Micromegas with high resistivity anode

Prototype Micromegas chambers are constructed by using several types of high resistivity sheet materials as anodes. The resistive sheet is glued to the metal readout surface by a resistive adhesive layer. The resistive materials studied include: resistive glass sheets with resistivity ~10¹⁰ Ω·cm, carbon-black loaded polycarbonate sheets with resistivity ~10¹¹ Ω·cm and common glass sheets with resistivity ~10¹³ Ω·cm. Stretched 350 or 400 lpi stainless woven wire micromeshes are suspended on the surface of the resistive sheet using frames made of thermal bond films. Test results show prototypes with high resistivity anodes can be operated at high gas gain with good X-ray energy resolution. Rates of sparks and the amount of charges in these sparks in prototypes with resistive anodes are significantly reduced compared to those in chambers without resistive anode. The rate capability of these prototypes is studied by using intense X-ray gun.