Chikahisa Honda

Surface Degradation of Silicone Rubber Exposed to Corona Discharge

This paper describes the surface degradation of unfilled high-temperature vulcanized silicone rubber (HTV-SR) resulting from creeping corona discharges under atmospheric pressure. In this paper, HTV-SR specimens were exposed to corona stress generated by a parallel needle-plate electrode system; furthermore, physicochemical analyses were conducted on the surface layer of SR before and after corona discharge treatment. The results showed that the plasma impingement from the corona discharge can cause physical and chemical damages to the SR surface. In addition, it was demonstrated that instead of hydrophobic CH 3 groups, hydrophilic OH groups that are by-products of aging may be formed on the surface of aged SR; furthermore, the corona discharge plays an important role in the loss of hydrophobicity

Evaluation of insulation performance of polymeric surface using a novel separation technique of leakage current

This paper describes a novel method to separate the leakage current, obtained in polymeric materials during a salt fog aging test, into three components of conductive current, corona discharge current and dry band arc discharge current. First, we investigated that the relationship between optical emissions due to discharges and a leakage current. Based on experimentally defined discharge types, the separation of the leakage current was carried out. Finally, the polymer surface was analyzed using an electron spectroscopy for chemical analysis (ESCA), and the change in the polymeric constituents was evaluated. The results showed that the cumulative charges due to the dry band arc discharge and the corona discharge to the total charge were about 20 and 10%, respectively. It was also found that a high temperature vulcanized (HTV) silicone rubber could retain its insulation performance better than a room temperature vulcanized (RTV).

Mechanism for change in leakage current waveform on a wet silicone rubber surface-a study using a dynamic 3-D model

This paper describes the results of experiments and simulations made to examine the waveform of leakage current flowing through the surface of HTV (high temperature vulcanized) silicone rubber specimen exposed to clean fog. Water droplets were placed on the surface of specimen energized with AC voltage and investigations of the surface state were done by a high-speed video camera in a wet condition produced by sprayed clean fog. Simultaneously, according to the experimental condition, a dynamic 3-D model was built to calculate the electric field and current density distribution on the specimen surface by a finite element software. A conducting water layer is formed due to the deformation of droplets and the development of dry band arcing. This caused large distortion and nonlinearly which increased the odd harmonic components in the leakage current waveform. This is in good agreement with the simulating calculation. The information from the leakage current frequency characteristic was extracted and correlated with the insulation surface condition. It can be considered as a diagnostic index for electrical characteristics and insulation state of polymer insulators in the wet condition.

Electrohydrodynamic behaviour of water droplet on an electrically stressed hydrophobic surface

This paper describes the electrification characteristics of water droplets on a hydrophobic surface and their influence on the induced discharge in an ac electric field. Tests were conducted by placing water droplets with different conductivities and volumes on an electrically stressed silicone rubber (SR) sheet, and their electrohydrodynamic behaviours were observed using a high-speed video camera. It is demonstrated that a locally high electric field at the tip of a droplet can trigger corona discharges, and droplets are always charged negatively during a corona discharge process. The deposited droplets are deformed and synchronized with the ac field. Once the deformation becomes noticeable, it increases rapidly until the droplet becomes mechanically unstable and ejects water filaments from its vertices. This can bridge the electrode gap and result in a flashover. In addition, the volume and conductivity of the water droplets have a marked effect on the mode of corona discharge and flashover development.

Investigation of the thermalization of sputtered atoms in a magnetron discharge using laser‐induced fluorescence

The thermalization of sputtered atoms in a magnetron discharge was investigated using laser‐induced fluorescence. The results clearly indicated for the first time that the velocity distribution agrees well with the Thompson formula [M. W. Thompson, Philos. Mag. 18, 377 (1968)] for d/λ≪1, while a thermalized component becomes appreciable for d/λ≳1, where d is the distance from the cathode surface and λ is the mean free path of sputtered atoms for collisions with filling gas atoms.

Experimental and numerical analyses of electron temperature and density distributions in a magnetic neutral loop discharge plasma

In order to study the plasma structure and its application to processing, experimental and numerical analyses of the distribution of the electron temperature (Te) and electron density (ne) in a neutral loop discharge (NLD) plasma were performed. From the experiments, NLD plasma possesses Te and ne peaks. In the cases of NL radii of RNL=80, 100, and 120 mm, the maximum values measured for Te were around the NL. However, the ne peaks of the cases mentioned were located about 30–40 mm radially inward of the NL. We calculated the electron behavior in three dimensions to analyze these measured results, taking into consideration the actual experimental conditions such as the magnetic field, antenna position, and chamber walls. We found electrons are trapped in a region that is more inward of the NL due to a mirror field that causes the peak of ne. Also it is shown that good plasma uniformity could be obtained by dynamically controlling these Te and ne peaks.

Transient Change in the Velocity Distribution Functions of Sputtered Atoms during Initial Dose in Ion-Beam Bombardment

Velocity distribution functions of sputtered iron-atoms under argon-ion bombardment were directly measured with a rapid-frequency-scan dye laser. Each measured profile was fitted with the Thompson formula, and an equivalent surface binding energy was estimated at each ion dose. The surface binding energy thus obtained was near the formation energy of iron in iron oxides at a low ion dose (less than 1×1019 ions/m2), but approached the sublimation energy of a pure iron above 5×1019 ions/m2.

Water absorption, hydrophobicity characteristics and surface change of polymer

This paper describes the weight change of alumina trihydrate filled silicone rubbers during a water absorption process and the surface changes involved. The weight changes for some samples were particularly examined after being dipped in warm water (20/spl sim/80/spl deg/C). Worthwhile results are obtained as follows. For the individual samples, it was found that the rates of weight change increased with increasing temperature. It is understood that silicone oil in the samples soaked in hot water of 80/spl deg/C for 500 hours begins to be dissolved from basic silicone polymers. Thus the rate of the change in weight decreases in comparison with the virgin sample with time. Because the binding energy of Si-C (4.5 eV) is lower than that of Si-O (8.3 eV), Si-C is broken more easily due to heating, and a remarkable decrease of Si-CH/sub 3/ was observed after being dipped in warm water.

Laser diagnostics of edge plasmas and laser diagnostics of plasmas for industrial applications (invited)

In plasma physics, laser diagnostics were first developed to probe the core region of magnetically confined high‐temperature plasmas, but the advent of various new lasers has turned out to be useful for edge plasma studies. The recent developments of various arc and glow discharges for industrial plasma applications have required measurement of the same quantities as in the edge plasma studies and expertise in the latter has been fully exploited for the former. The experience thus gained has then been used for the advantage in the studies of edge plasma behavior in high‐temperature plasmas. The interplay of these two fields of plasma studies, where laser diagnostics of plasmas (which we call ‘‘laser‐aided plasma diagnostics’’) is extensively used, is discussed.

Transient local magnetic field measurement in a bumpy torus by rapid‐frequency‐scan laser spectroscopy

A new technique for local magnetic field measurement in a bumpy torus NBT‐1M (which is a magnetic plasma confinement device) has been developed using a rapid‐frequency‐scan (RAFS) laser system combined with sodium atomic beam probing. The RAFS laser beam excites the sodium D1 transition in the plasma cavity, and the Zeeman pattern is determined with laser fluorescence spectroscopy in a single laser shot. From the Zeeman splitting, the transient magnetic field distribution in the plasma, produced by electron cyclotron resonance heating (ECH), is measured with an accuracy of ±3.2%, a spatial resolution of 5 mm, and a temporal resolution of 5 μs.