Hotspot power balance in alpha-particle dominated ICF implosions*

Recent advances in inertial confinement fusion (ICF) experiments on the National Ignition Facility (NIF) have led to a tripling of the fusion energy yield to 170 kJ. These experiments have entered a qualitatively new regime where the energy flow in the hotspot is dominated by alpha-particle self-heating. We report on analysis, based on experimental data and simulations, of the power balance in the hotspot which indicates that the static Lawson criterion is exceed at the time of maximum compression, i.e., the instantaneous alpha heating rate in the hotspot exceeds all power losses. To achieve ignition the remaining step required is to maintain a positive net heating rate in the hotspot during the expansion phase where PdV work performed by the hotspot gives rise to an additional energy loss term.