Generation Of Quasistatic Magnetic Field Research Articles

Generation of a quasi-static magnetic field by a circularly polarised laser pulse due to tunnelling gas ionisation

We present a theoretical model of the quasi-static magnetic field generation in a laser channel, which is formed behind the front of a short laser pulse that ionises a gas. The generation of a magnetic field is caused by the appearance of the electron pressure anisotropy during tunnelling ionisation of atoms. In the considered case of subrelativistic laser light intensities, the generated magnetic field can reach ∼1 MG with an energy transformation ratio of about 1 %, which paves the way for identifying the proposed mechanism when use is made of a wide class of ultrashort pulse lasers.

Twisted Kinetic Plasma Waves

Similarly to electromagnetic waves, plasma waves can also carry an orbital angular momentum. A key distinction from electromagnetic waves is that plasma waves are intrinsically coupled to electrons and may deposit their momentum with electrons, resulting in their secular motion and generation of quasistatic magnetic fields. In this paper, we present an analysis of kinetic plasma waves carrying an orbital angular momentum in the paraxial approximation by considering the energy and momentum exchange between the wave and electrons and the average electron motion induced by plasma wave damping.

On the Theory of Quasi-Static Magnetic Field Generation Caused by Electromagnetic Wave Incidence on Semi-Infinite Plasma

Quasi-static magnetic field generation caused by the oblique incidence of a p-polarized electromagnetic wave on a semi-infinite plasma, in which the electron density exceeds the critical value, is considered. It is shown that the appearance of magnetic fields is caused by excitation of a nonlinear surface current at the zero harmonic of the pump wave.

All-optical magnetization switching by counterpropagataion or two-frequency pulses using the plasmon-induced inverse Faraday effect in magnetoplasmonic structures

In this Letter we study the generation of quasi-static magnetic fields by the plasmon-induced inverse Faraday effect and propose a magneto-optical waveguide structure for achieving magnetization switching at sub-ps time in a nano-confined magneto-optical structure. In particular we show that the direction of the generated quasi-static field in a magneto-optical dielectric cavity side-coupled to a metal-insulator-metal (MIM) waveguide depends sensitively on the wavelength of the surface plasmon polaritions (SPP). This phenomenon could open up a new energy-efficient ultrafast method for nano-confined all-optical magnetization switching by two-frequency pulses.

Dynamic model of target charging by short laser pulse interactions.

A model providing an accurate estimate of the charge accumulation on the surface of a metallic target irradiated by a high-intensity laser pulse of fs-ps duration is proposed. The model is confirmed by detailed comparisons with specially designed experiments. Such a model is useful for understanding the electromagnetic pulse emission and the quasistatic magnetic field generation in laser-plasma interaction experiments.

Laser-driven platform for generation and characterization of strong quasi-static magnetic fields

Quasi-static magnetic-fields up to 800 T are generated in the interaction of intense laser pulses (500 J, 1 ns, ) with capacitor-coil targets of different materials. The reproducible magnetic-field peak and rise-time, consistent with the laser pulse duration, were accurately inferred from measurements with GHz-bandwidth inductor pickup coils (B-dot probes). Results from Faraday rotation of polarized optical laser light and deflectometry of energetic proton beams are consistent with the B-dot probe measurements at the early stages of the target charging, up to ns, and then are disturbed by radiation and plasma effects. The field has a dipole-like distribution over a characteristic volume of 1 mm3, which is consistent with theoretical expectations. These results demonstrate a very efficient conversion of the laser energy into magnetic fields, thus establishing a robust laser-driven platform for reproducible, well characterized, generation of quasi-static magnetic fields at the kT-level, as well as for magnetization and accurate probing of high-energy-density samples driven by secondary powerful laser or particle beams.

Gigagauss-scale quasistatic magnetic field generation in a snail-shaped target.

A simple setup for the generation of ultra-intense quasistatic magnetic fields, based on the generation of electron currents with a predefined geometry in a curved snail (or 'escargot') target, is proposed and analyzed. Particle-in-cell simulations and qualitative estimates show that gigagauss scale magnetic fields may be obtained with existent laser facilities. The described mechanism of the strong magnetic field generation may be useful in a wide range of applications, from laboratory astrophysics to magnetized inertial confinement fusion schemes.

Effects of the electron spin on the nonlinear generation of quasi-static magnetic fields in a plasma

AbstractThrough an extended kinetic model, we study the nonlinear generation of quasi-static magnetic fields by high-frequency fields in a plasma, taking into account the effects of the electron spin. It is found that although the largest part of the nonlinear current in a moderate density, moderate temperature plasma is due to the classical terms, the spin may still give a significant contribution to the magnetic field generation mechanism. Applications of our results are discussed.

Generation of quasistatic magnetic fields in the interaction of counterpropagating laser pulses in a low-density plasma

The effect of generation of quasistatic magnetic fields in the interaction of counterpropagating moderate-intensity laser pulses in a low-density plasma is considered. It is shown that the onset of strong magnetic fields is attributed to small-scale large-amplitude plasma waves excited in the region of interaction of laser pulses under the action of the averaged ponderomotive forces. The spatial distribution of quasistatic magnetic fields is investigated, as well as the structure of the magnetic-field and current lines.

Quasi-static magnetic field generation due to a linearly polarized laser beam propagating in plasma

Quasi-static magnetic field generation due to propagation of a linearly polarized laser beam in homogeneous, underdense plasma, is presented. The magnetic field is generated due to the interaction of a narrow laser beam with plasma, for which the ponderomotive force dominates over space charge force between electrons and ions. In addition, for narrow beams, the longitudinal component of the laser field becomes significant and therefore contributes to the generation of the quasi-static magnetic field.

Generation of strong quasistatic magnetic fields in interactions of ultraintense and short laser pulses with overdense plasma targets

An analytical fluid model is proposed for the generation of strong quasistatic magnetic fields during normal incidence of a short ultraintense Gaussian laser pulse with a finite spot size on an overdense plasma. The steepening of the electron density profile in the originally homogeneous overdense plasma and the formation of electron cavitation as the electrons are pushed inward by the laser are included self-consistently. It is shown that the appearance of the cavitation plays an important role in the generation of quasistatic magnetic fields: the strong plasma inhomogeneities caused by the formation of the electron cavitation lead to the generation of a strong axial quasistatic magnetic field Bz. In the overdense regime, the generated quasistatic magnetic field increases with increasing laser intensity, while it decreases with increasing plasma density. It is also found that, in a moderately overdense plasma, highly intense laser pulses can generate magnetic fields approximately 100 MG and greater due to the transverse linear mode conversion process.

Nonlinear response of a relativistic plasma to intense fields: Generation of strong quasistatic magnetic fields

The generation of quasistatic magnetic fields by nonlinear interactions of two high-frequency waves are studied on the basis of a correct relativistic kinetic theory for a thermal plasma. The plasma response in the presence of nonlinear excitations is a nonlinear current, which is calculated here within the framework of the relativistic theory. Quasistationary magnetic fields are generated due to the magnetization current. The latter is derived solving the kinetic integrals in the long wavelength limit and it holds for arbitrary plasma temperatures. It also allows for deducing the magnetization currents at nonrelativistic or ultrarelativistic temperatures. The magnitude of quasistationary magnetic fields is estimated for fully relativistic plasma temperatures, where the relativistic contribution dominates. For typical laboratory or numerical experiments the magnetic field strength can reach values higher than 10 MG.

Fluid theory for quasistatic magnetic field generation in intense laser plasma interaction

Based on the ten-moment Grad system of hydrodynamic equations, a self-consistent fluid model is presented for the generation of quasistatic magnetic fields in relativistic intense laser plasma interaction. In this model, the nondiagonal stress tensor is taken into account and the generalized vorticity is proved to be not conserved, which are different from previous ideal fluid models. In the quasistatic approximation, where the low-frequency phase speed vp is much smaller than the electron thermal speed vte, the axial magnetic field Bz and the azimuthal one Bθ are derived. It is found that the condition vp⪢vte used as the cold fluid approximation by previous papers is improper, where the derived Bz is incomplete and one magnetization current for Bz associated with the electron thermal motion does not appear. The profiles of both Bz and Bθ are analyzed. Their dependence on the laser intensity is discussed.

Three-dimensional dynamics of relativistic flows in pair plasmas with force-free magnetic configuration

Dynamics of the relativistic flow in pair plasmas with force-free magnetic configuration is investigated by using a three-dimensional fully relativistic electromagnetic particle-in-cell code. This study is an extension of the work by Haruki and Sakai [Phys. Plasmas 8, 1538 (2001)] that was done in a two-dimensional force-free magnetic configuration. They found that during the early stage of the interaction there occurs the streaming instability, which induces the electromagnetic perturbations associated with generation of quasi-static magnetic field. In the nonlinear stage the force-free magnetic field becomes unstable against the firehose instability and then magnetic islands are formed through magnetic reconnection. The dissipated magnetic field energy is converted to the plasma heating as well as the high-energy particle production. It is found that the three-dimensional configuration could result in completely different dynamics, except for the initial phase where the streaming instability develops. It is also found that the dynamical interaction between the force-free magnetic configuration and the relativistic plasma flows develops sequentially through four different physical processes: (I) The phase of streaming instability, (II) the phase of magnetic reconnection triggered by the first streaming instability, (III) the phase of Alfvén wave excitation through the magnetic reconnection process, and (IV) the phase of dissipation of the Alfvén waves through the magnetic reconnection. It is shown that three-dimensional Alfvén waves with helical magnetic structures can be excited through complicated three-dimensional tearing instability triggered from the streaming instability. During these dynamical processes the pair plasma can be heated through the magnetic reconnection and also the high-energy particles are generated. The interaction process between the force-free collisionless plasmas and the relativistic plasma flows may play an important role for the effective magnetic field energy dissipation, formation of filament structures, and high-energy particle production in astrophysical plasmas.

Quasistatic Magnetic Field Generation by an Intense Ultrashort Laser Pulse in Underdense Plasma

The quasistatic magnetic field created in the interaction of intense ultrashort laser pulses with underdense plasmas has been investigated by two-dimensional particle simulation. The relativistic ponderomotive force and plasma wave excited in self-modulation processes can drive intense electron current mainly in the propagation direction. As a result, an azimuthal, multi-mega Gauss order quasi-static magnetic field can be generated around the laser beam.

Numerical Simulation of Electromagnetic Filamentation and Hollowing Instabilities during Collisions of Counter-Streaming Plasmas

We present the results of two dimensional PIC (Particle-in-Cell) simulations of plasma cloud collisions. We investigate two different types of the plasma configuration: in the first one the initial configuration is assumed to have the slab form and the second configuration has a form of the cylindrical. In both cases we found that the counterstreaming motion of the plasmas is unstable with respect to the electromagnetic mode excitation with the developing of the hollow structures in the electron density distribution, the formation of the electric current filaments and the merging of the filaments and quasistatic magnetic field generation.

Generation of a Small-Scale Quasi-Static Magnetic Field and Fast Particles during the Collision of Electron-Positron Plasma Clouds

We present the results of analytical studies and 2D3V PIC simulations of electron-positron plasma cloud collisions. We concentrate on the problem of quasi-static magnetic field generation. It is shown from linear theory, using relativistic two-fluid equations for electron-positron plasmas, that the generation of a quasi-static magnetic field can be associated with the counterstreaming instability. A two-dimensional relativistic particle simulation provides good agreement with the above linear theory and shows that, in the nonlinear stage of the instability, about 5.3% of the initial plasma flow energy can be converted into magnetic field energy. It is also shown from the simulation that the quasi-static magnetic field undergoes a collisionless change of structure, leading to large-scale, long-living structures and the production of high-energy particles. These processes may be important for understanding the production of high-energy particles in the region where two pulsar winds collide.

Quasistatic magnetic field generation in initially inhomogeneous plasma

We consider the interaction of arbitrary amplitude circularly polarized (c.p.) laser pulses with under-dense, cold, unmagnetized, initially inhomogeneous electron plasmas. Confirming the applicability of the formalism given in our recent paper and deriving the correct expression for the LF drag current we have shown the possibility of strong QSM field generation by spatially uniform c.p. laser radiation in initially strongly inhomogeneous underdense plasma. Investigating the different initial density profiles for laser-produced plasmas, where the density scale length is typically of the order of that of the laser beam amplitude and taking into account the electron cavitation by relativistically strong short laser pulses, we have shown the advantage of the convex initial density profile compared to the concave one (or to the initially homogeneous plasma) to generate immense magnetic fields (∼200 MG and greater) in the self-channelling regime by the currently available intense laser pulses.

Generation Of Magnetic Field And Fast Particles During Collision Of Electron-Positron Plasma Clouds

We present results of analytical studies and 2D3V PIC simulations of electron-positron plasma cloud collisions. We concentrate on the problem of quasi-static magnetic field generation. It is shown from linear theory, using relativistic two-fluid equations for electron-positron plasmas, that the generation of a quasi-static magnetic field can be associated with the counter-streaming instability. A two-dimensional relativistic particle simulation provides good agreement with the above linear theory and that, in the nonlinear stage of the instability, about 5.3 % of the initial plasma flow energy can be converted to magnetic field energy. It is also shown from the simulation that the quasi-static magnetic field undergoes a collision-less change of structure, leading to large scale, long living structures and the production of high-energy particles. These processes may be important for understanding of production of high-energy particles in the region where two pulsar winds collide.

Magnetic fields from high-intensity laser pulses in plasmas

In a plasma interacting with ultra-short, high-intensity laser pulses, the magnetic part of the Lorentz force on the electrons can become as important as the electric part. In this case, we can expect the magnetic field to change the pattern of the nonlinear laser-pulse - plasma interaction drastically. The relativistic nonlinearities introduced by the magnetic interaction are of general interest in relation to the field of ultra-strong electromagnetic waves propagating in media, high-energy space plasmas and laser - plasma interaction under laboratory conditions. We present a summary of analytical and numerical results concerning the generation of quasi-static magnetic fields by high-intensity laser pulses in underdense plasmas and in thin plasma foils, and discuss the dynamical effects of these fields on the plasma motion and on the pulse propagation. This analysis indicates that phenomena such as current pinching, reconnection of magnetic-field lines and vortex propagation etc, that have been previously discussed in the case of space and laboratory plasmas, are also important for laser - plasma interactions.