Table of contents

The Workshop and Symposium on the Physics of Low-Energy Stored and Trapped Particles, PSTP-87, was organized by the Research Institute of Physics (AFI) and held at the Royal Swedish Academy of Sciences, Stockholm, June 14-18, 1987. One reason for the conference was the 50th Anniversary celebrated by AFI in 1987, having started out as the Nobel Institute for Physics under the directorship of Manne Siegbahn in 1937. More important, though, was the fact that AFI presently is replacing its basic research equipment. Having relied for nearly four decades on the world's largest conventional cyclotron, the Institute is now constructing a storage ring with electron cooling for heavy ions, a very difficult but challenging project named CRYRING. When organizing the conference, our main idea was to bring together representatives of the rather well-established group of scientists relying on the use of ion traps and scientists planning to use the new generation of heavy ion storage rings. After all, what is a storage ring but a gigantic ion trap!

The conference met with an overwhelming interest, which finally stabilized around 160 participants, more than double the number we had originally hoped for. The program featured invited talks, most of which are presented here in the order they appeared in the program. Round-table panel discussions were organized in the evenings, summaries of most of them are published herein. An extended poster session at AFI resulted in a fair number of contributed papers which are included in the last part of the proceedings. Participants were thus kept busy from Sunday noon until late Thursday afternoon - maybe somewhat too busy according to certain accompanying persons!

To make the scientific burden somewhat more bearable, a half-day excursion to the archipelago of Stockholm was planned and performed, even though the weather was miserable. During the conference dinner, held on the island of Sandhamn, a spontaneous form of coherent excitation at one of the tables produced several limericks, one of which summarizes most of the conference theme:

A physicist wanted to bring An ion trap to a ring. The ions were cold, Done with lasers, I'm told. For research it was just the right thing.

We want to thank all the invited speakers, roundtable chairmen and poster contributors for their high scientific level as well as for their clever and stimulating presentations (also true for the anonymous limerick composers), which very much contributed to the success of the conference. Also we would like to thank the staffs of the Research Institute of Physics and the Royal Swedish Academy of Sciences for their help regarding practical details of the arrangements. Finally, economic support from our sponsors is gratefully acknowledged.

The Research Institute of Physics celebrates its fiftieth anniversary with a Workshop and Symposium on the Physics of Low-Energy Stored and Trapped Particles. On July 1, 1937, Professor Manne Siegbahn was appointed the first director of the Institute. Because of this celebration a personal account is given of Manne Siegbahn's contribution to atomic structure physics. Comments will also be given on the procedure in the Swedish Academy of Sciences when Siegbahn in 1925 received the 1924 Nobel Prize for Physics "for his discoveries and research in the field of X-ray spectroscopy".

An introductory overview is given of the history, the status and future trends of storage rings with beam cooling. Achievements obtained with cooling rings are outlined, the main cooling methods operational in circular machines are recalled and some features of the "ion coolers" now under construction or planned are briefly discussed.

It is concluded that the combination of the storage and beam cooling techniques will continue to lead to new discoveries and surprises.

General considerations regarding the transfer of DC beans of ions into storage rings and electromagnetic traps are presented. A system is described which has achieved 50% injection efficiency from a pulsed ion gun into an RFQ trap. Schemes are proposed for adapting this system to the efficient injection of ISOL beams into traps and for injecting the extracted beam of an ion storage ring into a trap.

Antiprotons from the Low Energy Antiproton Ring of CERN are slowed from 21 MeV to below 3 keV by being passed through 3 mm of material, mostly Be. While still in flight, the kilo-electron volt antiprotons are captured in a Penning trap created by the sudden application of a 3-kV potential. Antiprotons are held for 100 s and more. Prospects are now excellent for much longer trapping times under better vacuum conditions. This demonstrates the feasibility of a greatly improved measurement of the inertial mass of the antiproton and opens the way to other intriguing experiments. The possibility of producing antihydrogen by merging cold, trapped plasmas of positrons and antiprotons is discussed.

Basic design principles of ion storage rings are discussed and relevant projects or design studies are briefly reviewed. Special attention is spent to principle limitations for intensity, quality and life-time of stored heavy ion beams. The most limiting effects are space charge forces and large cross sections of heavy ions for scattering, charge changing and ionization. Finally, some new experimental possibilities with stored and cooled ion beams are described.

Obtaining pressures between 10^-12 and 10^-14 Torr inside vacuum systems operating at room temperature imposes severe limitations on the choice of materials and pumps. If the proper choice is made and the proper procedures are followed, the main obstacle to achieving such low pressure results from the hydrogen outgassing of the metal walls of the vacuum system. However, at the lower end of this range and for pumping systems based on getter pumps (both titanium sublimation and non-evaporable getter pumps), methane may become the main component of the residual gas pressure.

Although a large effort has been devoted to developing suitable gauges, only a few of them have been actually tested at the extreme vacuum for which they were designed. Furthermore, none of the commercially available instruments is adequate for pressures below 10^-12 Torr.

The basic physical phenomena which contribute to defining the vacuum condition inside a system operating in this pressure range are reviewed. Guidelines to the selection of materials and pumps are given and discussed with the help of some examples.

The experimental conditions of electron cooling in storage rings with magnetically confined electron beams are discussed. Particular attention is paid to "fast" electron cooling, which will be important for low-energy ion storage rings. Measurements of cooling rates and of equilibrium ion beam temperatures are reviewed. A short report is given on the recent development work for electron cooling at the CERN Low-Energy Antiproton Ring (LEAR), and on related electron beam diagnostic experiments. Conclusions are drawn in view of electron cooling at future ion storage rings.

Dielectronic recombination rates have been measured for several charge states of isoelectronic Li-like, Be-like, B-like and Na-like ions. We observed the amount of electron capture attending the passage of MeV/nucleon ion beams through a collinear, magnetically confined space-charge-limited electron beam as a function of relative energy. The experimental rates are consistent in magnitude and shape with rates determined from distorted-wave calculations of the dielectronic-recombination cross sections.

This paper summarizes the basic parameters characterizing a laser cooling configuration. It is stressed that the cooling of a trapped particle introduces additional frequency parameters, the trap frequencies, as compared with the free particles case. These can be used to classify the trapped situation in various limiting cases. The main theoretical results obtained in these limiting cases are outlined.

From the many different cooling schemes for particles stored in electromagnetic traps three schemes which seem to be most generally applicable to a large variety of systems are discussed in detail. Special emphasize is placed on obtaining fast cooling rates in large storage structures which will allow more efficient use of particles injected from accelerators into these devices.

We have used stored ion methods to improve resolution and sensitivity in optical spectroscopy. Single atomic ions have been confined by electric and magnetic fields, cooled by laser radiation pressure to temperatures on the order of 1 mK, and probed spectroscopically with narrowband lasers. The absorption resonance of a single Hg⁺ ion has been observed by a decrease in the transmitted light intensity. An ultraviolet transition in Hg⁺ has been observed with a linewidth of only 30 kHz. Quantum jumps to and from metastable levels of Hg⁺ have been observed and used to determine radiative decay rates and to infer the existence of photon antibunching. Quantum jumps have also been observed in single Mg⁺ ions.

A mass spectrometer has been set up at the on-line isotope separator ISOLDE at CERN/Geneva. Mass-separated radioactive ions are stored in a Penning trap. Their mass is determined by a measurement of the cyclotron frequency in the magnetic field of a superconducting magnet. A resolving power of up to 300 000 and a precision of some 10 keV were determined in case of mass measurements of neutron-deficient Rb and Cs isotopes.

A new technique to stop negatively charged particles inside a cyclotron field is motivated and presented. Its ability to produce a sufficient number of antiprotonic atoms is demonstrated with experimental results at target gas pressures previously not attainable. Thus the knowledge of the cascade process in antiprotonic hydrogen could be extended considerably and the strong interaction parameters in this system could be measured with good precision. It could also be shown that antiprotonic noble gas atoms up to Krypton are ionized completely. Moreover, the possibility to extract slow antiprotons out of the center of the cyclotron trap is discussed shortly.

For quite a while it has been realized that some discrete quantum numbers are conserved in some interactions but not in others. The most conspicuous cases are parity P, charge conjugation C, and the product CP which are conserved in strong and electromagnetic interactions but not in weak interactions. The question arises whether for some of the other conserved quantities, which are conserved in strong, electromagnetic and weak interactions, there is an interaction intermediate in strength between weak and gravitational which violates these quantum numbers, e.g., baryon number B and lepton number L. The possibility exists that these conservation laws, if they are broken at all, are only broken by the gravitational force which would make the mass of an intermediate boson which induces the breakdown equal to the Planck mass.

A new type of electron spectrometer is under construction at Mainz University that allows a measurement of the β-spectrum of tritium with high resolution and transmission in order to determine the neutrino rest mass. It consists of a source that contains atomic tritium, trapped in a high magnetic field, and a solenoid retarding spectrometer.

An updated survey of mostly experimental spectroscopy work in Seattle on an individual closely-confined isolated atomic or elementary particle is presented. The classical notion of an atomic particle at rest in free space is discussed, and shown to be approximable by zero-point confinement of the particle in a laboratory trap. An important tool for cooling the particle, and in the case of an electron, for obtaining directly the difference of spin and cyclotron frequencies v_s, v_c, is side band excitation. The quantum numbers of the geonium "atom", an electron in a Penning trap, have been continuously monitored in a non-destructive way by the new "continuous" Stern-Gerlach effect. In this way the g-factors of electron and positron have been determined to unprecedented precision,

½g ≡ v_s/v_c ≡ 1.001 159 652 188(4),

providing the most severe tests of QED and of the CPT symmetry theorem, for charged elementary particles. From the close agreement of experimental and theoretical g-values a new, 10⁴ × smaller, value for the electron radius, R_g < 10^-20 cm, may be extracted. Other important results are: confinement of the individual positron, Priscilla, for 3 months, a tenfold suppression of the natural width of the cyclotron resonance, detection of an isomeric (cyclotron-excited) state via mass-spectroscopy, isolation and continuous detection of an individual proton, confinement of ≈ 100 antiprotons slowed to ≈ 3000 eV, confinement of a Ba⁺ ion to 13 ≈ 100 nm, and the demonstration of quantum jumps in geonium and in an isolated, individual regular atomic particle, Ba⁺. Some new experiments are proposed.

A brief review is given of the experimental and theoretical status of the muon g-2 factor. The theoretical motivation for an improved determination of g-2 is presented, and a new AGS experiment under development at Brookhaven National Laboratory is discussed.

We consider various methods (longitudinal and transverse cooling, focusing and reflection) of controlling the motion of atoms in a beam in a resonant laser field by means of the dissipative force of laser light pressure and the potential gradient force which are required to realize various types of optical traps for slow neutral atoms. We anticipate the extension of these methods for molecules in the future.

We briefly discuss the preparation of a single cold ion in an rf trap, and the concept of "quantum jumps" which requires a single atomic particle for verification. Recent corresponding experiments have demonstrated interruptions of the laser-excited resonance fluorescence, which are the signature of the particles performing quantum jumps to and from a metastable level, under weak excitation of the corresponding transition. The time density of the jumps obeys a Poissonian distribution in agreement with theoretical models. With three trapped ions, the high rate of multiple jumps suggests the presence of collective interaction.

Condensation phenomena may be observed within the cooled ion beams contained in heavy-ion storage rings. Their properties have been investigated with the techniques of molecular dynamics. The results indicate interesting possibilities - crystallization would occur in cylindrical shells with two-dimensional order in each shell, yet an overall approximate bcc pattern in the correlation function. Similar results are seen in a spherical geometry that may crudely approximate a cold plasma in a Penning trap.

If there is either time reversal (T) or parity symmetry (P) there can be no electric dipole moment for particles whose orientations are fully specified by the orientations of their spin angular momenta. As a result there have been extensive searches for electric dipole moments of particles as tests of these symmetries. CP non-conservation has been observed which implies non-conservation of T if CPT is conserved, but CP non-conservation has only been seen in the decay of the artificially produced K_L⁰. The history of the searches for a neutron electric dipole moment is briefly summarized. The most sensitive current experiments utilize ultra cold neutrons stored in bottles whose walls totally reflect the neutrons. These experiments are described and the current results are given. The results are compared with the predictions of theories that account for the known CP non-conservation in the decay of the K_L⁰.

Laser spectroscopy is discussed as a source of information about nuclear physics properties. The quantities measured in such an experiment are atomic physics properties, namely the isotope shift and the hyperfine structure of the optical fluorescence spectra in the visible wavelength band. Nuclear physics information describing properties of the ground state and isomeric states of a nucleus can be extracted from these data, namely nuclear magnetic dipole moments, nuclear electric quadrupole moments, nuclear spins and the changes of the mean square charge radii between isotopes. Some recent results are reported as examples. The method of collinear fast-atomic-beam spectroscopy using the isotopically pure beams of on-line mass-separators and a very similar technique which has been proposed to study the hyperfine structure of hydrogen-like ions in the storage ring for cooled ions, ESR, under construction at GSI, are discussed.

Various applications of beams of antiprotons and positronium in atomic-collision processes are discussed. By a more detailed presentation of a recent collision experiment involving MeV antiprotons, it is demonstrated how valuable information on atomic interaction can be obtained by comparing equivelocity proton/antiproton results. Methods of forming thermal beams of positronium are reviewed, and plans for a few first-generation experiments are presented.

An electron beam ion trap has been built for the production of very-highly-charged ions and the study of their collisions with electrons. A high density electron beam is used to trap, ionize and excite the ions for spectroscopic measurements. X-ray spectra from neon-like Ba⁴⁶⁺ are reported and a theory of "evaporative" cooling is developed to explain why these ions are retained in the trap for surprisingly long times.

Ion traps afford the opportunity to study the collisions of ions at or below electronvolt energies: energies typically much lower than are possible with conventional ion beams. Long observation times in traps permit investigations with small cross sections, and controlled multiple collisions of projectiles with the same stored particle lead to the possibility of the preparation of particular ionic states for study. Experimental efforts in ion storage have been directed toward the production of ions with higher charge, ion confinement with lower energy, and toward the optimization of certain measurements, in parallel with the study of collision interactions. A significant theoretical effort has been directed at low energy electron transfer collisions of multi-charged ions with hydrogen atoms, and with helium and molecular hydrogen as well. Certain measurements of electron transfer from H₂ and H to stored, multi-charged ions are discussed.

Improved understanding of fundamental ion-ion interactions is expected to emerge from research carried out with ion storage rings. In this short survey the significant advantages and unique features that make stored ions useful targets for collision experiments are reviewed and discussed. It is pointed out that improvements to existing ion-ion experiments, as well as qualitatively new experiments, should occur over the next few years as ion storage rings become available for atomic physics. Some new experiments are suggested which are difficult if not impossible with present-day technology, but which seem feasible at storage rings facilities.

The energies of highly excited, high-charge-state recoil ions produced by fast heavy-ion impact on target atoms ("hammer" method) have been compared with the energies of similar-charge-state recoil ions produced by vacancy cascades subsequent to inner-shell photoabsorption of tuned synchrotron radiation X-rays ("scalpel" method). These comparisons show that the "hammer" method leads to recoil ion temperatures typically 4 orders of magnitude lower than those which occur in plasma sources in which ions of similar ionization and excitation states have comparable abundance, while the "scalpel" method leads to temperatures up to 6 orders of magnitude lower. Advantages and drawbacks of each method for potential precision spectroscopy of stored or trapped high charge state ions, and for production of extracted beams of low emittance for use in secondary ion-atom collison studies at eV to keV energies are discussed.

Photodetachment experiments with atomic and molecular negative ions have been carried out using a Penning ion trap. The experiments provide new information about photodetachment in the presence of a static magnetic field and about photodetachment in the presence of a strong laser field.

By use of the microwave-optical double resonance technique high precision values of hyperfine splitting constants of ions, confined electrodynamically in traps, have been obtained in recent years. Improved sensitivity has made possible the first investigation of unstable isotopes of Ba⁺ which are available in minute quantities only. The precision is similar as for the stable isotopes and represents a first step to a systematic study of the Bohr-Weißkopf-effect in chains of isotopes. Furthermore the possibility of g_J-factor measurements in the hydrogen molecular ion is discussed and first results are presented which may lead to a determnation of QED- and relativistic corrections in the most elementary molecule.

Theories of gravity abound whereas experiments in gravity are few in number. An important experiment in gravity that has not been performed is the measurement of the gravitational acceleration of antimatter. Although there have been attempts to infer this property from those of normal matter, none of these theoretical arguments are compelling. Modern theories of gravity that attempt to unify gravity with the other forces of nature predict that in principle antimatter can fall differently than normal matter in the Earth's field. Some of these supergravity theories predict that antimatter will fall faster and that normal matter will fall with a small Baryon-number dependence in the Earth's field. All of these predictions violate the Weak Equivalence Principle, a cornerstone of General Relativity, but are consistent with CPT conservation. In our approved experiment at LEAR (PS-200) we will test the Weak Equivalence Principle for antimatter by measuring the gravitational acceleration of the antiproton. Through a series of deceleration stages, antiprotons from LEAR will be lowered in energy to ∼ 4 Kelvin at which energy the gravitational effect will be measureable. The measurement will employ the time-of-flight technique wherein the antiprotons are released vertically in a drift tube. The spectrum of time-of-flight measurements can be used to extract the gravitational acceleration experienced by the particles. The system will be calibrated using H^- ions which simulate the electromagnetic behavior of the antiproton yet are baryons to ∼ 0.1%. To extract the gravitational acceleration of the antiproton relative to the H^- ion with a statistical precision of 1% will require the release of ∼ 10⁶-10⁷ particles.

A report from a panel discussion on electron cooling in storage rings.

Some recent achievements and possible experiments on cooled and trapped ions and atoms are summarized. Particular emphasis is given to a discussion of cooling limits in traps, recent advances of neutral atom trapping, cooling by velocity selective optical pumping, condensation and ordering in ion traps and possible future applications of confined cold particles.

This paper outlines the discussion which took place at the "round table" on experimental atomic physics in heavy-ion storage rings.

The "Physics in Traps" panel speculates on possible experiments for high precision mass spectroscopy, the use of recoil ions, applications to laboratory astrophysics, potential condensed matter experiments, and new ideas for optical and magnetic traps for neutral particles.

First experimental results demonstrating stochastic cooling of an ion cloud in a Penning trap are reported.

The dynamics of ion clouds in Paul traps has been experimentally investigated. Kinetic energy and the width of the spatial distribution of ions has been measured. Their dependence on the trap's operating conditions is compared with the results of a recent model calculation based on Brownian motion.

In this contribution we investigate the loss of a stored beam of Ar¹⁵⁺ ions through dielectronic recombination (DR) with copropagating, equal velocity electrons (e.g., in an electron cooler). We find that the Ar¹⁵⁺ 1s²2s ion can undergo dielectronic recombination through a set of doubly excited states 1s²2p10l in Ar¹⁴⁺ that lies just above the ionization limit. Recombination occurs when the DR resonance profile overlaps the electron velocity profile as viewed from the reference frame of an ion. The recombination rate coefficient is found for the case of a flattened electron distribution interacting with a one-dimensional ion beam. Losses generally depend upon the electron density and temperature, the initial and final ion temperatures, the cooling rate, and very sensitively on the energies of the participating auto-ionizing states. We find, however, for the model adopted, that the losses depend only weakly on the ion temperature. Using typical values for electron and ion temperatures and the present theoretical atomic data, we find that DR losses of a continuously cooled Ar¹⁵⁺ ion beam are negligible, giving a beam storage half-life which is much longer than those due to electron capture from the rest gas and radiative recombination from the electron beam. In a worst case, where the energy of the maximum DR cross section was chosen to coincide with the maximum of the electron energy distribution, the conclusion based on the original data is still valid.

A method for producing antihydrogen by the + Ps → + e^- reaction is described. Included are the calculated capture cross sections, and short descriptions of the electrostatic slow positron beam, positronium-formation, and the antiproton ion trap to be used for antihydrogen production. With present available technology, collimated monoenergetic beams with an energy of a few keV and an intensity in the order of one per second can be produced by this method. Possible enhancements of this rate are discussed.

CELSIUS is a cooler storage ring under construction in Uppsala. It will be used for nuclear and particle physics with ions (up to A ≈ 100) with energies up to 470 MeV/nucleon as well as protons with energies up to 1360 MeV. An electron cooler with electron energies up to 300 keV and current of 2.8 A will be used to cool the stored particles. An experimental station including a cluster gas-jet target, a fiber target, and a common scattering chamber is being built. A hydrogen pellet target has been proposed by the WASA collaboration. Experiments have been proposed for a number of studies in light and heavy ion nuclear physics and in elementary particle physics.

We have started an experimental program to develop an ultracold electron beam, which can be used together with a standard electron cooling device in the Heidelberg Test Storage Ring TSR. In contrast to the standard-type design using electron beam extraction from a heated cathode, the ultracold beam is produced by photoemission of electrons from a cooled semiconductor crystal irradiated with an intense near-infrared laser light beam. Adiabatic acceleration is expected to provide ordering of the electron beam itself. Besides the cooling of ion beams to extremely low temperatures, with the aim of obtaining crystallization, the ultracold beam will constitute an excellent target for atomic physics experiments.

Recent work on the electron cooling device at the CERN Low Energy Antiproton Ring (LEAR) is summarized. This included an improvement of the collector performance and of the vacuum. Relations between the different cooler parameters were measured with a view to simplifying the control system. Results of vacuum tests performed before the installation in LEAR are presented, and a short description of the status of the cooling device after its installation is given.

A synchrotron-storage ring for very highly charged heavy ions is under construction at the Research Institute of Physics in Stockholm. A short technical description of the ring and its injector is given.

The transverse motion of charged particles in a beam moving in a dominantly axial magnetic field, generated by connected coils of solenoidal and toroidal symmetry, is examined. Space-charge effects in the beam are taken into account to some extent. Approaches to the problem of calculating the transverse motion of the particles are discussed. A computer-program was developed to approximately solve the general non-linear problem. The program makes it possible to study the spatial transverse energy distribution of the particles in the beam as it moves through the magnetic elements. The magnetic fields used in the calculations are artificial, but measured fields could also be used as input to the program.

Negative Hydrogen ions from a duoplasmatron ion source at energies between 2 and 10 KeV have been captured in flight into a standard Penning Trap. A positive identification of the ion species was achieved with resonant excitation of the axial motion as well as the cyclotron motion. An exponential decay of the signal associated with the H^- ions was observed. This decay was accompanied by an increase of a signal from a particle species stored in the trap at very low energy. These particles are interpreted as electrons liberated from the H^- ions in collisions with residual gas molecules. The lifetime of H^- ions under the specific circumstances has been studied, and the results were found to agree with estimates using the known rate constants and the pressures present inside the trap.

The advantages of multiply charged ions in Penning traps, coupled with demonstrated ICR linewidths of 0.1 ppb indicate that the rf mass spectrometer developed at the University of Washington is capable of weighing the ground state Lamb shift of hydrogen-like uranium to better than 10%. Recent experiments with the creation of fully stripped ¹²C⁶⁺ in a Penning trap via electron impact ionization suggest that a similar approach should work to obtain fully stripped ²³⁸U⁹²⁺; however the loss in ionization cross-section which scales as Z^-4 must be overcome.

Thomson scattering of laser light was applied to a relativistic cooling electron beam. High-power laser pulses were necessary because of the very low scattering cross section. A spectrometer of high resolution and large background suppression factor in combination with time-gated photon counting served for signal detection. Analysis of Doppler shift and broadening of the backscattered light provided the determination of the electron beam energy with a precision of 2 × 10^-3, and an upper limit of the longitudinal energy spread of 10^-3 eV. A ratio of longitudinal to transverse electron temperature of 10^-2 was found, indicating a flattened velocity distribution as is expected from the acceleration of the electrons.

The increased accuracy of the experiments studying parity non-conserving effects in atoms calls for improvement also in the atomic calculations which are necessary to connect the experimental results to fundamental parameters. We show how the method of iterative solution of the two-dimensional "pair equation" can be used to treat the effect of pair correlation to all orders, also in the calculations of parity non-conserving transition elements.

A new collector design for electron coolers was done in the Karlsruhe electron cooling group at LEAR (CERN). The performance of the collector was tested in a linear set-up with an electron beam of energies lower than 18 keV and a current of up to 1.25 A. In this range, current loss rates below 6 × 10^-5 were achieved at a collector perveance of ⩽27 μA V^-3/2. The maximum collector perveance in the present set-up is 37 μA V^-3/2.

The δ-electron emission probability d³P(b, E_e, Φ_e, q_f)/dE_edΦ_edq_f as a function of the electron energy E_e, impact parameter b, and projectile final charge state q_f has been measured for 0.53 MeV/u F⁸⁺ + Ne at an electron emission angle Φ_e = 0° and d²P(b, E_e, Φ_e)/dE_edΦ_e for 0.25 MeV/u He²⁺ + Ne at Φ_e = 90°, and are compared to previous results for 0.53 MeV/u F⁸⁺ + Ne at an electron emission angle Φ_e = 90°. For both collision systems at Φ_e = 90° a minimum in the emission probability d²P towards small b has been found and both shapes of the b-dependence appear quite similar, whereas for F on Ne a dramatic change in the relative b dependence of the probability d²P between Φ_e = 90° and Φ_e = 0° has been observed. All measured dependences can be explained qualitatively in the framework of strong collisionally oriented Ne-L substrates.

Classical dynamics is used to analyze the motion of individual ions in axisymmetric traps subject to charge-changing and momentum-changing collisions. By means of a series of transformations, equilibrium distributions of the ions are determined for arbitrary radial and axial trap potentials, under the assumption that the radial and axial motions are independent. These calculations will be useful for interpreting experiments on trapped ions and for understanding the behavior of confinement ion sources.

A small heavy-ion storage ring is presently under construction in Aarhus. The ring will be injected with singly-charged low-energy ions from a 200 kV ion accelerator and at a later stage with multiply-charged high-energy ions from an EN tandem accelerator. Conversion of the ring into a synchrotron radiation source by the addition of a 100 MeV microtron electron injector is now in the planning stage.

We present the results of some simulations of the laser cooling process for a single ion in a Penning ion trap. The situation is rather more complicated than in an r.f. trap, due to the presence of the magnetron drift. We show that under some circumstances the ion can get into an orbit which is different from the usual one in the trap, and that in order to apply laser cooling in this case one has to use a different procedure from the conventional one. We also present heating and cooling curves for the ion as a function of laser frequency and as a function of time.

A pilot study has lead to evidence for the successful trapping of externally created supra-thermal multiply-charged heavy ions in an electrostatic trap. Recoil ions produced by heavy-ion impact on atoms in a gas target have been extracted from the collision region and formed into a charge-analysed secondary ion beam. Some of these ions have been captured into an electrostatic ion trap designed to allow for the ion beam divergence and the finite observation angle of the detector. Such a confinement of ions in a trap is a prerequisite for the measurement of lifetimes in the range of 10 μs to 10 ms of long-lived excited states of multiply-charged ions.

The spatial and energetic properties of an ion cloud confined in an RF quadrupole trap, together with the lifetimes of the confined ions, have been computed by statistical methods and recently by a simulation method.

The influences of different parameters such as ion mass, buffer gas mass, working point in the stability diagram, "weak" space-charge and shape of the velocity distribution of the cooling buffer gas have been investigated and are described.