Studying shock dynamics and in-flight $\rho $R asymmetries in NIF implosions using proton spectroscopy

Ignition-scale, indirect-drive implosions of CH capsules filled with D$^{3}$He gas have been studied with proton spectroscopy at the NIF. Spectral measurements of D$^{3}$He protons produced at the shock-bang time provide information about the shock dynamics and in-flight characteristics of these implosions. The observed energy downshift of the D$^{3}$He-proton spectra are interpreted with a self-consistent 1-D model to infer $\rho $R, shell R$_{cm}$, and yield at this time. The observed $\rho $R at shock-bang time is substantially higher for implosions where the laser drive is on until near the compression-bang time (``short-coast'') while longer-coasting implosions generate lower $\rho $R at shock-bang time. This is most likely due to a larger temporal difference between the shock- and compression-bang time in the long-coast implosions ($\sim$800ps) than in the short-coast implosions ($\sim$400ps). These differences are determined from the D$^{3}$He proton spectra and in-flight x-ray radiography data, and it is found to contradict radiation-hydrodynamic simulations, which predict a 700 -- 800ps temporal difference independent of coasting time. A large variation in the shock proton yield is also observed in the dataset, which is interpreted with a Guderley shock model and found to correspond to $\sim 2 \times$ variation in incipient hot-spot adiabat caused by shock heating. This variation may affect the compressibility of NIF implosions. Finally, data from multiple proton spectrometers placed at the pole and equator reveal large $\rho $R asymmetries, which are interpreted as mode-2 polar or azimuthal asymmetries. At the shock-bang time (CR $\sim 3-5$), asymmetry amplitudes $\ge $10{\%} are routinely observed. Compared to compression-bang time x-ray self-emission symmetry, no apparent asymmetry-amplitude growth is observed, which is in contradiction to several growth models. This is attributed to a lack of correspondence between shell and hot-spot symmetry at peak compression, as discussed in recent computational studies [R.H.H. Scott et al., Phys. Rev. Lett. 110, 075001 (2013)].