5 research outputs found
Beam model of Doppler backscattering
We use beam tracing -- implemented with a newly-written code, Scotty -- and
the reciprocity theorem to derive a model for the linear backscattered power of
the Doppler Backscattering (DBS) diagnostic. Our model works for both the
O-mode and X-mode in tokamak geometry (and certain regimes of stellarators). We
present the analytical derivation of our model and its implications on the DBS
signal localisation and the wavenumber resolution. To determine these two
quantities, we find that it is the curvature of the field lines and the
magnetic shear that are important, rather than the curvature of the cut-off
surface. We also provide an explicit formula for the hitherto poorly-understood
quantitative effect of the mismatch angle. Consequently, one can use this model
to correct for the attenuation due to mismatch, avoiding the need for empirical
optimisation. This is especially important in spherical tokamaks, since the
magnetic pitch angle is large and varies both spatially and temporally.Comment: This is the version that passed peer review. No major changes, but
many improvements to writing styl
Structural Color 3D Printing By Shrinking Photonic Crystals
The rings, spots and stripes found on some butterflies, Pachyrhynchus
weevils, and many chameleons are notable examples of natural organisms
employing photonic crystals to produce colorful patterns. Despite advances in
nanotechnology, we still lack the ability to print arbitrary colors and shapes
in all three dimensions at this microscopic length scale. Commercial nanoscale
3D printers based on two-photon polymerization are incapable of patterning
photonic crystal structures with the requisite ~300 nm lattice constant to
achieve photonic stopbands/ bandgaps in the visible spectrum and generate
colors. Here, we introduce a means to produce 3D-printed photonic crystals with
a 5x reduction in lattice constants (periodicity as small as 280 nm), achieving
sub-100-nm features with a full range of colors. The reliability of this
process enables us to engineer the bandstructures of woodpile photonic crystals
that match experiments, showing that observed colors can be attributed to
either slow light modes or stopbands. With these lattice structures as 3D color
volumetric elements (voxels), we printed 3D microscopic scale objects,
including the first multi-color microscopic model of the Eiffel Tower measuring
only 39-microns tall with a color pixel size of 1.45 microns. The technology to
print 3D structures in color at the microscopic scale promises the direct
patterning and integration of spectrally selective devices, such as photonic
crystal-based color filters, onto free-form optical elements and curved
surfaces
Validating and optimising mismatch tolerance of Doppler backscattering measurements with the beam model
We use the beam model of Doppler backscattering (DBS), which was previously
derived from beam tracing and the reciprocity theorem, to shed light on
mismatch attenuation. This attenuation of the backscattered signal occurs when
the wavevector of the probe beam's electric field is not in the plane
perpendicular to the magnetic field. Correcting for this effect is important
for determining the amplitude of the actual density fluctuations. Previous
preliminary comparisons between the model and Mega-Ampere Spherical Tokamak
(MAST) plasmas were promising. In this work, we quantitatively account for this
effect on DIII-D, a conventional tokamak. We compare the predicted and measured
mismatch attenuation in various DIII-D, MAST, and MAST-U plasmas, showing that
the beam model is applicable in a wide variety of situations. Finally, we
performed a preliminary parameter sweep and found that the mismatch tolerance
can be improved by optimising the probe beam's width and curvature at launch.
This is potentially a design consideration for new DBS systems
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2020 taxonomic update for phylum Negarnaviricota (Riboviria: Orthornavirae), including the large orders Bunyavirales and Mononegavirales
In March 2020, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. At the genus rank, 20 new genera were added, two were deleted, one was moved, and three were renamed. At the species rank, 160 species were added, four were deleted, ten were moved and renamed, and 30 species were renamed. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV