arXiv subjects

S. A. Pikuz

Publications and source records attributed to S. A. Pikuz.

8 recordsLinked to original sources

arXiv2024

Demonstration of The Brightest Nano-size Gamma Source

Gamma rays selectively interact with nuclei, induce and mediate nuclear reactions and elementary particle interactions, and exceed x-rays in penetrating power and thus are indispensable for analysis and modification of dense objects. Yet, the available gamma sources lack sufficient power and brightness. The predicted and highly desirable laser-driven gamma flash, from here on termed "Gamma Flash", based on inverse Compton scattering from solid targets at extreme irradiances (>$10^{23}W/cm^2$), would be the highest-power and the brightest terrestrial gamma source with a 30-40% laser-to-gamma energy conversion. However, Gamma Flash remains inaccessible experimentally due to the Bremsstrahlung background. Here we experimentally demonstrate a new interaction regime at the highest effective irradiance where Gamma Flash scaled quickly with the laser power and produced several times the number of Bremsstrahlung photons. Simulations revealed an attosecond, Terawatt Gamma Flash with a nanometre source size achieving a record brightness exceeding $~10^{23}photons/mm^2mrad^2s$ per 0.1% bandwidth at tens of MeV photon energies, surpassing astrophysical Gamma Ray Bursts. These findings could revolutionize inertial fusion energy by enabling unprecedented sub-micrometre/femtosecond resolution radiography of fuel mixing instabilities in extremely-compressed targets. The new gamma source could facilitate significant advances in time-resolved nuclear physics, homeland security, nuclear waste management and non-proliferation, while opening possibilities for spatially-coherent gamma rays.

physics.plasm-ph↗

arXiv2022

Direct imaging of shock wave splitting in diamond at Mbar pressures

The propagation of a shock wave in solids can stress them to ultra-high pressures of millions of atmospheres. Understanding the behavior of matter at these extreme pressures is essential to describe a wide range of physical phenomena, including the formation of planets, young stars and cores of super-Earths, as well as the behavior of advanced ceramic materials subjected to such stresses. Under megabar (Mbar) pressure, even a solid with high strength exhibits plastic properties, causing the shock wave to split in two. This phenomenon is described by theoretical models, but without direct experimental measurements to confirm them, their validity is still in doubt. Here, we present the results of an experiment in which the evolution of the coupled elastic-plastic wave structure in diamond was directly observed and studied with submicron spatial resolution, using the unique capabilities of the X-ray free-electron laser. The direct measurements allowed, for the first time, the fitting and validation of a strength model for diamond in the range of several Mbar by performing continuum mechanics simulations in 2D geometry. The presented experimental approach to the study of shock waves in solids opens up new possibilities for the direct verification and construction of the equations of state of matter in the ultra-high pressure range, which are relevant for the solution of a variety of problems in high energy density physics.

physics.plasm-ph↗

arXiv2021

A portable X-pinch design for x-ray diagnostics of warm dense matter

We describe the design and x-ray emission properties (temporal, spatial, and spectral) of Dry Pinch I, a portable X-pinch driver developed at Imperial College London. Dry Pinch I is a direct capacitor discharge device, 300x300x700 mm3 in size and approximately 50 kg in mass, that can be used as an external driver for x-ray diagnostics in high-energy-density physics experiments. Among key findings, the device is shown to reliably produce 1.1 +- 0.3 ns long x-ray bursts that couple approximately 50 mJ of energy into photon energies from 1 to 10 keV. The average shot-to-shot jitter of these bursts is found to be 10 +- 4.6 ns using a combination of x-ray and current diagnostics. The spatial extent of the x-ray hot spot from which the radiation emanates agrees with previously published results for X-pinches suggesting a spot size of 10 +- 6 um in the soft energy region (1-10 keV) and 190 +- 100 um in the hard energy region (>10 keV). These characteristics mean that Dry Pinch I is ideally suited for use as a probe in experiments driven in the laboratory or at external facilities when more conventional sources of probing radiation are not available. At the same time, this is also the first detailed investigation of an X-pinch operating reliably at current rise rates of less than 1 kA/ns.

physics.plasm-ph↗

arXiv2020

Laser scattering by submicron droplets originated during the electrical explosion of thin metal wires

This paper presents the results of studying of dispersed media formation during the electrical explosion of thin metal wires in vacuum by using low-current generators ($\sim 1$-$10$~kA). Particular attention is paid to the analysis of the composition and structure of the corresponding explosion products as well as to the problem of their visualization using simultaneous laser interferometry and shadow imaging at two wavelengths (1.064~$μ$m and 0.532~$μ$m). Our findings point to the fact that the important role in the visualization of the explosion products belongs to multiple scattering by submicron droplets of dense condensed matter, which are mixed with metal vapor. The hypothesis on the existence of submicron droplets in the products of exploding metal wires correlates with the results obtained by soft x-ray radiography combined with a laser probing technique. Taking into account the multiple scattering by submicron droplets, it is possible to significantly clarify the parameters of the explosion products visualized via laser probing techniques as well as to gain a deeper insight into the physics behind the electrical wire explosion.

physics.app-ph↗

arXiv2020

Enhanced x-ray emission arising from laser-plasma confinement by a strong transverse magnetic field

We analyze, using experiments and 3D MHD numerical simulations, the dynamics and radiative properties of a plasma ablated by a laser (1 ns, 10$^{12}$-10$^{13}$ W/cm$^2$) from a solid target, as it expands into a homogeneous, strong magnetic field (up to 30 T) transverse to its main expansion axis. We find that as soon as 2 ns after the start of the expansion, the plasma becomes constrained by the magnetic field. As the magnetic field strength is increased, more plasma is confined close to the target and is heated by magnetic compression. We also observe a dense slab that rapidly expands into vacuum after ~ 8 ns; however, this slab contains only ~ 2 % of the total plasma. As a result of the higher density and increased heating of the confined plasma, there is a net enhancement of the total x-ray emissivity induced by the magnetization.

physics.plasm-ph↗

arXiv2015

Observation of neutron emission in the process of X-pinch

The results of measuring the neutron flux in the process of the X-pinch are presented. The measurements were carried out using CR-39 track detectors. It was found that in the process of X-pinch recorded neutron emission over a wide energy range (from thermal to energies greater than 10 MeV) with an intensity of more than 108 neutrons per shot into 4π sr solid angle (assuming isotropy of radiation and localizing the source in the "hot spot"). Data of track detectors suggest that at the time of discharge produced fast neutrons are then slowed down and turned into thermal.

nucl-ex↗

arXiv2012

Exotic dense matter states pumped by relativistic laser plasma in the radiation dominant regime

The properties of high energy density plasma are under increasing scrutiny in recent years due to their importance to our understanding of stellar interiors, the cores of giant planets$^{1}$, and the properties of hot plasma in inertial confinement fusion devices$^2$. When matter is heated by X-rays, electrons in the inner shells are ionized before the valence electrons. Ionization from the inside out creates atoms or ions with empty internal electron shells, which are known as hollow atoms (or ions)$^{3,4,5}$. Recent advances in free-electron laser (FEL) technology$^{6,7,8,9}$ have made possible the creation of condensed matter consisting predominantly of hollow atoms. In this Letter, we demonstrate that such exotic states of matter, which are very far from equilibrium, can also be formed by more conventional optical laser technology when the laser intensity approaches the radiation dominant regime$^{10}$. Such photon-dominated systems are relevant to studies of photoionized plasmas found in active galactic nuclei and X-ray binaries$^{11}$. Our results promote laser-produced plasma as a unique ultra-bright x-ray source for future studies of matter in extreme conditions as well as for radiography of biological systems and for material science studies$^{12,13,14,15}$.

physics.plasm-ph↗

arXiv2010

5.5-7.5 MeV Proton generation by a moderate intensity ultra-short laser interaction with H2O nano-wire targets

We report on the first generation of 5.5-7.5 MeV protons by a moderate intensity short-pulse laser (4.5 \times 1017 W/cm^2, 50 fsec) interacting with H2O nano-wires (snow) deposited on a Sapphire substrate. In this setup, the laser intensity is locally enhanced by the tip of the snow nano-wire, leading to high spatial gradients. Accordingly, the plasma near the tip is subject to enhanced ponderomotive potential, and confined charge separation is obtained. Electrostatic fields of extremely high intensities are produced over the short scale length, and protons are accelerated to MeV-level energies.

physics.plasm-ph↗