Improving ultracold neutron traps coated with liquid helium using capillarity and electric field

To increase the storage time of ultracold neutrons (UCNs) inside the material traps it is promising to cover the trap walls by liquid 4He, a material which does not absorb neutrons at all. The rough side wall of UCN trap holds the required amount of 4He by the capillary effects, but the edges of the wall roughness remain insufficiently coated. Here we propose to apply an electric voltage to these rough side walls of UCN traps to increases the thickness of liquid He on the wall edges and to cover the entire wall surface by sufficiently thick helium films. This completely protects UCNs from being absorbed inside the trap walls. We estimate the required electric field and voltage for several possible designs of UCN traps. This improvement may give rise to a new generation of ultracold neutron traps with very long storage time. We also estimate the influence of this electric field on the dispersion of ripplons-the quanta surface waves, which give the main contribution to the inelastic UCN scattering at low temperature.

Automated summary

To increase the storage time of ultracold neutrons (UCNs) in material traps, the idea of covering the trap walls with liquid helium (4He) is proposed. By applying an electric voltage to the rough side walls of the UCN traps, the thickness of liquid helium on the wall edges can be increased, ensuring complete protection of UCNs from absorption inside the trap walls. This improvement may result in the development of new-generation ultracold neutron traps with remarkably long storage time, while also considering the influence of the electric field on the dispersion of ripplons.