Персона: Кочетков, Юрий Владимирович
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Implementation of amplitude-phase analysis of complex interferograms for measurement of spontaneous magnetic fields in laser generated plasma
© 2020 Author(s).Generation of spontaneous magnetic fields (SMFs) is one of the most interesting phenomena accompanying an intense laser-matter interaction. One method of credible SMFs measurements is based on the magneto-optical Faraday effect, which requires simultaneous measurements of an angle of polarization plane rotation of a probe wave and plasma electron density. In classical polaro-interferometry, these values are provided independently by polarimetric and interferometric images. Complex interferometry is an innovative approach in SMF measurement, obtaining information on SMF directly from a phase-amplitude analysis of an image called a complex interferogram. Although the theoretical basis of complex interferometry has been well known for many years, this approach has not been effectively employed in laser plasma research until recently; this approach has been successfully implemented in SMF measurement at the Prague Asterix Laser System (PALS). In this paper, proprietary construction solutions of polaro-interferometers are presented; they allow us to register high-quality complex interferograms in practical experiments, which undergo quantitative analysis (with an original software) to obtain information on the electron density and SMFs distributions in an examined plasma. The theoretical foundations of polaro-interferometric measurement, in particular, complex-interferometry, are presented. The main part of the paper details the methodology of the amplitude-phase analysis of complex interferograms. This includes software testing and examples of the electron density and SMF distribution of a laser ablative plasma generated by irradiating Cu thick planar targets with an iodine PALS laser at an intensity above about 1016 W/cm2.
On the proton radiography of magnetic fields in targets irradiated by intense picosecond laser pulses
© Published under licence by IOP Publishing Ltd.Proton radiography is a common diagnostic technique in laser-driven magnetic field generation studies. It is based on measuring proton beam deflection in electromagnetic fields induced around the target with the help of radiochromic film stacks. Unraveling information recorded in experimental radiographs and extracting the field profiles is not always a straightforward task. In this paper, some aspects of data analysis by reproducing experimental radiographs in numerical simulations are described. The approach allows determining the field strength and structure in the target area for various target geometries.
Kilotesla plasmoid formation by a trapped relativistic laser beam
A strong quasistationary magnetic field is generated in hollow targets with curved internal surface under the action of a relativistically intense picosecond laser pulse. Experimental data evidence the formation of quasistationary strongly magnetized plasma structures decaying on a hundred picoseconds timescale, with the magnetic field strength of the kilotesla scale. Numerical simulations unravel the importance of transient processes during the magnetic field generation and suggest the existence of fast and slow regimes of plasmoid evolution depending on the interaction parameters. The proposed setup is suited for perspective highly magnetized plasma application and fundamental studies. © 2022 American Physical Society.
Neural network analysis of quasistationary magnetic fields in microcoils driven by short laser pulses
Optical generation of kilo-tesla scale magnetic fields enables prospective technologies and fundamental studies with unprecedentedly high magnetic field energy density. A question is the optimal configuration of proposed setups, where plenty of physical phenomena accompany the generation and complicate both theoretical studies and experimental realizations. Short laser drivers seem more suitable in many applications, though the process is tangled by an intrinsic transient nature. In this work, an artificial neural network is engaged for unravelling main features of the magnetic field excited with a picosecond laser pulse. The trained neural network acquires an ability to read the magnetic field values from experimental data, extremely facilitating interpretation of the experimental results. The conclusion is that the short sub-picosecond laser pulse may generate a quasi-stationary magnetic field structure living on a hundred picosecond time scale, when the induced current forms a closed circuit. © 2022, The Author(s).
Elaboration of 3-frame complex interferometry for optimization studies of capacitor-coil optical magnetic field generators
Recently developed three-frame complex-interferometry system driven by a Ti:Sa laser with 40 fs pulse has been installed at the PALS (Prague Asterix Laser System) laser facility. This unique diagnostic allows for the first time to perform simultaneous measurements of B-field in the coil region of the capacitor-coil targets (CCT) and the self-generated B-field (SMF) of the diode plasma in between the CCT-plates. CCT were irradiated by the PALS iodine laser (lambda = 1315 nm) with energy in the range 250-500 J and pulse duration of 350 ps at full width at half maximum. The operation of this diagnostic system and methodologies for quantitative data analysis are presented in this study, including: (i) obtaining information about the induction of the magnetic field in the CCT coil based on measurements of the Faraday effect in the TGG (Terbium Gallium Garnet) paramagnetic crystal at the coil vicinity and (ii) determining magnetic field and current density distributions in the capacitor region of the CCT by analysis of the complex interferograms. The preliminary measurements confirmed the high potential of the reported setup for optimization studies of CCT targets.
Hot electron retention in laser plasma created under terawatt subnanosecond irradiation of Cu targets
Laser plasma created by intense light interaction with matter plays an important role in high-energy density fundamental studies and many prospective applications. Terawatt laser-produced plasma related to the low collisional and relativistic domain may form supersonic flows and is prone to the generation of strong spontaneous magnetic fields. The comprehensive experimental study presented in this work provides a reference point for the theoretical description of laser-plasma interaction, focusing on the hot electron generation. It experimentally quantifies the phenomenon of hot electron retention, which serves as a boundary condition for most plasma expansion models. Hot electrons, being responsible for nonlocal thermal and electric conductivities, are important for a large variety of processes in such plasmas. The multiple-frame complex-interferometric data providing information on time resolved spontaneous magnetic fields and electron density distribution, complemented by particle spectra and x-ray measurements, were obtained under irradiation of the planar massive Cu and plastic-coated targets by the iodine laser pulse with an intensity of above 10(16)W cm(-2). The data shows that the hot electron emission from the interaction region outside the target is strongly suppressed, while the electron flow inside the target,i.e.in the direction of the incident laser beam, is a dominant process and contains almost the whole hot electron population. The obtained quantitative characterization of this phenomenon is of primary importance for plasma applications spanning from ICF to laser-driven discharge magnetic field generators.
Multi MeV high charge electron beam source utilizing 1 TW laser and shock wave in gas jet target
The high charge electron beam is generated at interaction of 1 TW laser pulse with gas target tailored by nanosecond prepulse forming a shock wave. Propagation of intense femtosecond pulse through complex plasma slab accelerates electrons up to 10 MeV. The debris free target has potential to kHz laser application and electrons energy enhancement using more powerful femtosecond laser pulse. © 2022 IEEE.
Electron accelerator driven by 1TW femtosecond laser pulses: Targetry, principles and prospects
Complex interferometry of magnetized plasma: Accuracy and limitations
© 2021 Author(s).Expanding laser plasmas, produced by high energy laser radiation, possess both high thermal and magnetic field energy densities. Characterization of such plasma is challenging but may provide essential information needed for understanding its physical behavior. Among the standard experimental techniques used for plasma diagnostics, conventional interferometry is one of the most convenient, informative, and accurate. Attempts to extract more information from each laser shot on large facilities have led to development of complex interferometry, which allows us to reconstruct both plasma electron density and magnetic field distributions from a single data object. However, such a benefit requires more accurate processing, critically important in some situations. This work focuses on quasi-axisymmetric interaction geometry. Starting from basic principles, we present a general analysis, consider main error sources, and obtain plasma density and magnetic field distributions with their derived error bars. A regularization procedure, significantly decreasing an error near the plasma symmetry axis, is proposed and analyzed in detail. With use of synthetic datasets, the presented analysis is generally universal for quasi-axisymmetric plasmas.