Optical readout of a two phase liquid argon TPC using CCD camera and THGEMs

Abstract

This paper presents a preliminary study into the use of CCDs to image secondary scintillation light generated by THick Gas Electron Multipliers (THGEMs)in a two phase LAr TPC. A Sony ICX285AL CCD chip was mounted above adouble THGEM in the gas phase of a 40 litre two-phase LAr TPC with themajority of the camera electronics positioned externally via afeedthrough. An Am-241 source was mounted on a rotatable motionfeedthrough allowing the positioning of the alpha source either insideor outside of the field cage. Developed for and incorporated into theTPC design was a novel high voltage feedthrough featuring LArinsulation. Furthermore, a range of webcams were tested for operationin cryogenics as an internal detector monitoring tool. Of the range ofwebcams tested the Microsoft HD-3000 (model no:1456) webcam was foundto be superior in terms of noise and lowest operating temperature.In ambient temperature and atmospheric pressure 1 ppm pure argon gas,the THGEM gain was ≈ 1000 and using a 1 msec exposure the CCDcaptured single alpha tracks. Successful operation of the CCD camerain two-phase cryogenic mode was also achieved. Using a 10 sec exposurea photograph of secondary scintillation light induced by the Am-241source in LAr has been captured for the first time.