R. Emmerich

Precision Lamb-shift polarimeter for polarized atomic and ion beams

The Lamb-shift polarimeter described here enables the polarization of a beam of hydrogen (deuterium) atoms, or of a slow proton (deuteron) beam, to be measured with an absolute precision better than 1% within a few seconds. The polarimeter measures the intensity ratios of Lyman-α transitions after Stark quenching of metastable hyperfine substates that were selected in a spin filter. For that purpose the hydrogen (deuterium) atoms are ionized in a Glavish-type ionizer. By charge exchange of the protons (deuterons) in cesium vapor, atoms in the metastable 2S state are produced. For a hydrogen beam of 3×1016 atoms/s, ∼3×106 photons/s are registered in a photomultiplier, i.e., the polarimeter efficiency is about 10−10. The signal-to-background ratio in the Lyman-α spectrum is excellent, thus beam intensities of one to two orders of magnitude less would still be sufficient to carry out a precise measurement. The different components of the polarimeter affect the measured polarization in several ways. It was, t...

Background reduction by a getter pump around the ionization volume of a Lamb-shift polarimeter and possible improvements of polarized ion sources

The Koln–Julich Lamb-shift polarimeter is used to measure the nuclear polarization of the hydrogen or deuterium beam produced with the atomic-beam source for the polarized target at the ANKE spectrometer at COSY-Julich. The precision of the earlier results had been dominated by the recombination of atoms in the ionizer. Protons or deuterons from the dissociative ionization of unpolarized recombined H2 or D2 molecules had strongly contributed to the extracted ion beam. To suppress this effect, in the new ionizer a nonevaporable getter pump of about 2000l∕s H2 or D2 pumping speed surrounds the ionization volume. It reduces the extracted current of unpolarized ions, produced from the recombined molecular gas, by a factor of about 20 compared with the earlier value, which reduces the error of the polarization measurements to about 0.5%. Now the H2 or D2 molecules in the ionization volume predominantly are those which are contained in the incoming beam from the atomic beam source. This allows the measurement o...

Deuteron Spin Dichroism: From Theory to First Experimental Results

The production of tensor polarization in an unpolarized deuteron beam after passage through unpolarized carbon targets, which includes the effect of deuteron spin dichroism, has been observed for the first time. Theoretical background, experimental setup, and results of the experiment are presented.

The polarized internal gas target for ANKE at COSY-Jülich

A polarized internal hydrogen and deuterium gas target for the magnetic spectrometer ANKE in the COSY-Julich storage ring is being developed. The polarized atomic beam will feed a storage cell. At present, the beam intensity measured with use of a compression tube is 6.4⋅1016 H atoms per second. The nuclear polarization of the beam and the target gas will be investigated with a Lamb-shift polarimeter. First studies on the COSY beam properties have been performed with an aperture at the ANKE-target position. They will be extended with prototypes of cell tubes as soon as a new target chamber is available.

Extra Physics with an ABS and a Lamb-shift Polarimeter

The polarized internal gas target of the ANKE experiment is only used for a few months per year for hadron physics at the cooler synchrotron COSY. In the meantime, the whole setup or components like the ABS or the Lamb-shift polarimeter can be used for other experiments. We present various projects, from atomic and molecular physics to a neutrino experiment, for which the existing hardware can be used.

A Precision Lamb‐shift Polarimeter for the Polarized Gas Target at ANKE/COSY

The Lamb‐shift polarimeter [1], described here, allows the polarization measurement of a beam of hydrogen (deuterium) atoms, or of a slow proton (deuteron) beam (500 – 2000 eV) with an absolute precision better than 1% within a few s. For a hydrogen beam of 3 ⋅ 1016 atoms/s, 3 ⋅ 106 photons/s are registered in a photomultiplier. The signal‐to‐background ratio in the Lyman‐α spectrum is excellent, thus beam intensities of one to two orders of magnitude less would still be sufficient to carry out a precise measurement. Therefore, it will be possible to extract a few percent of the atoms from a storage cell to measure the polarization in the cell. In order to obtain absolute nuclear polarization values the polarization derived from the Lyman‐α spectrum has to be corrected by a number of correction factors calculated with high precision from the behaviour of different components of the polarimeter.