Numerical simulations on cleaning the neutron trap for measuring the   neutron lifetime
  We present the results of numerical simulations of the dynamical behavior of trajectories of ultra cold neutrons (UCN) in a magnetic trap. The main goal of our simulations was to optimize the trap parameters in order to minimize the characteristic times for removing from the trap those untrapped neutrons with relatively long escape times (cleaning the trap). Our results demonstrate that, by a proper choice of the trap parameters cleaning times can be reduced to 15 sec, or even less. Many other dynamical characteristics of the neutrons in the trap, including the conservation of the adiabatic invariant which characterizes the orientation of the magnetic moment along the local magnetic field, are also discussed. 
Vyacheslav N. Gorshkov and Gennady P. Berman (Complex Systems Group,   T-13, Los Alamos National Laboratory)