| We present discharge rate measurements for two Micromegas detectors using a photon beam
impinging a CH2 target in the Hall B of the Jefferson Laboratory. One detector was equipped with
an additional GEM foil, and a reduction of the discharge probability by two orders of magnitude
compared to the stand-alone Micromegas was observed. The detectors were placed in the FROST
solenoid providing a longitudinal magnetic field up to 5 T. It allowed for precise measurements
of the discharge probability dependence with a diffusion reducing magnetic field, for a possible
use of Micromegas in the Forward Vertex Tracker (FVT) of the future CLAS12 spectrometer.
Between 0 and 5 T, the discharge probability increased by a factor of 10 for polar angles between
19° and 34°, thus requiring the use of additional GEM foils to withstand the standard CLAS12
luminosity |
