  The possible use of a Spherical Proportional Counter for the search of
neutrinoless double beta decay is investigated in the R2D2 R&D project. Dual
charge and scintillation light readout may improve the detector performance.
Tests were carried out with pure argon at 1.1 bar using a 6x6 mm2 silicon
photomultiplier. Scintillation light was used for the first time to trigger in
a spherical proportional counter. The measured drift time is in excellent
agreement with the expectations from simulations. Furthermore the light signal
emitted during the avalanche development exhibits features that could be
exploited for event characterisation.
