Direct Energy Converter from Laser Energy to Electricity with Laser-produced Plasma HIROSHI HOMMA, TATSUO OKAMOTO, MASAO YAMAUCHI, CHOBEI YAMABE & KENJI HORII Summary A method of power transmission using a laser beam for a very long distance has been proposed. The characteristics of the direct energy converter from laser energy to electricity with laser-produced plasma are reported here. It is found that the efficiency of (where and r]3 are the conversion efficiency from laser energy to ion energy and from plasma ion energy to electricity) increases with laser output using a carbon target. 1. Introduction It has been proposed to use a laser beam for ultra-long distance energy transmission, for instance from a developing area which is rich in natural energy to a consuming area where there is need for a large amount of energy, or from a solar power satellite to the earth and between the satellite stations [1]—[6]. We report here the characteristics of a laser-produced plasma and plasma direct converter. They are used in a direct energy conversion using plasma. 2. Principle of Direct Energy Converter from Laser Energy to Electricity The principle of energy conversion from laser energy to electricity is shown in Fig. 1. At first, the laser beam is irradiated on a solid target in a vacuum chamber to produce the plasma, and the laser energy is converted to the kinetic energy of the produced plasma. The produced plasma expands and enters into a PDC (Plasma Direct Converter). Both ions and electrons are included in the plasma but the mass of an ion is very large compared with that of an electron. Therefore, the ion kinetic energy is very large compared with the electron kinetic energy. Since the ions carry most of the kinetic energy of the plasma, the PDC converts the ion kinetic energy to electricity. The electrons in the plasma which enter into the PDC are repelled by the suppressor grid which has an applied negative voltage to separate ions and electrons electrostatically. The ions are decelerated by the field between the suppressor grid and the ion collector to which is applied a positive voltage, and some of the ions reach the The authors are with the Department of Electrical Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464, Japan. This paper was presented at the sixth ISAS Space Energy Symposium, 12-13 March 1987.
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