Study of the strong electrostatic fields leaved after an interaction between an intense electron beam and plasma

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Langmuir wave becomes unstable at the large amplitude, and possibly produces a number of localized wave packets of Langmuir wave, which is called a caviton. The nonlinear properties are investigated strongly in the theory of the strong Langmuir turbulent. Generally, measurements of the electric field is difficult, and the 3-dimensional structure of the caviton which is predicted from the theory is not revealed well. The purpose of this research is to study such turbulence field using electron-beam probing-technique. The diagnosis is well known as a method to measure un-known electric field from deflection of the trajectory of a probing beam. Usually a well-focused parallel beam is used for this purpose, and we employed this type of beam for previous experiments. Our study showed difficulties of the method, because the observed deflections could not be attributed only to the caviton fields but other mechanisms. Large ambiguities were left there.At first, the technical problems, that deg … More rade the quality of the data, are solved. It makes possible to detect a probing beam that has much lower density, and raise the reliability of the measurement, and give another possibility. Second, a shadowgraph technique using an electron beam is tried. This is first report to apply the technique for diagnostic. An employment of a large diameter probing-beam makes it possible to detect the special distribution of the deflection. Many bubbles were found in the beam pattern images. It is apparent that a sophisticated field, which is like the one expected from the turbulent theory, exists in our plasma. The averaged size of babbles is change by the plasma density and is estimated about 20 times of the Debye-length in the experiment. On the other side, a theoretical investigation pointed out the fact that the deflection angle becomes prominent only when the cavitons are at final stage of the collapse. It is possible to explain why the small babbles are observed in the experiment, though the turbulent theory says the population of the caviton with larger size is expected to be higher. Less