The Effect of Helium on Burn in Directly Driven Glass Capsules

Experiments on the Omega laser confirm the previous observation (Rygg \textit{et al.} (\textit{Phys. Plasmas}, \textbf{13}, 052702 (2006)) of an abnormal degradation of D+D(n) and D+$^{3}$He(p) yields in hydrodynamically equivalent capsules as the $^{3}$He fraction is increased. The degradation remained using $^{4}$He. These implosions used either 23 kJ of laser energy in a 1000ps square pulse, or 13 kJ in a 600ps pulse, onto 900 micron diameter, $\sim $ 4.3 micron thick glass shells filled with 10 atm of deuterium or hydrodynamically equivalent mixtures with He. Measured ion temperatures would be the same for all mixtures in hydrodynamically equivalent capsules. For the 1000ps implosions they are. But for 600ps implosions the ion temperature increases with $^{3}$He concentration, showing a deviation from equivalency. Work supported by US DOE/NNSA, performed at LANL, operated by LANS LLC under Contract DE-AC52-06NA25396.