Cable attenuation study of Tibet water Cherenkov muon detector array-A

This work aims at online calibration of signal attenuation of the long cable used in Tibet water Cherenkov muon detector array-A （Tibet MD-A） under the Tibet air shower array.Based on a waterproof connection of the signal cable to PMT （R3600 0 6） and characters of the high voltage divider,terminal reflection method is used for measuring the signal attenuation with a practical way to eliminate contribution of the pulse baseline.Comparison measurement data-taking method （with charge-to-digital conversion） was carried out by using open-ended cables,confirming that terminal reflection method is a fast and convenient,and suitable to online calibration of the signal attenuation for Tibet MD-A.At 26℃,the measured attenuation coefficient with the 250-m cable connected permanently to the PMT,was ～13.9%.The cable frequency response was measured by using the sinusoidal signals.The method could be used to study time dispersion of signals produced with Tibet MD-A detector via Fourier analysis.