Measurement and prediction of the speed-dependent throughput of a magnetic octupole velocity filter including nonadiabatic effects

A magnetic octupole filter set in a $90°$ curve produces $\approx {10}^8$ cold Rb atoms/s by filtering low-velocity particles from a thermal source. We measure the speed distribution of Rb exiting the filter to be 3.5 K using a Rydberg-atom time-of-flight scheme in which Rb is excited via the process $5s{}^2{S}_{1/2}\to 5p{}^2{P}_{3/2}^o\to 32d{}^{2}D.\mathrm{}$ We develop a general theory of the transmission and speed distribution of particles emitted from such a source including nonadiabatic effects. A detailed Monte Carlo simulation using the theory accurately reproduces the experimental results. We show that for Cs, Li, and Rb atoms and ${\mathrm{S}}_2$ molecules, nonadiabatic effects do not dramatically effect the performance of the filter, and that the output flux temperatures for a wide variety of filter configurations are well fit to a simple functional form.