be converted to electric power (process II). Hence, a conversion system from laser to electric power is composed of these processees. Here we consider the method in process II. First, we consider the scattered wave. The scattered wave has a sufficiently lesser frequency if the density of the REB is small and the y value is large enough. It is well known that, in the microwave region, the electromagnetic wave can be rectified with good efficiency [3]. Hence, through the rectification, the power of the electromagnetic wave can be converted to DC electric power. If an appropriate value of the REB density and the y value is chosen so that the scattered wave is in a microwave region, this energy can be converted to DC electric power through the rectification. The fraction of energy converted to the acceleration of the REB is much greater than that to the scattered wave. Hence the conversion of the kinetic energy of the REB increased through the interaction with the laser beam is more important. We propose a method in which a microwave is generated intermediately, and the resultant microwave is converted to DC power. To generate a micro wave, an idea of the free electron laser can be applied [5]. That is, the accelerated REB is introduced to the wiggler field (the rippled magnetic field). Through the interaction with the rippled magnetic field, the REB generates the electromagnetic wave expending its kinetic energy. The efficiency of generating the electromagnetic wave increases with the intensity of the rippled magnetic field. The generated electromagnetic wave has a frequency; where kf is a wave number 2^/A defined by the spacing A of the rippled magnetic field. For an appropriate spacing of the rippled magnetic field and an appropriate y value, the generated electromagnetic field falls in a microwave region. The efficiency of the free electron laser is not so high. Hence the remaining REB must be reused to save its energy. In this closed system, a steady state operation is inevitable. To maintain the steady state of the REB, the intensity of the rippled magnetic field must be controlled so that only the excess energy of the REB is converted to the microwave. Fig. 5 shows a schematic drawing of the system. The REB which is accelerated through the interaction with the incident laser beam (region I) is turned by 180°, and passes through the rippled magnetic field in which the microwave is generated (region II). After that, it is turned by 180° and, again, passes through the region interacting with the incident laser. At regions I and II, the microwave is generated which can be
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