Experiments with Supersonic Beams as a Source of Cold Atoms

Position in Trapping Coils Position in Trapping Coils Position in Trapping Coils
Figure 5.9: Magnetic field values on the axis of the trapping coils measured by Faraday
rotation. The dashed lines indicate the center of the two trapping coils. The field
measurements are taken 2.5 mm apart. The plot on the left shows the field for a
single coil, while the plot in the center and on the right show the fields with the coils
running in Helmholtz and anti-Helmholtz configurations respectively. In all three
configurations, the current in the coils is 450 A.
are held in position on the chamber by Delrin clamps, which also hold the final three
slowing coils of the coilgun. Once wound and clamped in position, the coils are
epoxied (Epo-Tek 353nd) and wrapped with epoxy impregnated nylon cloth. This
ensures that the coils do not shift or move under the exerted magnetic forces. The
center of the trapping volume is located 2.99 cm from the center of the last coilgun
coil, and the coils are 2.7 cm apart, measured center-to-center. A photo of the trap
coils on the chamber is shown in figure 5.8.
The magnetic field values on the axis of the trapping coils, measured by Fara-
day rotation, is shown in figure 5.9. When 450A is run through a single coil, the peak
field on axis is 1.05 T. The measured field at the center of a coil is higher when the
coils are run in Helmholtz configuration, with a measured peak field of 1.11 T. When
the coils are run in anti-Helmholtz configuration, the field value on axis is lower,
0.85 T. In anti-Helmholtz configureation, the field is at a minimum at the center of
the trap, creating a 100 mK deep trapping potential. The oscillation period for a
hydrogen atom in this potential is approximately 1 ms.
Atoms in the trap need to adiabatically follow the field, as discussed in section
129