Experiments with Supersonic Beams as a Source of Cold Atoms

Signal [V]
2.5
2.0
1.5
1.0
0.5
reference beam
240 A
320 A
400 A
0.16
0.08
0.0
4.5 5.0 5.5 6.0 6.5
0.0
Time of flight [ms]
6.0 6.2 6.4
Figure 4.19: A plot of the time of flight results of the metastable neon beam, varying
the current in the coils of the 18 stage coilgun. Each curve is an average of 10 shots
and each timing file generated had an initial phase of 55 ◦ . The larger currents lead
to greater magnetic fields, and thus more slowing.
in the coils, and the results of this investigation are presented in figure 4.18. Rather
than set a specific constant phase angle for the entire slower however, the numerical
simulation which creates the timing file is set to switch the coil off at a certain constant
time before the atom would arrive at the center of the coil. Since the atoms are being
slightly slowed, this is equivalent an almost linear variation of the phase angle for
each coil. The phase angles used are 49 ◦ −51 ◦ ,55 ◦ −58 ◦ ,and61 ◦ −64 ◦ , which yielded
final speeds of 431.2 ± 6.0 m/s, 409.3 ± 9.1 m/s, and 403 ± 16 m/s respectively. As can
be seen in the figure, greater phase angles lead to more slowing, but also to a smaller
phase stable region, reducing the number of slowed atoms.
Varying the current in the coils allows the effects of magnetic field strength to
be examined. The currents used are 400, 320, and 240 A, and the results can be seen
in figure 4.19. The current was not reduced below 240 A because at lower currents
the magnetic fields were no longer strong enough to separate the slowed peak from
the main beam. These currents correspond to peak magnetic fields in the coils of 3.6,
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