Computational optimization of indirect-driven targets for ignition on the Iskra-6 laser facility

Abstract

In Russia, the Iskra-6 laser facility with pulse energy of up to 300 kJ and nanosecond pulse duration was being planned Kirillov et al., 2000!. The possibility of thermonuclear ignition with this laser energy was a goal of the theoretical investigation at RFNC-VNIITF. Results of one-dimensional~1D! and two-dimensional~2D! modeling of indirectdriven targets for ignition on the Iskra-6 laser facility are presented. Sensitivity of cryogenic single-shell and non-cryogenic double-shell targets to radiation flux non-uniformity and shells roughness are studied.

Assessing the prospects for achieving double-shell ignition on the National Ignition Facility using vacuum hohlraums

“…[8], and expected lower levels of laser backscatter with the reverse-ramp pulse shape. The mode of double-shell ignition will be volume ("PdV") instead of "hot spot" as in the cryogenic baseline design.…”

“…Hot-spot ignition on the NIF requires a threshold fuel temperature of nearly 10 keV, whereas volume ignition is predicted to occur at ≈ 4 keV as a result of radiation trapping by the high-Z inner shell. Due to the low threshold-ignition temperature for double shells, added robustness to candidate sources of asymmetry, e.g., x-ray flux and particular classes of fabrication errors, is predicted [8]. With little need for isentropic preparation of the roomtemperature fuel, careful pulse shaping for pre-forming the pusher (as in hot-spot ignition) is unnecessary since the in situ high-Z inner shell reaches the required density (>1000 g/cm 3 ) after converging by only a factor-of-10.…”

An indirect-drive non-cryogenic double-shell path to 1ω Nd-laser hybrid inertial fusion–fission energy

“…A main advantage of this design is room temperature fielding instead of cryogenic preparation below the triple point of DT (≈19 K). Other benefits include loose tolerances on shock timing, relaxed requirements on lowest-order x-ray flux symmetry control [4], expected low levels of laser backscatter with a flattop laser pulse shape and vacuum-hohlraum fielding, predicted high thermonuclear burn fractions (>50%) and low ignition-threshold temperatures (T i ≈ 4 keV). Due to the volume-ignition mode, isentropic preparation of the fuel is not needed, and the required high pusher density (ρ p > 1000 g cm −3 ) is achieved by converging the Au-Cu inner shell by only ≈10×.…”

Prospects for Demonstrating Double-Shell Ignition on the National Ignition Facility

“…[2] Benefits of double-shell targets include room-temperature deuteriumtritium (DT) fuel preparation, predicted minimal hohlraum-plasma-mediated laser backscatter, low threshold-ignition temperatures (=4 keV) for relaxed hohlraum x-ray flux asymmetry tolerances, [3] and loose shock timing requirements. On the other hand, double-shell ignition presents several challenges, including room-temperature containment of high-pressure DT (790 atm) in the inner shell; strict concentricity requirements on the two shells; development of nanoporous, low-density, metallic foams for structural support of the inner shell and hydrodynamic instability mitigation; and effective control of perturbation growth on the high-Atwood number interface between the DT fuel and the high-Z inner shell.…”