Measurement of Kinetic-Scale Current Filamentation Dynamics and Associated Magnetic Fields in Interpenetrating Plasmas

We present the first local, quantitative measurements of ion current filamentation and magnetic field amplification in interpenetrating plasmas, characterizing the dynamics of the ion Weibel instability. The interaction of a pair of laser-generated, counterpropagating, collisionless, supersonic plasma flows is probed using optical Thomson scattering (TS). Analysis of the TS ion-feature revealed anticorrelated modulations in the density of the two ion streams at the spatial scale of the ion skin depth c/omega(pi) = 120 mu m, and a correlated modulation in the plasma current. The inferred current profile implies a magnetic field amplitude similar to 30 +/- 6 T, corresponding to similar to 1% of the flow kinetic energy, indicating that magnetic trapping is the dominant saturation mechanism.