Update on Ignition Target Fabrication Specifications

Solid deuterium–tritium surface roughness in a beryllium inertial confinement fusion shell

“…One ignition target design for the NIF has an ablator which is a 2 mm diameter, 150 µm wall beryllium shell doped with approximately 1% copper. [1,2] Successful ignition experiments require both the ablator and fuel layers to be smooth and uniformly thick spherical shells. [2] Copped-doped beryllium Be(Cu) shells are produced by sputter deposition on a spherical mandrel and subsequently mechanically polished.…”

“…[1,2] Successful ignition experiments require both the ablator and fuel layers to be smooth and uniformly thick spherical shells. [2] Copped-doped beryllium Be(Cu) shells are produced by sputter deposition on a spherical mandrel and subsequently mechanically polished. [3] D-T solidifies at 19.7 K with a vapor pressure of 140 torr, thus effectively eliminating the option of mechanical machining or polishing.…”

X-ray imaging of cryogenic deuterium-tritium layers in a beryllium shell

“…This design can tolerate roughner D-T surfaces, compared to plastic ablators which require less than 1 µm RMS D-T surfaces to ignite. [1,2] Characterization of the solid D-T surface roughness is requried to compare ignition experiments with simulations. However, only limited characterization of the solid D-T fuel layer inside of the Be(Cu) shell has been possible.…”

Diamond Ablators for Inertial Confinement Fusion

“…The same holes can later be used for filling the target with DT. The specifications for NIF baseline capsules requires fill holes with a diameter of <5 μm, 4,9 which translates into an aspect ratio of ~20 for an ~100-μm-thick ablator. We evaluated both FIB and laser based micromachining: Using a XeF 2 assisted FIB technique, 17,18 we were able to drill a round hole, tapering from ~12 μm (entrance) to ~5 μm (exit), through a 90-μm-thick freestanding diamond film at a rate of 2 μm/min (Fig.…”

“…1 The baseline design for indirect-drive ignition targets for NIF consists of a two-millimeter-diameter spherical shell ("ablator") with a wall thickness 75-130 μm made of a low-Z material, filled with a frozen layer of deuterium-tritium (DT) fuel and a central DT gas core. [2][3][4][5][6][7][8][9] Although copper-doped beryllium and plasma polymers are currently the primary candidates for the ICF ablator application, diamond seems to be a very promising material due to a unique combination of physical properties: 1) The opacity / albedo properties of diamond for 250 -300 eV photons, together with its high atomic density, provide for efficient energy absorption and a high ablation rate whereby reducing Rayleigh-Taylor instabilities at the ablation front; 10 2) The extremely high yield strength of diamond allows room temperature handling of filled targets there the DT fuel develops a pressure in the order of 1000 atm; 3) The broad-band optical transparency of diamond 11 (from ultraviolet to far infrared, 0.22 -20 μm) allows the use of optical techniques to smooth the DT ice layer; 4) Finally, the high thermal conductivity (up to 23 W cm -1 K -1 at 300 K 12 ) of diamond simplifies the cryogenic system requirements.…”