TPG, test results

TPG is the acronym for Time Projection Chamber with GEM amplification, high-granularity hexaboard read-out and FADC electronics. We have constructed a TPG read-out module, called TPG-head, with three GEM foils and a multilayer board, called hexaboard, covered with 710 000 hexagonal pads of 300 mum size. The total active area of this module is a disk of 30 cm diameter. The 710 000 pads are read by three sets of 576 strips dephased by 120 degrees. Each strip is read by a FADC channel with 100 ns sampling time. The module is mounted in a test-bed formed by a cylindrical field cage of 80 cm diameter and 150 cm length inside a solenoidal magnet that operates with a magnetic field up to B=0.7 Tesla. Tests with X-ray sources show an intrinsic spatial resolution of the order of 40 mum. The threshold for transverse momentum measurement of low energy tracks is below 0.1 MeV/c with a magnetic field of 0.07 Tesla. At 0.7 Tesla the intrinsic space point resolution of the chamber is such that the error on the measurement of the transverse momentum is DeltaP_tsime0.1 MeV/c in absence of distortions from the drift region

I. Introduction

TPG is the acronym for Time Projection Chamber [1] with GEM amplification, hexaboard read-out and FADC electronics. TPG [2] uses GEM foils [3] for electron multiplication and a read out board with hexagonal pads connected to three sets of strips at 120 degrees [4]–[6]. The principle and practical advanctages of the choice of GEM and hexaboard to equip a TPC imaging chamber have been discussed in [1], [7] and summarized in [8]. The use of GEM foils in the multiplication region introduces several advantages [4]: •

decoupling of multiplication and signal generation processes;

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flexibility in the design of the read-out plane;

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minimization of the positive ion feedback into the drift region;

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minimization of distortion effects.