Ph.D. Thesis - Physics

Figure 6-10: Photograph of the surface-electrode PCB trap, known as “Bastille,” used for
ablation loading experiments. The rf electrodes are spaced by 2 mm center to center, leading
to an ion height above the surface of 0.8 mm, as predicted by numerical modeling. The
long center electrode is held at rf ground, but may have a dc offset applied to it. The
segmented electrodes on the sides carry dc potentials for confinement along the long axis of
the trap, as well as elimination of stray electric fields. The wirebonds visible on the edge of
the electrodes connect them to gold pads on the CPGA chip carrier.
To summarize this section, a PCB ion trap was loaded with the aid of buffer gas us-
ing electron impact ionization. The buffer gas allows sufficient ion signal and lifetimes
to perform compensation measurements before loading in UHV with reasonable lifetimes
(O(minutes)) is achieved. There are two primary lessons from this work: the first is that
exposure to dielectric must be minimized to limit the surface area that can trap charges
that act on the ions; the second is that methods for loading ions must be found that lead
to less accumulation of charge. Buffer-gas loading was a useful expedient in this work, but
is not ideal as a long-term solution, since it results in a much higher UHV pressure than is
possible without it.
We therefore turn to a different ion trap setup and study ablation loading of surface-
electrode traps.
6.4 The second-generation PCB ion trap
Follwing successful trapping in San Quentin, we produced a new surface-electrode PCB
trap. This trap, known as “Bastille,” has become a real “workhorse” to us, since it traps
so reliably that it may be used first in a new apparatus to verify that everything else is
working before a new trap is tested. In this section we present the design of this trap, a
photograph of which is shown in Fig. 6-10.
142