The kinetic energy of ocean currents is very large in quantity and unexhausted. The Kuroshio current along the east-coast of Japan is the typical current in the world, and the total energy in the current is estimated to be about 1.9×1010 watts. In the method of changing the kinetic energy into the electric power, there is the method of mechanical generation and direct generation. The mechanical method is classified into the method of rotating and drawing. The direct method is the same as the traditional MHD generator, but the working fluid is the ocean current instead of the plasma flow, that is, the direct method of the ocean current generation is based on the unexhausted energy. The direct generation plant has no moving part and the construction is simpler than the plant based on the method of rotating and drawing. In this case, the ocean current is transformed into electric power through the process consisted of three stages such as increasing velocity stage, generating power stage and restoring pressure stage. In the first stage, the energy density of the ocean current is raised so as to increase the efficiency of power generation. In the second stage, the electric power is generated by means of the MHD method, and the power is conducted to a load through electrodes. In the last stage, the pressure of ocean current is restored and the current in MHD duct flows out to the sea. For 100kW generator, the MHD duct is 10m in width, in height and in length and the magnetic flux density must be 3 teslas. As results, the efficiency of the power generation is raised to 28%. A superconducting magnet of 15m in diameter is necessary in order to keep the magnetic flux of high density over the wide duct. The magnet requires the electric power of 30-50kW to be maintained at 4.2K. Taking consideration of such points, the following two items have to be realized with a view of making the ocean power plant practicable; (i) lowering the price of superconducting magnets, (ii) development of superconducting magnets working at LH2 temperature.
Using a diamond anvil high pressure cell, the superconducting transition temperature has been determined by a new technique. The technique is based on an a.c. bridge method, and the sensitivity is improved by shield plates of a high-Tc superconductor, by which the magnetic flux is concentrated in the sample. The technique has been applied for measurements of the superconducting transition of lead as a function of temperature and pressure.