Experiments with Supersonic Beams as a Source of Cold Atoms

the temperature of these atoms is significally affected. Turning the trap on too soon
results in increased temperature because the atoms are not yet at rest in the center
of the trap. Similarly, turning the trap on too late results in the trapping of atoms
that have been reflected from the magnetic field of the rear coil, again raising the
temperature of the trapped atoms.
Simulation results presented in figure 5.20 show the phase space distributions
of the trapped atoms along each axis of the trap. Of the 10,000 simulated atoms
that enter the coilgun, 481 remain in the trap 10 ms after the trap is turned on. This
corresponds to about 10 trap oscillation periods, meaning that most of that atoms
with unstable trajectories have left the trapping region. The calculated temperature
of the trapped atoms is 62 mK. While most of the atoms have energies that are
below the overall trap depth (indicated by the ellipses in figure 5.20), some atoms
have a larger energy. This is possible because the trap is significantly deeper in the
Z direction than in the radial direction, and the velocity components are not well
mixed. The trapping efficiency shown in these simulations is significantly higher than
the slowing efficieny of neon and oxygen at the lowest velocities, which indicates the
benefits of the refinements made to the coilgun.
5.3.2 Ejection Simulations
Detecting trapped hydrogen atoms will probably require them to be ejected
from the trap and onto a detector. For atoms which have been excited to a metastable
state this could be an MCP; for ground state atoms some kind of ionization could be
used to detect the atoms. Given that the atoms must exit the trapping volume (and
most likely the trapping chamber itself) for this to work, it is important to consider
the best way to get the atoms from the trap to a detector. For the simulations shown
here, the detector is assumed to be the Ardara Technologies ionizer and quadrupole,
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