Direct Energy Conversion from a Laser Beam by using a Relativistic Electron Beam TAKASHI ABE Summary In space activity, the energy remotely transmitted by means of a laser beam is valuable for many purposes. This energy can be used as electric power through an energy converter. In this paper, a new energy converter is proposed, in which a relativistic electron beam is used. In this method, the operation of high power density is possible while maintaining a high efficiency, since the unconverted laser beam is transmitted rather than absorbed in the converter. 1. Introduction A remotely powered vehicle is most promising for future space activity [1], The laser beam is a favourable candidate for the remote transmission of power generated at a central power station, because it diverges less during transmission. In a remotely powered vehicle, a laser beam can be mainly used in two ways: (1) it can be used as power for a propulsion system; and (2) it can be used as electric power through an energy converter. In this paper, we consider the latter. To be practical, a laser converter must (1) be properly matched to the laser wavelength, (2) exhibit high energy conversion efficiency, (3) operate at high power density, (4) have a high ratio of peak power to system weight, (5) operate reliably, and (6) not be excessively expensive to manufacture. Of these necessary converter characteristics, the most important are high efficiency and high power density operation. A high conversion efficiency and the capability to operate at a high power density are closely linked. The need for good conversion efficiency is obvious. However, what happens to the fraction of energy that is not converted, especially at high power density, is crucial. If this power is converted to heat, high temperatures result which may reduce efficiency and require major cooling systems. Converters that transmit unconverted power rather than absorb it could have significant advantages in thermal management, efficiency, stability, and reliability. From this perspective we propose a method in which the relativistic electron beam (REB) is used in order to convert the laser energy to electric power. 2. Interaction Between Laser and REB We consider a laser beam which propagates in parallel to REB (see Fig. 1). We have analysed earlier a phenomenon which occurs in this situation, and here we first review Takashi Abe, Institute of Space and Astronautical Sciences, Meguro-ku, Komaba 4-6-1, Tokyo 153, Japan.
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