Experiments with Supersonic Beams as a Source of Cold Atoms

(a) (b)
Figure 4.14: A CAD image of the 18 stage coilgun (a) and a picture of the apparatus
(b). There are 20 stages pictured here, but two of the coils became inoperable after
the apparatus was placed in vacuum. Figure Courtesy Christian Parthey.
copper discs are also water cooled by a copper water line that is indium soldered to
the discs, allowing some of the heat to be removed from the coils. A CAD image and
photo of this setup is shown in figure 4.14.
Since this coilgun was intended simply as a proof-of-principle experiment, a
separate vacuum chamber was not built to house the coils. They were instead placed
into the existing rotor chamber. The supersonic beam chamber is un-modified from
the chamber described in section 3.3.1 (except that the discharge plates are mounted
to the nozzle), and the rotor chamber is essentially unchanged. The 5 mm skimmer
is mounted 30 cm from the nozzle, as it was in the paddle experiment. The center
of the first coil is located in the rotor chamber 59 cm from the nozzle. The coilgun
mounted inside the rotor chamber can be seen in figure 4.15.
The one significant change from the rotor vacuum chamber is in the detection
system. The metastable atoms are detected using a micro-channel plate (MCP)
instead of an RGA. The MCP (El Mul Technologies) detects the metastable neon
atoms because the ionization energy of the coating on the MCP is lower than the
excitation energy of the neon causing a free electron to be created when a metastable
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