Performance and Characterization of Large-Area (400 × 200 mm2) PPACs Using 40Ar Beams at the KoBRA Spectrometer

The performance of a large-area 400 × 200 mm2 parallel plate avalanche counter (PPAC) developed for the focal plane of the KoBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) facility is reported. To maintain high resolution over the extended width, a triple-segmented delay-line readout was implemented for the X-axis. Detection efficiency, position resolution, and timing resolution were measured using 40Ar beams at 8, 12, and 16 MeV/u as a function of isobutane gas pressure (2–8 Torr) and anode high voltage (400–670 V). Position calibration was carried out using a hole mask with known hole positions and validated across multiple beam energies. Detection efficiencies of >99% were achieved for both X and Y axes at all beam energies. The intrinsic position resolution at the detector center, after deconvolving the geometric contribution of the calibration hole aperture, was approximately 460 μm (σ) with a time-to-digital converter (TDC) and improved to 320 μm (σ) with a waveform digitizer. The single-anode timing resolution was 165 ps (σ). These results validate the large-area PPAC for heavy-ion beam tracking at KoBRA and establish a performance baseline for future experiments with secondary beams.