Advances in ion-source, accelerator and beam-cooling technology have made it possible to produce high-quality beams of atomic ions in arbitrary charged states as well as molecular and cluster ions that are internally cold Ion beams of low emittance and narrow momentum spread are obtained in a new generation of ion storage-cooler rings dedicated to atomic and molecular physics The long storage times ( approximately 5<or approximately= tau <or approximately=days) allow the study of very slow processes occurring in charged (positive and negative) atoms, molecules and clusters Interactions of ions with electrons and/or photons can be studied by merging the stored ion beam with electron and laser beams The physics of storage rings spans particles having a charge-to-mass ratio ranging from <0002(C60+ and C70+) to 04-10 (H+, D+, He2+, , U92+) and collision processes ranging from <1 MeV to approximately 70 GeV It incorporates, in addition to atomic and molecular physics, tests of fundamental physics theories and atomic physics bordering on nuclear and chemical physics This exciting development concerning ion storage rings has taken place within the last five to six years

https://iopscience.iop.org/article/10.1088/0034-4885/58/10/003/pdf

Atomic and molecular physics with ion storage rings

We have performed for the first time precision spectroscopy on a coasting fast7Li+ ion beam in a storage ring. The ion beam moving with 6.4% speed of light was first electron cooled and then merged with two counterpropagating laser beams acting on two different hyperfine transitions sharing a common upper level (λ-system). One laser was frequency locked to thea
3
127J2 hfs frequency component established as a secondary frequency standard at 514 nm. The second laser was tuned over theλ-resonance, which was recorded relative to127J2 hfs components. This experiment is sensitive to the time dilation in fast moving frames and will lead to new limits for the verification of special relatively. The present status of the experiment and perspectives in accuracy are discussed.

Measurement of the transverse Doppler shift using a stored relativistic 7 Li + ion beam

Monte Carlo simulations of molecular gas flow: some applications in accelerator vacuum technology using a versatile personal computer program

In this paper, we shall discuss the effect of laser-stimulated transitions on the rate of radiative electron-ion recombination, considering in particular merged beams of electrons and protons or highly charged ions. We shall present theoretical predictions concerning the spontaneous and stimulated recombination rates and discuss the limitation of the stimulated rate by photoionization. The emphasis in this discussion will be on transitions into Rydberg states, which play an important role especially for recombination involving highly charged ions. Recent experiments demonstrating laser-stimulated recombination in merged electron and proton beams will be reviewed and a perspective of future experiments will be given.

Laser-Stimulated Radiative Recombination

The IUCF (Indiana University Cyclotron Facility) 270-keV electron cooling system has demonstrated collection efficiencies of 100% (+0/-2 p.p.m.) operating with a 2-A electron beam (0.4 A/cm/sup 2/). In addition, a very complete set of longitudinal drag rate measurements have been completed. These measurements span rest frame electron-proton velocity differences of over three orders of magnitude and include the region where the average longitudinal electron-proton velocity difference is less than the electron beam longitudinal velocity spread (a region which has not previously been measured). No obvious Schottky signal suppression (evidence of beam crystallization) has been observed for low-intensity cooled proton beams, though many interesting collective phenomena have been observed for high-intensity cooled proton beams. >

Status and performance of the IUCF 270 keV electron cooling system

The first results are presented of electron cooling experiments in the Low-Energy Antiproton Ring (LEAR) at CERN, performed with a proton beam of about 50 and 21 MeV. The number of stored protons ranged from 107 to 3 × 109. Cooling times of the order 1 s and proton drag rates of up to 0.7 MeV/s were obtained. The capture of cooling electrons by protons producing hydrogen atoms was used to derive an effective electron temperature (0.25 eV). From the angular profile of the neutral hydrogen beam an upper limit of 3π mm.mrad could be deduced for the horizontal equilibrium proton-beam emittance. The lowest equilibrium momentum spread was 2 × 105 (FWHM), as derived from the analysis of the longitudinal Schottky signal. This Schottky signal exhibited an unusual behaviour with beam intensity and under certain conditions showed a doublepeak structure which was associated with collective beam noise. For very cold beams transverse instabilities were observed, which resulted in a rapid spill-off of protons and a stabilization at lower intensities. The threshold of these instabilities was raised by heating the proton or the electron beam. The cooling of a bunched proton beam was investigated. The reduction of the proton momentum spread led to bunch lengths of about 2 m, containing 3 × 108 protons.

/pdf/first-results-of-electron-cooling-experiments-at-lear-2qo6agpun3.pdf

H. Haseroth

Papers

First results of electron cooling experiments at LEAR

The LEAR electron cooler