The tokamak with the aspect ratio less than 2 is called spherical tokamak (ST), since the plasma is naturally elongated and has a spherical shape. It is being theoretically and experimentally shown that ST has a high potential to confine the very high beta plasma (beta=plasma pressure/magnetic pressure). The blanket module can be easily replaced in ST. If the internal transport barrier and the high bootstrap current fraction are established in ST, the economical fusion reactor would be more realistic.

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We describe the sparkover voltage and time (V-t) characteristics and the discharge development process in SF₆ at 0.1MPa for quasi-uniform field gaps with steep-front square impulse and fast-oscillating impulse voltages. A square impulse voltage has a very short rise time of 20ns and a fast oscillating impulse voltage has a frequency of approximately 30MHz and rise time of 20ns. Both impulse voltages can be generated up to 10µs. Optical observation in the test gap clarifies the discharge development process. We discuss the difference in discharge development for the square and oscillating impulse voltages.

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The influence of non-axisymmetric instabilities, specifically the n=1 toroidal mode, was studied on the magnetic flux contours that are numerically reconstructed by use of magnetic field profiles measured in Proto-TS-4 device. The device has a cylindrical vacuum vessel with a couple of coaxial magnetized plasma guns at both ends and a magnetic flux conserver with a side axial length of 600mm and a diameter of 940mm. The main measurement system consists of a 2-dimensional magnetic probe array on the poloidal plane(r-z plane) with two components, B_z and B_t(total 84 channel pick-up coils). The B_z field data are used to reconstruct the poloidal magnetic surfaces(Ψ) on the assumption that plasma configuration has axisymmetry. In this study, deformation of the reconstructed flux contours has been studied particularly when the plasma configurations were subjected to a macroscopic instability, specifically n=1 toroidal mode instability. The influence of this component on the reconstructed contours was analytically calculated and the results were qualitatively compared with the contours experimentally observed. Types of n=1 error, namely, shift or tilt, on the reconstructed magnetic surface were also qualitatively discussed.

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We propose a high speed iris detection method for man-machine interface. In order to communicate between humans and computers comfortably, it is required that high speed processing and adapting the changes of the face direction and the individual variation of the face. Our iris detection method consists of a face detection function, a facial parts extraction function and an iris detection function. The face detection function adapts to individual variation or a light condition by using standard skin color method which decides the standard skin color by a color histogram every frame. The facial parts extraction function adapts to changes of face direction and the individual variation in order to by using the hybrid template matching which consists the four directional features field and the color different features. The iris detection function performs high speed and stable detection by segmentation of iris region using color information and the Hough transform. We conducted the comparison experiment with our past method which uses the least approximation method. By this result, processing time of our method realized equivalent to our past method. In addition, accuracy rate of iris detection with our method improved.

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The characteristics of the torch plasma exposed to the crosswind, varying from 0 to 11000 cm/s, have been investigated. The torch plasma behavior was observed and the arc voltage was measured. The voltage gradient of the torch plasma increased with increasing velocity of the crosswind. The results suggest that the augmentation of the voltage gradient was considered mainly as the influence of the cooling effect caused by the crosswind.

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Following two previous papers on the comparative studies of the electron density distributions for a single compact torus (CT) and a spherical tokamak (ST), and for the a single ST and a merged ST, a comparative study on the dynamics of the electron density profile during and after the CT and ST plasma merging process was performed. The sharpness of the peak in the electron density profile around the mid-plane just after the merging of CT with a low safety factor (q value) such as RFP or spheromak is found to be related to the speed of the magnetic axis during the plasma merging process. It is also found that the electron density gradient near the plasma edge in a high q ST is larger than that of a low q CT. High q ST is found to be provided with the magnetic structure which is able to sustain a large thermal pressure by a strong j×B force. Despite these differences in the electron density profile between CT and ST during merging, the confinement characteristics evaluated from the number of electrons confined within the magnetic separatrix after the completion of the merging is almost similar between in the merging CT and in the merging ST. For all configurations, the electron density profiles after the completion of the merging are analogous to those of the corresponding single configuration produced without the merging process.

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A new type of ozone generator using a micro hollow cathode discharge has been developed and evaluated on its operating characteristics. The electrode system consists of two thin metal cathodes and a ceramic spacer with a center hole of a few 100 µm diameter. By feeding high- pressure oxygen gas through the center hole, the residence time of the oxygen gas within the discharge space decreases to the order of micro second. The ozone generation efficiency increases up to 45 g/kWh at the ozone concentration of 7.6 g/Nm³ without any cooling systems. In this ozone generating system, the ozone decomposition mechanisms such as electron impacts and the heat rise of oxygen gas are effectively removed by decreasing the gas-residence time.

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When a solid insulator is exposed to a high electric field in vacuum, electrons released from the triple junction at the cathode collide with the insulator and charge up its surface through an electron hopping process called the Secondary Emission Electron Avalanche (SEEA) mechanism.The process ultimately reaches an equilibrium state of charging.In a recent study, we have clarified that roughening the surface obstructs the charging since it provides a barrier against electrons in the hopping process. In this study, we apply this result to set the charging within a limited region on the surface of an insulator. That is, we have mechanically processed the surface of a cylindrical insulator into smooth and rough regions. By observing the charging with an electrostatic probe and an optical method, we show that electrification concentrates on the smooth region. In addition, we have succeeded in controlling the path of the flashover successive to the charging. The controlling method will help us to conduct further studies on the flashover mechanism in vacuum.

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An experiment on the Plasma-Based Ion Implantation (PBII) has been performed using a trench-shape model electrode in order to clarify the geometrical effect of the workpiece on the ion sheath dynamics and on the spatial distribution of ions incident upon the workpiece. The ion current (which includes the secondary electron current) is measured on the top, side and bottom surfaces of the electrode simultaneously. The condition for the trench not to be filled with the ion sheath is derived analytically by applying the model of cylindrical sheath evolution. Experimental observations show good consistency with this condition ; that is, the sheath is formed along the inner surface of the trench without the sheath overlapping and almost the same amount of ion flux is detected on the top, side and bottom surfaces if the condition is satisfied. Furthermore, the trench-shape electrode is found to require much longer time period than the planar one for the initial plasma density distribution to be recovered after the voltage pulse is terminated. This suggests that the geometry of the workpiece affects the maximum repetition rate and therefore the efficiency of PBII.

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The correlation between electrical degradation and valence states of additives in the Bi₂O₃ and MnO₂(Bi-MnO₂) or Mn₂O₃(Bi-Mn₂O₃) added ZnO varistors and Bi₂O₃ and CoO(Bi-CoO) or Co₃O₄(Bi-Co₃O₄) added varistors was investigated by ICTS and XPS measurements. The results of ICTS and XPS measurements showed that Mn as the additive contributes differently to the factors of degradation in the cases of Bi-MnO₂ and Bi-Mn₂O₃ added ZnO and Co as the additive contributes similarly to the factors of degradation in the cases of Bi-CoO and Bi-Co₃O₄ added ZnO. The recovery of varistor characteristics of Bi-Mn-Co added ZnO added Co₃O₄ after degradation was more remarkable than that of the sample added CoO by the thermal annealing. The results of ICTS measurements showed that the interface states changed for Bi-Mn-Co added ZnO after the thermal annealing. XPS spectra of the Co-2p_3/2 orbit and Mn-2p_3/2 orbit for Bi-Mn-Co added ZnO showed different binding energies after degradation.

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It was found that carbon with an extremely steady characteristic can be obtained by baking the furan resin, one sort of thermoset high polymer in the condition of 3-4°C/h up to 200°C and 7-8°C/ h above 200°C respectively in N₂ gas and He gas atmosphere. Relatively few researches have been done so far of the high molecule carbon as a bulk material such as the one we did. The application as an industrial material can be expected by further elucidation of physical properties. We are trying its material as one or two of applications, the one is useful for long life impact printing types as the high-speed computer-printer. In this report, we will report on the relationship between the baking temperature and the surface hardness as well as the baking temperature and superior wear resistance as part of study for the improvement and completion of the material. The surface hardness of carbonized furan resin is reinforced in proportion to the baking temperature from 500°C to 1250°C, and indicated the maximum at 1250°C. Its hardness indicated 429 at H_V, and 449 at H_K. Wear resistance is increased between 500°C-1250°C.

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Dissolved water in insulating liquid had been regarded as a kind of impurities that deteriorate electrical properties. Recently, the state and the behavior of water molecules in liquid were measured by IR method. And it had been analyzed where water molecules bond around dielectric molecule and how many molecules gather around polar base among the alkyl chain. The transformer oil consists of saturated hydrocarbons that are composed of the various length of alkyl chain. So in the case that hydrocarbon molecules include the polar base such as carbonyl group and ketonic group because of aging and oxidizing, it should be cared that water cluster interact with not only polar groups but also hydrophobic groups. In this paper, water was dissolved in ketonic compound with various length of alkyl chain. The effects of hydrophobic groups on the ratio of water clusters and on the conduction of water cluster were discussed. As a result, when the alkyl chain of ketonic compound become long, the ratio of small water clusters such as dimer and trimmer decreased. And the result from the relationship between the ratio of water clusters and the conductivity, it was appeared that the small water cluster contribute to increase of conductivity.

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In order to clarify the mechanisms of partial discharge (PD) and tree degradation, PD characteristics of an artificially-simulated tree channel in low-density polyethylene (LDPE) were investigated. During the application of AC voltage, new tree channels were formed at the tip of the artificial channel. PD characteristics of an artificial channel with 2 mm in length and 30 µm in diameter remarkably changed after the inception of very small trees. After the tree inception, the number of PD pulses increased and light emission due to PD extended to a whole channel and new tree channel. A few minutes after the tree inception, the number of negative PD pulses decreased and its magnitude became large. These results suggest the change in PD mechanism by tree inception and tree propagation. From these results, the mechanisms of PD in a tree channel and tree propagation were discussed. These results are applicable to insulation diagnosis.

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Nitrogen doped carbon film has been grown on silicon substrate at temperature of 60 degrees in the methanol-ammonia solution. The substrate was negatively biased with a dc potential less than 100 V for current density of 4 mA/cm² as constant-current electrolysis. The work function and the resistivity of the film decreased remarkably. From the results of Raman spectra and X-ray photoelectron spectroscopy, it was also confirmed that the film is amorphous containing only small amounts of diamond component, and nitrogen atoms are doped in the film though containing some organic residue.

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