Experiments with Supersonic Beams as a Source of Cold Atoms

Table 4.2: Final velocities (vf), simulated final velocities of the synchronous atom
(vs), coil phases, and temperatures (T ) of the beams shown in figure 4.30.
vf [m/s] vs [m/s] phase [degrees] T [mK]
(a) 446.5 ± 2.5 – – 525 ± 10
(b) 222 ± 11 220 36.4 ◦ 108 ± 22
(c) 184.7 ± 7.6 185 38.7 ◦ 184 ± 39
(d) 142.7 ± 9.1 139 41.0 ◦ 117 ± 32
(e) 109.9 ± 5.4 110 42.1 ◦ 147 ± 34
(f) 84.1 ± 3.1 83 43.0 ◦ 79 ± 20
(g) 70.3 ± 7.4 67 43.4 ◦ 92 ± 57
(h) 55.8 ± 4.7 53 43.7 ◦ 106 ± 59
55.8 ± 4.7 m/s. The full results of the slowing are summarized in table 4.2.
The time-of-flight profiles of the slowed beams show internal structure, which
changes with the coil phase used. This is likely due to the anharmonicity of the
magnetic potential of a coil, which causes the atoms to oscillate at different frequencies
longitudinally as they are slowed. Hence, the velocity distribution of the slowed peak
is not expected uniform, as reflected in the features in the slow beam time-of-flight
signal. This phenomenon is also observed and characterized in the pulsed electric
field decelerator [78].
It should also be noted how well the predicted velocity of the synchronous
atom (from the numerical simulation that generates the timing parameters of the coil
for a particular phase) matches with the measured final velocity of the slowed beam.
This is likely due to the phase stability of the coilgun, which makes the system robust
against small errors in coil position or coil timing. It also indicates that the finite
element calculations of the field profiles of the coil are reasonably accurate.
An estimate of the slowed flux can be done assuming that each metastable neon
atom hitting the surface creates exactly one free electron at the front of the MCP.
After accounting for the gain of the MCP (≈ 10 5 ), and the gain of the current amplifier
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