Laboratory disruption of scaled astrophysical outflows by a misaligned magnetic field

Wave-driven electron inward transport in a magnetic nozzle

Plasma flows in divergent magnetic fields resembling a magnetic nozzle can be found over wide scales ranging from astrophysical objects to terrestrial plasma devices. Plasma detachment from a magnetic nozzle is a frequent occurrence in natural plasmas, e.g., plasma ejection from the Sun and release from the Sun's magnetic field, forming the solar wind. Plasma detachment has also been a challenging problem relating to space propulsion devices utilizing a magnetic nozzle, especially the detachment of the magnetized electrons having a gyro-radius smaller than the system's scale is required to maintain zero net current exhausted from the system. Here we experimentally demonstrate that a cross-field transport of the electrons toward the main nozzle axis, which contributes to neutralizing the ions detached from the nozzle, is induced by the spontaneously excited magnetosonic wave having the frequency considerably higher than the ion cyclotron frequency and close to the lower hybrid frequency, driving an E × B drift that only effects the electrons. Wave-induced transport and loss have been one of many important issues in plasma physics over the past several decades. Conversely, the presently observed electron inward transport has a beneficial effect on the detachment by reducing the divergence of the expanding plasma beam; this finding will open a new perspective for the role of waves and instabilities in plasmas.

X-ray Self-Emission Imaging of Hydrodynamic Laser-Induced Astrophysical Phenomena

In this article, we present an overview of the application of X-ray self-emission methods for the imaging of hydrodynamic astrophysical phenomena in laboratory-scale experiments. Typical diagnostic approaches, their advantages, drawbacks, and application perspectives are considered. We show that X-ray imaging and spectroscopy methods with 2D and even 1D spatial resolution are valuable for numerous laboratory astrophysical problems. Furthermore, the methods revealed the hydrodynamic evolution, the spatial shape and structure, and spatial features of important parameters such as electron density and plasma temperature of astrophysical objects and related phenomena, which are also required for the verification of astrophysical models.

Magnetic field amplification driven by the gyro motion of charged particles

Spontaneous magnetic field generation plays important role in laser-plasma interactions. Strong quasi-static magnetic fields affect the thermal conductivity and the plasma dynamics, particularly in the case of ultra intense laser where the magnetic part of Lorentz force becomes as significant as the electric part. Kinetic simulations of giga-gauss magnetic field amplification via a laser irradiated microtube structure reveal the dynamics of charged particle implosions and the mechanism of magnetic field growth. A giga-gauss magnetic field is generated and amplified with the opposite polarity to the seed magnetic field. The spot size of the field is comparable to the laser wavelength, and the lifetime is hundreds of femtoseconds. An analytical model is presented to explain the underlying physics. This study should aid in designing future experiments.

Retrieving Transient Magnetic Fields of Ultrarelativistic Laser Plasma via Ejected Electron Polarization

Interaction of an ultrastrong short laser pulse with nonprepolarized near-critical density plasma is investigated in an ultrarelativistic regime, with an emphasis on the radiative spin polarization of ejected electrons. Our particle-in-cell simulations show explicit correlations between the angle resolved electron polarization and the structure and properties of the transient quasistatic plasma magnetic field. While the magnitude of the spin signal is the indicator of the magnetic field strength created by the longitudinal electron current, the asymmetry of electron polarization is found to gauge the islandlike magnetic distribution which emerges due to the transverse current induced by the laser wave front. Our studies demonstrate that the spin degree of freedom of ejected electrons could potentially serve as an efficient tool to retrieve the features of strong plasma fields.

High-repetition rate solid target delivery system for PW-class laser-matter interaction at ELI Beamlines

L3-HAPLS (High-repetition-rate Advanced Petawatt Laser System) at ELI (Extreme Light Infrastructure) Beamlines currently delivers 0.45 PW pulses (12 J in 27 fs) at 3.3 Hz repetition rate. A fresh target surface for every shot was placed at the laser focus using an in-house tape target system designed to withstand large laser intensities and energies. It has been tested for different material thicknesses (25 and 7.6 µm), while L3-HAPLS delivered laser shots for energies ranging from 1 to 12 J. A technical description of the tape target system is given. The device can be used in diverse geometries needed for laser-matter interaction studies by providing an ≈300° free angle of view on the target in the equatorial plane. We show experimental data demonstrating the shot-to-shot stability of the device. An x-ray crystal spherical spectrometer was set up to measure the Kα yield stability, while a GHz H-field probe was used to check the shot-to-shot electromagnetic pulse generation. Finally, we discuss short and mid-term future improvements of the tape target system for efficient user operation.