# The Polarized Internal Gas Target of ANKE

Since 2005 the ANKE spectrometer is equipped with a polarized internal target (PIT). It consists of a polarized atomic beam source (ABS) following the Stern-Gerlach experiment to produce a polarized atomic beam, a huge target chamber including a storage cell and a Lamb-shift polarimeter to control and tune the polarization. Therefore, at ANKE double-polarized experiments, i.e. with polarized beam and target, are now possible for nuclear and hadron physics and will allow to measure spin-correlation coefficients.

The polarized internal gas target of ANKE consists of three major elements:

• The Atomic Beam Source (ABS) providing intense beam of hydrogen or deuterium atoms with high degree of polarization;
• The target chamber hosting the openable storage-cell and Silicon Tracking Telescopes;
• The Lamb-shift polarimeter providing fast and precise measurement of the atomic jet polarization and used for fine tuning of the ABS’ high frequency transition units at various magnetic fields of the D2 spectrometer dipole at ANKE.

Molecular hydrogen or deuterium gas is dissociated into atoms in the rf-field of the dissociator. After passing the beam formation elements (nozzle and skimmer), atoms are filtered by a strong inhomogeneous magnetic field of a group of sextupole magnets according to their electron spin projection as in Stern’s and Gerlach’s experiment. Thus, only atoms in hyperfine states with mJ=+1/2 are focused on the axis. A following “radio frequency transition unit” 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 provides a focused beam of atoms in the selected hyperfine states with certain projection of a nuclear spin.

If the polarized atoms of the ABS will cross the COSY beam the influence of the nuclear spin on the nuclear forces can be investigated. But the amount of polarized atoms in the jet target is rather low (1011atoms/cm2). Therefore, a T-shaped storage cell is used to store the atoms inside. By this, the target density is increased by a factor of more than 100, but at the same time the interaction region of beam and target grows from a few mm to 37 cm.

A Lamb-Shift polarimeter is able to filter hydrogen or deuterium atoms due to their different nuclear spins. At the end, the amount of atoms with spin +1/2 or -1/2 for hydrogen or +1, 0 or -1 for deuterium can be separately determined and the polarization is measured with a precision down to ±0.5 % within a few seconds.

### Atomic Beam Source

• target gas: hydrogen or deuterium
• beam intensity: 7.6×1016atoms/s (H-beam in 2 hyperfine states)
• beam dimensions at the interaction point: σ= 2.85 ± 0.42 mm
• beam polarization

HydrogenDeuterium

Pz=+0.89

Pz=-0.96

Pz=+0.88

Pz=-0.91

Pzz=+0.90

Pzz=-1.71

### Lambshift Polarimeter

• target gas: H, D, H2, D2
• precission: ±0.5 %
• sensitivity: ~1014atoms/s
• measuring time t: 2 ↔60 s

### Target chamber

• Also suitable for solid state and Cluster jet targets;
• Strong pumping system provides UHV conditions for COSY operation;
• Large volume is available for STT and openable/fixed storage cells

# Contact persons in IKP-2:



Dr. Ralf Engels