High-PR implosions for fast-ignition fuel assembly

Thick, 40  Îm plastic shells filled with 25-35 atm of D2 or DHe3 were imploded on a low-adiabat (αâ‰≈1.3) and with a low-implosion velocity (â∼2×107  cm/s) on the OMEGA laser to generate massive cores of compressed plasma with high areal densities optimal for fast ignition. The targets are driven by 20-kJ relaxation adiabat-shaping laser pulses to keep the inner portion of the shell nearly Fermi degenerate. The measured kinetic energy downshift of proton spectra is in good agreement with the theoretical predictions yielding burn-averaged areal densities of 0.130±0. 017  g/cm2 and peak PR during the burn of about 0.24±0.018  g/ cm2, the largest PR measured on OMEGA to date. The same implosions with empty plastic shells are expected to reach 1. 3  g/cm2 across the core (i.e., 2PR) enough to stop fast electrons with energies up to 4.5 MeV typical of fast ignition scenarios.