Volume 69, Issue 7, July 1998
Index of content:
69(1998); http://dx.doi.org/10.1063/1.1148981View Description Hide Description
A new technique of gaining optical access to the large volume, high pressure environment using optical fibers is reported. High pressure experiments of light transmission through optical fibers brought out through the gasket region in optically opaque, solid medium cubic anvil pressure cells have been performed in a large volume cubic apparatus. Photographic records of the transmitted light signal, taken at constant pressure settings, demonstrate optical continuity up to pressures of 12 kbar on metal tube-encased fibers. Progressive degradation in light intensity is observed with increasing pressure. Time exposure photographs taken during loading track the movement of the fiber in the gasket during extrusion. At pressures above 14 kbar, the maximum pressure of optical continuity through a fiber in this study, microbending of the fiber in the gasket region causes fracture and termination of the optical path.
Transfer of samples between separated ultrahigh vacuum instruments for semiconductor surface studies69(1998); http://dx.doi.org/10.1063/1.1148982View Description Hide Description
A simple, portable ultrahigh vacuum (UHV) chamber is described to transport samples prepared in a molecular beam epitaxy machine to a photoelectron spectrometer for surface studies of III-V semiconductors. Special care is devoted to maintain UHV conditions during the sample transfer and to remove possible sources of contamination, especially by degassing the chamber joint exposed to air during the transport. Low energy electron diffractionpatterns taken before and after transport, subsequent x-ray photoelectron spectroscopy tests of surface purity, as well as the observed dispersion curve of GaAs (001) superstructure confirm that method of transport does not cause significant (detectable) surface contamination.
69(1998); http://dx.doi.org/10.1063/1.1148983View Description Hide Description
The centrifuge hydrogen pellet injection system at ASDEX Upgrade was extended for inboard launching. Successful and efficient inboard pellet refueling was realized up to pellet velocities of about 400 m/s. In order to achieve maximum available pellet particle rates of the system still at the low centrifuge revolution needed in this velocity range, the injector has been modified. Thus, operational conditions have been developed yielding the potential to inject pellets at rather low speed but high repetition rate. Since pellets injected from the inboard are obviously not hampered by the low velocity but show better performance than fast pellets injected from the outside, this scheme seems to allow for an efficient and flexible particle refueling of hot plasmas. The system is now capable of launching pellet series at rates up to 60 Hz at a speed of 240 m/s. With the biggest available pellet size, this enables a pellet particle flux of
69(1998); http://dx.doi.org/10.1063/1.1148984View Description Hide Description
A simple spot-welding apparatus has been developed for the fabrication of stable electrodes used in the measurement of transport properties in condensed matter physics. The apparatus is especially suited for the use of brittle and small sized samples of rare-earth intermetallic compounds (REICs). The spot welding is made by a sharp pulse (150 A and several μs), generated by the precise time generation IC in a capacitor discharge circuit, to avoid breaking the sample. Stable electrodes of six 15 μ Au wires can be made on a REIC sample with length less than 1 mm.