Speaker
joao veloso
(university of aveiro)
Description
A novel gas-avalanche patterned hole electron multiplier, based on the 2D-THCOBRA concept, is presented.
The microdot-THCOBRA (µdot-THCOBRA) presented in this work has active area of 10 × 10 cm2 and was specially designed for imaging purposes. It is a double-sided structure made out of a 0.4 mm thick G10 plate, covered with 50 µm of copper on both sides. Similarly to the 2D-THCOBRA, on the bottom side a pattern of strips is etched: a circular electrode surrounding each hole with 0.2 mm wide (cathode) and an anode strip about 0.2 mm wide. After the chemical etching of the Cu strips, the whole surface on the bottom side of the structure is covered with a DuPont Coverlay film. Then, part of the Coverlay layer is photochemically removed creating small dots around the holes which allow to concentrate more efficiently the electric field lines in that region, in order to increase the gain near the anode electrodes. The Coverlay layer is also removed from the cathode strips.
The top electrode of the structure is segmented in strips disposed orthogonally to the anode strips, in order to achieve the second dimension, for imaging purposes. Two orthogonal resistive lines connect the anode strips, and the top strips, respectively, for position sensitivity.
A study of the charge gain as a function of the voltage applied in the electrodes of the µdot-THCOBRA including gain stability and count rate capability will be presented, for different filling gases.
