Highly charged heavy ions (HCI) represent a new rich field for atomic theory and a challenging test for atomic calculations concerning total binding energies as determined by mass measurements in traps, g-factors in one-electron systems, and lifetimes and hyperfine structures in few-electron systems. The aim of the mass measurements is to achieve a relative accuracy of 10-10. With this accuracy inner-shell correlations and possibly many-body QED effects could be detected. The aim of the theoretical work is to use the methods of Relativistic Many-Body Perturbation Theory (RMBPT) and Multi-Configuration Dirac-Fock (MCDF) - partly developed by the network members - to calculate these inner-shell effects. This will constitute an important test for many-body effects due to correlations and quantum electrodynamics.
The g-factor of the free electron has been measured with an extraordinary accuracy. The g-factor of the bound electron differs from that of the free electron due to binding corrections. These effects become quite important in strong fields of heavy HCI like U91+. The first-order bound-state corrections, including QED effects, are presently being calculated by members of this network. These calculations together with high-precision measurements of the g-factor aim at testing QED in the combined magnetic and strong electric nuclear field.
A very attractive feature of HITRAP is the determination of atomic lifetimes for radioactive isotopes, which can be delivered by the fragment separator at GSI. The lifetimes of long-lived states in HCI represent an excellent test for atomic wave functions. The aim of this project is to determine the nuclear moments by the changes in the lifetimes due to the hyperfine interaction.
Strong individual collaborations exist already today between the theory teams as well as between the theory and experimental teams, which have lead to very interesting developments. In order to achieve the goals mentioned above intensified collaboration between the groups will be of crucial importance.
In the case of the g-factor of the bound electron in hydrogen-like systems, measurements have been performed until now only for H and He+. In heavy systems like U91+, the relativistic and QED corrections in extremely high fields cause a deviation from the value of the g-factor of the free electron by 10%. A measurement of this deviation with high accuracy of 10-7 or better will result in the first clean precision test of the electromagnetic interaction in a new regime, i.e. the magnetic sector of QED in extremely strong fields.
The cooling of HCI is essential for high accuracy. Until now, there is no experience throughout the world. EUROTRAPS will develop electron, positron and resistive cooling for HCI. The use of positrons for cooling of HCI to liquid helium temperatures is possible, the positrons themselves (once injected into the high magnetic field of the Penning trap) are subject to very quick self-cooling due to synchrotron radiation, and charge changing collisions (as in the case of cooling by electrons) are avoided.
Several American groups are pursuing the accumulation of positrons in traps, mainly motivated by the challenge of producing antihydrogen, but also for a broad range of applications spanning atomic physics, surface physics, biology and chemistry. The EUROTRAPS network aims at the first facility in Europe that will accumulate, store and cool positrons. Furthermore, a new technique will be developed which is based on a pulsed electron accelerator producing positrons by bremsstrahlung. The positrons will be injected into a trap and cooled. The goal is to cool HCI and to study e+-HCI collisions for the first time and at very low temperatures. But other applications of a high-intensity, brilliant source of positrons become possible like cluster or surface studies.
The use of Penning traps in physics for precision spectroscopy is until now restricted to a few places in Europe. Only the groups at Mainz, GSI, CERN and Stockholm operate such devices. In addition, two American groups have installed Penning traps at CERN/Geneva for experiments with antiprotons. A major objective of EUROTRAPS is to transfer advanced expertise in the utilisation of Penning traps to other European countries. In this way, groups needing traps in other disciplines of physics like nuclear physics, accelerator physics, studies by use of synchrotron radiation, and surface physics, but without experience in trap technology, will benefit from the know-how of the networking teams. Clouds of radioactive nuclei stored and cooled in a trap will allow one to study electron-neutrino correlation in the beta decay with until now unprecedented precision. Furthermore, industry will profit from the expertise in Penning traps, and the existing gap between developments in physics laboratories and those in companies (the latter mainly for applications in chemistry and biology) will be bridged. Very recently, scientists from GANIL/Caen and the University of CAEN have asked, if the teams of the EUROTRAPS network could help in designing a Penning trap system for the SPIRAL project at GANIL.