Ideas for a Superconducting Second-Generation Magneto-Gravitational Trap for Measurement of the Neutron Lifetime

Ideas are presented for a second-generation UCN trap (UCNtau2) with the same basic geometry as the existing UCNtau trap at LANL, but with a trapping field produced by an array of side-by-side superconducting "banana" coils in place of the permanent magnets of UCNtau. The coils employ NbTi/Cu superconducting cables and operate at a current that is less than 50% of the critical current at the peak field in the windings. The effective trapping field of UCNtau is ~0.8 T and the trap depth approximately 0.47 m. If the trapping field were to be increased, for example, to 2 T, the trap depth could be increased to 1.2 m and simple scaling of the present trap geometry would give a trap volume of 15 times the present volume, or about 6.3 m³. The simplest filling scheme is to fill the trap with the trapping field off, containing the neutrons with a material liner, and then to ramp the current to the design value, after which the UCNs are contained by the trapping field. Alternative filling schemes that do not require coil ramping are also under consideration and will be described in other talks.