Relaxation of Hydrogen and Deuterium Atoms in Storage

This contribution describes operation and results of a polarimeter, as it will be used for HER-MES, obtained at an atomic beam test source with test storage cells of mean wall collision numbers up to 3500. The HERMES experiment at the HERA electron storage ring is designed to study the spin structure of the nucleons. It will measure spin dependent deep inelastic scattering from the proton and neutron using the longitudinally polarized electron beam at energies between 30 and 35 GeV. The HERMES target design is a thin walled storage cell which is fed by a high intensity source of polarized hydrogen and deuterium atoms, providing a target thickness of 1 10 14 atoms cm ?2. A small fraction of the stored gas is allowed to exit the cell through an additional tube forming a probe atomic beam which is analysed in a Breit Rabi polarimeter 1], using sextupole magnets, adiabatic high frequency transitions, quadrupole mass spectrometer analyses and single ion detection. In order to sample atoms which have undergone many wall collisions the axis of the sample tube is tilted with respect to the axis of the feed tube. The polarization of the target gas inside the storage cell decreases with increasing dwell time in the interaction section due to spin exchange collisions 2], wall bounces and interaction with the electron bunches. The sample beam is analyzed by means of a system of sextupole magnets which focusses atoms in electron spin states m j = +1=2 into the atomic beam detector and deeecting the opposite electron spin states. Adiabatic high frequency transitions (HFTs), which are induced between the hyperrne components of the sample beam in front of the sextupole magnets, lead to a change in the atomic beam signal which is proportional to the diierence of the populations of the states involved. By detecting signal ratios of HFT on/oo for three (in the case of deuterium ve) diierent HFTs in addition to the normalization condition i n i = 1 the relative occupation numbers n i of the hyperrne structure population inside the beam are obtained. For hydrogen we use a cavity at 1428 MHz in a strong eld transition (SFT) to exchange the hf states j2i and j4i, and a coil at 68.2 MHz in a medium eld transition (MFT) to exchange the hf states j1i and j3i or j2i and j3i, depending on the respective static eld setting. …