10.2 Magnetic trapping 223radial confinement for atoms in low-field-seeking states. To confine these
atoms in the axial direction the trap has two pairs of co-axial coils with
currents that flow in the same direction to produce a field along thez-
axis whose magnitude is shown in Fig. 10.4. These so-called pinch coils^4
(^4) The term ‘pinch coils’ arises from the
concept of pinching off the ‘magnetic
tube’ containing the atoms. The Ioffe
trap configuration was originally devel-
oped to confine plasma.
have a separation greater than that of Helmholtz coils, so the field along
zhas a minimum midway between the coils (where dBz/dz=0). The
Ioffe coil Pinch coil
Detection
beam
Atom
cloud
Atomic
beam Mirror
Compensation coil
CCD camera
MOT
beam
MOT
beam
MOT
beam
MOT
beam
MOT
beam
MOT
beam
MOT
beam
Magnetic
field coils
MOT
beam
MOT
beam
MOT
beam
MOT
beam
MOT
beam
Atomic beam source
MOT and magnetic trap
Fig. 10.5A general view of an appa-
ratus to load an Ioffe–Pritchard mag-
netictrapwithlaser-cooledatomsfrom
a magneto-optical trap. (The MOT
has a different arrangement of coils to
that described in Section 9.4 but the
same principle of operation.) This ex-
perimental apparatus was constructed
by the team of Professor Jook Wal-
raven at the FOM Institute, Amster-
dam. (Figure courtesy of Dr Kai Dieck-
mann, Dieckmannet al. (1998).) Copy-
right 1998 by the American Physical
Society.