Studies of micromegas chambers using UV-laser-photoelectrons

Micro Pattern Gaseous Detectors (MPGD) are a new and very promising type of gaseous detector for future experiments. Their big advantages are that they are radiation hard and also provide a spatial resolution of several microns. But at the moment, there are still unavoidable discharges occurring randomly, which reduce the achievable gain and can destroy the readout and the detector with time. This talk will present a dedicated test setup, that has been built to investigate geometries of readout structures for MPGD, in order to eliminate or minimize discharges and achieve higher rate capabilities without the application of resistive layers. The measuring principle of the test chamber is to simulate tracks of charged particles. This is done by creating photo electrons in the drift room above the MPGD on aluminum strips with the help of a UV laser. The electrons are guided by a homogenous drift field to the detector. In contrast to using particles from radioactive sources or a test beam, the spatial and temporal conditions of the electron release are very well known. The setup can be modified easily to control the point of impact of the electrons on the detector. First studies such as gain gain measurements of a Micromegas and drift velocity measurements of electrons in ArCO₂ have been carried out successfully and are presented as proof of a good performance of the MPGD test chamber.