parallel to the increase in REB density, and it may break the stability of the REB ring. The study relating to this phenomenon remains to be conducted. In parallel to the REB acceleration, the thermalization of the REB (i.e., the spread of the energy spectrum of the REB) is induced [2]. This thermalization of the REB may break condition (2) which guarantees the acceleration of the REB through the nonlinear interaction. Furthermore it may reduce the efficiency of the free electron laser [5]. It is an important factor when the efficiency is considered for the energy conversion system in a closed form. 5. Conclusion A new energy converter from a laser energy to DC power is proposed. In this system, the acceleration of the REB through the interaction with the incident laser is utilized. The increment of the kinetic energy of the REB is converted to DC power, generating a microwave intermediately. Compactness and an appropriate efficiency can be accomplished by choosing appropriate parameters. Furthermore, the operation of high power density keeping a high efficiency is possible, since unconverted laser energy is transmitted rather than absorbed in the converter. REFERENCES [1] DeYoung, R.J. et al. (1983). NASA SP-464. [2] Abe, Takashi (1986) Physics of Fluids, 29, p. 3394. [3] Gutmann, R.J. & Borrego, J.M. (1979) IEEE Transactions, M.T.T. 27, p. 958. [4] Landau, L.D. & Lifshitz, E.M. (1975) The Classical Theory of Fields, Pergamon Press. [5] Kroll, N.M. & McMillin, W.A. (1978) Physical Review A, 17, p. 300.
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