Measuring symmetry of implosions in cryogenic Hohlraums at the NIF using gated x-ray detectors (invited)

Abstract

Ignition of imploding inertial confinement capsules requires, among other things, controlling the symmetry with high accuracy and fidelity. We have used gated x-ray imaging, with 10 μm and 70 ps resolution, to detect the x-ray emission from the imploded core of symmetry capsules at the National Ignition Facility. The measurements are used to characterize the time dependent symmetry and the x-ray bang time of the implosion from two orthogonal directions. These measurements were one of the primary diagnostics used to tune the parameters of the laser and Hohlraum to vary the symmetry and x-ray bang time of the implosion of cryogenically cooled ignition scale deuterium/helium filled plastic capsules. Here, we will report on the successful measurements performed with up to 1.2 MJ of laser energy in a fully integrated cryogenics gas-filled ignition-scale Hohlraum and capsule illuminated with 192 smoothed laser beams. We will describe the technique, the accuracy of the technique, and the results of the variation in symmetry with tuning parameters, and explain how that set was used to predictably tune the implosion symmetry as the laser energy, the laser cone wavelength separation, and the Hohlraum size were increased to ignition scales. We will also describe how to apply that technique to cryogenically layered tritium-hydrogen-deuterium capsules.

Investigation of ion kinetic effects in direct-drive exploding-pusher implosions at the NIF

“…60 X-ray bang times were measured using the south pole bang time (SPBT) diagnostic 61 and gated x-ray imaging diagnostics, hGXI 57 and GXD. 58 These measured bang times are summarized and compared to draco-simulated DD-neutron bang times in Table IV. Uncertainty in the pTOF-measured DD-neutron bang time is ∼±120 ps, while the uncertainty in the D 3 He-proton bang time measurements is ∼±100 ps.…”

“…56 X-ray emission gives a sense of the core size around bang time and may be used to estimate the implosion convergence and the length scale of the fuel, which can be compared to λ ii to evaluate the likely impact of ion kinetic effects. Gated x-ray imaging diagnostics, the hardened gated x-ray imager (hGXI) 57 and the gated x-ray detector (GXD), 58 were used to capture images of the implosions. Figure 6 shows a measured x-ray emission image from the imploded core as captured by hGXI on shot N121128, ∼100 ps before bang time (no image at bang time was obtained).…”

Analysis of the National Ignition Facility ignition hohlraum energetics experiments

“…The final diagnostic that we will compare to simulations is the gated x-ray detector (GXD), which takes multiple time-resolved images of the self-emission of the imploding capsule through a hole in the side of the hohlraum wall [22]. The GXD has a spatial resolution of 10µm and temporal resolution of 70-ps.…”

Symmetry tuning with megajoule laser pulses at the National Ignition Facility

“…Images of the capsule self-emission are collected with a CCD based gated x-ray detector [16] on the equator at 90-78 (Theta-Phi) in the NIF chamber coordinates [17]. A pinhole imaging snout is mounted to the GXD having a pinhole array with 8 m diameter pinholes.…”