Correction factor for the number of incident protons using correlation between SEC1 and PMIEA822 radiation monitor in the CHARM during Run 2

In the CHARM facility, the beam intensity is obtained from the counts in the secondary emission chamber, denoted as SEC1. However, the SEC1 shows the nonlinear counting efficiency when the beam intensity was lower than around 1e11 proton per pulse. The beam intensity could be varied from 1e9 to 5e11 proton per pulse. Due to the nonlinearity of the SEC1 counting efficiency, the conversion to the number of incident protons is not applicable in the low beam intensity region around 1e9 protons per pulse. Thus, an air-filled plastic ionization chamber (PMIEA822 radiation monitor), which is installed in the irradiation room, is used to determine the correction factor that is used for compensating the nonlinear effect of the SEC1 for low-intensity proton beam. The correction factor was determined by checking the ratio of the readings from the PMIEA822 radiation monitor to the SEC1. In this report, the number of incident protons was analytically corrected with the correlation between SEC1 and PMIEA822 radiation monitor. The corrections were applied by multiplying the correction factors with the beam intensity determined by the SEC1 counts.