674 research outputs found
Optoelectronic developments for remote-handled maintenance tasks in ITER
Remotely handled maintenance tools operated in the future International Thermonuclear Experimental Reactor (ITER) will face a harsh radiation environment, with total dose level requirements of several MGy. Optical fiber data communication has been considered as an alternative to conventional electronic transmission between the control room and remote handled maintenance equipment, mainly owing to its insentivity to electro-magnetic interference and to its wavelength encoded multiplexing capabilities. In this paper we summarise main results obtained at SCK•CEN over the past years towards the development of radiation tolerant fibre-optic communication links and report on the radiation tolerance of various individual optical components such as optical fibres, laser diodes and photodetectors, as well as their associated electronic driver circuits
Coexistence of Self-Organized Criticality and Intermittent Turbulence in the Solar Corona
An extended data set of extreme ultraviolet images of the solar corona
provided by the SOHO spacecraft are analyzed using statistical methods common
to studies of self-organized criticality (SOC) and intermittent turbulence
(IT). The data exhibits simultaneous hallmarks of both regimes, namely power
law avalanche statistics as well as multiscaling of structure functions for
spatial activity. This implies that both SOC and IT may be manifestations of a
single complex dynamical process entangling avalanches of magnetic energy
dissipation with turbulent particle flows.Comment: 4 pages, 4 figure
Gel spinning of porous poly(methyl methacrylate)) fibres
Solutions of poly(methyl methacrylate) in 1-butanol demix on cooling. By solution extrusion, fibres are produced which have an oriented porosity. The relation between this morphology, the phase diagram and the extrusion procedure is discussed
On the ultraviolet signatures of small scale heating in coronal loops
Studying the statistical properties of solar ultraviolet emission lines could
provide information about the nature of small scale coronal heating. We expand
on previous work to investigate these properties. We study whether the
predicted statistical distribution of ion emission line intensities produced by
a specified heating function is affected by the isoelectronic sequence to which
the ion belongs, as well as the characteristic temperature at which it was
formed. Particular emphasis is placed on the strong resonance lines belonging
to the lithium isoelectronic sequence. Predictions for emission lines observed
by existing space-based UV spectrometers are given. The effects on the
statistics of a line when observed with a wide-band imaging instrument rather
than a spectrometer are also investigated. We use a hydrodynamic model to
simulate the UV emission of a loop system heated by nanoflares on small,
spatially unresolved scales. We select lines emitted at similar temperatures
but belonging to different isoelectronic groups: Fe IX and Ne VIII, Fe XII and
Mg X, Fe XVII, Fe XIX and Fe XXIV. Our simulations confirm previous results
that almost all lines have an intensity distribution that follows a power-law,
in a similar way to the heating function. However, only the high temperature
lines best preserve the heating function's power law index (Fe XIX being the
best ion in the case presented here). The Li isoelectronic lines have different
statistical properties with respect to the lines from other sequences, due to
the extended high temperature tail of their contribution functions. However,
this is not the case for Fe XXIV which may be used as a diagnostic of the
coronal heating function. We also show that the power-law index of the heating
function is effectively preserved when a line is observed by a wide-band
imaging instrument rather than a spectromenter
The SWAP EUV Imaging Telescope Part I: Instrument Overview and Pre-Flight Testing
The Sun Watcher with Active Pixels and Image Processing (SWAP) is an EUV
solar telescope on board ESA's Project for Onboard Autonomy 2 (PROBA2) mission
launched on 2 November 2009. SWAP has a spectral bandpass centered on 17.4 nm
and provides images of the low solar corona over a 54x54 arcmin field-of-view
with 3.2 arcsec pixels and an imaging cadence of about two minutes. SWAP is
designed to monitor all space-weather-relevant events and features in the low
solar corona. Given the limited resources of the PROBA2 microsatellite, the
SWAP telescope is designed with various innovative technologies, including an
off-axis optical design and a CMOS-APS detector. This article provides
reference documentation for users of the SWAP image data.Comment: 26 pages, 9 figures, 1 movi
Signatures of the slow solar wind streams from active regions in the inner corona
Some of local sources of the slow solar wind can be associated with
spectroscopically detected plasma outflows at edges of active regions
accompanied with specific signatures in the inner corona. The EUV telescopes
(e.g. SPIRIT/CORONAS-F, TESIS/CORONAS-Photon and SWAP/PROBA2) sometimes
observed extended ray-like structures seen at the limb above active regions in
1MK iron emission lines and described as "coronal rays". To verify the
relationship between coronal rays and plasma outflows, we analyze an isolated
active region (AR) adjacent to small coronal hole (CH) observed by different
EUV instruments in the end of July - beginning of August 2009. On August 1 EIS
revealed in the AR two compact outflows with the Doppler velocities V =10-30
km/s accompanied with fan loops diverging from their regions. At the limb the
ARCH interface region produced coronal rays observed by EUVI/STEREO-A on July
31 as well as by TESIS on August 7. The rays were co-aligned with open magnetic
field lines expanded to the streamer stalks. Using the DEM analysis, it was
found that the fan loops diverged from the outflow regions had the dominant
temperature of ~1 MK, which is similar to that of the outgoing plasma streams.
Parameters of the solar wind measured by STEREO-B, ACE, WIND, STEREO-A were
conformed with identification of the ARCH as a source region at the
Wang-Sheeley-Arge map of derived coronal holes for CR 2086. The results of the
study support the suggestion that coronal rays can represent signatures of
outflows from ARs propagating in the inner corona along open field lines into
the heliosphere.Comment: Accepted for publication in Solar Physics; 31 Pages; 13 Figure
Acoustic Power Absorption and its Relation with Vector Magnetic Field of a Sunspot
The distribution of acoustic power over sunspots shows an enhanced absorption
near the umbra--penumbra boundary. Earlier studies revealed that the region of
enhanced absorption coincides with the region of strongest transverse potential
field. The aim of this paper is to (i) utilize the high-resolution vector
magnetograms derived using Hinode SOT/SP observations and study the
relationship between the vector magnetic field and power absorption and (ii)
study the variation of power absorption in sunspot penumbrae due to the
presence of spine-like radial structures. It is found that (i) both potential
and observed transverse fields peak at a similar radial distance from the
center of the sunspot, and (ii) the magnitude of the transverse field, derived
from Hinode observations, is much larger than the potential transverse field
derived from SOHO/MDI longitudinal field observations. In the penumbra, the
radial structures called spines (intra-spines) have stronger (weaker) field
strength and are more vertical (horizontal). The absorption of acoustic power
in the spine and intra-spine shows different behaviour with the absorption
being larger in the spine as compared to the intra-spine.Comment: 18 pages, 7 figures, In Press Solar Physics, Topical Issue on
Helio-and-Astroseismolog
A statistical study of SUMER spectral images: events, turbulence, and intermittency
We analyze a series of full-Sun observations, which was performed with the
SoHO/SUMER instrument between March and October 1996. Some parameters
(radiance, shift and width) of the S VI 93.3 nm, S VI 94.4 nm, and Lyman
Epsilon line profiles were computed on board. Radiances and line-of-sight
velocities in a large central region of the Sun are studied statistically:
distributions of solar structures, field Fourier spectra and structure
functions are obtained. The structures have distributions with power-law tails,
the Fourier spectra of the radiance fields also display power laws, and the
normalized structure functions of the radiance and velocity fields increase at
small scales. These results support the idea of the existence of small scales,
created by turbulence, and of intermittency of the observed fields. These
properties may provide insight into the processes needed for heating the
transition region, or, if confirmed in the corona, the corona itself. The
difficulties encountered in this analysis, especially for the velocity data,
underline the needs for sensitive ultraviolet imaging spectrometers.Comment: 10 pages, 13 figures, Astronomy & Astrophysics, in pres
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