Observation of Stagnation in Counter-Streaming Laser-Created Plasmas with Optical Thomson Scattering*

We present optical Thomson scattering data from counter-streaming plasma jet experiments and argue that the observed slowing is due to stagnation.  The jets were created on the OMEGA laser (Laboratory for Laser Energetics, Rochester, NY) by rear-irradiating thin acrylic cones.  The resulting jets were probed with a 526.5 nm Thomson beam in both single jet and head-on configurations.  From the single jet Thomson measurements, we determined that over the timeframe of 12 to 18 ns, mass density increased from 10^-7 to 10^-4 gm/cc while velocity fell from 300 to 100 km/s.  Using these plasma parameters, we find that the interpenetration-to-stagnation transition occurred when the ion-ion mean free path was roughly 1 mm.