Proton drift effects in beam neutron lifetime experiments

In beam neutron lifetime experiments conducted at ILL and NIST, the neutron beam passes through a quasi-Penning trap that confines neutron decay protons for subsequent counting. The trap features an axial magnetic field throughout and electric fields with axial and radial components near the ends of the trap. In general the trajectory of a charged particle in the adiabatic regime of a strong magnetic field is a helical motion around the magnetic field line coupled with a drift velocity perpendicular to the field line caused by ExB and field gradient effects. This drift mainly produces a slow azimuthal magnetron orbit about the trap axis. However breaking of azimuthal symmetry by the trap fields may cause radial drifts and a possible loss of protons from the trap. Results of recent analysis and simulations of these effects will be presented.