Search

The characteristics of the of the ion streams are investigated by using an electrostatic ion energy analyzer and placing different ion collectors at various angles with respect to the target normal. The ion energy distribution as a function of the ion charge state is measured and the comparison of the properties of different ion groups generated by laser beams at two different energies is carried out.

Multidimensional modeling of phenomena and processes occurring during the expansion of the laser-produced plasma for different irradiation conditions related to both the laser beam parameters and the target constructions is a very complex issue, especially when modeling requires consideration of kinetic processes associated with the development of various types of microscopic instability. Multidimensional PIC codes create such a possibility, but their use is limited to modeling phenomena even in a very narrow timescale due to the limited computational capabilities of current supercomputers. For this reason, the paper attempts to interpret the results of the spontaneous magnetic field (SMF) measurements obtained during the PALS (Prague Asterix Laser System) experiment [Pisarczyk et al., AIP Adv. 10, 115201 (2020); Pisarczyk et al., Phys. Plasmas 22, 102706 (2015)] based on the 2D magneto-hydrodynamic (MHD) model [Jach et al., Computer Modeling of Dynamic Interaction of Bodies by Free Point Method (PWN, Warsaw, 2011)]. The MHD equations were used with included arbitrary (i) current of hot electrons treating it as an additional external current and (ii) ion-sound instability responsible for the increase in anomalous resistance in areas with high temperature and low-density plasma. The spatial distribution of magnetic fields and current density obtained from 2D modeling are in acceptable agreement with the experimental results [Pisarczyk et al., Plasma Phys. Controlled Fusion 62, 115020 (2020); Zaraś-Szydłowska et al., AIP Adv. 10, 115201 (2020); Pisarczyk et al., Phys. Plasmas 22, 102706 (2015)]. The inclusion of temporal changes in anomalous resistance in modeling allowed us to explain the persistence of high SMF amplitude at the level of several megagauss after the laser pulse ended due to the effect of magnetic field freezing. [ABSTRACT FROM AUTHOR]

This paper describes design, development, and implementation of a multi-channel magnetic electron spectrometer for the application in laser–plasma interaction experiments carried out at the Prague Asterix Laser System. Modular design of the spectrometer allows the setup in variable configurations to evaluate the angular distribution of hot electron emission. The angular array configuration of the electron spectrometers consists of 16 channels mounted around the target. The modules incorporate a plastic electron collimator designed to suppress the secondary radiation by absorbing the wide angle scattered electrons and photons inside the collimator. The compact model of the spectrometer measures electron energies in the range from 50 keV to 1.5MeV using ferrite magnets and from 250 keV to 5MeV using stronger neodymium magnets. An extended model of the spectrometer increases the measured energy range up to 21MeV or 35MeV using ferrite or neodymium magnets, respectively. Position to energy calibration was obtained using the particle tracking simulations. The experimental results show the measured angularly resolved electron energy distribution functions from interaction with solid targets. The angular distribution of hot electron temperature, the total flux, and the maximum electron energy show a directional dependence. The measured values of these quantities increase toward the target normal. For a copper target, the average amount of measured electron flux is 1.36 × 1011, which corresponds to the total charge of about 21 nC. [ABSTRACT FROM AUTHOR]

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 1016 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. [ABSTRACT FROM AUTHOR]

Acceleration of ions to multi-MeV energies is investigated in various plasma devices to better understand processes in astrophysical plasmas and to develop efficient accelerators for a variety of applications. This paper reports the production of proton, deuteron, and electron beams in a z-pinch—a cylindrically symmetric plasma column that is compressed by its own magnetic field. For this work, the GIT-12 pulsed-power generator was used to drive a novel configuration of z-pinch that dramatically enhanced ion acceleration associated with disruption of the current by instabilities in the compressed plasma. During the disruption of 3 MA current, hydrogen ions were accelerated up to at least 50 MeV, which is almost a hundred-times the ion energy provided by the generator driving voltage of 0.6 MV. Under optimal conditions, the total numbers of hydrogen ions with energies above 20 and 50 MeV were 4 × 1013 and 1011, respectively. Accelerated deuterons produced one 20 ns (full width at half maximum) pulse of fast neutrons via D(d, n)3He and other nuclear reactions. A maximum neutron output of (1.0 ± 0.2) × 1012 neutrons/sr was observed downstream, i.e., in the anode to cathode direction. In this direction, the maximum neutron energy reached 58 ± 7 MeV. Both ion and neutron beams in our experiment reached an end-point energy of about 60 MeV, which is the highest value observed in pulsed-power devices. A localized peak voltage of ≳60 MV was driven by the inductive energy that was stored around the plasma column and that was extracted during a sub-nanosecond current drop. Considering the natural occurrence of current-carrying columns in laboratory and space plasmas, the current interruption observed in z-pinches could represent a more general physical process that contributes to the efficient conversion of magnetic energy into the energy of particle beams in various plasmas. [ABSTRACT FROM AUTHOR]

The laser-induced Cavity Pressure Acceleration (CPA) scheme [S. Borodziuk et al., Appl. Phys. Lett. 95, 231501 (2009)] allows for effective transformation of the laser energy into the kinetic energy of plasma streams and dense plasma objects. It has been proven that using long-wavelength laser beams, with relatively low energies (up to 500 J for λ1 = 1.315 µm and FWHM = 350 ps), it is possible to accelerate macroparticles to very high velocities (above 107 cm/s). The study of neutron yield showed the benefit of CPA in delivering ion temperatures and density sufficient to reach the thermonuclear region. [ABSTRACT FROM AUTHOR]

A single-crystal silicon carbide (SiC) detector was used for measurements of soft x rays, electrons, and ion emission from laser-generated plasma obtained with the use of the Prague Asterix Laser System (PALS) at intensities of the order of 1016 W/cm2 and pulse duration of 300 ps. Measurements were performed by varying the laser intensity and the nature of the irradiated target. The spectra obtained by using the SiC detector show not only the photopeak due to UV and soft x-ray detection, but also various peaks due to the detection of energetic charged particles. Time-of-flight technique was employed to determine the ion kinetic energy of particles emitted from the plasma and to perform a comparison between SiC and traditional ion collectors. The detector was also employed by inserting absorber films of different thickness in front of the SiC surface in order to determine, as a first approximation, the mean energy of the soft x-ray emission from the plasma. [ABSTRACT FROM AUTHOR]

A monocrystalline diamond detector was used for measurements of soft x-ray and ion emission from laser plasma obtained with the use of the PALS Asterix laser at intensities on the order of 1016 W/cm2 and pulse duration of 300 ps. Measurements were performed by varying the laser intensity and the focal position of the laser beam with respect to the target position. The spectra were obtained with the use of a diamond detector, which was without a filter, and showed not only the photopeak due to UV and soft x rays but also the ions emitted from the plasma. The detector was employed with absorbers of different thicknesses to determine, as a first approximation, the energy distribution of soft x-ray emission from the plasma. The time-of-flight technique was employed to determine the ion kinetic energies. [ABSTRACT FROM AUTHOR]