1,721,745 research outputs found
Low-noise time-resolved optical sensing of electromagnetic pulses from petawatt laser-matter interactions
No full textWe report on the development and deployment of an optical diagnostic for single-shot measurement of the electric-field components of electromagnetic pulses from high-intensity laser-matter interactions in a high-noise environment. The electro-optic Pockels effect in KDP crystals was used to measure transient electric fields using a geometry easily modifiable for magnetic field detection via Faraday rotation. Using dielectric sensors and an optical fibre-based readout ensures minimal field perturbations compared to conductive probes and greatly limits unwanted electrical pickup between probe and recording system. The device was tested at the Vulcan Petawatt facility with 1020 W cm-2 peak intensities, the first time such a diagnostic has been used in this regime. The probe crystals were located ~1.25 m from target and did not require direct view of the source plasma. The measured signals compare favourably with previously reported studies from Vulcan, in terms of the maximum measured intra-crystal field of 10.9 kV/m, signal duration and detected frequency content which was found to match the interaction chamber's horizontal-plane fundamental harmonics of 76 and 101 MHz. Methods for improving the diagnostic for future use are also discussed in detail. Orthogonal optical probes offer a low-noise alternative for direct simultaneous measurement of each vector field component. © 2017 The Author(s)
Experimental study of fusion neutron and proton yields produced by petawatt-laser-irradiated D2-3He or CD4-3He clustering gases
No full textWe report on experiments in which the Texas Petawatt laser irradiated a mixture of deuterium or deuterated methane clusters and helium-3 gas, generating three types of nuclear fusion reactions: D(d,3He)n, D(d,t)p, and 3He(d,p)4He. We measured the yields of fusion neutrons and protons from these reactions and found them to agree with yields based on a simple cylindrical plasma model using known cross sections and measured plasma parameters. Within our measurement errors, the fusion products were isotropically distributed. Plasma temperatures, important for the cross sections, were determined by two independent methods: (1) deuterium ion time of flight and (2) utilizing the ratio of neutron yield to proton yield from D(d,3He)n and 3He(d,p)4He reactions, respectively. This experiment produced the highest ion temperature ever achieved with laser-irradiated deuterium clusters. © 2013 American Physical Society
Experiment on laser interaction with a planar target for conditions relevant to shock ignition
No full textWe report the experiment conducted on the Prague Asterix Laser System (PALS) laser facility dedicated to make a parametric study of the laser-plasma interaction under the physical conditions corresponding to shock ignition thermonuclear fusion reactions. Two laser beams have been used: the auxiliary beam, for preplasma creation on the surface of a plastic foil, and the main beam to launch a strong shock. The ablation pressure is inferred from the volume of the crater in the Cu layer situated behind the plastic foil and by shock breakout chronometry. The population of fast electrons is analyzed by Kα emission spectroscopy and imaging. The preplasma is characterized by three-frame interferometry, x-ray spectroscopy and ion diagnostics. The numerical simulations constrained with the measured data gave a maximum pressure in the plastic layer of about 90 Mbar. © 2014 The Royal Swedish Academy of Sciences
New scheme to produce aneutronic fusion reactions by laser-accelerated ions
No full textThe development of high-intensity lasers has opened the field of nuclear reactions initiated by laser-accelerated particles. One possible application is the production of aneutronic fusion reactions for clean fusion energy production. We propose an innovative scheme based on the use of two targets and present the first results obtained with the ELFIE facility (at the LULI Laboratory) for the proton-boron-11 (p-11B) fusion reaction. A proton beam, accelerated by the Target Normal Sheat Acceleration mechanism using a short laser pulse (12 J, 350 fs, 1.056 m, 1019 W cm-2), is sent onto a boron target to initiate fusion reactions. The number of reactions is measured with particle diagnostics such as CR39 track-detectors, active nuclear diagnostic, Thomson Parabola, magnetic spectrometer, and time-of-flight detectors that collect the fusion products: the α-particles. Our experiment shows promising results for this scheme. In the present paper, we discuss its principle and advantages compared with another scheme that uses a single target and heating mechanisms directly with photons to initiate the same p-11B fusion reaction. © 2015 Cambridge University Press
Multi probes measurements at the PALS Facility Research Centre during high intense laser pulse interactions with various target materials
No full textDuring the interaction of high intense laser pulse with solid target, a large amount of hot electrons is produced and a giant Electromagnetic Pulse (EMP) is generated due to the current flowing into the system target-target holder, as well as due to the escaping charged particles in vacuum. EMP production for different target materials is investigated inside and outside the target chamber, using monopole antenna, super wide-band microstrip antenna and Moebius antenna. The EMP consists in a fast transient magnetic field lasting hundreds of nanosecond with frequencies ranging from MHz to tens of GHz. Measurements of magnetic field and return target current in the range of kA were carried out by an inductive target probe (Cikhardt J. et al. Rev. Sci. Instrum. 85 (2014) 103507). © The Authors, published by EDP Sciences, 2018
EMP characterization at PALS on solid-target experiments
No full textWe describe the characterization of electromagnetic pulses (EMPs) in experiments on solid targets at PALS laser facility in Prague, for energy up to 600 J and intensity up to 1016 W cm-2 at focus. Measurements of EMPs have been performed by different conductive probes placed inside and outside the experimental chamber. We show results for different targets and probe configurations, and illustrate effects of spurious direct coupling of these transient fields with the read-out apparatus, which are important for high-energy and high-intensity laser-plasma experiments. The related countermeasures are described and demonstrated to be very effective for improving the signal-to-noise ratio, at expenses of measured bandwidths. They allowed us to detect the EMP components due to the intense neutralization currents flowing through the target holder, and those possibly due to wakefields associated with emitted charged particles, which resulted in these experiments to be of the same order of magnitude. It is the first time both discharge current and associated EMP are effectively measured in the same nanosecond-scale experiment, where this EMP contribution is effectively detected by conductive probes. A remarkable agreement was obtained from comparison of the detected EMP profile with measured neutralization current. We also show the results achieved by means of electromagnetic simulations of fields in the modeled experimental chamber, in particular in the regions where the probes were actually placed during the experiments, and compare them with measured signals. It appears that conductive probes have limitations for the measurement of the high-frequency components of the EMP fields. The illustrated results are of primary importance for the hot topic of EMP characterization and minimization in plants for inertial-confinement-fusion (NIF, LMJ, PETAL) as well as for laser-plasma acceleration (PETAL, ELI, Apollon⋯). © 2018 ENEA
Electro-optic analysis of the influence of target geometry on electromagnetic pulses generated by petawatt laser-matter interactions
No full textWe present an analysis of strong laser-driven electromagnetic pulses using novel electro-optic diagnostic techniques. A range of targets were considered, including thin plastic foils (20-550 nm) and mass-limited, optically-levitated micro-targets. Results from foils indicate a dependence of EMP on target thickness, with larger peak electric fields observed with thinner targets. Spectral analysis suggests high repeatability between shots, with identified spectral features consistently detected with 30 MeV energies, suggesting the discharge current contribution to EMP is dominant. © The Authors, published by EDP Sciences, 2018
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