Experiments with Supersonic Beams as a Source of Cold Atoms

Figure 5.13: Time of flight plot of the ratio of D(×100) to D2 with and without the
discharge firing. The noise on either side of this signal is meaningless as the signals
go to 0 and the increased noise is a result of dividing by nearly 0. The greater ratio
of D to D2 with the discharge indicates that the discharge is working properly and
producing atomic hydrogen, but that it is covered by the background signal due to
molecular hydrogen.
which is then detected. This second channel is an undesired background which causes
a significant problem.
The background signal due to the cracking of hydrogen molecules in the ionizer
causes atomic hydrogen to be observed even without firing the discharge. In fact, the
observed atomic hydrogen signal actually decreases when the discharge is fired, since
the beam is heated by the discharge and less of it arrives at the detector. It is thus
difficult to determine the quality of the beam and discharge. However, one method
of examining the beam did produce interesting results, and this was to look at the
ratio of atomic deuterium to molecular deuterium, with and without the discharge
(deuterium is chosen for its heavier mass, ensuring more atoms stay on the centerline
of the beam). Doing this allows the effect of the discharge to be seen more clearly
and shows that atomic deuterium is being produced by the discharge, but that the
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