuit configuration, and conductor current and temperature. Verification of the modeling results has been accomplished by comparison of analysis results with data obtained from quench heater tests of DCA 311-321. Predictions for effective conductor enthalpy and time to normal zone initiation were found to correlate well with actual test data. Predictions have been made for the performance of heater designs for the GDSS prototype dipole magnets.<<ETX>>

A test facility for 200 kA SMES/ETM conductors

The test facility and the procedures used to characterize two full-scale copper-stabilized cable-in-conduit superconductors are described. The critical current at 1.8 K was 280 kA at a total field of 5.8 T, 260 kA at 6.4 T, and 215 kA at 7.4 T. The stability margin at 200 kA and 4 to 5 T was 70 to 80 mJ/cm/sup 3/ of metal. No significant performance degradation was observed after more than 600 load cycles.

Collider dipole magnet field angle measurement

Methods and devices for measuring the prototype Superconducting Super Collider (SSC) dipole magnetic field angle with respect to a vertical reference are discussed. An internal research and development project was conducted to develop a low-cost device for production measurement of the SSC dipole field verticality. The system employs Hall probes, a level sensor, and precision electronics interfaced to a personal computer to perform this critical measurement at discrete points along the magnet beam axis. Specification, component selection, mechanical and electrical design, calibration, and test results are presented.

Design considerations for an inductive heater for conductor stability testing

A discussion is presented of the considerations and the lessons learned in designing inductive heaters for stability testing of a 200-kA conductor for superconducting magnetic energy storage (SMES). Two separate tests were run using different inductive heater designs: the first was a long heater about a subcable pitch in length (50 cm) and was wound with inner and outer coils with currents flowing in opposite directions to minimize stray fields; the second was a short coil about 2 cm long without an inner coil. The thermocouples were used in both tests to measure the total energy delivered to the conductor. In order to calculate the stability margin, it is necessary to know the energy delivered per unit volume of conductor. For the long heater with inner and outer coils, the energy distribution has been calculated to be fairly uniform along the length of the heater. However, for a single short heater, the losses are distributed in a very non-uniform fashion; in fact, they are considerably higher at the test conductor ends due to coupling losses induced by the radial field component. Another design consideration in the test was to let the LRC circuit ring, with the hope of increasing the efficiency of energy transfer to the test conductor. The main conclusions of this study are that the induced heating in the test conductor will depend on the cabling geometry, resistance, and applied field distributions and that great care must be taken to correctly interpret stability margin results based on inductive heat input to very large cabled conductors.