Performance study of a novel sampling TPC prototype detector based on THGEM

IntroductionTime projection chamber (TPC) with micropattern gaseous detectors (MPGDs) as readout has been one of the research hotspots in recent years. MPGD-based TPC has been applying to many experiments due to its high spatial and energy resolutions in 3D track measurement.
PurposeA novel sampling TPC detector based on thick gaseous electron multiplier (THGEM) was developed to measure the low-energy electron tracks online from 0.1 to 50 MeV with a 100 \upmu \hbox m spatial resolution in a vacuum tank. The tracks will be extrapolated to determine the hit positions on a target about 200 mm behind the TPC.
Methods and materialsA new type of self-developed THGEM detector was chosen as the TPC readout unit. The field cage has two 50 \times 50\,\hbox mm^2 windows welded by Gold-plated tungsten wires for low-energy electrons passing through. The front-end electronics was designed with a self-developed application specific integrated circuit chip, i.e., CASA-GEM. Seven columns of readout pads were used to equidistantly sample the electron tracks in a length of 75 mm. Each column has 72 pads of 0.56 \times 0.56 \,\hbox mm^2 and two additional strips along each column for drift time measurement. Both Geant4 and Garfield++ were chosen to simulate and optimize the detector, such as the penetration efficiency, electric field in field cage and operating gas pressure.
ResultsThe design and the preliminary performances of the TPC detector were verified by beam test and \beta source test. A drift velocity of 3.415 \pm 0.103\,\hbox cm/ \mu \hbox s was measured at 125 V/cm in \hbox Ar + \hbox iC_4\hbox H_10 ~(97:3) for \pi ^- . The electron detection efficiency is about 88% for \beta source. And the gain of the double THGEM reached more than 1.0 \times 10^4 .