N. Hermanspahn

HITRAP: A Facility for Experiments with Trapped Highly Charged Ions

HITRAP is a planned ion trap facility for capturing and cooling of highly charged ions produced at GSI in the heavy-ion complex of the UNILAC-SIS accelerators and the ESR storage ring. In this facility heavy highly charged ions up to uranium will be available as bare nuclei, hydrogenlike ions or few-electron systems at low temperatures. The trap for receiving and studying these ions is designed for operation at extremely high vacuum by cooling to cryogenic temperatures. The stored highly charged ions can be investigated in the trap itself or can be extracted from the trap at energies up to about 10 keV/q. The proposed physics experiments are collision studies with highly charged ions at well-defined low energies (eV/u), high-accuracy measurements to determine the g-factor of the electron bound in a hydrogen-like heavy ion and the atomic binding energies of few-electron systems, laser spectroscopy of HFS transitions and X-ray spectroscopy.

Observing a single hydrogen-like ion in a Penning trap at T = 4 K

We describe how a single hydrogen-like ion (C5+) is prepared, cooled with the method of resistive cooling and non-destructively detected with the image-current technique in a cryogenic Penning trap at T = 4 K. The storage time for C5+-ions in the cryogenically pumped vacuum chamber is longer than six months. The experimental techniques of preparing, cooling and detecting highly-charged ions in a Penning trap are relevant for precision experiments such as g-factor measurements, mass spectroscopy and laser spectroscopy.

The g Factor of Hydrogenic Ions: A Test of Bound State QED

We present a new experimental value for the magnetic moment of the electron bound in hydrogenlike carbon (12C5+): g exp = 2.001 041 596 (5). The experiment was carried out on a single 12C5+ ion stored in a Penning trap. The high accuracy was made possible by spatially separating the induction of spin flips and the analysis of the spin direction. Experiment and theory test the bound-state QED contributions to the gJ factor of a bound electron to a precision of 1%. We discuss also implications of the experiment on the knowledge of the electron mass.

The magnetic moment anomaly of the electron bound in hydrogenic ions

The measurement of the g factor of the electron bound in a hydrogenic ion is a high-accuracy test of the theory of Quantum Electrodynamics (QED) in strong fields. Here we report on the measurement of the g factor of the bound electron in hydrogenic carbon (12C5+). In our experiment a single 12C5+ ion is stored in a Penning trap. The electronic spin state of the ion is monitored via the continuous Stern-Gerlach effect in a quantum non-demolition measurement. Quantum jumps between the two spin states (spin up and spin down) are induced by a microwave field at the spin precession frequency of the bound electron. The g factor of the bound electron is obtained by varying the microwave frequency and counting the number of spin flips. The comparison of our experimental value for the g factor of the bound electron, gexp(12C5+)=2.001041596(5), with the theoretical value of gth=2.001041591(7) shows excellent agreement and confirms the recent non-perturbative calculations by T. Beier et al.The measurement of the g factor of the electron bound in a hydrogenic ion is a high-accuracy test of the theory of Quantum Electrodynamics (QED) in strong fields. Here we report on the measurement of the g factor of the bound electron in hydrogenic carbon (12C5+). In our experiment a single 12C5+ ion is stored in a Penning trap. The electronic spin state of the ion is monitored via the continuous Stern-Gerlach effect in a quantum non-demolition measurement. Quantum jumps between the two spin states (spin up and spin down) are induced by a microwave field at the spin precession frequency of the bound electron. The g factor of the bound electron is obtained by varying the microwave frequency and counting the number of spin flips. The comparison of our experimental value for the g factor of the bound electron, gexp(12C5+)=2.001041596(5), with the theoretical value of gth=2.001041591(7) shows excellent agreement and confirms the recent non-perturbative calculations by T. Beier et al.

Testing atomic structure theories with high accuracy mass measurements on highly charged ions

The mass of a highly charged ion is the sum of the mass of the nucleus, the mass of the electrons and the electronic binding energies. High accuracy mass measurements on highly charged ions in a sequence of different charge states yield informations on atomic binding energies, i.e., the ionisation potentials. In our contribution we discuss the possibility of determining atomic binding energies of highly charged ions to better than 20 eV via cyclotron frequency measurements in a Penning trap. At this level of accuracy different contributions to the binding energies, like relativistic corrections, Breit corrections and QED corrections, can be measured.

The g-factor of hydrogen-like ions

We report on the first direct measurement of the g-factor of a highly charged ion. The experimental determination of the magnetic moment (g-factor) of the bound electron in hydrogen-like ions is an important test of the theory of Quantum Electrodynamics in strong nuclear Coulomb fields. For this purpose a single hydrogen-like ion is stored in the magnetic field of a Penning trap. The g-factor is measured by inducing spin flip transitions with a microwave field at the Larmor precession frequency of the bound electron. The magnetic field is calibrated by measuring the cyclotron frequency of the stored ion. The first results were obtained for a hydrogen-like carbon ion (C5+). The experimental precision is high enough to verify the relativistic contribution to the g-factor on the 10−3 level.