The Heating Neutral Beam Injectors (HNBs) for ITER will have to deliver 16.7 MW beams of H/D particles at 1 MeV energy. The beams will be produced from H−/D− ions, generated by a radiofrequency ...plasma source coupled to an ion acceleration system. A prototype of the ITER HNB ion source is being tested in the SPIDER experiment, part of the ITER Neutral Beam Test Facility at Consorzio RFX. Reaching the design targets for beam current density and fraction of coextracted electrons is only possible by evaporating cesium in the source, in particular on the plasma facing grid (PG) of the acceleration system. In this way the work function of the surfaces decreases, significantly increasing the amount of surface reactions that convert neutrals and positive ions into H−/D−. It is then of paramount importance to monitor the density of negative ions and the density of Cs in the proximity of the PG. Monitoring the Cs spatial distribution along the PG is also essential to guarantee the uniformity of the beam current. In SPIDER, this is possible thanks to the Cavity Ringdown Spectroscopy (CRDS) and the Laser absorption Spectroscopy diagnostics (LAS), which provide line-integrated measurements of negative ion density and neutral, ground state Cs density, respectively. The paper discusses the CRDS and LAS measurements as a function of input power and of the magnetic and electric fields used to reduce the coextraction of electrons. Negative ion density data are in qualitative agreement with the analogous measurements in Cs-free conditions. In agreement with simulations, Cs density is peaked in the center of the source; a top/bottom non uniformity is also present. Several effects of plasma on Cs deposition and negative ion production are presented.
TDCOSMO Birrer, S; Shajib, A J; Galan, A ...
Astronomy & astrophysics,
11/2020, Letnik:
643
Journal Article
Recenzirano
Odprti dostop
The H0LiCOW collaboration inferred via strong gravitational lensing time delays a Hubble constant value of H0 = 73.3−1.8+1.7 km s−1 Mpc−1, describing deflector mass density profiles by either a ...power-law or stars (constant mass-to-light ratio) plus standard dark matter halos. The mass-sheet transform (MST) that leaves the lensing observables unchanged is considered the dominant source of residual uncertainty in H0. We quantify any potential effect of the MST with a flexible family of mass models, which directly encodes it, and they are hence maximally degenerate with H0. Our calculation is based on a new hierarchical Bayesian approach in which the MST is only constrained by stellar kinematics. The approach is validated on mock lenses, which are generated from hydrodynamic simulations. We first applied the inference to the TDCOSMO sample of seven lenses, six of which are from H0LiCOW, and measured H0 = 74.5−6.1+5.6 km s−1 Mpc−1. Secondly, in order to further constrain the deflector mass density profiles, we added imaging and spectroscopy for a set of 33 strong gravitational lenses from the Sloan Lens ACS (SLACS) sample. For nine of the 33 SLAC lenses, we used resolved kinematics to constrain the stellar anisotropy. From the joint hierarchical analysis of the TDCOSMO+SLACS sample, we measured H0 = 67.4−3.2+4.1 km s−1 Mpc−1. This measurement assumes that the TDCOSMO and SLACS galaxies are drawn from the same parent population. The blind H0LiCOW, TDCOSMO-only and TDCOSMO+SLACS analyses are in mutual statistical agreement. The TDCOSMO+SLACS analysis prefers marginally shallower mass profiles than H0LiCOW or TDCOSMO-only. Without relying on the form of the mass density profile used by H0LiCOW, we achieve a ∼5% measurement of H0. While our new hierarchical analysis does not statistically invalidate the mass profile assumptions by H0LiCOW – and thus the H0 measurement relying on them – it demonstrates the importance of understanding the mass density profile of elliptical galaxies. The uncertainties on H0 derived in this paper can be reduced by physical or observational priors on the form of the mass profile, or by additional data.
The radiation response of a phosphorus-doped multimode optical fiber is investigated under both transient (pulsed X-rays) and steady-state (γ- and X-rays) irradiations. The influence of a H 2 ...preloading on the fiber radiation-induced attenuation (RIA) in the 300-2000-nm wavelength range has been characterized. To better understand the impact of this treatment, online behaviors of fiber samples containing different amounts of gas are compared from glass saturation (100%) to less than 1%. In addition to these in situ experiments, additional postirradiation spectroscopic techniques have been performed such as electron paramagnetic resonance or luminescence measurements to identify the different point defects responsible for the induced losses and their H 2 dependence. All our data at room temperature (RT) highlight a strong positive impact of H 2 , even at very low concentrations, on the RIA. Hydrogen quickly passivates (t <; 1 s) most of the defects responsible for the visible-near-IR RIA, mainly phosphorus oxygen hole centers (POHC) and P1 defects. However, 1 year after the H 2 loading at RT or when operating at liquid nitrogen temperature, the RIA levels of the not-treated and H 2 -loaded fiber become comparable. The obtained results provide a better understanding of the potential and limitations of H 2 -loading treatment to design radiation-hardened fiber links.
TDCOSMO Millon, M; Courbin, F; Bonvin, V ...
Astronomy & astrophysics,
10/2020, Letnik:
642
Journal Article
Recenzirano
Odprti dostop
We present six new time-delay measurements obtained from Rc-band monitoring data acquired at the Max Planck Institute for Astrophysics (MPIA) 2.2 m telescope at La Silla observatory between October ...2016 and February 2020. The lensed quasars HE 0047−1756, WG 0214−2105, DES 0407−5006, 2M 1134−2103, PSJ 1606−2333, and DES 2325−5229 were observed almost daily at high signal-to-noise ratio to obtain high-quality light curves where we can record fast and small-amplitude variations of the quasars. We measured time delays between all pairs of multiple images with only one or two seasons of monitoring with the exception of the time delays relative to image D of PSJ 1606−2333. The most precise estimate was obtained for the delay between image A and image B of DES 0407−5006, where τAB = −128.4−3.8+3.5 d (2.8% precision) including systematics due to extrinsic variability in the light curves. For HE 0047−1756, we combined our high-cadence data with measurements from decade-long light curves from previous COSMOGRAIL campaigns, and reach a precision of 0.9 d on the final measurement. The present work demonstrates the feasibility of measuring time delays in lensed quasars in only one or two seasons, provided high signal-to-noise ratio data are obtained at a cadence close to daily.
•We assess the co-movement among natural rates in 10 OECD countries and the euro area.•Spillovers rose since the late nineties and common factors are key drivers.•They also spiked around recessions ...and financial and sovereign debt crises.•Our results suggest the need for more policy coordination and a (lower) “new normal”.•A very gradual and uncertain monetary normalisation path is on the way.
Using quarterly data for 10 OECD countries and the Euro area and a Kalman filtering technique, we investigate the international co-movement among natural interest rates. We show that the US is the main source of global spillovers and global/common factors appear to be key drivers of such co-movement. Indeed, global liquidity is a net transmitter of shocks, while quantitative easing (QE) and the US Dollar are net recipients of shocks. We also find that total spillovers among natural interest rates have been rising since the late nineties, spiking at around economic recessions, periods of US monetary policy tightening, the global financial crisis and the Eurozone sovereign debt crisis. From a policy perspective, our findings suggest: (i) the need of more monetary policy coordination among countries to tackle common drivers of natural rates; (ii) the importance of complementing monetary policy with macro-financial stabilisation tools to ease the global constraints that it faces; (iii) a very gradual and uncertain monetary normalisation path, subject to spikes in financial markets' volatility; and (iv) a (lower) “new normal” level for real policy rates.
In this work, the formation of micrometer-size crystalline monolayer (1L) MoS2 flakes with triangular shape and a central multilayer core is obtained by the sulfurization at 800 °C of pre-deposited ...ultrathin MoOx films (1.2–1.8 nm) on c-sapphire substrates. The thickness uniformity, crystalline quality, doping and strain distribution in the MoS2 flakes as a function of the initial MoOx thickness was evaluated by micro-Raman (μR) mapping. The excellent crystalline quality of the triangular 1L-MoS2 flakes was confirmed by micro-photoluminescence (μPL) maps, showing a very intense peak at ∼1.85 eV, that decreases in the central part, as expected for multilayers MoS2. A biaxial strain of ∼0.38–0.4% was deduced from the μPL data, in perfect agreement with μR results. Our results show how the sulfurization of pre-deposited MoOx films on c-sapphire allows, under proper conditions, to obtain 1L-MoS2 flakes with quality comparable to the one typically reported by the conventional chemical vapour deposition, with important implications for device applications.
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•Micrometer crystalline 1L-MoS2 flakes are obtained on c-sapphire by the sulfurization of pre-deposited ultrathin MoOx films.•The thickness uniformity, doping and strain distribution in the MoS2 flakes was evaluated by Raman mapping.•The crystalline quality of the 1L-MoS2 flakes was confirmed by PL spectroscopy, showing an intense peak at ∼1.85 eV.
We describe the simple fabrication of SiO
2
sol-gel monoliths embedding highly luminescent carbon nanodots (CDs) sensitive to metal ions. The pristine CDs we synthesize display an intense dual ...emission consisting in two fluorescence bands in the green and violet region, and we demonstrate that this photoluminescence is substantially unchanged when the dots are incorporated in the SiO
2
matrix. The emission of these CDs is quenched by interactions with Cu
2+
ions, which can be used to detect these ions with a detection limit of 1 μM. The chromophores remain accessible to diffusing Cu
2+
ions even after embedding CDs in the sol-gel monolith, where their detection capabilities are preserved. Such a result provides the proof-of-principle of a new sensing scheme, where CDs are exploited as active sensing centers of metal transition ions within a solid-state device. The different interaction mechanisms of CDs with copper, in liquid and solid phase, are analyzed in detail and discussed in terms of different accessibility of their chromophores when the dots are incorporated in the SiO
2
matrix.
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