  China Jinping Underground Laboratory provides an ideal site for solar, geo-,
and supernova neutrino studies. With a prototype neutrino detector running
since 2017, containing 1-ton liquid scintillator, we tested its experimental
hardware, performed the detector calibration and simulation, and measured its
radioactive backgrounds, as an early stage of the Jinping Neutrino Experiment
(JNE). We investigated the radon background and implemented the nitrogen
sealing technology to control it. This paper presents the details of these
studies and will serve as a key reference for the construction and optimization
of the future large detector of JNE.
