A. Vassiliev

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...

24 segment high field permanent sextupole magnets

We report on the design, construction, and magnetic field measurements of a system of high field sextupole magnets made from NdFeB compounds. The magnets are utilized as a focusing system for neutral hydrogen (or deuterium) atoms in a polarized atomic beam source based on Stern–Gerlach spin separation. Each magnet consists of 24 segments of permanently magnetized material differing in remanence and coercivity to reduce demagnetization. According to quadratic extrapolation to the pole tip the magnetic flux density reaches values of up to B0=1.69 T. Three-dimensional field calculations using the MAFIA code were carried out to optimize the magnet performance and to avoid demagnetization by selecting appropriate materials for the individual segments. Measurements of the radial, azimuthal, and longitudinal magnetic flux density distributions were carried out by means of a small Hall probe (100×200×15 μm3). The measurements with the small probe permitted to extract experimentally higher order multipole componen...

The Polarized Internal Gas Target of ANKE at COSY

For future few‐nucleon interaction studies with polarized beams and targets at COSY‐Julich, a polarized internal‐storage cell gas target is currently being developed and will be implemented in the near future at ANKE. The polarized atomic beam source, which will feed the target, provides beam intensities of 7.4 ⋅ 1016 atoms/s in two hyperfine states of hydrogen. The implementation of the target at the internal spectrometer ANKE constitutes a major technological enterprise. The differential pumping system at ANKE has already been installed, as well as a new large target chamber to accomodate storage cells in the future, a new set of small‐aperture horizontal and vertical beam position monitors, and a system of target‐near detectors. In order to determine the nuclear polarization of the target, a Lamb‐Shift polarimeter is currently set up. Tests with prototype storage cells aiming at the identification of cell dimensions suitable for the ANKE target are underway.

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.

Cross section measurements of the polarized d+3He and d+d reactions at low energies

The reactions of thermonuclear fusion in d+t, d+3He, d+d plasma at energies from several keV to 200 keV play a key role both in astrophysics problems (primordial nucleosynthesis, internal energy of stars) and in practical problem of the thermonuclear reactor development. Recent theoretical calculations show the essential influence of nuclear polarization on total cross section in these reactions. We present the experimental setup for d−d and d+3He differential cross section measurements at low energies.

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.