Electromagnetic Fields of a Laboratory Axial Plasma Jet

Measurement are presented of the time-varying electromagnetic fields of a plasma jet directed along the background magnetic field in an ambient plasma. The jet is formed by irradiating a solid carbon target at $\sim 1 \times 10^{10}$W/cm$^{2}$ suspended in a cylindrical argon plasma ($B_{0}=750$G, $n_{e}=5\times 10^{12}$/cm$^{3}$) so that the parallel expansion velocity matches the ambient Alfven speed. The experiments are conducted in the Large Plasma Device (LAPD) which operates at a 1 Hz cadence (matching the laser-target firing) and allows the collection of ensemble datasets. Measurements are made in two orthogonal planes that intersect the diamagnetic cavity formed by the laser-produced plasma jet. Three-axis magnetic induction coils as well as a novel emissive probe reveal the total electric field: $E = -\nabla V_{p} - \partial_{t} A$. The measured symmetry in the $xy$ plane is exploited to form a cylidrically symmetric reconstruction of the dynamic, three-dimensional process.