E. Steffens

The HERA polarimeter and the first observation of electron spin polarization at HERA

Abstract Electron spin polarizations of about 8% were observed at HERA in November 1991. In runs during 1992, utilizing special orbit corrections, polarization values close to 60% have been achieved. In this paper the polarimeter, the machine conditions, the data analysis, the first results and plans for future measurements are described.

The first achievement of longitudinal spin polarization in a high energy electron storage ring

A pair of spin rotators has been installed in the electron ring of HERA. Longitudinal spin polarizations up to 65% have been reached reproducibly during dedicated measurement time. This is the first time that longitudinal spin polarization has been produced in a high energy electron storage ring.

Polarization monitors for polarized heavy ion beams

Abstract Reactions of various spin type are discussed in respect to their use as calibrator and monitor for polarized heavy ion beams.

The FILTEX / HERMES polarized hydrogen atomic beam source

The FILTEX/HERMES atomic beam source (ABS) for polarized hydrogen is described. Recent improvements concern mainly the optimization of the beam forming system and a new design of the sextupole magnet system. For a precise measurement (error 5%) of the output flow a calibrated compression tube was installed. The output flow of 0.81×1017 H atoms per second in two hyperfine substates was constant within 2% in a long-term measurement over 16 h. At the FILTEX test experiment, the target density in the storage cell fed by the ABS was constant within the experimental error of 4% over a period of four months.

The source of polarized heavy ions (PSI) at the Heidelberg MP tandem

Abstract The new polarized source at the Heidelberg MP tandem is described. The source produces beams of 6 Li , 7 Li and 23 Na ions, which are preaccelerated to 150–200 keV and injected into the MP tandem. The results of the first test runs are presented. A 44 MeV 7 Li beam has been produced and the polarization was detected in a nuclear reaction. A Na beam will be accelerated during one of the next few runs. Improvements of the polarization by laser optical pumping are discussed.

Polarized heavy ion beams at tandem accelerators

Abstract The production of negative polarized heavy ions and their acceleration by tandem accelerators is reviewed. Particular emphasis is given to the polarized lithium and sodium beams at the Heidelberg EN tandem. The problem of depolarization of an incompletely-stripped beam is discussed using experimental results on the Na beam as an example. The advantages involved in using tandems with high terminal voltages for the acceleration of polarized ion beams heavier than lithium is stressed.

The interaction of aligned 7Li with 58Ni

Abstract Elastic and inelastic scattering of aligned 7 Li on 58 Ni was studied experimentally for several energies between 14 and 22 MeV. Complete sets of second-rank tensor analyzing powers were measured for two energies, 14.2 and 22.0 MeV. The shape-effect model has been used for a qualitative interpretation of the data. The success of this model indicates the spectroscopic deformation of 7 Li to be the main source of the observed second-rank tensor analyzing powers. The result enters the formulation of the diffraction as well as the optical model both of which are used to improve the analysis of the data. Besides the parameters which determine the central interaction the spectroscopic deformation was the only adjustable parameter. The deformation was found to be negative, in agreement with the oblate shape of 7 Li. However the extracted value of the deformation varies within a factor of two when comparing different experiments and/or analyses with different models. The second-rank tensor analyzing powers for projectile excitation are roughly explained by the assumption that the angular momentum transfer is perpendicular to the momentum transfer.

Nuclear spin polarized alkali beams (Li and Na): Production and acceleration

Abstract Recent improvements of the Heidelberg source for polarized heavy ions (PSI) are described. By means of optical pumping in combination with the existing multipole separation magnet the beam figure of merit (polarization 2 × intensity) was doubled. 7 Li and 23 Na atomic beams can now be produced in pure hyperfine magnetic substrates. Fast switching of the polarization is achieved by an adiabatic medium field transition. The hyperfine magnetic substate population is determined by laser-induced fluorescence spectroscopy. In routine operation atomic beams with nuclear polarization p α ≧ 0.85 ( α = z, zz) are obtained. The acceleration of polarized 23 na − ions by a 12 MV tandem accelerator introduces a new problem: the energy at the terminal stripper foil is not sufficient to produce a usable yield of naked ions. For partially stripped ions hyperfine interaction of the remaining electrons with the nuclear spin reduces the polarization. Using in addition the Heidelberg postaccelerator 23 Na 9+ beams of energies between 49 and 184 MeV were obtained with an alignment on target of P zz ≊ 0.45 . 7 Li beams have also been accelerated up to 45 MeV with an alignment of P zz = 0.69.

High spin polarization at the HERA electron storage ring

Abstract This paper describes the progress made in 1992 towards increasing the vertical electron beam polarization at HERA. Utilizing harmonic spin-orbit corrections and beam tuning, the vertical polarization has been increased from 15% to nearly 60% at a beam energy of 26.7 GeV. The long-term reproducibility of the polarization is excellent. Measurements of the build-up time and the energy dependence of the polarization are also described.

Elastic and inelastic scattering of polarised 7Li from 120Sn

The differential cross section and analysing powers iT11, TT20, T20, T21 and TT30 have been measured for both the elastic scattering of 44 MeV polarised 7Li from 120Sn and for projectile excitation to the 1/2 state at 478 keV. The data have bee fitted with coupled-channels calculations which include ground-state reorientation of the 7Li and coupling to excited states of 7Li. The sensitivity of the different observables to a number of coupling schemes is discussed. The potentials were derived from a double folding model which explicitly includes the 7Li deformation.