Observation of the "self-healing" of an error field island in the large helical device

It was observed that the vacuum magnetic island produced by an external error magnetic field in the large helical device shrank in the presence of plasma. This was evidenced by the disappearance of flat regions in the electron temperature profile obtained by Thomson scattering. This island behavior depended on the magnetic configuration in which the plasmas were produced.     

Observation of large CP violation in the neutral B meson system

We present a measurement of the standard model CP violation parameter sin2 phi(1) based on a 29.1 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. One neutral B meson is fully reconstructed as a J/psi K(S), psi(2S)K(S), chi(c1)K(S), eta(c)K(S), J/psi K(L), or J/psi K(*0) decay and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we determine sin2 phi(1) = 0.99+/-0.14(stat)+/-0.06(syst). We conclude that we have observed CP violation in the neutral B meson system.     

A structure analysis of Ag-adsorbed Si(111) surface by LEED/CMTA

The Ag induced superstructures on the Si(111) surface have been studied by low energy electron diffraction constant momentum transfer averaging (LEED/CMTA) technique. The vertical displacements of the atoms are determined from the analysis of the specularly reflected (00) beam intensities. Unexpected behavior of the Ag atoms is clarified: For the √3 × √3-Ag surface it is verified that the Ag atoms are embedded in the first double layer of Si, leading to a considerable rearrangement of the substrate. In contrast, for the 3 × 1-Ag surface, the Ag atoms are riding on the Si surface and the reconstruction of the substrate is small.     

Laser cooling of a single Ca+ ion: Observation of quantum jumps

This paper describes trapping and laser cooling of a Ca⁺ ion in an rf quadrupole ion trap. A single Ca⁺ ion is laser cooled to below 130 mK and quantum jumps are observed by exciting the ion into the metastable D _5/2 state via the P _3/2 state. The lifetime of the metastable D _5/2 state is estimated from the distribution of the dark periods of the quantum-jump signal. Collision-induced jumps between the metastable D _3/2 state and the D _5/2 state in a background gas are also directly observed.     

Proton diffusion in the superprotonic phase of [(NH4)1 − xRbx]3H(SO4)2 as studied by 1H spin-lattice relaxation

Proton diffusion in [(NH₄)_1 ? xRb_x]₃H(SO₄)₂ (0 < x < 1) has been studied by means of ¹H spin-lattice relaxation times, T₁. The relaxation times were measured at 200.13 MHz in the range of 296–490 K and at 19.65 MHz in the range of 300–470 K. In the high-temperature phase (phase I), translational diffusion of the acidic protons relaxes both the acidic protons and the ammonium protons. Spin diffusion averages the relaxation rate of the two kinds of protons, whereas proton exchange between them are slow. The spin-lattice relaxation times in phase I were analyzed theoretically, and parameters of proton diffusion were obtained. The mean residence time of the acidic protons increases with increase in x for [(NH₄)_1 ? xRb_x]₃H(SO₄)₂ (0 ≤ x ≤ 0.54). Rb₃H(SO₄)₂ does not obey this trend. The results of NMR well explain the macroscopic proton conductivity.     

Influence of current on field-driven domain wall motion in permalloy nanowires from time resolved measurements of anisotropic magnetoresistance

The motion of magnetic domain walls in permalloy nanowires is investigated by real-time resistance measurements. The domain wall velocity is measured as a function of the magnetic field in the presence of a current flowing through the nanowire. We show that the current can significantly increase or decrease the domain wall velocity, depending on its direction. These results are understood within a one-dimensional model of the domain wall dynamics which includes the spin transfer torque.     

Development of a two-color interferometer for observing wide range electron density profiles with a femtosecond time resolution

A two-color interferometer for preformed plasma characterization is developed. We observe the electron density distribution of preformed plasmas on a 5 μm-thick copper target irradiated with a high-intensity Ti:sapphire laser. The two-color interferometer extended the observable electron density region using a fundamental (800 nm) probe beam to cover the lower density region and a second harmonic (400 nm) probe beam to cover the higher density region, simultaneously. This characterization of the electron density distribution of preformed plasmas with femtosecond time resolution significantly contributes to the understanding of high-intensity laser–thin-foil interactions during high-energy electron, ion, and X-ray generation. PACS 52.38.-r; 52.50.Jm; 52.70.-m     

Quantitative analysis of optical power budget of bismuth oxide-based erbium-doped fiber

We investigated optical power budget of Bi₂O₃-based erbium-doped fiber (BIEDF). Lateral spontaneous emissions and scattering laser powers in the BIEDF were measured quantitatively by using an integrating sphere. Compared with the power of amplified spontaneous emission and signal detected at the output fiber end, it was found that considerable powers were consumed by the laterally emitting lights. As an optically undetected loss limits power conversion efficiency (PCE) of the fiber amplifier, the effect of nonradiative decay from the termination level of pump excited state absorption (pump ESA) was estimated from decay rate analyses of the relevant levels. The nonradiative loss was comparable to amplified signal power in the BIEDF when pumped with a 980-nm LD. Nonradiative decay following cooperative upconversion (CUP) process is also discussed using rate equations analysis.     

High-power microwave generation using a ferroelectric cathodeelectron gun

A two-stage 500 kV 200-A ferroelectric electron gun has been designed, fabricated, tested, and used in a high power microwave amplifier experiment. We report on the operational characteristics of the gun including measurements of the beam dynamics. The optimum conditions for application of the trigger and its timing are also reported. Faraday cup measurement shows that the beam radius is 4.1 mm, in good agreement with simulation. The gun is designed for use in traveling-wave tube amplifiers, and testing of an X-band amplifier driven by the gun is reported. A peak output power of 5.9 MW has been observed from a single stage amplifier driven by a 100 A. 450 kV beam. This corresponds to energy converging efficiency of 13.1% and is the first observation of high power (~MW) microwave generation using the beam generated from a ferroelectric cathode,     

Enhanced photon generation in a Nb/n-InGaAs/p-InP superconductor/semiconductor-diode light emitting device

We experimentally demonstrate Cooper pairs' drastic enhancement of the band-to-band radiative recombination rate in a semiconductor. Electron Cooper pairs injected from a superconducting electrode into an active layer by the proximity effect recombine with holes injected from a p-type electrode. The recombination of a Cooper pair with p-type carriers dramatically increases the photon generation probability of a light-emitting diode in the optical-fiber communication band. The measured radiative decay time rapidly decreases with decreasing temperature below the superconducting transition temperature of the niobium electrodes. Our results indicate the possibility to open up new interdisciplinary fields between superconductivity and optoelectronics.