[en] A high-performance superconducting analog-to-digital converter is described, comprising: a bidirectional binary counter having n stages of triple-junction reversible flip-flops connected together in a cascade arrangement from the least significant bit (LSB) to the most significant bit (MSB) where n is the number of bits of the digital output, each triple-junction reversible flip-flop including first, second and third shunted Josephson tunnel junctions and a superconducting inductor connected in a bridge circuit, the Josephson junctions and the inductor forming upper and lower portions of the flip-flop, each reversible flip-flop being a bistable logic circuit in which the direction of the circulating current determines the state of the circuit; and means for applying an analog input current to the bidirectional counter; wherein the bidirectional counter algebraically counts incremental changes in the analog input current, increasing the binary count for positive incremental changes in the analog current and decreasing the binary count for negative incremental changes in the current, and wherein the counter does not require a gate bias, thus minimizing power dissipation

[en] This thesis is devoted to two studies of low-frequency turbulence in toroidally confined plasma. Low-frequency turbulence is believed to play an important role in anomalous transport in toroidal confinement devices. The first study pertains the development of an analytic theory of ion-temperature-gradient-driven turbulence in tokamaks. Energy conserving, renormalized spectrum equations are derived and solved in order to obtain the spectra of stationary ion temperature gradient driven turbulence. Corrections to mixing length estimates are calculated explicitly. The resulting anomalous ion thermal diffusivity is derived and is found to be consistent with experimentally-deduced ion thermal diffusivities. The associated electron thermal diffusivity, particle and heat-pinch velocities are also calculated. The second study is devoted to the role of multiple helicity nonlinear interactions of tearing modes and dynamics of magnetic relaxation in a high-temperature current carrying plasma. To extend the resistive MHD theory of magnetic fluctuations and dynamo activity observed in the reversed field pinch, the fluid equations for high temperature regime are derived and basic nonlinear interaction mechanism and the effects of diamagnetic corrections to the MHD turbulence theory are studied for the case of fully developed, densely packed turbulence

[en] The ac Josephson effect provides a convenient source of electromagnetic oscillations which are voltage-tunable according to the relation f = 2eV/h. In principle, the frequency of oscillation can be anything from zero to a few terahertz for junctions made of lead- or niobium-based superconductors. In practice, the available power of a single Josephson junction is so extremely small that it is unable to sufficiently drive any mixing element in a receiver system. In addition, the impedance level is rather low for practical applications. Although there have been a number of previous successful attempts to phase lock Josephson junctions, they have all occurred at centimeter wavelengths, typically around 10GHz. At this frequency, one has an almost inexhaustible choice of commercial oscillators which provide more power quite conveniently and inexpensively. The situation is much different at short-millimeter and submillimeter wavelengths, that is, frequencies of 100's of GHz. The author investigated mutual phase locking of Josephson tunnel junctions at these frequencies. In the experiments with small arrays, he demonstrates the phase locking that numerical simulations and approximate analytical methods had predicted. Additionally, various phenomena associated with phase locking are discussed, as well as some more advanced schemes at explaining phase-locked Josephson junction arrays

[en] An analytic theory of ion-temperature-gradient-driven turbulence in tokamaks is presented. Energy-conserving, renormalized spectrum equations are derived and solved in order to obtain the spectra of stationary ion-temperature-gradient-driven turbulence. Corrections to mixing-length estimates are calculated explicitly. The resulting anomalous ion thermal diffusivity chi/sub i/ = 0.4[(π/2)ln(1 + eta/sub i/)]² [(1 + eta/sub i/)/tau]² rho/sub s/²c/sub s//L/sub s/ is derived and is found to be consistent with experimentally-deduced thermal diffusivities. The associated electron thermal diffusivity and particle and heat-pinch velocities are also calculated. The effect of impurity gradients on saturated ion-temperature-gradient-driven turbulence is discussed and a related explanation of density profile steepening during Z-mode operation is proposed. 35 refs., 4 figs

[en] An explicit formulation is developed to determine the width of a magnetic island separatrix generated by magnetic field perturbations in a general toroidal stellarator geometry. A conventional method is employed to recast the analysis in a magnetic flux coordinate system without using any simplifying approximations. The island width is seen to be proportional to the square root of the Fourier harmonic of B^ρ/B^ζ that is in resonance with the rational value of the rotational transform, where B^ρ and B^ζ are contravariant normal and toroidal components of the perturbed magnetic field, respectively. The procedure, which is based on a representation of three-dimensional flux surfaces by double Fourier series, allows rapid and fairly accurate calculation of the island widths in real vacuum field configurations, without the need to follow field lines through numerical integration of the field line equations. Numerical results of the island width obtained in the flux coordinate representation for the Advanced Toroidal Facility agree closely with those determined from Poincare puncture points obtained by following field lines. 22 refs., 5 tabs

[en] The ion temperature gradient driven (eta/sub i/) mode is proposed as a candidate for the cause of anomalous transport in high current reversed field pinches. A 'four-field' fluid model is derived to describe the coupled nonlinear evolution of resistive interchange and eta/sub i/ modes. A renormalized theory is discussed, and the saturation level of the fluctuations is analytically estimated. Transport scalings are obtained, and their implications discussed. In particular, these results indicate that pellet injection is a potentially viable mechanism for improving energy confinement in a high temperature RFP

[en] Previous studies have shown the resistive pressure-gradient-driven turbulence (RPGDT) is a likely cause of observed turbulent fluctuations and anomalous transport in magnetically confined plasmas. More recent study of RPGDT found a true saturation criterion and predicted significantly larger pressure diffusivity over simple mixing-length estimate. In this study, we investigate wavenumber spectrum for more detailed characteristics of this driven turbulence and consider an electromagnetic model with electron temperature evolution to study the effect of magnetic fluctuations on thermal transport

[en] Ion temperature gradients drive instabilities which are strong candidates for the cause of confinement degradation in high current RFP's. This paper investigates coupled resistive interchange-ion temperature gradient modes via a model based on two-fluid theory. Results show that ion modes can be a major channel for thermal losses and suggest that pellet injection is a potentially viable mechanism for improving energy confinement

[en] For the project of localization of nuclear fuel fabrication, the R and D to establish the fabrication technology of CANDU fuel bundle as well as PWR fuel assembly was carried out. The suitable boss height and the prober Beryllium coating thickness to get good brazing condition of appendage were studied in the fabrication process of CANDU fuel rod. Basic Studies on CANLUB coating method also were performed. Problems in each fabrication process step and process flow between steps were reviewed and modified. The welding conditions for top and bottom nozzles, guide tube, seal and thimble screw pin were established in the fabrication processes of PWR fuel assembly. Additionally, some researches for a part of PWR grid brazing problems are also carried out

[en] We analyze the center-of-mass order parameter in s-wave and d-wave superconductors and find a large spatial dc term in the s wave but none in the d wave. Thus, the d-wave hypothesis may reconcile high-temperature superconductivity with Hohenberg's theorem. The center-of-mass order parameter has nodes at Cu sites and peaks at O sites with opposite signs at x- and y-bonded oxygens. At boundaries, it attains opposite amplitudes for x and y edges. A singular Ginzburg-Landau parameter at T_c is predicted, which suggests that the maximum energy gap opens quickly