neutralization condition is satisfied, wc=Ln,Z where nt is the ion density, so S«,Z ( = «,, if Z=1 is assumed) is used instead of ne to calculate ad. The electron temperature Te is about lOeV for both cross-linked polyethylene and carbon target. Fig. 10 shows the dependence of the ion density on the laser energy. The crosslinked polyethylene plasma is not easily separated electrostatically because the ion density for the cross-linked polyethylene target is larger than that of the carbon as shown in Fig. 10 and the Debye length for the cross-linked polyethylene target is smaller than that of the carbon target. The relation between the conversion efficiency and the Debye length XD is shown in Table I. The ^3max is 40.8% (AD//=3.55) and 41.0% (zD/Z=3.38) at the laser energy 5.7J and 7.0J respectively. The r)3max varies little because XD/l is almost the same. But r]3max decreases when the laser energy is increased more because the ion density becomes larger and electrostatic separation is not as effective. So, the maximum efficiency of i]Jmax=333% is obtained for 2D/Z=2.86 at the laser energy of 7.6J. The properties of t]rri3max mentioned above are obtained because r]3max decreases in this manner.
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