Magnetic field generation, dynamics, and reconnection driven by relativistic intensity laser-plasma interactions*

In many astrophysical plasmas, magnetic field topology plays an impactful role in the plasma dynamics. Direct measurements of the outer space plasma conditions and fields are challenging, so laboratory studies of magnetic dynamics and reconnection provide an important platform for testing theories and characterizing different regimes. The extremely energetic class of astrophysical phenomena - including high-energy pulsar winds, gamma ray bursts, and jets from galactic nuclei - have plasma conditions where the energy density of the magnetic fields exceeds the rest mass energy density ($\sigma = B^2/(\mu_0 n_e m_e c^2) > 1$, the cold magnetization parameter). Here, we present experimental measurements, along with numerical modeling, of short-pulse, high-intensity laser-plasma interactions that produce extremely strong magnetic fields ($> 100 \; \rm{T}$). Three-dimensional particle-in-cell simulations show the plasma density and magnetic field characteristics satisfy $\sigma > 1$. The generation and the dynamics of these magnetic fields under different target conditions was studied, and relativistic intensity laser-driven, magnetic reconnection experiments were performed. Evidence of magnetic reconnection was identified by the plasma’s X-ray emission patterns, changes to the electron spectrum, and by measuring the reconnection timescales. Accessing relativistic conditions in the laboratory allows for further investigation that may provide insight into unresolved problems in space and astro-physics.