Experiments with Supersonic Beams as a Source of Cold Atoms

ameters. The coilgun chamber consists of a 6 inch OD cylindrical stainless steel
chamber, with 8 inch Conflat flanges on either end. The chamber is pumped by a
Varian 551 l/s turbomolecular pump, shown in blue. The pump keeps the chamber at
pressures below 1×10 −8 Torr, as measured by a cold cathode vacuum gauge (pink). As
in the proof-of-principle experiment, the beam is detected after slowing by an MCP
(feedthrough mount flange shown in red), which is mounted on a 50.8 mm translation
stage (shown in yellow, without the translation stage support structure). The center
of the first coil of the coilgun is located 555.7 mm from the exit of the nozzle, and
≈ 250mm from the base of the skimmer. The MCP is located 40.7mm (91.5mm) from
the center of the of the last coil in the coilgun with the translation stage retracted
(extended), and the distance from the nozzle to the MCP is 147.98 cm (153.06 cm).
The beam is slowed enough to be resolved from the main peak directly at the end of
the coilgun, so it is advantageous to have the detector as close as possible to the exit
of the coils to avoid losing flux transversely.
The electrical connections to the coils are made using an 8 inch Conflat blank,
with 3 50-pin D-Sub feedthroughs from Accu-Glass welded in. The in-vacuum con-
nectors are made from PEEK to ensure vacuum compatibility. Additionally, the wires
running from the feedthroughs to the coils are bundled together and wrapped in a
PEEK spiral to protect them. This also makes organizing the 64 pairs of wires some-
what simpler. While the feedthroughs worked without a problem for several tens of
thousands of pulses, they did eventually fail catastrophically (electrical failure, not
loss of vacuum) without warning. The data shown in the following section is taken
with the first set of feedthroughs. A higher isolation voltage set of feedthroughs was
purchased (1 kV instead of 600 V), but these too eventually failed after several tens of
thousands of shots, again without warning. Moving the coils out of vacuum became
a priority for the 3rd generation coilgun described in chapter 5.
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