The 45-T Hybrid Magnet System represents an important commitment for the new National High Magnetic Field Laboratory, and when completed, it will establish a new frontier for steady magnetic fields for research. This system will use a resistive insert to produce 31T on axis, with the remaining 14T contributed by a superconducting outsert with 616-mm warm bore. The superconducting outsert will be capable of providing over 15T on axis when operated alone. Progress on the design, development, and fabrication of the system has been steady. Several critical components and major subsystems have been completed and are now being tested in preparation for the overall system integration.
I-V characteristics and the distribution of electric potential were measured for Bi-2212/Ag composite tape in magnetic fields of various directions. An anomalous distribution of electric potential was observed especially in the magnetic fields perpendicular to the tape surface. Along the current direction in the vicinity of both edges of the superconducting oxide layer, a large voltage was measured. However, zero voltage was monitored in the middle area of samples. Large voltage was also measured across the current direction around both edges. These voltages are proportional to both the value of the applied current below Ic and the magnetic field component perpendicular to the tape surface. To explain this anomalous distribution of electric potential, we propose a model based on the Hall effect in silver substrate and current transfer from silver to superconductor.
So far, the use of superconducting magnets has been limited to chemical analysis and medical inspection. To develop a new use, we have tried to apply common MRI devices as nondestructive sugar content detector of watermelon. To estimate the sugar content, a new technique using multiple regression analysis of two NMR relaxation times was developed. It was found that the coefficient of multiple regression at the center of the watermelon exceeded 0.9 and the standard error of prediction was around 0.5, and that the over-ripened part of flesh called ‘nieka’ in watermelon could be distinguished because its T2 was much longer than that of the oridinary part. An evaluation rate of sugar content could be below 6s per watermelon. It is concluded that multiple analysis of T1 and T2 on intact watermelon can be applied as a non-invasive, nondestructive indicator of sugar content.
In order to discuss a pulse-tube refrigerator using thermoacoustic theory, one must know the behavior of oscillating fluid. Already proposed are two methods of estimating fluid behavior: simulation employing the virtual PV method and simulation using THERMOACOUSTICA based on the thermoacoustic theory. Here, we propose an other method of estimating fluid behavior without using simulation. Since the thermoacoustic theory is one of the linear theories, a pulse-tube refrigerator is represented by an electric circuit, except for parts where the temperature distribution is inhomogeneous. The pulse-tube part, where the temperature is inhomogeneous, is permitted to be represented by an electric circuit, because thermodynamic process of fluid in the part is isentropic in good approximation. Thus, a pulse-tube refrigerator except for the regenerator corresponds to an equivalent circuit. Oscillating pressure and volume velocity correspond to AC voltage and AC current, respectively. Work flow corresponds to electric power transmitted and fluid channel to a transmission line with loss. The kinematic energy of fluid corresponds to the energy of a magnetic field, potential energy due to gas-spring to the energy of an electric field, dissipation of the kinetic energy to dissipation due to series resistance of inductance in the equivalent circuit and dissipation of the potential energy to parallel resistance of capacitance in the circuit. Numerical examples clarify the difference of fluid behavior in the pulse-tube part among the basic pulse-tube, orifice type and double inlet refrigerators. Finally proposed are experimental approaches of estimating circuit parameters and a new method of controlling third generation pulse-tube refrigerators.