Central spar and module joint Patent

Design and development of module joint clamping device for application to solar array constructio

Orbital plasma tests for Harvard OSO-D experiment

Orbital plasma tests for OSO-D experimen

Fluid Models for Kinetic Effects on Coherent Nonlinear Alfven Waves. I. Fundamental Theory

Collisionless regime kinetic models for coherent nonlinear Alfven wave dynamics are studied using fluid moment equations with an approximate closure anzatz. Resonant particle effects are modelled by incorporating an additional term representing dissipation akin to parallel heat conduction. Unlike collisional dissipation, parallel heat conduction is presented by an integral operator. The modified derivative nonlinear Schrodinger equation thus has a spatially nonlocal nonlinear term describing the long-time evolution of the envelope of parallel-propagating Alfven waves, as well. Coefficients in the nonlinear terms are free of the 1/(1-beta) singularity usually encountered in previous analyses, and have very a simple form which clarifies the physical processes governing the large amplitude Alfvenic nonlinear dynamics. The nonlinearity appears via coupling of an Alfvenic mode to a kinetic ion-acoustic mode. Damping of the nonlinear Alfven wave appears via strong Landau damping of the ion-acoustic wave when the electron-to-ion temperature ratio is close to unity. For a (slightly) obliquely propagating wave, there are finite Larmor radius corrections in the dynamical equation. This effect depends on the angle of wave propagation relative to B_0 and vanishes for the limit of strictly parallel propagation. Explicit magnetic perturbation envelope equations amenable to further analysis and numerical solution are obtained. Implications of these models for collisionless shock dynamics are discussed.Comment: 34 pages (including 6 figures

Impact of Resonant Magnetic Perturbations on Zonal Modes, Drift-Wave Turbulence and the L-H Transition Threshold

We study the effects of Resonant Magnetic Perturbations (RMPs) on turbulence, flows and confinement in the framework of resistive drift-wave turbulence. This work was motivated, in parts, by experiments reported at the IAEA 2010 conference [Y. Xu {\it et al}, Nucl. Fusion \textbf{51}, 062030] which showed a decrease of long-range correlations during the application of RMPs. We derive and apply a zero-dimensional predator-prey model coupling the Drift-Wave Zonal Mode system [M. Leconte and P.H. Diamond, Phys. Plasmas \textbf{19}, 055903] to the evolution of mean quantities. This model has both density gradient drive and RMP amplitude as control parameters and predicts a novel type of transport bifurcation in the presence of RMPs. This model allows a description of the full L-H transition evolution with RMPs, including the mean sheared flow evolution. The key results are: i) The L-I and I-H power thresholds \emph{both} increase with RMP amplitude |\bx|, the relative increase of the L-I threshold scales as \Delta P_{\rm LI} \propto |\bx|^2 \nu_*^{-2} \gyro^{-2}, where $\nu_*$ is edge collisionality and \gyro is the sound gyroradius. ii) RMPs are predicted to \emph{decrease} the hysteresis between the forward and back-transition. iii) Taking into account the mean density evolution, the density profile - sustained by the particle source - has an increased turbulent diffusion compared with the reference case without RMPs which provides one possible explanation for the \emph{density pump-out} effect.Comment: 30 pages, IAEA-based articl

Fabrication of Pd-Cr wire

Fabrication of Pd-13 percent Cr alloy wires is described. Melting, casting, swaging and annealing processes are discussed. Drawing to reach two diameters (0.003 inch and 0.00176 inch) of wire is described. Representative micrographs of the Pd-Cr alloy at selected stages during wire fabrication are included. The resistance of the wire was somewhat lower, by about 15 to 20 percent, than comparable wire of other alloys used for strain gages

Breaking Kelvin: Circulation conservation and vortex breakup in MHD at low Magnetic Prandtl Number

In this paper we examine the role of weak magnetic fields in breaking Kelvin's circulation theorem and in vortex breakup in two-dimensional magnetohydrodynamics for the physically important case of a low magnetic Prandtl number (low $Pm$) fluid. We consider three canonical inviscid solutions for the purely hydrodynamical problem, namely a Gaussian vortex, a circular vortex patch and an elliptical vortex patch. We examine how magnetic fields lead to an initial loss of circulation $\Gamma$ and attempt to derive scaling laws for the loss of circulation as a function of field strength and diffusion as measured by two non-dimensional parameters. We show that for all cases the loss of circulation depends on the integrated effects of the Lorentz force, with the patch cases leading to significantly greater circulation loss. For the case of the elliptical vortex the loss of circulation depends on the total area swept out by the rotating vortex and so this leads to more efficient circulation loss than for a circular vortex.Comment: 21 pages, 12 figure

Stabilization, pointing and command control of a balloon-borne 1-meter telescope

A 1-meter balloon-borne telescope has been constructed and flown to observe far-infrared radiation from celestial sources. The attitude control systems must perform to the diffraction limit of the telescope for stabilization and have positioning capability for source acquisition. These and associated systems are discussed in detail, as is the command control of the payload as a whole

Measurement of representative landfill gas migration samples at landfill perimeters: a case study

This paper describes the development of a fully integrated autonomous system based on existing infrared sensing technology capable of monitoring landfill gas migration (specifically carbon dioxide and methane) at landfill sites. Sampling using the described system was validated against the industry standard, GA2000 Plus hand held device, manufactured by Geotechnical Instruments Inc. As a consequence of repeated sampling during validation experiments, fluctuations in the gas mixtures became apparent. This initiated a parallel study into what constitutes a representative sample of landfill gas migration as reported to the Environmental Protection Agency. The work described in this paper shows that gas mixture concentrations change with depth of extraction from the borehole well, but with evidence of a steady state after a time