Grapevine red blotch virus (GRBV), the causative agent of grapevine red blotch disease, is widespread across the United States and causes a delay in ripening events in grapes. This study evaluates ...the effects of GRBV on Cabernet Sauvignon grape berry composition, grafted on two different rootstocks (110R and 420A) in two seasons (2016 and 2017). Total soluble solids, acidity, and anthocyanin concentrations were monitored through ripening and at harvest. Phenolic and volatile compounds were also analyzed at harvest to determine genotypic and environmental influences on disease outcome. Sugar accumulation through ripening was lower in diseased fruit (RB (+)) than healthy fruit across rootstock and season. GRBV impact was larger in 2016 than 2017, indicating a seasonal effect on disease expression. In general, anthocyanin levels and volatile compound accumulation was lower in RB (+) fruit than healthy fruit. Total phenolic composition and tannin content was higher in RB (+) fruit than healthy fruit in only 110R rootstock. Overall, GRBV impacted Cabernet Sauvignon grape composition crafted on rootstock 110R more than those crafted on rootstock 420A.
In multi-pulse laser wakefield acceleration (MP-LWFA) a plasma wave is driven by a train of low-energy laser pulses separated by the plasma period, an approach which offers a route to driving plasma ...accelerators with high efficiency and at high pulse repetition rates using emerging technologies such as fibre and thin-disk lasers. Whilst these laser technologies are in development, proof-of-principle tests of MP-LWFA require a pulse train to be generated from a single, high-energy ultrafast pulse. Here we demonstrate the generation of trains of up to 7 pulses with pulse separations in the range 150–170fs from single 40fs pulses produced by a Ti:sapphire laser.
We demonstrate optical guiding of high-intensity laser pulses in long, low-density hydrodynamic optical-field-ionized (HOFI) plasma channels. An axicon lens is used to generate HOFI plasma channels ...with on-axis electron densities as low asne(0)=1.5×1017cm−3and matched spot sizes in the range20μm≲WM≲40μm. Control of these channel parameters via adjustment of the initial cell pressure and the delay after the arrival of the channel-forming pulse is demonstrated. For laser pulses with a peak axial intensity of4×1017Wcm−2, highly reproducible, high-quality guiding over more than 14 Rayleigh ranges is achieved at a pulse repetition rate of 5 Hz, limited by the available channel-forming laser and vacuum pumping system. Plasma channels of this type would seem to be well suited to multi-GeV laser wakefield accelerators operating in the quasilinear regime.
We demonstrate through experiments and numerical simulations that low-density, low-loss, meter-scale plasma channels can be generated by employing a conditioning laser pulse to ionize the neutral gas ...collar surrounding a hydrodynamic optical-field-ionized (HOFI) plasma channel. We use particle-in-cell simulations to show that the leading edge of the conditioning pulse ionizes the neutral gas collar to generate a deep, low-loss plasma channel which guides the bulk of the conditioning pulse itself as well as any subsequently injected pulses. In proof-of-principle experiments, we generate conditioned HOFI (CHOFI) waveguides with axial electron densities of n_{e0}≈1×10^{17}cm^{-3} and a matched spot size of 26μm. The power attenuation length of these CHOFI channels was calculated to be L_{att}=(21±3)m, more than two orders of magnitude longer than achieved by HOFI channels. Hydrodynamic and particle-in-cell simulations demonstrate that meter-scale CHOFI waveguides with attenuation lengths exceeding 1 m could be generated with a total laser pulse energy of only 1.2 J per meter of channel. The properties of CHOFI channels are ideally suited to many applications in high-intensity light-matter interactions, including multi-GeV plasma accelerator stages operating at high pulse repetition rates.
In recent years, hydrodynamic optical-field-ionized (HOFI) channels have emerged as a promising technique to create laser waveguides suitable for guiding tightly focused laser pulses in a plasma, as ...needed for laser-plasma accelerators. While experimental advances in HOFI channels continue to be made, the underlying mechanisms and the roles of the main parameters remain largely unexplored. In this paper, we propose a start-to-end simulation pipeline of the HOFI channel formation and the resulting laser guiding and use it to explore the underlying physics and the tunability of HOFI channels. This approach is benchmarked against experimental measurements. HOFI channels are shown to feature excellent guiding properties over a wide range of parameters, making them a promising and tunable waveguide option for laser-plasma accelerators.
We generalize the temporally encoded spectral shifting (TESS) analysis for measuring plasma wakefields using spectral interferometry to dissimilar probe pulses of arbitrary spectral profile and to ...measuring nonlinear wakefields. We demonstrate that the Gaussian approximation used up until now results in a substantial miscalculation of the wakefield amplitude, by a factor of up to two. A method to accurately measure higher amplitude quasilinear and nonlinear wakefields is suggested, using an extension to the TESS procedure, and we place some limits on its accuracy in these regimes. These extensions and improvements to the analysis demonstrate its potential for rapid and accurate on-shot diagnosis of plasma wakefields, even at low plasma densities.
A machine learning model was created to predict the electron spectrum generated by a GeV-class laser wakefield accelerator. The model was constructed from variational convolutional neural networks, ...which mapped the results of secondary laser and plasma diagnostics to the generated electron spectrum. An ensemble of trained networks was used to predict the electron spectrum and to provide an estimation of the uncertainty of that prediction. It is anticipated that this approach will be useful for inferring the electron spectrum prior to undergoing any process that can alter or destroy the beam. In addition, the model provides insight into the scaling of electron beam properties due to stochastic fluctuations in the laser energy and plasma electron density.
Lyman continuum and line emission are thought to be important agents in the
reionization of the early universe. Haro 11 is a rare example of a local galaxy
in which Ly$\alpha$ and continuum emission ...have escaped without being absorbed
or scattered by ambient gas and dust, potentially as a consequence of feedback
from its X-ray sources. We build on our previous Chandra analysis of Haro 11 by
analyzing three new observations. Our subpixel spatial analysis reveals that
the two previously known X-ray sources are each better modelled as ensembles of
at least 2 unresolved point sources. The spatial variability of these
components reveals X1 as a dynamical system where one luminous X-ray source
($L_{\rm X} \sim 10^{41}$ erg s$^{-1}$) fades as a secondary source begins to
flare. These might be intermediate mass black holes or low luminosity active
galactic nuclei near the center of the galaxy in the process of merging.
Optical emission line diagnostics drawn from the literature suggest that while
the galaxy as a whole is consistent with starburst signatures of ionization,
the individual regions wherein the X-ray sources reside are more consistent
with AGN/composite classification. The sources in X2 exhibit some degree of
flux variability. X2a dominates the flux of this region during most
observations ($L_{\rm X} \sim 6\ \times\ 10^{40}$ erg s$^{-1}$), and gives the
only evidence in the galaxy of a soft Ultra-Luminous X-ray source capable of
high energy winds, which we suggest are responsible for allowing the coincident
Ly$\alpha$ emission to escape.
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