No abstract

A new technique is described for the isochoric heating (i.e., heating at constant volume) of matter to high energy-density plasma states (>10(5) J/g) on a picosecond time scale (10(-12)sec). An intense, collimated, ultrashort-pulse beam of protons--generated by a high-intensity laser pulse--is used to isochorically heat a solid density material to a temperature of several eV. The duration of heating is shorter than the time scale for significant hydrodynamic expansion to occur; hence the material is heated to a solid density warm dense plasma state. Using spherically shaped laser targets, a focused proton beam is produced and used to heat a smaller volume to over 20 eV. The technique described of ultrafast proton heating provides a unique method for creating isochorically heated high-energy density plasma states.

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Experiments on the interaction of intense, ultrafast pulses with large van der Waals bonded clusters have shown that these clusters can explode with substantial kinetic energy and that the explosion of deuterium clusters can drive nuclear fusion reactions. Producing explosions in deuterated methane clusters with a 100 fs, 100 TW laser pulse, it is found that deuterium ions are accelerated to sufficiently high kinetic energy to drive deuterium nuclear fusion. From measurements of cluster size and ion energy via time of flight methods, it is found that these exploding deuterated methane clusters exhibit higher ion energies than explosions of comparably sized neat deuterium clusters, in accord with recent theoretical predictions. From measurements of the plume size and peak density, the relative contribution to the fusion yield from both beam target and intrafilament fusion is discussed.

Collimated jets of carbon and fluorine ions up to 5 MeV/nucleon ( approximately 100 MeV) are observed from the rear surface of thin foils irradiated with laser intensities of up to 5 x 10 (19)W/cm(2). The normally dominant proton acceleration could be surpressed by removing the hydrocarbon contaminants by resistive heating. This inhibits screening effects and permits effective energy transfer and acceleration of other ion species. The acceleration dynamics and the spatiotemporal distributions of the accelerating E fields at the rear surface of the target are inferred from the detailed spectra.