Controlled shock shells and intracluster fusion reactions in the explosion of large clusters

Abstract

The ion phase-space dynamics in the Coulomb explosion of very large ͑ϳ10 6 -10 7 atoms͒ deuterium clusters can be tailored using two consecutive laser pulses with different intensities and an appropriate time delay. For suitable sets of laser parameters ͑intensities and delay͒, large-scale shock shells form during the explosion, thus highly increasing the probability of fusion reactions within the single exploding clusters. In order to analyze the ion dynamics and evaluate the intracluster reaction rate, a one-dimensional theory is used, which approximately accounts for the electron expulsion from the clusters. It is found that, for very large clusters ͑initial radius ϳ100 nm͒, and optimal laser parameters, the intracluster fusion yield becomes comparable to the intercluster fusion yield. The validity of the results is confirmed with three-dimensional particle-in-cell simulations.

Dynamics and control of the expansion of finite-size plasmas produced in ultraintense laser-matter interactions

“…In fact, as shown in Ref. [17], the intracluster-reaction rates exhibit a sharp, time-resolved peak right after the shock-shell formation. In order to compute the actual number of shockdriven, intracluster fusion reactions, it is necessary to sum up all possible contributions from collisions between ions belonging to different velocity branches.…”

“…[15], and explored in self-consistent simulations in Refs. [16,17]. In fact, if the initial density is a decreasing function of r, the repulsive Coulomb field reaches its maximum within the ion sphere [13,15] (cf.…”

“…As the expansion continues, the shock shell widens radially, involving an ever larger portion of the ion cloud. The physical interest of such pronounced, large-scale shock shells resides in the appearance of large relative velocities within a single exploding cluster, which can lead to energetic ion-ion collisions, thus opening the way to intracluster nuclear fusion reactions [15,16,17] (e.g., in the case of D or D-T clusters).…”

“…Ref. [17]) reveals that optimal delay/intensity combinations exist that maximize N . For very large clusters (R 0 100 nm) and optimal double-pump configuration, the intracluster reaction yield can become comparable with the interluster neutron yield, with ∼ 10% of the fusion reactions arising from intracluster collisions [17].…”

Ergodic model for the expansion of spherical nanoplasmas

“…For simplicity, the ion density n i is written under the hypothesis of no ion overtaking (∂r i /∂r 0 = 0) [21]; however, the model can be easily generalized to include many-branched shock shells [13,15,21,22] and different ion species.…”