The Next Generation of Neutron Lifetime Experiments at Los Alamos Neutron Science Center

UCN$\tau +$, now in development at the Los Alamos Neutron Science Center, is an upgrade of the UCN$\tau$ experiment. Recently the UCN$\tau$ experiment reported the most precise measurement of the free neutron lifetime using trapped ultracold neutrons (UCN), specifying the lifetime with an uncertainty of 0.041% (0.36 s). High precision neutron decay data determines the coupling constants for the weak interaction of the nucleon without nuclear structure-dependent effects, with the current precision from UCN$\tau$ now within a factor of two of the limiting theoretical uncertainties due to radiative corrections. Given the sensitivity precision neutron decay measurements offer to new physics (through unitarity tests, for example), an upgrade to UCN$\tau$ with a factor of two or greater improvement to the precision is greatly motivated. The UCN$\tau +$ upgrade focuses on increasing the loaded number of UCN in the magneto-gravitational trap and improving the high rate performance of the UCN$\tau$ \textit{in situ} detector. We provide an overview of the UCN$\tau +$ project, focusing on recent work modeling an adiabatic transport system to load the trap. In addition, we explore the transport parameters to optimize the gains obtained from cooling over-threshold UCN.