Development of a novel MPGD-based drift chamber for the NSCL/FRIB S800 spectrometer

The performance of a novel tracking detector developed for the focal plane of the NSCL/FRIB S800 magnetic spectrometer is presented. The detector comprises a large-area drift chamber equipped with a hybrid Micro-Pattern Gaseous Detector (MPGD)-based readout. The latter consists of a position-sensitive Micromegas detector preceded by a two-layer M-THGEM multiplier as a pre-amplification stage. The signals from the Micromegas readout are processed by a data acquisition system based on the General Electronics for TPC (GET). The drift chamber has an effective area of around 60 × 30 cm2, which matches to the very large acceptance of the S800 spectrometer. This work discusses in detail the results of performance evaluation tests carried out with a low-energy alpha-particles source, and with high-energy heavy-ion beams with the detector installed at the S800 focal plane. In this latter case, the detector was irradiated with a 150 MeV/u 78Kr36+ beam as well as a heavy-ion fragmentation cocktail beam produced by the 78Kr36+ beam impinging on a thin beryllium target. The new detector allows sub-millimeter position resolution in both dispersive and non-dispersive directions. The new read out scheme, coupled to the GET electronics, has several advantages compared to the old Cathode Readout Drift Chamber (CRDC), including a four time higher detection rate (of around 20 kHz), multi-hit capability, and a better operation stability. The new improved performance are needed to take full advantage of FRIB's rare-isotope beam portfolio and expected high intensity.