is about 100°C and that of carbon (graphite) is about 35OO°C. So the ionization rate of cross-linked polyethylene is small because many neutral particles are vaporized by the laser beam before the ionized plasma is produced. The ionization rate of plasma is needed to be large because the PDC does not convert the kinetic energy of neutral particles. 4. Considerations of Targets and Laser-produced Plasma Carbon and cross-linked polyethylene are used as targets in this experiment. We now consider, from the experimental results, what is the best target for this energy converter from laser energy to electricity. As is described in 3.1, it is better that the ion density be small because the Debye length should be large to separate the ions and electrons electrostatically in the PDC. In other words, if there are two kinds of plasma and each plasma has the same ion kinetic energy, it is better that the ion density is small for the electrostatic separation. Therefore a desirable plasma is considered to satisfy the following conditions: (1) ion density is small; (2) mass of an ion is large; (3) velocity of ions is large. (2) and (3) are given because such plasma has the same kinetic energy with smaller ion density. The ions of the plasma produced with carbon target are only carbon ions, and it is supposed that in the plasma produced with cross-linked polyethylene there are carbon ions and hydrogen ions in the ratio of 1 to 2. A hydrogen ion is almost 10 times lighter than that of a carbon ion. So it is supposed enough that there are a lot of light hydrogen ions in the plasma produced with cross-linked polyethylene. Fig. 12 shows
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