Ph.D. Thesis - Physics
Ph.D. Thesis - Physics
Ph.D. Thesis - Physics
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Figure 6-6: <strong>Ph</strong>otograph of the trap with the top plate mounted 6.3 above. A slit is cut in<br />
the top plate for ion fluorescence detection.<br />
ment of a copper-plated PCB, was mounted above the trap using standoffs (as shown in<br />
Fig. 6-6). Connections to the trap were made by soldering Kapton-coated wires, connected<br />
to the electrical feedthrough, to the trap using 80/20 Au/Sn solder, applied with an ul-<br />
trasonic soldering iron. The other components of the experiment, the vacuum chamber,<br />
imaging optics, and laser system, will not be discussed here, since they are very similar to<br />
those used in Ch. 5, excepting that a titanium sublimation pump was not yet part of the<br />
setup, but that a leak valve for introducing a helium buffer gas was.<br />
6.3 Buffer gas loading and micromotion compensation in a<br />
PCB ion trap<br />
6.3.1 Experimental setup and ion loading<br />
San Quentin was loaded using the most conventional method for loading ion traps, electron<br />
impact ionization. In this method, a resistive oven containing solid metal pieces of the<br />
element to be ionized and trapped (c.f. Sec. 5.3.1) is aligned, across the trap, to a filament,<br />
which in our case is made of thoriated tungsten. This filament is called an electron gun,<br />
or e-gun. Current is flowed through both the oven and the e-gun. The current through<br />
the e-gun causes emission of electrons, which can be enhanced by applying a (negative)<br />
bias voltage to the filament. The electrons strike neutral atoms evaporated from the oven<br />
within the trap region, with some probability removing an electron from the neutral atoms<br />
and leaving the newly-minted ion with a sufficiently small kinetic energy to remain in the<br />
trapping region. If the ion is immediately Doppler-cooled by lasers that pass through the<br />
trapping region, this can increase the loading rate, but only works if the lasers are already<br />
well-aligned to the trap center.<br />
The electron impact ionization process is quite reliable, and it serves to ionize almost<br />
any species. This fact can be viewed in both a positive and a negative light: one can load<br />
ions without having a frequency-stabilized set of lasers, as is required for photoionization<br />
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