GAPS Detector Cooling System: Results from Antarctic Ground Tests

The General Antiparticle Spectrometer (GAPS) experiment aims to elucidate the nature of dark matter by detecting low-energy antinuclei using a long-duration scientific balloon over Antarctica. The GAPS detector consists of a tracker made of lithium-drifted Silicon detectors, surrounded by two layers of Time-of-Flight (TOF) plastic scintillators. To achieve an energy resolution of 4 keV FWHM in the 20–100 keV range, the Silicon detectors are cooled to −40◦C using Multi-loop Capillary Heat Pipes (MCHPs), specifically developed for GAPS. The MCHPs transport heat from the detectors to a radiator attached to the payload’s sidewall. On the ground, the radiator is directly cooled by the Ground Cooling System (GCS) to enable detector testing. The GCS consists of a chiller, a cold plate, and insulating foam. GAPS has completed successful instrument commissioning during this past Antarctic launch season. During this period, we conducted cooling tests to investigate the detector performance using the GCS. Unfortunately, GAPS was not able to launch in the past season due to weather. GAPS remains assembled at the LDB site and stands ready for its first scientific ballon flight in the austral summer of 2025-2026. In this talk, we will present the results of the ground tests conducted during the 2024/25 season, with a particular focus on the performance of the cooling system.