Tests and simulations of GEM foils for use in an active target gaseous detector

Sammanfattning: The HIE-ISOLDE post accelerator at CERN has recently come online, en- abling the use of radioactive ion beams with energies of up to 10 MeV/u. An active target gaseous detector is under development for use in some of the experiments. The first investigation of the electron amplification stage with gas electron multipliers has been performed. To this end, a small prototype GEM detector was built and tested. The results from these tests are com- pared with simulations done with the package Garfield++. The gain was measured for three different gas mixtures of Ar/CO 2 in the ratios 70/30, 76/24, and 82/18. The gain for these cases were ca 1500, 4500, and 15000. The simulations of the gain for the same gas mixtures gave the result 1100, 3000, and 9500. The measurements and the simulations show good agree- ment, but worse with less quencher in the gas mixture. A charge up test of the detector was performed resulting in a charge up time of roughly five hours and a relative gain increase of 1.6. The spread of the electron cloud at the readout plane was simulated and was in the order of ∼1 mm. Practical handling routines for changing of GEM foils in the detector in a clean room were also developed.