Study of VUV detector based on thinner THGEM for CDEX

In the China Dark matter EXperiments (CD EX), HPGe is the main target detector while liquid Ar is used to provide the low temperature working environment for HPGe detector. In the meantime, as a scintillation detector, it is also served as a veto detector. Gaseous avalanche Photomultipliers (GPMT) is one of the most promising candidates for the readout of scintillation light from liquid Ar, that is, 128nm Vacuum Ultraviolet light (VUV). Compared with PMT, the GPMT has many advantages, such as lower radioactivity. A kind of GPMT is researched in this study based on THGEM coated with CsI. The influence of different parameters on the THGEM is studied and finally an optimized thinner THGEM (thickness 0.2mm) is selected. CsI is deposited successfully on the top layer of the thinner THGEM by vacuum evaporation. The electric field near the photocathode and gas flowing through the chamber are investigated to get the best working conditions. Simulations and experiment verification are performed and the first detection of VUV using thinner THGEM is carried out successfully.