Generation of megatesla magnetic fields by intense-laser-driven microtube implosions

Nanowire implosion under laser amplified spontaneous emission pedestal irradiation

Nanowire array targets exhibit high optical absorption when interacting with short, intense laser pulses. This leads to an increased yield in the production of accelerated particles for a variety of applications. However, these interactions are sensitive to the laser prepulse and could be significantly affected. Here, we show that an array of aligned nanowires is imploded when irradiated by an Amplified Spontaneous Emission pedestal of a [Formula: see text] laser with an intensity on the order of [Formula: see text]. Using radiation hydrodynamics simulations, we demonstrate that the electron density profile is radially compressed at the tip by the rocket-like propulsion of the ablated plasma. The mass density compression increases up to [Formula: see text] when a more dense nanowire array is used. This is due to the ablation pressure from the neighboring nanowires. These findings offer valuable information for selecting an appropriate target design for experiments aimed at enhancing production of accelerated particles.

Efficient Generation of Axial Magnetic Field by Multiple Laser Beams with Twisted Pointing Directions

Strong laser-driven magnetic fields are crucial for high-energy-density physics and laboratory astrophysics research, but generation of axial multikilotesla fields remains a challenge. The difficulty comes from the inability of a conventional linearly polarized laser beam to induce the required azimuthal current or, equivalently, angular momentum (AM). We show that several laser beams can overcome this difficulty. Our three-dimensional kinetic simulations demonstrate that a twist in their pointing directions enables them to carry orbital AM and transfer it to the plasma, thus generating a hot electron population carrying AM needed to sustain the magnetic field. The resulting multikilotesla field occupies a volume that is tens of thousands of cubic microns and it persists on a picosecond timescale. The mechanism can be realized for a wide range of laser intensities and pulse durations. Our scheme is well suited for implementation using multikilojoule petawatt-class lasers, because, by design, they have multiple beamlets and because the scheme requires only linear polarization.

Kilotesla plasmoid formation by a trapped relativistic laser beam

A strong quasistationary magnetic field is generated in hollow targets with curved internal surface under the action of a relativistically intense picosecond laser pulse. Experimental data evidence the formation of quasistationary strongly magnetized plasma structures decaying on a hundred picoseconds timescale, with the magnetic field strength of the kilotesla scale. Numerical simulations unravel the importance of transient processes during the magnetic field generation and suggest the existence of fast and slow regimes of plasmoid evolution depending on the interaction parameters. The proposed setup is suited for perspective highly magnetized plasma application and fundamental studies.

Laser cluster interaction in ambient magnetic fields for accelerating electrons in two stages without external injection

In the few-cycle pulse regime of laser-cluster interaction (intensity [Formula: see text], wavelength [Formula: see text] nm), laser absorption is mostly collisionless and may happen via anharmonic resonance (AHR) process in the overdense (cluster) plasma potential. Many experiments, theory and simulation show average absorbed energy per cluster-electron ([Formula: see text]) close to the electron's ponderomotive energy ([Formula: see text]) in the collisionless regime. In this work, by simple rigid sphere model (RSM) and detailed particle-in-cell (PIC) simulation, we show enhanced [Formula: see text] 30-70[Formula: see text]-a 15-30 fold increase-with an external (crossed) magnetic field near the electron-cyclotron resonance (ECR). Due to relativistic mass increase, electrons quickly deviate from the standard (non-relativistic) ECR, but time-dependent relativistic-ECR (RECR) happens which also contributes to enhanced [Formula: see text]. Here laser is coupled to electrons in two stages, i.e, AHR and ECR/RECR. To probe further we retrieve the phase-difference [Formula: see text] between the driving electric field and corresponding velocity component for each electron (in PIC and RSM). We find absorption by electron via AHR happens in a very short interval [Formula: see text] for less than half a laser period where [Formula: see text] remains close to [Formula: see text] (necessary condition for maximum laser absorption) and then [Formula: see text] drops to its initial [Formula: see text] (meaning no absorption) after such short-lived AHR. On the contrary, auxiliary magnetic field near the ECR modifies AHR scenario inside the cluster and also helps maintaining the required phase [Formula: see text] for the liberated cluster-electron accompanied by frequency matching for ECR/RECR for a prolonged [Formula: see text] (which covers 50-60% of the laser pulse through pulse maxima) even after AHR-leading to jump in [Formula: see text] 30-70[Formula: see text]. We note that to realize the second stage of enhanced energy coupling via ECR/RECR, the first stage via AHR is necessary.

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.

Emission of electromagnetic waves as a stopping mechanism for nonlinear collisionless ionization waves in a high-β regime

A high energy density plasma embedded in a neutral gas is able to launch an outward-propagating nonlinear electrostatic ionization wave that traps energetic electrons. The trapping maintains a strong sheath electric field, enabling rapid and long-lasting wave propagation aided by field ionization. Using 1D3V kinetic simulations, we examine the propagation of the ionization wave in the presence of a transverse MG-level magnetic field with the objective to identify qualitative changes in a regime where the initial thermal pressure of the plasma exceeds the pressure of the magnetic field (β>1). Our key finding is that the magnetic field stops the propagation by causing the energetic electrons sustaining the wave to lose their energy by emitting an electromagnetic wave. The emission is accompanied by the magnetic field expulsion from the plasma and an increased electron loss from the trapping wave structure. The described effect provides a mechanism mitigating rapid plasma expansion for those applications that involve an embedded plasma, such as high-flux neutron production from laser-irradiated deuterium gas jets.