Effects of Alpha-ion Stopping on Ignition and Ignition Criteria in Inertial Confinement Fusion Experiments*

With the advent of burning plasmas at the National Ignition Facility (NIF), alpha physics has become a driving factor in theoretical understanding and experimental behavior. In this presentation, the effect of direct alpha-ion heating is discussed rather than the more often mentioned alpha-electron heating. The results show that the alpha-ion heating can alter ignition thresholds and experimental performance. In the case of the recently ignited NIF implosion N210808, 30% of the 3.5 MeV alpha energy is deposited into the DT fuel ions given the measured 11 keV temperature. This situation that not only affects ignition criteria but is itself a signature of ignition.