26,165 research outputs found
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
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
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
Plus Charge Prevalence in Cosmic Rays: Room for Dark Matter in the Positron Spectrum
The unexpected energy spectrum of the positron/electron ratio is interpreted
astrophysically, with a possible exception of the 100-300 GeV range. The data
indicate that this ratio, after a decline between GeV, rises steadily
with a trend towards saturation at 200-400GeV. These observations (except for
the trend) appear to be in conflict with the diffusive shock acceleration (DSA)
mechanism, operating in a \emph{single} supernova remnant (SNR) shock. We argue
that ratio can still be explained by the DSA if positrons are
accelerated in a \emph{subset} of SNR shocks which: (i) propagate in clumpy gas
media, and (ii) are modified by accelerated CR \emph{protons}. The protons
penetrate into the dense gas clumps upstream to produce positrons and,
\emph{charge the clumps positively}. The induced electric field expels
positrons into the upstream plasma where they are shock-accelerated. Since the
shock is modified, these positrons develop a harder spectrum than that of the
CR electrons accelerated in other SNRs. Mixing these populations explains the
increase in the ratio at GeV. It decreases at GeV
because of a subshock weakening which also results from the shock modification.
Contrary to the expelled positrons, most of the antiprotons, electrons, and
heavier nuclei, are left unaccelerated inside the clumps. Scenarios for the
100-300 GeV AMS-02 fraction exceeding the model prediction, including, but not
limited to, possible dark matter contribution, are also discussed.Comment: 36 pages, 6 figure
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