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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ameters. The coilgun chamber consists <strong>of</strong> a 6 inch OD cylindrical stainless steel<br />
chamber, <strong>with</strong> 8 inch Conflat flanges on either end. The chamber is pumped by a<br />
Varian 551 l/s turbomolecular pump, shown in blue. The pump keeps the chamber at<br />
pressures below 1×10 −8 Torr, <strong>as</strong> me<strong>as</strong>ured by a cold cathode vacuum gauge (pink). As<br />
in the pro<strong>of</strong>-<strong>of</strong>-principle experiment, the beam is detected after slowing by an MCP<br />
(feedthrough mount flange shown in red), which is mounted on a 50.8 mm translation<br />
stage (shown in yellow, <strong>with</strong>out the translation stage support structure). The center<br />
<strong>of</strong> the first coil <strong>of</strong> the coilgun is located 555.7 mm from the exit <strong>of</strong> the nozzle, and<br />
≈ 250mm from the b<strong>as</strong>e <strong>of</strong> the skimmer. The MCP is located 40.7mm (91.5mm) from<br />
the center <strong>of</strong> the <strong>of</strong> the l<strong>as</strong>t coil in the coilgun <strong>with</strong> the translation stage retracted<br />
(extended), and the distance from the nozzle to the MCP is 147.98 cm (153.06 cm).<br />
The beam is slowed enough to be resolved from the main peak directly at the end <strong>of</strong><br />
the coilgun, so it is advantageous to have the detector <strong>as</strong> close <strong>as</strong> possible to the exit<br />
<strong>of</strong> the coils to avoid losing flux transversely.<br />
The electrical connections to the coils are made using an 8 inch Conflat blank,<br />
<strong>with</strong> 3 50-pin D-Sub feedthroughs from Accu-Gl<strong>as</strong>s welded in. The in-vacuum con-<br />
nectors are made from PEEK to ensure vacuum compatibility. Additionally, the wires<br />
running from the feedthroughs to the coils are bundled together and wrapped in a<br />
PEEK spiral to protect them. This also makes organizing the 64 pairs <strong>of</strong> wires some-<br />
what simpler. While the feedthroughs worked <strong>with</strong>out a problem for several tens <strong>of</strong><br />
thousands <strong>of</strong> pulses, they did eventually fail cat<strong>as</strong>trophically (electrical failure, not<br />
loss <strong>of</strong> vacuum) <strong>with</strong>out warning. The data shown in the following section is taken<br />
<strong>with</strong> the first set <strong>of</strong> feedthroughs. A higher isolation voltage set <strong>of</strong> feedthroughs w<strong>as</strong><br />
purch<strong>as</strong>ed (1 kV instead <strong>of</strong> 600 V), but these too eventually failed after several tens <strong>of</strong><br />
thousands <strong>of</strong> shots, again <strong>with</strong>out warning. Moving the coils out <strong>of</strong> vacuum became<br />
a priority for the 3rd generation coilgun described in chapter 5.<br />
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