Résumé du preprint Irfu-11-70

Discharge rate measurements for Micromegas detectors in presence of a longitudinal magnetic field
B. Moreno, S. Aune, J. Ball, G. Charles, A. Giganon, P. Konczykowski, C. Lahonde-Hamdoun, H. Moutarde, S. Procureur, F. Sabatié
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