Experiments to Control Atom Number and Phase-Space Density in ...
Experiments to Control Atom Number and Phase-Space Density in ...
Experiments to Control Atom Number and Phase-Space Density in ...
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BGauss<br />
250<br />
200<br />
150<br />
100<br />
50<br />
30 20 10 0 10 20 30zcm<br />
Figure 7.16: Axial field profile of the MOT coils. The solid l<strong>in</strong>e is the calculated field,<br />
experimentally determ<strong>in</strong>ed field strengths are shown <strong>in</strong> blue.<br />
large temperature gradients an <strong>in</strong>terlock system is <strong>in</strong>stalled. The <strong>in</strong>terlock s<strong>to</strong>ps the<br />
current <strong>to</strong> the MOT coils if either the cool<strong>in</strong>g water is not flow<strong>in</strong>g or the temperature<br />
of the coils is exceed<strong>in</strong>g 30 ◦ C.<br />
7.2.3 Feshbach Coils<br />
The most difficult set of coils <strong>to</strong> design is the pair of Feshbach coils which are<br />
located <strong>in</strong>side the reentrant viewport, as shown <strong>in</strong> figure 7.17. For fast evaporative<br />
cool<strong>in</strong>g a constant magnetic field must be tuned near the Feshbach resonance located at<br />
834 G. Because the trap depth of the optical dipole trap is significantly lowered dur<strong>in</strong>g<br />
the evaporation sequence, any forces exerted by magnetic field gradients can possibly<br />
lead <strong>to</strong> traploss. A homogeneous field is therefore necessary. The Feshbach coils are<br />
consequently designed <strong>in</strong> Helmholtz-configuration.<br />
The <strong>in</strong>ner diameter of the coils is 29.5 mm, fitt<strong>in</strong>g around the w<strong>in</strong>dow of the<br />
reentrant viewport; the outer diameter is about 45 mm. They are separated by approx-<br />
imately 36 mm. The coils are wound from flat copper wire with dimensions 0.43 mm×<br />
7.6 mm, (MWS Wire Industries, 41137). Each coil has 26 w<strong>in</strong>d<strong>in</strong>gs, lead<strong>in</strong>g <strong>to</strong> a mag-<br />
netic field strength of 6.34 G/A. To create the required fields strengths, a current of up<br />
108