One of mechanisms of electron emission under high field is generally known as the Fowler-Nordheim Theory. In this theory, electron emission sources are assumed by the projections where the field strength is multiplied. The nonuniformity of the field strength is expressed by the Field-Enhancement-Factor: β. The β has been used to represent the sharpness of the emission source. However, the electron emission sources are merely imaginary one, because these have not been confirmed visually.
In this study, in order to investigate the field emission more closely, we used the Micro-Channel-Plate (MCP) with luminescent screen anode, and observed the location and behavior with applied time of the emission sources by CCD Camera. As the results, the electron emlssiom cathode was not observed from whole surface uniformmly but from points. It was found that the electrons were emitted from the micro-points located at the metal surface and there are a lot of micro-points at the surface. And, observing the behavior of micro-points with applied voltage time, it was found that the creation and disappearance of micro-points were repeated on the cathode surface. However, almost points do not emit electrons again. Inaddtion, the aging effect of micro-points by electron emission was not confirmed.

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Oxygen-free copper is widely used in such devices as particle acceleraters, satellites, surface analyzers etc. Under ultrahigh vacuum condition electrical breakdown will be influenced by electrode bulk conditions such as gas absorption, impurity contents etc. as well as the electrode surface conditions. Using an in situ electrode surface cleaning system, the vacuum breakdown strength of vacuum degassed oxygen free copper electrodes satisfying ASTM-F-68 specification of Class 1, Class 3 and Class 5 is measured. Breakdown experiments reveal that the conditioning effect of vacuum gap is most significant in Class 1 electrodes. Any Class 1 electrode processings, except for annealing, do not improve the breakdown field at the first voltage application after the processing. The electrode annealing processing in vacuum environment is effective in improving the breakdown field at the first voltage application. It is discussed that the annealing releases the mechanical stresses due to electrode surface shaping.

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Breakdown phenomena in alumina windows for high-power rf use is studied. A multipactor due to high yields of secondary electron emission causes F-center oxygen vacancies of alumina, which induces surface melting. High-purity alumina without micro-porosities or pre-existing F-centers are durable under high-power rf operation. TiN coatings can effecitively suppress the multipactor, when the thickness is optimized so as to reduce secondary electrons and to avoid any excessive heating due to rf loss. The surface discharge observed on the TiN coated surface during higher power operation indicates the electron-trapping in surface defects and the electron avalanche accompanied by luminescence.

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We have studied the effect of ceramics coating on the surface charging of solid insulator in Vacuum by employing Monte Carlo simulation method, in which we analyze the electron multiplication on the surface due to the secondary electron emission process. The simulation consists of a two dimensional field analysis and the analysis of the energy of electrons impinging upon the insulator surface. We firstly discuss variations of the electron energy and the secondary emission rate on ordinary organic insulator (PMMA) and demonstrate the appropriateness of our simulation method, then the charging on coated insulator is analyzed. The insulator is in the shape of a cylinder or a negatively angled conical frustum. The coating with Cr₂O₃ or Al₂O₃ on PMMA insulator has examined. The maximum secondary emission rate of Cr₂O₃ is smaller than 1, however, Al₂O₃ has the rate larger than 6. The simulation for the Cr₂O₃ coated surface shows that only a small part of the cathode side of the surface is charged negative irrespective of the insulator shape. It is found that the density of the negative charge is so high as to make electrons emitted from the cathode junction fly away from the insulator surface. The negative charge on the insulator with Cr₂O₃ thus prohibits interactions between the surface and the electrons from cathode, resulting in reduction of gas desoprion from the surface and in improvement of the insulation ability of the insulator.

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Knowledge of cathode spot motion on a graphite cathode in a vacuum arc deposition apparatus is important for producing a diamond-like carbon film from the view point of droplet suppression. In this paper, the motion of graphite cathode spot is observed and its velocity is measured. The experimental conditions are as follows; cathode dediameter: 64mmφ, hydrogen gas flow rate: 10ml/min, arc current: 50A, pressure: 0.2 and 0.05Pa and magnetic flux density: 3-25mT.
The results are summarized as follows; (1) The cathode spot is driven to retrograde direction by applying radial magnetic field on the cathode surface. (2) The retrograde velocity increases as the magnetic flux density increases and as the pressure decreases. (3) The velocity is less than 10^-2 of that for Ti or Al cathode under the same experimental conditions. (4) When the magnetic flux density exceeds about 8mT, the cathode spot extinguishes on the way of moving or immediately after ignition. (5) The maximum velocities obtainable are 20 and 25mm/s at pressures of 0.2 and 0.05Pa, respectively.
Those measurement results are interpreted as follows; thermoelectronic emission is required for the formation of graphite cathode spot and it takes some time for the surface to be heated up to emit enough electrons. As a result, the velocity is very slow and limited by a certain value.

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Anode mode and arc voltage of Ti cathode N2 vacuum arc are investigated as a function of pressure (10-2-5×102Pa) and arc current (15-150A). New anode mode of luminous surface mode is found and footpoint mode can be steadily realized in this experiment. The following results are obtained. With increasing pressure, anode mode shifts from no-luminous mode to unsteady footpoint mode, steady footpoint mode, luminous surface mode and anode spot mode. As the arc current decreases, the pressure at which the mode shifts decreases.
Plasma parameters in the plasma space between cathode and anode are measured with static electric probes. The following results are obtained. Potential distribution is flat for the no-luminous mode. Anode drop appears for the steady footpoint mode and plasma drop as well as anode drop appears for the luminous surface mode. For the luminous surface mode, electron temperature increases as the electric field increases in the plasma space. From these results, it is considered that the luminance of anode surface is due to the increasing electron temperature in consequence of the increasing electric field near the anode surface.

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Anode phenomena in vacuum arcs are investigated using a cylindrical metal collector surrounding the arc which is generated by a 60 Hz sinusoidal half-wave current (up to 40 kA) in a demauntable vacuum chamber.
Current/voltage characteristics at the collector after anode-spot formation show that positive collector current reverses its direction and floating potential of the collector descends below cathode potential. These findings are attributed to negatively charged carriers flowing from anodic vacuum arc to the collector.
Magnetic mass discrimination between electron and negative metal ion in charge carriers is performed with a circular collector placed in front of a magnetic filter that have a magnetic field strength of about 500 gauss by a pair of permanent magnets. A combined analysis of these studies suggested that a significant amount of negative metal ion is possibly created in the anodic copper vacuum arc.

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A coaxial plasma gun which generates a rapidly rotating plasma in a magnetic field has been developed to improve the plasma centrifuge. It is demonstrated that a magnetic field stronger than a critical value is essential to stabilize the high-current vacuum discharge of the plasma gun and to make the plasma production and acceleration reproducible. For example, the critical field is 250G for the discharge current of 13kA and the anode-cathode spacing of 7.5mm. A model is presented in which the critical field is assumed to be determined from the trapping of ionizing electrons in the annular anode-cathode gap. A qualitative agreement is achieved between the model and experiment.

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The low voltage switching characteristics of a triggered vacuum gap has been investigated experimentally in the range 50 to 2, 500 volts.
Specially, the following items have been examined: (1) effect of minimum firing voltage and switching time on the polarity of the main gap voltage; (2) relation between minimum firing voltage and di/dt of main current; and (3) observation of cathode spots by using high-speedstreak camera.
Furthermore, it has been found that the gap could be triggered as low as 50V with switching time 10μs. Minimum firing voltage and switching time are small with a positive main gap voltage than a negative one. Minimum firing voltage and switching time decrease with increasing di/dt of main current. Minimum firing voltage increases when the duration of trigger current is less than 10μs. In the initial stage of discharge, bright cathode spots are observed on the trigger electrode. With the firing on the anode the light emission accompanying the main discharge differs from that for firing on the cathode.

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Compared with the conventional cold cathodes, such as graphite, hacksaw blades, carbon felt or knife edges, the corona-plasma cathode has been found to be advantageous in vacuum discharge with regard to their lifetime and X-ray emission uniformity. In this paper, we present an experimental result on the characteristics of the flash X-ray source employing a corona-plasma cathode in the relatively low operating voltage range, 20-50kV. A simple, longlifetime and inexpensive corona-plasma cathode X-ray preionization source are achievable operating in low voltage range. We will study about both the discharge characteristics of the tube: (1) the characteristics of the discharge initiation and development, (2) the cross-sectional shape of electron beam, and (3) the velocities of the expanding plasma, and the operational characteristics of the X-ray source: (1) the dependence of X-ray output on both electrode separation and applied voltage, (2) X-ray spatial distribution, and (3) X-ray spectral distribution. These experimental results are also contrasted with a field-emission mode operated with same cathode.

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A pulsed discharge in vacuum accompanies with a X-ray flash. The author has made a trigger initiating discharge vacuum tube, and is now under experiments with it, to produce a single and high energy X-ray flash. In operating the tube, two circuits are needed. They are a main circuit and a triggering circuit. Energy of a X-ray flash is limited by the circuit condition of the main circuit. In step of experiments, the triggering circuit become important. Because the triggering circuit affects to not only the switching time, but also waveform of the X-ray flash. The experimental results are as follows. (1) Uprising of the anode voltage brings a decreasing the rise time and increasing the crest value of the X-ray flash. (2) A smaller capacitance in the triggering circuit leads out a X-ray flash with a shorter rise time. From these results, some discussion was described on a capability of waveform operation of the X-ray flash by controlling the triggering capacitance.

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Experiments of the laser guided discharge in air below 1kPa were carried out by using YAG laser. The pressure of the air is set to be from 10 to 1kPa. The following results are obtained: The laser beam effectively guides the discharge at lower pressures as far as the discharge can appear. For given pressure and voltage, there is an optimum guide distance, which brings the most effective guide by the laser beam. Range of voltages for effective laser guidance becomes narrow as increasing of the air pressure. Minimum voltage for laser guided discharge is a function of a variable defined as (air pressure)×(discharge gap).This function behaves like the Paschen's law for a virtual gas with low electric insulation.

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Silicon wafer is often used for a micromachine because of its excellent mechanical characteristics. However, silicon shows a large adhesive force at a high temperature, so it is predicted that a movement of micromachine would get worse with increase of a temperature. Therefore, it is necessary to understand the effect of the temperature on static friction for silicon wafer and it is also necessary to reduce an adhesive force at a high temperature.
In the present study, static friction coefficients of silicon wafer against silicon wafer, SiO₂ and Al thin films were measured by using a milimeter sized mover at the temperature from 20°C to 200°C. We also measured an adhesive forces of silicon wafer against silicon wafer, SiO₂ and Al thin films with increasing a temperature.
It was found that the static friction coefficient of silicon wafer against silicon wafer was increased with the increase of the temperature. This caused by the increase of the adhesive force between silicon wafers. However, if we depositted an SiO₂ and Al thin films on the surface of a silicon wafer with the thickness over 100nm, the frictional force did not vary the temperature and those showed an almost constant small value.

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PPLP (Polypropylene Laminated Paper) is a prominent insulating material with high dielectric breakdown strength and low dielectric loss, having been actually used for OF cables in EHV/UHV transmission systems. Nevertheless, the dielectric breakdown mechanism of PPLP has not been cleared sufficiently. The work reported here concerns the breakdown studies in oil-impregnated paper systems with a standard 1.2/50μs impulse voltage wave simulating lightning. The effects of PP (Polypropylene) films on the impulse breakdown strength of oil-impregnated PPLP systems were studied, compared with the impulse breakdown mechanism of oil-impregnated kraft paper systems. As a result, this paper emphasizes that concerning the impulse break-down mechanism of laminated oil-impregnated papers, there is a great difference between the cases of including PP films and of being made of kraft papers only. It has been found from the detailed investigation of the experimental results that the positive charges, especially trapped on the surface of the PP films, may be most important factor affecting the impulse breakdown strength. A fundamental and practical suggestion is made from the viewpoints of raising the impulse breakdown strength of the OF cables insulated with PPLP, based on the experimental results.

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