Studies of fast electron coupling efficiency using bookend targets

Hollow cone targets are widely studied to understand their effects on laser coupling to fast electrons relevant to the FI concept for ICF. ``Bookend'' targets fabricated out of two planar copper foils (100\textit{$\mu $m} x 100\textit{$\mu $m} x 20\textit{$\mu $m}) joined at one edge, making an angle between the two halves similar to an open book, were designed to mock-up the cone geometry in 2D. Experiments were performed on Titan laser at LLNL with the laser delivering approximately 10$^{20}$\textit{W/cm}$^{2}$ to the target ($\sim $150$J$, 0.7\textit{ps}). K$_{\alpha }$ emission measurements from Cu K$_{\alpha }$ imagers (spatially resolved) and a Highly Ordered Pyrolitic Graphite (HOPG) crystal (spectrally resolved) are presented for the Cu bookend targets for various opening angles and laser prepulse levels. The results are compared to recent bookend experiments on the MTW laser at LLE and previously reported studies of hollow cone targets at LLNL.\footnote{L. Van Woerkom et al., Phys. Plasmas 15, 056304~(2008)}