Mapping of Strip Line Beam Position Monitor at HLS LINAC Based on Logarithm Ratio Processing Method

A non-interceptive precise strip line beam position monitor (BPM) for HLS LINAC was redesigned. Before installation, a mapping of strip line BPM was carried out on a workbench with a precision of less than 5 μm, based on logarithm ratio method, which has a larger dynamic range and linearity than traditional ration between difference and sum. The mapping workbench, logarithm ratio processing system and automatic mapping program were described. The results of mapping are horizontal sensitivity of BPM system 1.55 dB/mm, vertical sensitivity 1.48 dB/mm, resolution of beam position 42 μm, offset between electronic center and mechanical one （0.212，0.450） mm.