Turbulent, megagauss magnetic fields in intense, ultrashort laser pulse interaction with solids

Intense laser-plasma interactions provide a novel and fascinating platform to simulate astrophysical scenarios. Giant magnetic fields (10² - 10³ megagauss) are created when a relativistic intensity >10¹⁸ W/cm², ultrashort laser pulse interacts with plasma created on a solid. Here we present snapshots of these megagauss magnetic fields, capturing their picosecond-scale evolution with micron-precision. The plasma created by an 800 nm laser is probed at density of ∼10²² electrons/cc at 266 nm. This density is so far the highest at which plasma probing has been performed. The Fourier spectrum of these megagauss magnetic fields shows a power-law behaviour for the magnetic energy, which provides the signature of magnetic turbulence. Detailed particle-in-cell simulations have shown that the relativistic hot electron transport in a hot dense laser-generated plasma suffers from several instabilities including the Weibel instability, which leads to the spatial separation of forward and return currents and eventually lead to the filamentary structure. The currents subsequently get Weibel-separated, followed by the tearing and coalescence instabilities, which produce current channels and thereby filamentary magnetic field structures. These results are fundamentally interesting in the context of fast ignition of laser fusion, laser-based acceleration of protons, ions and neutral particles, the feasibility of experimentally verifying such instability mechanisms in astrophysical magnetic fields, mimic observations of kinetic Alfven wave turbulence in the earth's magneto-sheath, solar flares and solar wind and simulating intra-planetary matter existing at ultrahigh pressures. (author)