The origins of electrons and ions in uranium vapor generated by electron-beam evaporation have been determined. Measurements were made for the electron emission current due to high-energy electron-beam irradiation on a uranium surface (backscattered electrons, etc.), thermionic emission current from the melt surface, and electron current due to vapor ionization. Comparison of these currents confirmed that vapor ionization was the main electron generation process at evaporation surface temperatures above 2200 K. The ionized vapor formed a weakly ionized plasma of very low electron temperature: The degree of ionization ≤1%, electron temperature ≤0.3 eV. The electron-impact ionization process contributed mainly to plasma formation. Beam electrons, their backscattered electrons, and secondary electrons from the beam-irradiated uranium surface were the source electrons for this process. Thermal ionization was the next major process. In addition to the plasma formation model, plasma behavior in vapor was described by a one-dimensional symmetric expansion model. The calculated degree of ionization was in good agreement with the measured value over a wide range of evaporation temperatures and electron-beam currents.

Articles you may be interested inDevelopment of flexible array eddy current probes for complex geometries and inspection of magnetic parts using magnetic sensors AIP Conf.ABSTRACT. We developed a signal evaluation system of flexible array eddy current testing (ECT) probes for inspecting complexly shaped metal surfaces. Our probes employ excitation and pickup coil pairs arrayed on a bendable substrate to measure curved targets. Since the developed probes produce signals due to the change in the relative position between the coil pair, an evaluation module for flaw signal identification is integrated into the system. The identification utilizes signal phase combination of the coil pairs. It is represented as a two-dimensional diagram constituting the phase values of two of the coil pairs with different positions. The phase of signals around flaws is significantly affected by their orientations. The diagram is therefore capable of separating flaw information from other information and of imaging flaw positions. We applied the system to complex geometric mock-ups. Flaw signals were successfully identified and the images obtained for identified positions could be used to efficiently measure the length of surface flaws by the 12 decibel down method.

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