Bibliothek

Notizen: A new simulation method has been developed to investigate the excitation and saturation processes of toroidal Alfvén eigenmodes (TAE modes). The background plasma is described by a magnetohydrodynamic (MHD) fluid model, while the kinetic evolution of energetic alpha particles is followed by the drift kinetic equation. The magnetic fluctuation of n=2 mode develops and saturates at the level of 1.8×10−3 of the equilibrium field when the initial beta of alpha particles is 2% at the magnetic axis. After saturation, the TAE mode amplitude shows an oscillatory behavior with a frequency corresponding to the bounce frequency of the alpha particles trapped by the TAE mode. The decrease of the power transfer rate from the alpha particles to the TAE mode, which is due to the trapped particle effect of a finite-amplitude wave, causes the saturation. From the linear growth rate the saturation level can be estimated. © 1995 American Institute of Physics.

Notizen: Grid power loading in a multistage, multigrid accelerator was calorimetrically measured using the Japan Atomic Energy Institute 400 keV accelerator. This is the first result on the grid power loading in the multistage accelerator. It is turned out that the extracted electrons are effectively suppressed in an extractor. The leakage of the electrons extracted from the source plasma to the first acceleration grid, the second grid and the grounded grid were no more than 0.8%, 0.2%, and nearly zero of the extracted electron current, respectively. Under the optimum beam optics that gives the lowest beam divergence, the power loadings of the acceleration grids were dominated by acceleration of the stripped electrons. At a typical source operating pressure of 0.3 Pa, the power loadings of a first acceleration grid, a second acceleration grid, and a grounder grid were 3.4%, 5.0%, and 2.8% of the total beam power, respectively. From the comparison with the calculated grid power loading, it is found that the stripped electrons can be intercepted by intermediate acceleration grids before fully accelerated. © 1998 American Institute of Physics.

Notizen: The first results of the performance test of the large negative ion source for a JT-60U negative-ion-based neutral beam injector (N-NBI) are presented. The ion source consists of a cesium seeded multicusp plasma generator, where negative ions are produced via volume and surface processes, a 110 cm×45 cm multiaperture extractor, and a three-stage electrostatic accelerator. After negative ion production and voltage holding tests in test stands, the ion source was installed in the N-NBI system and the full power test began. Up to now, the ion source has produced 400 keV, 5.9 A (2.4 MW) D− ion beams, the world highest D− current and beam power, with a pulse duration of 0.1 s. © 1996 American Institute of Physics.

Notizen: The acceleration grid heat load was measured for the first time as a function of the bias voltage, with the source filling gas pressure using a 400 keV three-stage electrostatic accelerator with multi-aperture. The bias voltage dependence shows that leakage of electrons extracted with H− ions to an accelerator is suppressed efficiently in the extractor. The heat load is mainly due to electrons stripped from H− ions at a high source pressure. The heat load due to the stripped electrons could be suppressed effectively by reducing the source pressure. It was confirmed experimentally that reduction of the source pressure is important to suppress the electron acceleration. © 1996 American Institute of Physics.

Notizen: Technologies producing high power negative ion beams have been highly developed over the years at Japan Atomic Energy Research Institute for use in neutral beam injectors for heating the thermonuclear fusion plasmas. At present, it is possible to produce multiampere H−/D− ion beams quasicontinuously at energies of more than a few hundred keV with a good beam optics of beamlet divergence of a few mrad. Based on these technologies, two research and development projects have been initiated; one is to develop a 22 A/500 keV/10 s D− ion source for the neutral beam injector for JT-60U, and the other is to develop a 1 A/1 MeV/60 s H− ion source to demonstrate high current negative ion acceleration up to the energy of 1 MeV, the energy required for the neutral beam injector for the International Thermonuclear Experimental Reactor. © 1996 American Institute of Physics.

Notizen: Nowadays contact recording has become one of the most important mechanisms for high-density recording of HDD. The contact recording head is always subject to friction when sliding. If the friction causes vibration on the sliding head, the swaying of the head is likely to lead to some undesirable bit shifts. The authors previously measured the head movement in sliding with a Watrous-type suspension where it was verified that the front edge of the head fell down to the disk surface because the rotational center of the pitching motion of the head was located above the sliding surface, inducing a heavy sticking. In order to prevent the sticking from occurring, we have already proposed RCC (remote centered compliance) suspension (15 mm in thickness) which consists of a pair of inclined plates. With this suspension, the front edge of the head is raised up because of the enhanced location of the rotational center which is now below the sliding surface. In this article we present a newly designed micro-RCC suspension (125 μm in thickness) for an acutal small MR head (1×1×0.5 mm) of the contact recording. It has two pairs of the inclined plates structure for two-axis frictions which are caused by seeking and tracking motions of the head, respectively.This suspension is fabricated from a 125 μm thick sheet of polyimide using the ultraviolet laser beam. We evaluate its movement in sliding at low speed (50 μm/s) and at high speed (2 m/s) under a 10 mN load on a sputtered disk, respectively. The normal and frictional forces are measured by a micro two-axis force sensor (0.01 mN resolution) with parallel-plate structure and the pitching motion of the head is measured by an inclination sensor by means of laser reflection angle measurement (10 μrad resolution). From the experiment at low speed, we have clarified that the head yields a stable friction (0.15±0.02 mN) and has the nose-up attitude (0 to + 100 μrad). In addition, from the evaluation at high speed, we have observed the stable read-back signal (±7% modulation) because of the stable motion without any sticking. As a reference suspension, we prepare a micro-Winchester-type suspension. From the similar evaluation, we have identified that the reference head shows unstable friction (0.25±0.1 mN) with the nose-down attitude (0 to −500 μrad) and an unstable signal (±50% modulation). We have confirmed through these observations that the micro-RCC suspension will be an indispensable tool for contact recording in order to realize a stable recording against the friction. © 1996 American Institute of Physics.

Notizen: We have investigated optical properties of ZnTe epilayers, Zn1−xMgxSeyTe1−y epilayers, and ZnTe/Zn1−xMgxSeyTe1−y quantum wells (QWs) grown on (100)-InAs substrates by molecular beam epitaxy. We observed several sharp photoluminescence lines close to the excitonic position and no detectable luminescence from deep levels in ZnTe epilayers. Bright luminescence has been obtained from Zn1−xMgxSeyTe1−y epilayers which are lattice matched with InAs. The band alignment of ZnTe/Zn1−xMgxTe QWs was found to be type I. The reduction of the band gap energy of the ZnTe layer due to a tensile strain was confirmed in this structure. Nearly lattice-matched ZnTe/Zn1−xMgxSeyTe1−y QWs have been fabricated. A type II band alignment was observed for many of these QWs. We estimated bowing parameters not only of the band gap but also of the valence band for ZnSeyTe1−y. © 1997 American Institute of Physics.

Notizen: Graphite samples are heated in a diamond anvil cell with a CO2 laser above 11 GPa. A light transparent phase has appeared after heating, which is quenchable at ambient conditions. The Raman spectrum shows that the phase is a fine-grained cubic diamond. Images by a high resolution transmission electron microscope indicate that the diamond has twins and stacking faults of nanometer size. The electron diffraction pattern shows that the stacking fault cannot be explained by a diamond polytype such as a hexagonal diamond. The cathodoluminescence pattern exhibits the "band-A" emission, which is derived from the defects of the cubic diamond. © 1998 American Institute of Physics.

Notizen: The refractive indices of diluted magnetic semiconductor Cd1−xMnxTe films on sapphire substrates have been determined by m-line spectroscopy to precision 0.001 at the wavelengths λ=670, 785, and 1150 nm. Using these data, we designed double-layer Cd1−xMnxTe structures on a GaAs substrate, achieving the integration of the magneto-optical waveguide on a semiconductor substrate. Good optical confinement of the waveguide mode was confirmed. © 1997 American Institute of Physics.

Notizen: The voltage and film composition dependence of leakage currents of ferroelectric SrBi2Ta2O9 thin films, sandwiched between Pt has been studied. Schottky emission dominated the leakage current at voltages above the ohmic conduction regime, while space charge limited currents (SCLC), for which the observed temperature dependence is correctly predicted in Rose's theory, appeared to dominate the leakage current in high conductivity SrBi2Ta2O9 thin films including bismuth-excess samples. A consequence of the latter was the observation of negative differential resistivity in high conductivity SrBi2Ta2O9 thin films. X-ray photoemission spectroscopy depth profiling indicated that Bi has diffused into the ferroelectric–metal interface and also influenced the electronic conduction mechanism of the ferroelectric capacitors. Confirmation of this was found through the current–voltage dependence of Pt/SrBi2Ta2O9/Bi, which is compatible with space charge limited currents. The theory of Rose was successfully applied to the temperature and voltage dependencies of leakage currents in Bi-excess SBT; this is the first application of such theories to ferroelectric films and results in a generalization of the Child's Law approximation for space-charge-limited currents. A single fitting parameter T*=315±20 K satisfied data at the voltages 3〈V〈4 and temperatures 300 K〈T〈400 K most useful for engineering device applications. © 1998 American Institute of Physics.