  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.
