This paper discusses the exotic magnetic phenomena that are unfamiliar to cryogenic and superconducting engineers. The magnetic effects on water, fuel and air are discussed, then the magnetic effects on chemical reaction, polymerization and crystal growth. Further experimental studies are necessary for a better understanding of these effects, but exotic applied magnetics are a treasure trove of seeds for creating new industry and new business where superconducting magnets will play essential roles.
The rapid increase in the demand for electric power and the reduced load factor in Japan have encouraged the development of SMES (superconducting magnetic energy storage) systems for utility power grid applications. The Ministry of International Trade and Industry launched an 8-year national project to develop and establish the component technologies required to realize a small scale 100kWh/40MW SMES and its practical application in the utility network. The key component technologies developed in the project consist of a superconducting coil, a quench detection system, a power converter, a circuit breaker and a persistent current switch. A model coil for the core of the SMES system has been designed and fabricated. Performance tests in cooperation with The Japan Atomic Energy Research Institute were successfully completed in 1996. The following paper describes in detail the test results and their subsequent evaluation. The model coil is presently installed in the test facilities at Lawrence Livermore National Laboratory, in the United States, for long-term excitation testing. The tests are part of an international cooperation plan with the U.S. Department of Energy (DOE).
A SMES model coil was fabricated as R & D item in the development of component technologies for a 480MJ/20MW SMES pilot plant. The coil consists of four double-pancake windings. The coil is the same diameter but half the number of pancakes that will be needed for a SMES pilot plant. The NbTi cable-in-conduit conductor and superconducting joints between the double pancakes are cooled by a forced flow of supercritical helium. Prior to fabrication, various characteristics of the cable-in-conduit were measured by full-sized short samples from actual conductors and by scaled short samples from scaled conductors. The critical current of the scaled short samples was in agreement with that calculated from one strand of the conductor. The impedance between arbitrary dual-oxide coated strands in the full-size conductor was measured to be smaller than that obtained from two Cr-plated strands, which showed a good degree of stability in another coil. It was estimated that oxide-coated conductors would have high stability. Through fabrication of a model coil, it was demonstrated that a large forced-flow coil for a small-scale 100kWh SMES device could be manufactured.
A model coil of a superconducting magnetic energy storage (SMES) device, which is a forced-cooled Nb-Ti coil, has been fabricated and a performance test at cryogenic temperatures has been carried out. The SMES model coil is composed of 4 dual pancakes and its total weight is 4.5t. The applied conductors are cable-in-conduit conductors cooled by supercritical helium (SHe) at 4.5K and 0.7MPa. SHe is supplied to the SMES model coil and the structure by a reciprocating bellows pump. The test facility is located at the International Thermonuclear Experimental Reactor (ITER) common test facility, was constructed for the testing of an ITER central solenoid model coil. In the experiments, cool-down was finished within 10 days under controlled temperature differences in the SMES model coil. During cool-down and 4.5K operation, pressure drop characteristics of the conductor were measured and the friction factor estimated. The pressure drop characteristics of the SMES model coil were in good agreement with those of the previous cable-in-conduit conductor. During static operation without current, the heat load and refrigerator operation conditions were measured. The heat load of the SMES model coil is 7.5W, which is within the expected value.
An experiment of a SMES model coil was successfully carried out at the ITER test facility of the Japan Atomic Energy Research Institute (JAERI) in 1996, in collaboration with the International Superconductivity Technology Center (ISTEC). The coil was charged up to its rated current of 20kA at 2.8T without quenching, and then charged up to 35.4kA for extended testing. The electromagnetic performance of the coil was tested by measuring critical current (Ic) and current sharing temperature (Tcs), and no degradation was observed.
The mechanical performance of a SMES model coil was measured by strain gauges, displacement gauges and acoustic emission (AE) sensors attached to the coil surface during an overcharge test. The displacements of the SMES model coil were proportional to the squared currents during charging up until 35.4kA. It was clear that the coil became deformed elastically by the electromagnetic force during overcharging. The test results obtained by the measurement of strains were compared with calculated results obtained by finite element method analysis. As a result of the comparison, good agreement was found in both stresses, and the values were sufficiently small. It was demonstrated that the coil had no problem regarding mechanical performance. It was clarified that AE signals significantly decreased in the current region after repeated excitation. Furthermore, the characteristics of AE signals were different from the coil windings with coil supports. The wave of AE signals in the windings was minimal ms and more than 100kHz, and in the coil support more than 10ms but less than 40kHz.
The stability of the SMES model coil was investigated at the transport currents from 10 to 30kA and coolant temperatures of 4.5 and 6.0K. The initial normalcy was created by applying 20ms and 1kHz inductive heating pulse. Stability simulation was carried out by using numerical code POCHI, which was developed by JAERI. Since the simulation results are in good agreement with the experiment, the stability of the SMES conductor can be evaluated to be higher than current shearing temperature in the case of recovery. It can be concluded that the stability of the SMES conductor is sufficiently high. Furthermore, the stability of margin of the SMES pilot plant is calculated to be 830mJ/cm3 at the nominal point (20kA-4.5K). The SMES pilot plant is therefore expected to be stable for nominal operation.
A model coil for superconducting magnetic energy storage (SMES model coil) has been developed to establish the component technologies needed for a small-scale 100kWh SMES device. The SMES model coil was fabricated, and then performance tests were carried out in 1996. The coil was successfully charged up to around 30kA and down to zero at the same ramp rate of magnetic field experienced in a 100kWh SMES device. AC loss in the coil was measured by an enthalpy method as parameters of ramp rate and flat top current. The results were evaluated by an analysis and compared with short-sample test results. The measured hysteresis loss is in good agreement with that estimated from the short-sample results. It was found that the coupling loss of the coil consists of two major coupling time constants. One is a short time constant of about 200ms, which is in agreement with the test results of a short real conductor. The other is a long time constant of about 30s, which could not be expected from the short sample test results.