Experiments with Supersonic Beams as a Source of Cold Atoms

Normalized Effusive Beam Flux
Normalized Effusive Beam Flux
0.0006
0.0004
0.0002
0.0015
0.001
0.0005
a Helium at 300 K
0.
0
0 500 1000 1500 2000 2500 3000
Velocity ms
c Neon at 300 K
0.016
0.011
0.
0
0 200 400 600 800 1000 1200 1400
Velocity ms
0.0055
0.033
0.022
0.011
Normalized Supersonic Beam Flux
Normalized Supersonic Beam Flux
Normalized Effusive Beam Flux
Normalized Effusive Beam Flux
0.001
0.0005
0.003
0.002
0.001
b Helium at 77 K
0.
0 200 400 600 800 1000 1200 1400
Velocity ms
d Neon at 77 K
0.
0
0 100 200 300 400 500 600 700
Velocity ms
0.028
0.014
0
0.025
0.017
0.0083
Figure 2.1: The velocity distribution for supersonic and effusive beams are compared
for Helium and Neon beams at reservoir temperatures of 300 K and 77 K. The
distributions are normalized to aid the comparison of flux at a particular velocity.
The temperatures of the supersonic beams are taken from experimental data from
the UT supersonic valve and experiments performed in Uzi Even’s lab at Tel Aviv
University [28].
called the quitting surface. Since the beam is no longer collisional downstream of the
quitting surface, finding the velocity distribution at the quitting surface is sufficient
to characterize the beam. The velocity distribution can be modeled as an anisotropic
Maxwellian
m m
p(v) =
2πkBT 2πkBT⊥
Normalized Supersonic Beam Flux
Normalized Supersonic Beam Flux
e − mv2 ⊥
2k B T ⊥ − m(v −w) 2
2k B T , (2.24)
where T and T⊥ are the temperatures along the axis of the beam and perpendicular
to the beam respectively, with the same notation used for v and v⊥.
In practice, the perpendicular temperature manifests as a loss of flux, since the
beam generally goes through several apertures before being used in an experiment.
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