Abstract
The process by which an existing magnetic field of ∼102–103 T may be amplified by an order of magnitude along the axis of laser propagation in underdense plasma by an intense laser pulse is investigated. The mechanism underlying the effect is understood to be ponderomotive in nature, initiated by the drift motion of electrons displaced by the laser pulse as they relax towards the axis, and sustained by a combination of quasistatic magnetic field structures and electron Hall and diamagnetic currents. We employ two- and three-dimensional particle-in-cell simulations to numerically investigate the process and find qualitative agreement with the scaling relations found in our theory model. The lifetime of the process is considered, and we find the major factor limiting its growth and lifetime is ion motion, which disrupts the electron currents necessary to sustain the induced magnetic field. This field is found to be of sufficient strength, and is long-lived enough to be relevant for study in relation to applications in radiation production and laboratory astrophysics.
Highlights
Fusion 63 (2021) 084001 field strengths on the order of 1 kT may be reached by using capacitor-coil targets [10, 11] and yet higher fields maybe achieved with so-called snail targets irradiated by intense lasers [12, 13]
We choose to use a cylindrical code for the parameter scans rather than a 2D code in order to better reproduce the 3D current structures that form, and we find that there is sufficiently good agreement between Osiris and FBPIC to justify its use [21]
The total energy contained in the magnetic fields does increase with density, as shown in figure 4(b) upper inset. This may indicate that a high density plasma with n0 ≥ 1 is capable of supporting very high magnetic fields, but with the requirement that the laser pulse is of high enough intensity to sufficiently heat the plasma and drive the requisite currents
Summary
Magnetic fields in plasmas are relevant to almost all laserplasma applications, as they are found universally in all plasma regimes from astrophysicsal to fusion and a need to understand them underpins many of the ongoing research efforts in plasma physics. Fusion 63 (2021) 084001 field strengths on the order of 1 kT may be reached by using capacitor-coil targets [10, 11] and yet higher fields maybe achieved with so-called snail targets irradiated by intense lasers [12, 13]. Such high field regimes offer access to new regimes of physics and applications under unprecedented conditions. The initial explanation of this is attributed to the transfer of angular momentum from an LG01 mode laser to the plasma, facilitated by the external magnetic field. A theoretical model is provided to explain the magnetic field generation qualitatively
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