Experiments with Supersonic Beams as a Source of Cold Atoms
Experiments with Supersonic Beams as a Source of Cold Atoms
Experiments with Supersonic Beams as a Source of Cold Atoms
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Energy meV<br />
0.05<br />
0.00<br />
0.05<br />
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4<br />
Magnetic Field T<br />
Figure 5.1: The hyperfine structure <strong>of</strong> the ground state <strong>of</strong> hydrogen. The transition<br />
between the low field and high field regimes takes place around .01 T, and at the<br />
fields used in the experiment described below the structure can be approximated <strong>as</strong><br />
two states, <strong>with</strong> magnetic moments <strong>of</strong> ± 1 Bohr magneton.<br />
provided by the expansion is sufficient to trap a significant portion <strong>of</strong> the beam.<br />
Furthermore, the magnetic properties <strong>of</strong> atomic hydrogen are ideal for use in the<br />
coilgun. Hydrogen is the lightest <strong>of</strong> the atoms <strong>with</strong> a m<strong>as</strong>s <strong>of</strong> 1 amu, and in the high<br />
field limit, h<strong>as</strong> a magnetic moment <strong>of</strong> ± 1 Bohr magneton. The hyperfine structure<br />
<strong>of</strong> the ground state <strong>of</strong> hydrogen <strong>as</strong> a function <strong>of</strong> magnetic field is shown in figure<br />
5.1. Because the transition between the high field and low field limits takes place<br />
around 0.01 T, the behavior <strong>of</strong> hydrogen in the fields <strong>of</strong> the coilgun and trap is<br />
nearly always that <strong>of</strong> the high field limit. The large magnetic moment to m<strong>as</strong>s ratio<br />
(the highest for ground state atoms), makes hydrogen ideal for use in the coilgun.<br />
The importance <strong>of</strong> precision me<strong>as</strong>urements on hydrogen isotopes, coupled <strong>with</strong> the<br />
excellent compatibility <strong>of</strong> hydrogen <strong>with</strong> the coilgun method, motivates the work<br />
described here. It should also be noted that the coilgun method h<strong>as</strong> been pursued<br />
independently and in parallel to the one described here [21, 22], and been used to<br />
confine hydrogen and deuterium for a few milliseconds [23, 24].<br />
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