Flowing plasma jets are increasingly investigated and used for surface treatments, including biological matter, and as soft ionization sources for mass spectrometry. They have the characteristic ...capability to transport energy from the plasma excitation region to the flowing afterglow, and therefore to a distant application surface, in a controlled manner. The ability to transport and deposit energy into a specimen is related to the actual energy transport mechanism. In case of a flowing helium plasma, the energy in the flowing afterglow may be carried by metastable helium atoms and long-lived helium dimer ions. In this work a systematic investigation of the optical and spectroscopic characteristics of a supersonic flowing helium plasma in vacuum and its afterglow as function of the helium gas density is presented. The experimental data are compared with numerical modeling of the plasma excitation and helium dimer ion formation supported by a Computational Fluid Dynamic simulation of the helium jet. The results indicate that the plasma afterglow is effectively due to helium dimer ions recombination via a three-body reaction.
The transport of hot, relativistic electrons produced by the interaction of an intense petawatt laser pulse with a solid has garnered interest due to its potential application in the development of ...innovative x-ray sources and ion-acceleration schemes. We report on spatially and temporally resolved measurements of megagauss magnetic fields at the rear of a 50-μm thick plastic target, irradiated by a multi-picosecond petawatt laser pulse at an incident intensity of ~10
W/cm
. The pump-probe polarimetric measurements with micron-scale spatial resolution reveal the dynamics of the magnetic fields generated by the hot electron distribution at the target rear. An annular magnetic field profile was observed ~5 ps after the interaction, indicating a relatively smooth hot electron distribution at the rear-side of the plastic target. This is contrary to previous time-integrated measurements, which infer that such targets will produce highly structured hot electron transport. We measured large-scale filamentation of the hot electron distribution at the target rear only at later time-scales of ~10 ps, resulting in a commensurate large-scale filamentation of the magnetic field profile. Three-dimensional hybrid simulations corroborate our experimental observations and demonstrate a beam-like hot electron transport at initial time-scales that may be attributed to the local resistivity profile at the target rear.
In the Shock Ignition scheme, the spike pulse intensity is well above the threshold of parametric instabilities, which produce a considerable amount of hot electrons that could be beneficial or ...detrimental to the ignition. To study their impact, an experiment has been carried out on the LMJ-PETAL facility with a goal to generate a strong shock inside a plastic layer under plasma conditions relevant to full-scale shock ignition targets. To evaluate the effect of hot electrons on the shock characteristics, laser temporal smoothing was either switched on or off, which in turns varies the quantity of hot electrons being generated. In this paper, we present preliminary results obtained during the experiment dedicated to the hot electron characterization. We present also calculations for the second part of the experiment, scheduled in 2020 and focused on the shock characterization.
We present a study of Yb:YAG active media slabs, based on a ceramic layered structure with different doping levels. We developed a procedure allowing 3D numerical analysis of the slab optical ...properties as a consequence of the thermal load induced by the pump process. The simulations are compared with a set of experimental results in order to validate the procedure. These structured ceramics appear promising in appropriate geometrical configurations, and thus are intended to be applied in the construction of High Energy Diode Pumped Solid State Laser (DPSSL) systems working in high repetition-rate pulsed regimes.
Lasers for Novel Accelerators Gizzi, L.A.; Koester, P.; Labate, L. ...
Journal of physics. Conference series,
11/2019, Letnik:
1350, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Novel accelerator schemes are rapidly emerging in the wake of laser-plasma acceleration research and involve advanced high-power laser drivers for their operation. Significant progress has been made ...in laser performance during the past decade, including repetition rate, average and peak power, and footprint, making these systems attractive for many applications, including novel accelerators. Here we discuss laser driver requirements for the proposed novel accelerator schemes, examine emerging technologies and introduce a viable laser driver concept for a first generation of plasma accelerators.
Since the observation of the first brown dwarf in 1995, numerous studies have led to a better understanding of the structures of these objects. Here we present a method for studying material ...resistivity in warm dense plasmas in the laboratory, which we relate to the microphysics of brown dwarfs through viscosity and electron collisions. Here we use X-ray polarimetry to determine the resistivity of a sulphur-doped plastic target heated to Brown Dwarf conditions by an ultra-intense laser. The resistivity is determined by matching the plasma physics model to the atomic physics calculations of the measured large, positive, polarization. The inferred resistivity is larger than predicted using standard resistivity models, suggesting that these commonly used models will not adequately describe the resistivity of warm dense plasma related to the viscosity of brown dwarfs.
The coupling of ultra-intense, ultra-short laser pulses with solid targets is heavily dependent on the properties of the vacuum–solid interface and is usually quite low. However, laser absorption can ...be enhanced via micro or nanopatterning of the target surface. Depending on the laser features and target geometry, conditions can be optimized for the generation of hot dense matter, which can be used to produce high-brightness radiation sources or even to accelerate particles to relativistic energies. In this context, ZnO nanowires were grown on metallic, thin-foil targets. The use of a thin-foil substrate was dictated by the need to achieve proton acceleration via target normal sheath acceleration at the rear side. The chemical process parameters were studied in-depth to provide control over the nanowire size, shape, and distribution. Moreover, the manufacturing process was optimized to provide accurate reproducibility of key parameters in the widest possible range and good homogeneity across the entire foil area.
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