Experiments with Supersonic Beams as a Source of Cold Atoms

prevent the determination of the isotopic shift of the 1S − 2S transition in tritium to
around 100 kHz with the apparatus described above.
5.4.2 An Adiabatic Coilgun
Beyond the problem of detection, research has continued on possible improve-
ments to the methods used to bring the cold samples produced by supersonic expan-
sion to rest in the lab frame. The most promising avenue for increasing the flux and
phase space density of the final sample is to trap the sample and then decelerate it,
as opposed to the current design which first slows and then traps the atoms. By trap-
ping the atoms in a moving magnetic trap, they are confined in all three dimensions
even though they are still moving quickly in the lab frame. Adiabatically decelerating
the moving trap will then bring the trapped particles to rest without decreasing the
phase space density, thereby allowing the high phase space densities produced by the
initial supersonic expansion to be maintained through the deceleration process. This
idea is proposed in [68].
There are several approaches to creating a moving trap which are appropri-
ate for the use in an adiabatic decelerator. Moving magnetic traps have been used
to transport atoms in cold atom experiments, both on microchips [121] and using
macroscopic coils [122], inspiring the concept of a moving magnetic trap decelerator,
though far greater velocities are needed to trap a supersonic beam in the co-moving
frame. The moving and decelerated trap concept has also been applied to moving
electrostatic traps for chips [123, 124] and for macroscopic electrodes [125], and these
designs have been able to capture and slow molecules in a supersonic beam. A mov-
ing, though not decelerated magnetic trap has also been used to capture and translate
metastable argon atoms in a supersonic beam [126]. An adiabatic magnetic deceler-
ator has been used to stop metastable neon atoms [127, 128]. These last experiments
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