A new transistor-like superconducting three terminal device called “Quiteron” is briefly reviewed. The article contains the basic concept of quasiparticle injection phenomena in a superconductor including the expected behavior both in the stationary state and in the transient state as well as the operation of Quiteron itself with or without external load. The factors which limit the ability of Quiteron are also discussed.
Electro-magnetic thruster is one of the ship propulsion methods in which the thrust is resulted from the interaction between magnetic field generated by the fixed magnet on the ship and electric current sent to the seawater. Consequently, the thrust is generated without any rotational parts such as a propeller. But this propulsion method requires high magnetic field density so that we have been trying to apply the superconducting coil to the electro-magnetic propulsion since 1973. In 1976, the first electro-magnetic propulsion model ship in the world, which was equipped with a small superconducting coil, was built and fundamental experiments has been carried out in our laboratory. We confirmed from the experience that superconducting magnets are essential to the propulsion method. In 1979, the second model ship of superconducting electro-magnetic thruster, ST-500, was built. The model ship is 3.6m in length, 700kg in weight and about 2 teslas in magnetic field. Our study on ST-500 has been evaluaed in the ship building world and invited to the international propeller conference held May, 1983. This article was prepared based on the paper presented in the conference.
The absolute ampere A would be actualized using two kinds of the gyromagnetic ratio of proton γp′ (low) and γp′ (high), which are measured by low and high magnetic field methods respectively with the maintained ampere. In the high magnetic field method, we measure the flux density B by weighing the force which acts on a rectangular coil, through which a known current is passing, in a magnetic field. In order to determine A with the uncertainty less than 1ppm (parts per million), the split type superconducting magnet with a wide homogeneous range better than 1ppm over 100mm length is needed. As a preliminary experiment, we have developed a small and split type superconducting magnet with the homogeneity better than 10ppm over 10mm. The dimensions are 155mm in diameter, 25mm in gap interval and 100mm in total length. A helmholtz type main coil and compensating pair coils were wound on the bobbin which was made of stainless steel SUS304. The main coil was connected to the compensating coils in series as usual. The measured homogeneity of magnetic field was less than that obtained from a calculation with the dimensions. It has been clearified that the inhomogeneity was caused by the magnetization of a part of weld in the bobbin. However the inhomogeneity is reproducible. In order to improve the inhomogeneity, the compensating coil are remade and the remade coils are not connected with main coil in contrast to the former coils. So we are able to control the compensating coil current independently of main coil current to cancel the extramagnetic field. When the main coil current remained constant to be about 60A, we adjusted finely the current of compensating coil measuring the distribution of magnetic field by means of nuclear magnetic resonance of proton. When the current through compensating coil was 17A, a high homogeneity better than 10ppm over 10mm was obtained. The advantage of this method is that the total magnetic field, that is sum of the magnetic field from main and compensating coils and an extramagnetic field, is homogenized. The magnetic field distribution is changed rather freely, so even a secular change of extramagnetic field can be corrected. A little deformation of coil and the interval of gap is taken place generally by the contraction in cooling or by the electromagnetic force between pair coils. Sometimes earth magnetic field influences the distribution, Those unexpected inhomogeneous magnetic field should be canceled by the method as mentioned above. Therefore, it is expectedto make a split type superconducting magnet with the homogeneity better than 1 ppm over 100mm length. We have also measured the stability of magnetic field by means of nuclear magnetic resonance of proton. The decrement of resonance frequency corresponds to the decrement of the magnetic field and also is proportional to the decrement of the persistent current. The rate of the derement was 5.8×10-6/hr.
Reduced size cable-in-conduit conductors with a parameter of various void fractions were fabricated, prior to the full size conductor, to study the relation of the critical current and bending strain. The reduced size conductor has 3 (0.61φmm wire)×6 composites in conduit where the void fraction is changed from 30% to 50%. The conductor with -50% void fraction has critical bending strain (εbc) of -0.9% which is nearly equal to εbc of the strand, while the conductor with void fraction below -40% behaves like a compacted composite and its εbc is below -0.5%.