Takehisa Shibuya

Observation of molecular assisted recombination via negative ions formation in a divertor plasma simulator, TPDSHEET-IV

Abstract Molecular assisted recombination (MAR) via negative ions formation has been observed in a linear plasma simulator. A small amount of hydrogen gas puffed into a hydrogen plasma strongly reduced the heat flux to the target and rapidly increased the density of negative ions of hydrogen atom, n H − , in the circumference of the plasma, while the conventional radiative and three-body recombination processes disappeared. n H − is localized in the outer region where electrons exist ( n e ∼5×10 17 m −3 , T e =3–5 eV). The peak value of n H − is 1.2×10 17 m −3 and the ratio of n H − / n e in the outer region goes up to over 20%. These results can be well explained by taking the mutual neutralization between the negative and positive ions of MAR in the detached plasma into account.

Ion source with plasma cathode for ion assisted deposition

Abstract An ion source with a plasma cathode has been developed to attain a long lifetime for oxygen ion production. In this ion source, a plasma of a nonreactive working gas serves as a cathode in place of a thermionic tungsten hot cathode used in the Kaufman ion source. This ion source consists of two compartments, i.e. a plasma generator provided with a metallic hot cathode and a plasma chamber interconnected by a narrow tapered duct. The pressure difference between the two parts made by differential pumping prevents the feed gas supplied to the plasma chamber from flowing into the plasma generator. Mass spectrometry results show that this ion source has the ability of generating a considerable amount of O+ ions. This ion source is also eminently suitable for oxygen ion production.

Production of oxygen plasmas using radio-frequency magnetron-discharge

Abstract A new type of oxygen ion source has been developed in order to substantially prolong the lifetime of a conventional oxygen ion source for various plasma processes. In this ion source, an oxygen plasma is produced by coupling a 13.56 MHz radio-frequency (rf) field to a pair of rf electrodes placed in the region of a line cusp field. Two electrodes are positioned in such a way that accelerated electrons undergo magnetron type motion around them, efficiently producing a plasma around the electrodes (rf magnetron discharge). This plasma diffuses along the magnetic field line into the center region of the cusp field where the field strength is almost nil. The above process makes it possible to produce a large volume of uniform plasma. As a result, extraction of a large area oxygen-ion-beam from the new ion source is relatively easy. The lifetime of this ion source is virtually limitless, because it does not have any corrosive parts, such as a hot filament. The new ion source can be used with any kind of reactive gases as well as oxygen.

Plasma filament ion source for high current implanter

Abstract A plasma filament ion source has been developed as a long lifetime ion source for use in ion implanters. In this ion source, a plasma filament replaces a conventional metallic filament used in a Freeman type ion source. This ion source consists of two compartments, i.e. a plasma generator and an ion source chamber interconnected by a tapered narrow duct. The pressure difference between the two parts made by differential pumping prevents the feed gas from flowing into the plasma generator. With any combination of a plasma filament of either argon or neon and a feed gas of either AsF 5 or PF 5 , the lifetime was found to be more than 90 h with an extraction voltage of 40 kV and a corresponding ion current density of 20 mA/cm 2 ; a considerable amount of As + and P + ions were observed in mass spectra. This ion source is eminently suitable for oxygen ion production and useful for realizing a full cryopumping ion implanter system.

Application of photo-doping phenomenon in amorphous chalcogenide GeS2 film to optical device

Photodoping phenomenon is observed when a double-layer consisting of an amorphous chalcogenide film (As2S3, GeS2, GeSe2 etc.) and a metal (Ag, Cu etc.) film is illuminated by light. The metal diffuses abnormally into the amorphous chalcogenide layer. Amorphous chalcogenide films of GeS2 with an Ag over layer exhibited large increase of refractive index through the abnormal doping of Ag by irradiating the light around the absorption edge of the GeS2 chalcogenide. In this study, we aimed the application of this effect for the fabrication of optical devices and fabricated various micro doped patterns by using a laser beam. Mask less pattering with refractive index modified films are possible by manipulating the scanning of the laser beam. Micro gratings were fabricated using a confocal laser microscope to work as both fabrication and observation system. Waveguides were also fabricated by scanning the laser beam for photodoping. Holographic gratings were fabricated by utilizing the photodoping of the two beam interference pattern, which showed the possibility to produce large scale optical devices or mass production.

Development of Lighting System for Hologram Using High Power LEDs

LED became popular rapidly by the appearance of blue LED. In this study, we aim to fabricate the illumination system using high brightness LED for the hologram illumination instead of the conventional halogen lamp.

Emissive probe measurement of electron temperature in recombining plasma produced in the linear divertor simulator TPD-II

Abstract Emissive probe (EP) measurement of the electron temperature Te, which was proposed by Shindo et al. [Rev. Sci. Instrum. 59 (1988) 2002] is applied to the measurement of Te in the detached recombining plasma produced in the linear divertor simulator. In the determination of Te by the EP method, we consider application limits based on the space-charge-limit effect studied by Ye and Takamura [Phys. Plasmas 7 (2000) 3457]. We have observed that as neutral pressure is increased for developing the plasma detachment, Te obtained with the EP decreases from a few eV to 0.4 eV, on the other hand, the Langmuir probe (LP) method gives anomalously high Te of 3–9 eV. The EP method yields more reliable value of Te than the LP method does. The electron temperature obtained through the spectroscopic method is also shown.

Holography for physics education in universities and colleges

Fundamental experiment of holographic memory was carried out for university students to understand thebasic concept of the memory as a large format storge method of next generation. We performed holographic data recording experiment using simple two beam optical systems. Multiple recording to enhance storage capacity was also successfully performed.

Control of the well-type radial potential profile in the magnetized plasma flow produced by a dc discharge

The control of the well-type radial potential profile in a dc plasma by applying bias potential, VE, to the end plate is investigated experimentally. The experimental evidence that a plasma space potential, Φp, increases at the circumference of the plasma with the increase of VE is interpreted qualitatively by the experimental results of the current drawn by the segmented end plate, and of the relationship of Φp to VE. For the dc discharge the value of Φp at the center of the plasma is naturally settled on the value somewhat lower than the anode potential, the electron sheath therefore appears in front of the end plate and expands radially as VE is increased. Electrons are drawn from the circumference of the plasma to the end plate, inducing the nonambipolar radial electron flux. Since the cross-field electron mobility is not sufficiently large, the inwardly directed radial electric field becomes stronger. The role of electron sheath formed is crucial in actively controlling the radial potential profile i...

Plasma cathode oxygen‐ion source

A plasma cathode ion source has been developed to attain a long lifetime in oxygen‐ion production. In this ion source, a plasma of a nonreactive gas serves as a cathode in place of a thermionic tungsten hot cathode used in the conventional Kaufman ion source. An anode ring with an annular slit mounted on the top of the ion source contributes to raising spatial uniformity in the ion current density. At 15 cm from the top of the ion source, a current density of 680 μA/cm2 was obtained with a value of 0.85 for the uniformity (defined as the ratio of the lowest density to the highest) in an area of 15 cm diameter. Mass spectrometry results show that considerable amounts of O+ and O2+ ions, especially of O+ ions, as well as Ar+ ions, are contained in ion beams produced by this source. In an oxygen‐ion production test, the ion source could continuously be operated for 61 h. It was confirmed that the ion energy distribution in the beam can be well controlled by the anode ring voltage. In an experiment of oxygen‐...