Collisionless shock gas jet experiments at OMEGA*

We report OMEGA experiments utilizing a gas jet system to produce and study collisionless shocks. A hollow CH hemisphere is illuminated with lasers to produce a supersonic plasma flow. The plasma flow collides with a hydrogen gas jet and the two plasmas interact to form a collisionless shock. Imaging Thomson scattering measurements clearly show density and temperature jumps. Density increases by a factor of about 3 and temperature by a factor of about 5. The plasma flow velocity is measured to be greater than 1500 km/s leading to carbon-carbon collision mean free path of about 2 cm which is much larger than the shock front thickness (about 100 um). This indicates that the system is collisionless. Proton radiography data show a shock structure that evolves in time.