Commissioning of an MPGD-based Drift Chamber for Heavy-ion Tracking in FRIB's Sweeper magnet system

Abstract A newly developed drift chamber equipped with an innovative hybrid Micro-Pattern Gaseous Detector based readout was commissioned at FRIB. The detector consists of a Multi-layer Thick Gas Electron Multiplier (M-THGEM) mounted over a high-granularity, position-sensitive readout board. Denoted as the Micro-Pattern Drift Chamber (MPDC), the new device is used to provide tracking capability as part of the detectors of the Sweeper magnet system for neutron-invariant-mass spectrometry at the Facility for Rare Isotope Beams (FRIB). The localization of impinging ions in a 30 × 30 cm 2 drift area is derived by processing the charge-avalanche distribution induced on the segmented readout board. The signals induced on the readout pads are processed by a compact, multi-channel Data Acquisition System (DAQ) based on the Scalable Readout System (SRS). To facilitate synchronization with other detector systems of the Sweeper magnet system, the SRS has been configured to accept an external trigger. The performance of the MPDC was evaluated using a low-rate α-particle source ( 228 Th) and the commissioning of two MPDCs in the Sweeper magnet system was carried out with a 17 C beam and a cocktail beam of heavy ions ( Z = 8 to 20, with energy of 120 MeV/u). A sub-millimeter position resolution in both dispersive and non-dispersive coordinates was obtained at moderate rates (≈ 1300 pps) with a good operation stability (no discharges). The performance met tracking requirements and enabled the launch of the experimental campaign of neutron invariant-mass experiments at FRIB. The Sweeper magnet system has been thus fully commissioned, and two experiments have been successfully conducted using the new MPDC-based tracking system.