NIF Invited: The role of diagnostics in forming an ICF implosion precise enough for target gain >1 at the National Ignition Facility*

It has long been known that high fidelity implosions are needed for ignition. The level of precision is such that simulations need to be augmented by accurate measurements. The increasing accuracy of the diagnostics on NIF has driven a high enough level of laser and target precision for ignition and burn [1]. The hohlraum drive history and time resolved drive symmetry are accurately measured by x-ray emission, shock velocity in complex witness plates and time resolved emission and absorption x-radiography of witness capsules.  The measurements led to a refinement of the laser power, inter-beam color differences and hohlraum morphology. Examples from the associated diagnostics will shown. The causes of degradations of capsule implosion, assembly, stagnation and burn, such as mounting geometry, capsule filling tube, and capsule low and high spatial frequency non-sphericity have long been qualitatively known.  Measurements of time resolved x-ray and neutron imaging, directionally resolved neutron and x-ray spectroscopy and time resolved thermonuclear burn have quantified the effect of these degradations, driving laser and target improvements. Examples of the x-ray and neutron imaging diagnostics, x-ray, neutron and gamma burn history and spectroscopy will be shown. The recent burning implosions are diagnosed with neutron hardened diagnostics. Examples will be shown of much higher yields and ion temperatures, shorter burn histories and exploding, structured x-ray emission.  This work performed under the auspices of the U.S. Department of Energy by General Atomics under Contract 89233119CNA000063.

 

[1] H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022).