Penning traps beamline

We have built a full Penning traps beamline to implement Quantum Mass Spectrometry. Some of the elements are similar to those existing in Penning trap facilities devoted to perform mass measurements on exotic nuclei (ISOLTRAP, SHIPTRAP, IGISOL).

Figure 1 shows a sketch of the Penning traps beamline. The ions are produced by laser desorption using metallic targets. They are delivered in short pulses to the Penning traps through a transfer section comprising many electrostatic lenses and deflectors. The Penning trap system comprises two traps, each of them centered in a high homogeneous region of the 7-tesla magnetic field provided by the superconducting solenoid. The first Penning trap (preparation trap) has been built following the specifications of the preparation Penning trap for MATS at FAIR. The second Penning trap is an open-ring trap developed by the group. Ions can be detected by time-of-flight using a micro-channel plate detector (MCP) or from the electric current they induced in the trap electrodes using the amplifiers developed by our group. Calcium ions can be detected through the fluorescence photons from the S1/2-->P1/2 transition and also using the above-mentioned amplifier together with a quartz crystal which allows improving sensitivity.


Figura 1: Sketch of the Penning traps beamline at the University of Granada.

The beamline is in operation. Currently we are working to reach Doppler cooling of a single 40Ca+ ion in the open-ring 7-tesla Penning trap. Subsequently we want to reach the ground state. 40Ca+ will be the sensor ion for Quantum Mass Spectrometry. 7 tesla is the largest magnetic-field strength used for laser-cooling experiments worldwide. This has made this experiment very challenging in the first stage. Figure 2 shows the level scheme to perform Doppler cooling in 7 tesla. For this intensity one has to consider the first and second order Zeeman effect and the J-mixing. All this requires a total of 10 laser beams, 8 of them to pump from metastable states, which has needed a complex and unique laser system.


Figure 2: Level scheme for 40Ca+ in a 7-tesla magnetic field. The blue-solid lines indicate the transitions for Doppler cooling. The red-solid lines indicate the transitions for pumping (854 and 866 nm) that one has to drive in order to prevent stopping the cooling process. The red-dashed lines indicate those transitions which can be generated using an electro-optical modulator.

Up to date it has been possible to perform Doppler cooling of a small 40Ca+ ion cloud confined in the 7-tesla Penning trap, in the axial and radial directions. In November 2019, we have built a cryogenic structure in order to reduce the residual pressure in the area closest to the trap volume, since this is the limiting factor in our experiment to reach the single-ion sensitivity.


  • M. J. Gutiérrez, J. Berrocal, J. M. Cornejo, F. Domínguez, J. J. Del Pozo, I. Arrazola, J. Bañuelos, P. Escobedo, O. Kaleja, L. Lamata, R. A. Rica, S. Schmidt, M. Block, E. Solano and D. Rodríguez.
    “The TRAPSENSOR facility: an open-ring 7 tesla Penning trap for laser-based precision experiments”
    New Journal of Physics 21 023023 (2019)