Experiments with Supersonic Beams as a Source of Cold Atoms
Experiments with Supersonic Beams as a Source of Cold Atoms
Experiments with Supersonic Beams as a Source of Cold Atoms
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<strong>of</strong> an MCP, and thus will not be detected. However, the RGA used to detect helium<br />
in chapter 3 can also be used to detect molecular oxygen. The oxygen is ionized by<br />
electron impact and accelerated into a quadrupole which provides m<strong>as</strong>s filtering. The<br />
ions are then detected <strong>with</strong> an electron multiplier. The RGA is mounted on the same<br />
translation stage <strong>as</strong> the MCP, which again permits me<strong>as</strong>urement <strong>of</strong> the velocity <strong>of</strong><br />
the beam. However, the ionization region <strong>of</strong> the RGA h<strong>as</strong> some depth, <strong>as</strong> compared<br />
to the flat MCPm, which creates inherent uncertainty in the position <strong>of</strong> an oxygen<br />
molecule when it is ionized and subsequently detected. The distance from the end<br />
<strong>of</strong> the coilgun to the ionizer <strong>with</strong> the translation stage in the retracted(extended)<br />
position is 100 mm(150.8mm).<br />
4.6.3 Oxygen Data and Results<br />
The results <strong>of</strong> the oxygen slowing are now presented. Using the oxygen-krypton<br />
mixture described above, and <strong>with</strong> the nozzle cooled to 150 K, the oxygen beam<br />
<strong>with</strong>out any slowing h<strong>as</strong> a velocity <strong>of</strong> 389 ± 5 m/s <strong>with</strong> a standard deviation <strong>of</strong><br />
28 m/s. This corresponds to a temperature <strong>of</strong> 3.0 K. This is significantly hotter that<br />
the previous beams described here. Clustering in the beam is the likely explanation<br />
<strong>of</strong> the incre<strong>as</strong>ed beam temperature, <strong>as</strong> the valve is operated close to the condensation<br />
temperature <strong>of</strong> the krypton carrier g<strong>as</strong>.<br />
Time-<strong>of</strong>-flight pr<strong>of</strong>iles <strong>of</strong> the oxygen beam are presented in figure 4.33. The<br />
coilgun is operated at constant ph<strong>as</strong>e, where the ph<strong>as</strong>es used are between 47.8 ◦ and<br />
63.2 ◦ . This corresponds to slowing <strong>of</strong> the beam to 242 m/s at the lowest ph<strong>as</strong>e, and<br />
to 83 m/s at the highest ph<strong>as</strong>e. For the 83 m/s beam, over 95% <strong>of</strong> the initial kinetic<br />
energy is removed. A full summary <strong>of</strong> the slowing results can be found in table 4.3.<br />
The time-<strong>of</strong>-flight pr<strong>of</strong>ile in the graph on the right in figure 4.33 shows the<br />
entire beam, including the perturbed f<strong>as</strong>t beam. As is clear from the figure, the<br />
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