57,183 research outputs found
Nonlinear gyrofluid computation of edge localised ideal ballooning modes
Three dimensional electromagnetic gyrofluid simulations of the ideal
ballooning mode blowout scenario for tokamak edge localized modes (ELMs) are
presented. Special emphasis is placed on energetic diagnosis, examining changes
in the growth rate in the linear, overshoot, and decay phases. The saturation
process is energy transfer to self generated edge turbulence which exhibits an
ion temperature gradient (ITG) mode structure. Convergence in the decay phase
is found only if the spectrum reaches the ion gyroradius. The equilibrium is a
self consistent background whose evolution is taken into account. Approximately
two thirds of the total energy in the edge layer is liberated in the blowout.
Parameter dependence with respect to plasma pressure and the ion gyroradius is
studied. Despite the violent nature of the short-lived process, the transition
to nonlinearity is very similar to that found in generic tokamak edge
turbulence.Comment: The following article has been submitted to Physics of Plasmas. After
it is published, it will be found at http://pop.aip.org
ASSESSMENT OF RISK WHEN CONTRACT CROPS ARE INCLUDED AMONG OTHER CROP ALTERNATIVES
Crop Production/Industries, Risk and Uncertainty,
Caustic Structures and Detectability of Circumbinary Planets in Microlensing
Recent discoveries of circumbinary planets in Kepler data show that there is
a viable channel of planet formation around binary main sequence stars.
Motivated by these discoveries, we have investigated the caustic structures and
detectability of circumbinary planets in microlensing events. We have produced
a suite of animations of caustics as a function of the projected separation and
angle of the binary host to efficiently explore caustic structures over the
entire circumbinary parameter space. Aided by these animations, we have derived
a semi-empirical analytic expression for the location of planetary caustics,
which are displaced in circumbinary lenses relative to those of planets with a
single host. We have used this expression to show that the dominant source of
caustic motion will be due to the planet's orbital motion and not that of the
binary star. Finally, we estimate the fraction of circumbinary microlensing
events that are recognizable as such to be significant (5-50 percent) for
binary projected separations in the range 0.1-0.5 in units of Einstein radii.Comment: 15 pages, 1 table, 18 figures. Accepted for publication in Ap
Correlation length scalings in fusion edge plasma turbulence computations
The effect of changes in plasma parameters, that are characteristic near or
at an L-H transition in fusion edge plasmas, on fluctuation correlation lengths
are analysed by means of drift-Alfven turbulence computations. Scalings by
density gradient length, collisionality, plasma beta, and by an imposed shear
flow are considered. It is found that strongly sheared flows lead to the
appearence of long-range correlations in electrostatic potential fluctuations
parallel and perpendicular to the magnetic field.Comment: Submitted to "Plasma Physics and Controlled Fusion
Electron irradiation of tandem junction solar cells
The electrical behavior of 100 micron thick tandem junction solar cells manufactured by Texas Instruments was studied as a function of 1 MeV electron fluence, photon irradiation, and 60 C annealing. These cells are found to degrade rapidly with radiation, the most serious loss occurring in the blue end of the cell's spectral response. No photon degradation was found to occur, but the cells did anneal a small amount at 60 C
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Development of low cost packaged fibre optic sensors for use in reinforced concrete structures
There is an ongoing need to measure strains in reinforced concrete structures more reliably and under a range of circumstances e.g. long term durability (such as effects of cracking and reinforcement corrosion), response to normal working loads and response under abnormal load conditions. Fibre optic sensors have considerable potential for this purpose and have the additional advantages, including of immunity to electromagnetic interference and light weight (Grattan et al., 2000). This is important in railway scenarios and particularly so when the lines are electrified. Their small size allows for easy installation. However, their use as commercial ‘packaged’ devices (traditionally seen as necessary to achieve adequate robustness) is limited by their high cost relative to other sensor devices such as encapsulated electric resistance strain gauges. This paper describes preliminary work to produce a cost-effective and easy-to-use technique for encapsulating fibre optic sensors in resin using 3D printing techniques to produce a robust, inexpensive ‘packaged’ sensor system suitable for use with concrete structures. The work done to date has shown this to be a convenient and economical way of producing multiple sensors which were suitable for both surface mounting and embedment in reinforced concrete structures. The proof-of-concept testing to which the trial packages were subjected is described in the paper and the results indicate that 3D printed packages have considerable potential for further development and use in a variety of civil engineering applications, competing well with more conventional sensor systems
Influence of temperature fluctuations on plasma turbulence investigations with Langmuir probes
The reliability of Langmuir probe measurements for plasma-turbulence
investigations is studied on GEMR gyro-fluid simulations and compared with
results from conditionally sampled I-V characteristics as well as self-emitting
probe measurements in the near scrape-off layer of the tokamak ASDEX Upgrade.
In this region, simulation and experiment consistently show coherent in-phase
fluctuations in density, plasma potential and also in electron temperature.
Ion-saturation current measurements turn out to reproduce density fluctuations
quite well. Fluctuations in the floating potential, however, are strongly
influenced by temperature fluctuations and, hence, are strongly distorted
compared to the actual plasma potential. These results suggest that
interpreting floating as plasma-potential fluctuations while disregarding
temperature effects is not justified near the separatrix of hot fusion plasmas.
Here, floating potential measurements lead to corrupted results on the ExB
dynamics of turbulent structures in the context of, e.g., turbulent particle
and momentum transport or instability identification on the basis of
density-potential phase relations
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