position. The current in the magnetic coil builds up to maximum at about 0.8 ms and decreases to 1/e at 2 ms. The laser is synchronized to irradiate the target with the maximum of the magnetic field. The receiving diameter of the PDC is 4 cm and its grid has about 40% transmittance with 400 meshes per inch. The resistance of 1 kfl is used as a collector load. As the shape of the magnetic coil is desired to be conical because the expansion plasma is forced to have one direction (i.e., normal to the PDC) after reflection at the magnetic wall. The distance between the PDC and the target is set at 30 cm to avoid the influence of the end of the coil. 5. EXPERIMENTAL RESULTS The output waveforms of the PDC are shown in Figs. 7(a) and 7(b) for both cases without and with magnetic field. The peak of the output voltage increases and the duration of the waveform is also longer with the magnetic field. In the case of no magnetic field, it seems that a large part of the produced plasma runs away to the R-direction and the ions cannot be collected by the collector. But, on the contrary, with magnetic field, the plasma is reflected at the magnetic wall and some of them are introduced to the collector. The dependence of magnetic field of the converter output is shown in Fig. 8. The converter output with the magnetic current of lb ~ 1150 A (this corresponds to B ~ 0.08 T is about thirty times larger than that of lb=Q. When the converter whose effective diameter is increased from 4 to 22 cm is set at 50 cm in front of the target, the output of the converter of about 2x 10 4 J(~8.2 W) has been obtained at Vc ~ 50 V. In this case, the conversion efficiency of the PDC is about 0.07%. As the conversion efficiency is too small, a multistage Venetian blind direct energy converter (1) has to be used considering the spread of the energy distribution of the incident ions. The detailed experimental results of the parameters of the produced plasma, its behavior and the output characteristics of the PDC will be reported in other papers (6,12). As the efficiency of the electrostatic separation is not good in the high density plasma, the expansion distance of the plasma has to be made long and the plasma density must be low enough to separate the ions from the electrons effectively. (1) The converter output increases up to about thirty times by surface magnetic confinement. But, in this case, the energy for the generation of the magentic field is very large compared with the converter output, and so the total efficiency decreases. Surface magnetic confinement is expected to be used in the large- scale device in the future. (2) When the effective diameter of the converter is increased from 4 to 22 cm, the converter output increases up to about 1300 times without the magnetic confinement. CONCLUSION The characteristics of power transmission using a laser beam has been described, and a fundamental study in which we have turned our attention to only the direct energy converter from laster energy to electricity has been done. The obtained results are as follows.
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