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

The performance of a large-area $400 \times 200$ mm$^2$ 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 $^{40}$Ar 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 $\gt$99% were achieved for both the x- and the y-axis at all beam energies. The intrinsic position resolution at the detector center, after deconvolving the geometric contribution of the calibration hole aperture, was approximately $460\,\mu$m ($\sigma$) with a time-to-digital converter and improved to $320\,\mu$m ($\sigma$) with a waveform digitizer. The single-anode timing resolution was $165 \,{\rm ps}$ ($\sigma$). 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.