Abstract
One of the three x-ray detectors of the CERN Axion Solar Telescope (CAST) experiment searching for solar axions is a time projection chamber (TPC) with a multi-wire proportional counter (MWPC) as a readout structure. Its design has been optimized to provide high sensitivity to the detection of the low intensity x-ray signal expected in the CAST experiment. A low hardware threshold of 0.8 keV is set to a safe level during normal data taking periods, and the overall efficiency for the detection of photons coming from conversion of solar axions is 62%. Shielding has been installed around the detector, lowering the background level to 4.10 × 10−5 counts cm−2 s−1 keV−1 between 1 and 10 keV. During phase I of the CAST experiment the TPC has provided robust and stable operation, thus contributing with a competitive result to the overall CAST limit on axion–photon coupling and mass.
Highlights
The CERN Solar Axion Telescope (CAST) is the most sensitive implementation of the “helioscope” concept to look for hypothetical axions coming from the Sun (Sikivie 1983)
CAST makes use of a decommissioned LHC prototype magnet with a length of 9.3 m, providing a 9 Tesla field to trigger the conversion of solar axions into X-rays, which can be detected by the three different X-ray detectors placed at both ends of the magnet (Zioutas et al 1999)
The purpose of the present paper is to describe one of the detector systems of CAST: the time projection chamber (TPC)
Summary
The CERN Solar Axion Telescope (CAST) is the most sensitive implementation of the “helioscope” concept to look for hypothetical axions (or axion-like particles) coming from the Sun (Sikivie 1983). As in a Multi Wire Proportional Chamber (MWPC), the avalanche process that amplifies the signal is developed, allowing a position sensitive readout of the original event. The specific requirements of the CAST experiment (sensitivity to a low intensity X-ray signal peaking at ∼ 4 keV and vanishing at around 10 keV), necessitated some original approaches in the construction of the CAST TPC. Our paper is structured as follows: in section 2 description of the detector itself and the shielding installed is given.
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