[en] The efficiency of electron cooling can be improved by reducing the temperature of the electrons. If the magnetic field at the location of the electron gun is stronger than in the region where the electrons interact with the ions, and the field gradient is adiabatic with respect to the cyclotron motion of the electrons, the resulting expansion of the electron beam reduces its transverse temperature by a factor equal to the ratio between the two fields. A ten times expanded electron beam was introduced in the CRYRING electron cooler in the summer of 1993, and similar arrangements have since then been made at the TSR ring in Heidelberg and at ASTRID in Aarhus. The reduction of the transverse electron temperature has increased cooling rates with large factors, and improves the energy resolution and increases count rates when the cooler is used as an electron target for ion-electron recombination experiments

[en] Studies of electron cooling with an adiabatically expanded electron beam have been performed at CRYRING. Measurements of the longitudinal drag force using three different methods are described and are compared with measurements at other electron coolers. The processes that determine the electron temperature, longitudinally and transversally, are reviewed, and the effect of the beam expansion on these processes is discussed. It is described how the electron temperature can influence the outcome of recombination measurements, and how such measurements can be used to determine the electron temperature, and an example of such a measurement is given. (orig.)

[en] A method of obtaining an electron beam in an electron cooler where the transverse temperature is lower than the cathode temperature is presented. The method is based on the fact that the kinetic energy transverse to the magnetic field, mv²_{perpendicularto} /2, of an electron that passes through a negative magnetic-field gradient is reduced by a factor equal to the ratio between the initial and final field strengths, provided that the field change is adiabatic with respect to the cyclotron motion of the electrons. The requirements on the magnetic field and the effects on cooling forces are discussed. It is concluded that a reduction in transverse electron temperature by a factor of 10 to 120 K is realistic for an electron cooler such as the one in CRYRING. (orig.)

[en] Exact solutions to a one-dimensional, time-dependent Schroedinger equation with two colliding delta-function potentials of different strengths are presented. The equation can serve as a model for resonant and quasi-resonant ion-atom collisions. Electrons initially bound to one of the potentials may be transferred to the other potential or to a continuum state and probabilities for these processes are calculated. The model reproduces the damped oscillatory behaviour of the charge-transfer probability seen in quasi-resonant collisions when the collision energy is varied. (author)

[en] The design of the CRYRING electron cooler, including magnets, electron gun and collector, and the vacuum system, is described. Light and heavy atomic ions and molecular ions have been cooled at ion energies between 0.29 and 10.9 MeV per nucleon. Experiments in atomic and molecular physics have been performed using the cooler both for beam cooling and as an electron target. Measurements of longitudinal drag forces and resulting estimates of transverse and longitudinal electron temperature are presented. (orig.)

[en] Recent experiments have shown oscillatory structures in angular differential cross sections for two-electron capture by C⁴⁺ from He at energies between 300 and 1500 eV. Using semiclassical and semiquantal methods, the authors have computed theoretical cross sections for this process and good agreement with the experiments found. The oscillations are identified as Stueckelberg oscillations and special attention is drawn to a rainbow appearing in the semiclassical cross sections. This rainbow is shown to be due to the definition of the semiclassical deflection functions and that it vanishes with the semiquantal method. (author)

[en] In the CRYRING storage ring weak beams of electron-cooled highly charged ions have been studied. When the intensity of the ion beam decays below a certain limit the momentum spread of the beam show a sudden transition to a state with much lower momentum spread. Similar observations have earlier been made at GSI, and have been interpreted as a one-dimensional ordering of the beam. For a beam of 7.4 MeV/u Xe³⁶⁺ we have varied the electron density and studied how that affects the particle number at transition, the momentum spread of the ion beam, and the Schottky power. The transition occurs at particle distances between 1 and 35 cm, depending on the cooling rate.

[en] This paper describes an adiabatic electron gun for the CRYRING electron cooler. The criteria for adiabatic acceleration are briefly summarized and results from calculations of the transverse electron temperature as a function of gun perveance and magnetic field are presented

[en] The European Spallation Source (ESS) will provide neutrons for a wide range of experiments in fields such as chemistry, physics, materials science, biology and pharmacology. Once completed in 2027, ESS will enable new areas of neutron science due to its brightness and long neutron pulse capability. Neutrons are produced at ESS via a spallation process driven by a 2 GeV, 2 MW (upgradeable to 5 MW) proton linac. The bulk of the acceleration in the linac is provided by superconducting RF cavities operating at 2 K. This paper gives an overview of ESS, describes the linac design and details the current status of the accelerator. The use of In-kind partners and heat recovery is also discussed. (author)

[en] Two different experiments have observed oscillations in the angular scattering intensity for the ground-state double-capture reaction C⁴⁺ + He-> C²⁺ + He²⁺ + Q at laboratory impact energies ranging from 300 eV to 1.5 keV. They were first observed as oscillations in the low-energy tail of energy gain distributions and were later verified in a direct angular differential cross section measurement. A two-state curve-crossing model is used to explain the oscillations as Stueckelberg oscillations deriving from an interference between two different reaction paths leading to the same scattering angle. (author)