Diagnosing Low-Mode (l ≤ 6) Asymmetries in the Explosion Phase of Laser-Direct-Drive Deuterium–Tritium Cryogenic Implosions on OMEGA

Low-mode (l ≤ 6) asymmetries, seeded by initial nonuniformities and amplified by hydrodynamic instabilities, are a possible performance degradation mechanism for laser-direct-drive implosions on OMEGA. We have identified, on the basis of radiation-hydrodynamic simulations, an x-ray emission limb at the corona–fuel interface that persists through and after stagnation. This signature is intrinsic to the current deuterium–tritium cryogenic implosions and therefore presents a valuable diagnostic opportunity. The diagnostic potential is explored using 2-D and 3-D radiation-hydrodynamic simulations of beam-mode patterning and a large l = 2 drive asymmetry—two leading candidates for performance limitations of the cryogenic implosions. Based on the 2-D and 3-D simulations, low-mode asymmetries in the implosion can degrade the neutron yield by over 30% when compared with the 1-D symmetric case. The diagnostic sensitivity for low modes will be presented and compared to other x-ray and knock-on deuteron diagnostics. Planning is underway for routine application to cryogenic implosion experiments on OMEGA.