the dependence of the ion (plasma) density on velocity. The ion density with crosslinked polyethylene is larger than that with carbon but the ion (plasma) velocity with cross-linked polyethylene is not much larger than that with carbon. In other words, light hydrogen ions are expected to accelerate by laser energy but they are not accelerated too much. Therefore heavy materials are expected to be good targets for the PDC. Next, the following plasma is good according to the results shown in 3.2. (4) Ionization rate is large: the ionization rate with a carbon target is 10 times larger than that with cross-linked polyethylene, so the ionization rate seems to vary so much with target materials. It is important to select the target materials from the point of view of the ionization rate. As mentioned above, one of the problems is to select a target which satisfies conditions (l)-(4). 5. Conclusions The results obtained in this experiment are as follows: (1) When cross-linked polyethylene is used as a target, the ion density increases with laser energy and the electrostatic separation is not achieved completely and the conversion efficiency in the PDC ^3max has a maximum value at some laser energy. (2) The ionization rate of the plasma increases with laser energy. The ionization rate of the plasma at the laser energy of 7.0J is 67.1% using carbon target and 5.9% using cross-linked polyethylene target. (3) Heavy materials are expected to be good targets. (4) The rh-t]jmax increases with laser energy using a carbon target. REFERENCES [1] Horii, K. (1972) Bulletin of The Electro-technical Laboratory, 36, p. 279. [2] Kuriki, K. et al. (1981) Technical Report of the Institute of Space and Aeronautical Science, University of Tokyo, 17, p. 287. [3] Yamabe, C. et al. (1985) Proceedings of The Fourth ISAS Space Energy Symposium, p. 15. [4] Yamabe, C. et al. (1985) Space Solar Power Review, 5, p. 333. [5] Yamauchi, M., Homma, H. et al. (1986) Papers of Technical Meeting on Plasma (IEE, Japan, EP-86-37). [6] Homma, H., Yamauchi, M. et al. (1986) Proceedings of the Meeting of Tokai Branch of IEE, Japan, p. 22. [7] Yamauchi, M., Homma, H., Nakamura, T., Yamabe, C. & Horii, K., The Review of Laser Engineering (accepted for publication).
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