Design and Calibration of High Energy Particle Monitor on board HXMT(Insight)

High Energy Particle Monitor(HPM) on board Hard X-ray Modulation Telescope (HXMT) is used to detect the charged particles to give warning signals for the entry and exit of South Atlantic Anomaly (SAA). A typical design of plastic scintillator coupled with small photomultiplier tube (PMT) is adopted for its high stability and reliability. The window threshold for electron is about 1 MeV, and that for proton is about 20 MeV. In combination with the ground calibration and Geant4 simulation, a relation among the PMT high voltage and an average count rate of HPM in SAA is built in details. It supplies a recommended PMT high voltage to the HPM. The HPM in-orbit performance and the SAA area monitor map measured by the HPM are introduced in the last part of this paper. During more than two years flight, the HPM is found working well and steadily provides accurate warning signals for the HXMT.