Experiments with Supersonic Beams as a Source of Cold Atoms

5.2 The Hydrogen Apparatus
The apparatus constructed to slow and trap a supersonic beam of hydrogen is
different from the coilgun used to slow neon and oxygen. The differences are primarily
due to the increased magnetic moment to mass ratio of hydrogen, which significantly
lowers the magnetic field strength requirements while still permitting slowing in a
short distance. The lower field requirements permit the coils to be increased in size.
This increases number of atoms slowed due to the increased aperture and allows the
coils to be removed from vacuum, reducing the experimental complexity. The new coil
geometry and electronics are described, along with the advantages of this change in
geometry. The experiment also integrates a magnetic trap at the end of the coilgun,
and the method by which the atoms can be trapped is explained, along with the
trap design and electronics. Finally, since the beam consists of hydrogen, the beam
creation and detection are changed.
5.2.1 Slowing Coils and Electronics
The greatly increased magnetic moment to mass ratio of hydrogen ( 1amu ),
3 μB
1.8 μB
compared with metastable neon ( ) or molecular oxygen ( ), permits smaller
20 amu 32 amu
fields to be used in a convenient laboratory scale coilgun. An increase in the coil size
is thus feasible, which results in several advantages. The most significant advantage of
using larger coils is that the coils can be moved outside of the vacuum envelope, greatly
reducing the experimental complexity. Outside of vacuum, the need for feedthroughs
is eliminated and the coils can be cooled much more easily, allowing the repetition rate
of the experiment to be increased and reducing the time required to take data. The
larger coils require a modification to the switching electronics since the inductance of
a coil increases with its size.
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1 μB