Assembly and Test for the Large GEM detector for pRad experiment at JLab Hall B

pRad (proton charge radius) is a novel magnetic-spectrometer-free ep scattering experiment designed to measure the proton charge radius at a very low Q$^2$ region (10$^{-4}$ $\sim$ 10$^{-2}$ (GeV/c)$^2$) at Jefferson Lab Hall B, it needs a high-resolution position detector. We will report the fabrication and test for world-largest GEM detector designed and built for pRad experiment. In this report, we will talk about the assembly process and the testing results for pRad GEM chamber.