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Author name code: golding
ADS astronomy entries on 2022-09-14
author:"Golding, Thomas Peter"
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Title: Development of III-V barrier diode radiation-hard infrared
detectors for space applications
Authors: Wheeler, R.; Mason, I.; Jerram, P.; Stocken, P.; Jordan,
D.; Willis, M.; Carmichael, M.; Craig, A. P.; Golding, T.; Marshall,
A. R. J.
2020SPIE11537E..0JW Altcode:
Opto-electronic devices destined for space must be suitably
radiation-hard, meaning that they must be resilient to the effects of
high energy radiation in space. For high performance IR (infrared)
space-based applications, the current material of choice is MCT
(Mercury Cadmium Telluride). MCT is difficult and therefore expensive
to fabricate and the constituent materials are becoming increasingly
restricted by regulation. The new generation of barrier diode
detectors based on III-V materials offer a promising alternative to
MCT, providing comparable performance whilst offering devices that
are compatible with volume manufacturing processes. As part of a
DASA Space-to-Innovate Phase 1 funded project we have developed a
novel radiation hard unipolar barrierbased ABaT™ III-V MWIR diode
detector. The detector is being subjected to gamma and proton radiation
testing to demonstrate its suitability for space environments. To
compare the radiation performance of this diode, a number of other
typical III-V detector diode structures have been fabricated and
tested. In this paper we present the results of the project so far
and future plans to develop this into detector arrays.
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Title: Formation of the helium extreme-UV resonance lines
Authors: Golding, T. P.; Leenaarts, J.; Carlsson, M.
2017A&A...597A.102G Altcode: 2016arXiv161000352G
Context. While classical models successfully reproduce intensities
of many transition region lines, they predict helium extreme-UV
(EUV) line intensities roughly an order of magnitude lower than the
observed value. <BR /> Aims: Our aim is to determine the relevant
formation mechanism(s) of the helium EUV resonance lines capable of
explaining the high intensities under quiet Sun conditions. <BR />
Methods: We synthesised and studied the emergent spectra from a 3D
radiation-magnetohydrodynamics simulation model. The effects of coronal
illumination and non-equilibrium ionisation of hydrogen and helium
are included self-consistently in the numerical simulation. <BR />
Results: Radiative transfer calculations result in helium EUV line
intensities that are an order of magnitude larger than the intensities
calculated under the classical assumptions. The enhanced intensity
of He Iλ584 is primarily caused by He II recombination cascades. The
enhanced intensity of He IIλ304 and He IIλ256 is caused primarily by
non-equilibrium helium ionisation. <BR /> Conclusions: The analysis
shows that the long standing problem of the high helium EUV line
intensities disappears when taking into account optically thick
radiative transfer and non-equilibrium ionisation effects.
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Title: Non-equilibrium helium ionization in the solar atmosphere
Authors: Golding, Thomas Peter
2017PhDT.......215G Altcode:
No abstract at ADS
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Title: The cause of spatial structure in solar He I 1083 nm multiplet
images
Authors: Leenaarts, Jorrit; Golding, Thomas; Carlsson, Mats; Libbrecht,
Tine; Joshi, Jayant
2016A&A...594A.104L Altcode: 2016arXiv160800838L
Context. The He I 1083 nm is a powerful diagnostic for inferring
properties of the upper solar chromosphere, in particular for the
magnetic field. The basic formation of the line in one-dimensional
models is well understood, but the influence of the complex
three-dimensional structure of the chromosphere and corona has however
never been investigated. This structure must play an essential role
because images taken in He I 1083 nm show structures with widths
down to 100 km. <BR /> Aims: We aim to understand the effect of
the three-dimensional temperature and density structure in the
solar atmosphere on the formation of the He I 1083 nm line. <BR />
Methods: We solved the non-LTE radiative transfer problem assuming
statistical equilibrium for a simple nine-level helium atom that
nevertheless captures all essential physics. As a model atmosphere we
used a snapshot from a 3D radiation-MHD simulation computed with the
Bifrost code. Ionising radiation from the corona was self-consistently
taken into account. <BR /> Results: The emergent intensity in the He
I 1083 nm is set by the source function and the opacity in the upper
chromosphere. The former is dominated by scattering of photospheric
radiation and does not vary much with spatial location. The latter
is determined by the photonionisation rate in the He I ground state
continuum, as well as the electron density in the chromosphere. The
spatial variation of the flux of ionising radiation is caused
by the spatially-structured emissivity of the ionising photons
from material at T ≈ 100 kK in the transition region. The hotter
coronal material produces more ionising photons, but the resulting
radiation field is smooth and does not lead to small-scale variation
of the UV flux. The corrugation of the transition region further
increases the spatial variation of the amount of UV radiation in the
chromosphere. Finally we find that variations in the chromospheric
electron density also cause strong variation in He I 1083 nm
opacity. We compare our findings to observations using SST, IRIS and
SDO/AIA data. <P />A movie associated to Fig. 4 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201628490/olm">http://www.aanda.org</A>
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Title: Non-equilibrium Helium Ionization in an MHD Simulation of
the Solar Atmosphere
Authors: Golding, Thomas Peter; Leenaarts, Jorrit; Carlsson, Mats
2016ApJ...817..125G Altcode: 2015arXiv151204738G
The ionization state of the gas in the dynamic solar chromosphere can
depart strongly from the instantaneous statistical equilibrium commonly
assumed in numerical modeling. We improve on earlier simulations of
the solar atmosphere that only included non-equilibrium hydrogen
ionization by performing a 2D radiation-magnetohydrodynamics
simulation featuring non-equilibrium ionization of both hydrogen
and helium. The simulation includes the effect of hydrogen Lyα and
the EUV radiation from the corona on the ionization and heating
of the atmosphere. Details on code implementation are given. We
obtain helium ion fractions that are far from their equilibrium
values. Comparison with models with local thermodynamic equilibrium
(LTE) ionization shows that non-equilibrium helium ionization leads to
higher temperatures in wavefronts and lower temperatures in the gas
between shocks. Assuming LTE ionization results in a thermostat-like
behavior with matter accumulating around the temperatures where the
LTE ionization fractions change rapidly. Comparison of DEM curves
computed from our models shows that non-equilibrium ionization leads
to more radiating material in the temperature range 11-18 kK, compared
to models with LTE helium ionization. We conclude that non-equilibrium
helium ionization is important for the dynamics and thermal structure
of the upper chromosphere and transition region. It might also help
resolve the problem that intensities of chromospheric lines computed
from current models are smaller than those observed.
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Title: Detailed and Simplified Nonequilibrium Helium Ionization in
the Solar Atmosphere
Authors: Golding, Thomas Peter; Carlsson, Mats; Leenaarts, Jorrit
2014ApJ...784...30G Altcode: 2014arXiv1401.7562G
Helium ionization plays an important role in the energy balance of the
upper chromosphere and transition region. Helium spectral lines are also
often used as diagnostics of these regions. We carry out one-dimensional
radiation-hydrodynamics simulations of the solar atmosphere and
find that the helium ionization is set mostly by photoionization and
direct collisional ionization, counteracted by radiative recombination
cascades. By introducing an additional recombination rate mimicking
the recombination cascades, we construct a simplified three-level
helium model atom consisting of only the ground states. This model
atom is suitable for modeling nonequilibrium helium ionization in
three-dimensional numerical models. We perform a brief investigation of
the formation of the He I 10830 and He II 304 spectral lines. Both lines
show nonequilibrium features that are not recovered with statistical
equilibrium models, and caution should therefore be exercised when
such models are used as a basis for interpretating observations.
