D. Krämer

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.

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.

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.

Electron cooling of heavy ions

Abstract The electron cooling device of the Heidelberg cooler storage ring has come into operation and for the first time has cooled ions heavier than protons. These experiments have proven that the cooling force is increasing with the charge of the ion. Cooling in the longitudinal and transverse phase space can increase the phase space density by up to four orders of magnitude. The usefulness of the method to increase the lifetime and the intensity of the stored particles was demonstrated resulting in a number of 3 × 10 10 carbon particles which were successfully cooled and stored.

One year of operation at the Heidelberg TSR

Abstract After one year of operation the heavy ion storage ring TSR at the Heidelberg Max-Planck Institut fur Kernphysik has reached full performance. As designed 1000 turns are accumulated by a combination of multiturn and rf stacking. Due to phase space compression by an electron cooler the momentum spread of the beams is Δp/p = 10−5 −10−4 depending on the heating by intrabeam scattering. The cooled beam lifetime is pushed to the limits set by charge exchange processes as electron capture for bare nuclei and electron stripping for incompletely stripped ion beams. As the vacuum pressure is P ≤ 10−10 Torr at present, beam lifetimes range from τ = 36 h for 21 MeV protons to 20 s for 7 MeV Be+. Intensities of up to 18 mA (3 × 1010 particles) C6+ beam have been stacked by applying phase space cooling during injection. For these high intensities the splitting of the longitudinal Schottky noise signal showed irregular behaviour with respect to the expected Δƒ ∼ I 1 2 scaling law.

The Heidelberg Heavy Ion Test Storage Ring TSR

The Heavy Ion Test Storage Ring TSR [1] is an experimental facility for accelerator, atomic and nuclear physics studies presently under construction at the Heidelberg Max-Planck-Institute. The storage ring is designed for heavy ions of up ∼ 30 MeV/u at a charge to mass ratio of qA = 0.5, corresponding to a magnetic rigidity of Bρ = 1.5 Tm. Phase space compression using electron cooling [2] will be applied in the TSR to produce ion beams of extreme quality and at the same time to reduce the large transverse emittances and momentum spread which build up in the sophisticated injection technique used to reach heavy ion currents in the mA range. The beams equilibrium emittance and momentum distribution after cooling will be limited just by intrabeam scattering and the interaction in an internal target. Furthermore the very broad rigidity acceptance of the TSR will permit operation with simultaneous storage of several neighboring charge states of ions. This report will review the major design features and give the status of the ring project.

Study of the one-neutron transfer reactions induced by polarized 7Li ON 26Mg and 120Sn

Abstract Angular distributions of the cross sections and analyzing powers up to third rank have been measured for the one-neutron transfer reactions 26Mg(7Li,6Li)27Mg, 120Sn(7Li,6Li)121Sn and 120Sn(7Li, 8Li)129Sn initiated by polarized 7Li ions of 44 MeV. Third-rank analyzing power has been measured for the first time in transfer reactions. Coupled-channels calculations in which the ground and first excited states of 7Li are coupled together by collective interactions and one-neutron transfers are calculated in exact finite range explain the experimental data for low-lying states in final nuclei. Extracted spectroscopic factors are in good agreement with those obtained from other one-neutron transfer reactions on the same targets.

NEW DEVELOPMENTS IN POLARIZED ION SOURCES

A new atomic beam type polarized alkali ion source has been installed at the MP tandem accelerator in Heidelberg. By thermal evaporation and collimation Li and Na atomic beams are formed. Polarization is produced by optical pumping and a 4-pole Stern-Gerlach magnet which results in beams in a single Zeeman m-state. The population is shifted to any m-state by an adiabatic high frequency transition in a medium field (MFT). The purity of m-state population has been measured to be between 0.95 and 0.98, which results in nuclear polarization P > 0.9, s=z,zz. At the surface ionizer of the ion source beams of 15 to 65 μA of positive ions have been extracted of optically pumped Li and Na ions, respectively.

Radiofrequency stacking experiments at the Heidelberg test storage ring

Abstract Combined multiturn injection scheme and radiofrequency stacking have been employed, at the Heidelberg test storage ring, to fill both the horizontal transverse and the longitudinal phase spaces: an intensity enhancement factor of approximately 800 was thus obtained in the stored beam with respect to the injected one.

Design and Test of a Superconducting Quarter-Wave-Resonator

A superconducting quarter-wave-resonator at 325 MHz has been designed that could be used as a debuncher for the Heidelberg postaccelerator. The design study utilized the computer codes SUPERFISH and URMEL as well as a theory considering the quarter-wave-resonator as a piece of transmission line shorted at one end. These calculations were used to optimize Hp/¿acc, Ep/¿acc and U/¿acc2. According to measurements with a model resonator the copper body of a first prototype resonator has been machined. In first experiments with an electrochemically plated lead surface an unloaded quality Q0 = 6 × 107 has been measured. The highest accelerating field obtained in that test amounted to ¿acc = 1.8 MV/m at Q0 = 1.0 × 107.