Y. Sentoku

Self-proton/ion radiography of laser-produced proton/ion beam from thin foil targets

Protons and multicharged ions generated from high-intensity laser interactions with thin foil targets have been studied with a 100 TW laser system. Protons/ions with energies up to 10 MeV are accelerated either from the front or the rear surface of the target material. We have observed for the first time that the protons/ions accelerated from the front surface of the target, in a direction opposite to the laser propagation direction, are turned around and pulled back to the rear surface, in the laser propagation direction. This proton/ion beam is able to create a self-radiograph of the target and glass stalk holding the target itself recorded through the radiochromic film stack. This unique result indicates strong long-living (ns time scale) magnetic fields present in the laser-produced plasma, which are extremely important in energy transport during the intense laser irradiation. The magnetic field from laser main pulse expands rapidly in the preformed plasma to rotate the laser produced protons. Radiati...

3D Evolution of the Boundary Layer Formed During the Expansion of a Laserplasma in a Magnetic Field in Vacuum

Summary form only given. Explosive sub-Alfvenic plasma expansions occur in a variety of space and astrophysical events. A laboratory simulation was performed to investigate such interactions. The plasma flow was created by ablation of a solid CH2 target with up to 0.1 PW/cm2 pulses of the Tomcat Nd:glass laser. It expanded in vacuum in the azimuthal magnetic fields with strength up to 20 T generated by high current discharges of the Zebra pulsed-power generator. The expanding plasma was diagnosed with two-frame laser interferometry and schlieren imaging. The plasma expansion was asymmetric in directions parallel and perpendicular to the magnetic field. A dynamic boundary layer with steep density gradient formed at the plasma-field interface. The density modulations observed at the interface in schlieren images suggest the onset of instabilities in this high beta plasma. Comparing the growth in planes parallel and perpendicular to the field indicates flute-like instabilities (with k parallel=0). As the expansion proceeds, the space-scale of the modulation appears to decrease. We will present experimental observations pointing to the instability growth. We will make detailed comparison between experiment and theory