Magnetic field amplification to the gigagauss scale via dynamos driven by femtosecond lasers

Reaching gigagauss magnetic fields opens new horizons both in atomic and plasma physics. At these magnetic field strengths, the electron cyclotron energy $\hbar\omega_{c}$ becomes comparable to the atomic binding energy (the Rydberg), and the cyclotron frequency $\omega_{c}$ approaches the plasma frequency at solid state densities that significantly modifies optical properties of the target. The generation of such strong quasistatic magnetic fields in laboratory remains a challenge. Using supercomputer simulations, we demonstrate how it can be achieved all-optically by irradiating a micro-channel target by a circularly polarized relativistic femtosecond laser. The laser pulse drives a strong electron vortex along the channel wall, inducing a megagauss longitudinal magnetic field in the channel by the inverse Faraday effect. This seed field is then amplified up to a gigagauss level and maintained on a picosecond time scale via dynamos driven by plasma thermal expansion off the channel walls. Our scheme sets a possible platform for producing long living extreme magnetic fields in laboratories using readily available lasers. The concept might also be relevant for applications such as magneto-inertial fusion.