[en] Alfven wave heating experiments have been conducted on the PRETEXT tokamak. Theoretical developments of dispersion relations and polarizations of two Alfven modes lead to the Alfven resonance layer where a coupling mechanism (mode conversion) converts the compressional wave to the shear wave or to the kinetic Alfven wave. A coupling network is also required for matching the rf source and cable impedance to the antenna impedance. The design of a matching network and guidelines for impedance matching with plasma is discussed. An electronic processing unit has been designed and used for monitoring the change of antenna impedance or Q during the plasma discharge. Measuements on two antennas showed clearly that the antennas do interfere with each other and form a Fourier specrum which alters the plasma loading resistance as predicted. The loading resistances are higher than those calculated from present theory. The dependence of the loading resistance on magnetic field has been observed, density dependence during plasma shots has not been clarified however. This is because that only mush loading can be detected through present arrangement, which is relatively insensitive to the density evolution during plasma shots

[en] Electron-cyclotron-heating experiments have been carried out on the Doublet III tokamak. Two 60-GHz gyrotrons were used to generate about 255 kW of power delivered to the plasma in the ordinary-mode polarization. The antenna launches a 16₀ FWHM beam from the large major radius side (outside) of the plasma at a beam center angle of 12₀ from a major radius. Pulses up to 85 msec long were applied, with the fundamental resonance (21.4 kG) near the plasma center. Plasma current was 300 to 350 kA, and the configuration was mostly expanded boundary with an elongation of 1.4 to 1.6 and density of 2 to 3 x 10₁₃ cm^-₃. Electron-temperature increases up to 1 keV at the plasma center due to ECH are found by Thomson scattering and electron-cyclotron radiation at the second harmonic. Soft x-ray analysis also shows central electron heating and profile broadening when the resonance is moved outside of the plasma center

[en] The transmission and launching scheme being used for the ECH experiments at 60 GHz on Doublet III and its operation at high power is described. The system uses the TE⁰¹ to TE¹¹ mode converter at the antenna. The system provides an acceptable load to the gyrotron, rarely arcs, and maintains good mode purity

[en] We describe the elements of a transmission and launching system used to transmit 200 kW of 60 GHz power per gyrotron in the 2 MW ECH experiment on the Doublet III tokamak. Various system components such as mode converters, waveguide bends, and directional couplers, as well as system efficiency and operation, are discussed

[en] In this Letter, we investigate new method of generating and controlling quantum coherences between two two-level quantum systems by using the spatial phase of one single-mode incident laser pulse. We take two identical semiconductor quantum dots as an illustration. Our method is to use the spatial phase of the laser pulse at the different positions of the quantum systems for the operations similar to two-qubit operations in the quantum computer language, rather than to employ the frequently used dipole-dipole interactions between them. In the present Letter, a specific operation similar to two-qubit quantum operation is examined numerically. Our investigation demonstrates that the spatial phase will also be useful for quantum operations

No abstract available

[en] Transient heat conduction in the reactor vessel wall is investigated by considering the temperature dependence of thermal conductivity. The problem is described by a nonlinear partial differential equation, which is numerically simulated to show the transient temperature distribution in the reactor vessel wall due to failure of the reactor cooling system. The orthogonal collocation method is employed to tackle the nonlinear simulation and found to be quite accurate in predicting the transient temperature response. It is observed that the effect of variable thermal conductivity is very significant and, in many real circumstances, predictions of the transient temperature distributions will not be adequate without taking into account the variable thermal conductivity. (Auth.)

[en] Kinetic and thermodynamic studies of the terbium oxides between the Tb₂O/sub 3+delta/ (n = 4) and Tb₇O₁₂ (n = 7) phases of the homolgous series, Tb/sub n/O/sub 2n-2/, have been carried out as a function of oxygen pressure at 708, 740, 772, and 806⁰C. The thermodynamic study shows a reproducible hysteresis loop which depends on the temperature and pressure. The kinetic study was carried out by measuring the weight gain of an oxide sample in an oxygen atmosphere as a function of time. The results are interpreted by a mixed-model mechanism of diffusion and phase boundary reaction control. The relative fit of the data with other models, including the phenomenological model previously found satisfactory for a related reaction, is shown. The kinetics in the final stage are strongly affected by the existence of pseudophase behavior near Tb₇O₁₂. From measurement of the oxygen pressure and temperature dependence of the observed rate constants, the activation energies for the diffusion process and phase boundary reaction process were determined to be -14 and 10 kcal/mole, respectively

[en] The dependence of the H-transfer rate constant of a solid phase tunneling reaction on temperature is analytically treated within the framework of a modified theory of radiationless transitions. Several intermolecular and soft intramolecular vibrations of reagents are taken into account, which result in oscillations of the potential barrier for the tunneling atom and thereby affect the value and temperature dependence of the rate constant. This treatment is used to interpret the experimental kinetic data of the fluorene-acridine reaction system involving hydrogen atom tunneling. It is shown that the correct estimations of the contributions related to both the reorganization of reagents and four types of promoting low-frequency vibrations (translational, librational and two intramolecular modes at 95 and 238 cm^-1) are needed to reproduce the observed data. The reaction system parameters required for such analysis are extracted from the results of quantum-chemical calculations of two-dimensional potential energy surfaces carried out at the DFT-B3LYP/6-31G* level

[en] Kinetic and thermodynamic studies between the ordered iota (n = 7 in Pr/sub n/O/sub 2n-2/) and the disordered α (PrO/sub 2-x/) phases have been carried out as a function of oxygen pressure at 655, 675, 695, and 715⁰C using a sample of small single crystals. The existence of a reproducible hysteresis loop, which depends on the temperature and pressure, having an inflection point around a composition PrO₁₇₅ is shown. The inflection point is interpreted as a phase of n = 8 in Pr/sub n/O/sub 2n-2/ (eta) coherently intergrown with n = 7, 9, and 10, giving an average composition of PrO₁₇₅. In order to interpret the kinetic data, various theoretical models were examined, for example, oxygen diffusion, a phase-boundary reaction control, or nucleation and growth. None of these models, however, is capable of correlating the experimental data. It was found that a plot of the reaction rate versus the ambient oxygen pressure extrapolates linearly to a finite pressure at zero rate, as was previously observed in the oxidation reaction between the eta and zeta phases of the same system. The model developed for the oxidation reaction between the eta and zeta phases has been modified by taking into account the intermediate phases around PrO₁₇₅, through which the reaction passes. The modified rate law has two reaction constants: the rate constant from the reactant transforming to the intermediate phase (k₁) and for the transformation from the intermediate to the product phase (k₂). The fit to the experimental curve is satisfactory for both the oxidation and reduction reaction. From the temperature dependence of the observed rate constants, the activation energy for the oxidation and reduction was determined to be 75.0 and 60.9 kcal/mole, respectively