78 research outputs found
Characterisation of detachment in the MAST-U Super-X divertor using multi-wavelength imaging of 2D atomic and molecular emission processes
In this work, we provide the first 2D spatially resolved description of radiative detachment in MAST-U Super-X L-mode divertor plasmas. The Super-X magnetic configuration was designed to achieve reduced heat- and particle loads at the divertor target compared to conventional exhaust solutions. We use filtered camera imaging to reconstruct 2D emissivity profiles in the poloidal plane for multiple atomic and molecular emission lines and bands. A set of deuterium fuelling scans is discussed that, together, span attached to deeply detached divertor states observed in MAST-U. Emissivity profiles facilitate separate analysis of locked-mode induced split branches of the scrape-off layer. Molecular deuterium Fulcher band emission front tracking reveals that the deuterium electron-impact ionisation front, for which it serves a proxy, detaches at different upstream electron densities in the split branches. Upon detachment of this ionisation front, Balmer emission attributed to molecular activated recombination appears near-target. We report a simultaneous radial broadening of the emission leg, consistent with previous SOLPS-ITER modelling. With increased fuelling this emission region detaches, implying electron temperatures below ⌠1 eV. In this phase, 2D Balmer line ratio reconstruction indicates an onset of volumetric direct electron-ion recombination near-target. At the highest fuelling rates this emission region moves off-target, suggesting a drop in near-wall electron density accompanying the low temperatures.</p
Runaway electron synchrotron radiation in a vertically translated plasma
Synchrotron radiation observed from runaway electrons (REs) in tokamaks
depends upon the position and size of the RE beam, the RE energy and pitch
distributions, as well as the location of the observer. We show that
experimental synchrotron images of a vertically moving runaway electron beam
sweeping past the detector in the TCV tokamak agree well with predictions from
the synthetic synchrotron diagnostic Soft. This experimental validation lends
confidence to the theory underlying the synthetic diagnostics which are used
for benchmarking theoretical models of and probing runaway dynamics. We present
a comparison of synchrotron measurements in TCV with predictions of kinetic
theory for runaway dynamics in uniform magnetic fields. We find that to explain
the detected synchrotron emission, significant non-collisional pitch angle
scattering as well as radial transport of REs would be needed. Such effects
could be caused by the presence of magnetic perturbations, which should be
further investigated in future TCV experiments.Comment: 7 pages, 4 figures. Accepted for publication in Nuclear Fusio
Initial Fulcher band observations from high resolution spectroscopy in the MAST-U divertor
High resolution Fulcher band spectroscopy was used in the MAST-U divertors
during Super-X and elongated conventional divertor density ramps with
fuelling from the mid-plane high-field side. In the Super-X case
(density ramp from Greenwald fraction 0.12 to 0.24), the upper divertor showed
ground state rotational temperatures of the molecules increasing
from 6000 K, starting at the detachment onset, to 9000 K during
deepening detachment. This was correlated with the movement of the Fulcher
emission region, which is correlated with the ionisation source. The increase
in rotational temperature did not occur near the divertor entrance, where the
plasma was still ionising. Qualitative agreement was obtained between the lower
and upper divertor. Similar rotational temperatures were obtained in the
elongated divertor before the detachment onset, although the increase in
rotational temperature during detachment was less clearly observed as less deep
detachment was obtained. %In the elongated conventional divertor there was some
qualitative agreement of this effect impeded by low signal.
The measured vibrational distribution of the upper Fulcher state (first four
bands) does not agree with a ground state Boltzmann distribution but shows a
different characteristic with an elevated population especially in the and bands. The populations of the and band
relative to the band are roughly proportional to the
temperature
Peanut yellow spot virus: A distinct tospovirus species based on serology and nucleic acid hybridisation
Nucleocapsids of peanut yellow spot virus (PYSV), purified from peanut (= groundnut) plant tissue, contained a protein with a molecular mass of 29 kDa. In ELISA and immuno-blot analysis the virus did not react with tomato spotted wilt virus (TSWV), Impatiens necrotic spot virus (INSV) and peanut bud necrosis virus (PBNV) antisera. PYSV contained three RNA species, a large (L) RNA (c.8900 nucleotides), a medium (M) RNA (c.4800 nucleotides) and a small (S) RNA (c.3000 nucleotides), similar to other tospoviruses. In addition, a fourth RNA species of approximately 1800 nucleotides was also present in purified preparations. Hybridisation analysis under high stringency conditions revealed no hybridisation between PYSV RNAs and cDNA probes representing the nucleocapsid (N) gene, the glycoprotein (GP) gene and the 3' half of the RNA polymerase gene of PBNV. PYSV genomic RNAs also failed to hybridise with cDNA probes from the GP genes of TSWV and INSV. In reciprocal tests, the cDNA clones of PYSV S and M RNAs did not hybridise with any of the PBNV RNAs. Based on the absence of serological relationships between PYSV and PBNV, TSWV and INSV and lack of nucleotide homology based on hybridisation studies between the PYSV RNAs and cDNA clones from PBNV, TSWV and INSV, PYSV should be considered as a distinct species of the genus Tospovirus under a new serogroup, putatively designated âV
The role of plasma-atom and molecule interactions on power \& particle balance during detachment on the MAST Upgrade Super-X divertor
First quantitative analysis of the detachment processes in the MAST Upgrade
Super-X divertor show an unprecedented impact of plasma-molecular interactions
involving molecular ions (likely ), resulting in strong ion sinks,
leading to a reduction of ion target flux. This starts to occur as the
ionisation source detaches from the target, leading to a build-up of molecules
below the ionisation source who get excited, resulting in Molecular Activated
Recombination (MAR) and Dissociation (MAD). The particle sinks in the divertor
chamber exceed the ion sources in the middle of the detached operational regime
before electron-ion recombination (EIR) starts to occur, demonstrating the
strong capabilities for particle exhaust in the Super-X Configuration. MAD is
the dominant volumetric neutral atom creation mechanism and results in
significant power losses. This, combined with electron-impact excitation
preceding ionisation, are the dominant power loss mechanisms in the divertor
chamber. As the plasma becomes more deeply detached, EIR starts to occur and
electron temperatures below 0.2 eV are achieved. Even at such low electron
temperature conditions, MAR is observed to be an important ion sink mechanism,
which suggests the presence of highly vibrationally excited molecules in the
cold detached regime. The total radiative power loss is consistent with
extrapolations of spectroscopic inferences to hydrogenic radiative power
losses, which suggests that intrinsic impurity radiation, despite the carbon
walls, is minor. These observations are observed in Ohmic L-mode, ELM-free
H-mode and type I ELMy H-mode discharges
Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor
We present the first analysis of the atomic and molecular processes at play
during detachment in the MAST-U Super-X divertor using divertor spectroscopy
data. Our analysis indicates detachment in the MAST-U Super-X divertor can be
separated into four sequential phases: First, the ionisation region detaches
from the target at detachment onset leaving a region of increased molecular
densities downstream. The plasma interacts with these molecules, resulting in
molecular ions ( and/or ) that further react
with the plasma leading to Molecular Activated Recombination and Dissociation
(MAR and MAD), which results in excited atoms and significant Balmer line
emission. Second, the MAR region detaches from the target leaving a sub-eV
temperature region downstream. Third, an onset of strong emission from
electron-ion recombination (EIR) ensues. Finally, the electron density decays
near the target, resulting in a density front moving upstream.
The analysis in this paper indicates that plasma-molecule interactions have a
larger impact than previously reported and play a critical role in the
intensity and interpretation of hydrogen atomic line emission characteristics
on MAST-U. Furthermore, we find that the Fulcher band emission profile in the
divertor can be used as a proxy for the ionisation region and may also be
employed as a plasma temperature diagnostic for improving the separation of
hydrogenic emission arising from electron-impact excitation and that from
plasma-molecular interactions.
We provide evidences for the presence of low electron temperatures (
eV) during detachment phases III-IV based on quantitative spectroscopy
analysis, a Boltzmann relation of the high-n Balmer line transitions together
with an analysis of the brightness of high-n Balmer lines
Impact of Divertor Shape on Divertor Performance in strongly Baffled Divertors on MAST Upgrade
Harnessing fusion energy efficiently requires optimising heat and particle
exhaust in the edge from the fusion core plasma, which can be achieved through
magnetic shaping of the divertor into Alternative Divertor Configurations
(ADCs). In this study, we leverage MAST-U's unique shaping capabilities, which
allow for a variation in the ratio of the magnetic field at the
X-point and target (), to investigate the power exhaust and
core-edge compatibility of ADCs.
Experiments show ADCs with large ratios drastically enhance
divertor performance, with heat and particle loads reduced by factors up to
and a 120 \% reduction in detachment onset. Notably, these benefits
are achieved without compromising core plasma conditions.
Our analysis attributes these improvements to the extra volume available
below the ionisation front in longer leg-length divertors. This facilitates
power dissipation and reduced particle loads through ion sinks from atomic
(Electron-Ion Recombination) and molecular (Molecular-Activated Recombination)
processes. The onset of divertor detachment and the evolution of the detachment
front agrees with analytic models and divertor exhaust simulations.
These insights emphasise the potential minor divertor geometry adjustments
can have on power exhaust. This study illuminates pathways for devising
optimised exhaust strategies in future fusion devices
Herbivore benefits from vectoring plant virus through reduction of period of vulnerability to predation
Herbivores can profit from vectoring plant pathogens because the induced defence of plants against pathogens sometimes interferes with the induced defence of plants against herbivores. Plants can also defend themselves indirectly by the action of the natural enemies of the herbivores. It is unknown whether the defence against pathogens induced in the plant also interferes with the indirect defence against herbivores mediated via the third trophic level. We previously showed that infection of plants with Tomato spotted wilt virus (TSWV) increased the developmental rate of and juvenile survival of its vector, the thrips Frankliniella occidentalis. Here, we present the results of a study on the effects of TSWV infections of plants on the effectiveness of three species of natural enemies of F. occidentalis: the predatory mites Neoseiulus cucumeris and Iphiseius degenerans, and the predatory bug Orius laevigatus. The growth rate of thrips larvae was positively affected by the presence of virus in the host plant. Because large larvae are invulnerable to predation by the two species of predatory mites, this resulted in a shorter period of vulnerability to predation for thrips that developed on plants with virus than thrips developing on uninfected plants (4.4 vs. 7.9Â days, respectively). Because large thrips larvae are not invulnerable to predation by the predatory bug Orius laevigatus, infection of the plant did not affect the predation risk of thrips larvae from this predator. This is the first demonstration of a negative effect of a plant pathogen on the predation risk of its vector
The role of plasmaâatom and molecule interactions on power & particle balance during detachment on the MAST Upgrade Super-X divertor
This paper shows first quantitative analysis of the detachment processes in the MAST Upgrade Super-X divertor (SXD). We identify an unprecedented impact of plasma-molecular interactions involving molecular ions (likely D2+ ), resulting in strong ion sinks (Molecular Activated RecombinationâMAR), leading to a reduction of ion target flux. The MAR ion sinks exceed the divertor ion sources before electron-ion recombination (EIR) starts to occur, suggesting that significant ionisation occurs outside of the divertor chamber. In the EIR region, TeâȘ0.2 eV is observed and MAR remains significant in these deep detached phases. The total ion sink strength demonstrates the capability for particle (ion) exhaust in the Super-X Configuration. Molecular Activated Dissociation is the dominant volumetric neutral atom creation process can lead to an electron cooling of 20% of PSOL . The measured total radiative power losses in the divertor chamber are consistent with inferred hydrogenic radiative power losses. This suggests that intrinsic divertor impurity radiation, despite the carbon walls, is minor in the divertor chamber. This contrasts previous TCV results, which may be associated with enhanced plasma-neutral interactions and reduced chemical erosion in the detached, tightly baffled SXD. The above observations have also been observed in higher heat flux (narrower SOL width) type I ELMy H-mode discharges. This provides evidence that the characterisation in this paper may be general
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