0000000000006966
AUTHOR
G. Tommaseo
Subharmonic excitation of the eigenmodes of charged particles in a Penning trap
When parametrically excited, a harmonic system reveals a nonlinear dynamical behaviour which is common to non-deterministic phenomena. The ion motion in a Penning trap -- which can be regarded as a system of harmonic oscillators -- offers the possibility to study anharmonic characteristics when perturbed by an external periodical driving force. In our experiment we excited an electron cloud stored in a Penning trap by applying an additional quadrupole r.f. field to the endcaps. We observed phenomena such as individual and center-of-mass oscillations of an electron cloud and fractional frequencies, so-called subharmonics, to the axial oscillation. The latter show a characteristic threshold b…
Axialisation, cooling and quenching of $\mathsf{Ba^+}$ ions in a Penning trap
Collisions of ions, stored in a Penning trap, with neutral background molecules usually lead to rapid ion loss from the trap unless the ions are excited by the sum of the frequencies of the reduced cyclotron and magnetron motion. Then the ions are cooled by collisions and are driven to the trap centre leading to substantial increase of the storage time. Furthermore in a three level system including a long living metastable state collisions deexcite this metastable state and increase the population density in the ionic ground state. In a laser spectroscopic experiment we demonstrate the advantages of collisions on Ba+ ions stored in a Penning trap. The combined action of metastable state que…
The $\mathsf{g_{\scriptscriptstyle J}}$ -factor in the ground state of Ca $^\mathsf{+}$
We have determined the $g_{\scriptscriptstyle J}$ -factor of the Ca + ion in the electronic 4S1/2 ground state on a cloud of ions confined in a Penning trap with a superimposed magnetic field of 1.43 T. We use a c.w. laser to prepare a Zeeman substate by optical pumping and induce $\Delta m_J=1$ transitions by a resonant microwave field at 40 GHz. Resonance is detected by a change in the fluorescence intensity originating from the ion cloud. We obtain a full width in the resonance of a few kHz and the fractional uncertainty of the line center, taking the average of several measurements, was 4 x 10-8. After calibrating the magnetic field by the cyclotron frequency of electrons stored in the …
Ion trap nuclear resonance on $\mathsf{^{151}Eu^ + }$
Laser-microwave double resonance techniques applied to a cloud of a natural mixture of Eu + isotopes confined in a Penning trap has been used to induce and detect nuclear Zeeman transitions. In spite of the complex level structure of Eu + and overlapping spectra from the two isotopes five different $\Delta m_I = 1$ transitions could be observed from which the nuclear magnetic moment can be derived. We obtain for 151 Eu + g I = 1.377 34(6) demonstrating the potential for high accuracy of the technique. The experiment can be considered as a feasibility test that precise spectroscopy data using the ion storage technique can be obtained of very complex ions and under unfavourable conditions.
Precise $\sf g_J$ - and $\sf g_I$ -factor measurements of Ba + isotopes
Laser-microwave double and triple resonance experiments were performed on clouds of Ba+ ions confined in a Penning ion trap to induce and detect electronic and nuclear spin flip transitions. Collisions with buffer gas molecules in the trap was used to reduce the lifetime of a long lived metastable state of the ions, in which population trapping might occur, and to cool the ions to the ambient temperature. Loss of ions from the trap by collisions were prevented by coupling the magnetron and reduced cyclotron motions by an additional r.f. field at the sum frequency of the two motions. Electronic Zeeman transitions in 138Ba+ and 135Ba+ were observed at a full width of about 3 kHz at a transiti…