  An open-ring ion trap, also referred to as transparent trap was initially
built up to perform $\beta$-$\nu$ correlation experiments with radioactive
ions. This trap geometry is also well suited to perform experiments with
laser-cooled ions, serving for the development of a new type of Penning trap,
in the framework of the project TRAPSENSOR at the University of Granada. The
goal of this project is to use a single $^{40}$Ca$^+$ ion as detector for
single-ion mass spectrometry. Within this project and without any modification
to the initial electrode configuration, it was possible to perform Doppler
cooling on $^{40}$Ca$^+$ ions, starting from large clouds and reaching single
ion sensitivity. This new feature of the trap might be important also for other
experiments with ions produced at Radioactive Ion Beam (RIB) facilities. In
this publication, the trap and the laser system will be described, together
with their performance with respect to laser cooling applied to large ion
clouds down to a single ion.
