  The performance of a Thick-COBRA (THCOBRA) gaseous detector is studied using
an optical readout technique. The operation principle of this device is
described, highlighting its operation in a gas mixture of Ar/CF4 (80/20%) for
visible scintillation light emission. The contributions to the total gain from
the holes and the anode strips as a function of the applied bias voltage were
visualized. The preservation of spatial information from the initial
ionizations was demonstrated by analyzing the light emission from 5.9keV X-rays
of an 55Fe source. The observed non-uniformity of the scintillation light from
the holes supports the claim of a space localization accuracy better than the
pitch of the holes. The acquired images were used to identify weak points and
sources of instabilities in view of the development of new optimized
structures.
