Experiments with Supersonic Beams as a Source of Cold Atoms

guided the design of the apparatus. These simulations indicated the loss mechanisms
that needed to be addressed when moving to a hydrogen specific coilgun. They also
helped to determine the required field and switching parameters needed to create an
effective magnetic trap. The simulation uses a variable step Runge-Kutta algorithm,
coded in Visual C++, which numerically calculates the trajectory of one atom at a
time. Monte-Carlo techniques allow the behavior of the beam to be determined by
randomly initializing each atom according to the expected distribution of the beam
entering the coilgun.
Once the design was finalized, simulations were run to optimize the switching
sequence, and to determine what performance could be expected. Data from these
simulations is shown below, indicating a trapping efficiency of 4.8%, at a temperature
of 62mK. As The detection of the trapped atoms may require ejecting them from the
trap onto a detector, this process is also simulated, showing an extraction efficiency
of 13%. Once the experimental parameters were finalized the measurements of the
fields in the slowing and trapping coils, as well as their switching paraments, are
inserted into the simulations. Furthermore, the dimensions used in the simulations
are matched with those in the physical apparatus.
5.3.1 Slowing and Trapping
The first simulations presented are only of the slowing process, without cur-
rent in the trapping coils. The simulated hydrogen beam has the same temperature
(525 mK) as the metastable neon beam measured in chapter 4. This temperature
value is used because the hydrogen is seeded into a neon carrier gas, which dominates
the behavior of the resulting beam. The initial velocity used is 527m/s which matches
the measured velocities of the beam. Variations in the real velocity of the initial beam
can be accounted for by varying the phase used in the coilgun so that the beam exits
142