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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Figure 4.15: A CAD image <strong>of</strong> the 18 stage coilgun placed in the rotor chamber. The<br />
center <strong>of</strong> the first coil is 59 cm from the nozzle, and the coilgun is 26.8cmfromthe<br />
center <strong>of</strong> the first coil to the center <strong>of</strong> the l<strong>as</strong>t coil. Figure Courtesy Christian Parthey.<br />
neon atom hits the surface (known <strong>as</strong> Penning ionization). The MCP is an array <strong>of</strong><br />
electron multiplier tubes that amplify the electron current produced by the impact<br />
<strong>of</strong> the met<strong>as</strong>tables. A bi<strong>as</strong> across the MCP sets the amplification gain: typical values<br />
are 1.6 kV for the bi<strong>as</strong> resulting in a gain <strong>of</strong> 10 6 . The circuit which bi<strong>as</strong>es the MCP<br />
is shown in figure 4.16, and the MCP used h<strong>as</strong> an 18 mm diameter active area.<br />
The position <strong>of</strong> the MCP is different from the position <strong>of</strong> the direct beam<br />
RGA from the rotor experiment. While the RGA w<strong>as</strong> 1.42 m from the nozzle, it is<br />
desirable to have the MCP be even farther away. The coilgun only slows a small<br />
fraction <strong>of</strong> the beam, and slows that fraction by only a few tens <strong>of</strong> meters per second.<br />
Having a long distance between the exit <strong>of</strong> the coilgun and the MCP incre<strong>as</strong>es the<br />
separation between the slowed and unslowed parts <strong>of</strong> the beam. Additionally, the<br />
MCP is mounted on a 5.08 cm translation stage that allows it to be moved closer<br />
to or farther from the coilgun. By observing the difference in time-<strong>of</strong>-flight <strong>of</strong> the<br />
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