Performance evaluation of Dual Gain Multi-layer Thick GEM for CAT with high-intensity heavy-ion beams

A prototype of dual gain multi-layer thick GEM was produced to construct large volume active target CAT-M. The GEM consists of alternate layers of electrodes and insulators, and effectively works as three layers of GEMs. The total thickness is 1.2 mm. Distortion of electric field in the GEM is expected to be small even if the area of the GEM become large because of its rigidness. The electrodes are divided into three regions to control gain at each region independently. In order to reduce space charges in drift region due to feedback ions and current at the electrodes caused by high intensity heavy-ion beams, gain in a region along the beams should be operated lower. Performance of the GEM was evaluated at a synchrotron accelerator facility HIMAC (project number: 15H307) by employing an active target CAT-S filled with 0.4-atm H₂ gas. A ¹³²Xe beam with the intensity up to 1 M particles per pulse was impinged into CAT-S. Position and beam intensity dependence of effective gas gains and energy resolutions have been obtained via track reconstruction.