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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.

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. Brown dwarfs are small stars that are believed to be made of a warm dense plasma that cannot support hydrogen fusion as larger stars do. Here, the authors present a method for studying the properties, such as resistivity, of warm dense plasmas in the laboratory.

Fast electron generation and transport in high-intensity laser–solid interactions induces X-ray emission and drives ion acceleration. Effective production of these sources hinges on an efficient laser absorption into the fast electron population and control of divergence as the beam propagates through the target. Nanowire targets can be employed to increase the laser absorption, but it is not yet clear how the fast electron beam properties are modified. Here we present novel measurements of the emittance of the exiting fast electron beam from irradiated solid planar and nanowire targets via a pepper-pot diagnostic. The measurements indicate a greater fast electron emittance is obtained from nanowire targets. Two-dimensional particle-in-cell simulations support this conclusion, revealing beam defocusing at the wire–substrate boundary, a higher fast electron temperature and transverse oscillatory motion around the wires.

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- μ m thick plastic target, irradiated by a multi-picosecond petawatt laser pulse at an incident intensity of ~10 20 W/cm 2 . 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.

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.

This work aim to prepare a program of studies on nuclear physics and astrophysics, which will be conducted at the new ELI-NP Laser facility, which actually is under construction in Bucharest, Romania. For the arguments treated, such activity has required also a multidisciplinary approach and knowledge in the fields of nuclear physics, astrophysics, laser and plasma physics join with also some competences on solid state physics related to the radiation detection. A part of this work has concerned to the experimental test, which have been performed in several laboratories and in order to study and increase the level of knowledge on the different parts of the project. In particular have been performed studies on the laser matter interaction at the ILIL laboratory of Pisa Italy and at the LENS laboratory in Catania, where (by using different experimental set-ups) has been investigated some key points concerning the production of the plasma stream. Test has been performed on several target configurations in terms of: composition, structure and size. All the work has been devoted to optimize the conditions of target in order to have the best performance on the production yields and on energies distribution of the inner plasma ions. A parallel activity has been performed in order to study the two main detectors, which will constitute the full detections system, which will be installed at the ELI-NP facility.

We report on an experimental study on the interaction of a high-contrast 40 fs duration 2 TW laser pulse with an argon-cluster target. A high-charge, homogeneous, large divergence electron beam with moderate kinetic energy (~2 MeV) is observed in the forward direction. The results show that an electron beam with a charge as high as 12 nC can be obtained using a table-top laser system. It was demonstrated that the accelerated electron beam is suitable for a variety of applications such as micro-radiography of thin samples in a wide field of view. It can also be applied for in vitro dosimetry studies.

In 1998 Bulanov et al. [Phys. Rev. E 58, R5257 (1998)] proposed a novel scheme for the production of high-quality electron beams in laser wakefield acceleration in which a controlled longitudinal nonlinear wave breaking is induced by a tailored electron density profile. This proposal was supported by both analytical and numerical results in a spatially one-dimensional configuration. In this paper we present results of a particle-in-cell simulation, two-dimensional in space and three-dimensional in the fields, of the interaction of an ultraintense laser pulse with a preformed plasma where the electron density decreases steeply from a first to a second plateau. We show that in our regime two-dimensional effects play a relevant role, allowing the production of well collimated, short and almost monochromatic electron beam. Remarkably low values of transverse and longitudinal normalized beam emittance ϵrmstr=9×10−2mmmrad and ϵrmslon=2mmkeV are obtained.

It was predicted that, when a fast electron beam with some angular spread is normally incident on a resistivity gradient, magnetic field generation can occur that can inhibit beam propagation [A. R. Bell et al., Phys. Rev. E 58, 2471 (1998)]. This effect can have consequences on the laser-driven ion acceleration. In the experiment reported here, we compare ion emission from laser irradiated coated and uncoated metal foils and we show that the ion beam from the coated target has a much smaller angular spread. Detailed hybrid numerical simulations confirm that the inhibition of fast electron transport through the resistivity gradient may explain the observed effect.