Experiments with Supersonic Beams as a Source of Cold Atoms

Figure 2.2: A CAD representation of the Even-Lavie supersonic nozzle. The complete
nozzle apparatus is shown in (a) with a pool type cryostat which allows the nozzle
to be cooled. Gas flows into the valve apparatus through the stainless steel tube on
the right side of the image into a stainless steel pressure tube (yellow). The front and
back of the tube are sealed using Dupont Kapton washers (red). The trumpet shaped
nozzle where the gas expands and exits is on the left. An empty section can be seen
surrounding the stainless steel pressure tube, and this is where the electromagnetic
drive coil (not shown in this image) is located. The interior of the pressure tube is
shown in (b). Gas enters the pressure tube (yellow) from the right and flows past
the plunger (green), spring (blue), and guiding ceramic inserts (orange) to the nozzle
exit (not depicted). The plunger forms a seal on the left side of the image with
the leftmost Kapton washer from (a), and is held in place by the spring. Current
in an electromagnetic coil produces a magnetic field that pulls the plunger to the
right, allowing gas to expand adiabatically into the vacuum until the magnetic field
is turned off and the plunger is pushed back into place by the spring. The motion of
the plunger is guided by the two alumina pieces. Figure Courtesy Max Riedel.
1/8’’
the overall temperature, as well as producing a very directional beam with a FWHM
opening angle of 16 ◦ [33]. The nozzle is unique in that it can produce pulses which
are only 10 μs FWHM in length, and the valve can operate at repetition rates over
40 Hz. The valve can operate with backing pressures of 100 atm and at temperatures
as low as 20 K. The short opening time is essential for these reservoir conditions, as
the vacuum system would be overwhelmed by the resulting gas load otherwise.
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