The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, is experimentally investigated. Ultrahigh contrast (~10(12)) pulses allow us to ...demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultrahigh intensity >10(19) W/cm(2). A maximum increase by a factor of 2.5 of the cutoff energy of protons produced by target normal sheath acceleration is observed with respect to plane targets, around the incidence angle expected for the resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance.
The dynamics of magnetic fields with an amplitude of several tens of megagauss, generated at both sides of a solid target irradiated with a high-intensity (~10(19) W/cm(2)) picosecond laser pulse, ...has been spatially and temporally resolved using a proton imaging technique. The amplitude of the magnetic fields is sufficiently large to have a constraining effect on the radial expansion of the plasma sheath at the target surfaces. These results, supported by numerical simulations and simple analytical modeling, may have implications for ion acceleration driven by the plasma sheath at the rear side of the target as well as for the laboratory study of self-collimated high-energy plasma jets.
We report on the selective acceleration of carbon ions during the interaction of ultrashort, circularly polarized and contrast-enhanced laser pulses, at a peak intensity of 5.5 × 1020 W/cm2, with ...ultrathin carbon foils. Under optimized conditions, energies per nucleon of the bulk carbon ions reached significantly higher values than the energies of contaminant protons ( 33 MeV / nucleon vs 18 MeV), unlike what is typically observed in laser-foil acceleration experiments. Experimental data, and supporting simulations, emphasize different dominant acceleration mechanisms for the two ion species and highlight an (intensity dependent) optimum thickness for radiation pressure acceleration; it is suggested that the preceding laser energy reaching the target before the main pulse arrives plays a key role in a preferential acceleration of the heavier ion species.
The emission of high-order harmonics in the extreme ultraviolet range from the interaction of a short, intense laser pulse with a grating target is investigated experimentally. When resonantly ...exciting a surface plasmon, both the intensity and the highest order observed for the harmonic emission along the grating surface increase with respect to a flat target. Harmonics are obtained when a suitable density gradient is preformed at the target surface, demonstrating the possibility to manipulate the grating profile on a nanometric scale without preventing the surface plasmon excitation. In support of this, the harmonic emission is spatiotemporally correlated to the acceleration of multi-MeV electron bunches along the grating surface. Particle-in-cell simulations reproduce the experimental results and give insight on the mechanism of high harmonic generation in the presence of surface plasmons.
The evolution of the filamentation instability produced by two counterstreaming, ultrarelativistic pair plasmas is studied with particle-in-cell simulations. Radiation friction effects are taken into ...account. Two-dimensional simulations are performed for both cases of the initial momenta being perpendicular (T mode) or parallel (P mode) to the simulation plane. In the initial stage, the instability is purely transverse for both modes and generates small-scale filaments which later merge into larger structures. Particle acceleration leads to a strong broadening of the energy spectrum with the formation of a peak at twice the initial energy for the T mode. In the non-linear stage, significant differences between T- and P modes in the evolution of the fields and in the spectra of accelerated particles are apparent. The presence of radiative losses does not change the dynamics of the instability but strongly affects the structure of the particle spectra in the ultrarelativistic regime (particle energy >100 MeV) and for high plasma densities (>1021 cm−3).
Increasing evidence demonstrates the benefits of palliative care among individuals with Parkinson's disease and related disorders (PDRD), but the critical components that contribute to therapeutic ...effects are not well understood.
To determine the specific items most responsive to a palliative care intervention in PDRD and identify key correlates of improvement in patient and care partner outcomes.
The main trial was a pragmatic comparative effectiveness trial of outpatient integrated palliative care compared to standard care among participants with PDRD (NCT02533921), showing significantly higher patient QOL at six months and lower care partner burden at 12 months. We used longitudinal regression models to analyze changes in subdomains of patient QOL and care partner burden and Spearman correlations to evaluate key correlates of change scores in patient and care partner outcomes. We performed a secondary analysis of data from 210 patients and 175 care partners.
Compared to controls, patients in the intervention reported greater improvement in perceptions of the “self as a whole” at six months (coeff = 0.22, P < 0.05) and care partners reported greater reduction in stress, anger, and loss of control at 12 months (coeff = -.40, -0.25, -0.31, P < 0.05). Positive change in numerous patient non-motor symptoms and grief correlated with improved patient QOL, reduced patient anxiety, and increased care partner spirituality. Alleviation of care partner anxiety and depression correlated with reduced care partner burden.
Specific benefits of an integrated palliative approach in PDRD include improvement in patient holistic self-impressions, care partner self-efficacy, and non-motor symptoms.
The acceleration of multi-MeV protons from the rear surface of thin solid foils irradiated by an intense (approximately 10(18) W/cm2) and short (approximately 1.5 ps) laser pulse has been ...investigated using transverse proton probing. The structure of the electric field driving the expansion of the proton beam has been resolved with high spatial and temporal resolution. The main features of the experimental observations, namely, an initial intense sheath field and a late time field peaking at the beam front, are consistent with the results from particle-in-cell and fluid simulations of thin plasma expansion into a vacuum.
The minimum fluidization velocity (Umf), bubble size characteristics, and tube-to-bed heat transfer coefficient (hc) of ilmenite particles are investigated at pressures up to 2000 kPa. The Umf was ...found to decrease with pressure for dsv ≥ 236 μm and remain constant for dsv ≤ 109 μm. Umf was compared to various Wen and Yu type correlations (Remf=C12+C2Ar−C1) with the Saxena & Vogel (1977) constants resulting in the best fit (AARD = 10.5%) for dsv ≤ 109 μm and the Chitester et al. (1984) constants resulting in the best fit (AARD = 6.4%) for dsv ≥ 236 μm. Pressure marginally effected bubble size relative to gas velocity, with the data fitting the Mori & Wen (1975) correlation best (AARD = 26.4%). The tube-to-bed heat transfer coefficient experienced a maximum with increasing gas velocity and marginally increased with pressure. The Molerus et al. (1995) correlation matched the atmospheric heat transfer data.
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•Small and dense ilmenite ore particles were fluidized at elevated pressures.•Influence of pressure on minimum fluidization was dependent on particle size.•Influence of pressure on bubble size was minor relative to gas velocity.•Surface-to-bed heat transfer coefficient was not greatly affected by pressure.•Several correlations were tested to predict key design parameters.
Light sail acceleration by ultrashort, superintense laser pulses is presently investigated as an approach to compact accelerators of matter. The usual light sail equation assumes a cycle-averaged ...light pressure, which becomes questionable for ultrashort pulse drivers or in the highly relativistic regime. Here, we remove such assumption and compute solutions of the light sail equations which show oscillations of the sail acceleration. The dependence of the final sail velocity on the temporal profile of extremely short pulses is discussed.
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