VOLUME IGNITION TARGETS DRIVEN BY PICOSECOND LASER-PULSES

Plasma foils of subcritical density illuminated by short and powerful laser pulses can undergo a huge internal explosion as a consequence of the strong outward acceleration suffered by the electrons at both edges of the plasma. The result of this type of non-linear Interaction beween the laser electric field and the plasma electrons is the division of the plasma into two halves, each one flying outwards from the initial center plane. If the laser intensity is high enough and the refraction index inside the plasma show the appropriate shape, both halves will be acceleratecd to very high speeds. The acceleration phase takes a few picoseconds. Such a plasma foil can be the pre-conditioned shell of an ICF target. Its internal electrostatic explosion will produce an outward flying semi-shell and an inwards flying one. The latter will act as the imploding fuel of that target. The central void of the shell closes after the acceleration phase. If the acceleration has been uniform across the 4 pi stereoradians, the fuel central collision will produce the untampered compression of the fuel due to inertial forces. Fusion conditions are achieved after a compression phase of some hundreds of picoseconds and a final fusion burst happens which lasts some tens of picoseconds. Preliminary results show that this model of laser direct drive of ICF can yield outstanding target performances. The main requirements are the uniformity of the laser intensity In order to produce uniform spherical accelerations and the very high laser power, of the order of 10(17) W/cm2 during a time period of few picoseconds.