Experiments with Supersonic Beams as a Source of Cold Atoms

Chapter 4
The Atomic and Molecular Coilgun: Using Pulsed
Magnetic Fields to Slow Supersonic Beams
As discussed in chapter 2, supersonic beams are remarkable for their general
applicability. Almost any atomic species, and many molecules as well, can be seeded
into a supersonic beam and cooled by the expansion. Because they serve as a nearly
universal source of cold atoms, they are the ideal starting point for a general method
of controlling atomic motion.
Since supersonic expansion is a very general method for producing cold atoms
and molecules, a general method of slowing and control provides a nearly universal
tool for producing cold samples for further study. Magnetic fields provide this ability.
On the atomic level nearly all atomic species are magnetic either in their ground state
or in an easily accessible metastable state. The physical mechanism through which
magnetic fields allow for control of atoms is the Zeeman effect.
Using a series of pulsed electromagnetic coils, and inspired by the macroscopic
coilgun [67], it is possible to produce the large fields needed to slow and stop su-
personic beams in a table-top scale experiment. The principle of operation of the
atomic coilgun is described in detail. Experiments using two generations of coilgun
are presented. The first coilgun has 18 pulsed coil stages, and slowed metastable neon
from 461 m/s to 403 m/s. The apparatus, including the coils and electronics used to
drive them, is described. The second generation coilgun, which slowed and stopped
metastable neon and molecular oxygen is also presented in this chapter. The exper-
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