Systematic Fuel Cavity Asymmetries in Directly Driven ICF Implosions

Direct-drive ICF could provide the additional energy needed for ignition. However, sub-scale experiments have reached only half the expected pressure. Simulations suggest asymmetry as the culprit [1]. Herein we assess symmetry by use of a novel imaging technique enabling diagnosis of the fuel-cavity shape as defined at the fuel-shell interface. In this approach, targets are slightly modified such that a Ti tracer layer is selectively placed only at the innermost surface of the ablator. The specificity of the emission to the fuel-shell interface, coupled with spectrally selective imaging, leads us to profoundly new imaging evidence asymmetries. Identifications are made with anticipated systematic asymmetries of shape during deceleration at convergence $\sim$15. An $\ell\sim1$ systematic asymmetry is revealed suggesting evidence of a blow-out which quashes pressure. [1] I. V. Igumenshchev \textit{et. al.} Phys. Plasmas \textbf{23}, 052702 (2016).