Atomic Beam Source (ABS)

Polarized atomic beam sources are a modern version of the Rabi apparatus to determine the energy differences of the hyperfine substates as a function of an external magnetic field. Meanwhile, their intensity of about 10¹⁷ atoms/s reached a limit, because intra-beam scattering avoids a higher flux. The values of the nuclear polarization are above 0.9, i.e. more than 95% of all atoms have the favored projection of the nuclear spin, either m_I=+1/2 or -1/2. For hydrogen it is possible to produce a beam of atoms in either one or in two hyperfine-substates and for deuterium always two substates are found in the beam.

Principle of an ABS

Molecular hydrogen or deuterium gas is dissociated into atoms in the radio-frequency induced plasma of the dissociator (magenta). After passing the beam formation elements (cooled nozzle (turquoise) and skimmer), atoms are filtered by a strong inhomogeneous magnetic field of a group of sextupole magnets (blue) according to their electron spin projection as in Stern’s and Gerlach’s experiment. Thus, only atoms in hyperfine states with m_J=+1/2 are focused on the axis. A following “radio frequency transition unit” (red) is employed to provide necessary transitions between hyperfine states with different projections of nuclear spin. Successive filtering by a strong inhomogeneous magnetic field of a second group of sextupole magnets (blue) provides a focused beam of atoms in the selected hyperfine states with certain projection of a nuclear spin. Another radio frequency transition (red) unit allows now to transmit the residual atoms in any other hyperfine substate.